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2840068 | https://en.wikipedia.org/wiki/Fluorosulfuric%20acid | Fluorosulfuric acid | Fluorosulfuric acid (IUPAC name: sulfurofluoridic acid) is the inorganic compound with the chemical formula . It is one of the strongest acids commercially available. It is a tetrahedral molecule and is closely related to sulfuric acid, , substituting a fluorine atom for one of the hydroxyl groups. It is a colourless liquid, although commercial samples are often yellow.
Properties
Fluorosulfuric acid is a free-flowing colorless liquid. It is soluble in polar organic solvents (e.g. nitrobenzene, acetic acid, and ethyl acetate), but poorly soluble in nonpolar solvents such as alkanes.
is one of the strongest known simple Brønsted acids. It has an H0 value of −15.1 compared to −12 for sulfuric acid. The combination of and the Lewis acid antimony pentafluoride produces "Magic acid", which is a far stronger protonating agent. These acids are categorized as "superacids", acids stronger than 100% sulfuric acid.
Reflecting its strong acidity, dissolves almost all organic compounds that are even weak proton acceptors. hydrolyzes slowly to hydrogen fluoride (HF) and sulfuric acid. The related triflic acid () retains the high acidity of but is more hydrolytically stable. The self-ionization of fluorosulfonic acid also occurs:
K = 4.0 × 10−8 (at 298 K)
isomerizes alkanes and catalyzes the alkylation of hydrocarbons with alkenes, although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent.
Production
Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide:
Alternatively, or can be treated with oleum at 250 °C. Once freed from HF by sweeping with an inert gas, HSO3F can be distilled in a glass apparatus.
Safety
Fluorosulfuric acid is considered to be highly toxic and extremely corrosive. It hydrolyzes to release HF. Addition of water to is similar to, and even more violent than, the addition of water to sulfuric acid.
| Physical sciences | Specific acids | Chemistry |
2840108 | https://en.wikipedia.org/wiki/Tropical%20cyclone%20preparedness | Tropical cyclone preparedness | Cyclone mitigation encompasses the actions and planning taken before a tropical cyclone strikes to mitigate damage and injury from the storm. Knowledge of tropical cyclone impacts on an area help plan for future possibilities. Preparedness may involve preparations made by individuals as well as centralized efforts by governments or other organizations. Tracking storms during the tropical cyclone season helps individuals know current threats. Regional Specialized Meteorological Centers and Tropical Cyclone Warning Centers provide current information and forecasts to help individuals make the best decision possible.
Potential impacts
Tropical cyclones out at sea cause large waves, heavy rain, flood and high winds, disrupting international shipping and, at times, causing shipwrecks. On land, strong winds can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge, or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.
The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes. Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall.
Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts. On average, the Gulf and east coasts of the United States suffer approximately US$5 billion (1995 US $) in cyclone damage every year. The majority (83%) of tropical cyclone damage is caused by severe hurricanes, category 3 or greater. However, category 3 or greater hurricanes only account for about one-fifth of cyclones that make landfall every year.
Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions, and by regulating the thermohaline circulation through upwelling. The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.
When hurricanes surge upon shore from the ocean, salt is introduced to many freshwater areas and raises the salinity levels too high for some habitats to withstand. Some are able to cope with the salt and recycle it back into the ocean, but others can not release the extra surface water quickly enough or do not have a large enough freshwater source to replace it. Because of this, some species of plants and vegetation die due to the excess salt. In addition, hurricanes can carry toxins and acids onto shore when they make landfall. The flood water can pick up the toxins from different spills and contaminate the land that it passes over. The toxins are very harmful to the people and animals in the area, as well as the environment around them. The flooding water can also spark many dangerous oil spills.
Recent windstorm activity, in the United States in particular, has focused interest in measures that can be used to lower the likelihood of damage to structures. Billions of dollars of damages have resulted from such strong winds and the manner in which structures have been built in the affected areas in the United States. Some building codes address mitigation measures. For example, the Florida Building Code, specifies the type of nail used to secure roof sheathing. The specification was determined by scientific research conducted by Florida International University's International Hurricane Research Center.
Individual preparedness
An important decision in individual preparedness is determining if and when to evacuate an area that will be affected by a tropical cyclone. Tropical cyclone tracking charts allow people to track ongoing systems to form their own opinions regarding where the storms are going and whether or not they need to prepare for the system being tracked, including possible evacuation. This continues to be encouraged by the National Oceanic and Atmospheric Administration and National Hurricane Center. Some agencies provide track storms in their immediate vicinity, while others cover entire ocean basins. One can choose to track one storm per map, use the map until the table is filled, or use one map per season. Some tracking charts have important contact information in case of an emergency or to locate nearby hurricane shelters. Tracking charts allow tropical cyclones to be better understood by the end user. If evacuation is not possible or necessary, other preparedness actions include storing supplies, securing a home against extreme winds and rain, and making plans with others prior to the storm's landfall.
Hurricane preparedness kits usually include drinkable water, sealed pre-prepared meals MRE, first-aid kits, prescription medications in sealed containers, waterproof battery-powered or hand-crank-powered flashlights and radios, a whistle or other sound-signaling device, a multi-tool with a knife, identification and medical cards, any necessary medical records, waterproof bags or portable waterproof containers, and other supplies helpful to a survival situation. If your pets will be with you make sure you include canned or dry food for them as well (any dry food included should be rotated every 2 months). You should also include veterinarian records and proof of vaccinations for all of your pets.
Preparedness also may include having discussed evacuation plans and routes, and informing others of those plans before a disaster occurs.
Evacuation to hurricane shelters is an option of last resort. Shelter space is first-come, first-served and only intended preserve human life. Buildings designated as shelters in Florida are required to only have been constructed to meet minimum code requirements applicable at the time of design. Some shelters are expected to protect occupants from wind and water but are not expected to provide food, water, sanitation, or bedding.
Based on preparedness of the people in a region, the preparedness level was greatly affected by the salary, race, age, etc. Many people are not prepared for the worst-case scenario, but they should be. Being prepared for a huge disaster is what will ultimately save your life if worse comes to worst.
Hospitals are needed to be prepared in advance for huge natural disasters. Nurses are in high demand when people are in trouble. They need to be prepared for ready for any situation that enters the hospital. After hurricanes such as Katrina and Rita, nurses are needed to be fully capable of any possible scenario.
Home retrofitting
An important decision a homeowner should make is to locate the building outside of range from the coast that is exposed to storm surge. Regardless of protection from the effects of wind, a building can be flooded or destroyed by storm surge waters.
To mitigate the effects of high winds and associated debris impact, the home can be examined out by an experienced hurricane mitigation professional. Many hurricane protection companies offer free consultations as part of their marketing strategy. The State of Florida has taken steps to help its homeowners in the area of hurricane preparedness through its My Safe Florida Home grant program. Qualified homeowners receive a free in-home assessment of their home's hurricane readiness. The state matches funds spent by the homeowner, up to a $5,000 limit.
When making these types of home improvements, there are two major areas of focus: the roof and the openings.
Homes may be retrofitted to withstand the extreme conditions of a tropical cyclone. Common modifications include reinforcing gabled roofs, applying additional adhesives to roof shingles, installing hurricane straps and clips to ensure the roof stays in place despite high winds. Hurricane resistant shutters, as well as impact resistant glass may help keep windows closed from driving rain, despite flying debris. Contrary to a common misconception, taping windows with masking or duct tape does not impact whether they will break.
External patio and pool screen enclosures are especially vulnerable during a hurricane. A homeowner who anticipates sustained winds greater than 100 mph may use a razor knife taped to a telescopic pole to cut down the screens from the enclosure's skeleton structure. This will prevent the screens from acting as a sail and pulling down the entire enclosure structure.
Reinforcing garage doors and entry doors is also common practice for hurricane preparing a home. Garage doors may be protected by fabric screens, made of a strong woven fabric, to keep out projectiles and to reinforce the door.
The goal of these mitigation measures and products is to decrease the likelihood of severe damage to a home. There is no guarantee that these measures will safeguard any home against any kind of storm and the projectiles that may come with a storm, but a well-protected home is far more likely to come through a hurricane in better shape than a home that has little or no protection.
Organized preparation
Hurricane mitigation uses policies to make buildings and other infrastructure more resistant to the effects of tropical cyclones. In addition to facilities themselves being at risk, the internal contents of the structures can be damaged as result of exposure to water if the building envelope is breached, usually as a result of the strong winds associated with hurricanes and tropical storms. Although the negative pressure caused by high velocity wind flowing over a building roof can cause the roof to fail with the building envelope intact, broken windows allow the air pressure to rise inside a building, creating an even greater pressure difference, and increasing the likelihood of roof failure. This pressure increase results after an opening, that is, a window or door, is breached after being struck and broken by wind blown debris.
| Physical sciences | Storms | Earth science |
2841242 | https://en.wikipedia.org/wiki/Fornax%20Cluster | Fornax Cluster | The Fornax Cluster is a cluster of galaxies lying at a distance of 19 megaparsecs (62 million light-years). It has an estimated mass of solar masses, making it the second richest galaxy cluster within 100 million light-years, after the considerably larger Virgo Cluster. It may be associated with the nearby Eridanus Group. It lies primarily in the constellation Fornax, with its southern boundaries partially crossing into the constellation of Eridanus, and covers an area of sky about 6° across or about 28 sq degrees.
The Fornax Cluster is a particularly valuable source of information about the evolution of such clusters due to its relatively close proximity to the Sun. It also shows the gravitational effects of a merger of a galaxy subgroup with the main galaxy group, which in turn lends clues about the associated galactic superstructure. At the centre of the cluster lies NGC 1399. Other cluster members include NGC 1316 (the group's brightest galaxy), NGC 1365, NGC 1427A, NGC 1427 and NGC 1404.
Structure
Fornax can be divided into two subclusters: the main cluster, centered on NGC 1399, and a subgroup 3 degrees to the southwest centered on the lenticular galaxy NGC 1316 that is currently in the process of infalling with the largest subcluster to merge with it, and whose galaxies are experiencing relatively strong star formation activity.
Intracluster medium
As with many other galaxy clusters, Fornax intracluster medium is filled with a hot, rarefied gas that emits X-rays. and contains a number of intergalactic stars, some of which have produced novae.
List of cluster members
(*) - Membership is uncertain
Gallery
| Physical sciences | Notable galaxy clusters | Astronomy |
2843057 | https://en.wikipedia.org/wiki/Strain%20%28injury%29 | Strain (injury) | A strain is an acute or chronic soft tissue injury that occurs to a muscle, tendon, or both. The equivalent injury to a ligament is a sprain. Generally, the muscle or tendon overstretches and partially tears, under more physical stress than it can withstand, often from a sudden increase in duration, intensity, or frequency of an activity. Strains most commonly occur in the foot, leg, or back. Immediate treatment typically used to include four steps abbreviated as R.I.C.E. (rest, ice, compression, elevation) before the role of inflammation was found to be helpful.
Signs and symptoms
Typical signs and symptoms of a strain include pain, functional loss of the involved structure, muscle weakness, contusion, and localized inflammation. A strain can range from mild overstretching to severe tears, depending on the extent of injury.
Cause
A strain can occur as a result of improper body mechanics with any activity (e.g., contact sports, lifting heavy objects) that can induce mechanical trauma or injury. Generally, the muscle or tendon overstretches and is placed under more physical stress than it can withstand. Strains commonly result in a partial or complete tear of a tendon or muscle, or they can be severe in the form of a complete tendon rupture. Strains most commonly occur in the foot, leg, or back. Acute strains are more closely associated with recent mechanical trauma or injury. Chronic strains typically result from repetitive movement of the muscles and tendons over a long period of time.
Degrees of Injury (as classified by the American College of Sports Medicine):
First degree (mildest) – little tissue tearing; mild tenderness; pain with full range of motion.
Second degree – torn muscle or tendon tissues; painful, limited motion; possibly some swelling or depression at the spot of the injury.
Third degree (most severe) – limited or no movement; severe acute pain, though sometimes painless straight after the initial injury
To establish a uniform definition amongst healthcare providers, in 2012 a Consensus Statement on suggested new terminology and classification of muscle injuries was published.
The classifications suggested were:
The major difference suggested was the use of "indirect" muscle injury verse "grade 1" to provide subclassifications when advanced images were negative.
Indirect Muscle Injury
FUNCTIONAL (Negative MSK US & MRI)
Type 1: Overexertion-related Muscle Disorder
Type 1a: Fatigue induced
Type 1b: DOMS
• Type 2: Neuromuscular muscle disorder
Type 2a: Spine-Related
Type 2b: Muscle-Related
STRUCTURAL MUSCLE INJURY (Positive MSK US & MRI)
• Type 3: Partial Muscle Tear
• Type 4: (Sub) total tear
DIRECT MUSCLE INJURY
• Bump or Cut: Contact-related
Risk factors
Although strains are not restricted to athletes and can happen while doing everyday tasks, people who play sports are more at risk for developing a strain. It is common for an injury to develop when there is a sudden increase in duration, intensity, or frequency of an activity.
Treatment
The first-line treatment for a muscular strain in the acute phase include five steps commonly known as P.R.I.C.E.
Protection: Apply soft padding to minimize impact with objects.
Rest: Rest is necessary to accelerate healing and reduce the potential for re-injury.
Ice: Apply ice to induce vasoconstriction, which will reduce blood flow to the site of injury. Never ice for more than 20 minutes at a time.
Compression: Wrap the strained area with a soft-wrapped bandage to reduce further diapedesis and promote lymphatic drainage.
Elevation: Keep the strained area as close to the level of the heart as is possible in order to promote venous blood return to the systemic circulation.
Immediate treatment is usually an adjunctive therapy of NSAIDs and Cold compression therapy. Cold compression therapy acts to reduce swelling and pain by reducing leukocyte extravasation into the injured area. NSAIDs such as Ibuprofen/paracetamol work to reduce the immediate inflammation by inhibiting Cox-1 and Cox-2 enzymes, which are the enzymes responsible for converting arachidonic acid into prostaglandin. However, NSAIDs, including aspirin and ibuprofen, affect platelet function (this is why they are known as "blood thinners") and should not be taken during the period when tissue is bleeding because they will tend to increase blood flow, inhibit clotting, and thereby increase bleeding and swelling. After the bleeding has stopped, NSAIDs can be used with some effectiveness to reduce inflammation and pain.
A new treatment for acute strains is the use of platelet rich plasma (PRP) injections which have been shown to accelerate recovery from non-surgical muscular injuries.
It is recommended that the person injured should consult a medical provider if the injury is accompanied by severe pain, if the limb cannot be used, or if there is noticeable tenderness over an isolated spot. These can be signs of a broken or fractured bone, a sprain, or a complete muscle tear.
| Biology and health sciences | Types | Health |
5162226 | https://en.wikipedia.org/wiki/Parareptilia | Parareptilia | Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period. Several ecological innovations were first accomplished by parareptiles among reptiles. These include the first reptiles to return to marine ecosystems (mesosaurs), the first bipedal reptiles (bolosaurids such as Eudibamus), the first reptiles with advanced hearing systems (nycteroleterids and others), and the first large herbivorous reptiles (the pareiasaurs). The only parareptiles to survive into the Triassic period were the procolophonoids, a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids, the procolophonids, rediversified in the Triassic, but subsequently declined and became extinct by the end of the period.
Compared to most eureptiles, parareptiles retained fairly "primitive" characteristics such as robust, low-slung bodies and large supratemporal bones at the back of the skull. While all but the earliest eureptiles were diapsids, with two openings at the back of the skull, parareptiles were generally more conservative in the extent of temporal fenestration. In its modern usage, Parareptilia was first utilized as a cladistically correct alternative to Anapsida, a term which historically referred to reptiles with solid skulls lacking holes behind the eyes. Nevertheless, not all parareptiles have 'anapsid' skulls, and some do have large holes in the back of the skull. They also had several unique adaptations, such as a large pit on the maxilla, a broad prefrontal-palatine contact, and the absence of a supraglenoid foramen of the scapula.
Like many other so-called 'anapsids', parareptiles were historically understudied. Interest in their relationships were reinvigorated in the 1990s, when several studies argued that Testudines (turtles and their kin) were members of Parareptilia. Although this would suggest that Parareptilia was not extinct after all, the origin of turtles is still heavily debated. Many other morphological or genetic analyses find more support for turtles among diapsid eureptiles such as sauropterygians or archosauromorphs, rather than parareptiles.
Description
Skull
Parareptilian skulls were diverse, from mesosaurs with elongated snouts filled with hundreds of thin teeth, to the snub-nosed, knob-encrusted skulls of pareiasaurs. Parareptile teeth were quite variable in shape and function between different species. However, they were relatively homogenous on the same skull. While most synapsids and many early eureptiles had a caniform region of enlarged fang-like teeth in the front half of the skull, very few parareptiles possessed caniform teeth.
Many amniotes have a row of small pits running along bones at the edge of the mouth, but parareptiles have only a few pits, with one especially large pit near the front of the maxilla. The rest of the skull was often strongly-textured by pits, ridges, and rugosities in most parareptile groups, occasionally culminating in complex bosses or spines. The maxilla is usually low, while the prefrontal and lacrimal bones in front of the eye are both fairly large. In all parareptiles except mesosaurs, the prefrontal has a plate-like inner branch which forms a broad contact with the palatine bone of the palate. A prominent hole, the foramen orbitonasale, is present at the intersection of the prefrontal, palatine, and lacrimal. Parareptilian palates also have toothless and reduced ectopterygoid bones, a condition taken to extremes in mesosaurs, which have lost the ectopterygoid entirely.
Most parareptiles had large orbits (eye sockets), significantly longer (from front-to-back) than the region of the skull behind the eyes. The jugal bone, which forms the lower and rear edge of the orbit, has a very thin suborbital process (front branch), usually no subtemporal process (lower rear branch), and a thick dorsal process (upper rear branch). The squamosal and quadratojugal bones, which lie behind the jugal, are quite large and are embayed from behind to accommodate the internal ears. Parareptiles were traditionally considered to have an ‘anapsid’-type skull, with the jugal, squamosal, and quadratojugal firmly sutured together without any gaps or slits between them. This principle still holds true for some subgroups, such as pareiasaurs. However, a growing number of parareptile taxa are known to have had an infratemporal fenestra, a large hole or emargination lying among the bones behind the eye. In some taxa, the margins of such openings may include additional bones such as the maxilla or postorbital. When seen from above, the rear edge of the skull is straight or has a broad median embayment. From inside to outside, the rear edge of the skull is formed by three pairs of bones: the postparietals, tabulars, and supratemporals. Parareptiles have particularly large supratemporals, which often extend further backwards than the tabulars.
Apart from the long, slender jaws of mesosaurs, most parareptile jaws were short and thick. The jaw joint is formed by the articular (in the lower jaw) and the quadrate (in the upper jaw). In many parareptiles, the jaw joint is shifted forwards on the skull past the rear part of the braincase. Jaw muscles attach to the coronoid process, a triangular spur in the rear half of the jaw. Both the tooth-bearing dentary bone and the posterior foramen intermandibularis (a hole on the inner surface of the jaw) reach as far back as the coronoid process. The surangular bone, which forms the upper rear part of the jaw, is narrow and plate-like.
Postcranial skeleton
There was some variation in the body shape of parareptiles, with early members of the group having an overall lizard-like appearance, with thin limbs and long tails. The most successful and diverse groups of parareptiles, the pareiasaurs and procolophonids, had massively-built bodies with reduced tails and stout limbs with short digits. This general body shape is shared with other ‘cotylosaurs’ such as captorhinids, diadectomorphs, and seymouriamorphs. Another general ‘cotylosaurian’ feature in parareptiles is the ‘swollen’ appearance of their vertebrae, which have wide and convex upper surfaces.
Parareptiles lacked a supraglenoid foramen on the scapula, a hole which is also absent in varanopids and neodiapsids. Most had a fairly short and thick humerus which was expanded near the elbow. Unlike early eureptiles, the outer part of the lower humerus possessed both a small supinator process and an ectepicondylar foramen and groove. The ulna generally has a poorly developed olecranon process, another trait in contrast with the earliest eureptiles.
Most parareptiles had an ilium which was fan-shaped and vertically (rather than horizontally) oriented, an unusual trait among early amniotes. The sacral ribs, which connect the spine to the ilium, were usually slender or fan-shaped, with large gaps between them. The hindlimbs were typically not much longer than the forelimbs, and had thick reptilian ankle bones and short toes. There are some exceptions, such as Eudibamus, an early Permian bolosaurid with very elongated hindlimbs.
History of classification
The name Parareptilia was coined by Olson in 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to the rest of the reptiles or Eureptilia ("true reptiles"). Olsen's term was generally ignored, and various taxa later known as parareptiles were generally not placed into exclusive groups with each other. Many were classified as 'cotylosaurs' (a wastebasket taxon of stout-bodied 'primitive' reptiles or reptile-like tetrapods) or 'anapsids' (reptiles without temporal fenestrae, such as modern turtles).
Parareptilia's usage was revived by cladistic studies, to refer to those traditional 'anapsids' that were thought to be unrelated to turtles. Gauthier et al. (1988) provided the first phylogenetic definitions for the names of many amniote taxa and argued that captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than typically applied). A name had to be found for a clade of various early-diversing Permian and Triassic reptiles no longer included in the anapsids. Olsen's term "parareptiles" was chosen to refer to this clade, although its instability within their analysis meant that Gauthier et al. (1988) were not confident enough to erect Parareptilia as a formal taxon. Their cladogram is as follows:
Laurin & Reisz (1995) found a slightly different topology, in which Reptilia is divided into Parareptilia and Eureptilia. They argued that Testudines (turtles) were members of Parareptilia; in fact, they explicitly defined Parareptilia as "Testudines and all amniotes more closely related to them than to diapsids". Captorhinidae was transferred to Eureptilia, while Parareptilia included turtles alongside many of the taxa named as such by Gauthier et al. (1988). There was one major exception: mesosaurs were placed outside both groups, as the sister taxon to the crown group Reptilia. Mesosaurs were still considered sauropsids, as they were closer to reptiles than to synapsids. The traditional group 'Anapsida' was rejected as a paraphyletic assemblage. The cladogram of Laurin & Reisz (1995) is provided below:
In contrast, several studies in the mid-to-late 1990s by Olivier Rieppel and Michael deBraga argued that turtles were actually lepidosauromorph diapsids related to the sauropterygians. The diapsid affinities of turtles have been supported by molecular phylogenies. The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics, since turtles possess an anapsid skull. This would make Parareptilia a totally extinct group with skull features that resemble those of turtles through convergent evolution. With turtles positioned outside of parareptiles, Tsuji and Müller (2009) redefined Parareptilia as "the most inclusive clade containing Milleretta rubidgei and Procolophon trigoniceps, but not Captorhinus aguti."
The cladogram below follows an analysis by M.S. Lee, in 2013.
The cladogram below follows the analysis of Li et al. (2018).
A 2020 study by David P. Ford and Roger B. J. Benson found that Parareptilia was nested within Diapsida as the sister group to Neodiapsida, with the clade containing Neodiapsida and Parareptilia dubbed Neoreptilia, which suggests that parareptiles were ancestrally diapsid. This excluded mesosaurs, which were again found to be basal among the sauropsids. Some studies have found Parareptilia to be paraphyletic, with some parareptiles more closely related to diapsids than to other parareptiles, with Simões et al. (2022) using Neoreptilia for the clade containing Procolophonomorpha+Neodiapsida.
Evolutionary history
The oldest known parareptiles are the bolosaur Erpetonyx and the acleistorhinid Carbonodraco from the Late Carboniferous (Moscovian-Gzhelian) of North America, which represents the only known Carboniferous parareptiles, indicating that the initial diversification of the group took place in the Late Carboniferous. Numerous parareptile lineages appeared during the early Permian and the group reached a cosmopolitan distribution. Parareptile diversity declined towards the end of the Permian and procolophonoids, which first appeared during the Late Permian, were the only group of parareptiles to survive the Permian–Triassic extinction event. Procolophonid diversity sharply declined beginning in the Middle Triassic, with the group becoming extinct by the end of the Triassic.
| Biology and health sciences | Parareptilia | Animals |
5165199 | https://en.wikipedia.org/wiki/Pattern%20hair%20loss | Pattern hair loss | Pattern hair loss (also known as androgenetic alopecia (AGA)) is a hair loss condition that primarily affects the top and front of the scalp. In male-pattern hair loss (MPHL), the hair loss typically presents itself as either a receding front hairline, loss of hair on the crown and vertex of the scalp, or a combination of both. Female-pattern hair loss (FPHL) typically presents as a diffuse thinning of the hair across the entire scalp.
Genetic research has identified alleles associated with male pattern hair loss. These alleles appear to be undergoing positive sexual selection in European and East Asian populations, as male pattern baldness may be seen as a masculine attribute associated with seniority and higher social status. The condition is caused by a combination of male sex hormones (balding never occurs in castrated men) and genetic factors.
Some research has found evidence for the role of oxidative stress in hair loss, the microbiome of the scalp, genetics, and circulating androgens; particularly dihydrotestosterone (DHT). Men with early onset androgenic alopecia (before the age of 35) have been deemed the male phenotypic equivalent for polycystic ovary syndrome (PCOS).
The cause in female pattern hair loss remains unclear; androgenetic alopecia for women is associated with an increased risk of polycystic ovary syndrome (PCOS).
Management may include simply accepting the condition or shaving one's head to improve the aesthetic aspect of the condition. Otherwise, common medical treatments include minoxidil, finasteride, dutasteride, or hair transplant surgery. Use of finasteride and dutasteride in women is not well-studied and may result in birth defects if taken during pregnancy.
By the age of 50, pattern hair loss affects about half of males and a quarter of females. It is the most common cause of hair loss. Both males aged 40–91 and younger male patients of early onset AGA (before the age of 35), had a higher likelihood of metabolic syndrome (MetS) and insulin resistance. With younger males, studies found metabolic syndrome to be at approximately a 4× increased frequency which is clinically deemed significant. Abdominal obesity, hypertension and lowered high density lipoprotein were also significantly higher for younger groups.
Signs and symptoms
Pattern hair loss is classified as a form of non-scarring hair loss.
Male-pattern hair loss begins above the temples and at the vertex (calvaria) of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a "Hippocratic wreath", and rarely progresses to complete baldness.
Female-pattern hair loss more often causes diffuse thinning without hairline recession; similar to its male counterpart, female androgenic alopecia rarely leads to total hair loss. The Ludwig scale grades severity of female-pattern hair loss. These include Grades 1, 2, 3 of balding in women based on their scalp showing in the front due to thinning of hair.
In most cases, receding hairline is the first starting point; the hairline starts moving backwards from the front of the head and the sides.
Causes
The cause of pattern hair loss is not yet fully understood. It appears to be the result of genetic changes that make the activity of hair follicles on the scalp become sensitive to the presence of androgenic hormones, cholesterol, and proteins such as insulin-like growth factor.
Hormones and genes
KRT37 is the only keratin that is regulated by androgens. This sensitivity to androgens was acquired by Homo sapiens and is not shared with their great ape cousins. Although Winter et al. found that KRT37 is expressed in all the hair follices of chimpanzees, it was not detected in the head hair of modern humans. As androgens are known to grow hair on the body, but decrease it on the scalp, this lack of scalp KRT37 may help explain the paradoxical nature of Androgenic alopecia as well as the fact that head hair anagen cycles are extremely long.
Male-pattern hair loss appears to be undergoing positive sexual selection in European and Asian populations. Male pattern hair loss may be seen as an expression of masculine sexual dimorphism rather than a disorder. Because of this, it is hypothesized that men with male pattern hair loss may be favored by heterosexual women as mates, because their hair loss is associated with seniority and higher social ranking, giving them increased sexual capital.
This is similar to the white stripe seen on male silver-back gorillas, associated with their advanced age and higher social ranking. The genetic evidence did not support this hypothesis in African populations, suggesting that within Africa, the evolutionary pressure for scalp hair (to protect against harsh sunlight) outweighed the selective benefits of male pattern hair loss.
Although it is generally accepted that male pattern baldness follows a pattern of autosomal dominant inheritance, more recent research has shown that approximately 80% of bald men have bald fathers. This is greater than would be expected if pattern balding were a purely autosomal trait, and may suggest that there is an important paternal route of inheritance, either through a Y-chromosome gene or a paternal imprinting effect.
The initial programming of pilosebaceous units of hair follicles begins in utero. The physiology is primarily androgenic, with dihydrotestosterone (DHT) being the major contributor at the dermal papillae. Men with premature androgenic alopecia tend to have lower than normal values of sex hormone-binding globulin (SHBG), follicle stimulating hormone (FSH), testosterone, and epitestosterone when compared to men without pattern hair loss. Although hair follicles were previously thought to be permanently gone in areas of complete hair loss, they are more likely dormant, as recent studies have shown the scalp contains the stem cell progenitor cells from which the follicles arose.
Transgenic studies have shown that growth and dormancy of hair follicles are related to the activity of insulin-like growth factor (IGF) at the dermal papillae, which is affected by DHT. Androgens are important in male sexual development around birth and at puberty. They regulate sebaceous glands, apocrine hair growth, and libido. With increasing age, androgens stimulate hair growth on the face, but can suppress it at the temples and scalp vertex, a condition that has been referred to as the 'androgen paradox'.
Men with androgenic alopecia typically have higher 5α-reductase, higher total testosterone, higher unbound/free testosterone, and higher free androgens, including DHT. 5-alpha-reductase converts free testosterone into DHT, and is highest in the scalp and prostate gland. DHT is most commonly formed at the tissue level by 5α-reduction of testosterone. The genetic corollary that codes for this enzyme has been discovered. Prolactin has also been suggested to have different effects on the hair follicle across gender.
Also, crosstalk occurs between androgens and the Wnt-beta-catenin signaling pathway that leads to hair loss. At the level of the somatic stem cell, androgens promote differentiation of facial hair dermal papillae, but inhibit it at the scalp. Other research suggests the enzyme prostaglandin D2 synthase and its product prostaglandin D2 (PGD2) in hair follicles as contributive.
These observations have led to study at the level of the mesenchymal dermal papillae. Types 1 and 2 5α reductase enzymes are present at pilosebaceous units in papillae of individual hair follicles. They catalyze formation of the androgen dihydrotestosterone from testosterone, which in turn regulate hair growth. Androgens have different effects at different follicles: they stimulate IGF-1 at facial hair, leading to growth, but can also stimulate TGF β1, TGF β2, dickkopf1, and IL-6 at the scalp, leading to catagenic miniaturization. Hair follicles in anaphase express four different caspases. Significant levels of inflammatory infiltrate have been found in transitional hair follicles. Interleukin 1 is suspected to be a cytokine mediator that promotes hair loss.
The fact that hair loss is cumulative with age while androgen levels fall as well as the fact that finasteride does not reverse advanced stages of androgenetic alopecia remains a mystery, but possible explanations are higher conversion of testosterone to DHT locally with age as higher levels of 5-alpha reductase are noted in balding scalp, and higher levels of DNA damage in the dermal papilla as well as senescence of the dermal papilla due to androgen receptor activation and environmental stress.
Metabolic syndrome
Multiple cross-sectional studies have found associations between early androgenic alopecia, insulin resistance, and metabolic syndrome, with low HDL being the component of metabolic syndrome with highest association. Linolenic and linoleic acids, two major dietary sources of HDL, are 5 alpha reductase inhibitors. Premature androgenic alopecia and insulin resistance may be a clinical constellation that represents the male homologue, or phenotype, of polycystic ovary syndrome. Others have found a higher rate of hyperinsulinemia in family members of women with polycystic ovarian syndrome. With early-onset AGA having an increased risk of metabolic syndrome, poorer metabolic profiles are noticed in those with AGA, including metrics for body mass index, waist circumference, fasting glucose, blood lipids, and blood pressure.
In support of the association, finasteride improves glucose metabolism and decreases glycated hemoglobin HbA1c, a surrogate marker for diabetes mellitus. The low SHBG seen with premature androgenic alopecia is also associated with, and likely contributory to, insulin resistance, and for which it still is used as an assay for pediatric diabetes mellitus.
Obesity leads to upregulation of insulin production and decrease in SHBG. Further reinforcing the relationship, SHBG is downregulated by insulin in vitro, although SHBG levels do not appear to affect insulin production. In vivo, insulin stimulates both testosterone production and SHBG inhibition in normal and obese men. The relationship between SHBG and insulin resistance has been known for some time; decades prior, ratios of SHBG and adiponectin were used before glucose to predict insulin resistance. Patients with Laron syndrome, with resultant deficient IGF, demonstrate varying degrees of alopecia and structural defects in hair follicles when examined microscopically.
Because of its association with metabolic syndrome and altered glucose metabolism, both men and women with early androgenic hair loss should be screened for impaired glucose tolerance and diabetes mellitus II. Measurement of subcutaneous and visceral adipose stores by MRI, demonstrated inverse association between visceral adipose tissue and testosterone/DHT, while subcutaneous adipose correlated negatively with SHBG and positively with estrogen. SHBG association with fasting blood glucose is most dependent on intrahepatic fat, which can be measured by MRI in and out of phase imaging sequences. Serum indices of hepatic function and surrogate markers for diabetes, previously used, show less correlation with SHBG by comparison.
Female patients with mineralocorticoid resistance present with androgenic alopecia.
IGF levels have been found lower in those with metabolic syndrome. Circulating serum levels of IGF-1 are increased with vertex balding, although this study did not look at mRNA expression at the follicle itself. Locally, IGF is mitogenic at the dermal papillae and promotes elongation of hair follicles. The major site of production of IGF is the liver, although local mRNA expression at hair follicles correlates with increase in hair growth. IGF release is stimulated by growth hormone (GH). Methods of increasing IGF include exercise, hypoglycemia, low fatty acids, deep sleep (stage IV REM), estrogens, and consumption of amino acids such as arginine and leucine. Obesity and hyperglycemia inhibit its release. IGF also circulates in the blood bound to a large protein whose production is also dependent on GH. GH release is dependent on normal thyroid hormone. During the sixth decade of life, GH decreases in production. Because growth hormone is pulsatile and peaks during sleep, serum IGF is used as an index of overall growth hormone secretion. The surge of androgens at puberty drives an accompanying surge in growth hormone.
The expression of insulin resistance and metabolic syndrome, AGA is related to being an increased risk factor for cardiovascular diseases, glucose metabolism disorders, type 2 diabetes, and enlargement of the prostate.
Age
A number of hormonal changes occur with aging:
Decrease in testosterone
Decrease in serum DHT and 5-alpha reductase
Decrease 3AAG, a peripheral marker of DHT metabolism
Increase in SHBG
Decrease in androgen receptors, 5-alpha reductase type I and II activity, and aromatase in the scalp
This decrease in androgens and androgen receptors, and the increase in SHBG are opposite the increase in androgenic alopecia with aging. This is not intuitive, as testosterone and its peripheral metabolite, DHT, accelerate hair loss, and SHBG is thought to be protective. The ratio of T/SHBG, DHT/SHBG decreases by as much as 80% by age 80, in numeric parallel to hair loss, and approximates the pharmacology of antiandrogens such as finasteride.
Free testosterone decreases in men by age 80 to levels double that of a woman at age 20. About 30% of normal male testosterone level, the approximate level in females, is not enough to induce alopecia; 60%, closer to the amount found in elderly men, is sufficient. The testicular secretion of testosterone perhaps "sets the stage" for androgenic alopecia as a multifactorial diathesis stress model, related to hormonal predisposition, environment, and age. Supplementing eunuchs with testosterone during their second decade, for example, causes slow progression of androgenic alopecia over many years, while testosterone late in life causes rapid hair loss within a month.
An example of premature age effect is Werner's syndrome, a condition of accelerated aging from low-fidelity copying of mRNA. Affected children display premature androgenic alopecia.
Permanent hair-loss is a result of reduction of the number of living hair matrixes. Long-term of insufficiency of nutrition is an important cause for the death of hair matrixes. Misrepair-accumulation aging theory suggests that dermal fibrosis is associated with the progressive hair-loss and hair-whitening in old people. With age, the dermal layer of the skin has progressive deposition of collagen fibers, and this is a result of accumulation of Misrepairs of derma. Fibrosis makes the derma stiff and makes the tissue have increased resistance to the walls of blood vessels. The tissue resistance to arteries will lead to the reduction of blood supply to the local tissue including the papillas. Dermal fibrosis is progressive; thus the insufficiency of nutrition to papillas is permanent. Senile hair-loss and hair-whitening are partially a consequence of the fibrosis of the skin.
Diagnosis
The diagnosis of androgenic alopecia can be usually established based on clinical presentation in men. In women, the diagnosis usually requires more complex diagnostic evaluation. Further evaluation of the differential requires exclusion of other causes of hair loss, and assessing for the typical progressive hair loss pattern of androgenic alopecia. Trichoscopy can be used for further evaluation. Biopsy may be needed to exclude other causes of hair loss, and histology would demonstrate perifollicular fibrosis. The Hamilton–Norwood scale has been developed to grade androgenic alopecia in males by severity.
Treatment
Combination therapy
Combinations of finasteride, minoxidil and ketoconazole are more effective than individual use.
Combination therapy of LLLT or microneedling with finasteride or minoxidil demonstrated substantive increases in hair count.
Androgen-dependent
Finasteride is a medication of the 5α-reductase inhibitors (5-ARIs) class. By inhibiting type II 5-AR, finasteride prevents the conversion of testosterone to dihydrotestosterone in various tissues including the scalp. Increased hair on the scalp can be seen within three months of starting finasteride treatment and longer-term studies have demonstrated increased hair on the scalp at 24 and 48 months with continued use. Treatment with finasteride more effectively treats male-pattern hair loss at the crown than male-pattern hair loss at the front of the head and temples.
Dutasteride is a medication in the same class as finasteride but inhibits both type I and type II 5-alpha reductase. Dutasteride is approved for the treatment of male-pattern hair loss in Korea and Japan, but not in the United States. However, it is commonly used off-label to treat male-pattern hair loss.
Androgen-independent
Minoxidil dilates small blood vessels; it is not clear how this causes hair to grow. Other treatments include tretinoin combined with minoxidil, ketoconazole shampoo, dermarolling (Collagen induction therapy), spironolactone, alfatradiol, topilutamide (fluridil), topical melatonin, and intradermal and intramuscular botulinum toxin injections to the scalp.
Female pattern
There is evidence supporting the use of minoxidil as a safe and effective treatment for female pattern hair loss, and there is no significant difference in efficiency between 2% and 5% formulations. Finasteride was shown to be no more effective than placebo based on low-quality studies. The effectiveness of laser-based therapies is unclear. Bicalutamide, an antiandrogen, is another option for the treatment of female pattern hair loss.
Procedures
More advanced cases may be resistant or unresponsive to medical therapy and require hair transplantation. Naturally occurring units of one to four hairs, called follicular units, are excised and moved to areas of hair restoration. These follicular units are surgically implanted in the scalp in close proximity and in large numbers. The grafts are obtained from either follicular unit transplantation (FUT) or follicular unit extraction (FUE). In the former, a strip of skin with follicular units is extracted and dissected into individual follicular unit grafts, and in the latter individual hairs are extracted manually or robotically. The surgeon then implants the grafts into small incisions, called recipient sites. Cosmetic scalp tattoos can also mimic the appearance of a short, buzzed haircut.
Technological treatments
Low-level laser therapy (LLLT)
Low-level laser therapy or photobiomodulation is also referred to as red light therapy and cold laser therapy. It is a non-invasive treatment option.
LLLT is shown to increase hair density and growth in both genders. The types of devices (hat, comb, helmet) and duration did not alter the effectiveness, with more emphasis to be placed on lasers compared to LEDs. Ultraviolet and infrared light are more effective for alopecia areata, while red light and infrared light is more effective for androgenetic alopecia.
Medical reviews suggest that LLLT is as effective or potentially more than other non invasive and traditional therapies like minoxidil and finasteride but further studies such as RCTs, long term follow up studies, and larger double blinded trials need to be conducted to confirm the initial findings.
Platelet-rich plasma (PRP)
Using ones own cells and tissues and without harsh side effects, PRP is beneficial for alopecia areata and androgenetic alopecia and can be used as an alternative to minoxidil or finasteride. It has been documented to improve hair density and thickness in both genders. A minimum of 3 treatments, once a month for 3 months are recommended, and afterwards a 3-6 month period of continual appointments for maintenance. Factors that determine efficacy include amount of sessions, double versus single centrifugation, age and gender, and where the PRP is inserted.
Future larger randomized controlled trials and other high quality studies are still recommended to be carried out and published for a stronger consensus. Further development of a standardized practice for procedure is also recommended.
Alternative therapies
Many people use unproven treatments. Regarding female pattern alopecia, there is no evidence for vitamins, minerals, or other dietary supplements. As of 2008, there is little evidence to support the use of lasers to treat male-pattern hair loss. The same applies to special lights. Dietary supplements are not typically recommended. A 2015 review found a growing number of papers in which plant extracts were studied but only one randomized controlled clinical trial, namely a study in 10 people of saw palmetto extract.
Research
A 2023 study on genetically engineered mice published in the journal PNAS found that increasing production of a particular microRNA in hair follicle stem cells, which naturally harden with age, softened the cells and stimulated hair growth. The authors of the study said the next research step is to introduce the microRNA into the stem cells using nanoparticles applied directly to the skin, with the goal of developing a similar topical application for humans.
Prognosis
Androgenic alopecia is typically experienced as a "moderately stressful condition that diminishes body image satisfaction". However, although most men regard baldness as an unwanted and distressing experience, they usually are able to cope and retain integrity of personality.
Although baldness is not as common in women as in men, the psychological effects of hair loss tend to be much greater. Typically, the frontal hairline is preserved, but the density of hair is decreased on all areas of the scalp. Previously, it was believed to be caused by testosterone just as in male baldness, but most women who lose hair have normal testosterone levels.
Epidemiology
Female androgenic alopecia has become a growing problem that, according to the American Academy of Dermatology, affects around 30 million women in the United States. Although hair loss in females normally occurs after the age of 50 or even later when it does not follow events like pregnancy, chronic illness, crash diets, and stress among others, it is now occurring at earlier ages with reported cases in women as young as 15 or 16.
For male androgenic alopecia, by the age of 50 30-50% of men have it, hereditarily there is an 80% predisposition. Notably, the link between androgenetic alopecia and metabolic syndrome is strongest in non-obese men.
Society and culture
Studies have been inconsistent across cultures regarding how balding men rate on the attraction scale. While a 2001 South Korean study showed that most people rated balding men as less attractive, a 2002 survey of Welsh women found that they rated bald and gray-haired men quite desirable. One of the proposed social theories for male pattern hair loss is that men who embraced complete baldness by shaving their heads subsequently signaled dominance, high social status, and/or longevity.
Biologists have hypothesized the larger sunlight-exposed area would allow more vitamin D to be synthesized, which might have been a "finely tuned mechanism to prevent prostate cancer" as the malignancy itself is also associated with higher levels of DHT.
Myths
Many myths exist regarding the possible causes of baldness and its relationship with one's virility, intelligence, ethnicity, job, social class, wealth, and many other characteristics.
Weight training and other types of physical activity cause baldness
Because it increases testosterone levels, many Internet forums have put forward the idea that weight training and other forms of exercise increase hair loss in predisposed individuals. Although scientific studies do support a correlation between exercise and testosterone, no direct study has found a link between exercise and baldness. However, a few have found a relationship between a sedentary life and baldness, suggesting exercise is causally relevant. The type or quantity of exercise may influence hair loss.
Testosterone levels are not a good marker of baldness, and many studies actually show paradoxical low testosterone in balding persons, although research on the implications is limited.
Baldness can be caused by emotional stress, sleep deprivation, etc.
Emotional stress has been shown to accelerate baldness in genetically susceptible individuals.
Stress due to sleep deprivation in military recruits lowered testosterone levels, but is not noted to have affected SHBG. Thus, stress due to sleep deprivation in fit males is unlikely to elevate DHT, which is one cause of male pattern baldness. Whether sleep deprivation can cause hair loss by some other mechanism is not clear.
Bald men are more 'virile' or sexually active than others
Levels of free testosterone are strongly linked to libido and DHT levels, but unless free testosterone is virtually nonexistent, levels have not been shown to affect virility. Men with androgenic alopecia are more likely to have a higher baseline of free androgens. However, sexual activity is multifactoral, and androgenic profile is not the only determining factor in baldness. Additionally, because hair loss is progressive and free testosterone declines with age, a male's hairline may be more indicative of his past than his present disposition.
Frequent ejaculation causes baldness
Many misconceptions exist about what can help prevent hair loss, one of these being that lack of sexual activity will automatically prevent hair loss. While a proven direct correlation exists between increased frequency of ejaculation and increased levels of DHT, as shown in a recent study by Harvard Medical School, the study suggests that ejaculation frequency may be a sign, rather than a cause, of higher DHT levels.
The only published study to test correlation between ejaculation frequency and baldness was probably large enough to detect an association (1,390 subjects) and found no correlation, although persons with only vertex androgenetic alopecia had fewer female sexual partners than those of other androgenetic alopecia categories (such as frontal or both frontal and vertex). One study may not be enough, especially in baldness, where there is a complex with age.
Other animals
Animal models of androgenic alopecia occur naturally and have been developed in transgenic mice; chimpanzees (Pan troglodytes); bald uakaris (Cacajao rubicundus); and stump-tailed macaques (Macaca speciosa and M. arctoides). Of these, macaques have demonstrated the greatest incidence and most prominent degrees of hair loss.
Baldness is not a trait unique to human beings. One possible case study is about a maneless male lion in the Tsavo area. The Tsavo lion prides are unique in that they frequently have only a single male lion with usually seven or eight adult females, as opposed to four females in other lion prides. Male lions may have heightened levels of testosterone, which could explain their reputation for aggression and dominance, indicating that lack of mane may at one time have had an alpha correlation.
Although nonhuman primates do not go bald, their hairlines do undergo recession. In infancy the hairline starts at the top of the supraorbital ridge, but slowly recedes after puberty to create the appearance of a small forehead.
| Biology and health sciences | Health and fitness: General | Health |
1404351 | https://en.wikipedia.org/wiki/Palpation | Palpation | Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine its size, shape, firmness, or location (for example, a veterinarian can feel the stomach of a pregnant animal to ensure good health and successful delivery).
Palpation is an important part of the physical examination; the sense of touch is just as important in this examination as the sense of sight is. Physicians develop great skill in palpating problems below the surface of the body, becoming able to detect things that untrained persons would not. Mastery of anatomy and much practice are required to achieve a high level of skill. The concept of being able to detect or notice subtle tactile signs and to recognize their significance or implications is called appreciating them (just as in general vocabulary one can speak of appreciating the importance of something). Nonetheless, some things are not palpable, which is why additional medical tests, such as medical imaging and laboratory tests, are often needed to make a diagnosis. However, many other problems are palpable. Examples include pulses, abdominal distension, cardiac thrills, fremitus, and various hernias, joint dislocations, bone fractures, and tumors, among others.
Uses
Palpation is used by physicians, as well as chiropractors, nurses, massage therapists, physical therapists, osteopaths and occupational therapists, to assess the texture of a patient's tissue (such as swelling or muscle tone), to locate the spatial coordinates of particular anatomical landmarks (e.g., to assess range and quality of joint motion), and assess tenderness through tissue deformation (e.g. provoking pain with pressure or stretching). In summary, palpation might be used either to determine painful areas and to qualify pain felt by patients, or to locate three-dimensional coordinates of anatomical landmarks to quantify some aspects of the palpated subject.
Palpation is typically used for thoracic and abdominal examinations, but can also be used to diagnose edema. Palpation is also a simple method of examining the pulse. It is used by veterinarians to check animals for pregnancy, and by midwives to determine the position of a fetus.
Tactile palpation is one of the oldest, simplest, and least expensive methods for approximate intraocular pressure assessment.
Quantitative palpation of anatomical landmarks for measurements must occur according to strict protocols if one wishes to achieve reproducible measurements. Palpation protocols are usually based on well-described definitions for the location of anatomical, usually skeletal, landmarks.
Locating anatomical landmarks
Locating anatomical landmarks can be performed using two palpation protocols: 1) manual palpation that allows the spatial location of landmarks using hands combined or not with three-dimensional (3D) digitizing, and 2) virtual palpation on 3D computer models obtained, for example, from medical imaging.
Manual palpation of skeletal landmarks (illustrated here on a patient's shoulder, see left image). The palpating hand locates the palpated landmarks with a satisfactory accuracy (below 1 cm). Reflective markers are part of the scientific protocol and allow further quantified motion analysis for joint disorders follow-up.
Virtual palpation of skeletal landmarks located on a 3D bone model (illustrated here on a patient's knee model obtained from medical imaging, see right image). Colored spheres on bones indicate palpated skeletal landmarks. This method combined with quantified manual palpation allows subject-specific visualization of joint behavior during particular motion tasks (e.g., walking, stair climbing, etc.).
The above protocols can be used independently. Manual palpation is used in clinical activities for various aims: identification of painful areas; positioning of particular pieces of equipment (electromyography electrodes, auscultation, external landmarks used in clinical motion analysis or body surface scanning); or measurements of morphological parameters (e.g., limb length). Virtual palpation alone is useful to quantify individual morphological parameters from medical imaging: limb length; limb orientation; joint angle; or distance between various skeletal locations.
Combining data from both manual and virtual palpation protocols allows achieving supplementary analysis: registration protocols aiming at building reference frames for motion representation according reproducible clinical conventions; to modelize joint kinematics accurately during musculoskeletal analysis; to align precisely orthopedic tools according to the individual anatomy of a patient; or to wrap and to scale surface textures to motion data when creating animation characters.
Use of standardized definitions for the above activities allows better result comparison and exchange; this is a key element for patient follow-up or the elaboration of quality clinical and research databases. Such definitions also allow acceptable repeat ability by individuals with different backgrounds (physiotherapists, medical doctors, nurses, engineers, etc.). If applied strictly, these definitions allow better data exchange and result comparison thanks to standardization of the procedure. Without anatomical landmark standardization, palpation is prone to error and poorly reproducible.
Elastography
Nowadays, the medical imaging modality of elastography can also be used to determine the stiffness of tissues. Manual palpation has several important limitations: it is limited to tissues accessible to the physician's hand, it is distorted by any intervening tissue, and it is qualitative but not quantitative. Elastography is able to overcome many these challenges and improve on the benefits of palpation.
Elastography is a relatively new technology and entered the clinic primarily in the last decade. The most prominent techniques use ultrasound or magnetic resonance imaging (MRI) to make both the stiffness map and an anatomical image for comparison.
Computerized palpation
While not widespread amongst elastography methods, computerized palpation is of interest here because it essentially uses palpation to measure the stiffness, whereas other techniques will obtain data using other methods. Computerized palpation, also called "tactile imaging", "mechanical imaging" or "stress imaging", is a medical imaging modality that translates the sense of touch into a digital image. The tactile image is a function of P(x,y,z), where P is the pressure on soft tissue surface under applied deformation and x,y,z are coordinates where pressure P was measured. Tactile imaging closely mimics manual palpation, since the probe of the device with a pressure sensor array mounted on its face acts similar to human fingers during clinical examination, slightly deforming soft tissue by the probe and detecting resulting changes in the pressure pattern.
Palpation under general anesthesia
Palpation under general anesthesia is sometimes necessary, such as when there is a need to palpate structures deep in the abdominal or pelvic cavity, since it would otherwise cause considerable patient discomfort and subsequent contraction of the abdominal muscles which would make the examination difficult. It is used, for example, in the staging of cervical cancer.
| Biology and health sciences | Diagnostics | Health |
1405654 | https://en.wikipedia.org/wiki/Thermolabile | Thermolabile | Thermolabile refers to a substance which is subject to, decomposition, or change in response to heat. This term is often used
describe biochemical substances.
For example, many bacterial exotoxins are thermolabile and can be easily inactivated by the application of moderate heat.
Enzymes are also thermolabile and lose their activity when the temperature rises.
Loss of activity in such toxins and enzymes is likely due to change in the three-dimensional structure of the toxin protein during exposure to heat.
In pharmaceutical compounds, heat generated during grinding may lead to degradation of thermolabile compounds.
This is of particular use in testing gene function. This is done by intentionally creating mutants which are thermolabile. Growth below the permissive temperature allows normal protein function, while increasing the temperature above the permissive temperature ablates activity, likely by denaturing the protein.
Thermolabile enzymes are also studied for their applications in DNA replication techniques, such as PCR, where thermostable enzymes are necessary for proper DNA replication. Enzyme function at higher temperatures may be enhanced with trehalose, which opens up the possibility of using normally thermolabile enzymes in DNA replication.
| Biology and health sciences | Basics | Biology |
1405965 | https://en.wikipedia.org/wiki/Horsecar | Horsecar | A horsecar, horse-drawn tram, horse-drawn streetcar (U.S.), or horse-drawn railway (historical), is an animal-powered (usually horse) tram or streetcar.
Summary
The horse-drawn tram (horsecar) was an early form of public rail transport, which developed out of industrial haulage routes that had long been in existence, and from the omnibus routes that first ran on public streets in the 1820s, using the newly improved iron or steel rail or 'tramway'. They were local versions of the stagecoach lines and picked up and dropped off passengers on a regular route, without the need to be pre-hired. Horsecars on tramlines were an improvement over the omnibus, because the low rolling resistance of metal wheels on iron or steel rails (usually grooved from 1852 on) allowed the animals to haul a greater load for a given effort than the omnibus, and gave a smoother ride.
The horse-drawn streetcar combined the low cost, flexibility, and safety of animal power with the efficiency, smoothness, and all-weather capability of a rail track. Animal power at the time was seen as safer than steam power in that early locomotives frequently suffered from boiler explosions. Rails were seen as all-weather because streets of the time might be poorly paved, or not paved at all, allowing wagon wheels to sink in mud during rain or snow.
History
Canada
In 1861, Toronto Street Railway horsecars replaced horse-drawn omnibuses as a public transit mode in Toronto. Electric streetcars later replaced the horsecars between 1892 and 1894. The Toronto Street Railway created Toronto's unique broad gauge of . The streets were unpaved, and a step rail was employed. The horsecars had flanged wheels and ran on the upper level of the step. Ordinary wagons and carriages ran on the broad lower step inside. This necessitated a wider gauge. This broad Toronto gauge is still used today by the Toronto streetcar system and three lines of the Toronto subway. The Metropolitan Street Railway operated a horsecar line in then-suburban North Toronto from 1885 until the line was electrified in 1890; this horsecar line also used Toronto gauge.
India
The first horse-drawn trams in India ran a distance between Sealdah and Armenian Ghat Street on 24 February 1873. The service was discontinued on 20 November of that year. The Calcutta Tramway Company was formed and registered in London on 22 December 1880. Metre-gauge horse-drawn tram tracks were laid from Sealdah to Armenian Ghat via Bowbazar Street, Dalhousie Square and Strand Road. The route was inaugurated by Viceroy Ripon on 1 November 1880. In 1882, steam locomotives were deployed experimentally to haul tram cars. By the end of the 19th century the company owned 166 tram cars, 1000 horses, seven steam locomotives and 19 miles of tram tracks. In 1900, electrification of the tramway and reconstruction of its tracks to (standard gauge) began. In 1902, the first electric tramcar in India ran from Esplanade to Kidderpore on 27 March and on 14 June from Esplanade to Kalighat.
The Bombay Tramway Company was set up in 1873. After a contract was signed between the Bombay Tramway Company, the municipality and the Stearns and Kitteredge company, the Bombay Presidency enacted the Bombay Tramways Act, 1874 licensing the company to run a horsecar tram service in the city. On 9 May 1874 the first horse-drawn carriage made its début in the city, plying the Colaba–Pydhone via Crawford Market, and Bori Bunder to Pydhonie via Kalbadevi routes. The initial fare was three annas (15 paise pre-decimalisation), and no tickets were issued. As the service became increasingly popular, the fare was reduced to two annas (10 pre-decimalisation paise). Later that year, tickets were issued to curb increasing ticket-less travel. Stearns and Kitteredge reportedly had a stable of 1,360 horses over the lifetime of the service.
United Kingdom
The first tram services in the world were started by the Swansea and Mumbles Railway in Wales, using specially designed carriages on an existing tramline built for horse-drawn freight dandies. Fare-paying passengers were carried on a line between Oystermouth, Mumbles and Swansea Docks from 1807. The Gloucester and Cheltenham Tramroad (1809) carried passengers although its main purpose was freight.
In spite of its early start, it took many years for horse-drawn streetcars to become widely acceptable across Britain; the American George Francis Train first introduced them to Birkenhead Corporation Tramways' predecessor in Birkenhead in 1860 but was jailed for "breaking and injuring" the highway when he next tried to lay the first tram tracks on the roads of London. An 1870 Act of Parliament overcame these legal obstacles by defining responsibilities and for the next three decades many local tramway companies were founded, using horse-drawn carriages, until replaced by cable, steam or electric traction. Many companies adopted a design of a partly enclosed double-decker carriage hauled by two horses. The last horse-drawn tram was retired from London in 1915. Horses continued to be used for light shunting well into the 20th century. The last horse used for shunting on British Railways was retired on 21 February 1967 in Newmarket, Suffolk.
United States
In the United States the very first streetcar appeared in New Orleans in 1832, operated by the Pontchartrain Railroad Company, followed by those in 1832 on the New York and Harlem Railroad in New York City. The latter cars were designed by John Stephenson of New Rochelle, New York, and constructed at his company in New York City. The earliest streetcars used horses and sometimes mules, usually two as a team, to haul the cars. Rarely, other animals were tried, including humans in emergency circumstances. By the mid-1880s, there were 415 street railway companies in the US operating over of track and carrying 188 million passengers per year using horsecars. By 1890 New Yorkers took 297 horsecar rides per capita per year. The average street car horse had a life expectancy of about two years.
Elsewhere
The first horse-drawn rail cars in Continental Europe were operated from 1828 by the České Budějovice - Linz railway. Europe saw a proliferation of horsecar use for new tram services from the mid-1860s, with many towns building new networks.
Tropical plantations (for products such as henequen and bananas) made extensive use of animal-powered trams for both passengers and freight, often employing the Decauville narrow-gauge portable track system. In some cases these systems were very extensive and evolved into interurban tram networks (as in the Yucatan, which sported over of such lines). Surviving examples may be found in both Brazil and the Yucatán, and some examples in the latter still use horsecars.
Decline
Problems with horsecars included the fact that any given animal could only work so many hours on a given day, had to be housed, groomed, fed and cared for day in and day out, and produced prodigious amounts of manure, which the streetcar company was charged with storing and then disposing. Since a typical horse pulled a streetcar for about a dozen miles () a day and worked for four or five hours, many systems needed ten or more horses in stable for each horsecar.
Horsecars were largely replaced by electric-powered streetcars following the invention by Frank J. Sprague of an overhead trolley system on streetcars for collecting electricity from overhead wires. His spring-loaded trolley pole used a wheel to travel along the wire. In late 1887 and early 1888, using his trolley system, Sprague installed the first successful large electric street railway system in Richmond, Virginia.
Long a transportation obstacle, the hills of Richmond included grades of over 10%, and were an excellent proving ground for acceptance of the new technology in other cities. Within a year, the economy of electric power had replaced more costly horsecars in many cities. By 1889, 110 electric railways incorporating Sprague's equipment had been begun or planned on several continents.
Many large metropolitan lines lasted well into the early twentieth century. New York City had a regular horsecar service on the Bleecker Street Line until its closure in 1917. Pittsburgh, Pennsylvania, had its Sarah Street line drawn by horses until 1923. The last regular mule-drawn cars in the US ran in Sulphur Rock, Arkansas, until 1926 and were commemorated by a U.S. postage stamp issued in 1983.
Toronto's horse-drawn streetcar operations ended in 1891. In other countries animal-powered tram services often continued well into the 20th century; the last mule tram service in Mexico City ended in 1932, and a mule tram in Celaya, Mexico, survived until 1954.
Operational horsecars
A few original horsecar lines have survived or have been revived as tourist attractions, and in recent years several replica horsecar lines have been built. Below is a list of locations around the world with operational horsecars that are open to the public.
| Technology | Animal-powered transport | null |
28923910 | https://en.wikipedia.org/wiki/Electronic%20engineering | Electronic engineering | Electronic engineering is a sub-discipline of electrical engineering that emerged in the early 20th century and is distinguished by the additional use of active components such as semiconductor devices to amplify and control electric current flow. Previously electrical engineering only used passive devices such as mechanical switches, resistors, inductors, and capacitors.
It covers fields such as analog electronics, digital electronics, consumer electronics, embedded systems and power electronics. It is also involved in many related fields, for example solid-state physics, radio engineering, telecommunications, control systems, signal processing, systems engineering, computer engineering, instrumentation engineering, electric power control, photonics and robotics.
The Institute of Electrical and Electronics Engineers (IEEE) is one of the most important professional bodies for electronics engineers in the US; the equivalent body in the UK is the Institution of Engineering and Technology (IET). The International Electrotechnical Commission (IEC) publishes electrical standards including those for electronics engineering.
History and development
Electronics engineering as a profession emerged following the identification of the electron in 1897 and the subsequent invention of the vacuum tube which could amplify and rectify small electrical signals, that inaugurated the field of electronics. Practical applications started with the invention of the diode by Ambrose Fleming and the triode by Lee De Forest in the early 1900s, which made the detection of small electrical voltages such as radio signals from a radio antenna possible with a non-mechanical device. The growth of electronics was rapid. By the early 1920s, commercial radio broadcasting and communications were becoming widespread and electronic amplifiers were being used in such diverse applications as long-distance telephony and the music recording industry.
The discipline was further enhanced by the large amount of electronic systems development during World War II in such as radar and sonar, and the subsequent peace-time consumer revolution following the invention of transistor by William Shockley, John Bardeen and Walter Brattain.
Specialist areas
Electronics engineering has many subfields. This section describes some of the most popular.
Electronic signal processing deals with the analysis and manipulation of signals. Signals can be either analog, in which case the signal varies continuously according to the information, or digital, in which case the signal varies according to a series of discrete values representing the information.
For analog signals, signal processing may involve the amplification and filtering of audio signals for audio equipment and the modulation and demodulation of radio frequency signals for telecommunications. For digital signals, signal processing may involve compression, error checking and error detection, and correction.
Telecommunications engineering deals with the transmission of information across a medium such as a co-axial cable, an optical fiber, or free space. Transmissions across free space require information to be encoded in a carrier wave in order to be transmitted, this is known as modulation. Popular analog modulation techniques include amplitude modulation and frequency modulation.
Once the transmission characteristics of a system are determined, telecommunication engineers design the transmitters and receivers needed for such systems. These two are sometimes combined to form a two-way communication device known as a transceiver. A key consideration in the design of transmitters is their power consumption as this is closely related to their signal strength. If the signal strength of a transmitter is insufficient the signal's information will be corrupted by noise.
Aviation-electronics engineering and Aviation-telecommunications engineering, are concerned with aerospace applications. Aviation-telecommunication engineers include specialists who work on airborne avionics in the aircraft or ground equipment. Specialists in this field mainly need knowledge of computer, networking, IT, and sensors. These courses are offered at such as Civil Aviation Technology Colleges.
Control engineering has a wide range of electronic applications from the flight and propulsion systems of commercial airplanes to the cruise control present in many modern cars. It also plays an important role in industrial automation. Control engineers often use feedback when designing control systems.
Instrumentation engineering deals with the design of devices to measure physical quantities such as pressure, flow, and temperature. The design of such instrumentation requires a good understanding of electronics engineering and physics; for example, radar guns use the Doppler effect to measure the speed of oncoming vehicles. Similarly, thermocouples use the Peltier–Seebeck effect to measure the temperature difference between two points.
Often instrumentation is not used by itself, but instead as the sensors of larger electrical systems. For example, a thermocouple might be used to help ensure a furnace's temperature remains constant. For this reason, instrumentation engineering is often viewed as the counterpart of control engineering.
Computer engineering deals with the design of computers and computer systems. This may involve the design of new computer hardware, the design of PDAs or the use of computers to control an industrial plant. Development of embedded systems—systems made for specific tasks (e.g., mobile phones)—is also included in this field. This field includes the microcontroller and its applications.
Computer engineers may also work on a system's software. However, the design of complex software systems is often the domain of software engineering which falls under computer science, which is usually considered a separate discipline.
VLSI design engineering VLSI stands for very large-scale integration. It deals with fabrication of ICs and various electronic components. In designing an integrated circuit, electronics engineers first construct circuit schematics that specify the electrical components and describe the interconnections between them. When completed, VLSI engineers convert the schematics into actual layouts, which map the layers of various conductor and semiconductor materials needed to construct the circuit.
Education and training
Electronics is a subfield within the wider electrical engineering academic subject. Electronics engineers typically possess an academic degree with a major in electronics engineering. The length of study for such a degree is usually three or four years and the completed degree may be designated as a Bachelor of Engineering, Bachelor of Science, Bachelor of Applied Science, or Bachelor of Technology depending upon the university. Many UK universities also offer Master of Engineering (MEng) degrees at the graduate level.
Some electronics engineers also choose to pursue a postgraduate degree such as a Master of Science, Doctor of Philosophy in Engineering, or an Engineering Doctorate. The master's degree is being introduced in some European and American Universities as a first degree and the differentiation of an engineer with graduate and postgraduate studies is often difficult. In these cases, experience is taken into account. The master's degree may consist of either research, coursework or a mixture of the two. The Doctor of Philosophy consists of a significant research component and is often viewed as the entry point to academia.
In most countries, a bachelor's degree in engineering represents the first step towards certification and the degree program itself is certified by a professional body. Certification allows engineers to legally sign off on plans for projects affecting public safety. After completing a certified degree program, the engineer must satisfy a range of requirements, including work experience requirements, before being certified. Once certified the engineer is designated the title of Professional Engineer (in the United States, Canada, and South Africa), Chartered Engineer or Incorporated Engineer (in the United Kingdom, Ireland, India, and Zimbabwe), Chartered Professional Engineer (in Australia and New Zealand) or European Engineer (in much of the European Union).
A degree in electronics generally includes units covering physics, chemistry, mathematics, project management and specific topics in electrical engineering. Initially, such topics cover most, if not all, of the subfields of electronics engineering. Students then choose to specialize in one or more subfields towards the end of the degree.
Fundamental to the discipline are the sciences of physics and mathematics as these help to obtain both a qualitative and quantitative description of how such systems will work. Today, most engineering work involves the use of computers and it is commonplace to use computer-aided design and simulation software programs when designing electronic systems. Although most electronic engineers will understand basic circuit theory, the theories employed by engineers generally depend upon the work they do. For example, quantum mechanics and solid-state physics might be relevant to an engineer working on VLSI but are largely irrelevant to engineers working with embedded systems.
Apart from electromagnetics and network theory, other items in the syllabus are particular to electronic engineering courses. Electrical engineering courses have other specialisms such as machines, power generation, and distribution. This list does not include the extensive engineering mathematics curriculum that is a prerequisite to a degree.
Supporting knowledge areas
The huge breadth of electronics engineering has led to the use of a large number of specialists supporting knowledge areas.
Elements of vector calculus: divergence and curl; Gauss' and Stokes' theorems, Maxwell's equations: differential and integral forms. Wave equation, Poynting vector. Plane waves: propagation through various media; reflection and refraction; phase and group velocity; skin depth. Transmission lines: characteristic impedance; impedance transformation; Smith chart; impedance matching; pulse excitation. Waveguides: modes in rectangular waveguides; boundary conditions; cut-off frequencies; dispersion relations. Antennas: Dipole antennas; antenna arrays; radiation pattern; reciprocity theorem, antenna gain.
Network graphs: matrices associated with graphs; incidence, fundamental cut set, and fundamental circuit matrices. Solution methods: nodal and mesh analysis. Network theorems: superposition, Thevenin and Norton's maximum power transfer, Wye-Delta transformation. Steady state sinusoidal analysis using phasors. Linear constant coefficient differential equations; time domain analysis of simple RLC circuits, Solution of network equations using Laplace transform: frequency domain analysis of RLC circuits. 2-port network parameters: driving point and transfer functions. State equations for networks.
Electronic devices: Energy bands in silicon, intrinsic and extrinsic silicon. Carrier transport in silicon: diffusion current, drift current, mobility, resistivity. Generation and recombination of carriers. p-n junction diode, Zener diode, tunnel diode, BJT, JFET, MOS capacitor, MOSFET, LED, p-i-n and avalanche photo diode, LASERs. Device technology: integrated circuit fabrication process, oxidation, diffusion, ion implantation, photolithography, n-tub, p-tub and twin-tub CMOS process.
Analog circuits: Equivalent circuits (large and small-signal) of diodes, BJT, JFETs, and MOSFETs. Simple diode circuits, clipping, clamping, rectifier. Biasing and bias stability of transistor and FET amplifiers. Amplifiers: single-and multi-stage, differential, operational, feedback and power. Analysis of amplifiers; frequency response of amplifiers. Simple op-amp circuits. Filters. Sinusoidal oscillators; criterion for oscillation; single-transistor and op-amp configurations. Function generators and wave-shaping circuits, Power supplies.
Digital circuits: Boolean functions (NOT, AND, OR, XOR,...). Logic gates digital IC families (DTL, TTL, ECL, MOS, CMOS). Combinational circuits: arithmetic circuits, code converters, multiplexers, and decoders. Sequential circuits: latches and flip-flops, counters, and shift-registers. Sample and hold circuits, ADCs, DACs. Semiconductor memories. Microprocessor 8086: architecture, programming, memory, and I/O interfacing.
Signals and systems: Definitions and properties of Laplace transform, continuous-time and discrete-time Fourier series, continuous-time and discrete-time Fourier Transform, z-transform. Sampling theorems. Linear Time-Invariant (LTI) Systems: definitions and properties; causality, stability, impulse response, convolution, poles and zeros frequency response, group delay and phase delay. Signal transmission through LTI systems. Random signals and noise: probability, random variables, probability density function, autocorrelation, power spectral density, and function analogy between vectors & functions.
Electronic Control systems
Basic control system components; block diagrammatic description, reduction of block diagrams — Mason's rule. Open loop and closed loop (negative unity feedback) systems and stability analysis of these systems. Signal flow graphs and their use in determining transfer functions of systems; transient and steady-state analysis of LTI control systems and frequency response. Analysis of steady-state disturbance rejection and noise sensitivity.
Tools and techniques for LTI control system analysis and design: root loci, Routh–Hurwitz stability criterion, Bode and Nyquist plots. Control system compensators: elements of lead and lag compensation, elements of proportional–integral–derivative (PID) control. Discretization of continuous-time systems using zero-order hold and ADCs for digital controller implementation. Limitations of digital controllers: aliasing. State variable representation and solution of state equation of LTI control systems. Linearization of Nonlinear dynamical systems with state-space realizations in both frequency and time domains. Fundamental concepts of controllability and observability for MIMO LTI systems. State space realizations: observable and controllable canonical form. Ackermann's formula for state-feedback pole placement. Design of full order and reduced order estimators.
Communications
Analog communication systems: amplitude and angle modulation and demodulation systems, spectral analysis of these operations, superheterodyne noise conditions.
Digital communication systems: pulse-code modulation (PCM), differential pulse-code modulation (DPCM), delta modulation (DM), digital modulation – amplitude, phase- and frequency-shift keying schemes (ASK, PSK, FSK), matched-filter receivers, bandwidth consideration and probability of error calculations for these schemes, GSM, TDMA.
Professional bodies
Professional bodies of note for electrical engineers USA's Institute of Electrical and Electronics Engineers (IEEE) and the UK's Institution of Engineering and Technology (IET). Members of the Institution of Engineering and Technology (MIET) are recognized professionally in Europe, as electrical and computer engineers. The IEEE claims to produce 30 percent of the world's literature in electrical and electronics engineering, has over 430,000 members, and holds more than 450 IEEE sponsored or cosponsored conferences worldwide each year. SMIEEE is a recognised professional designation in the United States.
Project engineering
For most engineers not involved at the cutting edge of system design and development, technical work accounts for only a fraction of the work they do. A lot of time is also spent on tasks such as discussing proposals with clients, preparing budgets and determining project schedules. Many senior engineers manage a team of technicians or other engineers and for this reason, project management skills are important. Most engineering projects involve some form of documentation and strong written communication skills are therefore very important.
The workplaces of electronics engineers are just as varied as the types of work they do. Electronics engineers may be found in the pristine laboratory environment of a fabrication plant, the offices of a consulting firm or in a research laboratory. During their working life, electronics engineers may find themselves supervising a wide range of individuals including scientists, electricians, programmers, and other engineers.
Obsolescence of technical skills is a serious concern for electronics engineers. Membership and participation in technical societies, regular reviews of periodicals in the field, and a habit of continued learning are therefore essential to maintaining proficiency, which is even more crucial in the field of consumer electronics products.
| Technology | Disciplines | null |
6786780 | https://en.wikipedia.org/wiki/Light%20pillar | Light pillar | A light pillar or ice pillar is an atmospheric optical phenomenon in which a vertical beam of light appears to extend above and/or below a light source. The effect is created by the reflection of light from tiny ice crystals that are suspended in the atmosphere or that comprise high-altitude clouds (e.g. cirrostratus or cirrus clouds). If the light comes from the Sun (usually when it is near or even below the horizon), the phenomenon is called a sun pillar or solar pillar. Light pillars can also be caused by the Moon or terrestrial sources, such as streetlights and erupting volcanoes.
Formation
Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos. The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air. Each flake acts as a tiny mirror which reflects light sources that are appropriately positioned below it (see drawing), and the presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column. The larger and more numerous the crystals, the more pronounced this effect becomes. More rarely, column-shaped crystals can cause light pillars as well. In very cold weather, the ice crystals can be suspended near the ground, in which case they are referred to as diamond dust.
Unlike a light beam, a light pillar is not physically located above or below the light source. Its appearance as a vertical line is an optical illusion, resulting from the collective reflection off the ice crystals; but only those that are in the common vertical plane, direct the light rays towards the observer (See drawing). This is similar to viewing a light source on a body of water. Ripples on the surface of the water reflect the light source in many directions, and those that happen to be aimed at the viewer, combine to form a bright line pointing toward the light source.
| Physical sciences | Atmospheric optics | Earth science |
30422155 | https://en.wikipedia.org/wiki/Interstellar%20ice | Interstellar ice | Interstellar ice consists of grains of volatiles in the ice phase that form in the interstellar medium. Ice and dust grains form the primary material out of which the Solar System was formed. Grains of ice are found in the dense regions of molecular clouds, where new stars are formed. Temperatures in these regions can be as low as , allowing molecules that collide with grains to form an icy mantle. Thereafter, atoms undergo thermal motion across the surface, eventually forming bonds with other atoms. This results in the formation of water and methanol. Indeed, the ices are dominated by water and methanol, as well as ammonia, carbon monoxide and carbon dioxide. Frozen formaldehyde and molecular hydrogen may also be present. Found in lower abundances are nitriles, ketones, esters and carbonyl sulfide. The mantles of interstellar ice grains are generally amorphous, becoming crystalline only in the presence of a star.
The composition of interstellar ice can be determined through its infrared spectrum. As starlight passes through a molecular cloud containing ice, molecules in the cloud absorb energy. This adsorption occurs at the characteristic frequencies of vibration of the gas and dust. Ice features in the cloud are relatively prominently in this spectra, and the composition of the ice can be determined by comparison with samples of ice materials on Earth. In the sites directly observable from Earth, around 60–70% of the interstellar ice consists of water, which displays a strong emission at 3.05 μm from stretching of the O–H bond.
In September 2012, NASA scientists reported that polycyclic aromatic hydrocarbons (PAHs), subjected to interstellar medium (ISM) conditions, are transformed, through hydrogenation, oxygenation and hydroxylation, to more complex organics - "a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively". Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."
Older than the Sun
Research published in the journal Science estimates that about 30–50% of the water in the Solar System, like the water on Earth, the discs around Saturn, and the meteorites of other planets, was present before the birth of the Sun.
Comet 67P/Churyumov–Gerasimenko
On 18 November 2014, spacecraft Philae revealed presence of large amount of water ice on the comet 67P/Churyumov–Gerasimenko, the report stating that "the strength of the ice found under a layer of dust on the first landing site is surprisingly high". The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument, which hammered a probe into the comet, estimated that the comet is hard as ice. "Although the power of the hammer was gradually increased, we were not able to go deep into the surface," explained Tilman Spohn from the DLR Institute for Planetary Research, who led the research team.
| Physical sciences | Basics_2 | Astronomy |
37027825 | https://en.wikipedia.org/wiki/International%20yard%20and%20pound | International yard and pound | The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959: Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States. The agreement defined the yard as exactly and the avoirdupois pound as exactly .
History
In October 1834, the British Houses of Parliament were destroyed in a fire. Among the items lost were the objects that defined the imperial standards of length and mass. New prototypes were subsequently created to replace the items lost in the fire, among them a new "yardstick" ruler in 1855, and with it a new formal definition of the yard. Two copies of the ruler were subsequently presented to the United States, which in turn adopted the measure for the United States national standard yard.
In 1866, the U.S. Congress passed a law that allowed, but did not require, the use of the metric system in trade and commerce. Included in the law was a table of conversion factors between the customary (i.e. English-derived) and metric units, among them a definition of the meter in terms of the yard, and the kilogram in terms of the pound. In 1893, the Mendenhall Order changed the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards. There were two factors that influenced the order: for one, the imperial standard yard of 1855 had been found to be unstable and shortening by measurable amounts. Secondly, the United States was a co-signee of the Treaty of the Metre of 1875 and had received two meter prototypes on which to base a new fundamental standard.
In the United Kingdom, a similar situation developed with the Weights and Measures Act 1897 legalizing the metric system, and Order in Council 411 (1898) defining the meter and kilogram in terms of the yard and pound. As a practical matter the British definitions were reversed, resulting in a de facto definition of the imperial yard as 36/39.370113 meter.
In the 1890s, Albert Michelson began conducting experiments in interferometry that led in 1903 to demonstrating the feasibility of using light waves as units of linear measurement. In 1908, two teams of researchers, one led by Michelson, defined the length of the international prototype meter in terms of light waves. In 1927, the International Bureau of Weights and Measures provisionally adopted the 1908 light-wave definition of the meter as a supplemental standard.
In 1930, the British Standards Institution adopted an inch of exactly 25.4 millimetres (mm), based on the 1927 light-wave definition of the meter. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known. In 1946, the British Commonwealth Scientific Conference recommended that members of the British Commonwealth adopt the inch as exactly 25.4 mm, and the 36-inch yard as exactly 0.9144 meters. The British Commonwealth Scientific Conference's recommendations were accepted by the Canadian Standards Association in 1951.
In October 1958, the International Committee on Weights and Measures made a recommendation that the meter be defined in atomic terms (specifically in terms of the orange line of krypton-86). To secure identical values for the yard and pound in precise measurements, representatives of six English-speaking nations—Australia, Canada, New Zealand, South Africa, United States and United Kingdom—agreed to adopt a common 'international yard and international pound'. According to that agreement, the international yard equals 0.9144 meters and the international pound equals 0.45359237 kilograms. The international yard was about two millionths of a meter longer than the imperial yard, while the international pound was about six ten-millionths of a kilogram lighter than the imperial pound.
The metric-based international yard and international pound were adopted by the United States National Bureau of Standards effective 1 July 1959. In Australia, the international yard and pound were instituted through Statutory Rule No. 142 of 1961, effective 1 January 1964. The UK adopted the international yard and pound for all purposes through the Weights and Measures Act 1963, effective 1 January 1964.
| Physical sciences | Measurement systems | Basics and measurement |
37031747 | https://en.wikipedia.org/wiki/Elaeis%20guineensis | Elaeis guineensis | Elaeis guineensis is a species of palm commonly just called oil palm but also sometimes African oil palm or macaw-fat. The first Western person to describe it and bring back seeds was the French naturalist Michel Adanson.
It is native to west and southwest Africa, specifically the area between Angola and The Gambia; the species name, guineensis, refers to the name for the area called Guinea, and not the modern country Guinea now bearing that name. The species is also now naturalised in Madagascar, Sri Lanka, Malaysia, Indonesia, Central America, Cambodia, the West Indies, and several islands in the Indian and Pacific Oceans. The closely related American oil palm E. oleifera and a more distantly related palm, Attalea maripa, are also used to produce palm oil.
E. guineensis was domesticated in West Africa along the south-facing Atlantic coast. There is insufficient documentation and insufficient research to make any guesses as to when this occurred. Human use of oil palms may date as far back as 5,000 years in Egypt; in the late 1800s, archaeologists discovered palm oil in a tomb at Abydos, Egypt dating back to 3000 BCE.
It is the principal source of palm oil. Oil palms can produce much more oil per unit of land area than most other oil-producing plants (about nine times more than soy and 4.5 times more than rapeseed).
Description
E. guineensis is monocotyledonous. Mature palms are single-stemmed and grow to tall. The leaves are pinnate and reach long. A young palm produces about 30 leaves a year. Established palms over 10 years produce about 20 leaves a year. The flowers are produced in dense clusters; each individual flower is small, with three sepals and three petals.
The palm fruit takes 5–6 months to develop from pollination to maturity. It is reddish, about the size of a large plum, and grows in large bunches. Each fruit is made up of an oily, fleshy outer layer (the pericarp), with a single seed (the palm kernel), also rich in oil. When ripe, each bunch of fruit weighs between depending on the age of the palm tree.
Planting
For each hectare of oil palm, which is harvested year-round, the annual production averages 20 tonnes of fruit yielding of palm oil and of seed kernels yielding of high-quality palm kernel oil, as well as of kernel meal. Kernel meal is processed for use as livestock feed.
All modern, commercial planting material consists of tenera palms or DxP hybrids, which are obtained by crossing thickshelled dura with shell-less pisifera. Although common commercial germinated seed is as thick-shelled as the dura mother palm, the resulting palm will produce thin-shelled tenera fruit. An alternative to germinated seed, once constraints to mass production are overcome, are tissue-cultured or "clonal" palms, which provide true copies of high-yielding DxP palms.
Genetics
Genome
Size: 1,800 megabase. First sequence available in 2013.
Chromosomes
Diploid, with a diploid number of 2n = 32.
Diversity
The Asian effective population size is very limited. The cultivars comprising cultivation in Asia descend from only four trees, which are themselves probably the result of a selfing of one parent.
Breeding
Unlike other relatives, oil palms do not produce offshoots; propagation is by sowing the seeds.
Several varieties and forms of E. guineensis have been selected that have different characteristics. These include:
Elais guineensis fo. dura
Elais guineensis var. pisifera
Elais guineensis fo. tenera
Before the Second World War, selection work had started in the Deli dura population in Malaya. Pollen was imported from Africa, and DxT and DxP crosses were made. Segregation of fruit forms in crosses made in the 1950s was often incorrect. In the absence of a good marker gene, there was no way of knowing whether control of pollination was adequate.
After the work of Beirnaert and Vanderweyen (1941), it became feasible to monitor the efficacy of controlled pollination. From 1963 until the introduction of the palm-pollinating weevil Elaeidobius kamerunicus in 1982, contamination in Malaysia's commercial plantings was generally low. Thrips, the main pollinating agent at that time, apparently rarely gained access to bagged female inflorescences. However, E. kamerunicus is much more persistent, and after it was introduced, Deli dura contamination became a significant problem. This problem apparently persisted for much of the 1980s, but in a 1991 comparison of seed sources, contamination had been reduced to below 2%, indicating control had been restored.
A 1992 study at a trial plot in Banting, Selangor, revealed the "yield of Deli dura oil palms after four generations of selection was 60% greater than that of the unselected base population. Crossing the dura and pisifera to give the thin-shelled tenera fruit type improved partitioning of dry matter within the fruit, giving a 30% increase in oil yield at the expense of shell, without changing total dry matter production."
Cros et al., 2014 find genomic selection is very effective in this crop.
Agronomic genes
In 2013, the gene responsible for controlling shell thickness was discovered, making it possible to verify tenera (DxP) status while palms are still in the nursery.
The gene regulates floral architecture. One of its epialleles, , reduces yield.
Pollination
E. guineensis is almost entirely pollinated by insects and not by wind. Elaeidobius kamerunicus is the most specially adapted pollination partner in Africa. It has been deliberately introduced into southeast Asia in 1981 and the results have been dramatic – Cik Mohd Rizuan et al., 2013 find good results in in Sabah. Contrary to earlier speculation, the introduced population was not too inbred, and inbreeding depression was not the cause of some incidences of lessened fruit set in SEA. Other causes have been proposed. E. kamerunicus and the pollination it provides can be negatively affected by nematodes.
Pests
Disease
Worldwide the two most impactful diseases are Ganoderma orbiforme (syn. Ganoderma boninense, basal stem rot, BSR, reviewed by Chong et al., 2017) and Phytophthora palmivora (bud rot, reviewed by Torres et al. 2016). The earliest stages of data gathering and investigation have been performed for disease resistance breeding however propagation material is not available and full breeding programs are not ongoing .
Ganoderma boninense/orbiforme, Basal Stem Rot (BSR)
Basal stem rot is the most serious disease of oil palm in Malaysia and Indonesia. Previously, research on basal stem rot was hampered by the failure to artificially infect oil palms with the fungus. Although Ganoderma had been associated with BSR, proof of its pathogenicity to satisfy Koch's postulate was only achieved in the early 1990s by inoculating oil palm seedling roots or by using rubber wood blocks. A reliable and quick technique was developed for testing the pathogenicity of the fungus by inoculating oil palm germinated seeds.
This fatal disease can lead to losses as much as 80% after repeated planting cycles. Ganoderma produces enzymes that degrade the infected xylem, thus causing serious problems to the distribution of water and other nutrients to the top of the palm. Ganoderma infection is well defined by its lesion in the stem. The cross-section of infected palm stem shows that the lesion appears as a light brown area of rotting tissue with a distinctive, irregularly shaped, darker band at the borders of this area. The infected tissue become as an ashen-grey powdery and if the palm remains standing, the infected trunk rapidly becomes hollow.
In a 2007 study in Portugal, scientists suggested control of the fungus on oil palms would benefit from further consideration of the process as one of white rot. Ganoderma is an extraordinary organism capable exclusively of degrading lignin to carbon dioxide and water; celluloses are then available as nutrients for the fungus. It is necessary to consider this mode of attack as a white rot involving lignin biodegradation, for integrated control. The existing literature does not report this area and appears to be concerned particularly with the mode of spread and molecular biology of Ganoderma. The white rot perception opens up new fields in breeding/selecting for resistant cultivars of oil palms with high lignin content, ensuring the conditions for lignin decomposition are reduced, and simply sealing damaged oil palms to stop decay. The spread likely is by spores rather than roots. The knowledge gained can be employed in the rapid degradation of oil palm waste on the plantation floor by inoculating suitable fungi, and/or treating the waste more appropriately (e.g. chipping and spreading over the floor rather than windrowing).
Markom et al., 2009 developed and successfully used an electronic nose system for detection.
Phytophthora palmivora
Phytophthora palmivora has caused a loss of of E. guineensis near San Lorenzo in Ecuador. The protozoa cause bud rot (Spanish: pudrición del cogollo). In reaction, growers there replanted using a hybrid of E. guineensis and E. oleifera, the South American oil palm.
Endophytic bacteria
Endophytic bacteria are organisms inhabiting plant organs that at some time in their life cycles can colonize the internal plant tissues without causing apparent harm to the host. Introducing endophytic bacteria to the roots to control plant disease is to manipulate the indigenous bacterial communities of the roots in a manner, which leads to enhanced suppression of soil-borne pathogens. The use of endophytic bacteria should thus be preferred to other biological control agents, as they are internal colonizers, with better ability to compete within the vascular systems, limiting Ganoderma for both nutrients and space during its proliferation. Two bacterial isolates, Burkholderia cepacia (B3) and Pseudomonas aeruginosa (P3) were selected for evaluation in the glasshouse for their efficacy in enhancing growth and subsequent suppression of the spread of BSR in oil palm seedlings.
Little leaf syndrome
Little leaf syndrome has not been fully explained, but has often been confused with boron deficiency. The growing point is damaged, sometimes by Oryctes beetles. Small, distorted leaves resembling those due to a boron deficiency emerge. This is often followed by secondary pathogenic infections in the spear that can lead to spear rot and palm death.
Cadang-cadang
Cadang-cadang disease is a viral disease that also infects coconuts.
Bursaphelenchus cocophilus/Red Ring Disease (RRD)
Red ring disease is caused by Bursaphelenchus cocophilus, see §Nematode pests below.
Insects as vectors
Besides direct damage to plant material, insects are also vectors of oil palm diseases.
Arthropod pests
Metisa plana
M. plana is a Lepidopteran moth and a major pest of oil palms in Malaysia. M. plana outbreaks in Malaysia are highly correlated with relative humidity. Relative humidity estimates based on satellite remote sensing data were fed into both regression models and neural networks. The predictions of both were found to be closely correlated with actual M. plana appearance on plantations, with the NN producing the best results.
Raoiella indica
R. indica was invading the Yucatan placing 11 states of Mexico under phytosanitary vigilance.
Rhynchophorus ferrugineus
R. ferrugineus has placed 13 states of Mexico under phytosanitary vigilance.
Other arthropods
Other arthropods include: Bagworm moths (the Psychidae family), the coconut rhinoceros beetle (Oryctes rhinoceros), Rhynchophorus palmarum (the South American palm weevil), Tirathaba mundella (the oil palm bunch moth), and Tirathaba rufivena (the coconut spike moth).
Vertebrate pests
Mammal pests
Besides direct damage to plant material, rats also predate on Elaeidobius kamerunicus, the African palm pollinating weevil.
Chimpanzees (Pan troglodytes) are known to use stones to crack open the nuts of E. guineensis, a rare example of tool use by animals.
Avian pests
Grey parrots (Psittacus erithacus) are known to prefer oil palm fruit in the wild. One of their chief predators, the palm-nut vulture (Gypohierax angolensis), also heavily depends on oil palm fruit for its diet, making up over 60% of the adult bird's diet and over 90% of the juvenile bird's diet (along with Raffia palm).
Nematode pests
Bursaphelenchus cocophilus is a nematode pest which is better known for infecting coconut palms. (It also afflicts a few other of the Arecaceae.) It causes "red ring disease", so named because it produces a red colored layer within the trunk of the tree, which looks like a red ring in a cross section cut. B. cocophilus is obligately transmitted as the third juvenile stage by vectors, specifically several species of weevil. Unlike congener B. xylophilus there are not thought to be any non plant hosts to serve as reservoir hosts for infection of E. guineensis. Besides direct infestation of the palm, other nematodes infest the pollinating weevil Elaeidobius kamerunicus, reducing pollination and yield.
Detection
Because each tree is relatively big and has an individual value, information about its pest and disease status is valuable. Although visual inspection is the oldest method, others are under development or occasional use.
Basal stem rot
Volatiles and microfocus X-ray fluorescence are two methods can be used to non-invasively detect pre-emergence Ganoderma orbiforme disease as a lab test. Sonic tomography is already in use with good results, at 96% accuracy. On the other hand satellite imagery and computer vision has low classification accuracy as to severity.
History
Oil palms were introduced to Java by the Dutch in 1848, and to Malaysia (then the British colony of Malaya) in 1910 by Scotsman William Sime and English banker Henry Darby. The species of palm tree Elaeis guineensis was taken to Malaysia from Eastern Nigeria in 1961. As noted it originally grew in West Africa. The southern coast of Nigeria was originally called the Palm oil coast by the first Europeans who arrived there and traded in the commodity. This area was later renamed the Bight of Biafra.
In traditional African medicine different parts of the plant are used as laxative and diuretic, as a poison antidote, as a cure for gonorrhea, menorrhagia, and bronchitis, to treat headaches and rheumatism, to promote healing of fresh wounds and treat skin infections.
In Yoruba religion, it is associated with its creation myth as the first tree that Ọbatala finds descending to earth; it is also believed as Ọrunmila's axis mundi connecting heaven and earth. Thus, oil palm fronds often mark areas of sacred religious important or incorporated in traditional orisha garment; its kernels are also prepared to use as a tool of receiving Ọrunmila's words to the babalawo.
In Cambodia, this palm was introduced as a decorative plant in public gardens, its Khmer name is dôô:ng préing (doong=palm, preing=oil).
Malaysia
In Malaysia, the first plantations were mostly established and operated by British plantation owners, such as Sime Darby and Boustead, and remained listed in London until the Malaysian government engineered their "Malaysianisation" throughout the 1960s and 1970s.
Federal Land Development Authority (Felda) is the world's biggest oil palm planter, with planted area close to 900,000 hectares in Malaysia and Indonesia. Felda was formed on July 1, 1956, when the Land Development Act came into force with the main aim of eradicating poverty. Settlers were each allocated 10 acres of land (about 4 hectares) planted either with oil palm or rubber, and given 20 years to pay off the debt for the land.
After Malaysia achieved independence in 1957, the government focused on value-added of rubber planting, boosting exports, and alleviating poverty through land schemes. In the 1960s and 1970s, the government encouraged planting of other crops, to cushion the economy when world prices of tin and rubber plunged. Rubber estates gave way to oil palm plantations. In 1961, Felda's first oil palm settlement opened, with 3.75 km2 of land. As of 2000, 6855.2 km2 (approximately 76%) of the land under Felda's programmes were devoted to oil palms. By 2008, Felda's resettlement broadened to 112,635 families, who work on 8533.13 km2 of agriculture land throughout Malaysia. Oil palm planting took up 84% of Felda's plantation landbank.
Felda's success led to the establishment of other development schemes to support the establishment of small-farmer oil palm cultivation. The Federal Land Consolidation and Rehabilitation Authority (FELCRA) was established in 1966 and the Sarawak Land Consolidation and Rehabilitation Authority (SALCRA) was formed in 1976. The primary objective of these organizations is to assist in the development of rural communities and reduce poverty through the cultivation of high yielding crops such as palm oil.
, SALCRA had developed 18 estates totalling approximately 51,000 hectares. That year the organization shared dividends with 16,374 landowners participating in the program.
Palm oil production
Oil is extracted from both the pulp of the fruit (palm oil, an edible oil) and the kernel (palm kernel oil, used in foods and for soap manufacture). For every 100 kg of fruit bunches, typically 22 kg of palm oil and 1.6 kg of palm kernel oil can be extracted.
The high oil yield of oil palms (as high as 7,250 liters per hectare per year) has made it a common cooking ingredient in Southeast Asia and the tropical belt of Africa. Its increasing use in the commercial food industry in other parts of the world is buoyed by its cheaper pricing, the high oxidative stability of the refined product, and high levels of natural antioxidants.
The oil palm originated in West Africa, but has since been planted successfully in tropical regions within 20 degrees of the equator. In the Republic of the Congo, or Congo Brazzaville, precisely in the Northern part, not far from Ouesso, local people produce this oil by hand. They harvest the fruit, boil it to let the water evaporate, then press what is left to collect the reddish-orange-colored oil.
In 1995, Malaysia was the world's largest producer, with a 51% of world share, but since 2007, Indonesia has been the world's largest producer, supplying approximately 50% of world palm oil volume.
Worldwide palm oil production for season 2011/2012 was , increasing to for 2012/13.
In 2010/2011, total production of palm kernels was .
In 2019 total production was E. guineensis is among the few tropical tree crops (along with bananas and citrus) with high productivity in actual growing conditions, i.e. outside of test plots.
The Urhobo people of Nigeria use the extract to make amiedi soup.
Social and environmental impacts
The social and environmental impact of oil palm cultivation is a highly controversial topic. Oil palm is a valuable economic crop and provides a major source of employment. It allows many small landholders to participate in the cash economy and often results in the upgrade of the infrastructure (schools, roads, telecommunications) within that area. According to the IBGE oil palm is a common crop in agroforestry practices in the Amazon. However, there are cases where native customary lands have been appropriated by oil palm plantations without any form of consultation or compensation, leading to social conflict between the plantations and local residents. In some cases, oil palm plantations are dependent on imported labour or illegal immigrants, with some concerns about the employment conditions and social impacts of these practices.
Biodiversity loss (including the potential extinction of charismatic species) is one of the most serious negative effects of oil palm cultivation. On the other hand, it also helps to push invasive species further, e.g. Anoplolepis gracilipes in southeast Asia. Large areas of already threatened tropical rainforest are often cleared to make way for palm oil plantations, especially in Southeast Asia, where enforcement of forest protection laws is lacking. In some states where oil palm is established, lax enforcement of environmental legislation leads to encroachment of plantations into protected areas, encroachment into riparian strips, open burning of plantation wastes, and release of palm mill pollutants such as palm oil mill effluent (POME) in the environment. Some of these states have recognised the need for increased environmental protection, resulting in more environment-friendly practices. Among those approaches is anaerobic treatment of POME, which can be a good source for biogas (methane) production and electricity generation. Anaerobic treatment of POME has been practiced in Malaysia and Indonesia. Like most wastewater sludge, anaerobic treatment of POME results in dominance of Methanosaeta concilii. It plays an important role in methane production from acetate, and the optimum condition for its growth should be considered to harvest biogas as renewable fuel.
Demand for palm oil has increased in recent years due to its use as a biofuel, but recognition that this increases the environmental impact of cultivation, as well as causing a food vs fuel issue, has forced some developed nations to reconsider their policies on biofuel to improve standards and ensure sustainability. However, critics point out that even companies signed up to the Roundtable on Sustainable Palm Oil continue to engage in environmentally damaging practices and that using palm oil as biofuel is perverse because it encourages the conversion of natural habitats such as forests and peatlands, releasing large quantities of greenhouse gases.
Carbon balance
Oil palm production has been documented as a cause of substantial and often irreversible damage to the natural environment. Its impacts include deforestation, habitat loss of critically endangered species, and a significant increase in greenhouse gas emissions.
The pollution is exacerbated because many rainforests in Indonesia and Malaysia lie atop peat bogs that store great quantities of carbon, which are released when the forests are cut down and the bogs are drained to make way for the plantations.
Environmental groups, such as Greenpeace, claim the deforestation caused by making way for oil palm plantations is far more damaging for the climate than the benefits gained by switching to biofuel. Fresh land clearances, especially in Borneo, are contentious for their environmental impact.
Despite thousands of square kilometres of land standing unplanted in Indonesia, tropical hardwood forests are being cleared for palm oil plantations. Furthermore, as the remaining unprotected lowland forest dwindles, developers are looking to plant peat swamp land, using drainage that begins an oxidation process of the peat which can release 5,000 to 10,000 years worth of stored carbon. Drained peat is also at very high risk of forest fire. There is a clear record of fire being used to clear vegetation for oil palm development in Indonesia, where in recent years drought and man-made clearances have led to massive uncontrolled forest fires, covering parts of Southeast Asia in haze and leading to an international crisis with Malaysia. These fires have been blamed on a government with little ability to enforce its own laws, while impoverished small farmers and large plantation owners illegally burn and clear forests and peat lands to develop the land rather than reap the environmental benefits it could offer.
Many of the major companies in the vegetable oil economy participate in the Roundtable on Sustainable Palm Oil, which is trying to address this problem. For example, in 2008, Unilever, a member of the group, committed to use only oil palm oil which is certified as sustainable, by ensuring the large companies and smallholders that supply it convert to sustainable production by 2015.
Meanwhile, much of the recent investment in new palm plantations for biofuel has been funded through carbon credit projects through the Clean Development Mechanism; however, the reputational risk associated with the unsustainable palm plantations in Indonesia has now made many funds wary of such investment.
Palm biomass as fuel
Some scientists and companies are going beyond using just the oil, and are proposing to convert fronds, empty fruit bunches and palm kernel shells harvested from oil palm plantations into renewable electricity, cellulosic ethanol, biogas, biohydrogen and bioplastic. Thus, by using both the biomass from the plantation as well as the processing residues from palm oil production (fibers, kernel shells, palm oil mill effluent), bioenergy from palm plantations can have an effect on reducing greenhouse gas emissions. Examples of these production techniques have been registered as projects under the Kyoto Protocol's Clean Development Mechanism.
By using palm biomass to generate renewable energy, fuels and biodegradable products, both the energy balance and the greenhouse gas emissions balance for palm biodiesel is improved. For every tonne of palm oil produced from fresh fruit bunches, a farmer harvests around 6 tonnes of waste palm fronds, 1 tonne of palm trunks, 5 tonnes of empty fruit bunches, 1 tonne of press fiber (from the mesocarp of the fruit), half a tonne of palm kernel endocarp, 250 kg of palm kernel press cake, and 100 tonnes of palm oil mill effluent. Some oil palm plantations incinerate biomass to generate power for palm oil mills. Some other oil palm plantations yield large amount of biomass that can be recycled into medium density fibreboards and light furniture. In efforts to reduce greenhouse gas emissions, scientists treat palm oil mill effluent to extract biogas. After purification, biogas can substitute for natural gas for use at factories. Anaerobic treatment of palm oil mill effluent, practiced in Malaysia and Indonesia, results in domination of Methanosaeta concilii. It plays an important role in methane production from acetate and the optimum condition for its growth should be considered to harvest biogas as renewable fuel.
Unfortunately, the production of palm oil has detrimental effects on the environment and is not considered to be a sustainable biofuel. The deforestation occurring throughout Malaysia and Indonesia as a result of the growing demand for this plant has made scarce natural habitats for orangutans and other rainforest dwellers. More carbon is released during the life cycle of a palm oil plant to its use as a biofuel than is emitted by the same volume of fossil fuels.
| Biology and health sciences | Arecales (inc. Palms) | Plants |
24369901 | https://en.wikipedia.org/wiki/Network%20covalent%20bonding | Network covalent bonding | A network solid or covalent network solid (also called atomic crystalline solids or giant covalent structures) is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule. Formulas for network solids, like those for ionic compounds, are simple ratios of the component atoms represented by a formula unit.
Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO2 units. Graphite and the mica group of silicate minerals structurally consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types holding the layers together. Disordered network solids are termed glasses. These are typically formed on rapid cooling of melts so that little time is left for atomic ordering to occur.
Properties
Hardness: Very hard, due to the strong covalent bonds throughout the lattice (deformation can be easier, however, in directions that do not require the breaking of any covalent bonds, as with flexing or sliding of sheets in graphite or mica).
Melting point: High, since melting means breaking covalent bonds (rather than merely overcoming weaker intermolecular forces).
Solid-phase electrical conductivity: Variable, depending on the nature of the bonding: network solids in which all electrons are used for sigma bonds (e.g. diamond, quartz) are poor conductors, as there are no delocalized electrons. However, network solids with delocalized pi bonds (e.g. graphite) or dopants can exhibit metal-like conductivity.
Liquid-phase electrical conductivity: Low, as the macromolecule consists of neutral atoms, meaning that melting does not free up any new charge carriers (as it would for an ionic compound).
Solubility: Generally insoluble in any solvent due to the difficulty of solvating such a large molecule.
Examples
Boron nitride (BN)
Diamond (carbon, C)
Quartz (SiO2)
Rhenium diboride (ReB2)
Silicon carbide (moissanite, carborundum, SiC)
Silicon (Si)
Germanium (Ge)
Aluminium nitride (AlN)
| Physical sciences | Alloys and ceramic compounds | Chemistry |
25784499 | https://en.wikipedia.org/wiki/Iron%20planet | Iron planet | An iron planet is a type of planet that consists primarily of an iron-rich core with little or no mantle. Mercury is the largest celestial body of this type in the Solar System (as the other terrestrial planets are silicate planets), but larger iron-rich exoplanets are called super-Mercuries.
Iron is the sixth most abundant element in the universe by mass after hydrogen, helium, oxygen, carbon, and neon.
Origin
Iron-rich planets may be the remnants of normal metal/silicate rocky planets whose rocky mantles were stripped away by giant impacts. Some are thought to consist of diamond fields. Current planet formation models predict iron-rich planets will form in close-in orbits or orbiting massive stars where the
protoplanetary disk presumably consists of iron-rich material.
Characteristics
Iron-rich planets are smaller and denser than other types of planets of comparable mass.
Such planets would have no plate tectonics or strong magnetic field as they cool rapidly after formation. These planets are not like Earth. Since water and iron are unstable over geological timescales, wet iron planets in the goldilocks zone may be covered by lakes of iron carbonyl and other exotic volatiles rather than water.
In science fiction, such a planet has been called a "Cannonball".
Candidates
An extrasolar planet candidate that may be composed mainly of iron is Kepler-974b.
A super-Mercury candidate is GJ 367b.
The star HD 23472 is orbited by two super-Mercuries.
HD 137496 b is a dense hot super-Mercury.
LHS 3844 b is potentially an Fe-rich super-Mercury.
| Physical sciences | Planetary science | Astronomy |
25786928 | https://en.wikipedia.org/wiki/Communicating%20vessels | Communicating vessels | Communicating vessels or communicating vases are a set of containers containing a homogeneous fluid and connected sufficiently far below the top of the liquid: when the liquid settles, it balances out to the same level in all of the containers regardless of the shape and volume of the containers. If additional liquid is added to one vessel, the liquid will again find a new equal level in all the connected vessels. This was discovered by Simon Stevin as a consequence of Stevin's Law. It occurs because gravity and pressure are constant in each vessel (hydrostatic pressure).
Blaise Pascal proved in the seventeenth century that the pressure exerted on a molecule of a liquid is transmitted in full and with the same intensity in all directions.
Applications
Since the days of ancient Rome, the concept of communicating vessels has been used for indoor plumbing, via aquifers and lead pipes. Water will reach the same level in all parts of the system, which acts as communicating vessels, regardless of what the lowest point is of the pipes – although in practical terms the lowest point of the system depends on the ability of the plumbing to withstand the pressure of the liquid.
In cities, water towers are frequently used so that city plumbing will function as communicating vessels, distributing water to higher floors of buildings with sufficient pressure.
Hydraulic presses, using systems of communicating vessels, are widely used in various applications of industrial processes.
| Physical sciences | Fluid mechanics | Physics |
22841263 | https://en.wikipedia.org/wiki/PSR%20B1937%2B21 | PSR B1937+21 | PSR B1937+21 is a pulsar located in the constellation Vulpecula a few degrees in the sky away from the first discovered pulsar, PSR B1919+21. The name PSR B1937+21 is derived from the word "pulsar" and the declination and right ascension at which it is located, with the "B" indicating that the coordinates are for the 1950.0 epoch. PSR B1937+21 was discovered in 1982 by Don Backer, Shri Kulkarni, Carl Heiles, Michael Davis, and Miller Goss.
It is the first discovered millisecond pulsar, with a rotational period of 1.557708 milliseconds, meaning it completes almost 642 rotations per second. This period was far shorter than astronomers considered pulsars capable of reaching, and led to the suggestion that pulsars can be spun-up by accreting mass from a companion.
The rotation of PSR B1937+21, along with other millisecond pulsars discovered later, are very stable in their rotation. They are capable of keeping time as well as atomic clocks. PSR B1937+21 is unusual in that it is one of few pulsars which occasionally emits particularly strong pulses. The flux density of the giant pulses emitted by PSR B1937+21 are the brightest radio emission ever observed. These properties of PSR B1937+21, and its unexpected discovery, are credited with helping revitalize research on pulsars.
Background
The first pulsar was discovered in 1967 by Jocelyn Bell and her PhD supervisor Antony Hewish using the Interplanetary Scintillation Array. Shortly after the discovery of pulsars, Franco Pacini and Thomas Gold independently suggested that pulsars are highly magnetized rotating neutron stars, which form as a result of a supernova at the end of the life of stars more massive than about 10 times the mass of the Sun. The radiation emitted by pulsars is caused by interaction of the plasma surrounding the neutron star with its rapidly rotating magnetic field. This interaction leads to emission "in the pattern of a rotating beacon," as emission escapes along the magnetic poles of the neutron star. The "rotating beacon" property of pulsars arises from the misalignment of their magnetic poles with their rotational poles.
Discovery
In the late 1970s, the radio source 4C21.53 captured the attention of radio astronomers, "because of its anomalously high level of interplanetary scintillation." As interplanetary scintillation is associated with compact radio sources, the interplanetary scintillation observations suggested that 4C21.53 might be a supernova remnant, but a pulsar survey carried out at Arecibo Observatory in 1974 by Russell Hulse and Joseph Taylor in the region did not discover a pulsar associated with 4C21.53. With the lack of success in finding a pulsar in the region, other explanations for the scintillation were explored, including suggestion of entirely new classes of objects. After realizing in 1982 that previous searches for a pulsar in the region of 4C21.53 were not sensitive to periods short enough to produce the observed scintillation, Don Backer initiated a search in the area that would be sensitive to a wide range of pulse periods and dispersion measures, including very short periods. The initial search plan was to sample at a rate of 500 Hz, which would have been insufficiently fast to detect a pulsar spinning at 642 Hz. To simplify the search apparatus, Backer's then student, Shri Kulkarni, sampled as quickly as was possible, and time averaged the signal over a period of 0.4 milliseconds, thus effectively sampling at 2500 Hz. As a result, Backer et al. determined in November 1982 that the source was a pulsar rotating every 1.558 milliseconds, a rate far beyond anything that astronomers studying pulsars had expected.
Characteristics
Age and spin down rate
When Backer et al. reported their finding in November 1982, they found that the rotation period of PSR B1937+21 was increasing at a rate of 3 seconds per second. Pulsars are expected to slow over time, as the energy that they emit is ultimately drawn from the rotational energy of the pulsar. Using the initially observed values for the period and spin down rate, and assuming a minimum period of 0.5 milliseconds for pulsars, the maximum age for PSR B1937+21 was found to be about 750 million years old. The estimate of the minimum possible period is obtained from the centrifugal break-up limit, which is the rotational period at which the centrifugal force and the self-gravity of the pulsar are equal. The value of the minimum rotational period depends upon the neutron star equation of state, with different models giving values between 0.3 and 1 millisecond, which corresponds to a rotation frequency of 1-3 kilohertz. There may be mechanisms such as gravitational radiation which keep the pulsar from reaching this absolute limit, but pulsars can spin no faster.
An age of no more than 750 million years for the PSR B1937+21 was at odds with the observations of the region in other wavelengths. No optical supernova remnant, nor bright x-ray source, had been observed in the vicinity of the PSR B1937+21. If PSR B1937+21 was that young, it would not have had time to move far from the site at which it formed. As neutron stars are formed as the result of supernova explosions, evidence of the explosion should be nearby for a young pulsar. If it was that young, it would also be expected to still be hot, in which case the thermal radiation from PSR B1937+21 would be observable at x-ray wavelengths. Venkatraman Radhakrishnan and G. Srinivasan used the lack of observed supernova remnant to argue that PSR B1937+21 had not formed with such a fast period, but instead had been "spun up" by a companion star which essentially gave the pulsar its angular momentum, a mechanism now generally used to explain millisecond pulsars. They also made a theoretical estimate of the necessary spin down rate to be 1 seconds per second. Backer et al. revised their estimate of the upper limit of the spin down rate just a month after the initial discovery, to 1 seconds per second, but the currently measured value is more nearly in line with the theoretical estimate, at 1.05 seconds per second. The age of PSR B1937+21 was also later determined to be 2.29 years, a value which is consistent with the observational evidence.
The companion which is supposed to have spun-up PSR B1937+21 is no longer present, making it one of few millisecond pulsars which does not have a stellar mass companion. The generally high occurrence of companions to millisecond pulsars is to be expected, considering a companion is necessary to spin-up millisecond pulsars to their short periods. However, millisecond pulsars do not actively accrete matter from a companion, but instead need to have only done this at some time in the past, and thus the lack of companion for PSR B1937+21 is not seen as a being in disagreement with the spin-up model. Possible mechanisms for creating isolated millisecond pulsars include evaporation of the donor star or tidal disruption of the system.
Pulses
During one period of rotation for PSR B1937+21, there are two peaks observed, known as the pulse and interpulse. PSR B1937+21 is unusual among pulsars in that it occasionally produces pulses far brighter than an average pulse. Until 1995, the sole other pulsar known to produce giant pulses was the Crab pulsar, and by 2006, there were 11 pulsars that had been observed to produce giant pulses out of more than 1500 known pulsars. The giant pulses of PSR B1937+21 were first observed in 1984, shortly after its discovery, but difficulty in observing single pulses of PSR B1937+21 due to its fast period meant that the pulses were not studied in more depth until a decade after they were first observed. In more recent follow up observations, more giant pulses have been found. These giant pulses have been observed to occur at the trailing edge of both the pulse and interpulse. The duration of these giant pulses is short compared to the period of the pulsar, lasting on the order of 10 nanoseconds. The flux density of observed pulses is somewhat variable, but has been observed to be as high as 6.5 W m−2Hz−1 (6.5 janskys). The brightness temperature of a pulse with such high flux density and such low duration exceeds 5 kelvins, making the pulses of PSR B1937+21 the brightest radio emission ever observed. PSR B1937+21 is intrinsically the most luminous millisecond pulsar. In addition to the radio pulses observed, pulses have been detected at x-ray wavelengths, which show the same pulse and interpulse pattern.
Evidence for companions
After the discovery of planetary mass companions around PSR B1257+12 in 1990 by Aleksander Wolszczan, data for PSR B1937+21 and other pulsars were analyzed for the presence of similar companions. By 1994, an upper limit of about one thousandth of the mass of Earth was determined for any companion of PSR B1937+21 within 2 astronomical units. In 1999, Aleksander Wolszczan reported variations in the times of arrival of pulses from PSR B1937+21, as well as previous analysis by Tokio Fukushima which suggested that these timing variations could be caused by a dwarf planet around the pulsar. The data were consistent with a companion having a mass similar to Ceres and located at 2.71 astronomical units from the pulsar, but data over a longer period of time are required in order to verify the proposed companion. More recent observations have not detected any regular periodic signal associated with this companion, but argue that the slight variations in pulse arrival times are consistent with an asteroid belt having a total mass less than 0.05 that of the Earth, but acknowledge that the detection of periodicity in pulse timing variations associated with individual asteroids is necessary to confirm the possible asteroid belt.
Significance
Until the discovery of PSR J1748-2446ad in 2006, which spins 716 times per second, PSR B1937+21 was
the fastest spinning neutron star known. At the time of its discovery, PSR B1937+21 extended the range of periods observed in pulsars by a factor of 20, it also extended the range of magnetic fields observed by a factor of 100,
with a magnetic field of 4.2 gauss (42 kT).
As the first discovered millisecond pulsar, PSR B1937+21 "sparked a 'theory frenzy'" by providing a new laboratory in which to study pulsars, neutron stars more generally, and perhaps even some other astrophysical problems such as gravitational waves.<ref
name="encounters"></ref> For instance, as the density required to spin at such high rates are comparable to nuclear densities, the fastest spinning millisecond pulsars are important in understanding how matter behaves at such densities. The initially high estimate of the spin down rate was also intriguing, as it implied a signal that could be directly detected by gravitational wave detectors, but the actual spin down rate put the expected signal below the sensitivity of current detectors. The currently accepted value spin down rate corresponds to a change in the rotational period of 1.5 Hz over the course of one million years. The stability of rotation of PSR B1937+21 is of the same order of the stability of the best atomic clocks, and is thus a tool used in establishing ephemeris time.
The discovery of B1937+21 launched "extensive pulsar surveys at all major radio observatories" and "happened to revitalize pulsar astronomy at a time when most people thought the field was moribund."
| Physical sciences | Notable stars | Astronomy |
2045961 | https://en.wikipedia.org/wiki/Darwin%27s%20frog | Darwin's frog | Darwin's frog (Rhinoderma darwinii), also called the Southern Darwin's frog, is a species of Chilean/Argentinian frog of the family Rhinodermatidae. It was discovered by Charles Darwin during his voyage on HMS Beagle. on a trip to Chile. In 1841, French zoologist André Marie Constant Duméril and his assistant Gabriel Bibron described and named Darwin's frog. The diet of R. darwinii consists mostly of herbivore invertebrates. R. darwinii is currently classified as an endangered species by the International Union for Conservation of Nature.
Darwin’s frog is most known for its unique method of brooding. The male will facilitate development of its tadpoles inside its vocal sac. This male brooding makes Darwin’s frog distinct from other frog species (as the only other frog that has this behavior is the R. rufum, which may be extinct).
Characteristics
Size
Darwin's frog is a small species with a snout–to–vent length of . The snout is elongated into a fleshy proboscis which gives the head a triangular shape. The limbs are relatively long and slender. The front feet are not webbed, but some of the toes on the back feet usually are.
Coloration
The upperparts of this species are variably colored in brown or green. Some brown individuals may have weakly defined V-shaped markings on the back, have central upperparts that are distinctly lighter brown than the flanks, or have whitish front limbs. Females are typically brown and tend to stay on substrates that match this color. Males are far more variable and occur on a wider range of substrates; in particular, brooding males often are often partially or completely green above. The throat is brownish and the remaining underparts are black with large white blotches in a pattern that is unique to each individual. In captivity, male R. darwinii have been shown to change color. These frogs that were initially brown changed to green over a year. This change in color is believed to be due to the green color of the environment these frogs were kept in.
Habitat and distribution
Darwin's frog is found in Chile and Argentina. R. darwinii is mainly found in the Valdivian Temperate Rain Forest which covers parts of both Chile and Argentina. In Chile, its range extends from Concepción Province to Palena Province and in Argentina from Neuquén Province and Río Negro Province. It is found in glades and forested areas at altitudes of up to about above mean sea level, in bogs and near slow-moving streams, and in a variety of vegetation types. It appears that a mixture of grassland, mossy areas, coarse woody debris, and young trees and bushes in a mature native forest provides its optimum habitat requirements. Short vegetation increases the retention of water while decreasing the temperature of the soil and providing concealment from predators. The population is fragmented and this frog has poor dispersal ability.
The Valdivian (their typical habitat) is decreasing in the north due to pine and eucalyptus agriculture expansion. This is removing some of the habitat of R. darwinii and forcing them south. The south Valdivian is more protected and is suitable for R. darwinii inhabitance.
Dispersal-constrained species distribution models have shown a decrease of up to 40% in habitat for R. darwinii over the years 1970 to 2010. The habitat for R. darwinii is expected to increase in the coming years. However, this emerging habitat is not likely to be inhabited by R. darwinii due to its inability to translocate to these new habitats.
Climate change is also expected to play a role in the habitat availability of R. darwinii. In the coming decades, R. darwinii is expected to have a reduced dispersion by up to 56%. This means that R. darwinii will be more localized to certain habitats in the future. R. darwinii populations are especially susceptible to damage due to wildfires. Using climate change models, wildfires are expected to increase at a dramatic rate which will negatively affect the R. darwinii habitat.
Conservation
Darwin's frog has undergone significant population declines due to habitat loss and degradation, largely from conversion of native forests to tree plantations.
Since 2018, the species is classified as Endangered on the IUCN Red List. A 2013 study reported results of a population survey conducted from 2008–2012, which found the species at just 36 of 223 previously recorded habitat sites, with small populations at those sites. The recent change in its conservation category in IUCN from Vulnerable to Endangered, arose from the Chile's amphibian reevaluation workshop for the Red List (Soto-Azat et al., 2015). The justification for its current category is due to its limited occupation area (estimated at 264 km2), severe fragmentation of its populations and continued decline.
Since October 2021, R. darwinii has been classified as Critically Depleted by the IUCN Green Status Assessment. It was determined that the survival of the species is highly dependent on conservation activities and its recovery potential is high.
Conservation Efforts
Due to its decline in the wild, captive colonies have been established as a precaution at two zoos in Chile, the National Zoo (working with the US Atlanta Botanical Garden) and Concepción Zoo (working with the University of Concepción and Germany's Leipzig Zoo).
In 2017, the IUCN SSC Amphibian Specialist Group formed a Binational Conservation Strategy that brought together 30 different countries. The goal of this group is to study R. darwinii in order to improve conservation efforts. The group details the unique characteristics (mouth brooding) as one justification for this increased conservation effort. The goal of the group is to understand key aspects of information related to R. darwinii by the year 2028.
Diet
The diet of R. darwinii's consists of detritivore, herbivore, and carnivore invertebrates. It has been observed to consume each type of invertebrate at a percentage consistent with their prevalence in the environment. The percentage at which carnivorous invertebrates are consumed is lower than herbivore or detritivore invertebrates. This difference can be explained because spiders are the predominant type of carnivore invertebrate prey that R. darwinii encounters. These spiders are able to evade the predation of R. darwinii effectively due to their evasion ability.
In the habitats where R. darwinii have been observed, there seem to be relatively high percentages of herbivore invertebrates. This could mean that R. darwinii seek environments with enriched herbivore invertebrates as a food source.
Rhinoderma darwinii style of predation has been characterized as "sit and wait". This method seems to conserve energy and allows R. darwinii to evade predators effectively.
Reproduction
Male R. darwinii will call to attract females in an attempt to mate. It has even been shown that male R. darwinii will call when brooding. R. darwinii use non-linear vocal phenomena (NLP) in order to attract and communicate with mates. Darwin’s frog has been shown to have distinct mating patterns based on population and body size. More research needs to be conducted in order to further explore the mating of R. darwinii.However, no brooding males have been observed copulating with females.
Additionally, females will generally lay 4-10 eggs at a time. Males can brood 5-8 tadpoles at a time. In certain cases, the female R. darwinii can lay up to forty eggs in a single leaf litter.
Parental care
The male, after about 3 to 4 weeks, notices the developing embryos beginning to move, and then he ingests the eggs and holds them in his vocal sac. Most brooding males are green colored individuals. The eggs hatch about 3 days later and the father continues to carry the tadpoles around in his vocal sac where they feed off their egg yolks and secretions produced by the wall of the sac until metamorphosis. At 6 weeks after tadpole ingestion, it was thought that the adult male does not consume food. However, in 1888 G. B. Howes dissected a brooding male R. darwinii and identified beetles and flies in its stomach. The large intestine of the adult male also resembled that of a normal individual. He concluded "that this extraordinary paternal instinct does not lead up to that self-abnegation." Following this, the small frogs hop out of the male's mouth and disperse.
In captivity, R. darwinii parents have been observed to leave the eggs unattended for around 3 weeks (some R. darwinii males will guard the eggs for these 3 weeks). Further, captive males have been shown to exhibit alloparental behavior. Foster males have been shown to take a defensive stance at the eggs (oviposition defense). They will go so far as to defend the eggs from the birth father of the eggs and will subsequently brood the kin of other males. In one experiment, the foster father ingested 8 tadpoles, and after brooding had been completed, the foster father produced 2 frogs. This means that the metamorphosis process is not 100% efficient. This observation is consistent across studies and there exist some proposed explanations for the alloparental behavior, which is especially rare among amphibians.
Two hypotheses for this behavior have been proposed:
Possible hypotheses for foster brooding
The first hypothesis is that foster fathers can improve upon their brooding skills by practicing. Improved brooding skills would result in males that can propagate more of their genes into the next generation.
The second hypothesis is that foster fathers can exhibit that they have had past breeding success by brooding tadpoles that aren't theirs. This means that these foster fathers are hoping that future mates will see them brooding and be more likely to mate with them.
These hypotheses propose ideas in which there is some advantage for males who brood offspring that are not theirs.
Possible hypotheses for the loss of tadpoles in metamorphosis
The loss of some tadpoles in the metamorphosis from tadpole to frog is a unique feature of R. darwinii. This observation is likely explained by these hypotheses:
The tadpoles that did not survive were converted into nutrition for the foster male and he digested them.
The tadpoles died in the vocal sac of the foster male. The nutrients from these dead tadpoles served as sustenance for the surviving tadpoles occupying the vocal sac of the foster male. This phenomenon of one embryo consuming another is termed adelphophagy. The vocal sac of R. darwinii does not seem to have the proper structure to facilitate adelphophagy and thus this proposal is unlikely to explain the incomplete metamorphosis observed.
R. darwinii exhibit rare behavior in terms of territoriality and parental care. In anuran species, parental care and territoriality are positively related. In R. darwinii, there is high parental care due to the ingestion of tadpoles by fathers. However, there is low territoriality exhibited by these R. darwinii males. In fact, neither females nor males of R. darwinii have been observed guarding eggs. These observations of R. darwinii were used to further develop the relationship between territoriality and parental care by establishing the role of oviposition defense. These observations suggest that anurans will exhibit territoriality with parental care if they defend oviposition sites.
Threats
Rhinoderma darwinii has been shown to be highly susceptible to Batrachochytrium dendrobatidis infection. The amphibian disease chytridiomycosis, caused by Batrachochytrium dendrobatidis fungal infection, is also a probable factor.
Rhinoderma darwinii seems to be less affected by chytridiomycosis when compared to other amphibians. However, Chytridiomycosis can still infect and kill R. darwinii. Previous studies have supported the idea that chytridiomycosis could be somewhat responsible for the decrease in R. darwinii populations observed in Chile and Argentina.
In recent years, studies have shown that R. darwinii have shown variation in Batrachochytrium dendrobatidis infection across populations. In populations where there were high Bd infection rates, there are observed to be higher population growth rates. Similarly, in populations with low Bd infection rates, there are observed to be lower population growth rates. Populations with higher Bd infections rates seemed to have the highest reproductive rates. This means that even though many individuals are dying of Bd infection, there are more individuals being born. There exists a positive relationship between Bd infection rate and the number of juvenile individuals for R. darwinii.
This odd feature of Bd infection and R. darwinii population growth prompted further investigation. The explanation for this observation is termed the “parasite-induced plasticity” hypothesis. This hypothesis says that individuals will devote more resources towards reproduction as opposed to survival. This increased devotion towards reproduction takes place over a single generation. This plasticity is beneficial to the infected individual because the infection will take over at some point so until that point the individual will try to have as many offspring as possible.
Use in research
Rhinoderma darwinii have been used to study size variation in body size of ectotherms. Previous research supported the hypothesis that larger body sizes were tied to higher seasonality because of an idea termed starvation resistance. Starvation resistance is the idea that the larger the size of an ectotherm, the less likely it is to “starve,” as it can use its body’s mass for fuel.
However, work done on R. darwinii supports another hypothesis. The name of the hypothesis supported by the experiment that shows greater seasonality leads to longer periods of time in the cold is termed the hibernation hypothesis. These animals in the cold are likely to hibernate and under hibernation will have a lower basal metabolic rate. This will lead to lower amounts of energy expended, and thus less of the ectotherm's body mass will be lost. This explanation offers an alternative to the starvation resistance hypothesis.
Rhinoderma darwinii seem to be chosen in this research due to their broad distribution in the habitats they reside in. This allows for researchers to study the same species in different climates, an important aspect in order to make claims about the relationship between body size and seasonality/climate.
| Biology and health sciences | Frogs and toads | Animals |
2046416 | https://en.wikipedia.org/wiki/Nuclear%20fuel | Nuclear fuel | Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other nuclear devices to generate energy.
Oxide fuel
For fission reactors, the fuel (typically based on uranium) is usually based on the metal oxide; the oxides are used rather than the metals themselves because the oxide melting point is much higher than that of the metal and because it cannot burn, being already in the oxidized state.
Uranium dioxide
Uranium dioxide is a black semiconducting solid. It can be made by heating uranyl nitrate to form .
This is then converted by heating with hydrogen to form UO2. It can be made from enriched uranium hexafluoride by reacting with ammonia to form a solid called ammonium diuranate, . This is then heated (calcined) to form and U3O8 which is then converted by heating with hydrogen or ammonia to form UO2. The UO2 is mixed with an organic binder and pressed into pellets. The pellets are then fired at a much higher temperature (in hydrogen or argon) to sinter the solid. The aim is to form a dense solid which has few pores.
The thermal conductivity of uranium dioxide is very low compared with that of zirconium metal, and it goes down as the temperature goes up. Corrosion of uranium dioxide in water is controlled by similar electrochemical processes to the galvanic corrosion of a metal surface.
While exposed to the neutron flux during normal operation in the core environment, a small percentage of the in the fuel absorbs excess neutrons and is transmuted into . rapidly decays into which in turn rapidly decays into . The small percentage of has a higher neutron cross section than . As the accumulates the chain reaction shifts from pure at initiation of the fuel use to a ratio of about 70% and 30% at the end of the 18 to 24 month fuel exposure period.
MOX
Mixed oxide, or MOX fuel, is a blend of plutonium and natural or depleted uranium which behaves similarly (though not identically) to the enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to low enriched uranium (LEU) fuel used in the light water reactors which predominate nuclear power generation.
Some concern has been expressed that used MOX cores will introduce new disposal challenges, though MOX is a means to dispose of surplus plutonium by transmutation. Reprocessing of commercial nuclear fuel to make MOX was done in the Sellafield MOX Plant (England). As of 2015, MOX fuel is made in France at the Marcoule Nuclear Site, and to a lesser extent in Russia at the Mining and Chemical Combine, India and Japan. China plans to develop fast breeder reactors and reprocessing.
The Global Nuclear Energy Partnership was a U.S. proposal in the George W. Bush administration to form an international partnership to see spent nuclear fuel reprocessed in a way that renders the plutonium in it usable for nuclear fuel but not for nuclear weapons. Reprocessing of spent commercial-reactor nuclear fuel has not been permitted in the United States due to nonproliferation considerations. All other reprocessing nations have long had nuclear weapons from military-focused research reactor fuels except for Japan. Normally, with the fuel being changed every three years or so, about half of the is 'burned' in the reactor, providing about one third of the total energy. It behaves like and its fission releases a similar amount of energy. The higher the burnup, the more plutonium is present in the spent fuel, but the available fissile plutonium is lower. Typically about one percent of the used fuel discharged from a reactor is plutonium, and some two thirds of this is fissile (c. 50% , 15% ).
Metal fuel
Metal fuels have the advantage of a much higher heat conductivity than oxide fuels but cannot survive equally high temperatures. Metal fuels have a long history of use, stretching from the Clementine reactor in 1946 to many test and research reactors. Metal fuels have the potential for the highest fissile atom density. Metal fuels are normally alloyed, but some metal fuels have been made with pure uranium metal. Uranium alloys that have been used include uranium aluminum, uranium zirconium, uranium silicon, uranium molybdenum, uranium zirconium hydride (UZrH), and uranium zirconium carbonitride. Any of the aforementioned fuels can be made with plutonium and other actinides as part of a closed nuclear fuel cycle. Metal fuels have been used in light-water reactors and liquid metal fast breeder reactors, such as Experimental Breeder Reactor II.
TRIGA fuel
TRIGA fuel is used in TRIGA (Training, Research, Isotopes, General Atomics) reactors. The TRIGA reactor uses UZrH fuel, which has a prompt negative fuel temperature coefficient of reactivity, meaning that as the temperature of the core increases, the reactivity decreases—so it is highly unlikely for a meltdown to occur. Most cores that use this fuel are "high leakage" cores where the excess leaked neutrons can be utilized for research. That is, they can be used as a neutron source. TRIGA fuel was originally designed to use highly enriched uranium, however in 1978 the U.S. Department of Energy launched its Reduced Enrichment for Research Test Reactors program, which promoted reactor conversion to low-enriched uranium fuel. There are 35 TRIGA reactors in the US and an additional 35 in other countries.
Actinide fuel
In a fast-neutron reactor, the minor actinides produced by neutron capture of uranium and plutonium can be used as fuel. Metal actinide fuel is typically an alloy of zirconium, uranium, plutonium, and minor actinides. It can be made inherently safe as thermal expansion of the metal alloy will increase neutron leakage.
Molten plutonium
Molten plutonium, alloyed with other metals to lower its melting point and encapsulated in tantalum, was tested in two experimental reactors, LAMPRE I and LAMPRE II, at Los Alamos National Laboratory in the 1960s. LAMPRE experienced three separate fuel failures during operation.
Non-oxide ceramic fuels
Ceramic fuels other than oxides have the advantage of high heat conductivities and melting points, but they are more prone to swelling than oxide fuels and are not understood as well.
Uranium nitride
Uranium nitride is often the fuel of choice for reactor designs that NASA produces. One advantage is that uranium nitride has a better thermal conductivity than UO2. Uranium nitride has a very high melting point. This fuel has the disadvantage that unless 15N was used (in place of the more common 14N), a large amount of 14C would be generated from the nitrogen by the (n,p) reaction.
As the nitrogen needed for such a fuel would be so expensive it is likely that the fuel would require pyroprocessing to enable recovery of the 15N. It is likely that if the fuel was processed and dissolved in nitric acid that the nitrogen enriched with 15N would be diluted with the common 14N. Fluoride volatility is a method of reprocessing that does not rely on nitric acid, but it has only been demonstrated in relatively small scale installations whereas the established PUREX process is used commercially for about a third of all spent nuclear fuel (the rest being largely subject to a "once through fuel cycle").
All nitrogen-fluoride compounds are volatile or gaseous at room temperature and could be fractionally distilled from the other gaseous products (including recovered uranium hexafluoride) to recover the initially used nitrogen. If the fuel could be processed in such a way as to ensure low contamination with non-radioactive carbon (not a common fission product and absent in nuclear reactors that don't use it as a moderator) then fluoride volatility could be used to separate the produced by producing carbon tetrafluoride. is proposed for use in particularly long lived low power nuclear batteries called diamond batteries.
Uranium carbide
Much of what is known about uranium carbide is in the form of pin-type fuel elements for liquid metal fast reactors during their intense study in the 1960s and 1970s. Recently there has been a revived interest in uranium carbide in the form of plate fuel and most notably, micro fuel particles (such as tristructural-isotropic particles).
The high thermal conductivity and high melting point makes uranium carbide an attractive fuel. In addition, because of the absence of oxygen in this fuel (during the course of irradiation, excess gas pressure can build from the formation of O2 or other gases) as well as the ability to complement a ceramic coating (a ceramic-ceramic interface has structural and chemical advantages), uranium carbide could be the ideal fuel candidate for certain Generation IV reactors such as the gas-cooled fast reactor. While the neutron cross section of carbon is low, during years of burnup, the predominantly will undergo neutron capture to produce stable as well as radioactive . Unlike the produced by using uranium nitrate, the will make up only a small isotopic impurity in the overall carbon content and thus make the entirety of the carbon content unsuitable for non-nuclear uses but the concentration will be too low for use in nuclear batteries without enrichment. Nuclear graphite discharged from reactors where it was used as a moderator presents the same issue.
Liquid fuels
Liquid fuels contain dissolved nuclear fuel and have been shown to offer numerous operational advantages compared to traditional solid fuel approaches. Liquid-fuel reactors offer significant safety advantages due to their inherently stable "self-adjusting" reactor dynamics. This provides two major benefits: virtually eliminating the possibility of a runaway reactor meltdown, and providing an automatic load-following capability which is well suited to electricity generation and high-temperature industrial heat applications.
In some liquid core designs, the fuel can be drained rapidly into a passively safe dump-tank. This advantage was conclusively demonstrated repeatedly as part of a weekly shutdown procedure during the highly successful Molten-Salt Reactor Experiment from 1965 to 1969.
A liquid core is able to release xenon gas, which normally acts as a neutron absorber ( is the strongest known neutron poison and is produced both directly and as a decay product of as a fission product) and causes structural occlusions in solid fuel elements (leading to the early replacement of solid fuel rods with over 98% of the nuclear fuel unburned, including many long-lived actinides). In contrast, molten-salt reactors are capable of retaining the fuel mixture for significantly extended periods, which increases fuel efficiency dramatically and incinerates the vast majority of its own waste as part of the normal operational characteristics. A downside to letting the escape instead of allowing it to capture neutrons converting it to the basically stable and chemically inert , is that it will quickly decay to the highly chemically reactive, long lived radioactive , which behaves similar to other alkali metals and can be taken up by organisms in their metabolism.
Molten salts
Molten salt fuels are mixtures of actinide salts (e.g. thorium/uranium fluoride/chloride) with other salts, used in liquid form above their typical melting points of several hundred degrees C. In some molten salt-fueled reactor designs, such as the liquid fluoride thorium reactor (LFTR), this fuel salt is also the coolant; in other designs, such as the stable salt reactor, the fuel salt is contained in fuel pins and the coolant is a separate, non-radioactive salt. There is a further category of molten salt-cooled reactors in which the fuel is not in molten salt form, but a molten salt is used for cooling.
Molten salt fuels were used in the LFTR known as the Molten Salt Reactor Experiment, as well as other liquid core reactor experiments. The liquid fuel for the molten salt reactor was a mixture of lithium, beryllium, thorium and uranium fluorides: LiF-BeF2-ThF4-UF4 (72-16-12-0.4 mol%). It had a peak operating temperature of 705 °C in the experiment, but could have operated at much higher temperatures since the boiling point of the molten salt was in excess of 1400 °C.
Aqueous solutions of uranyl salts
The aqueous homogeneous reactors (AHRs) use a solution of uranyl sulfate or other uranium salt in water. Historically, AHRs have all been small research reactors, not large power reactors.
Liquid metals or alloys
The dual fluid reactor (DFR) has a variant DFR/m which works with eutectic liquid metal alloys, e.g. U-Cr or U-Fe.
Common physical forms
Uranium dioxide (UO2) powder is compacted to cylindrical pellets and sintered at high temperatures to produce ceramic nuclear fuel pellets with a high density and well defined physical properties and chemical composition. A grinding process is used to achieve a uniform cylindrical geometry with narrow tolerances. Such fuel pellets are then stacked and filled into the metallic tubes. The metal used for the tubes depends on the design of the reactor. Stainless steel was used in the past, but most reactors now use a zirconium alloy which, in addition to being highly corrosion-resistant, has low neutron absorption. The tubes containing the fuel pellets are sealed: these tubes are called fuel rods. The finished fuel rods are grouped into fuel assemblies that are used to build up the core of a power reactor.
Cladding is the outer layer of the fuel rods, standing between the coolant and the nuclear fuel. It is made of a corrosion-resistant material with low absorption cross section for thermal neutrons, usually Zircaloy or steel in modern constructions, or magnesium with small amount of aluminium and other metals for the now-obsolete Magnox reactors. Cladding prevents radioactive fission fragments from escaping the fuel into the coolant and contaminating it. Besides the prevention of radioactive leaks this also serves to keep the coolant as non-corrosive as feasible and to prevent reactions between chemically aggressive fission products and the coolant. For example, the highly reactive alkali metal caesium which reacts strongly with water, producing hydrogen, and which is among the more common fission products.
Pressurized water reactor fuel
Pressurized water reactor (PWR) fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic is formed into pellets and inserted into Zircaloy tubes that are bundled together. The Zircaloy tubes are about in diameter, and the fuel cladding gap is filled with helium gas to improve heat conduction from the fuel to the cladding. There are about 179–264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a reactor core. Generally, the fuel bundles consist of fuel rods bundled 14×14 to 17×17. PWR fuel bundles are about long. In PWR fuel bundles, control rods are inserted through the top directly into the fuel bundle. The fuel bundles usually are enriched several percent in 235U. The uranium oxide is dried before inserting into the tubes to try to eliminate moisture in the ceramic fuel that can lead to corrosion and hydrogen embrittlement. The Zircaloy tubes are pressurized with helium to try to minimize pellet-cladding interaction which can lead to fuel rod failure over long periods.
Boiling water reactor fuel
In boiling water reactors (BWR), the fuel is similar to PWR fuel except that the bundles are "canned". That is, there is a thin tube surrounding each bundle. This is primarily done to prevent local density variations from affecting neutronics and thermal hydraulics of the reactor core. In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest BWR in the U.S. form the reactor core. Each BWR fuel rod is backfilled with helium to a pressure of about .
Canada deuterium uranium fuel
Canada deuterium uranium fuel (CANDU) fuel bundles are about long and in diameter. They consist of sintered (UO2) pellets in zirconium alloy tubes, welded to zirconium alloy end plates. Each bundle weighs roughly , and a typical core loading is on the order of 4500–6500 bundles, depending on the design. Modern types typically have 37 identical fuel pins radially arranged about the long axis of the bundle, but in the past several different configurations and numbers of pins have been used. The CANFLEX bundle has 43 fuel elements, with two element sizes. It is also about 10 cm (4 inches) in diameter, 0.5 m (20 in) long and weighs about 20 kg (44 lb) and replaces the 37-pin standard bundle. It has been designed specifically to increase fuel performance by utilizing two different pin diameters. Current CANDU designs do not need enriched uranium to achieve criticality (due to the lower neutron absorption in their heavy water moderator compared to light water), however, some newer concepts call for low enrichment to help reduce the size of the reactors. The Atucha nuclear power plant in Argentina, a similar design to the CANDU but built by German KWU was originally designed for non-enriched fuel but since switched to slightly enriched fuel with a content about 0.1 percentage points higher than in natural uranium.
Less-common fuel forms
Various other nuclear fuel forms find use in specific applications, but lack the widespread use of those found in BWRs, PWRs, and CANDU power plants. Many of these fuel forms are only found in research reactors, or have military applications.
Magnox fuel
Magnox (magnesium non-oxidising) reactors are pressurised, carbon dioxide–cooled, graphite-moderated reactors using natural uranium (i.e. unenriched) as fuel and Magnox alloy as fuel cladding. Working pressure varies from for the steel pressure vessels, and the two reinforced concrete designs operated at . Magnox alloy consists mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium metal fuel with a non-oxidising covering to contain fission products. This material has the advantage of a low neutron capture cross-section, but has two major disadvantages:
It limits the maximum temperature, and hence the thermal efficiency, of the plant.
It reacts with water, preventing long-term storage of spent fuel under water - such as in a spent fuel pool.
Magnox fuel incorporated cooling fins to provide maximum heat transfer despite low operating temperatures, making it expensive to produce. While the use of uranium metal rather than oxide made nuclear reprocessing more straightforward and therefore cheaper, the need to reprocess fuel a short time after removal from the reactor meant that the fission product hazard was severe. Expensive remote handling facilities were required to address this issue.
Tristructural-isotropic fuel
Tristructural-isotropic (TRISO) fuel is a type of micro-particle fuel. A particle consists of a kernel of UOX fuel (sometimes UC or UCO), which has been coated with four layers of three isotropic materials deposited through fluidized chemical vapor deposition (FCVD). The four layers are a porous buffer layer made of carbon that absorbs fission product recoils, followed by a dense inner layer of protective pyrolytic carbon (PyC), followed by a ceramic layer of SiC to retain fission products at elevated temperatures and to give the TRISO particle more structural integrity, followed by a dense outer layer of PyC. TRISO particles are then encapsulated into cylindrical or spherical graphite pellets. TRISO fuel particles are designed not to crack due to the stresses from processes (such as differential thermal expansion or fission gas pressure) at temperatures up to 1600 °C, and therefore can contain the fuel in the worst of accident scenarios in a properly designed reactor. Two such reactor designs are the prismatic-block gas-cooled reactor (such as the GT-MHR) and the pebble-bed reactor (PBR). Both of these reactor designs are high temperature gas reactors (HTGRs). These are also the basic reactor designs of very-high-temperature reactors (VHTRs), one of the six classes of reactor designs in the Generation IV initiative that is attempting to reach even higher HTGR outlet temperatures.
TRISO fuel particles were originally developed in the United Kingdom as part of the Dragon reactor project. The inclusion of the SiC as diffusion barrier was first suggested by D. T. Livey. The first nuclear reactor to use TRISO fuels was the Dragon reactor and the first powerplant was the THTR-300. Currently, TRISO fuel compacts are being used in some experimental reactors, such as the HTR-10 in China and the high-temperature engineering test reactor in Japan. In the United States, spherical fuel elements utilizing a TRISO particle with a UO2 and UC solid solution kernel are being used in the Xe-100, and Kairos Power is developing a 140 MWE nuclear reactor that uses TRISO.
QUADRISO fuel
In QUADRISO particles a burnable neutron poison (europium oxide or erbium oxide or carbide) layer surrounds the fuel kernel of ordinary TRISO particles to better manage the excess of reactivity. If the core is equipped both with TRISO and QUADRISO fuels, at beginning of life neutrons do not reach the fuel of the QUADRISO particles because they are stopped by the burnable poison. During reactor operation, neutron irradiation of the poison causes it to "burn up" or progressively transmute to non-poison isotopes, depleting this poison effect and leaving progressively more neutrons available for sustaining the chain-reaction. This mechanism compensates for the accumulation of undesirable neutron poisons which are an unavoidable part of the fission products, as well as normal fissile fuel "burn up" or depletion. In the generalized QUADRISO fuel concept the poison can eventually be mixed with the fuel kernel or the outer pyrocarbon. The QUADRISO concept was conceived at Argonne National Laboratory.
RBMK fuel
RBMK reactor fuel was used in Soviet-designed and built RBMK-type reactors. This is a low-enriched uranium oxide fuel. The fuel elements in an RBMK are 3 m long each, and two of these sit back-to-back on each fuel channel, pressure tube. Reprocessed uranium from Russian VVER reactor spent fuel is used to fabricate RBMK fuel. Following the Chernobyl accident, the enrichment of fuel was changed from 2.0% to 2.4%, to compensate for control rod modifications and the introduction of additional absorbers.
CerMet fuel
CerMet fuel consists of ceramic fuel particles (usually uranium oxide) embedded in a metal matrix. It is hypothesized that this type of fuel is what is used in United States Navy reactors. This fuel has high heat transport characteristics and can withstand a large amount of expansion.
Plate-type fuel
Plate-type fuel has fallen out of favor over the years. Plate-type fuel is commonly composed of enriched uranium sandwiched between metal cladding. Plate-type fuel is used in several research reactors where a high neutron flux is desired, for uses such as material irradiation studies or isotope production, without the high temperatures seen in ceramic, cylindrical fuel. It is currently used in the Advanced Test Reactor (ATR) at Idaho National Laboratory, and the nuclear research reactor at the University of Massachusetts Lowell Radiation Laboratory.
Sodium-bonded fuel
Sodium-bonded fuel consists of fuel that has liquid sodium in the gap between the fuel slug (or pellet) and the cladding. This fuel type is often used for sodium-cooled liquid metal fast reactors. It has been used in EBR-I, EBR-II, and the FFTF. The fuel slug may be metallic or ceramic. The sodium bonding is used to reduce the temperature of the fuel.
Accident tolerant fuels
Accident tolerant fuels (ATF) are a series of new nuclear fuel concepts, researched in order to improve fuel performance under accident conditions, such as loss-of-coolant accident (LOCA) or reaction-initiated accidents (RIA). These concerns became more prominent after the Fukushima Daiichi nuclear disaster in Japan, in particular regarding light-water reactor (LWR) fuels performance under accident conditions.
Neutronics analyses were performed for the application of the new fuel-cladding material systems for various types of ATF materials.
The aim of the research is to develop nuclear fuels that can tolerate loss of active cooling for a considerably longer period than the existing fuel designs and prevent or delay the release of radionuclides during an accident. This research is focused on reconsidering the design of fuel pellets and cladding, as well as the interactions between the two.
Spent nuclear fuel
Used nuclear fuel is a complex mixture of the fission products, uranium, plutonium, and the transplutonium metals. In fuel which has been used at high temperature in power reactors it is common for the fuel to be heterogeneous; often the fuel will contain nanoparticles of platinum group metals such as palladium. Also the fuel may well have cracked, swollen, and been heated close to its melting point. Despite the fact that the used fuel can be cracked, it is very insoluble in water, and is able to retain the vast majority of the actinides and fission products within the uranium dioxide crystal lattice. The radiation hazard from spent nuclear fuel declines as its radioactive components decay, but remains high for many years. For example 10 years after removal from a reactor, the surface dose rate for a typical spent fuel assembly still exceeds 10,000 rem/hour, resulting in a fatal dose in just minutes.
Oxide fuel under accident conditions
Two main modes of release exist, the fission products can be vaporised or small particles of the fuel can be dispersed.
Fuel behavior and post-irradiation examination
Post-Irradiation Examination (PIE) is the study of used nuclear materials such as nuclear fuel. It has several purposes. It is known that by examination of used fuel that the failure modes which occur during normal use (and the manner in which the fuel will behave during an accident) can be studied. In addition information is gained which enables the users of fuel to assure themselves of its quality and it also assists in the development of new fuels. After major accidents the core (or what is left of it) is normally subject to PIE to find out what happened. One site where PIE is done is the ITU which is the EU centre for the study of highly radioactive materials.
Materials in a high-radiation environment (such as a reactor) can undergo unique behaviors such as swelling and non-thermal creep. If there are nuclear reactions within the material (such as what happens in the fuel), the stoichiometry will also change slowly over time. These behaviors can lead to new material properties, cracking, and fission gas release.
The thermal conductivity of uranium dioxide is low; it is affected by porosity and burn-up. The burn-up results in fission products being dissolved in the lattice (such as lanthanides), the precipitation of fission products such as palladium, the formation of fission gas bubbles due to fission products such as xenon and krypton and radiation damage of the lattice. The low thermal conductivity can lead to overheating of the center part of the pellets during use. The porosity results in a decrease in both the thermal conductivity of the fuel and the swelling which occurs during use.
According to the International Nuclear Safety Center the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations.
The bulk density of the fuel can be related to the thermal conductivity.
Where ρ is the bulk density of the fuel and ρtd is the theoretical density of the uranium dioxide.
Then the thermal conductivity of the porous phase (Kf) is related to the conductivity of the perfect phase (Ko, no porosity) by the following equation. Note that s is a term for the shape factor of the holes.
Kf = Ko(1 − p/1 + (s − 1)p)
Rather than measuring the thermal conductivity using the traditional methods such as Lees' disk, the Forbes' method, or Searle's bar, it is common to use Laser Flash Analysis where a small disc of fuel is placed in a furnace. After being heated to the required temperature one side of the disc is illuminated with a laser pulse, the time required for the heat wave to flow through the disc, the density of the disc, and the thickness of the disk can then be used to calculate and determine the thermal conductivity.
λ = ρCpα
λ thermal conductivity
ρ density
Cp heat capacity
α thermal diffusivity
If t1/2 is defined as the time required for the non illuminated surface to experience half its final temperature rise then.
α = 0.1388 L2/t1/2
L is the thickness of the disc
For details see K. Shinzato and T. Baba (2001).
Radioisotope decay fuels
Radioisotope battery
An atomic battery (also called a nuclear battery or radioisotope battery) is a device which uses the radioactive decay to generate electricity. These systems use radioisotopes that produce low energy beta particles or sometimes alpha particles of varying energies. Low energy beta particles are needed to prevent the production of high energy penetrating bremsstrahlung radiation that would require heavy shielding. Radioisotopes such as plutonium-238, curium-242, curium-244 and strontium-90 have been used. Tritium, nickel-63, promethium-147, and technetium-99 have been tested.
There are two main categories of atomic batteries: thermal and non-thermal. The non-thermal atomic batteries, which have many different designs, exploit charged alpha and beta particles. These designs include the direct charging generators, betavoltaics, the optoelectric nuclear battery, and the radioisotope piezoelectric generator. The thermal atomic batteries on the other hand, convert the heat from the radioactive decay to electricity. These designs include thermionic converter, thermophotovoltaic cells, alkali-metal thermal to electric converter, and the most common design, the radioisotope thermoelectric generator.
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator (RTG) is a simple electrical generator which converts heat into electricity from a radioisotope using an array of thermocouples.
has become the most widely used fuel for RTGs, in the form of plutonium dioxide. It has a half-life of 87.7 years, reasonable energy density, and exceptionally low gamma and neutron radiation levels. Some Russian terrestrial RTGs have used ; this isotope has a shorter half-life and a much lower energy density, but is cheaper. Early RTGs, first built in 1958 by the U.S. Atomic Energy Commission, have used . This fuel provides phenomenally huge energy density, (a single gram of polonium-210 generates 140 watts thermal) but has limited use because of its very short half-life and gamma production, and has been phased out of use for this application.
Radioisotope heater unit (RHU)
A radioisotope heater unit (RHU) typically provides about 1 watt of heat each, derived from the decay of a few grams of plutonium-238. This heat is given off continuously for several decades.
Their function is to provide highly localised heating of sensitive equipment (such as electronics in outer space). The Cassini–Huygens orbiter to Saturn contains 82 of these units (in addition to its 3 main RTGs for power generation). The Huygens probe to Titan contains 35 devices.
Fusion fuels
Fusion fuels are fuels to use in hypothetical Fusion power reactors. They include deuterium (2H) and tritium (3H) as well as helium-3 (3He). Many other elements can be fused together, but the larger electrical charge of their nuclei means that much higher temperatures are required. Only the fusion of the lightest elements is seriously considered as a future energy source. Fusion of the lightest atom, 1H hydrogen, as is done in the Sun and other stars, has also not been considered practical on Earth. Although the energy density of fusion fuel is even higher than fission fuel, and fusion reactions sustained for a few minutes have been achieved, utilizing fusion fuel as a net energy source remains only a theoretical possibility.
First-generation fusion fuel
Deuterium and tritium are both considered first-generation fusion fuels; they are the easiest to fuse, because the electrical charge on their nuclei is the lowest of all elements. The three most commonly cited nuclear reactions that could be used to generate energy are:
2H + 3H → n (14.07 MeV) + 4He (3.52 MeV)
2H + 2H → n (2.45 MeV) + 3He (0.82 MeV)
2H + 2H → p (3.02 MeV) + 3H (1.01 MeV)
Second-generation fusion fuel
Second-generation fuels require either higher confinement temperatures or longer confinement time than those required of first-generation fusion fuels, but generate fewer neutrons. Neutrons are an unwanted byproduct of fusion reactions in an energy generation context, because they are absorbed by the walls of a fusion chamber, making them radioactive. They cannot be confined by magnetic fields, because they are not electrically charged. This group consists of deuterium and helium-3. The products are all charged particles, but there may be significant side reactions leading to the production of neutrons.
2H + 3He → p (14.68 MeV) + 4He (3.67 MeV)
Third-generation fusion fuel
Third-generation fusion fuels produce only charged particles in the primary reactions, and side reactions are relatively unimportant. Since a very small amount of neutrons is produced, there would be little induced radioactivity in the walls of the fusion chamber. This is often seen as the end goal of fusion research. 3He has the highest Maxwellian reactivity of any 3rd generation fusion fuel. However, there are no significant natural sources of this substance on Earth.
3He + 3He → 2 p + 4He (12.86 MeV)
Another potential aneutronic fusion reaction is the proton-boron reaction:
p + 11B → 3 4He (8.7 MeV)
Under reasonable assumptions, side reactions will result in about 0.1% of the fusion power being carried by neutrons. With 123 keV, the optimum temperature for this reaction is nearly ten times higher than that for the pure hydrogen reactions, the energy confinement must be 500 times better than that required for the D-T reaction, and the power density will be 2500 times lower than for D-T.
| Technology | Fuel | null |
2049869 | https://en.wikipedia.org/wiki/Ground%20tissue | Ground tissue | The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. This tissue system is present between the dermal tissue and forms the main bulk of the plant body.
Parenchyma cells have thin primary walls and usually remain alive after they become mature. Parenchyma forms the "filler" tissue in the soft parts of plants, and is usually present in cortex, pericycle, pith, and medullary rays in primary stem and root.
Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra mechanical and structural support, particularly in regions of new growth.
Sclerenchyma cells have thick lignified secondary walls and often die when mature. Sclerenchyma provides the main structural support to the plant.
Aerenchyma cells are found in aquatic plants. They are also known to be parenchyma cells with large air cavities surrounded by irregular cells which form columns called trabeculae.
Parenchyma
Parenchyma is a versatile ground tissue that generally constitutes the "filler" tissue in soft parts of plants. It forms, among other things, the cortex (outer region) and pith (central region) of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds. Parenchyma cells are often living cells and may remain meristematic, meaning that they are capable of cell division if stimulated. They have thin and flexible cellulose cell walls and are generally polyhedral when close-packed, but can be roughly spherical when isolated from their neighbors. Parenchyma cells are generally large. They have large central vacuoles, which allow the cells to store and regulate ions, waste products, and water. Tissue specialised for food storage is commonly formed of parenchyma cells.
Parenchyma cells have a variety of functions:
In leaves, they form two layers of mesophyll cells immediately beneath the epidermis of the leaf, that are responsible for photosynthesis and the exchange of gases. These layers are called the palisade parenchyma and spongy mesophyll. Palisade parenchyma cells can be either cuboidal or elongated. Parenchyma cells in the mesophyll of leaves are specialised parenchyma cells called chlorenchyma cells (parenchyma cells with chloroplasts). Parenchyma cells are also found in other parts of the plant.
Storage of starch, protein, fats, oils and water in roots, tubers (e.g. potatoes), seed endosperm (e.g. cereals) and cotyledons (e.g. pulses and peanuts)
Secretion (e.g. the parenchyma cells lining the inside of resin ducts)
Wound repair and the potential for renewed meristematic activity
Other specialised functions such as aeration (aerenchyma) provides buoyancy and helps aquatic plants float.
Chlorenchyma cells carry out photosynthesis and manufacture food.
The shape of parenchyma cells varies with their function. In the spongy mesophyll of a leaf, parenchyma cells range from near-spherical and loosely arranged with large intercellular spaces, to branched or stellate, mutually interconnected with their neighbours at the ends of their arms to form a three-dimensional network, like in the red kidney bean Phaseolus vulgaris and other mesophytes. These cells, along with the epidermal guard cells of the stoma, form a system of air spaces and chambers that regulate the exchange of gases. In some works, the cells of the leaf epidermis are regarded as specialised parenchymal cells, but the modern preference has long been to classify the epidermis as plant dermal tissue, and parenchyma as ground tissue.
Shapes of parenchyma:
Polyhedral (found in pallisade tissue of the leaf)
Spherical
Stellate (found in stem of plants and have well-developed air spaces between them)
Elongated (also found in pallisade tissue of leaf)
Lobed (found in spongy and pallisade mesophyll tissue of some plants)
Collenchyma
Collenchyma tissue is composed of elongated cells with irregularly thickened walls. They provide structural support, particularly in growing shoots and leaves (as seen, for example, the resilient strands in stalks of celery). Collenchyma cells are usually living, and have only a thick primary cell wall made up of cellulose and pectin. Cell wall thickness is strongly affected by mechanical stress upon the plant. The walls of collenchyma in shaken plants (to mimic the effects of wind etc.), may be 40–100% thicker than those not shaken.
There are four main types of collenchyma:
Angular collenchyma (thickened at intercellular contact points)
Tangential collenchyma (cells arranged into ordered rows and thickened at the tangential face of the cell wall)
Annular collenchyma (uniformly thickened cell walls)
Lacunar collenchyma (collenchyma with intercellular spaces)
Collenchyma cells are most often found adjacent to outer growing tissues such as the vascular cambium and are known for increasing structural support and integrity.
The first use of "collenchyma" () was by Link (1837) who used it to describe the sticky substance on Bletia (Orchidaceae) pollen. Complaining about Link's excessive nomenclature, Schleiden (1839) stated mockingly that the term "collenchyma" could have more easily been used to describe elongated sub-epidermal cells with unevenly thickened cell walls.
Sclerenchyma
Sclerenchyma is the tissue which makes the plant hard and stiff. Sclerenchyma is the supporting tissue in plants. Two types of sclerenchyma cells exist: fibers cellular and sclereids. Their cell walls consist of cellulose, hemicellulose, and lignin. Sclerenchyma cells are the principal supporting cells in plant tissues that have ceased elongation. Sclerenchyma fibers are of great economic importance, since they constitute the source material for many fabrics (e.g. flax, hemp, jute, and ramie).
Unlike the collenchyma, mature sclerenchyma is composed of dead cells with extremely thick cell walls (secondary walls) that make up to 90% of the whole cell volume. The term sclerenchyma is derived from the Greek σκληρός (sklērós), meaning "hard." It is the hard, thick walls that make sclerenchyma cells important strengthening and supporting elements in plant parts that have ceased elongation. The difference between sclereids is not always clear: transitions do exist, sometimes even within the same plant.
Fibers
Fibers or bast are generally long, slender, so-called prosenchymatous cells, usually occurring in strands or bundles. Such bundles or the totality of a stem's bundles are colloquially called fibers. Their high load-bearing capacity and the ease with which they can be processed has since antiquity made them the source material for a number of things, like ropes, fabrics and mattresses. The fibers of flax (Linum usitatissimum) have been known in Europe and Egypt for more than 3,000 years, those of hemp (Cannabis sativa) in China for just as long. These fibers, and those of jute (Corchorus capsularis) and ramie (Boehmeria nivea, a nettle), are extremely soft and elastic and are especially well suited for the processing to textiles. Their principal cell wall material is cellulose.
Contrasting are hard fibers that are mostly found in monocots. Typical examples are the fiber of many grasses, Agave sisalana (sisal), Yucca or Phormium tenax, Musa textilis and others. Their cell walls contain, besides cellulose, a high proportion of lignin. The load-bearing capacity of Phormium tenax is as high as 20–25 kg/mm², the same as that of good steel wire (25 kg/ mm²), but the fibre tears as soon as too great a strain is placed upon it, while the wire distorts and does not tear before a strain of 80 kg/mm². The thickening of a cell wall has been studied in Linum. Starting at the centre of the fiber, the thickening layers of the secondary wall are deposited one after the other. Growth at both tips of the cell leads to simultaneous elongation. During development the layers of secondary material seem like tubes, of which the outer one is always longer and older than the next. After completion of growth, the missing parts are supplemented, so that the wall is evenly thickened up to the tips of the fibers.
Fibers usually originate from meristematic tissues. Cambium and procambium are their main centers of production. They are usually associated with the xylem and phloem of the vascular bundles. The fibers of the xylem are always lignified, while those of the phloem are cellulosic. Reliable evidence for the fibre cells' evolutionary origin from tracheids exists. During evolution the strength of the tracheid cell walls was enhanced, the ability to conduct water was lost and the size of the pits was reduced. Fibers that do not belong to the xylem are bast (outside the ring of cambium) and such fibers that are arranged in characteristic patterns at different sites of the shoot.
The term "sclerenchyma" (originally Sclerenchyma) was introduced by Mettenius in 1865.
Sclereids
Sclereids are the reduced form of sclerenchyma cells with highly thickened, lignified walls.
They are small bundles of sclerenchyma tissue in plants that form durable layers, such as the cores of apples and the gritty texture of pears (Pyrus communis). Sclereids are variable in shape. The cells can be isodiametric, prosenchymatic, forked or elaborately branched. They can be grouped into bundles, can form complete tubes located at the periphery or can occur as single cells or small groups of cells within parenchyma tissues. But compared with most fibres, sclereids are relatively short. Characteristic examples are brachysclereids or the stone cells (called stone cells because of their hardness) of pears and quinces (Cydonia oblonga) and those of the shoot of the wax plant (Hoya carnosa). The cell walls fill nearly all the cell's volume. A layering of the walls and the existence of branched pits is clearly visible. Branched pits such as these are called ramiform pits. The shell of many seeds like those of nuts as well as the stones of drupes like cherries and plums are made up from sclereids.
These structures are used to protect other cells.
| Biology and health sciences | Plant tissues | null |
2050678 | https://en.wikipedia.org/wiki/Arsinoitherium | Arsinoitherium | Arsinoitherium is an extinct genus of paenungulate mammals belonging to the extinct order Embrithopoda. It is related to elephants, sirenians, and hyraxes. Arsinoitheres were superficially rhinoceros-like herbivores that lived during the Late Eocene and the Early Oligocene of North Africa from 36 to 30 million years ago, in areas of tropical rainforest and at the margin of mangrove swamps. A species described in 2004, A. giganteum, lived in Ethiopia about 27 million years ago.
Taxonomy
The best-known (and first-described) species is A. zitteli. Another species, A. giganteum, was discovered in the Ethiopian highlands of Chilga in 2003. The fossil teeth, far larger than those of A. zitteli, date to around 28–27 million years ago. While the Faiyum Oasis is the only site where complete skeletons of Arsinoitherium fossils were recovered, arsinoitheriids have been found in southeastern Europe, including Crivadiatherium from Romania, and Hypsamasia and Palaeoamasia from Turkey.
The generic name Arsinoitherium comes from Pharaoh Arsinoe II (after whom the Faiyum Oasis, the region in which the first fossils were found, was called during the Ptolemaic Kingdom), and the theríon "beast". The species epithet of the type species, A. zitteli, was given to it in honor of the eminent German paleontologist Karl Alfred Ritter von Zittel, regarded by some as the pioneer of paleontology in Egypt.
Description
Adults of the species A. zitteli stood around tall at the shoulders and in length. It weighed 2.5 tons, only slightly smaller than the modern white rhino and due to the similar features and sizes, Arsinoitherium is commonly thought to be an extinct rhinoceros species, but it is not closely related to rhinos; instead, their closest extant relatives are elephants and manatees. They were massive, slow-moving animals with forelimbs adapted for pulling strongly backwards rather than swinging forward, a feature typical of animals that punt themselves through shallow water or walk on soft, sticky ground. Fossils are found in sediments deposited in coastal swamps and warm, humid, heavily vegetated lowland forests across what is now Africa and Arabia.
The most noticeable features of Arsinoitherium were a pair of enormous horns above the nose and a second pair of tiny knob-like horns over the eyes. These were structurally similar to the horns of modern bovids. While reconstructions usually show them as similar to the ossicones of giraffes, in life each bony core may have been covered, like the horn cores of bovids, with a large horn of keratin. Both males and females had horns. While some investigators have described a larger and a smaller species from the same site, others have identified the difference in body and tooth size as sexual dimorphism. The skeleton is robust and the limbs were columnar, similar to those of elephants; the hips were also elephant-like, and arsinotheres were not built to run. Arsinoitherium had a full complement of 44 teeth, which is the primitive state of placental mammalian dentition. However, the genus had a unique and highly specialized way of chewing, shifting the jaw joint to produce constant pressure along its continuous row of teeth; it has been reconstructed as a highly selective browser.
Distribution
Fossils of Arsinoitherium have been found in:
Eocene
Aydim Formation, Oman
Idam Unit Formation, Libya
Djebel Chambi, Tunisia
Oligocene
Malembe, Angola
Jebel Qatrani Formation, Egypt
Chilga formation, Ethiopia
Erageleit Formation, Kenya
Ashawq Formation, Oman
Shumaysi Formation, Saudi Arabia
| Biology and health sciences | Other afrotheres | Animals |
2051037 | https://en.wikipedia.org/wiki/Environmental%20biotechnology | Environmental biotechnology | Environmental biotechnology is biotechnology that is applied to and used to study the natural environment. Environmental biotechnology could also imply that one try to harness biological process for commercial uses and exploitation. The International Society for Environmental Biotechnology defines environmental biotechnology as "the development, use and regulation of biological systems for remediation of contaminated environments (land, air, water), and for environment-friendly processes (green manufacturing technologies and sustainable development)".
Environmental biotechnology can simply be described as "the optimal use of nature, in the form of plants, animals, bacteria, fungi and algae, to produce renewable energy, food and nutrients in a synergistic integrated cycle of profit making processes where the waste of each process becomes the feedstock for another process".
Significance for agriculture, food security, climate change mitigation and adaptation and the MDGs
The IAASTD has called for the advancement of small-scale agro-ecological farming systems and technology in order to achieve food security, climate change mitigation, climate change adaptation and the realisation of the Millennium Development Goals. Environmental biotechnology has been shown to play a significant role in agroecology in the form of zero waste agriculture and most significantly through the operation of over 15 million biogas digesters worldwide.
Significance towards industrial biotechnology
Consider the effluents of starch plant which has mixed up with a local water body like a lake or pond. We find huge deposits of starch which are not so easily taken up for degradation by microorganisms except for a few exemptions. Microorganisms from the polluted site are scan for genomic changes that allow them to degrade/utilize the starch better than other microbes of the same genus. The modified genes are then identified. The resultant genes are cloned into industrially significant microorganisms and are used for economically processes like in pharmaceutical industry, fermentations... etc..
Similar situations can be encountered in the case of marine oil spills which require cleanup, where microbes isolated from oil rich environments like oil wells, oil transfer pipelines...etc. have been found having the potential to degrade oil or use it as an energy source. Thus they serve as a remedy to oil spills.
Microbes isolated from pesticide-contaminated soils may capable of utilizing the pesticides as energy source and hence when mixed along with bio-fertilizers, could serve as an insurance against increased pesticide-toxicity levels in agricultural platform.
On the other hand, these newly introduced microorganisms could create an imbalance in the environment concerned. The mutual harmony in which the organisms in that particular environment existed may have to face alteration and we should be extremely careful so as to not disturb the mutual relationships already existing in the environment of both the benefits and the disadvantages would pave way for an improvised version of environmental biotechnology.
Applications and Implications
Humans have long been manipulating genetic material through breeding and modern genetic modification for optimizing crop yield, etc.. There can also be unexpected, negative health and environmental outcomes. Environmental biotechnology is about the balance between the applications that provide for these and the implications of manipulating genetic material. Textbooks address both the applications and implications. Environmental engineering texts addressing sewage treatment and biological principles are often now considered to be environmental biotechnology texts. These generally address the applications of biotechnologies, whereas the implications of these technologies are less often addressed; usually in books concerned with potential impacts and even catastrophic events.
| Technology | Biotechnology | null |
2051142 | https://en.wikipedia.org/wiki/Mosasaurus | Mosasaurus | Mosasaurus (; "lizard of the Meuse River") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages of the Late Cretaceous. The genus was one of the first Mesozoic marine reptiles known to science—the first fossils of Mosasaurus were found as skulls in a chalk quarry near the Dutch city of Maastricht in the late 18th century, and were initially thought to be crocodiles or whales. One skull discovered around 1780 was famously nicknamed the "great animal of Maastricht". In 1808, naturalist Georges Cuvier concluded that it belonged to a giant marine lizard with similarities to monitor lizards but otherwise unlike any known living animal. This concept was revolutionary at the time and helped support the then-developing ideas of extinction. Cuvier did not designate a scientific name for the animal; this was done by William Daniel Conybeare in 1822 when he named it Mosasaurus in reference to its origin in fossil deposits near the Meuse River. The exact affinities of Mosasaurus as a squamate remain controversial, and scientists continue to debate whether its closest living relatives are monitor lizards or snakes.
The largest species, M. hoffmannii, is estimated to measure up to in maximum length, making it one of the largest mosasaurs. The skull of Mosasaurus had robust jaws and strong muscles capable of powerful bites using dozens of large teeth adapted for cutting prey. Its four limbs were shaped into paddles to steer the animal underwater. Its tail was long and ended in a downward bend and a paddle-like fluke. Mosasaurus possessed excellent vision to compensate for its poor sense of smell, and a high metabolic rate suggesting it was endothermic ("warm-blooded"), an adaptation in squamates only found in mosasaurs. There is considerable morphological variability across the currently-recognized species in Mosasaurus—from the robustly-built M. hoffmannii to the slender and serpentine M. lemonnieri—but an unclear diagnosis (description of distinguishing features) of the type species M. hoffmannii led to a historically problematic classification. As a result, more than fifty species have been attributed to the genus in the past. A redescription of the type specimen in 2017 helped resolve the taxonomy issue and confirmed at least five species to be within the genus. Another five species still nominally classified within Mosasaurus are planned to be reassessed.
Fossil evidence suggests Mosasaurus inhabited much of the Atlantic Ocean and the adjacent seaways. Mosasaurus fossils have been found in North and South America, Europe, Africa, Western Asia, and Antarctica. This distribution encompassed a wide range of oceanic climates including tropical, subtropical, temperate, and subpolar. Mosasaurus was a common large predator in these oceans and was positioned at the top of the food chain. Paleontologists believe its diet would have included virtually any animal; it likely preyed on bony fish, sharks, cephalopods, birds, and other marine reptiles including sea turtles and other mosasaurs. It likely preferred to hunt in open water near the surface. From an ecological standpoint, Mosasaurus probably had a profound impact on the structuring of marine ecosystems; its arrival in some locations such as the Western Interior Seaway in North America coincides with a complete turnover of faunal assemblages and diversity. Mosasaurus faced competition with other large predatory mosasaurs such as Prognathodon and Tylosauruswhich were known to feed on similar preythough they were able to coexist in the same ecosystems through niche partitioning. There were still conflicts among them, as an instance of Tylosaurus attacking a Mosasaurus has been documented. Several fossils document deliberate attacks on Mosasaurus individuals by members of the same species. Fighting likely took place in the form of snout grappling, as seen in modern crocodiles.
Research history
Discovery and identification
The first Mosasaurus fossil known to science was discovered in 1764 in a chalk quarry near Maastricht in the Netherlands in the form of a skull, which was initially identified as a whale. This specimen, cataloged as TM 7424, is now on display at the Teylers Museum in Haarlem. Later around 1780, the quarry produced a second skull that caught the attention of the physician Johann Leonard Hoffmann, who thought it was a crocodile. He contacted the prominent biologist Petrus Camper, and the skull gained international attention after Camper published a study identifying it as a whale. This caught the attention of French revolutionaries, who looted the fossil following the siege of Maastricht during the French Revolutionary Wars in 1794. In a 1799 narrative of this event by Barthélemy Faujas de Saint-Fond, the skull was allegedly retrieved by twelve grenadiers in exchange for an offer of 600 bottles of wine. This story helped elevate the fossil into cultural fame, but historians agree that the narrative was exaggerated.
After its seizure, the second skull was sent to the National Museum of Natural History, France in 1795 and later cataloged as MNHN AC 9648. By 1800, Camper's son Adriaan Gilles Camper concluded that the fossil, which by then was nicknamed the "great animal of Maastricht", belonged to a marine reptile sharing affinities to monitor lizards, but otherwise unlike any modern animal. Georges Cuvier confirmed the observations of Camper Jr. in a more in-depth study which was published in 1808. The skull became part of Cuvier's first speculations about the conception of extinction, which later led to his theory of catastrophism, a precursor to the theory of evolution. At the time, it was not believed that a species could go extinct, and fossils of animals were often interpreted as some form of an extant species. Cuvier's idea that there existed an animal unlike any today was revolutionary at the time, and in 1812 he proclaimed, "Above all, the precise determination of the famous animal from Maastricht seems to us as important for the theory of zoological laws, as for the history of the globe." In a 1822 work by James Parkinson, William Daniel Conybeare coined the genus Mosasaurus from the Latin Mosa "Meuse" and the Ancient Greek σαῦρος (saûros, "lizard"), all literally meaning "lizard of the Meuse", in reference to the river where the holotype specimen was discovered nearby. In 1829, Gideon Mantell added the specific epithet hoffmannii, in honor to Hoffmann. Later, the second skull is designated as the new species' holotype (defining example).
Later discoveries and other species
In 1804, the Lewis and Clark Expedition discovered a now-lost fossil skeleton alongside the Missouri River, which was identified as a long fish. Richard Ellis speculated in 2003 that this may have been the earliest discovery of the second species M. missouriensis, although competing speculations exist. In 1818, a fossil from Monmouth County, New Jersey became the first North American specimen to be correctly recognized as a Mosasaurus by scientists of the time.
The type specimen of M. missouriensis was first described in 1834 by Richard Harlan based on a snout fragment found along the river's Big Bend, in South Dakota. In reference to its discovery made in the river, he coined the specific epithet and initially identified it as a species of Ichthyosaurus but later as an amphibian named Batrachiosaurus. The rest of the skull had been discovered earlier by a fur-trapper, and it eventually came under the possession of prince Maximilian of Weid-Neuwied between 1832 and 1834. The fossil skull, now cataloged as RFWUIP 1327, was delivered to Georg August Goldfuss in Bonn for research, who published a study in 1845. The same year, Christian Erich Hermann von Meyer suspected that the skull and Harlan's snout were part of the same individual. Although the snout was noted as lost at the time, Joseph Leidy erected the new combination M. missouriensis after this suggestion in 1857, which has since entered common use. The snout was finally found in 2004 in the collections of the MNHN under the catalog number MNHN 9587, thus confirming the initial suspicion expressed by von Meyer and followed by other authors.
The third species was described in 1881 by Edward Drinker Cope from a fragmentary fossil skeleton having been discovered in New Jersey, now cataloged as AMNH 1380. In his description, the Cope thought that it represented a giant species of Clidastes and named it Clidastes conodon. In 1966, Donald Baird and Gerard R. Case reidentified it as a species of Mosasaurus. Although Cope did not provide the etymology for the specific epithet conodon, it is suggested that it could be a portmanteau meaning "conical tooth", derived from the Ancient Greek κῶνος (kônos, "cone") and ὀδών (odṓn, "tooth"), probably in reference to conical surface teeth smooth of the species.
The fourth species M. lemonnieri was described in 1889 by Louis Dollo on the basis of a relatively complete skull discovered in a quarry owned by the Solvay S.A. company in the Ciply Basin of Belgium. This skull, since numbered as IRSNB R28, is one of the many fossils donated by the then director of this quarry, Alfred Lemonnier, Dollo naming the species in his honor. Further mining of the quarry in subsequent years uncovered many additional well-preserved fossils, including multiple partial skeletons which collectively represented nearly the entire skeleton of the species. They were described by Dollo in later papers. Despite being one of the best anatomically represented species, M. lemonnieri was largely ignored in scientific literature. Theagarten Lingham-Soliar suggested two reasons for this neglect. First, M. lemonnieri fossils are endemic to Belgium and the Netherlands, which despite the famous discovery of the M. hoffmannii holotype attracted little attention from mosasaur paleontologists. Second, the species was overshadowed by the more famous and history-rich type species.
M. lemonnieri is a controversial taxon, and there is debate on whether it is a distinct species or not. In 1967, Dale Russell argued that M. lemonnieri and M. conodon are the same species and designated the former as a junior synonym per the principle of priority. In a 2000 study, Lingham-Soliar refuted this based on a comprehensive study of existing M. lemonnieri specimens, which was corroborated by a study on the M. conodon skull by Takehito Ikejiri and Spencer G. Lucas in 2014. In 2004, Eric Mulder, Dirk Cornelissen, and Louis Verding suggested M. lemonnieri could be a juvenile form of M. hoffmannii based on the argument that significant differences could be explained by age-based variation. However, the need for more research to confirm any hypotheses of synonymy was expressed.
The fifth species M. beaugei was described by Camille Arambourg in 1952 from isolated teeth originating from phosphate deposits in the Oulad Abdoun Basin and the Ganntour Basin in Morocco, the holotype tooth being cataloged as MNHN PMC 7. The species is named in honor of Alfred Beaugé, director at the time of the OCP Group, who invited Arambourg to participate in the research project and helped him to provide local fossils.
Early depictions
Scientists during the early and mid-1800s initially imagined Mosasaurus as an amphibious marine reptile with webbed feet and limbs for walking. This was based on fossils like the M. missouriensis holotype, which indicated an elastic vertebral column that Goldfuss in 1845 saw as evidence of an ability to walk and interpretations of some phalanges as claws. In 1854, Hermann Schlegel proved how Mosasaurus actually had fully aquatic flippers. He clarified that earlier interpretations of claws were erroneous and demonstrated how the phalanges show no indication of muscle or tendon attachment, which would make walking impossible. They are also broad, flat, and form a paddle. Schlegel's hypothesis was largely ignored by contemporary scientists but became widely accepted by the 1870s when Othniel Charles Marsh and Cope uncovered more complete mosasaur remains in North America.
One of the earliest depictions of Mosasaurus in paleoart is a life-size concrete sculpture created by Benjamin Waterhouse Hawkins between 1852 and 1854 as part of the collection of sculptures of prehistoric animals on display at the Crystal Palace Park in London. The restoration was primarily informed by Richard Owen's interpretation of the M. hoffmannii holotype and the anatomy of monitor lizards, so Hawkins depicted the animal as essentially a water-going monitor lizard. It was given a boxy head, nostrils at the side of the skull, large volumes of soft tissue around the eyes, lips reminiscent of monitor lizards, scales consistent with those in large monitors like the Komodo dragon, and a flipper. The model was deliberately sculpted incomplete, which Mark Witton believed was likely to save time and money. Many elements of the sculpture can be considered inaccurate, even for the time. It did not take into account Golduss' 1845 study of M. missouriensis which instead called for a narrower skull, nostrils at the top of the skull, and amphibious terrestrial limbs (the latter being incorrect in modern standards).
Description
Mosasaurus was a type of derived mosasaur, or a latecoming member with advanced evolutionary traits such as a fully aquatic lifestyle. As such, it had a streamlined body, an elongated tail ending with a downturn supporting a two-lobed fin, and two pairs of flippers. While in the past derived mosasaurs were depicted as akin to giant flippered sea snakes, it is now understood that they were more similar in build to other large marine vertebrates such as ichthyosaurs, marine crocodylomorphs, and archaeocete whales through convergent evolution.
Size
The type species, M. hoffmannii, is one of the largest marine reptiles known, though knowledge of its skeleton remains incomplete as it is mainly known from skulls. Russell (1967) wrote that the length of the jaw equalled one tenth of the body length in the species. Based on this ratio, Grigoriev (2014) used the largest lower jaw attributed to M. hoffmannii (CCMGE 10/2469, also known as the Penza specimen; measuring in length) to estimate a maximum length of . Using a smaller partial jaw (NHMM 009002) measuring and "reliably estimated at" when complete, Lingham-Soliar (1995) estimated a larger maximum length of via the same ratio. No explicit justification for the 1:10 ratio was provided in Russell (1967), and it has been considered to be probably overestimated by Cleary et al. (2018). In 2014, Federico Fanti and colleagues alternatively argued that the total length of M. hoffmannii was more likely closer to seven times the length of the skull, which was based on a near-complete skeleton of the related species Prognathodon overtoni. The study estimated that an M. hoffmannii individual with a skull measuring more than would have been up to or more than in length and weighed in body mass. Using the same ratio, Gayford et al. (2024) calculated the total length for the Penza specimen to be .
Isolated bones suggest some M. hoffmannii may have exceeded the lengths of the Penza specimen. One such bone is a quadrate (NHMM 003892) which is 150% larger than the average size, which Everhart and colleagues in 2016 reported can be extrapolated to scale an individual around in length. It was not stated whether they applied Russell's 1967 ratio, although Gayford et al. (2024) suggested it was likely.
M. missouriensis and M. lemonnieri are smaller than M. hoffmannii but are known from more complete fossils. Based on measurements of various Belgian skeletons, Dollo estimated M. lemonnieri grew to around in length. He also measured the dimensions of IRSNB 3119 and recorded that the skull constituted approximately one-eleventh of the whole body. Polcyn et al. (2014) estimated that M. missouriensis may have measured up to in length. Street (2016) noted that large M. missouriensis individuals typically had skulls exceeding lengths of . A particular near-complete skeleton of M. missouriensis is reportedly measured at in total length with a skull approaching in length. Based on personal observations of various unpublished fossils from Morocco, Nathalie Bardet et al. (2015) estimated that M. beaugei grew to a total length of , their skulls typically measuring around in length. With a referred skull measuring in length, M. conodon has been regarded as a small to medium-sized representative of the genus.
Skull
The skull of Mosasaurus is conical and tapers off to a short snout which extends a little beyond the frontmost teeth. In M. hoffmannii, this snout is blunt, while in M. lemonnieri it is pointed. Above the gum line in both jaws, a single row of small pits known as foramina are lined parallel to the jawline; they are used to hold the terminal branches of jaw nerves. The foramina along the snout form a pattern similar to the foramina in Clidastes skulls. The upper jaws in most species are robustly built, broad, and deep except in M. conodon, where they are slender. The disparity is also reflected in the dentary, the lower jawbone, although all species share a long and straight dentary. In M. hoffmannii, the top margin of the dentary is slightly curved upwards; this is also the case with the largest specimens of M. lemonnieri, although more typical skulls of the species have a near-perfectly straight jawline. The premaxillary bar, the long portion of the premaxillary bone extending behind the premaxillary teeth, is narrow and constricts near the middle in M. hoffmannii and M. lemonnieri like in typical mosasaurs. In M. missouriensis, the bar is robust and does not constrict. The external nares (nostril openings) are moderately sized and measure around 21–24% of the skull's length in M. hoffmannii. They are placed further toward the back of the skull than in nearly all other mosasaurs (exceeded only by Goronyosaurus), and begin above the fourth or fifth maxillary teeth. As a result, the rear portions of the maxilla (the main tooth-bearing bone of the upper jaw) lack the dorsal concavity that would fit the nostrils in typical mosasaurs.
The palate, which consists of the pterygoid bones, palatine bone, and nearby processes of other bones, is tightly packed to provide greater cranial stability. The neurocranium housed a brain which was narrow and relatively small compared to other mosasaurs. For example, the braincase of the mosasaur Plioplatecarpus marshi provided for a brain around twice the size of that in M. hoffmannii despite being only half the length of the latter. Spaces within the braincase for the occipital lobe and cerebral hemisphere are narrow and shallow, suggesting such brain parts were relatively small. The parietal foramen in Mosasaurus, which is associated with the parietal eye, is the smallest among mosasaurids. The quadrate bone, which connected the lower jaw to the rest of the skull and formed the jaw joint, is tall and somewhat rectangular in shape, differing from the rounder quadrates found in typical mosasaurs. The quadrate also housed the hearing structures, with the eardrum residing within a round and concave depression in the outer surface called the tympanic ala. The trachea likely stretched from the esophagus to below the back end of the lower jaw's coronoid process, where it split into smaller pairs of bronchi which extended parallel to each other.
Teeth
The features of teeth in Mosasaurus vary across species, but unifying characteristics include a design specialized for cutting prey, highly prismatic surfaces (enamel circumference shaped by flat sides called prisms), and two opposite cutting edges. Mosasaurus teeth are large and robust except for those in M. conodon and M. lemonnieri, which instead have more slender teeth. The cutting edges of Mosasaurus differ by species. The cutting edges in M. hoffmannii and M. missouriensis are finely serrated, while in M. conodon and M. lemonnieri serrations do not exist. The cutting edges of M. beaugei are neither serrated nor smooth, but instead possess minute wrinkles known as crenulations. The number of prisms in Mosasaurus teeth can slightly vary between tooth types and general patterns differ between speciesM. hoffmannii had two to three prisms on the labial side (the side facing lips) and no prisms on the lingual side (the side facing the tongue), M. missouriensis had four to six labial prisms and eight lingual prisms, M. lemonnieri had eight to ten labial prisms, and M. beaugei had three to five labial prisms and eight to nine lingual prisms.
Like all mosasaurs, Mosasaurus had four types of teeth, classified based on the jaw bones they were located on. On the upper jaw, there were three types: the premaxillary teeth, maxillary teeth, and pterygoid teeth. On the lower jaw, only one type, the dentary teeth, were present. In each jaw row, from front to back, Mosasaurus had: two premaxillary teeth, twelve to sixteen maxillary teeth, and eight to sixteen pterygoid teeth on the upper jaw and fourteen to seventeen dentary teeth on the lower jaw. The teeth were largely consistent in size and shape with only minor differences throughout the jaws (homodont) except for the smaller pterygoid teeth. The number of teeth in the maxillae, pterygoids, and dentaries vary between species and sometimes even individualsM. hoffmannii had fourteen to sixteen maxillary teeth, fourteen to fifteen dentary teeth, and eight pterygoid teeth; M. missouriensis had fourteen to fifteen maxillary teeth, fourteen to fifteen dentary teeth, and eight to nine pterygoid teeth; M. conodon had fourteen to fifteen maxillary teeth, sixteen to seventeen dentary teeth, and eight pterygoid teeth; M. lemonnieri had fifteen maxillary teeth, fourteen to seventeen dentary teeth, and eleven to twelve pterygoid teeth; and M. beaugei had twelve to thirteen maxillary teeth, fourteen to sixteen dentary teeth, and six or more pterygoid teeth. One indeterminate specimen of Mosasaurus similar to M. conodon from the Pembina Gorge State Recreation Area in North Dakota was found to have an unusual count of sixteen pterygoid teeth, far greater than in known species.
The dentition was thecodont (tooth roots deeply cemented within the jaw bone). Teeth were constantly shed through a process where the replacement tooth developed within the root of the original tooth and then pushed it out of the jaw. Chemical studies conducted on a M. hoffmannii maxillary tooth measured an average rate of deposition of odontoblasts, the cells responsible for the formation of dentin, at per day. This was by observing the von Ebner lines, incremental marks in dentin that form daily. It was approximated that it took the odontoblasts 511 days and dentin 233 days to develop to the extent observed in the tooth.
Postcranial skeleton
One of the most complete Mosasaurus skeletons in terms of vertebral representation (Mosasaurus sp.; SDSM 452) has seven cervical (neck) vertebrae, thirty-eight dorsal vertebrae (which includes thoracic and lumbar vertebrae) in the back, and eight pygal vertebrae (front tail vertebrae lacking haemal arches) followed by sixty-eight caudal vertebrae in the tail. All species of Mosasaurus have seven cervical vertebrae, but other vertebral counts vary among them. Various partial skeletons of M. conodon, M. hoffmannii, and M. missouriensis suggest M. conodon likely had up to thirty-six dorsal vertebrae and nine pygal vertebrae; M. hoffmannii had likely up to thirty-two dorsal vertebrae and ten pygal vertebrae; and M. missouriensis around thirty-three dorsal vertebrae, eleven pygal vertebrae, and at least seventy-nine caudal vertebrae. M. lemmonieri had the most vertebrae in the genus, with up to around forty dorsal vertebrae, twenty-two pygal vertebrae, and ninety caudal vertebrae. Compared to other mosasaurs, the rib cage of Mosasaurus is unusually deep and forms an almost perfect semicircle, giving it a barrel-shaped chest. Rather than being fused together, extensive cartilage likely connected the ribs with the sternum, which would have facilitated breathing movements and compression when in deeper waters. The texture of the bones is virtually identical with in modern whales, which indicates Mosasaurus possessed a high range of aquatic adaptation and neutral buoyancy as seen in cetaceans.
The tail structure of Mosasaurus is similar to relatives like Prognathodon, in which soft tissue evidence for a two-lobed tail is known. The tail vertebrae gradually shorten around the center of the tail and lengthen behind the center, suggesting rigidness around the tail center and excellent flexibility behind it. Like most advanced mosasaurs, the tail bends slightly downwards as it approached the center, but this bend is offset from the dorsal plane at a small degree. Mosasaurus also has large haemal arches located at the bottom of each caudal vertebra which bend near the middle of the tail, which contrasts with the reduction of haemal arches in other marine reptiles such as ichthyosaurs. These and other features support a large and powerful paddle-like fluke in Mosasaurus.
The forelimbs of Mosasaurus are wide and robust. The scapula and humerus are fan-shaped and wider than tall. The radius and ulna are short, but the former is taller and larger than the latter. The ilium is rod-like and slender; in M. missouriensis, it is around 1.5 times longer than the femur. The femur itself is about twice as long as it is wide and ends at the distal side in a pair of distinct articular facets (of which one connects to the ilium and the other to the paddle bones) that meet at an angle of approximately 120°. Five sets of metacarpals and phalanges (finger bones) were encased in and supported the paddles, with the fifth set being shorter and offset from the rest. The overall structure of the paddle is compressed, similar to in Plotosaurus, and was well-suited for faster swimming. In the hindlimbs, the paddle is supported by four sets of digits.
Interactive skeletal reconstruction of M. hoffmannii
(hover over or click on each skeletal component to identify the structure)
Classification
History of taxonomy
Because nomenclatural rules were not well-defined at the time, 19th century scientists did not give Mosasaurus a proper diagnosis during its initial descriptions, which led to ambiguity in how the genus is defined. This led Mosasaurus to become a wastebasket taxon containing as many as fifty different species. A 2017 study by Hallie Street and Michael Caldwell performed the first proper diagnosis and description of the M. hoffmannii holotype, which allowed a major taxonomic cleanup confirming five species as likely validM. hoffmannii, M. missouriensis, M. conodon, M. lemonnieri, and M. beaugei. The study also held four additional species from Pacific depositsM. mokoroa, M. hobetsuensis, M. flemingi, and M. prismaticusto be possibly valid, pending a future formal reassessment. Street & Caldwell (2017) was derived from Street's 2016 doctoral thesis, which contained a phylogenetic study proposing the constraining of Mosasaurus into four speciesM. hoffmannii, M. missouriensis, M. lemonnieri, and a proposed new species M. glycyswith M. conodon and the Pacific taxa recovered as belonging to different genera and M. beaugei view as a junior synonym of M. hoffmannii.
Systematics and evolution
As the type genus of the family Mosasauridae and the subfamily Mosasaurinae, Mosasaurus is a member of the order Squamata (which comprises lizards and snakes). Relationships between mosasaurs and living squamates remain controversial as scientists still fiercely debate on whether the closest living relatives of mosasaurs are monitor lizards or snakes. Mosasaurus, along with mosasaur genera Eremiasaurus, Plotosaurus, and Moanasaurus traditionally form a tribe within the Mosasaurinae variously called Mosasaurini or Plotosaurini.
Phylogeny and evolution of the genus
One of the earliest relevant attempts at an evolutionary study of Mosasaurus was done by Russell in 1967. He proposed that Mosasaurus evolved from a Clidastes-like mosasaur, and diverged into two lineages, one giving rise to M. conodon and another siring a chronospecies sequence which contained in order of succession M. ivoensis, M. missouriensis, and M. maximus-hoffmanni. However, Russell used an early method of phylogenetics and did not use cladistics.
In 1997, Bell published the first cladistical study of North American mosasaurs. Incorporating the species M. missouriensis, M. conodon, M. maximus, and an indeterminate specimen (UNSM 77040), some of his findings agreed with Russell (1967), such as Mosasaurus descending from an ancestral group containing Clidastes and M. conodon being the most basal of the genus. Contrary to Russell (1967), Bell also recovered Mosasaurus in a sister relationship with another group which included Globidens and Prognathodon, and M. maximus as a sister species to Plotosaurus. The latter rendered Mosasaurus paraphyletic (an unnatural grouping), but Bell (1997) nevertheless recognized Plotosaurus as a distinct genus.
Bell's study served as a precedent for later studies that mostly left the systematics of Mosasaurus unchanged, although some later studies have recovered the sister group to Mosasaurus and Plotosaurus to instead be Eremiasaurus or Plesiotylosaurus depending on the method of data interpretation used, with at least one study also recovering M. missouriensis to be the most basal species of the genus instead of M. conodon. In 2014, Konishi and colleagues expressed a number of concerns with the reliance on Bell's study. First, the genus was severely underrepresented by incorporating only the three North American species M. hoffmannii/M. maximus, M. missouriensis, and M. conodon; by doing so, others like M. lemonnieri, which is one of the most completely known species in the genus, were neglected, which affected phylogenetic results. Second, the studies relied on an unclean and shaky taxonomy of the Mosasaurus genus due to the lack of a clear holotype diagnosis, which may have been behind the genus's paraphyletic status. Third, there was still a lack of comparative studies of the skeletal anatomy of large mosasaurines at the time. These problems were addressed in Street's 2016 thesis in an updated phylogenetic analysis.
Conrad uniquely used only M. hoffmannii and M. lemonnieri in his 2008 phylogenetic analysis, which recovered M. hoffmannii as basal to a multitude of descendant clades containing (in order of most to least basal) Globidens, M. lemonnieri, Goronyosaurus, and Plotosaurus. This result indicated that M. hoffmannii and M. lemonnieri are not in the same genus. However, the study used a method unorthodox to traditional phylogenetic studies on mosasaur species because its focus was on the relationships of entire squamate groups rather than mosasaur classification. As a result, some paleontologists caution that lower-order classification results from Conrad's 2008 study such as the specific placement of Mosasaurus may contain technical problems, making them inaccurate.
The following cladogram on the left (Topology A) is modified from a maximum clade credibility tree inferred by a Bayesian analysis in the most recent major phylogenetic analysis of the Mosasaurinae subfamily by Madzia & Cau (2017), which was self-described as a refinement of a larger study by Simões et al. (2017). The cladogram on the right (Topology B) is modified from Street's 2016 doctoral thesis proposing a revision to the Mosasaurinae, with proposed new taxa and renamings in single quotations.
Paleobiology
Head musculature and mechanics
In 1995, Lingham-Soliar studied the head musculature of M. hoffmannii. Because soft tissue like muscles do not easily fossilize, reconstruction of the musculature was largely based on the structure of the skull, muscle scarring on the skull, and the musculature in extant monitor lizards.
In modern lizards, the mechanical build of the skull is characterized by a four-pivot geometric structure in the cranium that allows flexible movement of the jaws, possibly to allow the animals to better position them and prevent prey escape when hunting. In contrast, the frontal and parietal bones, which in modern lizards connect to form a flexible pivot point, overlap in the skull of M. hoffmannii. This creates a rigid three-pivot geometric cranial structure. These cranial structures are united by strong interlocking sutures formed to resist compression and shear forces caused by a downward thrust of the lower jaw muscles or an upward thrust of prey. This rigid but highly shock-absorbent structure of the cranium likely allowed a powerful bite force.
Like all mosasaurs, the lower jaws of Mosasaurus could swing forward and backward. In many mosasaurs like Prognathodon and M. lemonnieri, this function mainly served to allow ratchet feeding, in which the pterygoid and jaws would "walk" captured prey into the mouth like a conveyor belt. But especially compared to those in M. lemonnieri, the pterygoid teeth in M. hoffmannii are relatively small, which indicates ratchet feeding was relatively unimportant to its hunting and feeding. Rather, M. hoffmannii likely employed inertial feeding (in which the animal thrusts its head and neck backward to release a held prey item and immediately thrust the head and neck forward to close the jaws around the item) and used jaw adduction to assist in biting during prey seizure. The magnus adductor muscles, which attach to the lower jaws to the cranium and have a major role in biting function, are massive, indicating M. hoffmannii was capable of enormous bite forces. The long, narrow, and heavy nature of the lower jaws and attachment of tendons at the coronoid process would have allowed quick opening and closing of the mouth with little energy input underwater, which also contributed to the powerful bite force of M. hoffmannii and suggests it would not have needed the strong magnus depressor muscles (jaw-opening muscles) seen in some plesiosaurs.
Mobility and thermoregulation
Mosasaurus swam using its tail. The swimming style was likely sub-carangiform, which is exemplified today by mackerels. Its elongated paddle-like limbs functioned as hydrofoils for maneuvering the animal. The paddles' steering function was enabled by large muscle attachments from the outwards-facing side of the humerus to the radius and ulna and modified joints allowed an enhanced ability of rotating the flippers. The powerful forces resulting from utilization of the paddles may have sometimes resulted in bone damage, as evidenced by a M. hoffmannii ilium with significant separation of the bone's head from the rest of the bone likely caused by frequent shearing forces at the articulation joint.
The tissue structure of Mosasaurus bones suggests it had a metabolic rate much higher than modern squamates and its resting metabolic rate was between that of the leatherback sea turtle and that of ichthyosaurs and plesiosaurs. Mosasaurus was likely endothermic and maintained a constant body temperature independent of the external environment. Although there is no direct evidence specific to the genus, studies on the biochemistry of related mosasaur genera such as Clidastes suggests that endothermy was likely present in all mosasaurs. Such a trait is unique among squamates, the only known exception being the Argentine black and white tegu, which can maintain partial endothermy. This adaptation would have given several advantages to Mosasaurus, including increased stamina when foraging across larger areas and pursuing prey. It may have also been a factor that allowed Mosasaurus to thrive in the colder climates of locations such as Antarctica.
Sensory functions
Mosasaurus had relatively large eye sockets with large sclerotic rings occupying much of the sockets' diameter; the latter is correlated with eye size and suggests it had good vision. The eye sockets were located at the sides of the skull, which created a narrow field of binocular vision at around 28.5° but alternatively allowed excellent processing of a two-dimensional environment, such as the near-surface waters inhabited by Mosasaurus.
Brain casts made from fossils of Mosasaurus show that the olfactory bulb and vomeronasal organ, which both control the function of smell, are poorly developed and lack some structures in M. hoffmannii; this indicates the species had a poor sense of smell. In M. lemonnieri, these olfactory organs, although still small, are better developed and have some components lacking in M. hoffmannii. The lack of a strong sense of smell suggests that olfaction was not particularly important in Mosasaurus; instead, other senses like vision may have been more useful.
Feeding
Paleontologists generally agree that Mosasaurus was likely an active predator of a variety of marine animals. Fauna likely preyed upon by the genus include bony fish, sharks, cephalopods, birds, and marine reptiles such as other mosasaurs and turtles. It is unlikely Mosasaurus was a scavenger as it had a poor sense of smell. Mosasaurus was among the largest marine animals of its time, and with its large, robust cutting teeth, scientists believe larger members of the genus would have been able to handle virtually any animal. Lingham-Soliar (1995) suggested that Mosasaurus had a rather "savage" feeding behavior as demonstrated by large tooth marks on scutes of the giant sea turtle Allopleuron hoffmanni and fossils of re-healed fractured jaws in M. hoffmannii. The species likely hunted near the ocean surface as an ambush predator, using its large two-dimensionally adapted eyes to more effectively spot and capture prey. Chemical and structural data in the fossils of M. lemonnieri and M. conodon suggests they may have also hunted in deeper waters.
Carbon isotope studies on fossils of multiple M. hoffmannii individuals have found extremely low values of δ13C, the lowest in all mosasaurs for the largest individuals. Mosasaurs with lower δ13C values tended to occupy higher trophic levels, and one factor for this was dietary: a diet of prey rich in lipids such as sea turtles and other large marine reptiles can lower δ13C values. M. hoffmannii'''s low δ13C levels reinforces its likely position as an apex predator.
Currently, there are only two known examples of a Mosasaurus preserved with stomach contents. The first is a well-preserved partial skeleton of a small M. missouriensis dated about 75 million years old with dismembered and punctured remains of a long fish in its gut. This fish was much longer than the length of the mosasaur's skull, which measured in length, confirming that M. missouriensis consumed prey larger than its head by dismembering and consuming bits at a time. Due to coexistence with other large mosasaurs like Prognathodon, which specialized in robust prey, M. missouriensis likely specialized more on prey best consumed using cutting-adapted teeth in an example of niche partitioning. The second is from a subadult M. hoffmannii partial skeleton recovered from the same locality as the species' holotype near Maastricht, nicknamed "Lars". This specimen was reported in a 2024 conference to contain acid-corroded bones of a juvenile turtle reminiscent of Ctenochelys and of other distinct but unidentified animals in the gut region. Bones of an indeterminate bird or bird-like dinosaur were also found in association with the mosasaur, which could have also represented gut contents.Mosasaurus may have taught their offspring how to hunt, as supported by a fossil nautiloid Argonautilus catarinae with bite marks from two conspecific mosasaurs, one being from a juvenile and the other being from an adult. Analysis of the tooth marks by a 2004 study by Kauffman concluded that the mosasaurs were either Mosasaurus or Platecarpus. The positioning of both bite marks are at the direction the nautiloid's head would have been facing, indicating it was incapable of escaping and was thus already sick or dead during the attacks; it is possible this phenomenon was from a parent mosasaur teaching its offspring about cephalopods as an alternate source of prey and how to hunt one. An alternate explanation postulates the bite marks as from one individual mosasaur that lightly bit the nautiloid at first, then proceeded to bite again with greater force. However, there are differences in tooth spacing between both bites which indicate different jaw sizes.
Behavior and paleopathology
Intraspecific combat
There is fossil evidence that Mosasaurus engaged in aggressive and lethal combat with others of its kind. One partial skeleton of M. conodon bears multiple cuts, breaks, and punctures on various bones, particularly in the rear portions of the skull and neck, and a tooth from another M. conodon piercing through the quadrate bone. No injuries on the fossil show signs of healing, suggesting that the mosasaur was killed by its attacker by a fatal blow in the skull. Likewise, an M. missouriensis skeleton has a tooth from another M. missouriensis embedded in the lower jaw underneath the eye. In this case, there were signs of healing around the wound, implying survival of the incident. Takuya Konishi suggested an alternative cause of this example being head-biting behavior during courtship as seen in modern lizards. Attacks by another Mosasaurus are a possible cause of physical pathologies in other skulls, but they could have instead arisen from other incidents like attempted biting on hard turtle shells. In 2004, Lingham-Soliar observed that if these injuries were indeed the result of an intraspecific attack, then there is a pattern of them concentrating in the skull region. Modern crocodiles commonly attack each other by grappling an opponent's head using their jaws, and Lingham-Soliar hypothesized that Mosasaurus employed similar head-grappling behavior during intraspecific combat. Many of the fossils with injuries possibly attributable to intraspecific combat are of juvenile or sub-adult Mosasaurus, leading to the possibility that attacks on smaller, weaker individuals may have been more common. However, the attacking mosasaurs of the M. conodon and M. missouriensis specimens were likely similar in size to the victims. In 2006, Schulp and colleagues speculated that Mosasaurus may have occasionally engaged in cannibalism as a result of intraspecific aggression.
Diseases
There are some M. hoffmannii jaws with evidence of infectious diseases as a result of physical injuries. Two examples include IRSNB R25 and IRSNB R27, both having fractures and other pathologies in their dentaries. IRSNB R25 preserves a complete fracture near the sixth tooth socket. Extensive amounts of bony callus almost overgrowing the tooth socket are present around the fracture along with various osteolytic cavities, abscess canals, damages to the trigeminal nerve, and inflamed erosions signifying severe bacterial infection. There are two finely ulcerated scratches on the bone callus, which may have developed as part of the healing process. IRSNB R27 has two fractures: one had almost fully healed and the other is an open fracture with nearby teeth broken off as a result. The fracture is covered with a nonunion formation of bony callus with shallow scratch marks and a large pit connected to an abscess canal. Lingham-Soliar described this pit as resembling a tooth mark from a possible attacking mosasaur. Both specimens show signs of deep bacterial infection alongside the fractures; some bacteria may have spread to nearby damaged teeth and caused tooth decay, which may have entered deeper tissue from prior post-traumatic or secondary infections. The dentaries ahead of the fractures in both specimens are in good condition, suggesting that the arteries and trigeminal nerves had not been damaged; if they were, those areas would have necrotized due to lack of blood. The dentaries' condition suggests that the species may have had an efficient process of immobilizing the fracture during healing, which helped prevent damage to vital blood vessels and nerves. This, along with signs of healing, indicates that the fractures were not imminently fatal.
In 2006, Schulp and colleagues published a study describing a quadrate of M. hoffmannii with multiple unnatural openings and an estimated of tissue destroyed. This was likely a severe bone infection initiated by septic arthritis, which progressed to the point where a large portion of the quadrate was reduced to abscess. Extensive amounts of bone reparative tissue were also present, suggesting the infection and subsequent healing process may have progressed for a few months. This level of bone infection would have been tremendously painful and severely hampered the mosasaur's ability to use its jaws. The location of the infection may have also interfered with breathing. Considering how the individual was able to survive such conditions for an extended period of time, Schulp and colleagues speculated it switched to a foraging-type diet of soft-bodied prey like squid that could be swallowed whole to minimize jaw use. The cause of the infection remains unknown, but if it were a result of an intraspecific attack then it is possible one of the openings on the quadrate may have been the point of entry for an attacker's tooth from which the infection entered.
Avascular necrosis has been reported by many studies to be present in every examined specimen of M. lemonnieri and M. conodon. In examinations of M. conodon fossils from Alabama and New Jersey and M. lemonnieri fossils from Belgium, Rothschild and Martin in 2005 observed that the condition affected between 3-17% of the vertebrae in the mosasaurs' spines. Avascular necrosis is a common result of decompression illness; it involves bone damage caused by the formation of nitrogen bubbles from inhaled air decompressed during frequent deep-diving trips, or by intervals of repetitive diving and short breathing. This indicates that both Mosasaurus species may have either been habitual deep-divers or repetitive divers. Agnete Weinreich Carlsen considered it the simplest explanation that such conditions were a product of inadequate anatomical adaptation. Nevertheless, fossils of other mosasaurs with invariable avascular necrosis still exhibit substantial adaptations like eardrums that were well-protected from rapid changes in pressure.
Unnatural fusion of tail vertebrae has been documented in Mosasaurus, which occurs when the bones remodel themselves after damage from trauma or disease. A 2015 study by Rothschild and Everhart surveyed 15 Mosasaurus specimens from North America and Belgium and found cases of fused tail vertebrae in three of them. Two of these cases displayed irregular surface deformities around the fusion site caused by drainage of the vertebral sinuses, which is indicative of a bone infection. The causes of such infections are uncertain, but records of fused vertebrae in other mosasaurs suggest attacks by sharks and other predators as a possible candidate. The third case was determined to be caused by a form of arthritis based on the formation of smooth bridging between fused vertebrae.
Life history
It is likely that Mosasaurus was viviparous (giving live birth) like most modern mammals today. There is no evidence for live birth in Mosasaurus itself, but it is known in a number of other mosasaurs; examples include a skeleton of a pregnant Carsosaurus, a Plioplatecarpus fossil associated with fossils of two mosasaur embryos, and fossils of newborn Clidastes from pelagic (open ocean) deposits. Such fossil records, along with a total absence of any evidence suggesting external egg-based reproduction, indicates the likeliness of viviparity in Mosasaurus. Microanatomical studies on bones of juvenile Mosasaurus and related genera have found that their bone structures are comparable to adults. They do not exhibit the bone mass increase found in juvenile primitive mosasauroids to support buoyancy associated with a lifestyle in shallow water, implying that Mosasaurus was precocial: They were already efficient swimmers and lived fully functional lifestyles in open water at a very young age and did not require nursery areas to raise their young. Some areas in Europe and South Dakota have yielded concentrated assemblages of juvenile M. hoffmannii, M. missouriensis and/or M. lemonnieri. These localities are all shallow ocean deposits, suggesting that juvenile Mosasaurus may still have lived in shallow waters.
Paleoecology
Distribution, ecosystem, and ecological impactMosasaurus had a transatlantic distribution, with its fossils having been found in marine deposits on both sides of the Atlantic Ocean. These localities include the Midwest and East Coast of the United States, Canada, Europe, Turkey, Russia, the Levant, the African coastline from Morocco to South Africa, Brazil, Argentina, and Antarctica. During the Late Cretaceous, these regions made up the three seaways inhabited by Mosasaurus: the Atlantic Ocean, the Western Interior Seaway, and the Mediterranean Tethys. Multiple oceanic climate zones encompassed the seaways, including tropical, subtropical, temperate, and subpolar climates. The wide range of oceanic climates yielded a large diversity of fauna that coexisted with Mosasaurus.
Mediterranean Tethys
The Mediterranean Tethys during the Maastrichtian stage was located in what is now Europe, Africa, and the Middle East. In recent studies, the confirmation of paleogeographical affinities extended this range to areas across the Atlantic including Brazil and the East Coast state of New Jersey. It is geographically subdivided into two biogeographic provinces that respectively include the northern and southern Tethyan margins. The two mosasaurs Mosasaurus and Prognathodon appear to have been the dominant taxa, being widespread and ecologically diversified throughout the seaway.
The northern Tethyan margin was located around the paleolatitudes of 30–40°N, consisting of what is now the European continent, Turkey, and New Jersey. At the time, Europe was a scattering of islands with most of the modern continental landmass being underwater. The margin provided a warm-temperate climate with habitats dominated by mosasaurs and sea turtles. M. hoffmannii and Prognathodon sectorius were the dominant species in the northern province. In certain areas such as Belgium, other Mosasaurus species like M. lemonnieri were instead the dominant species, where its occurrences greatly outnumber those of other large mosasaurs. Other mosasaurs found in the European side of the northern Tethyan margin include smaller genera such as Halisaurus, Plioplatecarpus, and Platecarpus; the shell-crusher Carinodens; and larger mosasaurs of similar trophic levels including Tylosaurus bernardi and four other species of Prognathodon. Sea turtles such as Allopleurodon hoffmanni and Glyptochelone suickerbuycki were also prevalent in the area and other marine reptiles including indeterminate elasmosaurs have been occasionally found. Marine reptile assemblages in the New Jersey region of the province are generally equivalent with those in Europe; the mosasaur faunae are quite similar but exclude M. lemonnieri, Carinodens, Tylosaurus, and certain species of Halisaurus and Prognathodon. In addition, they exclusively feature M. conodon, Halisaurus platyspondylus and Prognathodon rapax. Many types of sharks such as Squalicorax, Cretalamna, Serratolamna, and sand sharks, as well as bony fish such as Cimolichthys, the saber-toothed herring Enchodus, and the swordfish-like Protosphyraena are represented in the northern Tethyan margin.
The southern Tethyan margin was located along the equator between 20°N and 20°S, resulting in warmer tropical climates. Seabeds bordering the cratons in Africa and Arabia and extending to the Levant and Brazil provided vast shallow marine environments. These environments were dominated by mosasaurs and marine side-necked turtles. Of the mosasaurs, Globidens phosphaticus is the characteristic species of the southern province; in the African and Arabian domain, Halisaurus arambourgi and Platecarpus ptychodon were also common mosasaurs alongside Globidens. Mosasaurus was not well-represented: the distribution of M. beaugei was restricted to Morocco and Brazil and isolated teeth from Syria suggested a possible presence of M. lemonnieri, although M. hoffmannii also had some presence throughout the province. Other mosasaurs from the southern Tethyan margin include the enigmatic Goronyosaurus, the shell-crushers Igdamanosaurus and Carinodens, Eremiasaurus, four other species of Prognathodon, and various other species of Halisaurus. Other marine reptiles such as the marine monitor lizard Pachyvaranus and the sea snake Palaeophis are known there. Aside from Zarafasaura in Morocco, plesiosaurs were scarce. As a tropical area, bony fish such as Enchodus and Stratodus and various sharks were common throughout the southern Tethyan margin.
Western Interior Seaway
Many of the earliest fossils of Mosasaurus were found in Campanian stage deposits in North America, including the Western Interior Seaway, an inland sea which once flowed through what is now the central United States and Canada, and connected the Arctic Ocean to the modern-day Gulf of Mexico. The region was shallow for a seaway, reaching a maximum depth of about . Extensive drainage from the neighboring continents, Appalachia and Laramidia, brought in vast amounts of sediment. Together with the formation of a nutrient-rich deepwater mass from the mixing of continental freshwater, Arctic waters from the north, and warmer saline Tethyan waters from the south, this created a warm and productive seaway that supported a rich diversity of marine life.
The biogeography of the region has been subdivided into two Interior Subprovinces characterized by different climates and faunal structures, and their borders are separated in modern-day Kansas. The oceanic climate of the Northern Interior Subprovince was likely a cool temperate one, while the Southern Interior Subprovince had warm temperate to subtropical climates. The fossil assemblages throughout these regions suggest a complete faunal turnover when M. missouriensis and M. conodon appeared at 79.5 Ma, indicating that the presence of Mosasaurus in the Western Interior Seaway had a profound impact on the restructuring of marine ecosystems. The faunal structure of both provinces was generally much more diverse prior to the appearance of Mosasaurus, during a faunal stage known as the Niobraran Age, than it was during the following Navesinkan Age.
In what is now Alabama within the Southern Interior Subprovince, most of the key genera including sharks like Cretoxyrhina and the mosasaurs Clidastes, Tylosaurus, Globidens, Halisaurus, and Platecarpus disappeared and were replaced by Mosasaurus. During the Navesinkan Age, Mosasaurus dominated the whole region, accounting for around two-thirds of all mosasaur diversity with Plioplatecarpus and Prognathodon sharing the remaining third. The Northern Interior Subprovince also saw a restructuring of mosasaur assemblages, characterized by the disappearance of mosasaurs like Platecarpus and their replacement by Mosasaurus and Plioplatecarpus. Some Niobraran genera such as Tylosaurus, Cretoxyrhina, hesperornithids, and plesiosaurs including elasmosaurs such as Terminonatator and polycotylids like Dolichorhynchops maintained their presence until around the end of the Campanian, during which the entire Western Interior Seaway started receding from the north. Mosasaurus continued to be the dominant genus in the seaway until the end of the Navesinkan Age at the end of the Cretaceous. Contemporaneous fauna included sea turtles such as Protostega and Archelon; many species of sea birds including Baptornis, Ichthyornis, and Halimornis; sharks such as the mackerel sharks Cretalamna, Squalicorax, Pseudocorax, and Serratolamna, the goblin shark Scapanorhynchus, the sand tiger Odontaspis, and the sawfish-like Ischyrhiza; and bony fish such as Enchodus, Protosphyraena, Stratodus, and the ichthyodectids Xiphactinus and Saurodon.
AntarcticaMosasaurus is known from late Maastrichtian deposits in the Antarctic Peninsula, specifically the López de Bertodano Formation in Seymour Island. Located within the polar circle at around 65°S, temperatures at medium to large water depths would have been around on average, while sea surface temperatures may have dropped below freezing and sea ice may have formed at times. Mosasaurus appears to be the most diverse mosasaur in the Maastrichtian Antarctica. At least two species of Mosasaurus have been described, but the true number of species is unknown as remains are often fragmentary and specimens are described in open nomenclature. These species include one comparable with M. lemonnieri, and another that appears to be closely related to M. hoffmannii. M. sp. has also been described. However, it is possible that such specimens may actually represent Moanasaurus, although this depends on the outcome of a pending revision of the genus. At least four other mosasaur genera have been reported in Antarctica, including Plioplatecarpus, the mosasaurines Moanasaurus and Liodon, and Kaikaifilu. The validity of some of these genera is disputed as they are primarily based on isolated teeth. Prognathodon and Globidens are also expected to be present based on distribution trends of both genera, although conclusive fossils have yet to be found. Other Antarctic marine reptiles included elasmosaurid plesiosaurs like Aristonectes and another indeterminate elasmosaurid. The fish assemblage of the López de Bertodano Formation was dominated by Enchodus and ichthyodectiformes.
Habitat preference
Known fossils of Mosasaurus have typically been recovered from deposits representing nearshore habitats during the Cretaceous period, with some fossils coming from deeper-water deposits. Lingham-Soliar (1995) elaborated on this, finding that Maastrichtian deposits in the Netherlands with M. hoffmannii occurrences represented nearshore waters around deep. Changing temperatures and an abundance in marine life were characteristic of these localities. The morphological build of M. hoffmannii, nevertheless, was best adapted for a pelagic surface lifestyle.
δ13C is also correlated with a marine animal's feeding habitat as isotope levels deplete when habitat is farther from the shoreline, so some scientists interpreted isotope levels as a proxy for habitat preference. Separate studies involving multiple Mosasaurus specimens have yielded consistently low δ13C levels of tooth enamel, indicating that Mosasaurus fed in more offshore or open waters. It has been pointed out how δ13C can be influenced by other factors in an animal's lifestyle, such as diet and diving behavior. To account for this, a 2014 study by T. Lynn Harrell Jr. and Alberto Perez-Huerta examined the concentration ratios of neodymium, gadolinium, and ytterbium in M. hoffmannii and Mosasaurus sp. fossils from Alabama, the Demopolis Chalk, and the Hornerstown Formation. Previous studies demonstrated that ratios of these three elements can act as a proxy for relative ocean depth of a fossil during early diagenesis without interference from biological processes, with each of the three elements signifying either shallow, deep, or fresh waters. The rare earth element ratios were very consistent throughout most of the examined Mosasaurus fossils, indicating consistent habitat preference, and clustered towards a ratio representing offshore habitats with ocean depths deeper than .
Interspecific competitionMosasaurus lived alongside other large predatory mosasaurs also considered apex predators, most prominent among them being the tylosaurines and Prognathodon. Tylosaurus bernardi, the only surviving species of the genus during the Maastrichtian, measured up to in length while the largest coexisting species of Prognathodon like P. saturator exceeded . These three mosasaurs preyed on similar animals such as marine reptiles.
A study published in 2013 by Schulp and colleagues specifically tested how mosasaurs such as M. hoffmannii and P. saturator were able to coexist in the same localities through δ13C analysis. The scientists utilized an interpretation that differences in isotope values can help explain the level of resource partitioning because it is influenced by multiple environmental factors such as lifestyle, diet, and habitat preference. Comparisons between the δ13C levels in multiple teeth of M. hoffmannii and P. saturator from the Maastrichtian-age Maastricht Formation showed that while there was some convergence between certain specimens, the average δ13C values between the two species were on average different. This is one indication of niche partitioning, where the two mosasaur genera likely foraged in different habitats or had different specific diets to coexist without direct competitive conflict. The teeth of P. saturator are much more robust than those of M. hoffmannii and were specifically equipped for preying on robust prey like turtles. While M. hoffmannii also preyed on turtles, its teeth were built to handle a wider range of prey less suited for P. saturator.
Another case of presumed niche partitioning between Mosasaurus and Prognathodon from the Bearpaw Formation in Alberta was documented in a 2014 study by Konishi and colleagues. The study found a dietary divide between M. missouriensis and P. overtoni based on stomach contents. Stomach contents of P. overtoni included turtles and ammonites, providing another example of a diet specialized for harder prey. In contrast, M. missouriensis had stomach contents consisting of fish, indicative of a diet specialized in softer prey. It was hypothesized that these adaptations helped maintain resource partitioning between the two mosasaurs.
Nevertheless, competitive engagement evidently could not be entirely avoided. There is also evidence of aggressive interspecific combat between Mosasaurus and other large mosasaur species. This is shown from a fossil skull of a subadult M. hoffmannii with fractures caused by a massive concentrated blow to the braincase; Lingham-Soliar (1998) argued that this blow was dealt by a ramming attack by T. bernardi, as the formation of the fractures were characteristic of a coordinated strike (and not an accident or fossilization damage), and T. bernardi was the only known coexisting animal likely capable of causing such damage, using its robust arrow-like elongated snout. This sort of attack has been compared to the defensive behavior of bottlenose dolphins using their beaks to kill or repel lemon sharks, and it has been speculated that T. bernardi dealt the offensive attack via an ambush on an unsuspecting Mosasaurus.
Extinction
By the end of the Cretaceous, mosasaurs were at the height of their evolutionary radiation, and their extinction was a sudden event. During the late Maastrichtian, global sea levels dropped, draining the continents of their nutrient-rich seaways and altering circulation and nutrient patterns, and reducing the number of available habitats for Mosasaurus. The genus adapted by accessing new habitats in more open waters. The last fossils of Mosasaurus, which include those of M. hoffmannii and indeterminate species, occur up to the Cretaceous-Paleogene boundary (K-Pg boundary). The demise of the genus was likely a result of the Cretaceous-Paleogene extinction event which also wiped out the non-avian dinosaurs. Mosasaurus fossils have been found less than below the boundary in the Maastricht Formation, the Davutlar Formation in Turkey, the Jagüel Formation in Argentina, Stevns Klint in Denmark, Seymour Island, and Missouri.M. hoffmannii fossils have been found within the K-Pg boundary itself in southeastern Missouri between the Paleocene Clayton Formation and Cretaceous Owl Creek Formation. Fossil vertebrae from the layer were found with fractures formed after death. The layer was likely deposited as a tsunamite, alternatively nicknamed the "Cretaceous cocktail deposit". This formed through a combination of catastrophic seismic and geological disturbances, mega-hurricanes, and giant tsunamis caused by the impact of the Chicxulub asteroid that catalyzed the K-Pg extinction event. As well as physical destruction, the impact also blocked out sunlight leading to a collapse of marine food webs. Any Mosasaurus surviving the immediate cataclysms by taking refuge in deeper waters would have died out due to starvation from a loss of prey.
One enigmatic occurrence of Mosasaurus sp. fossils is in the Hornerstown Formation, a deposit typically dated to be from the Paleocene Danian age, which was immediately after the Maastrichtian age. The fossils were found in association with fossils of Squalicorax, Enchodus, and various ammonites within a uniquely fossil-rich bed at the base of the Hornerstown Formation known as the Main Fossiliferous Layer. This does not mean Mosasaurus and its associated fauna survived the K-Pg extinction. According to one hypothesis, the fossils may have originated from an earlier Cretaceous deposit and were reworked into the Paleocene formation during its early deposition. Evidence of reworking typically comes from fossils worn down due to further erosion during their exposure at the time of redeposition. Many of the Mosasaurus fossils from the Main Fossiliferous Layer consist of isolated bones commonly abraded and worn, but the layer also yielded better-preserved Mosasaurus remains. Another explanation suggests the Main Fossiliferous Layer is a Maastrichtian time-averaged remanié deposit, which means it originated from a Cretaceous deposit with winnowed low-sediment conditions. A third hypothesis proposes that the layer is a lag deposit of Cretaceous sediments forced out by a strong impact by a tsunami, and what remained was subsequently refilled with Cenozoic fossils.
| Biology and health sciences | Prehistoric squamates | Animals |
21402632 | https://en.wikipedia.org/wiki/Electroencephalography | Electroencephalography | Electroencephalography (EEG)
is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex. It is typically non-invasive, with the EEG electrodes placed along the scalp (commonly called "scalp EEG") using the International 10–20 system, or variations of it. Electrocorticography, involving surgical placement of electrodes, is sometimes called "intracranial EEG". Clinical interpretation of EEG recordings is most often performed by visual inspection of the tracing or quantitative EEG analysis.
Voltage fluctuations measured by the EEG bioamplifier and electrodes allow the evaluation of normal brain activity. As the electrical activity monitored by EEG originates in neurons in the underlying brain tissue, the recordings made by the electrodes on the surface of the scalp vary in accordance with their orientation and distance to the source of the activity. Furthermore, the value recorded is distorted by intermediary tissues and bones, which act in a manner akin to resistors and capacitors in an electrical circuit. This means that not all neurons will contribute equally to an EEG signal, with an EEG predominately reflecting the activity of cortical neurons near the electrodes on the scalp. Deep structures within the brain further away from the electrodes will not contribute directly to an EEG; these include the base of the cortical gyrus, mesial walls of the major lobes, hippocampus, thalamus, and brain stem.
A healthy human EEG will show certain patterns of activity that correlate with how awake a person is. The range of frequencies one observes are between 1 and 30 Hz, and amplitudes will vary between 20 and 100 μV. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0.5–4 Hz), and theta (4–7 Hz). Alpha waves are observed when a person is in a state of relaxed wakefulness and are mostly prominent over the parietal and occipital sites. During intense mental activity, beta waves are more prominent in frontal areas as well as other regions. If a relaxed person is told to open their eyes, one observes alpha activity decreasing and an increase in beta activity. Theta and delta waves are not generally seen in wakefulness - if they are, it is a sign of brain dysfunction.
EEG can detect abnormal electrical discharges such as sharp waves, spikes, or spike-and-wave complexes, as observable in people with epilepsy; thus, it is often used to inform medical diagnosis. EEG can detect the onset and spatio-temporal (location and time) evolution of seizures and the presence of status epilepticus. It is also used to help diagnose sleep disorders, depth of anesthesia, coma, encephalopathies, cerebral hypoxia after cardiac arrest, and brain death. EEG used to be a first-line method of diagnosis for tumors, stroke, and other focal brain disorders, but this use has decreased with the advent of high-resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite its limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with CT, PET, or MRI.
Derivatives of the EEG technique include evoked potentials (EP), which involves averaging the EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory, or auditory). Event-related potentials (ERPs) refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science, cognitive psychology, and psychophysiological research.
Uses
Epilepsy
EEG is the gold standard diagnostic procedure to confirm epilepsy. The sensitivity of a routine EEG to detect interictal epileptiform discharges at epilepsy centers has been reported to be in the range of 29–55%. Given the low to moderate sensitivity, a routine EEG (typically with a duration of 20–30 minutes) can be normal in people that have epilepsy. When an EEG shows interictal epileptiform discharges (e.g. sharp waves, spikes, spike-and-wave, etc.) it is confirmatory of epilepsy in nearly all cases (high specificity), however up to 3.5% of the general population may have epileptiform abnormalities in an EEG without ever having had a seizure (low false positive rate) or with a very low risk of developing epilepsy in the future.
When a routine EEG is normal and there is a high suspicion or need to confirm epilepsy, it may be repeated or performed with a longer duration in the epilepsy monitoring unit (EMU) or at home with an ambulatory EEG. In addition, there are activating maneuvers such as photic stimulation, hyperventilation and sleep deprivation that can increase the diagnostic yield of the EEG.
Epilepsy Monitoring Unit (EMU)
At times, a routine EEG is not sufficient to establish the diagnosis or determine the best course of action in terms of treatment. In this case, attempts may be made to record an EEG while a seizure is occurring. This is known as an ictal recording, as opposed to an interictal recording, which refers to the EEG recording between seizures. To obtain an ictal recording, a prolonged EEG is typically performed accompanied by a time-synchronized video and audio recording. This can be done either as an outpatient (at home) or during a hospital admission, preferably to an Epilepsy Monitoring Unit (EMU) with nurses and other personnel trained in the care of patients with seizures. Outpatient ambulatory video EEGs typically last one to three days. An admission to an Epilepsy Monitoring Unit typically lasts several days but may last for a week or longer. While in the hospital, seizure medications are usually withdrawn to increase the odds that a seizure will occur during admission. For reasons of safety, medications are not withdrawn during an EEG outside of the hospital. Ambulatory video EEGs, therefore, have the advantage of convenience and are less expensive than a hospital admission, but they also have the disadvantage of a decreased probability of recording a clinical event.
Epilepsy monitoring is often considered when patients continue having events despite being on anti-seizure medications or if there is concern that the patient's events have an alternate diagnosis, e.g., psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders, migraine variants, stroke, etc. In cases of epileptic seizures, continuous EEG monitoring helps to characterize seizures and localize/lateralize the region of the brain from which a seizure originates. This can help identify appropriate non-medication treatment options. In clinical use, EEG traces are visually analyzed by neurologists to look at various features. Increasingly, quantitative analysis of EEG is being used in conjunction with visual analysis. Quantitative analysis displays like power spectrum analysis, alpha-delta ratio, amplitude integrated EEG, and spike detection can help quickly identify segments of EEG that need close visual analysis or, in some cases, be used as surrogates for quick identification of seizures in long-term recordings.
Other brain disorders
An EEG might also be helpful for diagnosing or treating the following disorders:
Brain tumor
Brain damage from head injury
Brain dysfunction that can have a variety of causes (encephalopathy)
Inflammation of the brain (encephalitis)
Stroke
Sleep disorders
It can also:
distinguish epileptic seizures from other types of spells, such as psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders and migraine variants
differentiate "organic" encephalopathy or delirium from primary psychiatric syndromes such as catatonia
serve as an adjunct test of brain death in comatose patients
prognosticate in comatose patients (in certain instances) or in newborns with brain injury from various causes around the time of birth
determine whether to wean anti-epileptic medications.
Intensive Care Unit (ICU)
EEG can also be used in intensive care units for brain function monitoring to monitor for non-convulsive seizures/non-convulsive status epilepticus, to monitor the effect of sedative/anesthesia in patients in medically induced coma (for treatment of refractory seizures or increased intracranial pressure), and to monitor for secondary brain damage in conditions such as subarachnoid hemorrhage (currently a research method).
In cases where significant brain injury is suspected, e.g., after cardiac arrest, EEG can provide some prognostic information.
If a patient with epilepsy is being considered for resective surgery to treat epilepsy, it is often necessary to localize the focus (source) of the epileptic brain activity with a resolution greater than what is provided by scalp EEG. In these cases, neurosurgeons typically implant strips and grids of electrodes or penetrating depth electrodes under the dura mater, through either a craniotomy or a burr hole. The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG), intracranial EEG (icEEG), or stereotactic EEG (sEEG). The signal recorded from ECoG is on a different scale of activity than the brain activity recorded from scalp EEG. Low-voltage, high-frequency components that cannot be seen easily (or at all) in scalp EEG can be seen clearly in ECoG. Further, smaller electrodes (which cover a smaller parcel of brain surface) allow for better spatial resolution to narrow down the areas critical for seizure onset and propagation. Some clinical sites record data from penetrating microelectrodes.
Home ambulatory EEG
Sometimes it is more convenient or clinically necessary to perform ambulatory EEG recordings in the home of the person being tested. These studies typically have a duration of 24–72 hours.
Research use
EEG and the related study of ERPs are used extensively in neuroscience, cognitive science, cognitive psychology, neurolinguistics, and psychophysiological research, as well as to study human functions such as swallowing. Any EEG techniques used in research are not sufficiently standardised for clinical use, and many ERP studies fail to report all of the necessary processing steps for data collection and reduction, limiting the reproducibility and replicability of many studies. Based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), EEG scans cannot be used reliably to assist in making a clinical diagnosis of ADHD. However, EEG continues to be used in research on mental disabilities, such as auditory processing disorder (APD), ADD, and ADHD. EEGs have also been studied for their utility in detecting neurophysiological changes in the brain after concussion, however, at this time there are no advanced imaging techniques that can be used clinically to diagnose or monitor recovery from concussion.
Advantages
Several other methods to study brain function exist, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetoencephalography (MEG), nuclear magnetic resonance spectroscopy (NMR or MRS), electrocorticography (ECoG), single-photon emission computed tomography (SPECT), near-infrared spectroscopy (NIRS), and event-related optical signal (EROS). Despite the relatively poor spatial sensitivity of EEG, the "one-dimensional signals from localised peripheral regions on the head make it attractive for its simplistic fidelity and has allowed high clinical and basic research throughput". Thus, EEG possesses some advantages over some of those other techniques:
Hardware costs are significantly lower than those of most other techniques
EEG prevents limited availability of technologists to provide immediate care in high traffic hospitals.
EEG only requires a quiet room and briefcase-size equipment, whereas fMRI, SPECT, PET, MRS, or MEG require bulky and immobile equipment. For example, MEG requires equipment consisting of liquid helium-cooled detectors that can be used only in magnetically shielded rooms, altogether costing upwards of several million dollars; and fMRI requires the use of a 1-ton magnet in, again, a shielded room.
EEG can readily have a high temporal resolution, (although sub-millisecond resolution generates less meaningful data), because the two to 32 data streams generated by that number of electrodes is easily stored and processed, whereas 3D spatial technologies provide thousands or millions times as many input data streams, and are thus limited by hardware and software. EEG is commonly recorded at sampling rates between 250 and 2000 Hz in clinical and research settings.
EEG is relatively tolerant of subject movement, unlike most other neuroimaging techniques. There even exist methods for minimizing, and even eliminating movement artifacts in EEG data
EEG is silent, which allows for better study of the responses to auditory stimuli.
EEG does not aggravate claustrophobia, unlike fMRI, PET, MRS, SPECT, and sometimes MEG
EEG does not involve exposure to high-intensity (>1 Tesla) magnetic fields, as in some of the other techniques, especially MRI and MRS. These can cause a variety of undesirable issues with the data, and also prohibit use of these techniques with participants that have metal implants in their body, such as metal-containing pacemakers
EEG does not involve exposure to radioligands, unlike positron emission tomography.
ERP studies can be conducted with relatively simple paradigms, compared with IE block-design fMRI studies
Relatively non-invasive, in contrast to electrocorticography, which requires electrodes to be placed on the actual surface of the brain.
EEG also has some characteristics that compare favorably with behavioral testing:
EEG can detect covert processing (i.e., processing that does not require a response)
EEG can be used in subjects who are incapable of making a motor response
EEG is a method widely used in the study of sport performance, valued for its portability and lightweight design
Some ERP components can be detected even when the subject is not attending to the stimuli
Unlike other means of studying reaction time, ERPs can elucidate stages of processing (rather than just the result)
the simplicity of EEG readily provides for tracking of brain changes during different phases of life. EEG sleep analysis can indicate significant aspects of the timing of brain development, including evaluating adolescent brain maturation.
In EEG there is a better understanding of what signal is measured as compared to other research techniques, e.g. the BOLD response in MRI.
Disadvantages
Low spatial resolution on the scalp. fMRI, for example, can directly display areas of the brain that are active, while EEG requires intense interpretation just to hypothesize what areas are activated by a particular response.
Depending on the orientation and location of the dipole causing an EEG change, there may be a false localization due to the inverse problem.
EEG poorly measures neural activity that occurs below the upper layers of the brain (the cortex).
Unlike PET and MRS, EEG cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc. can be found.
Often takes a long time to connect a subject to EEG, as it requires precise placement of dozens of electrodes around the head and the use of various gels, saline solutions, and/or pastes to maintain good conductivity, and a cap is used to keep them in place. While the length of time differs dependent on the specific EEG device used, as a general rule it takes considerably less time to prepare a subject for MEG, fMRI, MRS, and SPECT.
Signal-to-noise ratio is poor, so sophisticated data analysis and relatively large numbers of subjects are needed to extract useful information from EEG.
EEGs are not currently very compatible with individuals who have coarser and/or textured hair. Even protective styles can pose issues during testing. Researchers are currently trying to build better options for patients and technicians alike Furthermore, researchers are starting to implement more culturally-informed data collection practices to help reduce racial biases in EEG research.
With other neuroimaging techniques
Simultaneous EEG recordings and fMRI scans have been obtained successfully, though recording both at the same time effectively requires that several technical difficulties be overcome, such as the presence of ballistocardiographic artifact, MRI pulse artifact and the induction of electrical currents in EEG wires that move within the strong magnetic fields of the MRI. While challenging, these have been successfully overcome in a number of studies.
MRI's produce detailed images created by generating strong magnetic fields that may induce potentially harmful displacement force and torque. These fields produce potentially harmful radio frequency heating and create image artifacts rendering images useless. Due to these potential risks, only certain medical devices can be used in an MR environment.
Similarly, simultaneous recordings with MEG and EEG have also been conducted, which has several advantages over using either technique alone:
EEG requires accurate information about certain aspects of the skull that can only be estimated, such as skull radius, and conductivities of various skull locations. MEG does not have this issue, and a simultaneous analysis allows this to be corrected for.
MEG and EEG both detect activity below the surface of the cortex very poorly, and like EEG, the level of error increases with the depth below the surface of the cortex one attempts to examine. However, the errors are very different between the techniques, and combining them thus allows for correction of some of this noise.
MEG has access to virtually no sources of brain activity below a few centimetres under the cortex. EEG, on the other hand, can receive signals from greater depth, albeit with a high degree of noise. Combining the two makes it easier to determine what in the EEG signal comes from the surface (since MEG is very accurate in examining signals from the surface of the brain), and what comes from deeper in the brain, thus allowing for analysis of deeper brain signals than either EEG or MEG on its own.
Recently, a combined EEG/MEG (EMEG) approach has been investigated for the purpose of source reconstruction in epilepsy diagnosis.
EEG has also been combined with positron emission tomography. This provides the advantage of allowing researchers to see what EEG signals are associated with different drug actions in the brain.
Recent studies using machine learning techniques such as neural networks with statistical temporal features extracted from frontal lobe EEG brainwave data has shown high levels of success in classifying mental states (Relaxed, Neutral, Concentrating), mental emotional states (Negative, Neutral, Positive) and thalamocortical dysrhythmia.
Mechanisms
The brain's electrical charge is maintained by billions of neurons. Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials. Ions of similar charge repel each other, and when many ions are pushed out of many neurons at the same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal in the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by a voltmeter. Recording these voltages over time gives us the EEG.
The electric potential generated by an individual neuron is far too small to be picked up by EEG or MEG. EEG activity therefore always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation. If the cells do not have similar spatial orientation, their ions do not line up and create waves to be detected. Pyramidal neurons of the cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull.
Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges, spatial distributions and are associated with different states of brain functioning (e.g., waking and the various sleep stages). These oscillations represent synchronized activity over a network of neurons. The neuronal networks underlying some of these oscillations are understood (e.g., the thalamocortical resonance underlying sleep spindles), while many others are not (e.g., the system that generates the posterior basic rhythm). Research that measures both EEG and neuron spiking finds the relationship between the two is complex, with a combination of EEG power in the gamma band and phase in the delta band relating most strongly to neuron spike activity.
Method
In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. Many systems typically use electrodes, each of which is attached to an individual wire. Some systems use caps or nets into which electrodes are embedded; this is particularly common when high-density arrays of electrodes are needed.
Electrode locations and names are specified by the International 10–20 system for most clinical and research applications (except when high-density arrays are used). This system ensures that the naming of electrodes is consistent across laboratories. In most clinical applications, 19 recording electrodes (plus ground and system reference) are used. A smaller number of electrodes are typically used when recording EEG from neonates. Additional electrodes can be added to the standard set-up when a clinical or research application demands increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or net) can contain up to 256 electrodes more-or-less evenly spaced around the scalp.
Each electrode is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the voltage between the active electrode and the reference (typically 1,000–100,000 times, or 60–100 dB of power gain). In analog EEG, the signal is then filtered (next paragraph), and the EEG signal is output as the deflection of pens as paper passes underneath. Most EEG systems these days, however, are digital, and the amplified signal is digitized via an analog-to-digital converter, after being passed through an anti-aliasing filter. Analog-to-digital sampling typically occurs at 256–512 Hz in clinical scalp EEG; sampling rates of up to 20 kHz are used in some research applications.
During the recording, a series of activation procedures may be used. These procedures may induce normal or abnormal EEG activity that might not otherwise be seen. These procedures include hyperventilation, photic stimulation (with a strobe light), eye closure, mental activity, sleep and sleep deprivation. During (inpatient) epilepsy monitoring, a patient's typical seizure medications may be withdrawn.
The digital EEG signal is stored electronically and can be filtered for display. Typical settings for the high-pass filter and a low-pass filter are 0.5–1 Hz and 35–70 Hz respectively. The high-pass filter typically filters out slow artifact, such as electrogalvanic signals and movement artifact, whereas the low-pass filter filters out high-frequency artifacts, such as electromyographic signals. An additional notch filter is typically used to remove artifact caused by electrical power lines (60 Hz in the United States and 50 Hz in many other countries).
The EEG signals can be captured with opensource hardware such as OpenBCI and the signal can be processed by freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox.
As part of an evaluation for epilepsy surgery, it may be necessary to insert electrodes near the surface of the brain, under the surface of the dura mater. This is accomplished via burr hole or craniotomy. This is referred to variously as "electrocorticography (ECoG)", "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may also be placed into brain structures, such as the amygdala or hippocampus, structures, which are common epileptic foci and may not be "seen" clearly by scalp EEG. The electrocorticographic signal is processed in the same manner as digital scalp EEG (above), with a couple of caveats. ECoG is typically recorded at higher sampling rates than scalp EEG because of the requirements of Nyquist theorem – the subdural signal is composed of a higher predominance of higher frequency components. Also, many of the artifacts that affect scalp EEG do not impact ECoG, and therefore display filtering is often not needed.
A typical adult human EEG signal is about 10 μV to 100 μV in amplitude when measured from the scalp.
Since an EEG voltage signal represents a difference between the voltages at two electrodes, the display of the EEG for the reading encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage.
Sequential montage Each channel (i.e., waveform) represents the difference between two adjacent electrodes. The entire montage consists of a series of these channels. For example, the channel "Fp1-F3" represents the difference in voltage between the Fp1 electrode and the F3 electrode. The next channel in the montage, "F3-C3", represents the voltage difference between F3 and C3, and so on through the entire array of electrodes.
Referential montage Each channel represents the difference between a certain electrode and a designated reference electrode. There is no standard position for this reference; it is, however, at a different position than the "recording" electrodes. Midline positions are often used because they do not amplify the signal in one hemisphere vs. the other, such as Cz, Oz, Pz etc. as online reference. The other popular offline references are:
REST reference: which is an offline computational reference at infinity where the potential is zero. REST (reference electrode standardization technique) takes the equivalent sources inside the brain of any a set of scalp recordings as springboard to link the actual recordings with any an online or offline( average, linked ears etc.) non-zero reference to the new recordings with infinity zero as the standardized reference.
"linked ears": which is a physical or mathematical average of electrodes attached to both earlobes or mastoids.
Average reference montage The outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each channel.
Laplacian montage Each channel represents the difference between an electrode and a weighted average of the surrounding electrodes.
When analog (paper) EEGs are used, the technologist switches between montages during the recording in order to highlight or better characterize certain features of the EEG. With digital EEG, all signals are typically digitized and stored in a particular (usually referential) montage; since any montage can be constructed mathematically from any other, the EEG can be viewed by the electroencephalographer in any display montage that is desired.
The EEG is read by a clinical neurophysiologist or neurologist (depending on local custom and law regarding medical specialities), optimally one who has specific training in the interpretation of EEGs for clinical purposes. This is done by visual inspection of the waveforms, called graphoelements. The use of computer signal processing of the EEG – so-called quantitative electroencephalography – is somewhat controversial when used for clinical purposes (although there are many research uses).
Dry EEG electrodes
In the early 1990s Babak Taheri, at University of California, Davis demonstrated the first single and also multichannel dry active electrode arrays using micro-machining. The single channel dry EEG electrode construction and results were published in 1994. The arrayed electrode was also demonstrated to perform well compared to silver/silver chloride electrodes. The device consisted of four sites of sensors with integrated electronics to reduce noise by impedance matching. The advantages of such electrodes are: (1) no electrolyte used, (2) no skin preparation, (3) significantly reduced sensor size, and (4) compatibility with EEG monitoring systems. The active electrode array is an integrated system made of an array of capacitive sensors with local integrated circuitry housed in a package with batteries to power the circuitry. This level of integration was required to achieve the functional performance obtained by the electrode. The electrode was tested on an electrical test bench and on human subjects in four modalities of EEG activity, namely: (1) spontaneous EEG, (2) sensory event-related potentials, (3) brain stem potentials, and (4) cognitive event-related potentials. The performance of the dry electrode compared favorably with that of the standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio.
In 1999 researchers at Case Western Reserve University, in Cleveland, Ohio, led by Hunter Peckham, used 64-electrode EEG skullcap to return limited hand movements to quadriplegic Jim Jatich. As Jatich concentrated on simple but opposite concepts like up and down, his beta-rhythm EEG output was analysed using software to identify patterns in the noise. A basic pattern was identified and used to control a switch: Above average activity was set to on, below average off. As well as enabling Jatich to control a computer cursor the signals were also used to drive the nerve controllers embedded in his hands, restoring some movement.
In 2018, a functional dry electrode composed of a polydimethylsiloxane elastomer filled with conductive carbon nanofibers was reported. This research was conducted at the U.S. Army Research Laboratory. EEG technology often involves applying a gel to the scalp which facilitates strong signal-to-noise ratio. This results in more reproducible and reliable experimental results. Since patients dislike having their hair filled with gel, and the lengthy setup requires trained staff on hand, utilizing EEG outside the laboratory setting can be difficult. Additionally, it has been observed that wet electrode sensors' performance reduces after a span of hours. Therefore, research has been directed to developing dry and semi-dry EEG bioelectronic interfaces.
Dry electrode signals depend upon mechanical contact. Therefore, it can be difficult getting a usable signal because of impedance between the skin and the electrode. Some EEG systems attempt to circumvent this issue by applying a saline solution. Others have a semi dry nature and release small amounts of the gel upon contact with the scalp. Another solution uses spring loaded pin setups. These may be uncomfortable. They may also be dangerous if they were used in a situation where a patient could bump their head since they could become lodged after an impact trauma incident.
Currently, headsets are available incorporating dry electrodes with up to 30 channels. Such designs are able to compensate for some of the signal quality degradation related to high impedances by optimizing pre-amplification, shielding and supporting mechanics.
Limitations
EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of post-synaptic potentials: those generated in superficial layers of the cortex, on the crests of gyri directly abutting the skull and radial to the skull. Dendrites which are deeper in the cortex, inside sulci, in midline or deep structures (such as the cingulate gyrus or hippocampus), or producing currents that are tangential to the skull, make far less contribution to the EEG signal.
EEG recordings do not directly capture axonal action potentials. An action potential can be accurately represented as a current quadrupole, meaning that the resulting field decreases more rapidly than the ones produced by the current dipole of post-synaptic potentials. In addition, since EEGs represent averages of thousands of neurons, a large population of cells in synchronous activity is necessary to cause a significant deflection on the recordings. Action potentials are very fast and, as a consequence, the chances of field summation are slim. However, neural backpropagation, as a typically longer dendritic current dipole, can be picked up by EEG electrodes and is a reliable indication of the occurrence of neural output.
Not only do EEGs capture dendritic currents almost exclusively as opposed to axonal currents, they also show a preference for activity on populations of parallel dendrites and transmitting current in the same direction at the same time. Pyramidal neurons of cortical layers II/III and V extend apical dendrites to layer I. Currents moving up or down these processes underlie most of the signals produced by electroencephalography.
EEG thus provides information with a large bias in favor of particular neuron types, locations and orientations. So it generally should not be used to make claims about global brain activity. The meninges, cerebrospinal fluid and skull "smear" the EEG signal, obscuring its intracranial source.
It is mathematically impossible to reconstruct a unique intracranial current source for a given EEG signal, as some currents produce potentials that cancel each other out. This is referred to as the inverse problem. However, much work has been done to produce remarkably good estimates of, at least, a localized electric dipole that represents the recorded currents.
EEG vis-à-vis fMRI, fNIRS, fUS and PET
EEG has several strong points as a tool for exploring brain activity. EEGs can detect changes over milliseconds, which is excellent considering an action potential takes approximately 0.5–130 milliseconds to propagate across a single neuron, depending on the type of neuron. Other methods of looking at brain activity, such as PET, fMRI or fUS have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI, fUS) or metabolic activity (e.g., PET, NIRS), which are indirect markers of brain electrical activity.
EEG can be used simultaneously with fMRI or fUS so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent exactly the same brain activity.
There are technical difficulties associated with combining EEG and fMRI including the need to remove the MRI gradient artifact present during MRI acquisition. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI.
EEG can be used simultaneously with NIRS or fUS without major technical difficulties. There is no influence of these modalities on each other and a combined measurement can give useful information about electrical activity as well as hemodynamics at medium spatial resolution.
EEG vis-à-vis MEG
EEG reflects correlated synaptic activity caused by post-synaptic potentials of cortical neurons. The ionic currents involved in the generation of fast action potentials may not contribute greatly to the averaged field potentials representing the EEG. More specifically, the scalp electrical potentials that produce EEG are generally thought to be caused by the extracellular ionic currents caused by dendritic electrical activity, whereas the fields producing magnetoencephalographic signals are associated with intracellular ionic currents.
Normal activity
The EEG is typically described in terms of (1) rhythmic activity and (2) transients. The rhythmic activity is divided into bands by frequency. To some degree, these frequency bands are a matter of nomenclature (i.e., any rhythmic activity between 8–12 Hz can be described as "alpha"), but these designations arose because rhythmic activity within a certain frequency range was noted to have a certain distribution over the scalp or a certain biological significance. Frequency bands are usually extracted using spectral methods (for instance Welch) as implemented for instance in freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox.
Computational processing of the EEG is often named quantitative electroencephalography (qEEG).
Most of the cerebral signal observed in the scalp EEG falls in the range of 1–20 Hz (activity below or above this range is likely to be artifactual, under standard clinical recording techniques). Waveforms are subdivided into bandwidths known as alpha, beta, theta, and delta to signify the majority of the EEG used in clinical practice.
Comparison of EEG bands
The practice of using only whole numbers in the definitions comes from practical considerations in the days when only whole cycles could be counted on paper records. This leads to gaps in the definitions, as seen elsewhere on this page. The theoretical definitions have always been more carefully defined to include all frequencies. Unfortunately there is no agreement in standard reference works on what these ranges should be – values for the upper end of alpha and lower end of beta include 12, 13, 14 and 15. If the threshold is taken as 14 Hz, then the slowest beta wave has about the same duration as the longest spike (70 ms), which makes this the most useful value.
Wave patterns
Delta waves is the frequency range up to 4 Hz. It tends to be the highest in amplitude and the slowest waves. It is seen normally in adults in slow-wave sleep. It is also seen normally in babies. It may occur focally with subcortical lesions and in general distribution with diffuse lesions, metabolic encephalopathy hydrocephalus or deep midline lesions. It is usually most prominent frontally in adults (e.g. FIRDA – frontal intermittent rhythmic delta) and posteriorly in children (e.g. OIRDA – occipital intermittent rhythmic delta).
Theta is the frequency range from 4 Hz to 7 Hz. Theta is seen normally in young children. It may be seen in drowsiness or arousal in older children and adults; it can also be seen in meditation. Excess theta for age represents abnormal activity. It can be seen as a focal disturbance in focal subcortical lesions; it can be seen in generalized distribution in diffuse disorder or metabolic encephalopathy or deep midline disorders or some instances of hydrocephalus. On the contrary this range has been associated with reports of relaxed, meditative, and creative states.
Alpha is the frequency range from 8 Hz to 12 Hz. Hans Berger named the first rhythmic EEG activity he observed the "alpha wave". This was the "posterior basic rhythm" (also called the "posterior dominant rhythm" or the "posterior alpha rhythm"), seen in the posterior regions of the head on both sides, higher in amplitude on the dominant side. It emerges with closing of the eyes and with relaxation, and attenuates with eye opening or mental exertion. The posterior basic rhythm is actually slower than 8 Hz in young children (therefore technically in the theta range).
In addition to the posterior basic rhythm, there are other normal alpha rhythms such as the mu rhythm (alpha activity in the contralateral sensory and motor cortical areas) that emerges when the hands and arms are idle; and the "third rhythm" (alpha activity in the temporal or frontal lobes). Alpha can be abnormal; for example, an EEG that has diffuse alpha occurring in coma and is not responsive to external stimuli is referred to as "alpha coma".
Beta is the frequency range from 13 Hz to about 30 Hz. It is seen usually on both sides in symmetrical distribution and is most evident frontally. Beta activity is closely linked to motor behavior and is generally attenuated during active movements. Low-amplitude beta with multiple and varying frequencies is often associated with active, busy or anxious thinking and active concentration. Rhythmic beta with a dominant set of frequencies is associated with various pathologies, such as Dup15q syndrome, and drug effects, especially benzodiazepines. It may be absent or reduced in areas of cortical damage. It is the dominant rhythm in patients who are alert or anxious or who have their eyes open.
Gamma is the frequency range approximately 30–100 Hz. Gamma rhythms are thought to represent binding of different populations of neurons together into a network for the purpose of carrying out a certain cognitive or motor function.
Mu range is 8–13 Hz and partly overlaps with other frequencies. It reflects the synchronous firing of motor neurons in rest state. Mu suppression is thought to reflect motor mirror neuron systems, because when an action is observed, the pattern extinguishes, possibly because the normal and mirror neuronal systems "go out of sync" and interfere with one other.
"Ultra-slow" or "near-DC" activity is recorded using DC amplifiers in some research contexts. It is not typically recorded in a clinical context because the signal at these frequencies is susceptible to a number of artifacts.
Some features of the EEG are transient rather than rhythmic. Spikes and sharp waves may represent seizure activity or interictal activity in individuals with epilepsy or a predisposition toward epilepsy. Other transient features are normal: vertex waves and sleep spindles are seen in normal sleep.
There are types of activity that are statistically uncommon, but not associated with dysfunction or disease. These are often referred to as "normal variants". The mu rhythm is an example of a normal variant.
The normal electroencephalogram (EEG) varies by age. The prenatal EEG and neonatal EEG is quite different from the adult EEG. Fetuses in the third trimester and newborns display two common brain activity patterns: "discontinuous" and "trace alternant." "Discontinuous" electrical activity refers to sharp bursts of electrical activity followed by low frequency waves. "Trace alternant" electrical activity describes sharp bursts followed by short high amplitude intervals and usually indicates quiet sleep in newborns. The EEG in childhood generally has slower frequency oscillations than the adult EEG.
The normal EEG also varies depending on state. The EEG is used along with other measurements (EOG, EMG) to define sleep stages in polysomnography. Stage I sleep (equivalent to drowsiness in some systems) appears on the EEG as drop-out of the posterior basic rhythm. There can be an increase in theta frequencies. Santamaria and Chiappa cataloged a number of the variety of patterns associated with drowsiness. Stage II sleep is characterized by sleep spindles – transient runs of rhythmic activity in the 12–14 Hz range (sometimes referred to as the "sigma" band) that have a frontal-central maximum. Most of the activity in Stage II is in the 3–6 Hz range. Stage III and IV sleep are defined by the presence of delta frequencies and are often referred to collectively as "slow-wave sleep". Stages I–IV comprise non-REM (or "NREM") sleep. The EEG in REM (rapid eye movement) sleep appears somewhat similar to the awake EEG.
EEG under general anesthesia depends on the type of anesthetic employed. With halogenated anesthetics, such as halothane or intravenous agents, such as propofol, a rapid (alpha or low beta), nonreactive EEG pattern is seen over most of the scalp, especially anteriorly; in some older terminology this was known as a WAR (widespread anterior rapid) pattern, contrasted with a WAIS (widespread slow) pattern associated with high doses of opiates. Anesthetic effects on EEG signals are beginning to be understood at the level of drug actions on different kinds of synapses and the circuits that allow synchronized neuronal activity.
Artifacts
EEG is an extremely useful technique for studying brain activity, but the signal measured is always contaminated by artifacts which can impact the analysis of the data. An artifact is any measured signal that does not originate within the brain. Although multiple algorithms exist for the removal of artifacts, the problem of how to deal with them remains an open question. The source of artifacts can be from issues relating to the instrument, such as faulty electrodes, line noise or high electrode impedance, or they may be from the physiology of the subject being recorded. This can include, eye blinks and movement, cardiac activity and muscle activity and these types of artifacts are more complicated to remove. Artifacts may bias the visual interpretation of EEG data as some may mimic cognitive activity that could affect diagnoses of problems such as Alzheimer's disease or sleep disorders. As such the removal of such artifacts in EEG data used for practical applications is of the utmost importance.
Artifact removal
It is important to be able to distinguish artifacts from genuine brain activity in order to prevent incorrect interpretations of EEG data. General approaches for the removal of artifacts from the data are, prevention, rejection and cancellation. The goal of any approach is to develop methodology capable of identifying and removing artifacts without affecting the quality of the EEG signal. As artifact sources are quite different the majority of researchers focus on developing algorithms that will identify and remove a single type of noise in the signal. Simple filtering using a notch filter is commonly employed to reject components with a 50/60 Hz frequency. However such simple filters are not an appropriate choice for dealing with all artifacts, as for some, their frequencies will overlap with the EEG frequencies.
Regression algorithms have a moderate computation cost and are simple. They represented the most popular correction method up until the mid-1990s when they were replaced by "blind source separation" type methods. Regression algorithms work on the premise that all artifacts are comprised by one or more reference channels. Subtracting these reference channels from the other contaminated channels, in either the time or frequency domain, by estimating the impact of the reference channels on the other channels, would correct the channels for the artifact. Although the requirement of reference channels ultimately lead to this class of algorithm being replaced, they still represent the benchmark against which modern algorithms are evaluated.
Blind source separation (BSS) algorithms employed to remove artifacts include principal component analysis (PCA) and independent component analysis (ICA) and several algorithms in this class have been successful at tackling most physiological artifacts.
Physiological artifacts
Ocular artifacts
Ocular artifacts affect the EEG signal significantly. This is due to eye movements involving a change in electric fields surrounding the eyes, distorting the electric field over the scalp, and as EEG is recorded on the scalp, it therefore distorts the recorded signal. A difference of opinion exists among researchers, with some arguing ocular artifacts are, or may be reasonably described as a single generator, whilst others argue it is important to understand the potentially complicated mechanisms. Three potential mechanisms have been proposed to explain the ocular artifact.
The first is corneal retinal dipole movement which argues that an electric dipole is formed between the cornea and retina, as the former is positively and the latter negatively charged. When the eye moves, so does this dipole which impacts the electrical field over the scalp, this is the most standard view. The second mechanism is retinal dipole movement, which is similar to the first but differing in that it argues there is a potential difference, hence dipole across the retina with the cornea having little effect. The third mechanism is eyelid movement. It is known that there is a change in voltage around the eyes when the eyelid moves, even if the eyeball does not. It is thought that the eyelid can be described as a sliding potential source and that the impacting of blinking is different to eye movement on the recorded EEG.
Eyelid fluttering artifacts of a characteristic type were previously called Kappa rhythm (or Kappa waves). It is usually seen in the prefrontal leads, that is, just over the eyes. Sometimes they are seen with mental activity. They are usually in the Theta (4–7 Hz) or Alpha (7–14 Hz) range. They were named because they were believed to originate from the brain. Later study revealed they were generated by rapid fluttering of the eyelids, sometimes so minute that it was difficult to see. They are in fact noise in the EEG reading, and should not technically be called a rhythm or wave. Therefore, current usage in electroencephalography refers to the phenomenon as an eyelid fluttering artifact, rather than a Kappa rhythm (or wave).
The propagation of the ocular artifact is impacted by multiple factors including the properties of the subject's skull, neuronal tissues and skin but the signal may be approximated as being inversely proportional to the distance from the eyes squared. The electrooculogram (EOG) consists of a series of electrodes measuring voltage changes close to the eye and is the most common tool for dealing with the eye movement artifact in the EEG signal.
Muscular artifacts
Another source of artifacts are various muscle movements across the body. This particular class of artifact is usually recorded by all electrodes on the scalp due to myogenic activity (increase or decrease of blood pressure). The origin of these artifacts have no single location and arises from functionally independent muscle groups, meaning the characteristics of the artifact are not constant. The observed patterns due to muscular artifacts will change depending on subject sex, the particular muscle tissue, and its degree of contraction. The frequency range for muscular artifacts is wide and overlaps with every classic EEG rhythm. However most of the power is concentrated in the lower range of the observed frequencies of 20 to 300 Hz making the gamma band particularly susceptible to muscular artifacts. Some muscle artifacts may have activity with a frequency as low as 2 Hz, so delta and theta bands may also be affected by muscle activity. Muscular artifacts may impact sleep studies, as unconscious bruxism (grinding of teeth) movements or snoring can seriously impact the quality of the recorded EEG. In addition the recordings made of epilepsy patients may be significantly impacted by the existence of muscular artifacts.
Cardiac artifacts
The potential due to cardiac activity introduces electrocardiograph (ECG) errors in the EEG. Artifacts arising due to cardiac activity may be removed with the help of an ECG reference signal.
Other physiological artifacts
Glossokinetic artifacts are caused by the potential difference between the base and the tip of the tongue. Minor tongue movements can contaminate the EEG, especially in parkinsonian and tremor disorders.
Environmental artifacts
In addition to artifacts generated by the body, many artifacts originate from outside the body. Movement by the patient, or even just settling of the electrodes, may cause electrode pops, spikes originating from a momentary change in the impedance of a given electrode. Poor grounding of the EEG electrodes can cause significant 50 or 60 Hz artifact, depending on the local power system's frequency. A third source of possible interference can be the presence of an IV drip; such devices can cause rhythmic, fast, low-voltage bursts, which may be confused for spikes.
Abnormal activity
Abnormal activity can broadly be separated into epileptiform and non-epileptiform activity. It can also be separated into focal or diffuse.
Focal epileptiform discharges represent fast, synchronous potentials in a large number of neurons in a somewhat discrete area of the brain. These can occur as interictal activity, between seizures, and represent an area of cortical irritability that may be predisposed to producing epileptic seizures. Interictal discharges are not wholly reliable for determining whether a patient has epilepsy nor where his/her seizure might originate. (See focal epilepsy.)
Generalized epileptiform discharges often have an anterior maximum, but these are seen synchronously throughout the entire brain. They are strongly suggestive of a generalized epilepsy.
Focal non-epileptiform abnormal activity may occur over areas of the brain where there is focal damage of the cortex or white matter. It often consists of an increase in slow frequency rhythms and/or a loss of normal higher frequency rhythms. It may also appear as focal or unilateral decrease in amplitude of the EEG signal.
Diffuse non-epileptiform abnormal activity may manifest as diffuse abnormally slow rhythms or bilateral slowing of normal rhythms, such as the PBR.
Intracortical Encephalogram electrodes and sub-dural electrodes can be used in tandem to discriminate and discretize artifact from epileptiform and other severe neurological events.
More advanced measures of abnormal EEG signals have also recently received attention as possible biomarkers for different disorders such as Alzheimer's disease.
Remote communication
Systems for decoding imagined speech from EEG have applications such as in brain–computer interfaces.
EEG diagnostics
The Department of Defense (DoD) and Veteran's Affairs (VA), and U.S Army Research Laboratory (ARL), collaborated on EEG diagnostics in order to detect mild to moderate Traumatic Brain Injury (mTBI) in combat soldiers. Between 2000 and 2012, 75 percent of U.S. military operations brain injuries were classified mTBI. In response, the DoD pursued new technologies capable of rapid, accurate, non-invasive, and field-capable detection of mTBI to address this injury.
Combat personnel often develop PTSD and mTBI in correlation. Both conditions present with altered low-frequency brain wave oscillations. Altered brain waves from PTSD patients present with decreases in low-frequency oscillations, whereas, mTBI injuries are linked to increased low-frequency wave oscillations. Effective EEG diagnostics can help doctors accurately identify conditions and appropriately treat injuries in order to mitigate long-term effects.
Traditionally, clinical evaluation of EEGs involved visual inspection. Instead of a visual assessment of brain wave oscillation topography, quantitative electroencephalography (qEEG), computerized algorithmic methodologies, analyzes a specific region of the brain and transforms the data into a meaningful "power spectrum" of the area. Accurately differentiating between mTBI and PTSD can significantly increase positive recovery outcomes for patients especially since long-term changes in neural communication can persist after an initial mTBI incident.
Another common measurement made from EEG data is that of complexity measures such as Lempel-Ziv complexity, fractal dimension, and spectral flatness, which are associated with particular pathologies or pathology stages.
Economics
Inexpensive EEG devices exist for the low-cost research and consumer markets. Recently, a few companies have miniaturized medical grade EEG technology to create versions accessible to the general public. Some of these companies have built commercial EEG devices retailing for less than US$100.
In 2004 OpenEEG released its ModularEEG as open source hardware. Compatible open source software includes a game for balancing a ball.
In 2007 NeuroSky released the first affordable consumer based EEG along with the game NeuroBoy. This was also the first large scale EEG device to use dry sensor technology.
In 2008 OCZ Technology developed device for use in video games relying primarily on electromyography.
In 2008 the Final Fantasy developer Square Enix announced that it was partnering with NeuroSky to create a game, Judecca.
In 2009 Mattel partnered with NeuroSky to release the Mindflex, a game that used an EEG to steer a ball through an obstacle course. By far the best-selling consumer based EEG to date.
In 2009 Uncle Milton Industries partnered with NeuroSky to release the Star Wars Force Trainer, a game designed to create the illusion of possessing the Force.
In 2010, NeuroSky added a blink and electromyography function to the MindSet.
In 2011, NeuroSky released the MindWave, an EEG device designed for educational purposes and games. The MindWave won the Guinness Book of World Records award for "Heaviest machine moved using a brain control interface".
In 2012, a Japanese gadget project, neurowear, released Necomimi: a headset with motorized cat ears. The headset is a NeuroSky MindWave unit with two motors on the headband where a cat's ears might be. Slipcovers shaped like cat ears sit over the motors so that as the device registers emotional states the ears move to relate. For example, when relaxed, the ears fall to the sides and perk up when excited again.
In 2014, OpenBCI released an eponymous open source brain-computer interface after a successful kickstarter campaign in 2013. The board, later renamed "Cyton", has 8 channels, expandable to 16 with the Daisy module. It supports EEG, EKG, and EMG. The Cyton Board is based on the Texas Instruments ADS1299 IC and the Arduino or PIC microcontroller, and initially costed $399 before increasing in price to $999. It uses standard metal cup electrodes and conductive paste.
In 2015, Mind Solutions Inc released the smallest consumer BCI to date, the NeuroSync. This device functions as a dry sensor at a size no larger than a Bluetooth ear piece.
In 2015, A Chinese-based company Macrotellect released BrainLink Pro and BrainLink Lite, a consumer grade EEG wearable product providing 20 brain fitness enhancement Apps on Apple and Android App Stores.
In 2021, BioSerenity release the Neuronaute and Icecap a single-use disposable EEG headset that allows recording with equivalent quality to traditional cup electrodes.
Future research
The EEG has been used for many purposes besides the conventional uses of clinical diagnosis and conventional cognitive neuroscience. An early use was during World War II by the U.S. Army Air Corps to screen out pilots in danger of having seizures; long-term EEG recordings in epilepsy patients are still used today for seizure prediction. Neurofeedback remains an important extension, and in its most advanced form is also attempted as the basis of brain computer interfaces. The EEG is also used quite extensively in the field of neuromarketing.
The EEG is altered by drugs that affect brain functions, the chemicals that are the basis for psychopharmacology. Berger's early experiments recorded the effects of drugs on EEG. The science of pharmaco-electroencephalography has developed methods to identify substances that systematically alter brain functions for therapeutic and recreational use.
Honda is attempting to develop a system to enable an operator to control its Asimo robot using EEG, a technology it eventually hopes to incorporate into its automobiles.
EEGs have been used as evidence in criminal trials in the Indian state of Maharashtra. Brain Electrical Oscillation Signature Profiling (BEOS), an EEG technique, was used in the trial of State of Maharashtra v. Sharma to show Sharma remembered using arsenic to poison her ex-fiancé, although the reliability and scientific basis of BEOS is disputed.
A lot of research is currently being carried out in order to make EEG devices smaller, more portable and easier to use. So called "Wearable EEG" is based upon creating low power wireless collection electronics and 'dry' electrodes which do not require a conductive gel to be used. Wearable EEG aims to provide small EEG devices which are present only on the head and which can record EEG for days, weeks, or months at a time, as ear-EEG. Such prolonged and easy-to-use monitoring could make a step change in the diagnosis of chronic conditions such as epilepsy, and greatly improve the end-user acceptance of BCI systems. Research is also being carried out on identifying specific solutions to increase the battery lifetime of Wearable EEG devices through the use of the data reduction approach.
In research, currently EEG is often used in combination with machine learning. EEG data are pre-processed then passed on to machine learning algorithms. These algorithms are then trained to recognize different diseases like schizophrenia, epilepsy or dementia. Furthermore, they are increasingly used to study seizure detection. By using machine learning, the data can be analyzed automatically. In the long run this research is intended to build algorithms that support physicians in their clinical practice and to provide further insights into diseases. In this vein, complexity measures of EEG data are often calculated, such as Lempel-Ziv complexity, fractal dimension, and spectral flatness. It has been shown that combining or multiplying such measures can reveal previously hidden information in EEG data.
EEG signals from musical performers were used to create instant compositions and one CD by the Brainwave Music Project, run at the Computer Music Center at Columbia University by Brad Garton and Dave Soldier. Similarly, an hour-long recording of the brainwaves of Ann Druyan was included on the Voyager Golden Record, launched on the Voyager probes in 1977, in case any extraterrestrial intelligence could decode her thoughts, which included what it was like to fall in love.
History
In 1875, Richard Caton (1842–1926), a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in the British Medical Journal. In 1890, Polish physiologist Adolf Beck published an investigation of spontaneous electrical activity of the brain of rabbits and dogs that included rhythmic oscillations altered by light. Beck started experiments on the electrical brain activity of animals. Beck placed electrodes directly on the surface of the brain to test for sensory stimulation. His observation of fluctuating brain activity led to the conclusion of brain waves.
In 1912, Ukrainian physiologist Vladimir Vladimirovich Pravdich-Neminsky published the first animal EEG and the evoked potential of the mammalian (dog). In 1914, Napoleon Cybulski and Jelenska-Macieszyna photographed EEG recordings of experimentally induced seizures.
German physiologist and psychiatrist Hans Berger (1873–1941) recorded the first human EEG in 1924. Expanding on work previously conducted on animals by Richard Caton and others, Berger also invented the electroencephalograph (giving the device its name), an invention described "as one of the most surprising, remarkable, and momentous developments in the history of clinical neurology". His discoveries were first confirmed by British scientists Edgar Douglas Adrian and B. H. C. Matthews in 1934 and developed by them.
In 1934, Fisher and Lowenbach first demonstrated epileptiform spikes. In 1935, Gibbs, Davis and Lennox described interictal spike waves and the three cycles/s pattern of clinical absence seizures, which began the field of clinical electroencephalography. Subsequently, in 1936 Gibbs and Jasper reported the interictal spike as the focal signature of epilepsy. The same year, the first EEG laboratory opened at Massachusetts General Hospital.
Franklin Offner (1911–1999), professor of biophysics at Northwestern University developed a prototype of the EEG that incorporated a piezoelectric inkwriter called a Crystograph (the whole device was typically known as the Offner Dynograph).
In 1947, The American EEG Society was founded and the first International EEG congress was held. In 1953 Aserinsky and Kleitman described REM sleep.
In the 1950s, William Grey Walter developed an adjunct to EEG called EEG topography, which allowed for the mapping of electrical activity across the surface of the brain. This enjoyed a brief period of popularity in the 1980s and seemed especially promising for psychiatry. It was never accepted by neurologists and remains primarily a research tool.
An electroencephalograph system manufactured by Beckman Instruments was used on at least one of the Project Gemini manned spaceflights (1965–1966) to monitor the brain waves of astronauts on the flight. It was one of many Beckman Instruments specialized for and used by NASA.
The first instance of the use of EEG to control a physical object, a robot, was in 1988. The robot would follow a line or stop depending on the alpha activity of the subject. If the subject relaxed and closed their eyes therefore increasing alpha activity, the bot would move. Opening their eyes thus decreasing alpha activity would cause the robot to stop on the trajectory.
| Technology | Diagnostic technologies | null |
21402762 | https://en.wikipedia.org/wiki/Ironing | Ironing | Ironing is the use of an iron, usually heated, to remove wrinkles and unwanted creases from fabric. The heating is commonly done to a temperature of , depending on the fabric. Ironing works by loosening the bonds between the long-chain polymer molecules in the fibres of the material. While the molecules are hot, the fibres are straightened by the weight of the iron, and they hold their new shape as they cool. Some fabrics, such as cotton, require the addition of water to loosen the intermolecular bonds. Many modern fabrics (developed in or after the mid-twentieth century) are advertised as needing little or no ironing. Permanent press clothing was developed to reduce the ironing necessary by combining wrinkle-resistant polyester with cotton.
The first known use of heated metal to "iron" clothes is known to have occurred in China. The electric iron was invented in 1882, by Henry W. Seely. Seely patented his "electric flatiron" on June 6, 1882 (U.S. Patent no. 259,054).
Equipment
Iron
The iron is the small appliance used to remove wrinkles from fabric. It is also known as a clothes iron, steam iron, flat iron, smoothing iron or iron box.
On 15 February 1858 W. Vandenburg and J. Harvey patented an ironing table that facilitated pressing sleeves and pant legs. A truly portable folding ironing board was first patented in Canada in 1875 by John B. Porter. The invention also included a removable press board used for sleeves. In 1892 Sarah Boone obtained a patent in the United States for improvements to the ironing board, allowing for better quality ironing for shirt sleeves.
Ironing board cover sizes
Tailor's ham
A tailor's ham or dressmakers ham is a tightly stuffed pillow in the shape of a ham used as a mold when pressing curves such as sleeves or collars.
Commercial equipment
Commercial dry cleaning and full-service laundry providers usually use a large appliance called a steam press to do most of the work of ironing clothes. Alternatively, a rotary iron may be used.
Historically, larger tailors' shops included a tailor's stove, used to quickly and efficiently heat multiple irons. In many developing countries a cluster of solid irons, heated alternatively from a single heating source, are used for pressing clothes at small commercial outlets.
Recommended ironing temperatures
Another source suggests slightly higher temperatures; for example, 180-220 °C for cotton.
Chemistry
When the fabric is heated, the molecules are more easily reoriented. In the case of cotton fibres, which are derivatives of cellulose, the hydroxyl groups that crosslink the cellulose polymer chains are reformed at high temperatures and become somewhat "locked in place" upon cooling the item. In permanent press pressed clothes, chemical agents such as dimethylol ethylene urea are added as crosslinking agents.
| Technology | Household appliances | null |
21407814 | https://en.wikipedia.org/wiki/Marinoan%20glaciation | Marinoan glaciation | The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation.
Its beginning is poorly constrained, but occurred no earlier than 654.5 Ma (million years ago).
It ended approximately 632.3 ± 5.9 Ma
during the Cryogenian period. This glaciation possibly covered the entire planet, in an event called the Snowball Earth. The end of the glaciation was caused by volcanic release of carbon dioxide and dissolution of gas hydrates
and may have been hastened by the release of methane from equatorial permafrost.
Origin of name and history of terminology
The name is derived from the stratigraphic terminology of the Adelaide Geosyncline (Adelaide Rift Complex) in South Australia and is taken from the Adelaide suburb of Marino. The term Marinoan Series was first used in a 1950 paper by Douglas Mawson and Reg Sprigg to subdivide the Neoproterozoic rocks of the Adelaide area and encompassed all strata from the top of the Brighton Limestone to the base of the Cambrian. The corresponding time period, referred to as the Marinoan Epoch, spanned from the middle Cryogenian to the top of the Ediacaran in modern terminology. Mawson recognised a glacial episode within the Marinoan Epoch which he referred to as the Elatina glaciation after the 'Elatina Tillite' (now Elatina Formation) where he found the evidence. However, the term Marinoan glaciation came into common usage because it was the glaciation that occurred during the Marinoan Epoch, as distinct from the earlier glaciation during the Sturtian Epoch (the time period of deposition of the older Sturtian Series).
The term Marinoan glaciation was later applied globally to any glaciogenic formations assumed (directly or indirectly) to correlate with Mawson's original Elatina glaciation in South Australia. Recently, there has been a move to return to the term Elatina glaciation in South Australia because of uncertainties regarding global correlation and because an Ediacaran glacial episode (Gaskiers) also occurs within the wide-ranging Marinoan Epoch.
Cryogenian Snowball Earth
Emerging evidence suggests that the Earth underwent a number of glaciations during the Neoproterozoic era. There were three (or possibly four) significant ice ages during the late Neoproterozoic. These periods of nearly complete glaciation of Earth are often referred to as "Snowball Earth", where it is hypothesized that at times the planet was covered by ice thick. Of these glaciations, the Sturtian glaciation was the most significant, whereas the Marinoan was a shorter, but still worldwide glaciation. Other Cryogenian glaciations were probably small and not global as compared to the Marinoan or Sturtian glaciations.
During the Marinoan glaciation, characteristic glacial deposits indicate that Earth suffered one of the most severe ice ages in its history. Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.
The Earth may not have been fully covered in ice, as some computer simulations show an extreme slowdown of the hydrological cycle that inhibited new glacial formation before the Earth was fully ice-covered.
The melting of the Snowball Earth is associated with greenhouse warming due to the accumulation of high levels of carbon dioxide in the atmosphere. Deglaciation likely started in the mid-latitudes, as in the tropics, the intense hydrological cycle replenished snow rapidly. As the mid-latitudes became ice free, dust was blown from them into other regions, lowering albedo and speeding up deglaciation.
Evidence
Even though much evidence has been lost through geological changes, field investigations show evidence of the Marinoan glaciation in China, Svalbard archipelago and South Australia. In Guizhou Province, China, glacial rocks were found to be underlying and overlying a layer of volcanic ashes which contained zircon minerals, which could be dated through radioisotopes. Glacial deposits in South Australia are approximately the same age (about 630 Ma), confirmed by similar stable carbon isotopes, mineral deposits (including sedimentary barite), and other unusual sedimentary structures. Two diamictite-rich layers in the top of the Neoproterozoic strata of the northeastern Svalbard archipelago represent the first and final phases of the Marinoan glaciation. In Uruguay, evidence of the Marinoan glaciation is known from dropstones, diamictites, rhythmites, clast layers, and varve-like deposits.
According to Eyles and Young, the Marinoan is a second episode of Neoproterozoic glaciation (680–690 Ma) occurring in the Adelaide Geosyncline. According to them, "It is separated from the Sturtian by a thick succession of sedimentary rocks containing no evidence of glaciation. This glacial phase could correspond to the recently described Ice Brooke formation in the northern Cordillera."
Effects on life
The survival of benthic macroalgae indicates that there remained areas of suitable habitat for them in the photic zone along the coasts of mid-latitude continents during the Marinoan glaciation.
| Physical sciences | Events | Earth science |
5168174 | https://en.wikipedia.org/wiki/Sloth | Sloth | Sloths are a Neotropical group of xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their lives hanging upside down in the trees of the tropical rainforests of South America and Central America. Sloths are considered to be most closely related to anteaters, together making up the xenarthran order Pilosa.
There are six extant sloth species in two genera – Bradypus (three-toed sloths) and Choloepus (two-toed sloths). Despite this traditional naming, all sloths have three toes on each rear limb – although two-toed sloths have only two digits on each forelimb. The two groups of sloths are from different, distantly related families, and are thought to have evolved their morphology via parallel evolution from terrestrial ancestors. Besides the extant species, many species of ground sloths ranging up to the size of elephants (like Megatherium) inhabited both North and South America during the Pleistocene Epoch. However, they became extinct during the Quaternary extinction event around 12,000 years ago, along with most large animals across the Americas. The extinction correlates in time with the arrival of humans, but climate change has also been suggested to have contributed. Members of an endemic radiation of Caribbean sloths also formerly lived in the Greater Antilles but became extinct after humans settled the archipelago in the mid-Holocene, around 6,000 years ago.
Sloths are so named because of their very low metabolism and deliberate movements. Sloth, related to slow, literally means "laziness", and their common names in several other languages (e.g. , , , Romanian: leneș, Finnish: laiskiainen) also mean "lazy" or similar. Their slowness permits their low-energy diet of leaves and avoids detection by predatory hawks and cats that hunt by sight. Sloths are almost helpless on the ground but are able to swim. The shaggy coat has grooved hair that is host to symbiotic green algae which camouflage the animal in the trees and provide it nutrients. The algae also nourish sloth moths, some species of which exist solely on sloths.
Taxonomy and evolution
Sloths belong to the superorder Xenarthra, a group of placental mammals believed to have evolved in the continent of South America around 60 million years ago. One study found that xenarthrans broke off from other placental mammals around 100 million years ago. Anteaters and armadillos are also included among Xenarthra. The earliest xenarthrans were arboreal herbivores with sturdy vertebral columns, fused pelvises, stubby teeth, and small brains. Sloths are in the taxonomic suborder Folivora of the order Pilosa. These names are from the Latin 'leaf eater' and 'hairy', respectively. Pilosa is one of the smallest of the orders of the mammal class; its only other suborder contains the anteaters.
The Folivora are divided into at least eight families, only two of which have living species; the remainder are entirely extinct (†):
†Megalocnidae: the Greater Antilles sloths, a basal group that arose about 32 million years ago and became extinct about 5,000 years ago.
Superfamily Megatherioidea
Bradypodidae, the three-toed sloths, contains four extant species:
The brown-throated three-toed sloth (Bradypus variegatus) is the most common of the extant species of sloth, which inhabits the Neotropical realm in the forests of South and Central America.
The pale-throated three-toed sloth (Bradypus tridactylus), which inhabits tropical rainforests in northern South America. It is similar in appearance to, and often confused with, the brown-throated three-toed sloth, which has a much wider distribution. Genetic evidence indicates the two species diverged around six million years ago.
The maned three-toed sloth (Bradypus torquatus), now found only in the Atlantic Forest of southeastern Brazil.
The critically endangered pygmy three-toed sloth (Bradypus pygmaeus) which is endemic to the small island of Isla Escudo de Veraguas off the coast of Panama.
†Megalonychidae: ground sloths that existed for about 35 million years and went extinct about 11,000 years ago. This group was formerly thought to include both the two-toed sloths and the extinct Greater Antilles sloths.
†Megatheriidae: ground sloths that existed for about 23 million years and went extinct about 11,000 years ago; this family included the largest sloths.
†Nothrotheriidae: ground sloths that lived from approximately 11.6 million to 11,000 years ago. As well as ground sloths, this family included Thalassocnus, a genus of either semiaquatic or fully aquatic sloths.
Superfamily Mylodontoidea
Choloepodidae, the two-toed sloths, contains two extant species:
Linnaeus's two-toed sloth (Choloepus didactylus) found in Venezuela, the Guianas, Colombia, Ecuador, Peru, and Brazil north of the Amazon River.
Hoffmann's two-toed sloth (Choloepus hoffmanni) which inhabits tropical forests. It has two separate ranges, split by the Andes. One population is found from eastern Honduras in the north to western Ecuador in the south, and the other in eastern Peru, western Brazil, and northern Bolivia.
†Mylodontidae: ground sloths that existed for about 23 million years and went extinct about 11,000 years ago.
†Scelidotheriidae: collagen sequence data indicates this group is more distant from Mylodon than Choloepus is, so it has been elevated back to full family status.
Evolution
The common ancestor of the two existing sloth genera dates to about 28 million years ago, with similarities between the two- and three- toed sloths an example of convergent evolution to an arboreal lifestyle, "one of the most striking examples of convergent evolution known among mammals". The ancient Xenarthra included a significantly greater variety of species, with a wider distribution, than those of today. Ancient sloths were mostly terrestrial, and some reached sizes that rival those of elephants, as was the case for Megatherium.
Sloths arose in South America during a long period of isolation and eventually spread to a number of the Caribbean islands as well as North America. It is thought that swimming led to oceanic dispersal of pilosans to the Greater Antilles by the Oligocene, and that the megalonychid Pliometanastes and the mylodontid Thinobadistes were able to colonise North America about 9 million years ago, well before the formation of the Isthmus of Panama. The latter development, about 3 million years ago, allowed megatheriids and nothrotheriids to also invade North America as part of the Great American Interchange. Additionally, the nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic and, eventually, perhaps fully aquatic marine lifestyle. In Peru and Chile, Thalassocnus entered the coastal habitat beginning in the late Miocene. They presumably waded and paddled in the water for short period, but over a span of 4 million years, they eventually evolved into swimming creatures, becoming specialist bottom feeders of seagrasses, similar to the extant sirenians.
Both types of extant tree sloth tend to occupy the same forests; in most areas, a particular species of the somewhat smaller and generally slower-moving three-toed sloth (Bradypus) and a single species of the two-toed type will jointly predominate. Based on morphological comparisons, it was thought the two-toed sloths nested phylogenetically within one of the divisions of the extinct Greater Antilles sloths. Though data has been collected on over 33 different species of sloths by analyzing bone structures, many of the relationships between clades on a phylogenetic tree were unclear. Much of the morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear.
Recently obtained molecular data from collagen and mitochondrial DNA sequences fall in line with the diphyly (convergent evolution) hypothesis but have overturned some of the other conclusions obtained from morphology. These investigations consistently place two-toed sloths close to mylodontids and three-toed sloths within Megatherioidea, close to Megalonyx, megatheriids and nothrotheriids. They make the previously recognized family Megalonychidae polyphyletic, with both two-toed sloths and Greater Antilles sloths being moved away from Megalonyx. Greater Antilles sloths are now placed in a separate, basal branch of the sloth evolutionary tree.
Phylogeny
The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data.
Extinctions
The marine sloths of South America's Pacific coast became extinct at the end of the Pliocene following the closing of the Central American Seaway; the closing caused a cooling trend in the coastal waters which killed off much of the area's seagrass (and which would have also made thermoregulation difficult for the sloths, with their slow metabolism).
Ground sloths disappeared from both North and South America shortly after the appearance of humans about 11,000 years ago. Evidence suggests human hunting contributed to the extinction of the American megafauna. Ground sloth remains found in both North and South America indicate that they were killed, cooked, and eaten by humans. Climate change that came with the end of the last ice age may have also played a role, although previous similar glacial retreats were not associated with similar extinction rates.
Megalocnus and some other Caribbean sloths survived until about 5,000 years ago, long after ground sloths had died out on the mainland, but then went extinct when humans finally colonized the Greater Antilles.
Biology
Morphology and anatomy
Sloths can be long and, depending on the species, weigh from . Two-toed sloths are slightly larger than three-toed sloths. Sloths have long limbs and rounded heads with tiny ears. Three-toed sloths also have stubby tails about long.
Sloths are unusual among mammals in not having seven cervical vertebrae. Two-toed sloths have five to seven, while three-toed sloths have eight or nine. The other mammals not having seven are the manatees, with six.
Physiology
Sloths have colour vision but have poor visual acuity. They also have poor hearing. Thus, they rely on their sense of smell and touch to find food.
Sloths have very low metabolic rates (less than half of that expected for a mammal of their size), and low body temperatures: when active, and still lower when resting. Sloths are heterothermic, meaning their body temperature may vary according to the environment, normally ranging from , but able to drop to as low as , inducing torpor.
The outer hairs of sloth fur grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the extremities, but because sloths spend so much time with their limbs above their bodies, their hairs grow away from the extremities to provide protection from the elements while they hang upside down. In most conditions, the fur hosts symbiotic algae, which provide camouflage from predatory jaguars, ocelots, and harpy eagles. Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of commensal and parasitic arthropods. There are a large number of arthropods associated with sloths. These include biting and blood-sucking flies such as mosquitoes and sandflies, triatomine bugs, lice, ticks and mites. Sloths have a highly specific community of commensal beetles, mites and moths. The species of sloths recorded to host arthropods include the pale-throated three-toed sloth, the brown-throated three-toed sloth, and Linnaeus's two-toed sloth. Sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients.
Activity
Their limbs are adapted for hanging and grasping, not for supporting their weight. Muscle mass makes up only 25 to 30 percent of their total body weight. Most other mammals have a muscle mass that makes up 40 to 45 percent of their total body weight. Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort, and are used to drag themselves along the ground, since they cannot walk. On three-toed sloths, the arms are 50 percent longer than the legs.
Sloths move only when necessary and even then, very slowly. They usually move at an average speed of per minute but can move at a marginally higher speed of per minute if they are in immediate danger from a predator. While they sometimes sit on top of branches, they usually eat, sleep, and even give birth hanging from branches. They sometimes remain hanging from branches even after death. On the ground, the maximum speed of sloths is per minute. Two-toed sloths are generally better able than three-toed sloths to disperse between clumps of trees on the ground.
Sloths are surprisingly strong swimmers and can reach speeds of per minute. They use their long arms to paddle through the water and can cross rivers and swim between islands. Sloths can reduce their already slow metabolism even further and slow their heart rate to less than a third of normal, allowing them to hold their breath underwater for up to 40 minutes.
Wild brown-throated three-toed sloths sleep on average 9.6 hours a day. Two-toed sloths are nocturnal. Three-toed sloths are mostly nocturnal but can be active in the day. They spend 90 per cent of their time motionless.
Behavior
Sloths are solitary animals that rarely interact with one another except during breeding season, though female sloths do sometimes congregate, more so than do males.
Sloths descend about once every eight days to defecate on the ground. The reason and mechanism behind this behavior have long been debated among scientists. There are at least five hypotheses: 1) fertilize trees when feces are deposited at the base of the tree; 2) cover feces and avoid predation; 3) chemical communication between individuals; 4) pick up trace nutrients in their claws, that are then ingested; and 5) favor a mutualistic relationship with populations of fur moths. More recently, a new hypothesis has emerged, which presents evidence against the previous ones and proposes that all current sloths are descendants from species that defecated on the ground, and there simply has not been enough selective pressure to abandon this behavior, since cases of predation during defecation are actually very rare.
Diet
Baby sloths learn what to eat by licking the lips of their mother. All sloths eat the leaves of Cecropia.
Two-toed sloths are omnivorous, with a diverse diet of insects, carrion, fruits, leaves and small lizards, ranging over up to . Three-toed sloths, on the other hand, are almost entirely herbivorous (plant eaters), with a limited diet of leaves from only a few trees, and no other mammal digests its food as slowly.
They have made adaptations to arboreal browsing. Leaves, their main food source, provide very little energy or nutrients, and do not digest easily, so sloths have large, slow-acting, multi-chambered stomachs in which symbiotic bacteria break down the tough leaves. As much as two-thirds of a well-fed sloth's body weight consists of the contents of its stomach, and the digestive process can take a month or more to complete.
Three-toed sloths go to the ground to urinate and defecate about once a week, digging a hole and covering it afterwards. They go to the same spot each time and are vulnerable to predation while doing so. Considering the large energy expenditure and dangers involved in the journey to the ground, this behaviour has been described as a mystery. Recent research shows that moths, which live in the sloth's fur, lay eggs in the sloth's feces. When they hatch, the larvae feed on the feces, and when mature fly up onto the sloth above. These moths may have a symbiotic relationship with sloths, as they live in the fur and promote growth of algae, which the sloths eat. Individual sloths tend to spend the bulk of their time feeding on a single "modal" tree; by burying their excreta near the trunk of that tree, they may also help nourish it.
Reproduction
The pale- and brown-throated three-toed sloths mate seasonally, while the maned three-toed sloth breeds at any time of the year. The reproduction of pygmy three-toed sloths is currently unknown. Litters are of one newborn only, after six months' gestation for three-toed, and 12 months for two-toed. Newborns stay with their mother for about five months. In some cases, young sloths die from a fall indirectly because the mothers prove unwilling to leave the safety of the trees to retrieve the young. Females normally bear one baby every year, but sometimes sloths' low level of movement actually keeps females from finding males for longer than one year. Sloths are not particularly sexually dimorphic and several zoos have received sloths of the wrong sex.
The average lifespan of two-toed sloths in the wild is currently unknown due to a lack of full-lifespan studies in a natural environment. Median life expectancy in human care is about 16 years, with one individual at the Smithsonian Institution's National Zoo reaching an age of 49 years before her death.
Distribution
Although habitat is limited to the tropical rainforests of Central and South America, in that environment sloths are successful. On Barro Colorado Island in Panama, sloths have been estimated to constitute 70% of the biomass of arboreal mammals. Four of the six living species are currently rated "least concern"; the maned three-toed sloth (Bradypus torquatus), which inhabits Brazil's dwindling Atlantic Forest, is classified as "vulnerable", while the island-dwelling pygmy three-toed sloth (B. pygmaeus) is critically endangered. Sloths' lower metabolism confines them to the tropics, and they adopt thermoregulation behaviors of cold-blooded animals such as sunning themselves.
Human relations
The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and poachers. Their claws also provide another, unexpected deterrent to human hunters; when hanging upside-down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below.
Sloths are victims of animal trafficking where they are sold as pets. However, they generally make very poor pets, as they have such a specialized ecology.
The Sloth Institute Costa Rica is known for caring, rehabilitating and releasing sloths back into the wild. Also in Costa Rica, the Aviarios Sloth Sanctuary cares for sloths. It has rehabilitated and returned about 130 individuals to the wild. However, a report in May 2016 featured two former veterinarians from the facility who were critical of the sanctuary's efforts, accusing it of mistreating the animals.
| Biology and health sciences | Pilosa | null |
5171924 | https://en.wikipedia.org/wiki/Genet%20%28animal%29 | Genet (animal) | A genet (pronounced or ) is a member of the genus Genetta, which consists of 17 species of small African carnivorans. The common genet is the only genet present in Europe and occurs in the Iberian Peninsula, Italy and France.
Genet fossils from the Late Miocene and later have been found at sites in Ethiopia, Kenya and Morocco.
Classification
Genetta was named and described by Frédéric Cuvier in 1816. The number of species in the genus is controversial. The following were proposed as valid in 2005:
Extinct species
Genetta nyakitongwer – Early Pleistocene of Kenya
Genetta plesictoides – Late Pleistocene of Cyprus
Genetta and Poiana are estimated to have diverged about . Genetta species are estimated to have diverged at least starting with the Hausa genet, followed by the giant genet .
Characteristics
Genets are slender cat-like animals with a long body, a long ringed tail, large ears, a pointed muzzle and partly retractile claws. Their fur is spotted, but melanistic genets have also been recorded. They have musk glands and anal sacs. They also have perineal glands.
All genet species have a dark stripe along the spine; they differ in fur color and spot pattern. Their size varies between species from in head-to-body length with long tails; their tails are almost as long as head and body. They have large eyes with elliptical pupils; the iris is about the color of the fur. They can move their eyes within their sockets to a limited extent, and move their heads to focus on moving objects. Their pinnae have a fine layer of hair inside and outside. They can move the pinnae by about 80° from pointing forward to the side, and also from an erect position to pointing downwards. Their rhinarium is important for both sensing smell and touch.
Distribution and habitat
All genet species are indigenous to Africa. The common genet was introduced to southwestern Europe during historical times. It was brought from the Maghreb to Spain as a semi-domestic animal about 1000 to 1500 years ago, and from there spread to southern France and Italy. In Africa, it inhabits wooded habitats north of the Sahara, in savanna zones south of the Sahara to southern Africa and along the coast of Arabia, Yemen and Oman.
The Cape genet is endemic to fynbos, grassland and coastal forests in South Africa.
The South African small-spotted genet lives in woodland savanna, grassland, thickets, dry vlei areas in Angola, Namibia, South Africa and Zambia.
The rusty-spotted genet is widely distributed in sub-Saharan woodland savannah, savannah-forest mosaic, rain forest and montane forest up to an elevation of in Ethiopia.
The pardine genet lives in primary and secondary rainforests, gallery forests, moist woodlands, but also in plantations and suburban areas ranging from Senegal to the Volta River in Ghana.
The Abyssinian genet has been recorded in montane dry forest up to in Ethiopia.
The King genet is restricted to rainforest in the Congo Basin, Bioko Island, Ghana and Liberia.
The servaline genet lives in Central African lowland forests to high-altitude bamboo forest and coral rag thicket on Zanzibar.
The Angolan genet inhabits open miombo forest from Angola to central Tanzania.
The giant forest genet lives in rainforests of the Democratic Republic of the Congo and western Uganda.
The Hausa genet inhabits savannah and moist woodlands in West Africa.
G. letabae has been recorded in woodland savannah in Lesotho, Eswatini, Mozambique, Namibia and South Africa.
Johnston's genet inhabits dense rainforest in Upper Guinea.
The aquatic genet inhabits rainforests between the Congo River and the Rift Valley.
The crested servaline genet is endemic to Nigeria and Cameroon, where it inhabits scrub and primary deciduous forests.
Schouteden's genet inhabits rainforest, woodland savannah and savannah-forest mosaic in tropical Africa.
Bourlon's genet lives only in the Upper Guinean rainforests in West Africa.
Ecology and behavior
Genets are highly agile, have quick reflexes and exceptional climbing skills. They are the only viverrids able to stand on their hind legs. They walk, trot, run, climb up and down trees, and jump. They live on the ground, but also spend much of their time in trees. They are considered solitary, except during mating and when females have offspring.
They are omnivorous and opportunistically catch invertebrates and small vertebrates, but also feed on plants and fruit. Aquatic genets feed mainly on fish. Angolan genets are thought to feed on grasshoppers and other arthropods. Johnston's genet probably feeds mainly on insects.
In 2014, a camera trap in the Hluhluwe–Imfolozi Park captured a large spotted genet riding on the back of two different buffalo and a rhinoceros. This was the first time a genet was recorded hitch-hiking.
Females have up to five young in a litter. They rear their young alone.
Common genet females become sexually mature at the age of two years. After copulation, the gestation period lasts for 10 to 11 weeks. They are diestrous and give birth twice a year, during spring and late summer to autumn. Captive common genets have been known to live up to 13 years. A male genet lived for 22.7 years in captivity.
Threats
Loss of habitat due to deforestation and conversion of land to agriculture is a major threat for the crested servaline genet and Johnston's genet. Both genet species are also hunted for meat and skins. They are listed as Vulnerable on the IUCN Red Lists. These are also major threats for Bourlon's genet, which is classified as Near Threatened.
The aquatic genet may be affected by hunting, but major threats have not yet been identified. It is listed as Near Threatened on the IUCN Red List.
The king genet and the Abyssinian genet are so poorly known that threats cannot be identified. Both are listed as Data Deficient on the IUCN Red Lists.
The remaining genet species are not considered threatened and are listed as Least Concern on the IUCN Red Lists.
Etymology
The etymological origin of the word 'genet' is uncertain; it may be a derivation of the Arabic name djarnet. The English word comes from Old French 'genete', which came from Spanish 'gineta'.
As pets
Most genets that are kept as pets are common genets, rusty-spotted genets or Cape genets. As enforced by the Centers for Disease Control and Prevention (CDC), keeping a genet as a pet is prohibited across all states in the US. Although some states have specific laws regarding the possession of exotic pets, the possession and importation of genets is prohibited nationwide. Genet prices can exceed $1500 for both the purchase and shipment of the animal. Genets are not suited to life in captivity, and it is not recommended to keep one as a pet. They are solitary animals in the wild and will not get along well with other pets such as cats or dogs.
| Biology and health sciences | Other carnivora | Animals |
5173456 | https://en.wikipedia.org/wiki/Scalar%20field%20theory | Scalar field theory | In theoretical physics, scalar field theory can refer to a relativistically invariant classical or quantum theory of scalar fields. A scalar field is invariant under any Lorentz transformation.
The only fundamental scalar quantum field that has been observed in nature is the Higgs field. However, scalar quantum fields feature in the effective field theory descriptions of many physical phenomena. An example is the pion, which is actually a pseudoscalar.
Since they do not involve polarization complications, scalar fields are often the easiest to appreciate second quantization through. For this reason, scalar field theories are often used for purposes of introduction of novel concepts and techniques.
The signature of the metric employed below is .
Classical scalar field theory
A general reference for this section is Ramond, Pierre (2001-12-21). Field Theory: A Modern Primer (Second Edition). USA: Westview Press. , Ch 1.
Linear (free) theory
The most basic scalar field theory is the linear theory. Through the Fourier decomposition of the fields, it represents the normal modes of an infinity of coupled oscillators where the continuum limit of the oscillator index i is now denoted by . The action for the free relativistic scalar field theory is then
where is known as a Lagrangian density; for the three spatial coordinates; is the Kronecker delta function; and for the -th coordinate .
This is an example of a quadratic action, since each of the terms is quadratic in the field, . The term proportional to is sometimes known as a mass term, due to its subsequent interpretation, in the quantized version of this theory, in terms of particle mass.
The equation of motion for this theory is obtained by extremizing the action above. It takes the following form, linear in ,
where ∇2 is the Laplace operator. This is the Klein–Gordon equation, with the interpretation as a classical field equation, rather than as a quantum-mechanical wave equation.
Nonlinear (interacting) theory
The most common generalization of the linear theory above is to add a scalar potential to the Lagrangian, where typically, in addition to a mass term , the potential has higher order polynomial terms in . Such a theory is sometimes said to be interacting, because the Euler–Lagrange equation is now nonlinear, implying a self-interaction. The action for the most general such theory is
The factors in the expansion are introduced because they are useful in the Feynman diagram expansion of the quantum theory, as described below.
The corresponding Euler–Lagrange equation of motion is now
Dimensional analysis and scaling
Physical quantities in these scalar field theories may have dimensions of length, time or mass, or some combination of the three.
However, in a relativistic theory, any quantity , with dimensions of time, can be readily converted into a length, , by using the velocity of light, . Similarly, any length is equivalent to an inverse mass, , using the Planck constant, . In natural units, one thinks of a time as a length, or either time or length as an inverse mass.
In short, one can think of the dimensions of any physical quantity as defined in terms of just one independent dimension, rather than in terms of all three. This is most often termed the mass dimension of the quantity. Knowing the dimensions of each quantity, allows one to uniquely restore conventional dimensions from a natural units expression in terms of this mass dimension, by simply reinserting the requisite powers of and required for dimensional consistency.
One conceivable objection is that this theory is classical, and therefore it is not obvious how the Planck constant should be a part of the theory at all. If desired, one could indeed recast the theory without mass dimensions at all: However, this would be at the expense of slightly obscuring the connection with the quantum scalar field. Given that one has dimensions of mass, the Planck constant is thought of here as an essentially arbitrary fixed reference quantity of action (not necessarily connected to quantization), hence with dimensions appropriate to convert between mass and inverse length.
Scaling dimension
The classical scaling dimension, or mass dimension, , of describes the transformation of the field under a rescaling of coordinates:
The units of action are the same as the units of , and so the action itself has zero mass dimension. This fixes the scaling dimension of the field to be
Scale invariance
There is a specific sense in which some scalar field theories are scale-invariant. While the actions above are all constructed to have zero mass dimension, not all actions are invariant under the scaling transformation
The reason that not all actions are invariant is that one usually thinks of the parameters m and as fixed quantities, which are not rescaled under the transformation above. The condition for a scalar field theory to be scale invariant is then quite obvious: all of the parameters appearing in the action should be dimensionless quantities. In other words, a scale invariant theory is one without any fixed length scale (or equivalently, mass scale) in the theory.
For a scalar field theory with spacetime dimensions, the only dimensionless parameter satisfies = . For example, in = 4, only is classically dimensionless, and so the only classically scale-invariant scalar field theory in = 4 is the massless 4 theory.
Classical scale invariance, however, normally does not imply quantum scale invariance, because of the renormalization group involved – see the discussion of the beta function below.
Conformal invariance
A transformation
is said to be conformal if the transformation satisfies
for some function .
The conformal group contains as subgroups the isometries of the metric (the Poincaré group) and also the scaling transformations (or dilatations) considered above. In fact, the scale-invariant theories in the previous section are also conformally-invariant.
φ4 theory
Massive 4 theory illustrates a number of interesting phenomena in scalar field theory.
The Lagrangian density is
Spontaneous symmetry breaking
This Lagrangian has a symmetry under the transformation .
This is an example of an internal symmetry, in contrast to a space-time symmetry.
If is positive, the potential
has a single minimum, at the origin. The solution φ=0 is clearly invariant under the symmetry.
Conversely, if is negative, then one can readily see that the potential
has two minima. This is known as a double well potential, and the lowest energy states (known as the vacua, in quantum field theoretical language) in such a theory are invariant under the symmetry of the action (in fact it maps each of the two vacua into the other). In this case, the symmetry is said to be spontaneously broken.
Kink solutions
The 4 theory with a negative 2 also has a kink solution, which is a canonical example of a soliton. Such a solution is of the form
where is one of the spatial variables ( is taken to be independent of , and the remaining spatial variables). The solution interpolates between the two different vacua of the double well potential. It is not possible to deform the kink into a constant solution without passing through a solution of infinite energy, and for this reason the kink is said to be stable. For D>2 (i.e., theories with more than one spatial dimension), this solution is called a domain wall.
Another well-known example of a scalar field theory with kink solutions is the sine-Gordon theory.
Complex scalar field theory
In a complex scalar field theory, the scalar field takes values in the complex numbers, rather than the real numbers. The complex scalar field represents spin-0 particles and antiparticles with charge. The action considered normally takes the form
This has a U(1), equivalently O(2) symmetry, whose action on the space of fields rotates , for some real phase angle .
As for the real scalar field, spontaneous symmetry breaking is found if m2 is negative. This gives rise to Goldstone's Mexican hat potential which is a rotation of the double-well potential of a real scalar field through 2π radians about the V axis. The symmetry breaking takes place in one higher dimension, i.e., the choice of vacuum breaks a continuous U(1) symmetry instead of a discrete one. The two components of the scalar field are reconfigured as a massive mode and a massless Goldstone boson.
O(N) theory
One can express the complex scalar field theory in terms of two real fields, φ1 = Re φ and φ2 = Im φ, which transform in the vector representation of the U(1) = O(2) internal symmetry. Although such fields transform as a vector under the internal symmetry, they are still Lorentz scalars.
This can be generalised to a theory of N scalar fields transforming in the vector representation of the O(N) symmetry. The Lagrangian for an O(N)-invariant scalar field theory is typically of the form
using an appropriate O(N)-invariant inner product. The theory can also be expressed for complex vector fields, i.e. for , in which case the symmetry group is the Lie group SU(N).
Gauge-field couplings
When the scalar field theory is coupled in a gauge invariant way to the Yang–Mills action, one obtains the Ginzburg–Landau theory of superconductors. The topological solitons of that theory correspond to vortices in a superconductor; the minimum of the Mexican hat potential corresponds to the order parameter of the superconductor.
Quantum scalar field theory
A general reference for this section is Ramond, Pierre (2001-12-21). Field Theory: A Modern Primer (Second Edition). USA: Westview Press. , Ch. 4
In quantum field theory, the fields, and all observables constructed from them, are replaced by quantum operators on a Hilbert space. This Hilbert space is built on a vacuum state, and dynamics are governed by a quantum Hamiltonian, a positive-definite operator which annihilates the vacuum. A construction of a quantum scalar field theory is detailed in the canonical quantization article, which relies on canonical commutation relations among the fields. Essentially, the infinity of classical oscillators repackaged in the scalar field as its (decoupled) normal modes, above, are now quantized in the standard manner, so the respective quantum operator field describes an infinity of quantum harmonic oscillators acting on a respective Fock space.
In brief, the basic variables are the quantum field and its canonical momentum . Both these operator-valued fields are Hermitian. At spatial points , and at equal times, their canonical commutation relations are given by
while the free Hamiltonian is, similarly to above,
A spatial Fourier transform leads to momentum space fields
which resolve to annihilation and creation operators
where .
These operators satisfy the commutation relations
The state annihilated by all of the operators a is identified as the bare vacuum, and a particle with momentum is created by applying to the vacuum.
Applying all possible combinations of creation operators to the vacuum constructs the relevant Hilbert space: This construction is called Fock space. The vacuum is annihilated by the Hamiltonian
where the zero-point energy has been removed by Wick ordering. (See canonical quantization.)
Interactions can be included by adding an interaction Hamiltonian. For a φ4 theory, this corresponds to adding a Wick ordered term g:φ4:/4! to the Hamiltonian, and integrating over x. Scattering amplitudes may be calculated from this Hamiltonian in the interaction picture. These are constructed in perturbation theory by means of the Dyson series, which gives the time-ordered products, or n-particle Green's functions as described in the Dyson series article. The Green's functions may also be obtained from a generating function that is constructed as a solution to the Schwinger–Dyson equation.
Feynman path integral
The Feynman diagram expansion may be obtained also from the Feynman path integral formulation. The time ordered vacuum expectation values of polynomials in , known as the n-particle Green's functions, are constructed by integrating over all possible fields, normalized by the vacuum expectation value with no external fields,
All of these Green's functions may be obtained by expanding the exponential in J(x)φ(x) in the generating function
A Wick rotation may be applied to make time imaginary. Changing the signature to (++++) then turns the Feynman integral into a statistical mechanics partition function in Euclidean space,
Normally, this is applied to the scattering of particles with fixed momenta, in which case, a Fourier transform is useful, giving instead
where is the Dirac delta function.
The standard trick to evaluate this functional integral is to write it as a product of exponential factors, schematically,
The second two exponential factors can be expanded as power series, and the combinatorics of this expansion can be represented graphically through Feynman diagrams of the Quartic interaction.
The integral with g = 0 can be treated as a product of infinitely many elementary Gaussian integrals: the result may be expressed as a sum of Feynman diagrams, calculated using the following Feynman rules:
Each field (p) in the n-point Euclidean Green's function is represented by an external line (half-edge) in the graph, and associated with momentum p.
Each vertex is represented by a factor −g.
At a given order gk, all diagrams with n external lines and vertices are constructed such that the momenta flowing into each vertex is zero. Each internal line is represented by a propagator 1/(q2 + m2), where is the momentum flowing through that line.
Any unconstrained momenta are integrated over all values.
The result is divided by a symmetry factor, which is the number of ways the lines and vertices of the graph can be rearranged without changing its connectivity.
Do not include graphs containing "vacuum bubbles", connected subgraphs with no external lines.
The last rule takes into account the effect of dividing by [0]. The Minkowski-space Feynman rules are similar, except that each vertex is represented by −ig, while each internal line is represented by a propagator i/(q2−m2+iε), where the term represents the small Wick rotation needed to make the Minkowski-space Gaussian integral converge.
Renormalization
The integrals over unconstrained momenta, called "loop integrals", in the Feynman graphs typically diverge. This is normally handled by renormalization, which is a procedure of adding divergent counter-terms to the Lagrangian in such a way that the diagrams constructed from the original Lagrangian and counter-terms is finite. A renormalization scale must be introduced in the process, and the coupling constant and mass become dependent upon it.
The dependence of a coupling constant on the scale is encoded by a beta function, , defined by
This dependence on the energy scale is known as "the running of the coupling parameter", and theory of this systematic scale-dependence in quantum field theory is described by the renormalization group.
Beta-functions are usually computed in an approximation scheme, most commonly perturbation theory, where one assumes that the coupling constant is small. One can then make an expansion in powers of the coupling parameters and truncate the higher-order terms (also known as higher loop contributions, due to the number of loops in the corresponding Feynman graphs).
The -function at one loop (the first perturbative contribution) for the 4 theory is
The fact that the sign in front of the lowest-order term is positive suggests that the coupling constant increases with energy. If this behavior persisted at large couplings, this would indicate the presence of a Landau pole at finite energy, arising from quantum triviality. However, the question can only be answered non-perturbatively, since it involves strong coupling.
A quantum field theory is said to be trivial when the renormalized coupling, computed through its beta function, goes to zero when the ultraviolet cutoff is removed. Consequently, the propagator becomes that of a free particle and the field is no longer interacting.
For a 4 interaction, Michael Aizenman proved that the theory is indeed trivial, for space-time dimension ≥ 5.
For = 4, the triviality has yet to be proven rigorously, but lattice computations have provided strong evidence for this. This fact is important as quantum triviality can be used to bound or even predict parameters such as the Higgs boson mass. This can also lead to a predictable Higgs mass in asymptotic safety scenarios.
| Physical sciences | Particle physics: General | Physics |
3823804 | https://en.wikipedia.org/wiki/Ring%20flip | Ring flip | In organic chemistry, a ring flip (also known as a ring inversion or ring reversal) is the interconversion of cyclic conformers that have equivalent ring shapes (e.g., from a chair conformer to another chair conformer) that results in the exchange of nonequivalent substituent positions. The overall process generally takes place over several steps, involving coupled rotations about several of the molecule's single bonds, in conjunction with minor deformations of bond angles. Most commonly, the term is used to refer to the interconversion of the two chair conformers of cyclohexane derivatives, which is specifically referred to as a chair flip, although other cycloalkanes and inorganic rings undergo similar processes.
Chair flip
As stated above, a chair flip is a ring inversion specifically of cyclohexane (and its derivatives) from one chair conformer to another, often to reduce steric strain. The term, "flip" is misleading, because the direction of each carbon remains the same; what changes is the orientation. A conformation is a unique structural arrangement of atoms, in particular one achieved through the rotation of single bonds. A conformer is a conformational isomer, a blend of the two words.
Cyclohexane
There exist many different conformations for cyclohexane, such as chair, boat, and twist-boat, but the chair conformation is the most commonly observed state for cyclohexanes because it requires the least amount of energy. The chair conformation minimizes both angle strain and torsional strain by having all carbon-carbon bonds at 110.9° and all hydrogens staggered from one another.
The molecular motions involved in a chair flip are detailed in the figure on the right: The half-chair conformation (D, 10.8 kcal/mol, C2 symmetry) is the energy maximum when proceeding from the chair conformer (A, 0 kcal/mol reference, D3d symmetry) to the higher energy twist-boat conformer (B, 5.5 kcal/mol, D2 symmetry). The boat conformation (C, 6.9 kcal/mol, C2v symmetry) is a local energy maximum for the interconversion of the two mirror image twist-boat conformers, the second of which is converted to the other chair confirmation through another half-chair. At the end of the process, all axial positions have become equatorial and vice versa. The overall barrier of 10.8 kcal/mol corresponds to a rate constant of about 105 s–1 at room temperature.
Note that the twist-boat (D2) conformer and the half-chair (C2) transition state are in chiral point groups and are therefore chiral molecules. In the figure, the two depictions of B and two depictions of D are pairs of enantiomers.
As a consequence of the chair flip, the axially-substituted and equatorially-substituted conformers of a molecule like chlorocyclohexane cannot be isolated at room temperature. However, in some cases, the isolation of individual conformers of substituted cyclohexane derivatives has been achieved at low temperatures (–150 °C).
Axial and equatorial positions
As noted above, by transitioning from one chair conformer to another, all axial positions become equatorial and all equatorial positions become axial. Substituent groups in equatorial positions roughly follow along the equator of the cyclohexane ring and are perpendicular to the axis, while substituents in axial positions roughly follow the imaginary axis of the carbon ring and are perpendicular to the equator.
Diaxial interactions or axial-axial interactions is what the steric strain between an axial substituent and another axial group, typically a hydrogen, on the same side of a chair conformation ring. The interaction is labeled by the carbon number they come from. A 1,3-diaxial interaction happens between the atoms connected to the first and third carbons. The more interactions the more strain on the molecule and the conformations with the most strain are less likely to be seen. An example is cyclopropane which, because of its planar geometry, has six fully eclipsed carbon and axial hydrogen bonds making the strain 116 kJ/mol (27.7 kcal/mol). Strain can also be decreased when the carbon-carbon bond angles are close or at the preferred bond angle of 109.5°, meaning a ring having six tetrahedral carbons is typically lower than that of most rings.
Examples
Cyclohexane is a prototype for low-energy degenerate ring flipping. Two 1H NMR signals should be observed in principle, corresponding to axial and equatorial protons. However, due to the cyclohexane chair flip, only one signal is seen for a solution of cyclohexane at room temperature, as the axial and equatorial proton rapidly interconvert relative to the NMR time scale. The coalescence temperature at 60 MHz is ca. –60 °C. As a consequence of the chair flip, the axially-substituted and equatorially-substituted conformers of a molecule like chlorocyclohexane cannot be isolated at room temperature.
However, in some cases, the isolation of individual conformers of substituted cyclohexane derivatives has been achieved at low temperatures (–150 °C).
Most compounds with nonplanar rings engage in degenerate ring flipping. One well-studied example is titanocene pentasulfide, where the inversion barrier is high relative to cyclohexane's. Hexamethylcyclotrisiloxane on the other hand is subject to a very low barrier.
Bicycloalkanes are alkanes containing two rings that are connected to each other by sharing two carbon atoms. Orientation within bicycloalkanes is dependent on the cis or trans orientation of the hydrogen shared by the different rings instead of the methyl groups present in the rings.
Tetrodotoxin is one of the world's most potent toxins. It is made up of multiple six member rings set in chair conformations, with each ring but one containing an atom other than carbon.
| Physical sciences | Stereochemistry | Chemistry |
27653365 | https://en.wikipedia.org/wiki/Subfossil%20lemur | Subfossil lemur | Subfossil lemurs are lemurs from Madagascar that are represented by recent (subfossil) remains dating from nearly 26,000 years ago to approximately 560 years ago (from the late Pleistocene until the Holocene). They include both extant and extinct species, although the term more frequently refers to the extinct giant lemurs. The diversity of subfossil lemur communities was greater than that of present-day lemur communities, ranging to as high as 20 or more species per location, compared with 10 to 12 species today. Extinct species are estimated to have ranged in size from slightly over to roughly . Even the subfossil remains of living species are larger and more robust than the skeletal remains of modern specimens. The subfossil sites found around most of the island demonstrate that most giant lemurs had wide distributions and that ranges of living species have contracted significantly since the arrival of humans.
Despite their size, the giant lemurs shared many features with living lemurs, including rapid development, poor day vision, relatively small brains, and female-dominated hierarchies. They also had many distinct traits among lemurs, including a tendency to rely on terrestrial locomotion, slow climbing, and suspension instead of leaping, as well as a greater dependence on leaf-eating and seed predation. The giant lemurs likely filled ecological niches now left vacant, particularly seed dispersal for plants with large seeds. There were three distinct families of giant lemur, including the Palaeopropithecidae (sloth lemurs), Megaladapidae (koala lemurs), and Archaeolemuridae (monkey lemurs). Two other types were more closely related and similar in appearance to living lemurs: the giant aye-aye and Pachylemur, a genus of "giant ruffed lemurs".
Subfossil remains were first discovered on Madagascar in the 1860s, but giant lemur species were not formally described until the 1890s. The paleontological interest sparked by the initial discoveries resulted in an overabundance of new species names, the allocation of bones to the wrong species, and inaccurate reconstructions during the early 20th century. Discoveries waned during the mid-20th century; paleontological work resumed in the 1980s and resulted in the discovery of new species and a new genus. Research has recently focused on diets, lifestyle, social behavior, and other aspects of biology. The remains of the subfossil lemurs are relatively recent, with all or most species dating within the last 2,000 years. Humans first arrived on Madagascar around that time and hunting likely played a role in the rapid decline of the lemurs and the other megafauna that once existed on the large island. Additional factors are thought to have contributed to their ultimate disappearance. Oral traditions and recent reports of sightings by Malagasy villagers have been interpreted by some as suggesting either lingering populations or very recent extinctions.
Diversity
Extinct giant lemurs
Until recently, giant lemurs existed in Madagascar. Although they are only represented by subfossil remains, they were modern forms, having adaptations unlike those seen in lemurs today, and are counted as part of the rich lemur diversity that has evolved in isolation for up to 60 million years. All 17 extinct lemurs were larger than the extant forms, including the largest living lemurs, the indri (Indri indri) and diademed sifaka (Propithecus diadema), which weigh up to . The estimated weights for the subfossil lemurs have varied. Techniques used for these weight estimations include the comparison of skull lengths, tooth size, the head diameter of the femur, and more recently, the area of cortical bone (hard bone) in long bones (such as the humerus). Despite the variations in the size estimates for some species, all subfossil lemurs were larger than living species, weighing or more, and one species may have weighed as much as .
All but one species, the giant aye-aye, are thought to have been active during the day. Not only were they unlike the living lemurs in both size and appearance, they also filled ecological niches that no longer exist or are now left unoccupied. Their remains have been found in most parts of the island, except for the eastern rainforests and the Sambirano domain (seasonal moist forests in the northwest of the island), where no subfossil sites are known. Radiocarbon dates for subfossil lemur remains range from approximately 26,000 years BP (for Megaladapis in northern Madagascar at the Ankarana Massif) to around 500 years BP (for Palaeopropithecus in the southwest).
Characteristics
All of the extinct subfossil lemurs, including the smallest species (Pachylemur, Mesopropithecus, and the giant aye-aye), were larger than the lemur species alive today. The largest species were among the largest primates ever to have evolved. Due to their larger size, the extinct subfossil lemurs have been compared to large-bodied anthropoids (monkeys and apes), yet they more closely resemble the small-bodied lemurs. Like other lemurs, the subfossil lemurs did not exhibit appreciable differences in body or canine tooth size between males and females (sexual dimorphism). This suggests that they, too, exhibited female social dominance, possibly exhibiting the same levels of agonism (aggressive competition) seen in extant lemurs. Like other lemurs, they had smaller brains than comparably sized anthropoids. Most species also had a unique strepsirrhine dental trait, called a toothcomb, which is used for grooming. Even tooth development and weaning was rapid compared to similarly sized anthropoids, suggesting faster sexual maturity of their offspring. Most subfossil lemurs also had high retinal summation (sensitivity to low light), resulting in poor day vision (low visual acuity) compared to anthropoids. This has been demonstrated by the ratio between their relatively small orbits (eye sockets) and the relative size of their optic canal, which is comparable to that of other lemurs, not diurnal anthropoids.
These traits are shared among both living and extinct lemurs, but are uncommon among primates in general. Two prevailing hypotheses to explain these unique adaptations are the energy frugality hypothesis by Patricia Wright (1999) and the evolutionary disequilibrium hypothesis by Carel van Schaik and Peter M. Kappeler (1996). The energy frugality hypothesis expanded on Alison Jolly's energy conservation hypotheses by claiming that most lemur traits not only help conserve energy, but also maximize the use of highly limited resources, enabling them to live in severely seasonal environments with low productivity. The evolutionary disequilibrium hypothesis postulated that living lemurs are in the process of evolving to fill open ecological niches left by the recently extinct subfossil lemurs. For example, small nocturnal prosimians are typically nocturnal and monogamous, while the larger living lemurs are generally active both day and night (cathemeral) and live in small groups (gregarious). Cathemerality and increased gregariousness might indicate that the larger living lemurs are evolving to fill the role of the giant lemurs, which were thought to be diurnal (day-living) and more monkey-like in behavior. Since most giant subfossil lemurs have been shown to share many of the unique traits of their living counterparts, and not those of monkeys, Godfrey et al. (2003) argued that the energy frugality hypothesis seems to best explain both living and extinct lemur adaptations.
Despite the similarities, subfossil lemurs had several distinct differences from their lemur relatives. In addition to being larger, the subfossil lemurs were more dependent on leaves and seeds in their diet, rather than fruit. They utilized slow climbing, hanging, and terrestrial quadrupedalism for locomotion, rather than vertical clinging and leaping and arboreal quadrupedalism. Also, all but one of them—the giant aye-aye—are assumed to have been diurnal (due to their body size and small orbits), whereas many small lemurs are nocturnal and medium-sized are cathemeral.
Their skeletons suggest that most subfossil lemurs were tree-dwellers, adapted for living in forests and possibly limited to such habitats. Unlike some of the living species, the subfossil lemurs lacked adaptations for leaping. Instead, suspension, used by some indriids and ruffed lemurs, was extensively used in some lineages. Living lemurs are known to visit the ground to varying extents, but only the extinct archaeolemurids exhibit adaptations for semiterrestrial locomotion. Due to the size of the extinct subfossil lemurs, all were likely to travel on the ground between trees. They had shorter, more robust limbs, heavily built axial skeletons (trunks), and large heads and are thought to have shared the common lemur trait of low basal metabolic rates, making them slow-moving. Studies of their semicircular canals confirm this assumption, showing that koala lemurs moved slower than orangutans, monkey lemurs were less agile than Old World monkeys, and sloth lemurs exhibited slow movements like those of lorises and sloths.
Types
Sloth lemurs
The sloth lemurs (family Palaeopropithecidae) were the most species-rich group of the subfossil lemurs, with four genera and eight species. The common name is due to strong similarities in morphology with arboreal sloths, or in the case of Archaeoindris, with giant ground sloths. They ranged in size from some of the smallest of the subfossil lemurs, such as Mesopropithecus, weighing as little as , to the largest, Archaeoindris, weighing approximately . Their characteristic curved finger and toe bones (phalanges) suggest slow suspensory movement, similar to that of an orangutan or a loris, making them some of the most specialized mammals for suspension. Their day vision was very poor, and they had relatively small brains and short tails. Their diet consisted mostly of leaves, seeds, and fruit; dental wear analysis suggests they were primarily folivorous seed-predators.
Koala lemurs
The koala lemurs of the family Megaladapidae most closely resemble marsupial koalas from Australia. According to genetic evidence they were most closely related to the family Lemuridae, although for many years they were paired with the sportive lemurs of the family Lepilemuridae due to similarities in their skulls and molar teeth. They were slow climbers and had long forelimbs and powerful grasping feet, possibly using them for suspension. Koala lemurs ranged in size from an estimated ,. They had poor day vision, short tails, lacked permanent upper incisors, and had a reduced toothcomb. Their diet generally consisted of leaves, with some species being specialized folivores and others having a broader diet, possibly including tough seeds.
Monkey lemurs
Monkey lemurs, or baboon lemurs, share similarities with macaques; they have also been compared to baboons. Members of the family Archaeolemuridae, they were the most terrestrial of the lemurs, with short, robust forelimbs and relatively flat digits. They spent time on the ground, and were semi-terrestrial, spending time in trees to feed and sleep. They were heavy-bodied and ranged in size from approximately . They had relatively good day vision and large brains compared with other lemurs. Their robust jaws and specialized teeth suggest a diet of hard objects, such as nuts and seeds, yet other evidence, including fecal pellets, suggests they may have had a more varied diet, including leaves, fruit, and animal matter (omnivory). Dental wear analysis has shed some light on this dietary mystery, suggesting that monkey lemurs had a more eclectic diet, while using tough seeds as a fall-back food item. Within the family, the genus Archaeolemur was the most widespread in distribution, resulting in hundreds of subfossil specimens, and may have been one of the last subfossil lemurs to die out.
Giant aye-aye
An extinct, giant relative of the living aye-aye, the giant aye-aye shared at least two of the aye-aye's bizarre traits: ever-growing central incisors and an elongated, skinny middle finger. These shared features suggest a similar lifestyle and diet, focused on percussive foraging (tapping with the skinny digit and listening for reverberation from hollow spots) of defended resources, such as hard nuts and invertebrate larvae concealed inside decaying wood. Weighing as much as , it was between two-and-half and five times the size of living aye-aye. Alive when humans came to Madagascar, its teeth were collected and drilled to make necklaces.
Pachylemur
The only extinct member of the family Lemuridae, the genus Pachylemur contains two species that closely resembled living ruffed lemurs. Sometimes referred to as "giant ruffed lemurs", they were approximately three times larger than ruffed lemurs, weighing between . Despite their size, they were arboreal quadrupeds, possibly utilizing more suspensory behavior and cautious climbing than their sister taxon. Their skull and teeth were similar to those of ruffed lemurs, suggesting a diet high in fruit and possibly some leaves. The rest of its skeleton (postcrania) was much more robust and their vertebrae had distinctly different features.
Phylogeny
Determining the phylogeny of subfossil lemurs has been problematic because studies of morphology, developmental biology, and molecular phylogenetics have sometimes yielded conflicting results. All studies agree that the family Daubentoniidae (including the giant aye-aye) diverged first from the other lemurs at least 60 million years ago. The relationship between the remaining families has been less clear. Morphological, developmental, and molecular studies have offered support for lumping the four sloth lemur genera of the family Palaeopropithecidae with the family Indriidae (including the indri, sifakas, and woolly lemurs). The placement of family Megaladapidae has been more controversial, with similarities in teeth and skull features suggesting a close relationship with family Lepilemuridae (sportive lemurs). Molecular data, instead, indicate a closer relationship to family Lemuridae. Likewise, a relationship between family Archaeolemuridae and family Lemuridae has been suggested, based on morphological and developmental traits, yet molar morphology, the number of teeth in the specialized toothcomb, and molecular analysis support a closer relationship with the indriid–sloth lemur clade. Other subfossil lemurs, including the giant aye-aye and Pachylemur, are more easily placed due to strong similarities with existing lemurs (the aye-aye and ruffed lemurs, respectively).
Living species
Subfossil sites in Madagascar have yielded the remains of more than just extinct lemurs. Extant lemur remains have also been found, and radiocarbon dating has demonstrated that both types of lemur lived at the same time. In some cases living species are locally extinct for the area in which their subfossil remains were found. Because subfossil sites are found across most of the island, with the most notable exception being the eastern rainforest, both paleocommunity composition and paleodistributions can be determined. Geographic ranges have contracted for numerous species, including the indri, greater bamboo lemur, and ruffed lemurs. For instance, subfossil remains of the indri have been found in marsh deposits near Ampasambazimba in the Central Highlands and in other deposits in both central and northern Madagascar, demonstrating a much larger range than the small region on the east coast that it currently occupies. Even the greater bamboo lemur, a critically endangered species restricted to a small portion of the south-central eastern rainforest, has undergone significant range contraction since the mid-Holocene, with subfossil remains from Ankarana Massif in the far north of Madagascar dating to 2565 BCE ± 70 years. Combined with finds from other subfossil sites, data suggests that it used to range across the northern, northwestern, central, and eastern parts of the island. It is unclear whether these locations were wetter in the past or whether distinct subpopulations or subspecies occupied the drier forests, much like modern diversity of sifakas.
In addition to previously having expanded geographic ranges, extant subfossil lemurs exhibited significant variation in size. Researchers have noted that subfossil bones of living species are more robust and generally larger than their present-day counterparts. The relative size of living species may be related to regional ecological factors, such as resource seasonality, a trend that is still observable today, where individuals from the spiny forests are, on average, smaller than individuals from the southwestern succulent woodlands or the dry deciduous forests.
Ecology
As a group, the lemurs of Madagascar are extremely diverse, having evolved in isolation and radiated over the past 40 to 60 million years to fill many ecological niches normally occupied by other primates. In the recent past, their diversity was significantly greater, with 17 extinct species sharing body proportions and specializations with lorises and various non-primates, such as tree sloths, giant ground sloths, koalas, and striped possums (genus Dactylopsila). The diversity of lemur communities today can be as high as 10 to 12 species per region; communities of 20 or more lemur species existed as recently as 1,000 years ago in areas that now have no lemurs at all. Just like living species, many of the extinct species shared overlapping ranges with closely related species (sympatry) through niche differentiation (resource partitioning). Among all the late Quaternary assemblages of megafauna, only Madagascar was dominated by large primates.
Although anatomical evidence suggests that even the large, extinct species were adapted to tree-climbing, some habitats, including gallery forests and the spiny forests of southern Madagascar, in which they occurred would not have allowed them to be strictly arboreal. Even today, most lemur species will visit the ground to cross open areas, suggesting that the extinct species did the same. Monkey lemurs (family Archaeolemuridae), including Archaeolemur majori and Hadropithecus stenognathus, have been reconstructed as being primarily terrestrial. In contrast, the sloth lemurs (family Palaeopropithecidae) were highly arboreal despite the large size of some species.
Species of both extinct and living (extant) lemur vary in size based on habitat conditions, despite their differences in niche preference. Within related groups, larger species tend to inhabit wetter, more productive habitats, while smaller sister taxa are found in drier, less productive habitats. This pattern suggests that populations of both living and extinct lemur species had become geographically isolated by differences in habitat and evolved in isolation due to varying primary production within different ecosystems. Thermoregulation may also have played a role in the evolution of their increased body size. Yet despite this pressure to specialize and differentiate, some of the extinct subfossil lemurs, such as Archaeolemur, may have had island-wide distributions during the Holocene, unlike the living lemurs. If this is the case, it may suggest that some larger lemurs might have been more tolerant to regional differences in ecology than living lemurs.
Diet
Research on subfossil lemur diets, particularly in southern and southwestern Madagascar, has indicated that ecological communities have been significantly affected by their recent extinction. Many extinct subfossil lemurs were large-bodied leaf-eaters (folivores), seed predators, or both. Today, leaf-eating along with seed predation is only seen in mid-sized lemurs, and is far less common than it was in the past. Strict folivory is also less common, now found primarily in small lemurs. In certain cases, subfossil lemurs, such as the sloth lemurs and koala lemurs, may have used leaves as an important fallback food, whereas other species, such as the monkey lemurs and the giant aye-aye, specialized on structurally defended resources, such as hard seeds and wood-boring insect larvae. Last, Pachylemur was primarily a fruit eater (frugivorous). Subfossil lemur diets have been reconstructed using analytical tools, including techniques to compare tooth anatomy, structure, and wear; biogeochemistry (analysis of isotope levels, like carbon-13); and the dissection of fecal pellets associated with subfossil remains.
The diets of most subfossil lemurs, most notably Palaeopropithecus and Megaladapis, consisted primarily of C3 plants, which use a form of photosynthesis that results in higher water loss through transpiration. Other subfossil lemurs, such as Hadropithecus and Mesopropithecus, fed on CAM and C4 plants, which use more water-efficient forms of photosynthesis. Fruit and animal matter was more common in the diets of subfossil lemurs including Pachylemur, Archaeolemur, and the giant aye-aye. In southern and southwestern Madagascar, the subfossil lemurs of the spiny forests generally favored the C3 plants over the more abundant CAM plants, although closely related sympatric species may have fed upon the two types of plants in different ratios, allowing each to divide resources and coexist. Since plants produce defenses against leaf-eating animals, the extensive use of spines by plants in the spiny forests suggest that they evolved to cope with leaf-eating lemurs, large and small.
Seed dispersal
Giant subfossil lemurs are thought to have also played a significant role in seed dispersal, possibly targeting species that did not attract the seed dispersal services of the extinct elephant birds. Biogeochemistry studies have shown that they may have been the primary seed dispersers for the endemic and native C3 trees in the spiny forests. Terrestrial species may have dispersed seeds for small bushes as well as tall trees. Seed dispersal can involve passing seeds through the gut (endozoochory) or attaching the seeds to the animal's body (epizoochory), and both processes probably occurred with subfossil lemurs. Seeds from Uncarina species embed themselves in lemur fur, and likely did the same with subfossil lemurs. Seed dispersal biology is known for very few species in the spiny forest, including genera of plants suspected of depending on giant lemurs, such as Adansonia, Cedrelopsis, Commiphora, Delonix, Diospyros, Grewia, Pachypodium, Salvadora, Strychnos, and Tamarindus. For example, Delonix has edible pods that are rich in protein, and Adansonia fruits have a nutritious pulp and large seeds that may have been dispersed by Archaeolemur majori or Pachylemur insignis.
Seed size may be a limiting factor for some plant species, since their seeds are too large for living (extant) lemurs. The common brown lemur (Eulemur fulvus) can swallow seeds in diameter, while the black-and-white ruffed lemur (Varecia variegata) is capable of swallowing seeds up to in diameter. A large lemur, such as Pachylemur, which was more than twice the size of today's ruffed lemurs, could probably swallow even larger seeds. Seed dispersal limitations tied to megafaunal extinction are exhibited by Commiphora guillaminii. At present, this tree species has a short dispersal distance, but its genetics indicate higher levels of regional gene flow in the past, based on comparisons with a closely related species in Africa whose seeds are still dispersed by large animals.
Discovery and research
The writings of French colonial governor Étienne de Flacourt in the mid-17th century introduced the existence of giant Malagasy mammals to Western science with recorded eye-witness accounts from the local people of dangerous animals, hornless "water cows", and a large lemur-like creature referred to locally as the or . Today, the latter is thought to have been a species of Palaeopropithecus or possibly Megaladapis. Flacourt described it as:
Local tales of a (Malagasy for 'cow that is not a cow'), or pygmy hippopotamus, led French naturalist Alfred Grandidier to follow a village headman to a marsh in southwestern Madagascar, a site called Ambolisatra, which became the first known subfossil site in Madagascar. In 1868, Grandidier uncovered the first subfossil remains of lemurs—a humerus from Palaeopropithecus and a tibia of a sifaka. The Palaeopropithecus remains were not described for several decades, and it took decades more for the remains to be correctly paired with other sloth lemur remains. It was not until 1893 that giant lemur species were formally described, when Charles Immanuel Forsyth Major discovered and described a long, narrow skull of Megaladapis madagascariensis in a marsh. His discoveries in various marshes of central and southwestern Madagascar sparked paleontological interest, resulting in an overabundance of taxonomic names and confused assemblages of bones from numerous species, including non-primates. Specimens were distributed between European museums and Madagascar, often resulting in the loss of field data that went with the specimens, if the data had been recorded at all.
In 1905, Alfred Grandidier's son, Guillaume Grandidier, reviewed subfossil lemur taxonomy and determined that too many names had been created. His review established most of the presently known family and genera names for the extinct lemurs. Despite the taxonomic clarification, subfossil postcrania from different genera, particularly Megaladapis, Palaeopropithecus and Hadropithecus, continued to be incorrectly paired and sometimes assigned to non-primates. Since subfossil remains were often dredged from marshes one by one, pairing skulls with other bones was often guesswork based on size-matching, and was not very accurate as a consequence. Even as late as the 1950s, bones of non-primates were attributed to subfossil lemurs. One reconstruction of the confounded subfossil remains by paleontologist Herbert F. Standing depicted Palaeopropithecus as an aquatic animal that swam near the surface, keeping its eyes, ears, and nostrils slightly above water. Postcranial remains of Palaeopropithecus had previously been paired with Megaladapis by Guillaume Grandidier, who viewed it as a giant tree sloth, which he named Bradytherium. Standing's aquatic theory was supported by Italian paleontologist Giuseppe Sera, who reconstructed Palaeopropithecus as an "arboreal-aquatic acrobat" that not only swam in water but climbed trees and dove from there into the water. Sera took the aquatic theory further in 1938 by including other extinct lemurs, including Megaladapis, which he viewed as a thin ray-like swimmer that fed on mollusks and crustaceans while concealed underwater. It was primarily the paleontologist Charles Lamberton who correctly paired many of the confused subfossils, although others had also helped address problems of association and taxonomic synonyms. Lamberton also refuted Guillaume Grandidier's sloth theory for Megaladapis, as well as the aquatic lemur theory of Standing and Sera.
Excavations during the early 20th century by researchers like Lamberton failed to unearth any new extinct lemur genera. Fourteen of the approximately seventeen known species had previously been identified from field work in southern, western, and central Madagascar. When paleontological field work resumed in the early 1980s, new finds provided associated skeletal remains, including rare bones such as carpal bones (wrist bones), phalanges (finger and toe bones), and bacula (penile bone). In some cases, nearly complete hands and feet were found. Enough remains have been found for some groups to demonstrate the physical development of juveniles. Standard long-bone indices have been calculated in order to determine the intermembral index (a ratio that compares limb proportions), and body mass estimates have been made based on long-bone circumference measurements. Even preserved fecal pellets from Archaeolemur have been found, allowing researchers to learn about its diet. More recently, electron microscopy has allowed researchers to study behavioral patterns, and DNA amplification has helped with genetic tests that determine the phylogenetic relationships between the extinct and living lemurs.
A new genus of sloth lemur, Babakotia, was discovered in 1986 by a team led by Elwyn L. Simons of Duke University in karst caves on the Ankarana Massif in northern Madagascar. Along with Babakotia, a new species of Mesopropithecus, M. dolichobrachion, was also discovered, but not formally described until 1995. The same team has also helped promote new ideas about sloth lemur adaptations and the relationships among the four genera. They have also provided evidence that living species, such as the indri and the greater bamboo lemur, have lost much of their original range. In 2009, a new species of large sloth lemur, called Palaeopropithecus kelyus, was described from northwestern Madagascar by a Franco-Madagascan team. The new species was found to be smaller than the two previously known species from the genus, and its diet reportedly consisted of more hard-textured food. The resurgence in subfossil lemur work has also sparked new interest in Madagascar's small mammals, which have also been found at the subfossil sites. This has led to new ideas about the origins, diversity, and distribution of these animals.
The number of Malagasy subfossil sites containing subfossil lemurs has increased significantly since the mid-20th century. At that time, subfossil lemurs had only been found in the center, south, and southwest of the island. Since then, only the eastern rainforests have not been represented, and paleodistributions are now known for both extinct and living species around most of the island. Large quantities of subfossil lemur remains have been found in caves, marshes, and streambank sites in drier regions. The subfossil sites are clustered together geographically and are recent in age, mostly dating between 2,500 and 1,000 years old, with a few spanning back into the last glaciation, which ended 10,000 years ago.
Extinction
At least 17 species of giant subfossil lemur vanished during the Holocene, with all or most extinctions happening after the colonization of Madagascar by humans around 2,000 years ago. Madagascar's megafauna included not only giant lemurs, but also elephant birds, giant tortoises, several species of Malagasy hippopotamuses, Cryptoprocta spelea (a "giant fossa"), large crocodiles (Voay robustus), and Plesiorycteropus, a unique digging mammal, all of which died out during the same period. Madagascar's megafaunal extinctions were among the most severe for any continent or large island, with all endemic wildlife over disappearing, totaling approximately 25 species. The most severely impacted lemurs were generally large and diurnal, particularly the clade containing the living indriids and extinct sloth lemurs. Although only the indriids are alive today and represent only a small percentage of the living lemur species, this clade collectively contained the majority of the extinct giant lemur species.
By region, the Central Highlands lost the greatest number of lemur species. It has lost nearly all of its woodland habitat, but some lemur species still survive in isolated forest patches. Lemur diversity is tightly linked with plant diversity, which in turn decreases with increased forest fragmentation. In extreme cases, treeless sites such as the town of Ampasambazimba from the central region no longer support any of the lemur species represented in their subfossil record. Other locations no longer have giant subfossil lemurs, yet they still maintain forested habitat that could support them. Even though the giant lemurs have disappeared from these locations, while the smaller species survive in the forest patches that remain, the subfossil remains indicate that the living species used to be more widespread and coexisted with the extinct species. The Central Highlands saw the greatest species loss, but was not the only region or habitat type to witness extinctions. The least-understood region is the eastern rainforests, which have not yielded subfossil lemur remains. Consequently, it is impossible to know what percentage of lemur taxa were recently lost there; studies of Malagasy customs (ethnohistory) along with archaeological evidence suggests the eastern rainforests were more ecologically disturbed in the past than they are today. Hunting and trapping by humans may have severely impacted large lemurs in this region as well.
Comparisons of species counts from subfossil deposits and remnant populations in neighboring Special Reserves has further demonstrated decreased diversity in lemur communities and contracted geographic ranges. At Ampasambazimba in central Madagascar, 20 species of subfossil lemur have been found. At nearby Ambohitantely Reserve, only 20% of those species still survive. Only six of 13 species found at Ankilitelo and Ankomaka Caves in the southwest still survive at Beza Mahafaly Reserve. In the extreme north, the caves of Ankarana have yielded 19 species, yet only nine remain in the surrounding forests. In the northwest, 10 or 11 subfossil species have been found at Anjohibe, whereas only six species remain at nearby Ankarafantsika National Park.
As with the extinctions that occurred on other land masses during the late Pleistocene and Holocene (known as the Quaternary extinction event), the disappearance of Madagascar's megafauna is tightly linked with the arrival of humans, with nearly all extinctions dating to around the same time of the earliest evidence of human activity on the island or significantly later. The exact date of human arrival is unknown; a radius (arm bone) of a Palaeopropithecus ingens with distinct cut marks from the removal of flesh with sharp objects dates to 2325 ± 43 BP (2366–2315 cal yr BP). Based on this evidence from Taolambiby in the southwest interior, as well as other dates for human-modified dwarf hippo bones and introduced plant pollen from other parts of the island, the arrival of humans is conservatively estimated at 350 BCE. Measurements of stratigraphic charcoal and the appearance of exotic plant pollen dated from Holocene core samples confirm these approximated dates for human arrival in the southwestern corner of the island and further suggest that the central and northern parts of the island did not experience significant human impact until 700 to 1,500 years later. The humid forests of the lower interior of the island were the last to be settled (as shown by the presence of charcoal particles), possibly due to the prevalence of human diseases, such as plague, malaria, and dysentery. The entire island was not fully colonized by humans until the beginning of the second millennium CE.
The extinction of Madagascar's megafauna, including the giant lemurs, was one of the most recent in history, with large lemur species like Palaeopropithecus ingens surviving until approximately 500 years ago and one bone of the extinct Hippopotamus laloumena radiocarbon dated to about 100 years BP. An even wider extinction window for the subfossil lemurs, ranging up until the 20th century, may be possible if reports of unidentified animals are true. As recently as the early 17th century, dwindling populations of subfossil lemurs may have persisted in coastal regions where tree-cutting and uncontrolled fires had less of an impact. By that date, the Central Highlands' forests were mostly gone, with the exception of scattered forest fragments and strips. Along the northwest coast, forms such as Archaeolemur may have survived for more than a millennium after the arrival of humans. This is supported by radiocarbon dates for Archaeolemur from the Ankarana Massif dating to 975 ± 50 CE as well as archaeological data that show there was little human activity in the area until a few centuries ago, with low human population density along the northwest coast until nearly 1500 CE.
Hypotheses
In the 20th century, six hypotheses for explaining the extinction of the giant subfossil lemurs have been proposed and tested. They are known as the "Great Fire", "Great Drought", "Blitzkrieg", "Biological Invasion", "Hypervirulent Disease", and "Synergy" hypotheses. The first was proposed in 1927 when Henri Humbert and other botanists working in Madagascar suspected that human-introduced fire and uncontrolled burning intended to create pasture and fields for crops transformed the habitats quickly across the island. In 1972, Mahé and Sourdat proposed that the arid south had become progressively drier, slowly killing off lemur fauna as the climate changed. Paul S. Martin applied his overkill hypothesis or "blitzkrieg" model to explain the loss of the Malagasy megafauna in 1984, predicting a rapid die-off as humans spread in a wave across the island, hunting the large species to extinction. That same year, Robert Dewar speculated that introduced livestock outcompeted the endemic wildlife in a moderately fast series of multiple waves across the island. In 1997, MacPhee and Marx speculated that a rapid spread of hypervirulent disease might explain the die-offs that occurred after the appearance of humans worldwide, including Madagascar. Finally, in 1999, David Burney proposed that the complete set of human impacts worked together, in some cases along with natural climate change, and very slowly (i.e., on a time scale of centuries to millennia) brought about the demise of the giant subfossil lemurs and other recently extinct endemic wildlife.
Since all extinct lemurs were larger than the ones that currently survive, and the remaining large forests still support large populations of smaller lemurs, large size appears to have conveyed some distinct disadvantages. Large-bodied animals require larger habitats in order to maintain viable populations, and are most strongly impacted by habitat loss and fragmentation. Large folivores typically have slower reproductive rates, live in smaller groups, and have low dispersal rates (vagility), making them especially vulnerable to habitat loss, hunting pressure, and possibly disease. Large, slow-moving animals are often easier to hunt and provide a larger amount of food than smaller prey. Leaf-eating, large-bodied slow climbers, and semiterrestrial seed predators and omnivores disappeared completely, suggesting an extinction pattern based on habitat use.
Since the subfossil bones of extinct lemurs have been found alongside the remains of highly arboreal living lemur species, we know that much of Madagascar had been covered in forest prior to the arrival of humans; the forest coverage of the high plateau region has been debated. Humbert and other botanists suggested that the central plateau had once been blanketed in forest, later to be destroyed by fire for use by humans. Recent paleoenvironmental studies by Burney have shown that the grasslands of that region have fluctuated over the course of millennia and were not entirely created by humans. Similarly, the role humans played in the aridification of the south and southwest has been questioned, since natural drying of the climate started before human arrival. The marshes of the region (in which subfossil remains have been found) have dried up, subfossil sites have yielded a host of arboreal lemurs, and site names, such as Ankilitelo ('place of three or tamarind trees') suggest a recent wetter past. Pollen studies have shown that the aridification process began nearly 3,000 years ago, and peaked 1,000 years prior to the time of the extinctions. No extinctions occurred prior to the arrival of humans, and the recent climatic changes have not been as severe as those prior to human arrival, suggesting that humans and their effect on the vegetation did play a role in the extinctions. The central plateau lost more species than the dry south and southwest, suggesting that degraded habitats were more affected than arid habitats.
Over-hunting by humans has been one of the most widely accepted hypotheses for the ultimate demise of the subfossil lemurs. The extinctions and human hunting pressure are associated due to the synchronicity of human arrival and species decline, as well as the suspected naïveté of the Malagasy wildlife during the early encounters with human hunters. Despite the assumptions, evidence of butchery has been minimal until recently, although folk memories of rituals associated with the killing of megafauna have been reported. Archeological evidence for butchery of giant subfossil lemurs, including Palaeopropithecus ingens and Pachylemur insignis, was found on specimens from two sites in southwestern Madagascar, Taolambiby and Tsirave. The bones had been collected in the early 20th century and lacked stratigraphic records; one of the bones with tool marks had been dated to the time of the first arrival of humans. Tool-induced bone alterations, in the form of cuts and chop marks near joints and other characteristic cuts and fractures, indicated the early human settlers skinned, disarticulated, and filleted giant lemurs. Prior to these finds, only modified bones of dwarf hippos and elephant birds, as well as giant aye-aye teeth, had been found.
Although there is evidence that habitat loss, hunting, and other factors played a role in the demise of the subfossil lemurs, prior to the synergy hypothesis, each had its own discrepancies. Humans may have hunted the giant lemurs for food, but no signs of game-dependent butchery have been found. Madagascar was colonized by Iron-age pastoralists, horticulturalists, and fishermen, not big-game hunters. The blitzkrieg hypothesis predicts extinction within 100 and 1,000 years as humans sweep across the island, yet humans lived alongside the giant lemurs for more than 1,500 years. Alternatively, habitat loss and deforestation have been argued against because many giant lemurs were thought to be terrestrial, they are missing from undisturbed forested habitats, and their environment was not fully forested prior to the arrival of humans. Anthropologist Laurie Godfrey defended the effects of habitat loss by pointing out that most of the extinct lemurs have been shown to have been at least partly arboreal and dependent upon leaves and seeds for food, and also that these large-bodied specialists would be most vulnerable to habitat disturbance and fragmentation due to their low reproductive resilience and their need for large, undisturbed habitats. Still, much of the island remained covered in forest, even into the 20th century.
Linking human colonization to a specific cause for extinction has been difficult since human activities have varied from region to region. No single human activity can account for the extinction of the giant subfossil lemurs, but humans are still regarded as being primarily responsible. Each of the contributing human-caused factors played a role (having a synergistic effect) in varying degrees. The most widespread and adaptable species, such as Archaeolemur, were able to survive despite hunting pressure and human-caused habitat change until human population growth and other factors reached a tipping point, cumulatively resulting in their extinction.
Extinction timeline and the primary trigger
While it is generally agreed that both human and natural factors contributed to the subfossil lemur extinction, studies of sediment cores have helped to clarify the general timeline and initial sequence of events. Spores of the coprophilous fungus, Sporormiella, found in sediment cores experienced a dramatic decline shortly after the arrival of humans. Since this fungus cannot complete its life cycle without dung from large animals, its decline also indicates a sharp decline in giant subfossil lemur populations, as well as other large herbivores, starting around 230–410 cal yr CE. Following the decline of megafauna, the presence of charcoal particles increased significantly, starting in the southwest corner of the island, gradually spreading to the other coasts and the island's interior over the next 1,000 years. The first evidence for the introduction of cattle to the island dates to 1,000 years after the initial decline of coprophilous fungal spores.
The loss of grazers and browsers might have resulted in the accumulation of excessive plant material and litter, promoting more frequent and destructive wildfires, which would explain the rise in charcoal particles following the decline in coprophilous fungus spores. This in turn resulted in ecological restructuring through the elimination of the wooded savannas and preferred arboreal habitats on which the giant subfossil lemurs depended. This left their populations at unsustainably low levels, and factors such as their slow reproduction, continued habitat degradation, increased competition with introduced species, and continued hunting (at lower levels, depending on the region) prevented them from recovering and gradually resulted in their extinction.
Hunting is thought to have caused the initial rapid decline, referred to as the primary trigger, although other explanations may be plausible. In theory, habitat loss should affect frugivores more than folivores, since leaves are more widely available. Both large-bodied frugivores and large-bodied folivores disappeared simultaneously, while smaller species remained. Other large non-primate grazers also disappeared around the same time. Consequently, large body size has been shown to have the strongest link to the extinctions—more so than activity patterns or diet. Since large animals are more attractive as prey, fungal spores associated with their dung declined rapidly with the arrival of humans, and butchery marks have been found on giant subfossil lemur remains, hunting appears to be a plausible explanation for the initial decline of the megafauna.
By region, studies have revealed specific details that have helped outline the series of events that led to the extinction of the local megafauna. In the Central Highlands, dense forests existed until 1600 CE, with lingering patches persisting until the 19th and 20th centuries. Today, small fragments stand isolated among vast expanses of human-created savanna, despite an average annual rainfall that is sufficient to sustain the evergreen forests once found there. Deliberately set fires were the cause of the deforestation, and forest regrowth is restricted by soil erosion and the presence of fire-resistant, exotic grasses. In the southeast, an extended drought dating to 950 cal yr BP led to fires and transition of open grasslands. The drought may also have pushed humans populations to rely more heavily on bushmeat. Had humans not been present, the subfossil lemur populations might have adjusted to the new conditions and recovered. Had the drought not reduced the population of the subfossil lemurs, the pressure from the small number of people living in the region at the time might not have been enough to cause the extinctions. All of the factors that have played a role in past extinctions are still present and active today. As a result, the extinction event that claimed Madagascar's giant subfossil lemurs is still ongoing.
Lingering populations and oral tradition
Recent radiocarbon dates from accelerator mass spectrometry 14C dating, such as 630 ± 50 BP for Megaladapis remains and 510 ± 80 BP for Palaeopropithecus remains, indicate that the giant lemurs survived into modern times. It is likely that memories of these creatures persist in the oral traditions of some Malagasy cultural groups. Some recent stories from around Belo sur Mer in southwestern Madagascar might even suggest that some of the giant subfossil lemurs still survive in remote forests.
Flacourt's 1658 description of the or was the first mention of the now extinct giant lemurs in Western culture, but it is unclear if he saw it. The creature Flacourt described has traditionally been interpreted as a species of Megaladapis. The size may have been exaggerated, and the "round head and a human face" would not match Megaladapis, which had an enlarged snout and the least forward-facing eyes of all primates. The facial description, and the mention of a short tail, solitary habits, and other traits better match the most recent interpretation — Palaeopropithecus. Malagasy tales recorded by the 19th-century folklorist Gabriel Ferrand describing a large animal with a flat human-like face that was unable to negotiate smooth rock outcrops also best match Palaeopropithecus, which would also have had difficulty on flat smooth surfaces.
In 1995, a research team led by David Burney and Ramilisonina performed interviews in and around Belo sur Mer, including Ambararata and Antsira, to find subfossil megafaunal sites used early in the century by other paleontologists. During carefully controlled interviews, the team recorded stories of recent sightings of dwarf hippos (called ) and of a large lemur-like creature known as ; a report of the interviews was published in 1998 with encouragement from primatologist Alison Jolly and anthropologist Laurie Godfrey. In one interview, an 85-year-old man named Jean Noelson Pascou recounted seeing the rare up close in 1952. Pascou said that the animal looks similar to a sifaka, but had a human-like face, and was "the size of a seven-year-old girl". It had dark fur and a discernible white spot both on the forehead and below the mouth. According to Pascou, it was a shy animal that fled on the ground instead of in the trees. Burney interpreted the old man as saying that it moved in "a series of leaps", but Godfrey later claimed that "a series of bounds" was a better translation — a description that would closely match the foot anatomy of monkey lemurs, such as Hadropithecus and Archaeolemur. Pascou could also imitate its call, a long single "whoop", and said that would come closer and continue calling if he imitated the call correctly. The call Pascou imitated was comparable to that of a short call for an indri, which lives on the other side of Madagascar. When shown a picture of an indri, Pascou said did not look like that, and that it had a rounder face, more similar to a sifaka. Pascou also speculated that could stand on two legs and that it was a solitary animal.
Another interviewee, François, a middle-aged woodcutter who spent time in the forests inland (east) from the main road between Morondava and Belo sur Mer, and five of his friends, reported seeing recently. Their description of the animal and François's imitation of its long call were virtually identical to Pascou's. One of the young men insisted that its fur had a lot of white in it, but the other men could not confirm that. François and his friends reported that it had never climbed a tree in their presence, and that it flees on the ground in short leaps or bounds. When Burney imitated the sideways leaping of a sifaka moving on the ground, one of the men corrected him, pointing out that he was imitating a sifaka. The man's imitation of the gallop used was very baboon-like. The men also reported that imitating its call can draw the animal closer and cause it to continue calling.
Burney and Ramilisonina admitted that the most parsimonious explanation for the sightings was that was a misidentified sifaka or other larger living lemur species. The authors did not feel comfortable with such a dismissal because of their careful quizzing and use of unlabeled color plates during the interviews and because of the competence demonstrated by the interviewees in regards to local wildlife and lemur habits. The possibility of a wild introduced baboon surviving in the forests could not be dismissed. The descriptions of , with its terrestrial baboon-like gait, make Hadropithecus and Archaeolemur the most plausible candidates among the giant subfossil lemurs. At the very least, the stories support a wider extinction window for the giant subfossil lemurs, suggesting that their extinction was recent enough for such vivid stories to survive in the oral traditions of the Malagasy people.
| Biology and health sciences | Strepsirrhini | Animals |
24377796 | https://en.wikipedia.org/wiki/Geological%20history%20of%20oxygen | Geological history of oxygen | Although oxygen is the most abundant element in Earth's crust, due to its high reactivity it mostly exists in compound (oxide) forms such as water, carbon dioxide, iron oxides and silicates. Before photosynthesis evolved, Earth's atmosphere had no free diatomic elemental oxygen (O2). Small quantities of oxygen were released by geological and biological processes, but did not build up in the reducing atmosphere due to reactions with then-abundant reducing gases such as atmospheric methane and hydrogen sulfide and surface reductants such as ferrous iron.
Oxygen began building up in the prebiotic atmosphere at approximately 1.85 Ga during the Neoarchean-Paleoproterozoic boundary, a paleogeological event known as the Great Oxygenation Event (GOE). At current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years. In the absence of plants, the rate of oxygen production by photosynthesis was slower in the Precambrian, and the concentrations of O2 attained were less than 10% of today's and probably fluctuated greatly.
The increase in oxygen concentrations had wide ranging and significant impacts on Earth's biosphere. Most significantly, the rise of oxygen and the oxidative depletion of greenhouse gases (especially atmospheric methane) due to the GOE led to an icehouse Earth that caused a mass extinction of anaerobic microbes, but paved the way for the evolution of eukaryotes and later the rise of complex lifeforms.
Before the Great Oxidation Event
Photosynthetic prokaryotic organisms that produced O2 as a byproduct lived long before the first build-up of free oxygen in the atmosphere, perhaps as early as 3.5 billion years ago. The oxygen cyanobacteria produced would have been rapidly removed from the oceans by weathering of reducing minerals, most notably ferrous iron. This rusting led to the deposition of the oxidized ferric iron oxide on the ocean floor, forming banded iron formations. Thus, the oceans rusted and turned red. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event.
Effects on life
Early fluctuations in oxygen concentration had little direct effect on life, with mass extinctions not observed until around the start of the Cambrian period, . The presence of provided life with new opportunities. Aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen created new possibilities for life to explore. Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. 430-million-year-old fossilized charcoal produced by wildfires show that the atmospheric oxygen levels in the Silurian must have been equivalent to, or possibly above, present day levels. The maximum of 35% was reached towards the end of the Carboniferous period (about 300 million years ago), a peak which may have contributed to the large size of various arthropods, including insects, millipedes and scorpions. Whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant.
The Great Oxygenation Event had the first major effect on the course of evolution. Due to the rapid buildup of oxygen in the atmosphere, the mostly anaerobic microbial biosphere that existed during the Archean eon was devastated, and only the aerobes that had antioxidant capabilities to neutralize oxygen thrived out in the open. This then led to symbiosis of anaerobic and aerobic organisms, who metabolically complemented each other, and eventually led to endosymbiosis and symbiogenesis, the evolution of eukaryotes, during the Proterozoic eon, who were now actually reliant on aerobic respiration to survive. After the Huronian glaciation came to an end, the Earth entered a long period of geological and climatic stability known as the Boring Billion. However, this long period was noticeably euxinic, meaning oxygen was scarce and the ocean and atmosphere were significantly sulfidic, and that evolution then was likely comparatively slow and quite conservative.
The Boring Billion ended during the Neoproterozoic period with a significant increase in photosynthetic activities, causing oxygen levels to rise 10- to 20-fold to about one-tenth of the modern level. This rise in oxygen concentration, known as the Neoproterozoic oxygenation event or "Second Great Oxygenation Event", was likely caused by the evolution of nitrogen fixation in cyanobacteria and the rise of eukaryotic photoautotrophs (green and red algae), and often cited as a possible contributor to later large-scale evolutionary radiations such as the Avalon explosion and the Cambrian explosion, which not only trended in larger but also more robust and motile multicellular organisms. The climatic changes associated with rising oxygen also produced cycles of glaciation and extinction events, each of which created disturbances that sped up ecological turnovers. During the Silurian and Devonian periods, the colonization and proliferation on land by early plants (which evolved from freshwater green algae) further increased the atmospheric oxygen concentration, leading to the historic peak during the Carboniferous period.
Data show an increase in biovolume soon after oxygenation events by more than 100-fold and a moderate correlation between atmospheric oxygen and maximum body size later in the geological record. The large size of many arthropods in the Carboniferous period, when the oxygen concentration in the atmosphere reached 35%, has been attributed to the limiting role of diffusion in these organisms' metabolism. But J.B.S. Haldane's essay points out that it would only apply to insects. However, the biological basis for this correlation is not firm, and many lines of evidence show that oxygen concentration is not size-limiting in modern insects. Ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies – for instance, the appearance of flying competitors such as pterosaurs, birds, and bats.
Rising oxygen concentrations have been cited as one of several drivers for evolutionary diversification, although the physiological arguments behind such arguments are questionable, and a consistent pattern between oxygen concentrations and the rate of evolution is not clearly evident. The most celebrated link between oxygen and evolution occurred at the end of the last of the Snowball Earth glaciations, where complex multicellular life is first found in the fossil record. Under low oxygen concentrations and before the evolution of nitrogen fixation, biologically-available nitrogen compounds were in limited supply, and periodic "nitrogen crises" could render the ocean inhospitable to life. Significant concentrations of oxygen were just one of the prerequisites for the evolution of complex life. Models based on uniformitarian principles (i.e. extrapolating present-day ocean dynamics into deep time) suggest that such a concentration was only reached immediately before metazoa first appeared in the fossil record. Further, anoxic or otherwise chemically "inhospitable" oceanic conditions that resemble those supposed to inhibit macroscopic life re-occurred at intervals through the early Cambrian, and also in the late Cretaceous – with no apparent effect on lifeforms at these times. This might suggest that the geochemical signatures found in ocean sediments reflect the atmosphere in a different way before the Cambrian – perhaps as a result of the fundamentally different mode of nutrient cycling in the absence of planktivory.
An oxygen-rich atmosphere can release phosphorus and iron from rock, by weathering, and these elements then become available for sustenance of new species whose metabolisms require these elements as oxides.
See Also
Great oxygenation event
Neoproterozoic oxygenation event
Silurian-Devonian Terrestrial Revolution
| Physical sciences | Paleoclimate | Earth science |
24383048 | https://en.wikipedia.org/wiki/Cherenkov%20radiation | Cherenkov radiation | Cherenkov radiation () is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium (such as distilled water) at a speed greater than the phase velocity (speed of propagation of a wavefront in a medium) of light in that medium. A classic example of Cherenkov radiation is the characteristic blue glow of an underwater nuclear reactor. Its cause is similar to the cause of a sonic boom, the sharp sound heard when faster-than-sound movement occurs. The phenomenon is named after Soviet physicist Pavel Cherenkov.
History
The radiation is named after the Soviet scientist Pavel Cherenkov, the 1958 Nobel Prize winner, who was the first to detect it experimentally under the supervision of Sergey Vavilov at the Lebedev Institute in 1934. Therefore, it is also known as Vavilov–Cherenkov radiation. Cherenkov saw a faint bluish light around a radioactive preparation in water during experiments. His doctorate thesis was on luminescence of uranium salt solutions that were excited by gamma rays instead of less energetic visible light, as done commonly. He discovered the anisotropy of the radiation and came to the conclusion that the bluish glow was not a fluorescent phenomenon.
A theory of this effect was later developed in 1937 within the framework of Einstein's special relativity theory by Cherenkov's colleagues Igor Tamm and Ilya Frank, who also shared the 1958 Nobel Prize.
Cherenkov radiation as conical wavefronts had been theoretically predicted by the English polymath Oliver Heaviside in papers published between 1888 and 1889 and by Arnold Sommerfeld in 1904, but both had been quickly dismissed following the relativity theory's restriction of superluminal particles until the 1970s. Marie Curie observed a pale blue light in a highly concentrated radium solution in 1910, but did not investigate its source. In 1926, the French radiotherapist Lucien Mallet described the luminous radiation of radium irradiating water having a continuous spectrum.
In 2019, a team of researchers from Dartmouth's and Dartmouth-Hitchcock's Norris Cotton Cancer Center discovered Cherenkov light being generated in the vitreous humor of patients undergoing radiotherapy. The light was observed using a camera imaging system called a CDose, which is specially designed to view light emissions from biological systems. For decades, patients had reported phenomena such as "flashes of bright or blue light" when receiving radiation treatments for brain cancer, but the effects had never been experimentally observed.
Physical origin
Basics
While the speed of light in vacuum is a universal constant (), the speed in a material may be significantly less, as it is perceived to be slowed by the medium. For example, in water it is only 0.75c. Matter can accelerate to a velocity higher than this (although still less than c, the speed of light in vacuum) during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (can be polarized electrically) medium with a speed greater than light's speed in that medium.
The effect can be intuitively described in the following way. From classical physics, it is known that accelerating charged particles emit EM waves and via Huygens' principle these waves will form spherical wavefronts which propagate with the phase velocity of that medium (i.e. the speed of light in that medium given by , for , the refractive index). When any charged particle passes through a medium, the particles of the medium will polarize around it in response. The charged particle excites the molecules in the polarizable medium and on returning to their ground state, the molecules re-emit the energy given to them to achieve excitation as photons. These photons form the spherical wavefronts which can be seen originating from the moving particle. If , that is the velocity of the charged particle is less than that of the speed of light in the medium, then the polarization field which forms around the moving particle is usually symmetric. The corresponding emitted wavefronts may be bunched up, but they do not coincide or cross, and there are therefore no interference effects to consider. In the reverse situation, i.e. , the polarization field is asymmetric along the direction of motion of the particle, as the particles of the medium do not have enough time to recover to their "normal" randomized states. This results in overlapping waveforms (as in the animation) and constructive interference leads to an observed cone-like light signal at a characteristic angle: Cherenkov light.
A common analogy is the sonic boom of a supersonic aircraft. The sound waves generated by the aircraft travel at the speed of sound, which is slower than the aircraft, and cannot propagate forward from the aircraft, instead forming a conical shock front. In a similar way, a charged particle can generate a "shock wave" of visible light as it travels through an insulator.
The velocity that must be exceeded is the phase velocity of light rather than the group velocity of light. The phase velocity can be altered dramatically by using a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity, a phenomenon known as the Smith–Purcell effect. In a more complex periodic medium, such as a photonic crystal, one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction (see below) whereas ordinary Cherenkov radiation forms an acute angle with the particle velocity.
In their original work on the theoretical foundations of Cherenkov radiation, Tamm and Frank wrote, "This peculiar radiation can evidently not be explained by any common mechanism such as the interaction of the fast electron with individual atom or as radiative scattering of electrons on atomic nuclei. On the other hand, the phenomenon can be explained both qualitatively and quantitatively if one takes into account the fact that an electron moving in a medium does radiate light even if it is moving uniformly provided that its velocity is greater than the velocity of light in the medium."
Emission angle
In the figure on the geometry, the particle (red arrow) travels in a medium with speed such that
where is speed of light in vacuum, and is the refractive index of the medium. If the medium is water, the condition is , since for water at 20 °C.
We define the ratio between the speed of the particle and the speed of light as
The emitted light waves (denoted by blue arrows) travel at speed
The left corner of the triangle represents the location of the superluminal particle at some initial moment (). The right corner of the triangle is the location of the particle at some later time t. In the given time t, the particle travels the distance
whereas the emitted electromagnetic waves are constricted to travel the distance
So the emission angle results in
Arbitrary emission angle
Cherenkov radiation can also radiate in an arbitrary direction using properly engineered one dimensional metamaterials. The latter is designed to introduce a gradient of phase retardation along the trajectory of the fast travelling particle (), reversing or steering Cherenkov emission at arbitrary angles given by the generalized relation:
Note that since this ratio is independent of time, one can take arbitrary times and achieve similar triangles. The angle stays the same, meaning that subsequent waves generated between the initial time and final time t will form similar triangles with coinciding right endpoints to the one shown.
Reverse Cherenkov effect
A reverse Cherenkov effect can be experienced using materials called negative-index metamaterials (materials with a subwavelength microstructure that gives them an effective "average" property very different from their constituent materials, in this case having negative permittivity and negative permeability). This means that, when a charged particle (usually electrons) passes through a medium at a speed greater than the phase velocity of light in that medium, that particle emits trailing radiation from its progress through the medium rather than in front of it (as is the case in normal materials with, both permittivity and permeability positive). One can also obtain such reverse-cone Cherenkov radiation in non-metamaterial periodic media where the periodic structure is on the same scale as the wavelength, so it cannot be treated as an effectively homogeneous metamaterial.
In vacuum
The Cherenkov effect can occur in vacuum. In a slow-wave structure, like in a traveling-wave tube (TWT), the phase velocity decreases and the velocity of charged particles can exceed the phase velocity while remaining lower than . In such a system, this effect can be derived from conservation of the energy and momentum where the momentum of a photon should be ( is phase constant) rather than the de Broglie relation . This type of radiation (VCR) is used to generate high-power microwaves.
Collective Cherenkov
Radiation with the same properties of typical Cherenkov radiation can be created by structures of electric current that travel faster than light. By manipulating density profiles in plasma acceleration setups, structures up to nanocoulombs of charge are created and may travel faster than the speed of light and emit optical shocks at the Cherenkov angle. Electrons are still subluminal, hence the electrons that compose the structure at a time are different from the electrons in the structure at a time .
Characteristics
The frequency spectrum of Cherenkov radiation by a particle is given by the Frank–Tamm formula:
The Frank–Tamm formula describes the amount of energy emitted from Cherenkov radiation, per unit length traveled and per frequency . is the permeability and is the index of refraction of the material the charged particle moves through. is the electric charge of the particle, is the speed of the particle, and is the speed of light in vacuum.
Unlike fluorescence or emission spectra that have characteristic spectral peaks, Cherenkov radiation is continuous. Around the visible spectrum, the relative intensity per unit frequency is approximately proportional to the frequency. That is, higher frequencies (shorter wavelengths) are more intense in Cherenkov radiation. This is why visible Cherenkov radiation is observed to be brilliant blue. In fact, most Cherenkov radiation is in the ultraviolet spectrum—it is only with sufficiently accelerated charges that it even becomes visible; the sensitivity of the human eye peaks at green, and is very low in the violet portion of the spectrum.
There is a cut-off frequency above which the equation can no longer be satisfied. The refractive index varies with frequency (and hence with wavelength) in such a way that the intensity cannot continue to increase at ever shorter wavelengths, even for very relativistic particles (where v/c is close to 1). At X-ray frequencies, the refractive index becomes less than 1 (note that in media, the phase velocity may exceed c without violating relativity) and hence no X-ray emission (or shorter wavelength emissions such as gamma rays) would be observed. However, X-rays can be generated at special frequencies just below the frequencies corresponding to core electronic transitions in a material, as the index of refraction is often greater than 1 just below a resonant frequency .
As in sonic booms and bow shocks, the angle of the shock cone is directly related to the velocity of the disruption. The Cherenkov angle is zero at the threshold velocity for the emission of Cherenkov radiation. The angle takes on a maximum as the particle speed approaches the speed of light. Hence, observed angles of incidence can be used to compute the direction and speed of a Cherenkov radiation-producing charge.
Cherenkov radiation can be generated in the eye by charged particles hitting the vitreous humour, giving the impression of flashes, as in cosmic ray visual phenomena and possibly some observations of criticality accidents.
Uses
Detection of labelled biomolecules
Cherenkov radiation is widely used to facilitate the detection of small amounts and low concentrations of biomolecules. Radioactive atoms such as phosphorus-32 are readily introduced into biomolecules by enzymatic and synthetic means and subsequently may be easily detected in small quantities for the purpose of elucidating biological pathways and in characterizing the interaction of biological molecules such as affinity constants and dissociation rates.
Medical imaging of radioisotopes and external beam radiotherapy
More recently, Cherenkov light has been used to image substances in the body. These discoveries have led to intense interest around the idea of using this light signal to quantify and/or detect radiation in the body, either from internal sources such as injected radiopharmaceuticals or from external beam radiotherapy in oncology. Radioisotopes such as the positron emitters 18F and 13N or beta emitters 32P or 90Y have measurable Cherenkov emission and isotopes 18F and 131I have been imaged in humans for diagnostic value demonstration.
External beam radiation therapy has been shown to induce a substantial amount of Cherenkov light in the tissue being treated, due to electron beams or photon beams with energy in the 6 MV to 18 MV ranges. The secondary electrons induced by these high energy x-rays result in the Cherenkov light emission, where the detected signal can be imaged at the entry and exit surfaces of the tissue. The Cherenkov light emitted from patient's tissue during radiation therapy is a very low light level signal but can be detected by specially designed cameras that synchronize their acquisition to the linear accelerator pulses. The ability to see this signal shows the shape of the radiation beam as it is incident upon the tissue in real time.
Nuclear reactors
Cherenkov radiation is used to detect high-energy charged particles. In open pool reactors, beta particles (high-energy electrons) are released as the fission products decay. The glow continues after the chain reaction stops, dimming as the shorter-lived products decay. Similarly, Cherenkov radiation can characterize the remaining radioactivity of spent fuel rods. This phenomenon is used to verify the presence of spent nuclear fuel in spent fuel pools for nuclear safeguards purposes.
Astrophysics experiments
When a high-energy (TeV) gamma photon or cosmic ray interacts with the Earth's atmosphere, it may produce an electron–positron pair with enormous velocities. The Cherenkov radiation emitted in the atmosphere by these charged particles is used to determine the direction and energy of the cosmic ray or gamma ray, which is used for example in the Imaging Atmospheric Cherenkov Technique (IACT), by experiments such as VERITAS, H.E.S.S., MAGIC. Cherenkov radiation emitted in tanks filled with water by those charged particles reaching earth is used for the same goal by the Extensive Air Shower experiment HAWC, the Pierre Auger Observatory and other projects. Similar methods are used in very large neutrino detectors, such as the Super-Kamiokande, the Sudbury Neutrino Observatory (SNO) and IceCube. Other projects operated in the past applying related techniques, such as STACEE, a former solar tower refurbished to work as a non-imaging Cherenkov observatory, which was located in New Mexico.
Astrophysics observatories using the Cherenkov technique to measure air showers are key to determining the properties of astronomical objects that emit very-high-energy gamma rays, such as supernova remnants and blazars.
Particle physics experiments
Cherenkov radiation is commonly used in experimental particle physics for particle identification. One could measure (or put limits on) the velocity of an electrically charged elementary particle by the properties of the Cherenkov light it emits in a certain medium. If the momentum of the particle is measured independently, one could compute the mass of the particle by its momentum and velocity (see four-momentum), and hence identify the particle.
The simplest type of particle identification device based on a Cherenkov radiation technique is the threshold counter, which answers whether the velocity of a charged particle is lower or higher than a certain value (, where is the speed of light, and is the refractive index of the medium) by looking at whether this particle emits Cherenkov light in a certain medium. Knowing particle momentum, one can separate particles lighter than a certain threshold from those heavier than the threshold.
The most advanced type of a detector is the RICH, or ring-imaging Cherenkov detector, developed in the 1980s. In a RICH detector, a cone of Cherenkov light is produced when a high-speed charged particle traverses a suitable medium, often called radiator. This light cone is detected on a position sensitive planar photon detector, which allows reconstructing a ring or disc, whose radius is a measure for the Cherenkov emission angle. Both focusing and proximity-focusing detectors are in use. In a focusing RICH detector, the photons are collected by a spherical mirror and focused onto the photon detector placed at the focal plane. The result is a circle with a radius independent of the emission point along the particle track. This scheme is suitable for low refractive index radiators—i.e. gases—due to the larger radiator length needed to create enough photons. In the more compact proximity-focusing design, a thin radiator volume emits a cone of Cherenkov light which traverses a small distance—the proximity gap—and is detected on the photon detector plane. The image is a ring of light whose radius is defined by the Cherenkov emission angle and the proximity gap. The ring thickness is determined by the thickness of the radiator. An example of a proximity gap RICH detector is the High Momentum Particle Identification Detector (HMPID), a detector currently under construction for ALICE (A Large Ion Collider Experiment), one of the six experiments at the LHC (Large Hadron Collider) at CERN.
| Physical sciences | Theory of relativity | Physics |
6800529 | https://en.wikipedia.org/wiki/R136 | R136 | R136 (formerly known as RMC 136 from the Radcliffe Observatory Magellanic Clouds catalogue) is the central concentration of stars in the NGC 2070 star cluster, which lies at the centre of the Tarantula Nebula in the Large Magellanic Cloud. When originally named it was an unresolved stellar object (catalogued as HD 38268 and Wolf-Rayet star Brey 82) but is now known to include 72 class O and Wolf–Rayet stars within 5 parsecs (20 arc seconds) of the centre of the cluster. The extreme number and concentration of young massive stars in this part of the LMC qualifies it as a starburst region.
Properties
R136 produces most of the energy that makes the Tarantula Nebula visible. The estimated mass of the cluster is 450,000 solar masses, suggesting it may become a globular cluster in the future. R136 has around 200 times the stellar density of a typical OB association such as Cygnus OB2. The central R136 concentration of the cluster is about 2 parsecs across, although the whole NGC 2070 cluster is much larger.
R136 is thought to be less than 2 million years old. None of the member stars are significantly evolved, and none are thought to have exploded as supernova. Because of this, the cluster contains no red supergiants, blue hypergiants, or luminous blue variables. The brightest stars are WNh, O supergiants, and OIf/WN slash stars, all extremely massive fully convective stars. A small number of B-type main sequence stars have been detected in the outskirts of the cluster, but less massive and less luminous stars cannot be resolved from the dense cluster core at the large distance of the LMC.
R136a
R136a is the bright knot at the centre of R136. It consists of eight extremely massive stars, three of them Wolf-Rayet stars and the rest early O-class stars.
Components
The cluster contains many of the most massive and luminous stars known, including R136a1. Within the central 5 parsecs there are 32 of the hottest type O stars (O2.0–3.5), 40 other O stars, and 12 Wolf-Rayet stars, mostly of the extremely luminous WNh type. Within 150 parsecs there are a further and 19Wolf-Rayet stars. Several runaway stars have been associated with R136, including VFTS 682.
R136 was first resolved into three components R136a, R136b, and R136c. R136a was resolved using speckle interferometry and eventually space-based observations into as many as 24 components, dominated by R136a1, R136a2, and R136a3, all three being extremely massive WNh stars several million times more luminous than the sun.
Gallery
| Physical sciences | Notable star clusters | Astronomy |
915215 | https://en.wikipedia.org/wiki/Wide-gamut%20RGB%20color%20space | Wide-gamut RGB color space | The wide-gamut RGB color space (or Adobe Wide Gamut RGB) is a color space developed by Adobe Systems, that offers a large gamut by using pure spectral primary colors.
It is able to store a wider range of color values than sRGB or Adobe RGB color spaces. As a comparison, the wide-gamut RGB color space encompasses 77.6% of the visible colors specified by the CIELAB color space, while the standard Adobe RGB color space covers just 52.1% and sRGB covers only 35.9%.
When working in color spaces with such a large gamut, it is recommended to work in 16-bit per channel color depth to avoid posterization effects. This will occur more frequently in 8-bit per channel modes as the gradient steps are much larger.
As with sRGB, the color component values in wide-gamut RGB are not proportional to the luminances. Similar to Adobe RGB, a gamma of 2.2 is assumed, without the linear segment near zero that is present in sRGB. The precise gamma value is 563/256, or 2.19921875.
The white point corresponds to D50.
The chromaticities of the primary colors and the white point are as follows:
| Physical sciences | Basics | Physics |
915258 | https://en.wikipedia.org/wiki/Sheep%20farming | Sheep farming | Sheep farming or sheep husbandry is the raising and breeding of domestic sheep. It is a branch of animal husbandry. Sheep are raised principally for their meat (lamb and mutton), milk (sheep's milk), and fiber (wool). They also yield sheepskin and parchment.
Sheep can be raised in a range of temperate climates, including arid zones near the equator and other torrid zones. Farmers build fences, housing, shearing sheds, and other facilities on their property, such as for water, feed, transport, and pest control. Most farms are managed so sheep can graze pastures, sometimes under the control of a shepherd or sheep dog.
Farmers can select from various breeds suitable for their region and market conditions. When the farmer sees that a ewe (female adult) is showing signs of heat or estrus, they can organise for mating with males. Newborn lambs are typically subjected to lamb marking, which involves tail docking, mulesing, earmarking, and males may be castrated.
Sheep production worldwide
According to the FAOSTAT database of the United Nations Food and Agriculture Organization, the top five countries by number of head of sheep (average from 1993 to 2013) were: mainland China (146.5 million head), Australia (101.1 million), India (62.1 million), Iran (51.7 million), and the former Sudan (46.2 million). Approximately 540 million sheep are slaughtered each year for meat worldwide.
In 2013, the five countries with the largest number of head of sheep were mainland China (175 million), Australia (75.5 million), India (53.8 million), the former Sudan (52.5 million), and Iran (50.2 million). In 2018, Mongolia had 30.2 million sheep. In 2013, the number of head of sheep were distributed as follows: 44% in Asia, 28.2% in Africa; 11.2% in Europe, 9.1% in Oceania, 7.4% in the Americas.
The top producers of sheep meat (average from 1993 to 2013) were as follows: mainland China (1.6 million); Australia (618,000), New Zealand (519,000), the United Kingdom (335,000), and Turkey (288,857). The top five producers of sheep meat in 2013 were mainland China (2 million), Australia (660,000), New Zealand (450,000), the former Sudan (325,000), and Turkey (295,000).
U.S. sheep production
In the United States, inventory data on sheep began in 1867, when 45 million head of sheep were counted in the United States. The numbers of sheep peaked in 1884 at 51 million head, and then declined over time to almost 6 million head.
Between the 1960s and 2012, per capita per year consumption of lamb and mutton has declined from nearly five pounds (about 2 kg) to just about one pound (450g), because of competition from poultry, pork, beef, and other meats. Between the 1990s and 2012, U.S. sheep operations declined from around 105,000 to around 80,000 because of shrinking revenues and low rates of return. According to the Economic Research Service of the United States Department of Agriculture, the sheep industry accounts for less than one percent of U.S. livestock industry receipts.
Reproduction
Lambing
Most lambs are born outdoors. Ewes can be made to give birth in fall, winter, or spring months, either by artificial insemination or by facilitating natural mating. Fall lambing is generally not done as the lamb crop percentage is likely to be low; ewes often need hormone therapy to induce estrus and ovulation, and farm labor is often busy elsewhere during fall lambing. Furthermore, fall-born lambs can be weak and small because of heat stress during the summer gestation period. Spring lambing has the advantage of coinciding with the natural breeding and lambing seasons, but supplemental feed is often needed. The advantage of winter lambing is that the lambs are weaned in spring when pastures are most fertile. This allows the lambs to grow more quickly, and to be sold for slaughter during the summer (when prices are generally high), but it results in roughly one in every four newborn lambs dying within a few days of birth of malnutrition, disease, or exposure to the harsh cold. In the UK, it results in around 4 million newborn lamb deaths. "Accelerated lambing" is the practice of lambing more than once a year, typically every 6 to 8 months. The advantages of accelerated lambing include increased lamb production, having lambs available for slaughter at different seasons, year-round use of labor and facilities, and increased income per ewe. It requires intensive management, early weaning, exogenous hormones, and artificial impregnation. It is often used to make old or soon-to-be infertile ewes give birth one more time before they are slaughtered.
Lamb marking
After lambs are several weeks old, lamb marking is carried out. This involves ear tagging, docking, mulesing, and castrating.
Ear tags with numbers are attached, or ear marks are applied, for ease of later identification of sheep.
Tail docking is commonly done for welfare, having been shown to reduce risk of flystrike when compared to the alternative of letting sheep collect waste around their buttocks.
The Merino breed, accounting for around 80% of the wool produced in Australia, have been selectively bred to have wrinkled skin resulting in excessive amounts of wool while making them much more prone to flystrike. To reduce the risk of flystrike caused by soiling for the lambs who make it to summer, Merino lambs are often mulesed at the same time, which involves cutting off the skin around their buttocks and the base of their tail with metal shears. If the lambs are younger than 6 months, it is legal to do this in Australia without any pain relief.
Male lambs are typically castrated. Castration is performed on ram lambs not intended for breeding, although some shepherds choose to omit this for ethical, economic or practical reasons. A common castration technique is "elastration", which involves a thick rubber band being placed around the base of the infant's scrotum, obstructing the blood supply and causing atrophy. This method causes severe pain to the lambs who are provided no pain relief during the process. Elastration is also commonly used for docking.
Based on the preference of the shepherd, docking and castration are commonly done after 24 hours (to avoid interference with maternal bonding and consumption of colostrum) and are often done not later than one week after birth to minimize pain, stress, recovery time, and complications. Ram lambs that will either be slaughtered or separated from ewes before sexual maturity are not usually castrated. Objections to all these procedures have been raised by animal rights groups, but farmers defend them by saying they reduce costs, and inflict only temporary pain.
Healthcare
Nutrition
Although sheep primarily consume pasture roughage, they are sometimes given supplemental feed, such as corn and hay provided by the shepherds from their own fields.
Shearing
Sheep not meant to be eaten are typically shorn annually in a shearing shed. Ewes tend to be shorn immediately prior to lambing. Shearing can be done with either manual blades or machine shears. In Australia, sheep shearers are paid by the number of sheep shorn, not by the hour, and there are no requirements for formal training or accreditation. Because of this, it is alleged that speed is prioritised over precision and care of the animal.
Crutching
Crutching is the practice of removing wool for hygiene reasons, typically from around the face and buttocks.
Saleyards
Sheep sold for slaughter often pass through saleyards, also known as auctions.
Slaughter
When sheep can no longer produce enough wool to be considered profitable, they are sent to slaughter and sold as mutton, and lambs raised for meat are killed between 4 and 12 months of age. Sheep have a natural lifespan of 12–14 years.
Herding
Breeds
Environmental impact
George Monbiot's 2013 book Feral attacks sheep farming in the United Kingdom as "a slow-burning ecological disaster, which has done more damage to the living systems of this country than either climate change or industrial pollution. Yet scarcely anyone seems to have noticed." He particularly looks at sheep farming in Wales.
| Technology | Animal husbandry | null |
916571 | https://en.wikipedia.org/wiki/Tide%20pool | Tide pool | A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. These pools typically range from a few inches to a few feet deep and a few feet across. Many of these pools exist as separate bodies of water only at low tide, as seawater gets trapped when the tide recedes. Tides are caused by the gravitational pull of the sun and moon. A tidal cycle is usually about 25 hours and consists of two high tides and two low tides.
Tide pool habitats are home to especially adaptable animals, like snails, barnacles, mussels, anemones, urchins, sea stars, crustaceans, seaweed, and small fish. Inhabitants must be able to cope with constantly changing water levels, water temperatures, salinity, and oxygen content. At low tide, there is the risk of predators like seabirds. These pools have engaged the attention of naturalists and marine biologists, as well as philosophical essayists: John Steinbeck wrote in The Log from the Sea of Cortez, "It is advisable to look from the tide pool to the stars and then back to the tide pool."
Some examples have been artificially augmented to enable safer swimming (for example without waves or without sharks) in seawater at certain states of the tide.
Zones
The rocky shoreline exhibits distinct zones with unique characteristics. These zones are created by the tidal movements of water along the rocky shores from high to low-tide. They are:
The supralittoral zone or splash zone: area above the high-tide mark, which is virtually a terrestrial environment. Occasionally gets splashed, but never gets covered by the ocean.
The intertidal fringe: area around the high-tide mark.
The intertidal or littoral zone: area between the high and low-tide marks. Can be further divided into high, mid, and low intertidal zones, which are explained below in more depth.
The sublittoral or subtidal zone: area below the low-tide mark.
The presence and abundance of flora and fauna vary between zones along the rocky shore. This is due to niche adaptations in response to the varying tides and solar exposure.
Tide pools exist in the intertidal zone (the area within the tidal range), which is submerged by the sea at high tides and during storms. At other times, the rocks may undergo other extreme conditions, such as baking in the sun or being exposed to cold winds. Few organisms can survive such harsh conditions.
High Tide Zone
The high tide zone is flooded during each high tide, which occurs once or twice daily. Organisms must survive wave action, currents, and long exposure to the sun and open air. This zone is predominantly inhabited by seaweed and invertebrates, such as sea anemones, sea star, chitons, crabs, green algae, and mussels. Marine algae provide shelter for nudibranchs and hermit crabs. The same waves and currents that make life in the high tide zone difficult bring food to filter feeders and other intertidal organisms.
Mid Tide Zone
This zone is constantly covered and uncovered by water, so its inhabitants have adapted to surviving in these conditions. More plants and animals live here, compared to the high tide zone, because they are not exposed to drying conditions for so long. During low tide, anemones close up and mussels close their shells to keep in moisture. They reopen when the tide returns and brings them food.
Low Tide Zone
This area is mostly submerged and is exposed only during unusually low tide. It usually teems with life and has far more marine vegetation, especially seaweeds. Organisms in this zone do not have to be as well adapted to drying out and temperature extremes. Low tide zone organisms include abalone, anemones, brown seaweed, chitons, crabs, green algae, hydroids, isopods, limpets, mussels, and sometimes even small vertebrates such as fish. Seaweeds provide shelter for many animals, like sea slugs and urchins that are too fragile for other zones. These creatures can grow to larger sizes because there is more available energy and better water coverage: the water is shallow enough to allow additional sunlight for photosynthetic activity, with almost normal levels of salinity. This area is also relatively protected from large predators because of the wave action and shallow water.
Marine life
Tide pools provide a home for many organisms such as sea stars, mussels and clams. Inhabitants deal with a frequently changing environment: fluctuations in water temperature, salinity, and oxygen content. Hazards include waves, strong currents, exposure to midday sun and predators.
Waves can dislodge mussels and draw them out to sea. Gulls pick up and drop sea urchins to break them open. Sea stars prey on mussels and are eaten by gulls themselves. Black bears are known to sometimes feast on intertidal creatures at low tide. Although tide pool organisms must avoid getting washed away into the ocean, drying up in the sun, or being eaten, they depend on the tide pool's constant changes for food. Tide pools contain complex food webs that can vary based on the climate.
Fauna
The sea anemone Anthopleura elegantissima reproduces clones of itself through a process of longitudinal fission, in which the animal splits into two parts along its length.
The sea anemone Anthopleura sola often engages in territorial fights. The white tentacles (acrorhagi), which contain stinging cells, are for fighting. The sea anemones sting each other repeatedly until one of them moves.
Some species of sea stars can regenerate lost arms. Most species must retain an intact central part of the body to be able to regenerate, but a few can regrow from a single ray. The regeneration of these stars is possible because the vital organs are in the arms.
Sea urchins ("Echinoidia") move around tide pools with tube like feet. Different species of urchin have different colors, and many are seen in tide pools. With spines, some filled with poison like with "Toxopnesutes pileolus", that protect them from predators they feed almost undisturbed in tide pools. Algae and other microorganism are the food sources that attract them to the tide pools.
The presence of the California mussel increases the supply of inorganic nitrogen and phosphorus in coastal marine tide pools which allows the ecosystem the nutrients to be more productive. The shell of a California mussel is primarily composed of Aragonite and Calcite which are both polymorphs of Calcium carbonate. Climate change and ocean acidification has led to a decrease in these amounts important compounds in California Mussel shells over many years.
Lichens and barnacles live in the splash zone. Different barnacle species live at very tightly constrained elevations, with tidal conditions precisely determining the exact height of an assemblage relative to sea level. The intertidal zone is periodically exposed to sun and wind, conditions that can cause barnacles to become desiccated. These animals, therefore, need to be well adapted to water loss. Their calcite shells are impermeable, and they possess two plates which they slide across their mouth opening when not feeding. These plates also protect against predation.
Many species of Hermit crab are commonly found in tide pool environments. The long-wristed hermit crab (Pagurus longicarpus) has been found to become stranded in tide pools and are forced to inhabit gastropod shells in response to the rapidly changing temperature of the pools. Hermit crabs of different or the same species compete for the snail shells that are available.
Many fish species can live in tidepools. Tidepool fishes are those inhabiting the intertidal zone during part or the entirety of their life cycle, including residents displaying morphological, physiological and behavioral adaptations to withstand the fluctuating environment and non-residents that use the intertidal as juvenile habitat, feeding or refuge ground, or as transient space between nearshore areas. Tidepools fishes can be classified as residents and non-residents (sometimes called transients or visitors). Residents are those that spend the whole lifetime in the tidepools. Non-resident species are commonly divided into two groups: secondary residents (also known as partial residents or opportunists) and transients (which can be further classified as tidal and seasonal transients). Secondary residents are species that spend only a portion of their life history in tidepools, typically during their juvenile stage, before moving on to adult subtidal habitats. Transients, on the other hand, may temporarily inhabit tidepools for various reasons such as foraging, seeking refuge, or transit. Unlike residents, transients lack specialized adaptations for intertidal life and typically occupy large tidepools for a relatively short period, ranging from a single tidal cycle to a few months. The Tidepool sculpin is a species of fish that is named for its tide pool habitat. The Tidepool Sculpin has been found to show preferences for certain tide pools and will return to their tide pool of choice after being removed from it. This is a behavior known as Homing (biology). These fish crawl on the floor of tide pools using a back and forth movement of their tail fin and a rotating motion of their pectoral fins.
Multiple species of Amphipods (Amphipoda) can be found in coastal tide pools. These small crustaceans provide an important food source for predator species as well as limiting the growth of algae attached to vegetation.
Flora
Sea palms (Postelsia) look similar to miniature palm trees. They live in the middle to upper intertidal zones in areas with greater wave action. High wave action may increase nutrient availability and moves the blades of the thallus, allowing more sunlight to reach the organism so that it can photosynthesize. In addition, the constant wave action removes competitors, such as the mussel species Mytilus californianus.
Recent studies have shown that Postelsia grows in greater numbers when such competition exists; a control group with no competition produced fewer offspring than an experimental group with mussels; from this it is thought that the mussels provide protection for the developing gametophytes. Alternatively, the mussels may prevent the growth of competing algae such as Corallina or Halosaccion, allowing Postelsia to grow freely after wave action has eliminated the mussels.
Coralline algae "Corallinales" are predominant features of mid and low intertidal tide pools. Calcium carbonate (CaCO3) takes the form of calcite in their cell walls providing them with a hard outer shell. This shell protects from herbivores and desiccation due to lack of water and evaporation. Many forms of the Coralline algae bring herbivores, such as mollusks "Notoacmea", to the tide pools during high tides, increasing the biomass of the area. Once low tides comes, these herbivores are exposed to carnivores in the areas, fueling the food web.
Coastal predators
Tide pools are often surrounded by coastal predators who feed on tide pool flora and fauna. These predators play an important role in the tide pool food web and create competition for resources.
| Physical sciences | Oceanography | Earth science |
916971 | https://en.wikipedia.org/wiki/Nuclear%20marine%20propulsion | Nuclear marine propulsion | Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Nuclear propulsion is used primarily within naval warships such as nuclear submarines and supercarriers. A small number of experimental civil nuclear ships have been built.
Compared to oil- or coal-fuelled ships, nuclear propulsion offers the advantage of very long intervals of operation before refueling. All the fuel is contained within the nuclear reactor, so no cargo or supplies space is taken up by fuel, nor is space taken up by exhaust stacks or combustion air intakes. The low fuel cost is offset by high operating costs and investment in infrastructure, however, so nearly all nuclear-powered vessels are military.
Power plants
Basic operation of naval ship or submarine
Most naval nuclear reactors are of the pressurized water type, with the exception of a few attempts at using liquid sodium-cooled reactors. A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator; this water is kept under pressure so it does not boil. This circuit operates at a temperature of around . Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.
The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers on its way to the steam turbine. Spent steam at low pressure runs through a condenser cooled by seawater and returns to liquid form. The water is pumped back to the steam generator and continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water.
In the turbine, the steam expands and reduces its pressure as it imparts energy to the rotating blades of the turbine. There may be many stages of rotating blades and fixed guide vanes. The output shaft of the turbine may be connected to a gearbox to reduce rotation speed, then a shaft connects to the vessel's propellers. In another form of drive system, the turbine turns an electrical generator, and the electric power produced is fed to one or more drive motors for the vessel's propellers. The Russian, U.S. and British navies rely on direct steam turbine propulsion, while French and Chinese ships use the turbine to generate electricity for propulsion (turbo-electric transmission).
Some nuclear submarines have a single reactor, but Russian submarines have two, and so had . Most American aircraft carriers are powered by two reactors, but had eight. The majority of marine reactors are of the pressurized water type, although the U.S. and Soviet navies have designed warships powered with liquid metal cooled reactors.
Differences from land power plants
Marine-type reactors differ from land-based commercial electric power reactors in several respects.
While land-based reactors in nuclear power plants produce up to around 1600 megawatts of net electrical power (the nameplate capacity of the EPR), a typical marine propulsion reactor produces no more than a few hundred megawatts. Some small modular reactors (SMR) are similar to marine propulsion reactors in capacity and some design considerations and thus nuclear marine propulsion (whether civilian or military) is sometimes proposed as an additional market niche for SMRs. Unlike for land-based applications where hundreds of hectares can be occupied by installations like Bruce Nuclear Generating Station, at sea tight space limits dictate that a marine reactor must be physically small, so it must generate higher power per unit of space. This means its components are subject to greater stresses than those of a land-based reactor. Its mechanical systems must operate flawlessly under the adverse conditions encountered at sea, including vibration and the pitching and rolling of a ship operating in rough seas. Reactor shutdown mechanisms cannot rely on gravity to drop control rods into place as in a land-based reactor that always remains upright. Salt water corrosion is an additional problem that complicates maintenance.
As the core of a seagoing reactor is much smaller than a power reactor, the probability of a neutron intersecting with a fissionable nucleus before it escapes into the shielding is much lower. As such, the fuel is typically more highly enriched (i.e., contains a higher concentration of 235U vs. 238U) than that used in a land-based nuclear power plant, which increases the probability of fission to the level where a sustained reaction can occur. Some marine reactors run on relatively low-enriched uranium, which requires more frequent refueling. Others run on highly enriched uranium, varying from 20% 235U, to the over 96% 235U found in U.S. submarines, in which the resulting smaller core is quieter in operation (a big advantage to a submarine). Using more-highly enriched fuel also increases the reactor's power density and extends the usable life of the nuclear fuel load, but is more expensive and a greater risk to nuclear proliferation than less-highly enriched fuel.
A marine nuclear propulsion plant must be designed to be highly reliable and self-sufficient, requiring minimal maintenance and repairs, which might have to be undertaken many thousands of miles from its home port. One of the technical difficulties in designing fuel elements for a seagoing nuclear reactor is the creation of fuel elements that will withstand a large amount of radiation damage. Fuel elements may crack over time and gas bubbles may form. The fuel used in marine reactors is a metal-zirconium alloy rather than the ceramic UO2 (uranium dioxide) often used in land-based reactors. Marine reactors are designed for long core life, enabled by the relatively high enrichment of the uranium and by incorporating a "burnable poison" in the fuel elements, which is slowly depleted as the fuel elements age and become less reactive. The gradual dissipation of the "nuclear poison" increases the reactivity of the core to compensate for the lessening reactivity of the aging fuel elements, thereby extending the usable life of the fuel. The compact reactor pressure vessel is provided with an internal neutron shield, which reduces the damage to the steel from constant neutron bombardment.
Decommissioning
Decommissioning nuclear-powered submarines has become a major task for U.S. and Russian navies. After defuelling, U.S. practice is to cut the reactor section from the vessel for disposal in shallow land burial as low-level waste (see the ship-submarine recycling program). In Russia, whole vessels, or sealed reactor sections, typically remain stored afloat, although a new facility near Sayda Bay is to provide storage in a concrete-floored facility on land for some submarines in the far north.
Future designs
Russia built a floating nuclear power plant for its far eastern territories. The design has two 35 MWe units based on the KLT-40 reactor used in icebreakers (with refueling every four years). Some Russian naval vessels have been used to supply electricity for domestic and industrial use in remote far eastern and Siberian towns.
In 2010, Lloyd's Register was investigating the possibility of civilian nuclear marine propulsion and rewriting draft rules (see text under Merchant Ships).
Civil liability
Insurance of nuclear vessels is not like the insurance of conventional ships. The consequences of an accident could span national boundaries, and the magnitude of possible damage is beyond the capacity of private insurers. A special international agreement, the Brussels Convention on the Liability of Operators of Nuclear Ships, developed in 1962, would have made signatory national governments liable for accidents caused by nuclear vessels under their flag but was never ratified owing to disagreement on the inclusion of warships under the convention. Nuclear reactors under United States jurisdiction are insured by the provisions of the Price–Anderson Act.
Military nuclear ships
By 1990, there were more nuclear reactors powering ships (mostly military) than there were generating electric power in commercial power plants worldwide.
Under the direction of U.S. Navy Captain (later Admiral) Hyman G. Rickover, the design, development and production of nuclear marine propulsion plants started in the United States in the 1940s. The first prototype naval reactor was constructed and tested at the Naval Reactor Facility at the National Reactor Testing Station in Idaho (now called the Idaho National Laboratory) in 1953.
Submarines
The first nuclear submarine, , put to sea in 1955 (SS was a traditional hull classification symbol for U.S. submarines, while SSN denoted the first "nuclear" submarine).
The Soviet Union also developed nuclear submarines. The first types developed were the Project 627, NATO-designated with two water-cooled reactors, the first of which, K-3 Leninsky Komsomol, was underway under nuclear power in 1958.
Nuclear power revolutionized the submarine, finally making it a true "underwater" vessel, rather than a "submersible" craft, which could only stay underwater for limited periods. It gave the submarine the ability to operate submerged at high speeds, comparable to those of surface vessels, for unlimited periods, dependent only on the endurance of its crew. To demonstrate this was the first vessel to execute a submerged circumnavigation of the Earth (Operation Sandblast), doing so in 1960.
Nautilus, with a pressurized water reactor (PWR), led to the parallel development of other submarines like a unique liquid metal cooled (sodium) reactor in , or two reactors in Triton, and then the s, powered by single reactors, and a cruiser, , in 1961, powered by two reactors.
By 1962, the United States Navy had 26 operational nuclear submarines and another 30 under construction. Nuclear power had revolutionized the Navy. The United States shared its technology with the United Kingdom, while French, Soviet, Indian and Chinese development proceeded separately.
After the Skate-class vessels, U.S. submarines were powered by a series of standardized, single-reactor designs built by Westinghouse and General Electric. Rolls-Royce plc built similar units for Royal Navy submarines, eventually developing a modified version of their own, the PWR2.
The largest nuclear submarines ever built are the 26,500 tonne Russian . The smallest nuclear warships to date are the 2,700 tonne French attack submarines. The U.S. Navy operated an unarmed nuclear submarine, the NR-1 Deep Submergence Craft, between 1969 and 2008, which was not a combat vessel but was the smallest nuclear-powered submarine at 400 tons.
Aircraft carriers
The United States and France have built nuclear aircraft carriers.
French Navy
The sole French nuclear aircraft carrier example is , commissioned in 2001 (a successor is planned).
The French carrier is equipped with catapults and arresters. The has 42,000 tonnes, is the flagship of the French Navy (Marine Nationale). The ship carries a complement of Dassault Rafale M and E‑2C Hawkeye aircraft, EC725 Caracal and AS532 Cougar helicopters for combat search and rescue, as well as modern electronics and Aster missiles.
United States Navy
The United States Navy operates 11 carriers, all nuclear-powered:
: in service 1962–2012, powered by eight reactor units, is still the only aircraft carrier to house more than two nuclear reactors, with each A2W reactor taking the place of one of the conventional boilers in earlier constructions.
: ten 101,000-ton, 1,092 ft long fleet carriers, the first of which was commissioned in 1975. A Nimitz-class carrier is powered by two nuclear reactors providing steam to four steam turbines.
, one 110,000-ton, 1,106 ft long fleet carrier. The lead of the class , came into service in 2017, with another nine planned.
Destroyers and cruisers
Russian Navy
The Kirov class, Soviet designation 'Project 1144 Orlan' (sea eagle), is a class of nuclear-powered guided-missile cruisers of the Soviet Navy and Russian Navy, the largest and heaviest surface combatant warships (i.e. not an aircraft carrier or amphibious assault ship) in operation in the world. Among modern warships, they are second in size only to large aircraft carriers, and of similar size to World War II era battleships. The Soviet classification of the ship-type is "heavy nuclear-powered guided missile cruiser" (). The ships are often referred to as battlecruisers by Western defence commentators due to their size and general appearance.
United States Navy
The United States Navy at one time had nuclear-powered cruisers as part of its fleet. The first such ship was USS Long Beach (CGN-9). Commissioned in 1961, she was the world's first nuclear-powered surface combatant. She was followed a year later by USS Bainbridge (DLGN-25). While Long Beach was designed and built as a cruiser, Bainbridge began life as a frigate, though at that time the Navy was using the hull code "DLGN" for "destroyer leader, guided missile, nuclear".
The last nuclear-powered cruisers the Americans would produce would be the four-ship . was commissioned in 1976, followed by in 1977, in 1978 and finally in 1980. Ultimately, all these ships proved to be too costly to maintain and they were all retired between 1993 and 1999.
Other military ships
Communication and command ships
SSV-33 Ural (ССВ-33 Урал; NATO reporting name: Kapusta [Russian for "cabbage"]) was a command and control naval ship operated by the Soviet Navy. SSV-33s hull was derived from that of the nuclear-powered s with nuclear marine propulsion. SSV-33 served in electronic intelligence, missile tracking, space tracking, and communications relay roles. Due to high operating costs, SSV-33 was laid up.
SSV-33 carried only light defensive weapons. These were two AK-176 76 mm guns, four AK-630 30 mm guns, and four quadruple Igla missile mounts.
Nuclear-powered UUV
The Poseidon (, "Poseidon", NATO reporting name Kanyon), previously known by Russian codename Status-6 (), is a nuclear-powered and nuclear-armed unmanned underwater vehicle under development by Rubin Design Bureau, capable of delivering both conventional and nuclear payloads. According to Russian state TV, it is able to deliver a thermonuclear cobalt bomb of up to 200 megatonnes (four times as powerful as the most powerful device ever detonated, the Tsar Bomba, and twice its maximum theoretical yield) against an enemy's naval ports and coastal cities.
Civilian nuclear ships
The following are ships that are or were in commercial or civilian use and have nuclear marine propulsion.
Merchant ships
Nuclear-powered civil merchant ships have not developed beyond a few experimental ships. The U.S.-built , completed in 1962, was primarily a demonstration of civil nuclear power and was too small and expensive to operate economically as a merchant ship. The design was too much of a compromise, being neither an efficient freighter nor a viable passenger liner. The German-built , completed in 1968, a cargo ship and research facility, sailed some on 126 voyages over 10 years without any technical problems. It proved too expensive to operate and was converted to diesel. The Japanese , completed in 1972, was dogged by technical and political problems. Its reactor had significant radiation leakage and fishermen protested against the vessel's operation. All of these three ships used low-enriched uranium. Sevmorput, a Soviet and later Russian LASH carrier with icebreaking capability, has operated successfully on the Northern Sea Route since it was commissioned in 1988. , it is the only nuclear-powered merchant ship in service.
Civilian nuclear ships suffer from the costs of specialized infrastructure. The Savannah was expensive to operate since it was the only vessel using its specialized nuclear shore staff and servicing facility. A larger fleet could share fixed costs among more operating vessels, reducing operating costs.
Despite this, there is still interest in nuclear propulsion. In November 2010 British Maritime Technology and Lloyd's Register embarked upon a two-year study with U.S.-based Hyperion Power Generation (now Gen4 Energy), and the Greek ship operator Enterprises Shipping and Trading SA to investigate the practical maritime applications for small modular reactors. The research intended to produce a concept tanker-ship design, based on a 70 MWt reactor such as Hyperion's. In response to its members' interest in nuclear propulsion, Lloyd's Register has also re-written its 'rules' for nuclear ships, which concern the integration of a reactor certified by a land-based regulator with the rest of the ship. The overall rationale of the rule-making process assumes that in contrast to the current marine industry practice where the designer/builder typically demonstrates compliance with regulatory requirements, in the future the nuclear regulators will wish to ensure that it is the operator of the nuclear plant that demonstrates safety in operation, in addition to the safety through design and construction. Nuclear ships are currently the responsibility of their own countries, but none are involved in international trade. As a result of this work in 2014 two papers on commercial nuclear marine propulsion were published by Lloyd's Register and the other members of this consortium. These publications review past and recent work in the area of marine nuclear propulsion and describe a preliminary concept design study for a Suezmax tanker that is based on a conventional hull form with alternative arrangements for accommodating a 70 MWt nuclear propulsion plant delivering up to 23.5 MW shaft power at maximum continuous rating (average: 9.75 MW). The Gen4Energy power module is considered. This is a small fast-neutron reactor using lead–bismuth eutectic cooling and able to operate for ten full-power years before refueling, and in service last for a 25-year operational life of the vessel. They conclude that the concept is feasible, but further maturity of nuclear technology and the development and harmonisation of the regulatory framework would be necessary before the concept would be viable.
Nuclear propulsion has been proposed again on the wave of decarbonization of marine shipping, which accounts for 3–4% of global greenhouse gas emissions.
Merchant cargo ships
USNS American Explorer; United States tanker, converted to conventional power while under construction
, Japan (1970–1992); never carried commercial cargo, rebuilt as diesel engine powered RV Mirai in 1996
, Germany (1968–1979); re-powered with diesel engine in 1979
, United States (1962–1972)
Sevmorput, Russia (1988–present), ice-strengthened nuclear-powered lighter aboard ship (LASH) carrier
In December 2023, the Jiangnan Shipyard under the China State Shipbuilding Corporation officially released a design of a 24000 TEU-class container ship — known as the KUN-24AP — at Marintec China 2023, a premier maritime industry exhibition held in Shanghai. The container ship is reported to be powered by a thorium-based molten salt reactor, making it a first thorium-powered container ship and, if completed, the largest nuclear-powered container ship in the world.
Icebreakers
Nuclear propulsion has proven both technically and economically feasible for nuclear-powered icebreakers in the Soviet, and later Russian, Arctic. Nuclear-fuelled ships operate for years without refueling, and the vessels have powerful engines, well-suited to the task of icebreaking.
The Soviet icebreaker Lenin was the world's first nuclear-powered surface vessel in 1959 and remained in service for 30 years (new reactors were fitted in 1970). It led to a series of larger icebreakers, the 23,500 ton of six vessels, launched beginning in 1975. These vessels have two reactors and are used in deep Arctic waters. NS Arktika was the first surface vessel to reach the North Pole.
For use in shallow waters such as estuaries and rivers, shallow-draft, Taymyr-class icebreakers were built in Finland and then fitted with their single-reactor nuclear propulsion system in Russia. They were built to conform to international safety standards for nuclear vessels.
All nuclear-powered icebreakers have been commissioned by the Soviet Union or Russia.
(1959–1989; museum ship)
(1975–2008; decommissioned)
(1977–1992; scrapped)
(1985–2013; decommissioned)
(1989–present)
(1989–2014; decommissioned)
(1990–present)
(1992–present)
(2007–present)
(2020–present)
(2021–present)
(2022–present)
(2024–present)
| Technology | Power generation | null |
917400 | https://en.wikipedia.org/wiki/Potassium%20alum | Potassium alum | Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound first mentioned under various Sanskrit names in Ayurvedic medicinal texts such as , , and ; is chemically defined as the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution with space group Pa and lattice parameter of 12.18 Å. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.
Potassium alum is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.
History
Historically, potassium alum was used extensively in the wool industry from Classical antiquity, during the Middle Ages, and well into 19th century as a mordant or dye fixative in the process of turning wool into dyed bolts of cloth.
Antiquity
Egypt
Potassium alum was also known to the Ancient Egyptians, who obtained it from evaporites in the Western desert and reportedly used it as early as 1500 BCE to reduce the visible cloudiness (turbidity) in the water.
Mesopotamia
According to the expert on Middle Eastern history of chemistry Martin Levey, potassium alum is one of the few compounds known to the ancients that can be found relatively pure in nature, as well as one of only a few chemicals used in Mesopotamian chemical technology that can be identified with certainty. Both native and imported potassium alum was used. Together with other agents, potassium alum was used in glass-making, tanning, and in the dyeing of cloth, wood, and possibly hair. A tanning process using potassium alum is described in tablets from the first millennium BCE. When Levey wrote his article in 1958, no description of the dyeing process had been found, so it is not known how potassium alum was used in it. In Mesopotamian medicine potassium alum was used extensively, for example against itch, jaundice, some eye condition, and unidentified ailments.
According to Levey, potassium alum was used in "classical times" as a flux when soldering copper, in the fireproofing of wood, and in the separation of silver and gold, but that there is no evidence that these uses existed in Mesopotamia.
Greece
The production of potassium alum from alunite is archaeologically attested on the island Lesbos. This site was abandoned in the 7th century but dates back at least to the 2nd century CE.
Rome
Potassium alum was described under the name alumen or salsugoterrae by Pliny, and it is clearly the same as the stypteria (στυπτηρία) described by Dioscorides. However, the name alum and other names applied to this substance — like misy, sory, chalcanthum, and atramentum sutorium — were often applied to other products with vaguely similar properties or uses, such as iron sulfate or "green vitriol".
India and China
Potassium alum is mentioned in Ayurvedic texts namely Charak Samhita, Sushurta Samhita, and Ashtanga Hridaya with the name such as sphaṭika kṣāra, phitkari or saurashtri. It is used in traditional Chinese medicine with the name mingfan .
Middle Ages
In the 13th and 14th centuries, alum (from alunite) was a major import from Phocaea (Gulf of Smyrna in Byzantium) by Genoans and Venetians (and was a cause of war between Genoa and Venice) and later by Florence. After the fall of Constantinople, alunite (the source of alum) was discovered at Tolfa in the Papal States (1461). The textile dyeing industry in Bruges, and many locations in Italy, and later in England, required alum to stabilize the dyes onto the fabric (make the dyes "fast") and also to brighten the colors.
Modern era
England
Potassium alum was imported into England mainly from the Middle East, and, from the late 15th century onwards, the Papal States for hundreds of years. Its use there was as a dye-fixer (mordant) for wool (which was one of England's primary industries, the value of which increased significantly if dyed). These sources were unreliable, however, and there was a push to develop a source in England especially as imports from the Papal States ceased following the excommunication of Henry VIII.
With state financing, attempts were made throughout the 16th century, but without success until the early 17th century. An industry was founded in Yorkshire to process the shale, which contained the key ingredient, aluminium sulfate, and made an important contribution to the Industrial Revolution. One of the oldest historic sites for the production of alum from shale and human urine are the Peak alum works in Ravenscar, North Yorkshire. By the 18th century, the landscape of northeast Yorkshire had been devastated by this process, which involved constructing stacks of burning shale and fuelling them with firewood continuously for months. The rest of the production process consisted of quarrying, extraction, steeping of shale ash with seaweed in urine, boiling, evaporating, crystallisation, milling and loading into sacks for export. Quarrying ate into the cliffs of the area, the forests were felled for charcoal and the land polluted by sulfuric acid and ash.
Identification of the formula
In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum. The error was soon corrected by Johann Pott and Andreas Marggraf, who showed that the precipitate obtained when an alkali is poured into a solution of alum, namely alumina, is quite different from lime and chalk, and is one of the ingredients in common clay.
Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in sulfuric acid and adding potash or ammonia to the concentrated solution. In 1767, Torbern Bergman observed the need for potassium or ammonium sulfates to convert aluminium sulfate into alum, while sodium or calcium would not work.
At the time, potassium ("potash") was believed to be exclusively found on plants. However, in 1797, Martin Klaproth discovered the presence of potassium in the minerals leucite and lepidolite.
Louis Vauquelin then conjectured that potassium was likewise an ingredient in many other minerals. Given Marggraf and Bergman's experiments, he suspected that this alkali constituted an essential ingredient of natural alum. In 1797 he published a dissertation demonstrating that alum is a double salt, composed of sulfuric acid, alumina, and potash. In the same journal volume, Jean-Antoine Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself, confirming Vauquelin's results.
Characteristics
Potassium alum crystallizes in regular octahedra with flattened corners and is very soluble in water. The solution is slightly acidic and is astringent to the taste. Neutralizing a solution of alum with potassium hydroxide will begin to cause the separation of alumina .
When heated to nearly a red heat, it gives a porous, friable mass, which is known as "burnt alum". It fuses at in its own water of crystallization.
Natural occurrence
Potassium alum dodecahydrate occurs in nature as a sulfate mineral called alum-(K), typically as encrustations on rocks in areas of weathering and oxidation of sulfide minerals and potassium-bearing minerals.
In the past, potassium alum has been obtained from alunite (), mined from sulfur-containing volcanic sediments. Alunite is an associate and likely potassium and aluminium source. It has been reported at Vesuvius, Italy; east of Springsure, Queensland; in Alum Cave, Tennessee; Alum Gulch, Santa Cruz County, Arizona and the Philippine island of Cebu.
In order to obtain alum from alunite, it is calcined and then exposed to the action of air for a considerable time. During this exposure it is kept continually moistened with water, so that it ultimately falls to a very fine powder. This powder is then lixiviated with hot water, the liquor decanted, and the alum allowed to crystallize.
The undecahydrate also occurs as the fibrous mineral kalinite ().
Industrial production
Potassium alum historically was mainly extracted from alunite.
Potassium alum is now produced industrially by adding potassium sulfate to a concentrated solution of aluminium sulfate. The aluminium sulfate is usually obtained by treating minerals like alum schist, bauxite and cryolite with sulfuric acid. If much iron should be present in the sulfate then it is preferable to use potassium chloride in place of potassium sulfate.
Uses
Medicine and cosmetics
[[File:Potassium Alum Block India Shaving Aftershave.jpg|thumb|An ammonium alum block sold as an astringent in pharmacies in India (where it is widely known as Fitkiri (Bengali), Fitkari (Hindi)” ]]
Potassium alum is used in medicine mainly as an astringent (or styptic) and antiseptic.
Styptic pencils are rods composed of potassium alum or aluminum sulfate, used topically to reduce bleeding in minor cuts (especially from shaving) and abrasions, nosebleeds, and hemorrhoids, and to relieve pain from stings and bites. Potassium alum blocks are rubbed over the wet skin after shaving.
Potassium alum is also used topically to remove pimples and acne, and to cauterize aphthous ulcers in the mouth and canker sores, as it has a significant drying effect to the area and reduces the irritation felt at the site. It has been used to stop bleeding in cases of hemorrhagic cystitis and is used in some countries as a cure for hyperhidrosis.
It is used in dentistry (especially in gingival retraction cords) because of its astringent and hemostatic properties.
Potassium and ammonium alum are the active ingredients in some antiperspirants and deodorants, acting by inhibiting the growth of the bacteria responsible for body odor. Alum's antiperspirant and antibacterial properties contribute to its traditional use as an underarm deodorant. It has been used for this purpose in Europe, Mexico, Thailand (where it is called sarn-som), throughout Asia and in the Philippines (where it is called tawas). Today, potassium or ammonium alum is sold commercially for this purpose as a "deodorant crystal". Beginning in 2005 the US Food and Drug Administration no longer recognized it as a wetness reducer, but it is still available and used in several other countries, primarily in Asia.
Potassium alum was the major immunologic adjuvant used to increase the efficacy of vaccines, and has been used since the 1920s. But it has been almost completely replaced by aluminium hydroxide and aluminium phosphate in commercial vaccines.
Alum may be used in depilatory waxes used for the removal of body hair or applied to freshly waxed skin as a soothing agent.
In the 1950s, men sporting crewcut or flattop hairstyles sometimes applied alum to their hair, as an alternative to pomade, to keep the hair standing up.
Culinary
Potassium alum may be an acidic ingredient of baking powder to provide a second leavening phase at high temperatures (although sodium alum is more commonly used for that purpose). For example, potassium alum is frequently used in leavening of , a traditional Chinese fried bread, throughout China.
Alum was used by bakers in England during the 1800s to make bread whiter. This was theorized by some, including John Snow, to cause rickets. The Sale of Food and Drugs Act 1875 (38 & 39 Vict. c. 63) prevented this and other adulterations.
Potassium alum, under the name "alum powder", is found in the spice section of many grocery stores in the US. Its chief culinary use is in pickling recipes, to preserve and add crispness to fruit and vegetables.
Flame retardant
Potassium alum is used as a fire retardant to render cloth, wood, and paper materials less flammable.
Tanning
Potassium alum is used in leather tanning, in order to remove moisture from the hide and prevent rotting. Unlike tannic acid, alum doesn't bind to the hide and can be washed out of it.
Dyeing
Alum has been used since antiquity as mordant to form a permanent bond between dye and natural textile fibers like wool. It is also used for this purpose in paper marbling.
Chemical flocculant
Potassium alum has been used since remote antiquity for purification of turbid liquids. It is still widely used in the purification of water for drinking and industrial processes water, treatment of effluents and post-storm treatment of lakes to precipitate contaminants.
Between 30 and 40 ppm of alum for household wastewater, often more for industrial wastewater, is added to the water so that the negatively charged colloidal particles clump together into "flocs", which then float to the top of the liquid, settle to the bottom of the liquid, or can be more easily filtered from the liquid, prior to further filtration and disinfection of the water. Like other similar salts, it works by neutralizing the electrical double layer surrounding very fine suspended particles, allowing them to join into flocs.
The same principle is exploited when using alum to increase the viscosity of a ceramic glaze suspension; this makes the glaze more readily adherent and slows its rate of sedimentation.
Lake pigments
Aluminum hydroxide from potassium alum serves as a base for the majority of lake pigments.
Dissolving iron and steel
Alum solution has the property of dissolving steels while not affecting aluminium or base metals. Alum solution can be used to dissolve steel tool bits that have become lodged in machined castings.
Other
In traditional Japanese art, alum and animal glue were dissolved in water, forming a liquid known as dousa'' (:ja:礬水), and used as an undercoat for paper sizing.
Alum is an ingredient in some recipes for homemade modeling compounds, often called "play clay" or "play dough", intended for use by children.
Potassium alum was formerly used as a hardener for photographic emulsions (films and papers), usually as part of the fixer. It has now been replaced in that use by other chemicals.
Toxicology and safety
Potassium alum may be a weak irritant to the skin.
| Physical sciences | Sulfuric oxyanions | Chemistry |
918643 | https://en.wikipedia.org/wiki/Washer%20%28hardware%29 | Washer (hardware) | A washer is a thin plate (typically disk-shaped, but sometimes square) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring (Belleville washer, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer).
Washers are usually metal or plastic. High-quality bolted joints require hardened steel washers to prevent the loss of pre-load due to brinelling after the torque is applied. Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminium surfaces. They may also be used in rotating applications, as a bearing. A thrust washer is used when a rolling element bearing is not needed either from a cost-performance perspective or due to space restraints. Coatings can be used to reduce wear and friction, either by hardening the surface or by providing a solid lubricant (i.e. a self-lubricating surface).
The origin of the word is unknown. The first recorded use of the word was in 1346; however, the first time its definition was recorded was in 1611.
Rubber or fiber gaskets used in taps (or faucets, valves, and other piping connections) as seal against water leaks are sometimes referred to colloquially as washers; but, while they may look similar, washers and gaskets are usually designed for different functions and made differently.
Washer types
Most washers can be categorized into three broad types;
Plain washers, which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as electrical
Spring washers, which have axial flexibility and are used to prevent fastening or loosening due to vibrations
Locking washers, which prevent fastening or loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers.
Plain washers
Spring and locking washers
Lock washers, locknuts, jam nuts, and thread-locking fluid are ways to prevent vibration from loosening a bolted joint.
Gaskets
The term washer is often applied to various gasket types such as those used to seal the control valve in taps.
Specialised types
The DIN 125 metric washer standard refers to subtypes A and B. ISO 7089 calls these Form A and ISO 7090 calls them Form B. They are all the same overall size, but Form B is chamfered on one side.
Materials
Washers can be fabricated from a variety of materials including, but not limited to:
Steel – Carbon steel, spring steel, A2 (304) stainless steel, and A4 (316/316L) stainless steel
Non-ferrous metal – Copper, brass, aluminium, titanium, iron, bronze, and zinc
Alloy – Silicon bronze, Inconel, Monel, and Hastelloy
Plastic – Thermoplastics and thermosetting polymers such as polyethylene, PTFE (Teflon)
Nylon – Nylon 6, Nylon 66, Nylatron, and Tecamid MDS
Specialty – Fibers, ceramics, rubber, felt, leather, bimetals, and mica
Phenolic – The material has good electrical insulation, is lightweight, tough, has low moisture absorption, is heat resistant, and is resistant to chemicals and corrosion. Phenolic washers are substitutes for flat metallic washers in cases where electrical insulation is required. Phenolic washers are stamped out of large sheets of the phenolic material. The term "phenolic washer" is sometimes used for stamped washers from laminated materials such as paper, canvas, and Mylar.
Corrosion resistance
A number of techniques are used to enhance the corrosion resistant properties of certain washer materials:
Metallic coatings – Typical coatings used to produce corrosion resistant washers are zinc, cadmium, and nickel. Zinc coating acts as a sacrificial surface layer that falls victim to corrosive materials before the washer's material can be harmed. Cadmium produces a high-quality protective surface but is toxic, both biologically and environmentally. Nickel coatings add protection from corrosion only when the finish is dense and non-porous.
Electroplating – This method involves coating the washer by electrolytic deposition using metals such as chromium or silver.
Phosphating – A resilient, but abrasive surface is achieved by incorporating a zinc-phosphate layer and corrosion-protective oil.
Browning or bluing – Exposing the washer (typically steel) to a chemical compound or alkali salt solution causes an oxidizing chemical reaction, which results in the creation of a corrosion-resistant, colored surface. The integrity of the coating can be improved by treating the finished product with a water-displacing oil.
Chemical plating – This technique utilizes a nickel-phosphor alloy that is precipitated onto the washer surface, creating an extremely corrosion- and abrasive-resistant surface.
Type and form
The American National Standards Institute (ANSI) provides standards for general use flat washers. Type A is a series of steel washers at broad tolerances, where precision is not critical. Type B is a series of flat washers with tighter tolerances where outside diameters are categorized as "narrow", "regular" or "wide" for specific bolt sizes.
"Type" is not to be confused with "form" (but often is). The British Standard for Metric Series Metal Washers (BS4320), written in 1968, coined the term "form". The forms go from A to G and dictate the outside diameter and thickness of the flat washers.
Form A: Normal diameter, normal thickness
Form B: Normal diameter, light thickness
Form C: Large diameter, normal thickness
Form D: Large diameter, light thickness
Form E: Normal diameter, normal thickness
Form F: Large diameter, normal thickness
Form G: Largest diameter, larger thickness.Washer 'form' when comparing different washer material types is used quite freely by stockists. In relation to BS4320 specifically, washer forms 'A' to 'D' inclusive are designated 'bright metal' washers and are supplied self-finished in various metals including: steel alloys, brass, copper, etc. Whereas, BS4320 washer forms 'E' to 'G' inclusive are designated 'black' (uncoated) mild steel washers, which normally are specified with a supplementary protective coating supply condition.
Standard metric flat washers sizes
Washers of standard metric sizes equivalent to BS4320 Form A are listed in the table below. Measurements in the table refer to the dimensions of the washers as described by the drawing. Specifications for standard metric flat washers were known as DIN 125 (withdrawn) and replaced with ISO 7089. DIN (Deutsches Institut für Normung - German Institute for Standardization) standards are issued for a variety of components including industrial fasteners as Metric DIN 125 Flat Washers. The DIN standards remain common in Germany, Europe and globally even though the transition to ISO standards is taking place. DIN standards continue to be used for parts which do not have ISO equivalents or for which there is no need for standardization.
| Technology | Rigid components | null |
2848344 | https://en.wikipedia.org/wiki/Circuit%20design | Circuit design | In Electrical Engineering, the process of circuit design can cover systems ranging from complex electronic systems down to the individual transistors within an integrated circuit. One person can often do the design process without needing a planned or structured design process for simple circuits. Still, teams of designers following a systematic approach with intelligently guided computer simulation are becoming increasingly common for more complex designs. In integrated circuit design automation, the term "circuit design" often refers to the step of the design cycle which outputs the schematics of the integrated circuit. Typically this is the step between logic design and physical design.
Process
Traditional circuit design usually involves several stages. Sometimes, a design specification is written after liaising with the customer. A technical proposal may be written to meet the requirements of the customer specification. The next stage involves synthesising on paper a schematic circuit diagram, an abstract electrical or electronic circuit that will meet the specifications. A calculation of the component values to meet the operating specifications under specified conditions should be made. Simulations may be performed to verify the correctness of the design.
A breadboard or other prototype version of the design for testing against specification may be built. It may involve making any alterations to the circuit to achieve compliance. A choice as to a method of construction and all the parts and materials to be used must be made. There is a presentation of component and layout information to draughtspersons and layout and mechanical engineers for prototype production. This is followed by the testing or type-testing several prototypes to ensure compliance with customer requirements. Usually, there is a signing and approval of the final manufacturing drawings, and there may be post-design services (obsolescence of components, etc.).
Specification
The process of circuit design begins with the specification, which states the functionality that the finished design must provide but does not indicate how it is to be achieved . The initial specification is a technically detailed description of what the customer wants the finished circuit to achieve and can include a variety of electrical requirements, such as what signals the circuit will receive, what signals it must output, what power supplies are available and how much power it is permitted to consume. The specification can (and normally does) also set some of the physical parameters that the design must meet, such as size, weight, moisture resistance, temperature range, thermal output, vibration tolerance, and acceleration tolerance.
As the design process progresses, the designer(s) will frequently return to the specification and alter it to take account of the progress of the design. This can involve tightening specifications that the customer has supplied and adding tests that the circuit must pass to be accepted. These additional specifications will often be used in the verification of a design. Changes that conflict with or modify the customer's original specifications will almost always have to be approved by the customer before they can be acted upon.
Correctly identifying the customer needs can avoid a condition known as 'design creep', which occurs in the absence of realistic initial expectations, and later by failing to communicate fully with the client during the design process. It can be defined in terms of its results; "at one extreme is a circuit with more functionality than necessary, and at the other is a circuit having an incorrect functionality". Nevertheless, some changes can be expected. It is good practice to keep options open for as long as possible because it's easier to remove spare elements from the circuit later on than it is to put them in.
Design
The design process involves moving from the specification at the start to a plan that contains all the information needed to be physically constructed at the end; this happens typically by passing through several stages, although in the straightforward circuit, it may be done in a single step. The process usually begins with the conversion of the specification into a block diagram of the various functions that the circuit must perform, at this stage the contents of each block are not considered, only what each block must do, this is sometimes referred to as a "black box" design. This approach allows the possibly highly complex task to be broken into smaller tasks either by tackled in sequence or divided amongst members of a design team.
Each block is then considered in more detail, still at an abstract stage, but with a lot more focus on the details of the electrical functions to be provided. At this or later stages, it is common to require a large amount of research or mathematical modeling into what is and is not feasible to achieve. The results of this research may be fed back into earlier stages of the design process, for example if it turns out one of the blocks cannot be designed within the parameters set for it, it may be necessary to alter other blocks instead. At this point, it is also common to start considering both how to demonstrate that the design does meet the specifications, and how it is to be tested ( which can include self diagnostic tools ).
Finally, the individual circuit components are chosen to carry out each function in the overall design; at this stage, the physical layout and electrical connections of each component are also decided, this layout commonly taking the form of artwork for the production of a printed circuit board or Integrated circuit. This stage is typically highly time-consuming because of the vast array of choices available. A practical constraint on the design at this stage is standardization;. At the same time, a certain value of a component may be calculated for use in some location in a circuit; if that value cannot be purchased from a supplier, then the problem has still not been solved. To avoid this, a certain amount of 'catalog engineering' can be applied to solve the more mundane tasks within an overall design.
In general, the circuit principles of design flow are including but not limited to architecture scope definition, materials selection, schematic capture, PCB layout design that include power and signal integrity considition, test and validation.
Costs
Generally, the cost of designing circuits is directly tied to the final circuits' complexity. The greater the complexity (quantity of components and design novelty), the more hours of a skilled engineer's time will be necessary to create a functional product. The process can be tedious, as minute details or features could take any amount of time, materials and manpower to create. Like taking into account the effects of modifying transistor sizes or codecs. In the world of flexible electronics, replacing the, widely used, polyimide substrates with materials like PEN or PET to produce flexible electronics, could reduce costs by factors of 5-10.
Costs for designing a circuit are almost always far higher than production costs per unit, as the cost of production and function of the circuit depends greatly on the design of the circuit.
Although the typical PCB production methods involve subtractive manufacturing, there are methods that use an additive manufacturing process, such as using a 3D printer to "print" a PCB. This method is thought to cost less than additive manufacturing and eliminates the need for waste management altogether.
Verification and testing
Once a circuit has been designed, it must be both verified and tested. Verification is the process of going through each stage of a design and ensuring that it will do what the specification requires it to do. This is frequently a highly mathematical process and can involve large-scale computer simulations of the design. In any complicated design, it is very likely that problems will be found at this stage and may affect a large amount of the design work to be redone to fix them.
Testing is the real-world counterpart to verification; testing involves physically building at least a prototype of the design and then (in combination with the test procedures in the specification or added to it) checking the circuit does what it was designed to.
Design Software
In the Software of the visual DSD, the Logic Circuit of complement circuit is implemented by the compiling program code. These types of software programs are creating cheaper more efficient circuits for all types of circuits. We have implemented functional simulations to verify logic functions corresponding to logic expressions in our proposed circuits. The proposed architectures are modeled in VHDL language. Using this language will create more efficient circuits that will not only be cheaper but last longer. These are only two of many design software that help individuals plan there circuits for production.
Prototyping
Prototyping plays a significant role in the complex process of circuit design. This iterative process involves continuous refinement and correction of errors. The task of circuit design is demanding and requires meticulous attention to detail to avoid errors. Circuit designers are required to conduct multiple tests to ensure the efficiency and safety of their designs before they are deemed suitable for consumer use.
Prototyping is an integral part of electrical work due to its precise and meticulous nature. The absence of prototyping could potentially lead to errors in the final product. Circuit designers, who are compensated for their expertise in creating electrical circuits, bear the responsibility of ensuring the safety of consumers who purchase and use these circuits at home.
The risks associated with neglecting the prototyping process and releasing a flawed electrical circuit are significant. These risks include the potential for fires and overheated wires, which could result in burns or severe injuries to unsuspecting individuals.
Results
Every electrical circuit starts with a circuit board simulator of how the things will be put together at the end of the day and show how the circuit will work virtually. A blueprint is the drawing of the technical design and final product. After all, this is done, and you use the blueprint to put the circuit together, you will get the results of electrical circuits that are quite memorable. The circuit will run anything from a vacuum to a big TV in a movie theater. All of these take a long time and a certain skill not everyone can acquire. The electrical circuit is something most things we need in our everyday lives.
Documentation
Any commercial design will normally also include an element of documentation; the precise nature of this documentation will vary according to the size and complexity of the circuit and the country in which it is to be used. As a bare minimum, the documentation will normally include at least the specification and testing procedures for the design and a statement of compliance with current regulations. In the EU this last item will normally take the form of a CE Declaration listing the European directives complied with and naming an individual responsible for compliance.
Software
Altium Designer
EasyEDA
gEDA
KiCad
OrCAD
NI Multisim
SPICE
| Technology | Basics_4 | null |
2848730 | https://en.wikipedia.org/wiki/Cosmological%20horizon | Cosmological horizon | A cosmological horizon is a measure of the distance from which one could possibly retrieve information. This observable constraint is due to various properties of general relativity, the expanding universe, and the physics of Big Bang cosmology. Cosmological horizons set the size and scale of the observable universe. This article explains a number of these horizons.
Particle horizon
The particle horizon, also called the cosmological horizon, the comoving horizon, or the cosmic light horizon, is the maximum distance from which light from particles could have traveled to the observer in the age of the universe. It represents the boundary between the observable and the unobservable regions of the universe, so its distance at the present epoch defines the size of the observable universe. Due to the expansion of the universe, it is not simply the age of the universe times the speed of light, as in the Hubble horizon, but rather the speed of light multiplied by the conformal time. The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model.
In terms of comoving distance, the particle horizon is equal to the conformal time that has passed since the Big Bang, times the speed of light. In general, the conformal time at a certain time is given in terms of the scale factor by,
or
The particle horizon is the boundary between two regions at a point at a given time: one region defined by events that have already been observed by an observer, and the other by events which cannot be observed at that time. It represents the furthest distance from which we can retrieve information from the past, and so defines the observable universe.
Hubble horizon
Hubble radius, Hubble sphere (not to be confused with a Hubble bubble), Hubble volume, or Hubble horizon is a conceptual horizon defining the boundary between particles that are moving slower and faster than the speed of light relative to an observer at one given time. Note that this does not mean the particle is unobservable; the light from the past is reaching and will continue to reach the observer for a while. Also, more importantly, in the current expansion models, light emitted from the Hubble radius will reach us in a finite amount of time.
It is a common misconception that light from the Hubble radius can never reach us. In models assuming decreasing with time (some cases of Friedmann universe), while particles on the Hubble radius recede from us with the speed of light, the Hubble radius gets larger over time, so light emitted towards us from a particle on the Hubble radius will be inside the Hubble radius some time later. In such models, only light emitted from the cosmic event horizon or further will never reach us in a finite amount of time.
The Hubble velocity of an object is given by Hubble's law,
Replacing with speed of light and solving for proper distance we obtain the radius of Hubble sphere as
In an ever-accelerating universe, if two particles are separated by a distance greater than the Hubble radius, they cannot talk to each other from now on (as they are now, not as they have been in the past). However, if they are outside of each other's particle horizon, they could have never communicated. Depending on the form of expansion of the universe, they may be able to exchange information in the future. Today,
yielding a Hubble horizon of some 4.1 gigaparsecs. This horizon is not really a physical size, but it is often used as useful length scale as most physical sizes in cosmology can be written in terms of those factors.
One can also define a comoving Hubble horizon by simply dividing the Hubble radius by the scale factor
Event horizon
The particle horizon differs from the cosmic event horizon, in that the particle horizon represents the largest comoving distance from which light could have reached the observer by a specific time, while the cosmic event horizon is the largest comoving distance from which light emitted now can ever reach the observer in the future. The current distance to our cosmic event horizon is about , well within our observable range given by the particle horizon.
In general, the proper distance to the event horizon at time is given by
where is the time-coordinate of the end of the universe, which would be infinite in the case of a universe that expands forever.
For our case, assuming that dark energy is due to a cosmological constant Λ, there will be a minimum Hubble parameter He and a maximum horizon de which is often referred to as the only particle horizon:
Future horizon
In an accelerating universe, there are events which will be unobservable as as signals from future events become redshifted to arbitrarily long wavelengths in the exponentially expanding de Sitter space. This sets a limit on the farthest distance that we can possibly see as measured in units of proper distance today. Or, more precisely, there are events that are spatially separated for a certain frame of reference happening simultaneously with the event occurring right now for which no signal will ever reach us, even though we can observe events that occurred at the same location in space that happened in the distant past.
While we will continue to receive signals from this location in space, even if we wait an infinite amount of time, a signal that left from that location today will never reach us. The signals coming from that location will have less and less energy and be less and less frequent until the location, for all practical purposes, becomes unobservable. In a universe that is dominated by dark energy which is undergoing an exponential expansion of the scale factor, all objects that are gravitationally unbound with respect to the Milky Way will become unobservable, in a futuristic version of Kapteyn's universe.
Practical horizons
While not technically "horizons" in the sense of an impossibility for observations due to relativity or cosmological solutions, there are practical horizons which include the optical horizon, set at the surface of last scattering. This is the farthest distance that any photon can freely stream. Similarly, there is a "neutrino horizon" set for the farthest distance a neutrino can freely stream and a gravitational wave horizon at the farthest distance that gravitational waves can freely stream. The latter is predicted to be a direct probe of the end of cosmic inflation.
| Physical sciences | Physical cosmology | Astronomy |
2849297 | https://en.wikipedia.org/wiki/Oppositional%20defiant%20disorder | Oppositional defiant disorder | Oppositional defiant disorder (ODD) is listed in the DSM-5 under Disruptive, impulse-control, and conduct disorders and defined as "a pattern of angry/irritable mood, argumentative/defiant behavior, or vindictiveness." This behavior is usually targeted toward peers, parents, teachers, and other authority figures, including law enforcement officials. Unlike conduct disorder (CD), those with ODD do not generally show patterns of aggression towards random people, violence against animals, destruction of property, theft, or deceit. One-half of children with ODD also fulfill the diagnostic criteria for ADHD.
History
Oppositional defiant disorder was first defined in the DSM-III (1980). Since the introduction of ODD as an independent disorder, the field trials to inform its definition have included predominantly male subjects. Some clinicians have debated whether the diagnostic criteria would be clinically relevant for use with women, and furthermore, some have questioned whether gender-specific criteria and thresholds should be included. Additionally, some clinicians have questioned the preclusion of ODD when conduct disorder is present. According to Dickstein, the DSM-5 attempts to:
Epidemiology
ODD is a pattern of negative, defiant, disobedient, and hostile behavior, and it is one of the most prevalent disorders from preschool age to adulthood. This can include frequent temper tantrums, excessive arguing with adults, refusing to follow rules, purposefully upsetting others, getting easily irked, having an angry attitude, and vindictive acts. Children with ODD usually begin showing symptoms around age 6 to 8, although the disorder can emerge in younger children too. Symptoms can last throughout teenage years. The pooled prevalence is 3.6% up to age 18.
Oppositional defiant disorder has a prevalence of 1–11%. The average prevalence is approximately 3%. Gender and age play an important role in the rate of the disorder. ODD gradually develops and becomes apparent in preschool years, often before the age of eight years old. However, it is very unlikely to emerge following early adolescence.
There is a difference in prevalence between boys and girls, with a ratio of 1.4 to 1 before adolescence. Other research suggests a 2:1 ratio. Prevalence in girls tends to increase after puberty. Researchers have found that the general prevalence of ODD throughout cultures remains constant. However, the gendered disparities in diagnoses is only seen in Western cultures. It is unknown whether this reflects underlying differences in incidence or under-diagnosis of girls. Physical abuse at home is a significant predictor of diagnosis for girls only, and emotional responsiveness of parents is a significant predictor of diagnosis for boys only, which may have implications for how gendered socialization and received gender roles affect ODD symptoms and outcomes.
Children from lower-income backgrounds are more likely to be diagnosed with ODD. The correlative link between low income and ODD diagnosis is direct in boys, but in girls, the link is more complex; the diagnosis is associated with specific parental techniques such as corporal punishment which are in turn linked to lower income households. This disparity may be linked to a more general tendency of boys and men to display more externalized psychiatric symptoms, and girls to display more internalized ones (such as self-harm or anorexia nervosa).
In the United States, African Americans and Latinos are more likely to receive diagnoses of ODD or other conduct disorders compared to non-Hispanic White youth with the same symptoms, who are more likely to be diagnosed with ADHD. This has wide-ranging implications about the role of racial bias in how certain behaviors are perceived and categorized as either defiant or inattentive/hyperactive.
Prevalence of ODD and conduct disorder are significantly higher among children in foster care. One survey in Norway found that 14 percent met the criteria, and other studies have found a prevalence of up to 17 or even 29 percent. Low parental attachment and parenting style are strong predictors of ODD symptoms.
Earlier conceptions of ODD had higher rates of diagnosis. When the disorder was first included in the DSM-III, the prevalence was 25% higher than when the DSM-IV revised the criteria of diagnosis. The DSM-V made more changes to the criteria, grouping certain characteristics together in order to demonstrate that people with ODD display both emotional and behavioral symptoms. In addition, criteria were added to help guide clinicians in diagnosis because of the difficulty found in identifying whether the behaviors or other symptoms are directly related to the disorder or simply a phase in a child's life. Consequently, future studies may find that there was also a decline in prevalence between the DSM-IV and the DSM-V.
Signs and symptoms
The fourth revision of the Diagnostic and Statistical Manual (DSM-IV-TR) (now replaced by DSM-5) states that a person must exhibit four out of the eight signs and symptoms to meet the diagnostic threshold for ODD. These symptoms include:
Often loses temper
Is often touchy or easily annoyed
Is often angry and resentful
Often argues with authority figures or, for children and adolescents, with adults
Often actively defies or refuses to comply with requests from authority figures or with rules
Often deliberately annoys others
Often blames others for their own mistakes or misbehavior
Has been spiteful or vindictive at least twice within the past six months
These behaviors are mostly directed towards an authority figure such as a teacher or a parent. Although these behaviors can be typical among siblings, they must be observed with individuals other than siblings for an ODD diagnosis. Children with ODD can be verbally aggressive. However, they do not display physical aggressiveness, a behavior observed in conduct disorder. Furthermore, they must be perpetuated for longer than six months and must be considered beyond a normal child's age, gender and culture to fit the diagnosis. For children under five years of age, they must occur on most days over a period of six months. For children over five years of age, they must occur at least once a week for at least six months. If symptoms are confined to only one setting, most commonly home, it is considered mild in severity. If it is observed in two settings, it is characterized as moderate, and if the symptoms are observed in three or more settings, it is considered severe.
These patterns of behavior result in impairment at school or other social venues.
Etiology
There is no specific element that has yet been identified as directly causing ODD. Research looking precisely at the etiological factors linked with ODD is limited. The literature often examines common risk factors linked with all disruptive behaviors, rather than ODD specifically. Symptoms of ODD are also often believed to be the same as CD, even though the disorders have their own respective set of symptoms. When looking at disruptive behaviors such as ODD, research has shown that the causes of behaviors are multi-factorial. However, disruptive behaviors have been identified as being mostly due either to biological or environmental factors.
Genetic influences
Research indicates that parents pass on a tendency for externalizing disorders to their children that may be displayed in multiple ways, such as inattention, hyperactivity, or oppositional and conduct problems. Research has also shown that there is a genetic overlap between ODD and other externalizing disorders. Heritability can vary by age, age of onset, and other factors. Adoption and twin studies indicate that 50% or more of the variance causing antisocial behavior is attributable to heredity for both males and females. ODD also tends to occur in families with a history of ADHD, substance use disorders, or mood disorders, suggesting that a vulnerability to develop ODD may be inherited. A difficult temperament, impulsivity, and a tendency to seek rewards can also increase the risk of developing ODD. New studies into gene variants have also identified possible gene-environment (G x E) interactions, specifically in the development of conduct problems. A variant of the gene that encodes the neurotransmitter metabolizing enzyme monoamine oxidase-A (MAOA), which relates to neural systems involved in aggression, plays a key role in regulating behavior following threatening events. Brain imaging studies show patterns of arousal in areas of the brain that are associated with aggression in response to emotion-provoking stimuli.
Prenatal factors and birth complications
Many pregnancy and birth problems are related to the development of conduct problems. Malnutrition, specifically protein deficiency, lead poisoning or exposure to lead, and mother's use of alcohol or other substances during pregnancy may increase the risk of developing ODD. In numerous research, substance use prior to birth has also been associated with developing disruptive behaviors such as ODD. Although pregnancy and birth factors are correlated with ODD, strong evidence of direct biological causation is lacking.
Neurobiological factors
Deficits and injuries to certain areas of the brain can lead to serious behavioral problems in children. Brain imaging studies have suggested that children with ODD may have hypofunction in the part of the brain responsible for reasoning, judgment, and impulse control. Children with ODD are thought to have an overactive behavioral activation system (BAS), and an underactive behavioral inhibition system (BIS). The BAS stimulates behavior in response to signals of reward or non-punishment. The BIS produces anxiety and inhibits ongoing behavior in the presence of novel events, innate fear stimuli, and signals of non-reward or punishment. Neuroimaging studies have also identified structural and functional brain abnormalities in several brain regions in youths with conduct disorders. These brain regions are the amygdala, prefrontal cortex, anterior cingulate, and insula, as well as interconnected regions.
Social-cognitive factors
As many as 40 percent of boys and 25 percent of girls with persistent conduct problems display significant social-cognitive impairments. Some of these deficits include immature forms of thinking (such as egocentrism), failure to use verbal mediators to regulate their behavior, and cognitive distortions, such as interpreting a neutral event as an intentional hostile act.
Children with ODD have difficulty controlling their emotions or behaviors. In fact, students with ODD have limited social knowledge that is based only on individual experiences, which shapes how they process information and solve problems cognitively.
This information can be linked with the social information processing model (SIP) that describes how children process information to respond appropriately or inappropriately in social settings. This model explains that children will go through five stages before displaying behaviors: encoding, mental representations, response accessing, evaluation, and enactment.
However, children with ODD have cognitive distortions and impaired cognitive processes.
This will therefore directly impact their interactions and relationship negatively. It has been shown that social and cognitive impairments result in negative peer relationships, loss of friendship, and an interruption in socially engaging in activities.
Children learn through observational learning and social learning. Therefore, observations of models have a direct impact and greatly influence children's behaviors and decision-making processes. Children often learn through modeling behavior. Modeling can act as a powerful tool to modify children's cognition and behaviors.
Environmental factors
Negative parenting practices and parent–child conflict may lead to antisocial behavior, but they may also be a reaction to the oppositional and aggressive behaviors of children. Factors such as a family history of mental illnesses and/or substance use disorders as well as a dysfunctional family and inconsistent discipline by a parent or guardian can lead to the development of behavior disorders. Parenting practices not providing adequate or appropriate adjustment to situations as well as a high ratio of conflicting events within a family are causal factors of risk for developing ODD.
Insecure parent–child attachments can also contribute to ODD. Often little internalization of parent and societal standards exists in children with conduct problems. These weak bonds with their parents may lead children to associate with delinquency and substance use. Family instability and stress can also contribute to the development of ODD. Although the association between family factors and conduct problems is well established, the nature of this association and the possible causal role of family factors continues to be debated.
School is also a significant environmental context besides family that strongly influences a child's maladaptive behaviors. Studies indicate that child and adolescent externalizing disorders like ODD are strongly linked to peer network and teacher response. Children with ODD present hostile and defiant behavior toward authority including teachers which makes teachers less tolerant toward deviant children. The way in which a teacher handles disruptive behavior has a significant influence on the behavior of children with ODD. Negative relationships from the socializing influences and support network of teachers and peers increases the risk of deviant behavior. This is because the child consequently gets affiliated with deviant peers that reinforce antisocial behavior and delinquency. Due to the significant influence of teachers in managing disruptive behaviors, teacher training is a recommended intervention to change the disruptive behavior of ODD children.
In a number of studies, low socioeconomic status has also been associated with disruptive behaviors such as ODD.
Other social factors such as neglect, abuse, parents that are not involved, and lack of supervision can also contribute to ODD.
Externalizing problems are reported to be more frequent among minority-status youth, a finding that is likely related to economic hardship, limited employment opportunities, and living in high-risk urban neighborhoods. Studies have also found that the state of being exposed to violence was a contribution factor for externalizing behaviors to occur.
Diagnosis
For a child or adolescent to qualify for a diagnosis of ODD, behaviors must cause considerable distress for the family or interfere significantly with academic or social functioning. Such interference might manifest as challenges in learning at school, making friends, or placing the individual in harmful situations. These behaviors must also persist for at least six months. It is crucial to consider the bio-socio complexity in the expression and management of ODD. Biological factors such as genetics and neurodevelopmental variations interact with social factors like family dynamics, educational practices, and societal norms to influence the manifestation and recognition of ODD symptoms. The effects of ODD can be amplified by other disorders in comorbidity such as ADHD, depression, and substance use disorders. This intricate interplay between biological predispositions and social factors can lead to diverse clinical presentations, affecting the approaches to treatment and support.
Additionally, it has been observed that adults who were diagnosed with ODD as children tend to have a higher chance of being diagnosed with other mental illnesses in their lifetime, as well as being at a higher risk of developing social and emotional problems. This suggests that longitudinal support and intervention, taking into account the individual's biological makeup and social context, are vital for improving long-term outcomes for those with ODD.
Management
Approaches to the treatment of ODD include parent management training, individual psychotherapy, family therapy, cognitive behavioral therapy, and social skills training. According to the American Academy of Child and Adolescent Psychiatry, treatments for ODD are tailored specifically to the individual child, and different treatment techniques are applied for pre-schoolers and adolescents.
Children with oppositional defiant disorder tend to exhibit problematic behavior that can be very difficult to control. An occupational therapist can recommend family based education referred to as parent management training (PMT) in order to encourage positive parents and child relationships and reduce the child's tantrums and other disruptive behaviors. Since ODD is a neurological disorder that has biological correlates, an occupational therapist can also provide problem solving training to encourage positive coping skills when difficult situations arise, as well as offer cognitive behavioral therapy.
Psychopharmacological treatment
Psychopharmacological treatment is the use of prescribed medication in managing oppositional defiant disorder. Prescribed medications to control ODD include mood stabilizers, anti-psychotics, and stimulants. In two controlled randomized trials, it was found that between administered lithium and the placebo group, administering lithium decreased aggression in children with conduct disorder in a safe manner. However, a third study found the treatment of lithium over a period of two weeks invalid. Other drugs seen in studies include haloperidol, thioridazine, and methylphenidate which also is effective in treating ADHD, as it is a common comorbidity.
The effectiveness of drug and medication treatment is not well established. Effects that can result from taking these medications include hypotension, extrapyramidal symptoms, tardive dyskinesia, obesity, and increase in weight. Psychopharmacological treatment is found to be most effective when paired with another treatment plan, such as individual intervention or multimodal intervention.
Individual interventions
Individual interventions are focused on child-specific individualized plans. These interventions include anger control/stress inoculation, assertiveness training, a child-focused problem-solving skills training program, and self-monitoring skills.
Anger control and stress inoculation help prepare the child for possible upsetting situations or events that may cause anger and stress. They include a process of steps the child may go through.
Assertiveness training educates individuals in keeping a balance between passivity and aggression. It aims to help the child respond in a controlled and fair manner.
A child-focused problem-solving skills training program aims to teach the child new skills and cognitive processes that teach how to deal with negative thoughts, feelings, and actions.
Parent and family treatment
According to randomized trials, evidence shows that parent management training is most effective. It has strong influences over a long period of time and in various environments.
Parent-child interaction training is intended to coach the parents while involving the child. This training has two phases; the first phase is child-directed interaction, where the focus is to teach the child non-directive play skills. The second phase is parent-directed interaction, where the parents are coached on aspects including clear instruction, praise for compliance, and time-out for noncompliance. The parent-child interaction training is best suited for elementary-aged children.
Parent and family treatment has a low financial cost, which can yield an increase in beneficial results.
Multimodal intervention
Multimodal intervention is an effective treatment that looks at different levels including family, peers, school, and neighborhood. It is an intervention that concentrates on multiple risk factors. The focus is on parent training, classroom social skills, and playground behavior programs. The intervention is intensive and addresses barriers to individuals' improvement such as parental substance use or parental marital conflict.
An impediment to treatment includes the nature of the disorder itself, whereby treatment is often not complied with and is not continued or adhered to for adequate periods of time.
Comorbidity
Oppositional defiant disorder can be described as a term or disorder with a variety of pathways in regard to comorbidity. High importance must be given to the representation of ODD as a distinct psychiatric disorder independent of conduct disorder.
In the context of oppositional defiant disorder and comorbidity with other disorders, researchers often conclude that ODD co-occurs with an attention deficit hyperactivity disorder (ADHD), anxiety disorders, emotional disorders as well as mood disorders. Those mood disorders can be linked to major depression or bipolar disorder. Indirect consequences of ODD can also be related or associated with a later mental disorder. For instance, conduct disorder is often studied in connection with ODD. Strong comorbidity can be observed within those two disorders, but an even higher connection with ADHD in relation to ODD can be seen. For instance, children or adolescents who have ODD with coexisting ADHD will usually be more aggressive and have more of the negative behavioral symptoms of ODD, which can inhibit them from having a successful academic life. This will be reflected in their academic path as students.
Other conditions that can be predicted in children or people with ODD are learning disorders in which the person has significant impairments with academics and language disorders, in which problems can be observed related to language production and/or comprehension.
Criticism
Oppositional defiant disorder's validity as a diagnosis has been criticized since its inclusion in the DSM III in 1980. ODD was considered to produce minor impairment insufficient to qualify as a medical diagnosis, and was difficult to separate from conduct disorder, with some estimates that over 50% of those diagnosed with conduct disorder would also meet criteria for ODD. The diagnosis of ODD was also criticized for medicalizing normal developmental behavior. To address these problems, the DSM-III-R dropped the criterion of swearing and changed the cutoff from five of nine criteria, to four of eight. Most evidence indicated a dose–response relationship between the severity of symptoms and level of functional impairment, suggesting that the diagnostic threshold was arbitrary. Early field trials of ODD used subjects who were over 75% male.
Recent criticisms of ODD suggest that the use of ODD as a diagnosis exacerbates the stigma surrounding reactive behavior and frames normal reactions to trauma as personal issues of self-control. Anti-psychiatry scholars have extensively criticized this diagnosis through a Foucauldian framework, characterizing it as a tool of the psy apparatus which pathologizes resistance to injustice. Oppositional defiant disorder has been compared to drapetomania, a now-obsolete disorder proposed by Samuel A. Cartwright which characterized slaves in the Antebellum South who repeatedly tried to escape as being mentally ill.
Race and gender bias in the US
Research has shown that African Americans and Latino Americans are disproportionately likely to be diagnosed with ODD compared to White counterparts displaying the same symptoms, who are more likely to be diagnosed with ADHD. Assessment, diagnosis and treatment of ODD may not account for contextual problems experienced by the patient, and can be influenced by cultural and personal racial bias on the part of counselors and therapists. Many children diagnosed with ODD were, upon reassessment, found to better fit diagnoses of obsessive–compulsive disorder, bipolar disorder, attention deficit hyperactivity disorder, or anxiety disorder. Diagnoses of ODD or conduct disorder are not eligible for disability accommodation at school under the Individuals with Disabilities Education Act. When parents request accommodation for a diagnosed disorder which is eligible, such as ADHD, the request can be denied on the basis that such conditions are co-morbid with ODD. This bias in perception and diagnosis leads to defiant behaviors being medicalized and rehabilitated in White children, but criminalized for Latino and African American ones. Counselors working with children diagnosed with ODD reported that it was common for them to face stigma around the diagnosis in educational and justice systems, and that the diagnosis affected patients' self image. In one study over a quarter of children placed in the foster care system in the United States were found to have been diagnosed with ODD. Over half of children in the juvenile justice system have been diagnosed with ODD.
African American males are known to be more likely to be suspended or expelled from school, receive harsher sentences for the same offenses as defendants of different races, or be searched, assaulted or killed by police officers. The disproportionately high diagnosis of ODD in AA males may be used to rationalize these outcomes. In this manner, ODD diagnoses can serve as a mechanism of the school-to-prison pipeline. From this viewpoint, the ODD diagnosis frames expected reactions to injustice or trauma as defiant or criminal.
| Biology and health sciences | Mental disorders | Health |
2851214 | https://en.wikipedia.org/wiki/Absolute%20dating | Absolute dating | Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range, in contrast with relative dating, which places events in order without any measure of the age between events.
In archaeology, absolute dating is usually based on the physical, chemical, and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates (such as coins and historical records). For example, coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year. Absolute dating techniques include radiocarbon dating of wood or bones, potassium-argon dating, and trapped-charge dating methods such as thermoluminescence dating of glazed ceramics.
In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from younger organic remains (radiocarbon dating with ) to systems such as uranium–lead dating that allow determination of absolute ages for some of the oldest rocks on Earth.
Radiometric techniques
Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age. For example, techniques based on isotopes with half-lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.
Radiocarbon dating
One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains. This is a radiometric technique since it is based on radioactive decay. Cosmic radiation entering Earth's atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide. Carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. With death, the uptake of carbon-14 stops.
It takes 5,730 years for half the carbon-14 to decay to nitrogen; this is the half-life of carbon-14. After another 5,730 years, only one-quarter of the original carbon-14 will remain. After yet another 5,730 years, only one-eighth will be left.
By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact.
Limitations
The relatively short half-life of carbon-14, 5,730 years, makes dating reliable only up to about 60,000 years. The technique often cannot pinpoint the date of an archeological site better than historic records but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.
An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem. It is possible, particularly in dry, desert climates, for organic materials such as dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record. Thus, dating that particular tree does not necessarily indicate when the fire burned or the structure was built.
For this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating. The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard.
Potassium-argon dating
Other radiometric dating techniques are available for earlier periods. One of the most widely used is potassium–argon dating (K–Ar dating). Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.
Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice. K–Ar dating was used to calibrate the geomagnetic polarity time scale.
Luminescence dating
Thermoluminescence
Thermoluminescence testing also dates items to the last time they were heated. This technique is based on the principle that all objects absorb radiation from the environment. This process frees electrons within minerals that remain caught within the item.
Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light. This light can be measured to determine the last time the item was heated.
Radiation levels do not remain constant over time. Fluctuating levels can skew results – for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item. Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.
Because of these and other factors, Thermoluminescence is at the most about 15% accurate. It cannot be used to accurately date a site on its own. However, it can be used to confirm the antiquity of an item.
Optically stimulated luminescence (OSL)
Optically stimulated luminescence (OSL) dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to sunlight 'zeros' the luminescence signal. Upon burial, the sediment accumulates a luminescence signal as natural ambient radiation gradually ionises the mineral grains.
Careful sampling under dark conditions allows the sediment to be exposed to artificial light in the laboratory which releases the OSL signal. The amount of luminescence released is used to calculate the equivalent dose (De) that the sediment has acquired since deposition, which can be used in combination with the dose rate (Dr) to calculate the age.
Dendrochronology
Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year.
Dendrochronology has three main areas of application: paleoecology, where it is used to determine certain aspects of past ecologies (most prominently climate); archaeology, where it is used to date old buildings, etc.; and radiocarbon dating, where it is used to calibrate radiocarbon ages (see below).
In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands. Currently, the maximum for fully anchored chronologies is a little over 11,000 years from present.
Amino acid dating
Amino acid dating is a dating technique used to estimate the age of a specimen in paleobiology, archaeology, forensic science, taphonomy, sedimentary geology and other fields. This technique relates changes in amino acid molecules to the time elapsed since they were formed. All biological tissues contain amino acids. All amino acids except glycine (the simplest one) are optically active, having an asymmetric carbon atom. This means that the amino acid can have two different configurations, "D" or "L" which are mirror images of each other.
With a few important exceptions, living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization. Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.
| Physical sciences | Geochronology | Earth science |
31516478 | https://en.wikipedia.org/wiki/Frozen%20orbit | Frozen orbit | In orbital mechanics, a frozen orbit is an orbit for an artificial satellite in which perturbations have been minimized by careful selection of the orbital parameters. Perturbations can result from natural drifting due to the central body's shape, or other factors. Typically, the altitude of a satellite in a frozen orbit remains constant at the same point in each revolution over a long period of time. Variations in the inclination, position of the apsis of the orbit, and eccentricity have been minimized by choosing initial values so that their perturbations cancel out. This results in a long-term stable orbit that minimizes the use of station-keeping propellant.
Background and motivation
For spacecraft in orbit around the Earth, changes to orbital parameters are caused by the oblateness of the Earth, gravitational attraction from the Sun and Moon, solar radiation pressure and air drag. These are called perturbing forces. They must be counteracted by maneuvers to keep the spacecraft in the desired orbit. For a geostationary spacecraft, correction maneuvers on the order of per year are required to counteract the gravitational forces from the Sun and Moon which move the orbital plane away from the equatorial plane of the Earth.
For Sun-synchronous spacecraft, intentional shifting of the orbit plane (called "precession") can be used for the benefit of the mission. For these missions, a near-circular orbit with an altitude of 600–900 km is used. An appropriate inclination (97.8-99.0 degrees) is selected so that the precession of the orbital plane is equal to the rate of movement of the Earth around the Sun, about 1 degree per day.
As a result, the spacecraft will pass over points on the Earth that have the same time of day during every orbit. For instance, if the orbit is "square to the Sun", the vehicle will always pass over points at which it is 6 a.m. on the north-bound portion, and 6 p.m. on the south-bound portion (or vice versa). This is called a "Dawn-Dusk" orbit. Alternatively, if the Sun lies in the orbital plane, the vehicle will always pass over places where it is midday on the north-bound leg, and places where it is midnight on the south-bound leg (or vice versa). These are called "Noon-Midnight" orbits. Such orbits are desirable for many Earth observation missions such as weather, imagery, and mapping.
The perturbing force caused by the oblateness of the Earth will in general perturb not only the orbital plane but also the eccentricity vector of the orbit. There exists, however, an almost circular orbit for which there are no secular/long periodic perturbations of the eccentricity vector, only periodic perturbations with period equal to the orbital period. Such an orbit is then perfectly periodic (except for the orbital plane precession) and it is therefore called a "frozen orbit". Such an orbit is often the preferred choice for an Earth observation mission where repeated observations of the same area of the Earth should be made under as constant observation conditions as possible.
The Earth observation satellites are often operated in Sun-synchronous frozen orbits due to the observational advantages they provide.
Lunar frozen orbits
Low orbits
Through a study of many lunar orbiting satellites, scientists have discovered that most low lunar orbits (LLO) are unstable. Four frozen lunar orbits have been identified at 27°, 50°, 76°, and 86° inclination. NASA described this in 2006:
Lunar mascons make most low lunar orbits unstable ... As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will eventually crash into the Moon. ... [There are] a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27°, 50°, 76°, and 86°"—the last one being nearly over the lunar poles. The orbit of the relatively long-lived Apollo 15 subsatellite PFS-1 had an inclination of 28°, which turned out to be close to the inclination of one of the frozen orbits—but less fortunate PFS-2 had an orbital inclination of only 11°.
Elliptical inclined orbits
For lunar orbits with altitudes in the range, the gravity of Earth leads to orbit perturbations. Work published in 2005 showed a class of elliptical inclined lunar orbits resistant to this and are thus also frozen.
Classical theory
The classical theory of frozen orbits is essentially based on the analytical perturbation analysis for artificial satellites of Dirk Brouwer made under contract with NASA and published in 1959.
This analysis can be carried out as follows:
In the article orbital perturbation analysis the secular perturbation of the orbital pole from the term of the geopotential model is shown to be
which can be expressed in terms of orbital elements thus:
Making a similar analysis for the term (corresponding to the fact that the earth is slightly pear shaped), one gets
which can be expressed in terms of orbital elements as
In the same article the secular perturbation of the components of the eccentricity vector caused by the is shown to be:
where:
The first term is the in-plane perturbation of the eccentricity vector caused by the in-plane component of the perturbing force
The second term is the effect of the new position of the ascending node in the new orbital plane, the orbital plane being perturbed by the out-of-plane force component
Making the analysis for the term one gets for the first term, i.e. for the perturbation of the eccentricity vector from the in-plane force component
For inclinations in the range 97.8–99.0 deg, the value given by () is much smaller than the value given by () and can be ignored. Similarly the quadratic terms of the eccentricity vector components in () can be ignored for almost circular orbits, i.e. () can be approximated with
Adding the contribution
to () one gets
Now the difference equation shows that the eccentricity vector will describe a circle centered at the point ; the polar argument of the eccentricity vector increases with radians between consecutive orbits.
As
one gets for a polar orbit () with that the centre of the circle is at and the change of polar argument is 0.00400 radians per orbit.
The latter figure means that the eccentricity vector will have described a full circle in 1569 orbits.
Selecting the initial mean eccentricity vector as the mean eccentricity vector will stay constant for successive orbits, i.e. the orbit is frozen because the secular perturbations of the term given by () and of the term given by () cancel out.
In terms of classical orbital elements, this means that a frozen orbit should have the following mean elements:
Modern theory
The modern theory of frozen orbits is based on the algorithm given in a 1989 article by Mats Rosengren.
For this the analytical expression () is used to iteratively update the initial (mean) eccentricity vector to obtain that the (mean) eccentricity vector several orbits later computed by the precise numerical propagation takes precisely the same value. In this way the secular perturbation of the eccentricity vector caused by the term is used to counteract all secular perturbations, not only those (dominating) caused by the term. One such additional secular perturbation that in this way can be compensated for is the one caused by the solar radiation pressure, this perturbation is discussed in the article "Orbital perturbation analysis (spacecraft)".
Applying this algorithm for the case discussed above, i.e. a polar orbit () with ignoring all perturbing forces other than the and the forces for the numerical propagation one gets exactly the same optimal average eccentricity vector as with the "classical theory", i.e. .
When we also include the forces due to the higher zonal terms the optimal value changes to .
Assuming in addition a reasonable solar pressure (a "cross-sectional-area" of , the direction to the sun in the direction towards the ascending node) the optimal value for the average eccentricity vector becomes which corresponds to :, i.e. the optimal value is not anymore.
This algorithm is implemented in the orbit control software used for the Earth observation satellites ERS-1, ERS-2 and Envisat
Derivation of the closed form expressions for the J3 perturbation
The main perturbing force to be counteracted in order to have a frozen orbit is the " force", i.e. the gravitational force caused by an imperfect symmetry north–south of the Earth, and the "classical theory" is based on the closed form expression for this " perturbation". With the "modern theory" this explicit closed form expression is not directly used but it is certainly still worthwhile to derive it.
The derivation of this expression can be done as follows:
The potential from a zonal term is rotational symmetric around the polar axis of the Earth and corresponding force is entirely in a longitudinal plane with one component in the radial direction and one component with the unit vector orthogonal to the radial direction towards north. These directions and are illustrated in Figure 1.
In the article Geopotential model it is shown that these force components caused by the term are
To be able to apply relations derived in the article Orbital perturbation analysis (spacecraft) the force component must be split into two orthogonal components and as illustrated in figure 2
Let make up a rectangular coordinate system with origin in the center of the Earth (in the center of the Reference ellipsoid) such that points in the direction north and such that are in the equatorial plane of the Earth with pointing towards the ascending node, i.e. towards the blue point of Figure 2.
The components of the unit vectors
making up the local coordinate system (of which are illustrated in figure 2), and expressing their relation with , are as follows:
where is the polar argument of relative the orthogonal unit vectors and in the orbital plane
Firstly
where is the angle between the equator plane and (between the green points of figure 2) and from equation (12) of the article Geopotential model one therefore obtains
Secondly the projection of direction north, , on the plane spanned by is
and this projection is
where is the unit vector orthogonal to the radial direction towards north illustrated in figure 1.
From equation () we see that
and therefore:
In the article Orbital perturbation analysis (spacecraft) it is further shown that the secular perturbation of the orbital pole is
Introducing the expression for of () in () one gets
The fraction is
where
are the components of the eccentricity vector in the coordinate system.
As all integrals of type
are zero if not both and are even, we see that
and
It follows that
where
and are the base vectors of the rectangular coordinate system in the plane of the reference Kepler orbit with in the equatorial plane towards the ascending node and is the polar argument relative this equatorial coordinate system
is the force component (per unit mass) in the direction of the orbit pole
In the article Orbital perturbation analysis (spacecraft) it is shown that the secular perturbation of the eccentricity vector is
where
is the usual local coordinate system with unit vector directed away from the Earth
- the velocity component in direction
- the velocity component in direction
Introducing the expression for of () and () in () one gets
Using that
the integral above can be split in 8 terms:
Given that
we obtain
and that all integrals of type
are zero if not both and are even:
Term 1
Term 2
Term 3
Term 4
Term 5
Term 6
Term 7
Term 8
As
It follows that
| Physical sciences | Orbital mechanics | Astronomy |
20373503 | https://en.wikipedia.org/wiki/Yttrium | Yttrium | Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free element. 89Y is the only stable isotope and the only isotope found in the Earth's crust.
The most important present-day use of yttrium is as a component of phosphors, especially those used in LEDs. Historically, it was once widely used in the red phosphors in television set cathode ray tube displays. Yttrium is also used in the production of electrodes, electrolytes, electronic filters, lasers, superconductors, various medical applications, and tracing various materials to enhance their properties.
Yttrium has no known biological role. Exposure to yttrium compounds can cause lung disease in humans.
Etymology
The element is named after ytterbite, a mineral first identified in 1787 by the chemist Carl Axel Arrhenius. He named the mineral after the village of Ytterby, in Sweden, where it had been discovered. When one of the chemicals in ytterbite was later found to be a previously unidentified element, the element was then named yttrium after the mineral.
Characteristics
Properties
Yttrium is a soft, silver-metallic, lustrous and highly crystalline transition metal in group 3. As expected by periodic trends, it is less electronegative than its predecessor in the group, scandium, and less electronegative than the next member of period 5, zirconium. However, due to the lanthanide contraction, it is also less electronegative than its successor in the group, lutetium. Yttrium is the first d-block element in the fifth period.
The pure element is relatively stable in air in bulk form, due to passivation of a protective oxide () film that forms on the surface. This film can reach a thickness of 10 μm when yttrium is heated to 750 °C in water vapor. When finely divided, however, yttrium is very unstable in air; shavings or turnings of the metal can ignite in air at temperatures exceeding 400 °C. Yttrium nitride (YN) is formed when the metal is heated to 1000 °C in nitrogen.
Similarity to the lanthanides
The similarities of yttrium to the lanthanides are so strong that the element has been grouped with them as a rare-earth element, and is always found in nature together with them in rare-earth minerals. Chemically, yttrium resembles those elements more closely than its neighbor in the periodic table, scandium, and if physical properties were plotted against atomic number, it would have an apparent number of 64.5 to 67.5, placing it between the lanthanides gadolinium and erbium.
It often also falls in the same range for reaction order, resembling terbium and dysprosium in its chemical reactivity. Yttrium is so close in size to the so-called 'yttrium group' of heavy lanthanide ions that in solution, it behaves as if it were one of them. Even though the lanthanides are one row farther down the periodic table than yttrium, the similarity in atomic radius may be attributed to the lanthanide contraction.
One of the few notable differences between the chemistry of yttrium and that of the lanthanides is that yttrium is almost exclusively trivalent, whereas about half the lanthanides can have valences other than three; nevertheless, only for four of the fifteen lanthanides are these other valences important in aqueous solution (Ce, Sm, Eu, and Yb).
Compounds and reactions
As a trivalent transition metal, yttrium forms various inorganic compounds, generally in the +3 oxidation state, by giving up all three of its valence electrons. A good example is yttrium(III) oxide (), also known as yttria, a six-coordinate white solid.
Yttrium forms a water-insoluble fluoride, hydroxide, and oxalate, but its bromide, chloride, iodide, nitrate and sulfate are all soluble in water. The Y ion is colorless in solution due to the absence of electrons in the d and f electron shells.
Water readily reacts with yttrium and its compounds to form . Concentrated nitric and hydrofluoric acids do not rapidly attack yttrium, but other strong acids do.
With halogens, yttrium forms trihalides such as yttrium(III) fluoride (), yttrium(III) chloride (), and yttrium(III) bromide () at temperatures above roughly 200 °C. Similarly, carbon, phosphorus, selenium, silicon and sulfur all form binary compounds with yttrium at elevated temperatures.
Organoyttrium chemistry is the study of compounds containing carbon–yttrium bonds. A few of these are known to have yttrium in the oxidation state 0. (The +2 state has been observed in chloride melts, and +1 in oxide clusters in the gas phase.) Some trimerization reactions were generated with organoyttrium compounds as catalysts. These syntheses use as a starting material, obtained from and concentrated hydrochloric acid and ammonium chloride.
Hapticity is a term to describe the coordination of a group of contiguous atoms of a ligand bound to the central atom; it is indicated by the Greek letter eta, η. Yttrium complexes were the first examples of complexes where carboranyl ligands were bound to a d-metal center through a η-hapticity. Vaporization of the graphite intercalation compounds graphite–Y or graphite– leads to the formation of endohedral fullerenes such as Y@C. Electron spin resonance studies indicated the formation of Y and (C) ion pairs. The carbides YC, YC, and YC can be hydrolyzed to form hydrocarbons.
Isotopes and nucleosynthesis
Yttrium in the Solar System was created by stellar nucleosynthesis, mostly by the s-process (≈72%), but also the r-process (≈28%). The r-process consists of rapid neutron capture by lighter elements during supernova explosions. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars.
Yttrium isotopes are among the most common products of the nuclear fission of uranium in nuclear explosions and nuclear reactors. In the context of nuclear waste management, the most important isotopes of yttrium are Y and Y, with half-lives of 58.51 days and 64 hours, respectively. Though Y has a short half-life, it exists in secular equilibrium with its long-lived parent isotope, strontium-90 (Sr) (half-life 29 years).
All group 3 elements have an odd atomic number, and therefore few stable isotopes. Scandium has one stable isotope, and yttrium itself has only one stable isotope, Y, which is also the only isotope that occurs naturally. However, the lanthanide rare earths contain elements of even atomic number and many stable isotopes. Yttrium-89 is thought to be more abundant than it otherwise would be, due in part to the s-process, which allows enough time for isotopes created by other processes to decay by electron emission (neutron → proton). Such a slow process tends to favor isotopes with atomic mass numbers (A = protons + neutrons) around 90, 138 and 208, which have unusually stable atomic nuclei with 50, 82, and 126 neutrons, respectively. This stability is thought to result from their very low neutron-capture cross-section. Electron emission of isotopes with those mass numbers is simply less prevalent due to this stability, resulting in them having a higher abundance. 89Y has a mass number close to 90 and has 50 neutrons in its nucleus.
At least 32 synthetic isotopes of yttrium have been observed, and these range in atomic mass number from 76 to 108. The least stable of these is Y with a half-life of 25 ms and the most stable is Y with half-life 106.629 days. Apart from Y, Y, and Y, with half-lives of 58.51 days, 79.8 hours, and 64 hours, respectively; all other isotopes have half-lives of less than a day and most of less than an hour.
Yttrium isotopes with mass numbers at or below 88 decay mainly by positron emission (proton → neutron) to form strontium (Z = 38) isotopes. Yttrium isotopes with mass numbers at or above 90 decay mainly by electron emission (neutron → proton) to form zirconium (Z = 40) isotopes. Isotopes with mass numbers at or above 97 are also known to have minor decay paths of β delayed neutron emission.
Yttrium has at least 20 metastable ("excited") isomers ranging in mass number from 78 to 102. Multiple excitation states have been observed for Y and Y. While most yttrium isomers are expected to be less stable than their ground state; Y have longer half-lives than their ground states, as these isomers decay by beta decay rather than isomeric transition.
History
In 1787, part-time chemist Carl Axel Arrhenius found a heavy black rock in an old quarry near the Swedish village of Ytterby (now part of the Stockholm Archipelago). Thinking it was an unknown mineral containing the newly discovered element tungsten, he named it ytterbite and sent samples to various chemists for analysis.
Johan Gadolin at the University of Åbo identified a new oxide (or "earth") in Arrhenius' sample in 1789, and published his completed analysis in 1794. Anders Gustaf Ekeberg confirmed the identification in 1797 and named the new oxide yttria. In the decades after Antoine Lavoisier developed the first modern definition of chemical elements, it was believed that earths could be reduced to their elements, meaning that the discovery of a new earth was equivalent to the discovery of the element within, which in this case would have been yttrium.
Friedrich Wöhler is credited with first isolating the metal in 1828 by reacting a volatile chloride that he believed to be yttrium chloride with potassium.
In 1843, Carl Gustaf Mosander found that samples of yttria contained three oxides: white yttrium oxide (yttria), yellow terbium oxide (confusingly, this was called 'erbia' at the time) and rose-colored erbium oxide (called 'terbia' at the time). A fourth oxide, ytterbium oxide, was isolated in 1878 by Jean Charles Galissard de Marignac. New elements were later isolated from each of those oxides, and each element was named, in some fashion, after Ytterby, the village near the quarry where they were found (see ytterbium, terbium, and erbium). In the following decades, seven other new metals were discovered in "Gadolin's yttria". Since yttria was found to be a mineral and not an oxide, Martin Heinrich Klaproth renamed it gadolinite in honor of Gadolin.
Until the early 1920s, the chemical symbol Yt was used for the element, after which Y came into common use.
In 1987, yttrium barium copper oxide was found to achieve high-temperature superconductivity. It was only the second material known to exhibit this property, and it was the first-known material to achieve superconductivity above the (economically important) boiling point of nitrogen.
Occurrence
Abundance
Yttrium is found in most rare-earth minerals, and some uranium ores, but never in the Earth's crust as a free element. About 31 ppm of the Earth's crust is yttrium, making it the 43rd most abundant element. Yttrium is found in soil in concentrations between 10 and 150 ppm (dry weight average of 23 ppm) and in sea water at 9 ppt. Lunar rock samples collected during the American Apollo Project have a relatively high content of yttrium.
Yttrium is not considered a "bone-seeker" like strontium and lead. Normally, as little as is found in the entire human body; human breast milk contains 4 ppm. Yttrium can be found in edible plants in concentrations between 20 ppm and 100 ppm (fresh weight), with cabbage having the largest amount. With as much as 700 ppm, the seeds of woody plants have the highest known concentrations.
there are reports of the discovery of very large reserves of rare-earth elements in the deep seabed several hundred kilometers from the tiny Japanese island of Minami-Torishima Island, also known as Marcus Island. This location is described as having "tremendous potential" for rare-earth elements and yttrium (REY), according to a study published in Scientific Reports. "This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features," the study reads. The study shows that more than of rare-earth elements could be "exploited in the near future." As well as yttrium (Y), which is used in products like camera lenses and mobile phone screens, the rare-earth elements found are europium (Eu), terbium (Tb), and dysprosium (Dy).
Production
As yttrium is chemically similar to lanthanides, it occurs in the same ores (rare-earth minerals) and is extracted by the same refinement processes. A slight distinction is recognized between the light (LREE) and the heavy rare-earth elements (HREE), but the distinction is not perfect. Yttrium is concentrated in the HREE group due to its ion size, though it has a lower atomic mass.
Rare-earth elements (REEs) come mainly from four sources:
Carbonate and fluoride containing ores such as the LREE bastnäsite ((Ce, La, etc.)(CO)F) contain on average 0.1% yttrium compared to the 99.9% for the 16 other REEs. The main source of bastnäsite from the 1960s to the 1990s was the Mountain Pass rare earth mine in California, making the United States the largest producer of REEs during that period. The name "bastnäsite" is actually a group name, and the Levinson suffix is used in the correct mineral names, e.g., bästnasite-(Y) has Y as a prevailing element.
Monazite ((Ce, La, etc.)PO), which is mostly phosphate, is a placer deposit of sand created by the transportation and gravitational separation of eroded granite. Monazite as a LREE ore contains 2% (or 3%) yttrium. The largest deposits were found in India and Brazil in the early 20th century, making those two countries the largest producers of yttrium in the first half of that century. Of the monazite group, the Ce-dominant member, monazite-(Ce), is the most common one.
Xenotime, a REE phosphate, is the main HREE ore containing as much as 60% yttrium as yttrium phosphate (YPO). This applies to xenotime-(Y). The largest mine is the Bayan Obo deposit in China, making China the largest exporter for HREE since the closure of the Mountain Pass mine in the 1990s.
Ion absorption clays or Lognan clays are the weathering products of granite and contain only 1% of REEs. The final ore concentrate can contain as much as 8% yttrium. Ion absorption clays are mostly in southern China. Yttrium is also found in samarskite and fergusonite (which also stand for group names).
One method for obtaining pure yttrium from the mixed oxide ores is to dissolve the oxide in sulfuric acid and fractionate it by ion exchange chromatography. With the addition of oxalic acid, the yttrium oxalate precipitates. The oxalate is converted into the oxide by heating under oxygen. By reacting the resulting yttrium oxide with hydrogen fluoride, yttrium fluoride is obtained. When quaternary ammonium salts are used as extractants, most yttrium will remain in the aqueous phase. When the counter-ion is nitrate, the light lanthanides are removed, and when the counter-ion is thiocyanate, the heavy lanthanides are removed. In this way, yttrium salts of 99.999% purity are obtained. In the usual situation, where yttrium is in a mixture that is two-thirds heavy-lanthanide, yttrium should be removed as soon as possible to facilitate the separation of the remaining elements.
Annual world production of yttrium oxide had reached by 2001; by 2014 it had increased to . Global reserves of yttrium oxide were estimated in 2014 to be more than . The leading countries for these reserves included Australia, Brazil, China, India, and the United States. Only a few tonnes of yttrium metal are produced each year by reducing yttrium fluoride to a metal sponge with calcium magnesium alloy. The temperature of an arc furnace, in excess of 1,600 °C, is sufficient to melt the yttrium.
Applications
Consumer
The red component of color television cathode ray tubes is typically emitted from an yttria () or yttrium oxide sulfide () host lattice doped with europium (III) cation (Eu) phosphors. The red color itself is emitted from the europium while the yttrium collects energy from the electron gun and passes it to the phosphor. Yttrium compounds can serve as host lattices for doping with different lanthanide cations. Tb can be used as a doping agent to produce green luminescence. As such yttrium compounds such as yttrium aluminium garnet (YAG) are useful for phosphors and are an important component of white LEDs.
Yttria is used as a sintering additive in the production of porous silicon nitride.
Yttrium compounds are used as a catalyst for ethylene polymerization. As a metal, yttrium is used on the electrodes of some high-performance spark plugs. Yttrium is used in gas mantles for propane lanterns as a replacement for thorium, which is radioactive.
Garnets
Yttrium is used in the production of a large variety of synthetic garnets, and yttria is used to make yttrium iron garnets (, "YIG"), which are very effective microwave filters which were recently shown to have magnetic interactions more complex and longer-ranged than understood over the previous four decades. Yttrium, iron, aluminium, and gadolinium garnets (e.g. and ) have important magnetic properties. YIG is also very efficient as an acoustic energy transmitter and transducer. Yttrium aluminium garnet ( or YAG) has a hardness of 8.5 and is also used as a gemstone in jewelry (simulated diamond). Cerium-doped yttrium aluminium garnet (YAG:Ce) crystals are used as phosphors to make white LEDs.
YAG, yttria, yttrium lithium fluoride (LiYF), and yttrium orthovanadate (YVO) are used in combination with dopants such as neodymium, erbium, ytterbium in near-infrared lasers. YAG lasers can operate at high power and are used for drilling and cutting metal. The single crystals of doped YAG are normally produced by the Czochralski process.
Material enhancer
Small amounts of yttrium (0.1 to 0.2%) have been used to reduce the grain sizes of chromium, molybdenum, titanium, and zirconium. Yttrium is used to increase the strength of aluminium and magnesium alloys. The addition of yttrium to alloys generally improves workability, adds resistance to high-temperature recrystallization, and significantly enhances resistance to high-temperature oxidation (see graphite nodule discussion below).
Yttrium can be used to deoxidize vanadium and other non-ferrous metals. Yttria stabilizes the cubic form of zirconia in jewelry.
Yttrium has been studied as a nodulizer in ductile cast iron, forming the graphite into compact nodules instead of flakes to increase ductility and fatigue resistance. Having a high melting point, yttrium oxide is used in some ceramic and glass to impart shock resistance and low thermal expansion properties. Those same properties make such glass useful in camera lenses.
Medical
The radioisotope yttrium-90 (Y) is used to label drugs such as edotreotide and ibritumomab tiuxetan for the treatment of various cancers, including lymphoma, leukemia, liver, ovarian, colorectal, pancreatic and bone cancers. It works by adhering to monoclonal antibodies, which in turn bind to cancer cells and kill them via intense β-radiation from the Y (see monoclonal antibody therapy).
A technique called radioembolization is used to treat hepatocellular carcinoma and liver metastasis. Radioembolization is a low toxicity, targeted liver cancer therapy that uses millions of tiny beads made of glass or resin containing Y. The radioactive microspheres are delivered directly to the blood vessels feeding specific liver tumors/segments or lobes. It is minimally invasive and patients can usually be discharged after a few hours. This procedure may not eliminate all tumors throughout the entire liver, but works on one segment or one lobe at a time and may require multiple procedures.
Also see radioembolization in the case of combined cirrhosis and hepatocellular carcinoma.
Needles made of Y, which can cut more precisely than scalpels, have been used to sever pain-transmitting nerves in the spinal cord, and Y is also used to carry out radionuclide synovectomy in the treatment of inflamed joints, especially knees, in people with conditions such as rheumatoid arthritis.
A neodymium-doped yttrium–aluminium–garnet laser has been used in an experimental, robot-assisted radical prostatectomy in canines in an attempt to reduce collateral nerve and tissue damage, and erbium-doped lasers are coming into use for cosmetic skin resurfacing.
Superconductors
Yttrium is a key ingredient in the yttrium barium copper oxide (YBaCuO, aka 'YBCO' or '1-2-3') superconductor developed at the University of Alabama in Huntsville and the University of Houston in 1987. This superconductor is notable because the operating superconductivity temperature is above liquid nitrogen's boiling point (77.1 K). Since liquid nitrogen is less expensive than the liquid helium required for metallic superconductors, the operating costs for applications would be less.
The actual superconducting material is often written as YBa2Cu3O7–d, where d must be less than 0.7 for superconductivity. The reason for this is still not clear, but it is known that the vacancies occur only in certain places in the crystal, the copper oxide planes, and chains, giving rise to a peculiar oxidation state of the copper atoms, which somehow leads to the superconducting behavior.
The theory of low temperature superconductivity has been well understood since the BCS theory of 1957. It is based on a peculiarity of the interaction between two electrons in a crystal lattice. However, the BCS theory does not explain high temperature superconductivity, and its precise mechanism is still a mystery. What is known is that the composition of the copper-oxide materials must be precisely controlled for superconductivity to occur.
This superconductor is a black and green, multi-crystal, multi-phase mineral. Researchers are studying a class of materials known as perovskites that are alternative combinations of these elements, hoping to develop a practical high-temperature superconductor.
Lithium batteries
Yttrium is used in small quantities in the cathodes of some Lithium iron phosphate battery (LFP), which are then commonly called LiFeYPO chemistry, or LYP. Similar to LFP, LYP batteries offer high energy density, good safety and long life. But LYP offers higher cathode stability, and prolongs the life of the battery, by protecting the physical structure of the cathode, especially at higher temperatures and higher charging / discharge current. LYP batteries find use in stationary applications (off-grid solar systems), electric vehicles (some cars), as well other applications (submarines, ships), similar to LFP batteries, but often at improved safety and cycle life time. LYP cells have essentially the same nominal voltage as LFP, 3.25V, but the maximum charging voltage is 4.0V, and the charging and discharge characteristics are very similar.
Other applications
In 2009, Professor Mas Subramanian and associates at Oregon State University discovered that yttrium can be combined with indium and manganese to form an intensely blue, non-toxic, inert, fade-resistant pigment, YInMn blue, the first new blue pigment discovered in 200 years.
Precautions
Yttrium can be highly toxic to humans, animals and plants.
Water-soluble compounds of yttrium are considered mildly toxic, while its insoluble compounds are non-toxic. In experiments on animals, yttrium and its compounds caused lung and liver damage, though toxicity varies with different yttrium compounds. In rats, inhalation of yttrium citrate caused pulmonary edema and dyspnea, while inhalation of yttrium chloride caused liver edema, pleural effusions, and pulmonary hyperemia.
Exposure to yttrium compounds in humans may cause lung disease. Workers exposed to airborne yttrium europium vanadate dust experienced mild eye, skin, and upper respiratory tract irritation—though this may be caused by the vanadium content rather than the yttrium. Acute exposure to yttrium compounds can cause shortness of breath, coughing, chest pain, and cyanosis. The Occupational Safety and Health Administration (OSHA) limits exposure to yttrium in the workplace to over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) is over an 8-hour workday. At levels of , yttrium is immediately dangerous to life and health. Yttrium dust is highly flammable.
| Physical sciences | Chemical elements_2 | null |
20381199 | https://en.wikipedia.org/wiki/Megalictis | Megalictis | Megalictis (meaning "great weasel") is an extinct genus of large predatory mustelids that existed in North America during the "cat gap" from the Late Arikareean (Ar4) in the Miocene epoch. It is thought to have resembled a huge, jaguar-sized ferret, weighing up to .
History of discovery
The genus Megalictis was first described by W. D. Matthew in 1907, and assigned to the family Mustelidae. Two similar genera discovered at the same time, Aelurocyon (Peterson, 1907) and Paroligobunis (Peterson, 1910) were identified as synonymous with Megalictis in 1996 though Paroligobunis was re-established as a separate genus in 1998. P. R. Bjork, in 1970, assigned the genus to the subfamily Mellivorinae, whilst J. A. Baskin reassigned it to Oligobuninae in 1998. Three species have been identified in the genus: M. ferox, M. petersoni, and M. frazieri, whilst two more, Megalictis brevifacies and Megalictis simplicidens, have since been determined to be synonymous with M. ferox. Other synonyms of M. ferox include Aelurocyon brevifacies, Brachypsalis simplicidens and Paroligobunis simplicidens.
Specimens of M. ferox have been found at ten sites in South Dakota, Nebraska and Wyoming, dated to the Harrisonian period - from 24.8 to 20.6 million years ago. The 19 specimens so far identified have a wide range of sizes, which is believed to be evidence of extreme sexual dimorphism, a phenomenon where males and females of the species will grow to different sizes; a 1996 study rejected the possibility of multiple "morphologically uniform" but differently sized species as unlikely. However, later studies identified significant morphological variation in the joints of the forearms, which would not be consistent with sexual dimorphism. Andersson suggests that the identification of all of these as a single species may need revision.
Description
Megalictis was one of the largest terrestrial mustelids ever recorded, surpassing in size other mustelids like Ekorus, Eomellivora, and Plesiogulo. Recovered skulls of Megalictis ferox had similar condylobasal lengths to small modern jaguars, ranging from in length, and were almost as wide in mastoid width as those of some black bears, ranging from wide. The enlarged anterior edge of the cornoid process confers a wide gape relative to its short rostral length, suggesting Megalictis possessed a powerful bite force; together with blunt, stout postcanine teeth, Megalictis was well equipped to engage in osteophagy, similar to modern hyenas and wolverines. It has been described as having short stout legs, with short feet and long non-retractible claws, similar to a modern ferret but about twice the size, and noted that "the teeth indicate an animal fully as predaceous as the wolverine, but the skeleton points to more fossorial habits". Research comparing the joints of the forelegs to modern mammalian carnivores suggests that it waited in ambush and grappled with its prey, rather than hunting it down by pursuit like a modern cheetah.
| Biology and health sciences | Mustelidae | Animals |
1407416 | https://en.wikipedia.org/wiki/Environmental%20resource%20management | Environmental resource management | Environmental resource management or environmental management is the management of the interaction and impact of human societies on the environment. It is not, as the phrase might suggest, the management of the environment itself. Environmental resources management aims to ensure that ecosystem services are protected and maintained for future human generations, and also maintain ecosystem integrity through considering ethical, economic, and scientific (ecological) variables. Environmental resource management tries to identify factors between meeting needs and protecting resources. It is thus linked to environmental protection, resource management, sustainability, integrated landscape management, natural resource management, fisheries management, forest management, wildlife management, environmental management systems, and others.
Significance
Environmental resource management is an issue of increasing concern, as reflected in its prevalence in several texts influencing global sociopolitical frameworks such as the Brundtland Commission's Our Common Future, which highlighted the integrated nature of the environment and international development, and the Worldwatch Institute's annual State of the World reports.
The environment determines the nature of people, animals, plants, and places around the Earth, affecting behaviour, religion, culture and economic practices.
Scope
Environmental resource management can be viewed from a variety of perspectives. It involves the management of all components of the biophysical environment, both living (biotic) and non-living (abiotic), and the relationships among all living species and their habitats. The environment also involves the relationships of the human environment, such as the social, cultural, and economic environment, with the biophysical environment. The essential aspects of environmental resource management are ethical, economical, social, and technological. These underlie principles and help make decisions.
The concept of environmental determinism, probabilism, and possibilism are significant in the concept of environmental resource management.
Environmental resource management covers many areas in science, including geography, biology, social sciences, political sciences, public policy, ecology, physics, chemistry, sociology, psychology, and physiology. Environmental resource management as a practice and discourse (across these areas) is also the object of study in the social sciences.
Aspects
Ethical
Environmental resource management strategies are intrinsically driven by conceptions of human-nature relationships. Ethical aspects involve the cultural and social issues relating to the environment, and dealing with changes to it. "All human activities take place in the context of certain types of relationships between society and the bio-physical world (the rest of nature)," and so, there is a great significance in understanding the ethical values of different groups around the world. Broadly speaking, two schools of thought exist in environmental ethics: Anthropocentrism and Ecocentrism, each influencing a broad spectrum of environmental resource management styles along a continuum. These styles perceive "...different evidence, imperatives, and problems, and prescribe different solutions, strategies, technologies, roles for economic sectors, culture, governments, and ethics, etc."
Anthropocentrism
Anthropocentrism, "an inclination to evaluate reality exclusively in terms of human values," is an ethic reflected in the major interpretations of Western religions and the dominant economic paradigms of the industrialised world. Anthropocentrism looks at nature as existing solely for the benefit of humans, and as a commodity to use for the good of humanity and to improve human quality of life. Anthropocentric environmental resource management is therefore not the conservation of the environment solely for the environment's sake, but rather the conservation of the environment, and ecosystem structure, for humans' sake.
Ecocentrism
Ecocentrists believe in the intrinsic value of nature while maintaining that human beings must use and even exploit nature to survive and live. It is this fine ethical line that ecocentrists navigate between fair use and abuse. At an extreme of the ethical scale, ecocentrism includes philosophies such as ecofeminism and deep ecology, which evolved as a reaction to dominant anthropocentric paradigms. "In its current form, it is an attempt to synthesize many old and some new philosophical attitudes about the relationship between nature and human activity, with particular emphasis on ethical, social, and spiritual aspects that have been downplayed in the dominant economic worldview."
Economics
Main article: Economics
The economy functions within and is dependent upon goods and services provided by natural ecosystems. The role of the environment is recognized in both classical economics and neoclassical economics theories, yet the environment was a lower priority in economic policies from 1950 to 1980 due to emphasis from policy makers on economic growth. With the prevalence of environmental problems, many economists embraced the notion that, "If environmental sustainability must coexist for economic sustainability, then the overall system must [permit] identification of an equilibrium between the environment and the economy." As such, economic policy makers began to incorporate the functions of the natural environment – or natural capital – particularly as a sink for wastes and for the provision of raw materials and amenities.
Debate continues among economists as to how to account for natural capital, specifically whether resources can be replaced through knowledge and technology, or whether the environment is a closed system that cannot be replenished and is finite. Economic models influence environmental resource management, in that management policies reflect beliefs about natural capital scarcity. For someone who believes natural capital is infinite and easily substituted, environmental management is irrelevant to the economy. For example, economic paradigms based on neoclassical models of closed economic systems are primarily concerned with resource scarcity and thus prescribe legalizing the environment as an economic externality for an environmental resource management strategy. This approach has often been termed 'Command-and-control'. Colby has identified trends in the development of economic paradigms, among them, a shift towards more ecological economics since the 1990s.
Ecology
There are many definitions of the field of science commonly called ecology. A typical one is "the branch of biology dealing with the relations and interactions between organisms and their environment, including other organisms." "The pairing of significant uncertainty about the behaviour and response of ecological systems with urgent calls for near-term action constitutes a difficult reality, and a common lament" for many environmental resource managers. Scientific analysis of the environment deals with several dimensions of ecological uncertainty. These include: structural uncertainty resulting from the misidentification, or lack of information pertaining to the relationships between ecological variables; parameter uncertainty referring to "uncertainty associated with parameter values that are not known precisely but can be assessed and reported in terms of the likelihood…of experiencing a defined range of outcomes"; and stochastic uncertainty stemming from chance or unrelated factors. Adaptive management is considered a useful framework for dealing with situations of high levels of uncertainty though it is not without its detractors.
A common scientific concept and impetus behind environmental resource management is carrying capacity. Simply put, carrying capacity refers to the maximum number of organisms a particular resource can sustain. The concept of carrying capacity, whilst understood by many cultures over history, has its roots in Malthusian theory. An example is visible in the EU Water Framework Directive. However, "it is argued that Western scientific knowledge ... is often insufficient to deal with the full complexity of the interplay of variables in environmental resource management. These concerns have been recently addressed by a shift in environmental resource management approaches to incorporate different knowledge systems including traditional knowledge, reflected in approaches such as adaptive co-management community-based natural resource management and transitions management among others.
Sustainability
Sustainability in environmental resource management involves managing economic, social, and ecological systems both within and outside an organizational entity so it can sustain itself and the system it exists in. In context, sustainability implies that rather than competing for endless growth on a finite planet, development improves quality of life without necessarily consuming more resources. Sustainably managing environmental resources requires organizational change that instills sustainability values that portrays these values outwardly from all levels and reinforces them to surrounding stakeholders. The result should be a symbiotic relationship between the sustaining organization, community, and environment.
Many drivers compel environmental resource management to take sustainability issues into account. Today's economic paradigms do not protect the natural environment, yet they deepen human dependency on biodiversity and ecosystem services. Ecologically, massive environmental degradation and climate change threaten the stability of ecological systems that humanity depends on. Socially, an increasing gap between rich and poor and the global North–South divide denies many access to basic human needs, rights, and education, leading to further environmental destruction. The planet's unstable condition is caused by many anthropogenic sources. As an exceptionally powerful contributing factor to social and environmental change, the modern organisation has the potential to apply environmental resource management with sustainability principles to achieve highly effective outcomes. To achieve sustainable development with environmental resource management an organisation should work within sustainability principles, including social and environmental accountability, long-term planning; a strong, shared vision; a holistic focus; devolved and consensus decision making; broad stakeholder engagement and justice; transparency measures; trust; and flexibility.
Current paradigm shifts
To adjust to today's environment of quick social and ecological changes, some organizations have begun to experiment with new tools and concepts. Those that are more traditional and stick to hierarchical decision making have difficulty dealing with the demand for lateral decision making that supports effective participation. Whether it be a matter of ethics or just strategic advantage organizations are internalizing sustainability principles. Some of the world's largest and most profitable corporations are shifting to sustainable environmental resource management: Ford, Toyota, BMW, Honda, Shell, Du Port, Sta toil, Swiss Re, Hewlett-Packard, and Unilever, among others. An extensive study by the Boston Consulting Group reaching 1,560 business leaders from diverse regions, job positions, expertise in sustainability, industries, and sizes of organizations, revealed the many benefits of sustainable practice as well as its viability.
Although the sustainability of environmental resource management has improved, corporate sustainability, for one, has yet to reach the majority of global companies operating in the markets. The three major barriers to preventing organizations from shifting towards sustainable practice with environmental resource management are not understanding what sustainability is; having difficulty modeling an economically viable case for the switch; and having a flawed execution plan, or a lack thereof. Therefore, the most important part of shifting an organization to adopt sustainability in environmental resource management would be to create a shared vision and understanding of what sustainability is for that particular organization and to clarify the business case.
Stakeholders
Public sector
The public sector comprises the general government sector plus all public corporations including the central bank. In environmental resource management the public sector is responsible for administering natural resource management and implementing environmental protection legislation. The traditional role of the public sector in environmental resource management is to provide professional judgement through skilled technicians on behalf of the public. With the increase of intractable environmental problems, the public sector has been led to examine alternative paradigms for managing environmental resources. This has resulted in the public sector working collaboratively with other sectors (including other governments, private and civil) to encourage sustainable natural resource management behaviours.
Private sector
The private sector comprises private corporations and non-profit institutions serving households. The private sector's traditional role in environmental resource management is that of the recovery of natural resources. Such private sector recovery groups include mining (minerals and petroleum), forestry and fishery organisations. Environmental resource management undertaken by the private sectors varies dependent upon the resource type, that being renewable or non-renewable and private and common resources (also see Tragedy of the Commons). Environmental managers from the private sector also need skills to manage collaboration within a dynamic social and political environment.
Civil society
Civil society comprises associations in which societies voluntarily organise themselves and which represent a wide range of interests and ties. These can include community-based organisations, indigenous peoples' organisations and non-government organisations (NGOs). Functioning through strong public pressure, civil society can exercise their legal rights against the implementation of resource management plans, particularly land management plans. The aim of civil society in environmental resource management is to be included in the decision-making process by means of public participation. Public participation can be an effective strategy to invoke a sense of social responsibility of natural resources.
Tools
As with all management functions, effective management tools, standards, and systems are required. An environmental management standard or system or protocol attempts to reduce environmental impact as measured by some objective criteria. The ISO 14001 standard is the most widely used standard for environmental risk management and is closely aligned to the European Eco-Management and Audit Scheme (EMAS). As a common auditing standard, the ISO 19011 standard explains how to combine this with quality management.
Other environmental management systems (EMS) tend to be based on the ISO 14001 standard and many extend it in various ways:
The Green Dragon Environmental Management Standard is a five-level EMS designed for smaller organisations for whom ISO 14001 may be too onerous and for larger organisations who wish to implement ISO 14001 in a more manageable step-by-step approach,
BS 8555 is a phased standard that can help smaller companies move to ISO 14001 in six manageable steps,
The Natural Step focuses on basic sustainability criteria and helps focus engineering on reducing use of materials or energy use that is unsustainable in the long term,
Natural Capitalism advises using accounting reform and a general biomimicry and industrial ecology approach to do the same thing,
US Environmental Protection Agency has many further terms and standards that it defines as appropriate to large-scale EMS,
The UN and World Bank has encouraged adopting a "natural capital" measurement and management framework.
Other strategies exist that rely on making simple distinctions rather than building top-down management "systems" using performance audits and full cost accounting. For instance, Ecological Intelligent Design divides products into consumables, service products or durables and unsaleables – toxic products that no one should buy, or in many cases, do not realize they are buying. By eliminating the unsaleables from the comprehensive outcome of any purchase, better environmental resource management is achieved without systems.
Another example that diverges from top-down management is the implementation of community based co-management systems of governance. An example of this is community based subsistence fishing areas, such as is implemented in Ha'ena, Hawaii. Community based systems of governance allow for the communities who most directly interact with the resource and who are most deeply impacted by the overexploitation of said resource to make the decisions regarding its management, thus empowering local communities and more effectively managing resources.
Recent successful cases have put forward the notion of integrated management. It shares a wider approach and stresses out the importance of interdisciplinary assessment. It is an interesting notion that might not be adaptable to all cases.
Case Study: Kissidougou, Guinea (Fairhead, Leach)
Kissidougou, Guinea’s dry season brings about fires in the open grass fires which defoliate the few trees in the savanna. There are villages within this savanna surrounded by “islands” of forests, allowing for forts, hiding, rituals, protection from wind and fire, and shade for crops. According to scholars and researchers in the region during the late-19th and 20th centuries, there was a steady decline in tree cover. This led to colonial Guinea’s implementation of policies, including the switch of upland to swamp farming; bush-fire control; protection of certain species and land; and tree planting in villages. These policies were carried out in the form of permits, fines, and military repression.
But, Kissidougou villagers claim their ancestors’ established these islands. Many maps and letters evidence France’s occupation of Guinea, as well as Kissidougou’s past landscape. During the 1780s to 1860s “the whole country [was] prairie.” James Fairhead and Melissa Leach, both environmental anthropologists at the University of Sussex, claim the state’s environmental analyses “casts into question the relationships between society, demography, and environment.” With this, they reformed the state’s narratives: Local land use can be both vegetation enriching and degrading; combined effect on resource management is greater than the sum of their parts; there is evidence of increased population correlating to an increase in forest cover. Fairhead and Leach support the enabling of policy and socioeconomic conditions in which local resource management conglomerates can act effectively. In Kissidougou, there is evidence that local powers and community efforts shaped the island forests that shape the savanna’s landscape.
| Physical sciences | Earth science basics: General | Earth science |
1408929 | https://en.wikipedia.org/wiki/Metagenomics | Metagenomics | Metagenomics is the study of genetic material recovered directly from environmental or clinical samples by a method called sequencing. The broad field may also be referred to as environmental genomics, ecogenomics, community genomics or microbiomics.
While traditional microbiology and microbial genome sequencing and genomics rely upon cultivated clonal cultures, early environmental gene sequencing cloned specific genes (often the 16S rRNA gene) to produce a profile of diversity in a natural sample. Such work revealed that the vast majority of microbial biodiversity had been missed by cultivation-based methods.
Because of its ability to reveal the previously hidden diversity of microscopic life, metagenomics offers a powerful way of understanding the microbial world that might revolutionize understanding of biology. As the price of DNA sequencing continues to fall, metagenomics now allows microbial ecology to be investigated at a much greater scale and detail than before. Recent studies use either "shotgun" or PCR directed sequencing to get largely unbiased samples of all genes from all the members of the sampled communities.
Etymology
The term "metagenomics" was first used by Jo Handelsman, Robert M. Goodman, Michelle R. Rondon, Jon Clardy, and Sean F. Brady, and first appeared in publication in 1998. The term metagenome referenced the idea that a collection of genes sequenced from the environment could be analyzed in a way analogous to the study of a single genome. In 2005, Kevin Chen and Lior Pachter (researchers at the University of California, Berkeley) defined metagenomics as "the application of modern genomics technique without the need for isolation and lab cultivation of individual species".
History
Conventional sequencing begins with a culture of identical cells as a source of DNA. However, early metagenomic studies revealed that there are probably large groups of microorganisms in many environments that cannot be cultured and thus cannot be sequenced. These early studies focused on 16S ribosomal RNA (rRNA) sequences which are relatively short, often conserved within a species, and generally different between species. Many 16S rRNA sequences have been found which do not belong to any known cultured species, indicating that there are numerous non-isolated organisms. These surveys of ribosomal RNA genes taken directly from the environment revealed that cultivation based methods find less than 1% of the bacterial and archaeal species in a sample. Much of the interest in metagenomics comes from these discoveries that showed that the vast majority of microorganisms had previously gone unnoticed.
In the 1980s early molecular work in the field was conducted by Norman R. Pace and colleagues, who used PCR to explore the diversity of ribosomal RNA sequences. The insights gained from these breakthrough studies led Pace to propose the idea of cloning DNA directly from environmental samples as early as 1985. This led to the first report of isolating and cloning bulk DNA from an environmental sample, published by Pace and colleagues in 1991 while Pace was in the Department of Biology at Indiana University. Considerable efforts ensured that these were not PCR false positives and supported the existence of a complex community of unexplored species. Although this methodology was limited to exploring highly conserved, non-protein coding genes, it did support early microbial morphology-based observations that diversity was far more complex than was known by culturing methods. Soon after that in 1995, Healy reported the metagenomic isolation of functional genes from "zoolibraries" constructed from a complex culture of environmental organisms grown in the laboratory on dried grasses. After leaving the Pace laboratory, Edward DeLong continued in the field and has published work that has largely laid the groundwork for environmental phylogenies based on signature 16S sequences, beginning with his group's construction of libraries from marine samples.
In 2002, Mya Breitbart, Forest Rohwer, and colleagues used environmental shotgun sequencing (see below) to show that 200 liters of seawater contains over 5000 different viruses. Subsequent studies showed that there are more than a thousand viral species in human stool and possibly a million different viruses per kilogram of marine sediment, including many bacteriophages. Essentially all of the viruses in these studies were new species. In 2004, Gene Tyson, Jill Banfield, and colleagues at the University of California, Berkeley and the Joint Genome Institute sequenced DNA extracted from an acid mine drainage system. This effort resulted in the complete, or nearly complete, genomes for a handful of bacteria and archaea that had previously resisted attempts to culture them.
Beginning in 2003, Craig Venter, leader of the privately funded parallel of the Human Genome Project, has led the Global Ocean Sampling Expedition (GOS), circumnavigating the globe and collecting metagenomic samples throughout the journey. All of these samples were sequenced using shotgun sequencing, in hopes that new genomes (and therefore new organisms) would be identified. The pilot project, conducted in the Sargasso Sea, found DNA from nearly 2000 different species, including 148 types of bacteria never before seen. Venter thoroughly explored the West Coast of the United States, and completed a two-year expedition in 2006 to explore the Baltic, Mediterranean, and Black Seas. Analysis of the metagenomic data collected during this journey revealed two groups of organisms, one composed of taxa adapted to environmental conditions of 'feast or famine', and a second composed of relatively fewer but more abundantly and widely distributed taxa primarily composed of plankton.
In 2005 Stephan C. Schuster at Penn State University and colleagues published the first sequences of an environmental sample generated with high-throughput sequencing, in this case massively parallel pyrosequencing developed by 454 Life Sciences. Another early paper in this area appeared in 2006 by Robert Edwards, Forest Rohwer, and colleagues at San Diego State University.
Sequencing
Recovery of DNA sequences longer than a few thousand base pairs from environmental samples was very difficult until recent advances in molecular biological techniques allowed the construction of libraries in bacterial artificial chromosomes (BACs), which provided better vectors for molecular cloning.
Shotgun metagenomics
Advances in bioinformatics, refinements of DNA amplification, and the proliferation of computational power have greatly aided the analysis of DNA sequences recovered from environmental samples, allowing the adaptation of shotgun sequencing to metagenomic samples (known also as whole metagenome shotgun or WMGS sequencing). The approach, used to sequence many cultured microorganisms and the human genome, randomly shears DNA, sequences many short sequences, and reconstructs them into a consensus sequence. Shotgun sequencing reveals genes present in environmental samples. Historically, clone libraries were used to facilitate this sequencing. However, with advances in high throughput sequencing technologies, the cloning step is no longer necessary and greater yields of sequencing data can be obtained without this labour-intensive bottleneck step. Shotgun metagenomics provides information both about which organisms are present and what metabolic processes are possible in the community. Because the collection of DNA from an environment is largely uncontrolled, the most abundant organisms in an environmental sample are most highly represented in the resulting sequence data. To achieve the high coverage needed to fully resolve the genomes of under-represented community members, large samples, often prohibitively so, are needed. On the other hand, the random nature of shotgun sequencing ensures that many of these organisms, which would otherwise go unnoticed using traditional culturing techniques, will be represented by at least some small sequence segments.
High-throughput sequencing
An advantage to high throughput sequencing is that this technique does not require cloning the DNA before sequencing, removing one of the main biases and bottlenecks in environmental sampling. The first metagenomic studies conducted using high-throughput sequencing used massively parallel 454 pyrosequencing. Three other technologies commonly applied to environmental sampling are the Ion Torrent Personal Genome Machine, the Illumina MiSeq or HiSeq and the Applied Biosystems SOLiD system. These techniques for sequencing DNA generate shorter fragments than Sanger sequencing; Ion Torrent PGM System and 454 pyrosequencing typically produces ~400 bp reads, Illumina MiSeq produces 400-700bp reads (depending on whether paired end options are used), and SOLiD produce 25–75 bp reads. Historically, these read lengths were significantly shorter than the typical Sanger sequencing read length of ~750 bp, however the Illumina technology is quickly coming close to this benchmark. However, this limitation is compensated for by the much larger number of sequence reads. In 2009, pyrosequenced metagenomes generate 200–500 megabases, and Illumina platforms generate around 20–50 gigabases, but these outputs have increased by orders of magnitude in recent years.
An emerging approach combines shotgun sequencing and chromosome conformation capture (Hi-C), which measures the proximity of any two DNA sequences within the same cell, to guide microbial genome assembly. Long read sequencing technologies, including PacBio RSII and PacBio Sequel by Pacific Biosciences, and Nanopore MinION, GridION, PromethION by Oxford Nanopore Technologies, is another choice to get long shotgun sequencing reads that should make ease in assembling process.
Bioinformatics
The data generated by metagenomics experiments are both enormous and inherently noisy, containing fragmented data representing as many as 10,000 species. The sequencing of the cow rumen metagenome generated 279 gigabases, or 279 billion base pairs of nucleotide sequence data, while the human gut microbiome gene catalog identified 3.3 million genes assembled from 567.7 gigabases of sequence data. Collecting, curating, and extracting useful biological information from datasets of this size represent significant computational challenges for researchers.
Sequence pre-filtering
The first step of metagenomic data analysis requires the execution of certain pre-filtering steps, including the removal of redundant, low-quality sequences and sequences of probable eukaryotic origin (especially in metagenomes of human origin). The methods available for the removal of contaminating eukaryotic genomic DNA sequences include Eu-Detect and DeConseq.
Assembly
DNA sequence data from genomic and metagenomic projects are essentially the same, but genomic sequence data offers higher coverage while metagenomic data is usually highly non-redundant. Furthermore, the increased use of second-generation sequencing technologies with short read lengths means that much of future metagenomic data will be error-prone. Taken in combination, these factors make the assembly of metagenomic sequence reads into genomes difficult and unreliable. Misassemblies are caused by the presence of repetitive DNA sequences that make assembly especially difficult because of the difference in the relative abundance of species present in the sample. Misassemblies can also involve the combination of sequences from more than one species into chimeric contigs.
There are several assembly programs, most of which can use information from paired-end tags in order to improve the accuracy of assemblies. Some programs, such as Phrap or Celera Assembler, were designed to be used to assemble single genomes but nevertheless produce good results when assembling metagenomic data sets. Other programs, such as Velvet assembler, have been optimized for the shorter reads produced by second-generation sequencing through the use of de Bruijn graphs. The use of reference genomes allows researchers to improve the assembly of the most abundant microbial species, but this approach is limited by the small subset of microbial phyla for which sequenced genomes are available. After an assembly is created, an additional challenge is "metagenomic deconvolution", or determining which sequences come from which species in the sample.
Species diversity
Gene annotations provide the "what", while measurements of species diversity provide the "who". In order to connect community composition and function in metagenomes, sequences must be binned. Binning is the process of associating a particular sequence with an organism. In similarity-based binning, methods such as BLAST are used to rapidly search for phylogenetic markers or otherwise similar sequences in existing public databases. This approach is implemented in MEGAN. Another tool, PhymmBL, uses interpolated Markov models to assign reads. MetaPhlAn and AMPHORA are methods based on unique clade-specific markers for estimating organismal relative abundances with improved computational performances. Other tools, like mOTUs and MetaPhyler, use universal marker genes to profile prokaryotic species. With the mOTUs profiler is possible to profile species without a reference genome, improving the estimation of microbial community diversity. Recent methods, such as SLIMM, use read coverage landscape of individual reference genomes to minimize false-positive hits and get reliable relative abundances. In composition based binning, methods use intrinsic features of the sequence, such as oligonucleotide frequencies or codon usage bias. Once sequences are binned, it is possible to carry out comparative analysis of diversity and richness.
After binning, assembled contigs are collected into "bins" each representing a species-like collection of organisms (see: operational taxonomic unit), to the best ability of the binning tool. Each bin consists of a metagenome-assembled genome (MAG), as all included sequences can be thought of being derived from the genome of the organism being represented. Tools based on single-copy genes such as CheckM and BUSCO can then be used to estimate the completeness percentage and contamination percentage of the MAG.
Gene prediction
Metagenomic analysis pipelines use two approaches in the annotation of coding regions in the assembled contigs. The first approach is to identify genes based upon homology with genes that are already publicly available in sequence databases, usually by BLAST searches. This type of approach is implemented in the program MEGAN4. The second, ab initio, uses intrinsic features of the sequence to predict coding regions based upon gene training sets from related organisms. This is the approach taken by programs such as GeneMark and GLIMMER. The main advantage of ab initio prediction is that it enables the detection of coding regions that lack homologs in the sequence databases; however, it is most accurate when there are large regions of contiguous genomic DNA available for comparison. Gene prediction is usually done after binning.
Data integration
The massive amount of exponentially growing sequence data is a daunting challenge that is complicated by the complexity of the metadata associated with metagenomic projects. Metadata includes detailed information about the three-dimensional (including depth, or height) geography and environmental features of the sample, physical data about the sample site, and the methodology of the sampling. This information is necessary both to ensure replicability and to enable downstream analysis. Because of its importance, metadata and collaborative data review and curation require standardized data formats located in specialized databases, such as the Genomes OnLine Database (GOLD).
Several tools have been developed to integrate metadata and sequence data, allowing downstream comparative analyses of different datasets using a number of ecological indices. In 2007, Folker Meyer and Robert Edwards and a team at Argonne National Laboratory and the University of Chicago released the Metagenomics Rapid Annotation using Subsystem Technology server (MG-RAST) a community resource for metagenome data set analysis. As of June 2012 over 14.8 terabases (14x1012 bases) of DNA have been analyzed, with more than 10,000 public data sets freely available for comparison within MG-RAST. Over 8,000 users now have submitted a total of 50,000 metagenomes to MG-RAST. The Integrated Microbial Genomes/Metagenomes (IMG/M) system also provides a collection of tools for functional analysis of microbial communities based on their metagenome sequence, based upon reference isolate genomes included from the Integrated Microbial Genomes (IMG) system and the Genomic Encyclopedia of Bacteria and Archaea (GEBA) project.
One of the first standalone tools for analysing high-throughput metagenome shotgun data was MEGAN (MEta Genome ANalyzer). A first version of the program was used in 2005 to analyse the metagenomic context of DNA sequences obtained from a mammoth bone. Based on a BLAST comparison against a reference database, this tool performs both taxonomic and functional binning, by placing the reads onto the nodes of the NCBI taxonomy using a simple lowest common ancestor (LCA) algorithm or onto the nodes of the SEED or KEGG classifications, respectively.
With the advent of fast and inexpensive sequencing instruments, the growth of databases of DNA sequences is now exponential (e.g., the NCBI GenBank database ). Faster and efficient tools are needed to keep pace with the high-throughput sequencing, because the BLAST-based approaches such as MG-RAST or MEGAN run slowly to annotate large samples (e.g., several hours to process a small/medium size dataset/sample ). Thus, ultra-fast classifiers have recently emerged, thanks to more affordable powerful servers. These tools can perform the taxonomic annotation at extremely high speed, for example CLARK (according to CLARK's authors, it can classify accurately "32 million metagenomic short reads per minute"). At such a speed, a very large dataset/sample of a billion short reads can be processed in about 30 minutes.
With the increasing availability of samples containing ancient DNA and due to the uncertainty associated with the nature of those samples (ancient DNA damage), a fast tool capable of producing conservative similarity estimates has been made available. According to FALCON's authors, it can use relaxed thresholds and edit distances without affecting the memory and speed performance.
Comparative metagenomics
Comparative analyses between metagenomes can provide additional insight into the function of complex microbial communities and their role in host health. Pairwise or multiple comparisons between metagenomes can be made at the level of sequence composition (comparing GC-content or genome size), taxonomic diversity, or functional complement. Comparisons of population structure and phylogenetic diversity can be made on the basis of 16S rRNA and other phylogenetic marker genes, or—in the case of low-diversity communities—by genome reconstruction from the metagenomic dataset. Functional comparisons between metagenomes may be made by comparing sequences against reference databases such as COG or KEGG, and tabulating the abundance by category and evaluating any differences for statistical significance. This gene-centric approach emphasizes the functional complement of the community as a whole rather than taxonomic groups, and shows that the functional complements are analogous under similar environmental conditions. Consequently, metadata on the environmental context of the metagenomic sample is especially important in comparative analyses, as it provides researchers with the ability to study the effect of habitat upon community structure and function.
Additionally, several studies have also utilized oligonucleotide usage patterns to identify the differences across diverse microbial communities. Examples of such methodologies include the dinucleotide relative abundance approach by Willner et al. and the HabiSign approach of Ghosh et al. This latter study also indicated that differences in tetranucleotide usage patterns can be used to identify genes (or metagenomic reads) originating from specific habitats. Additionally some methods as TriageTools or Compareads detect similar reads between two read sets. The similarity measure they apply on reads is based on a number of identical words of length k shared by pairs of reads.
A key goal in comparative metagenomics is to identify microbial group(s) which are responsible for conferring specific characteristics to a given environment. However, due to issues in the sequencing technologies artifacts need to be accounted for like in metagenomeSeq. Others have characterized inter-microbial interactions between the resident microbial groups. A GUI-based comparative metagenomic analysis application called Community-Analyzer has been developed by Kuntal et al.
which implements a correlation-based graph layout algorithm that not only facilitates a quick visualization of the differences in the analyzed microbial communities (in terms of their taxonomic composition), but also provides insights into the inherent inter-microbial interactions occurring therein. Notably, this layout algorithm also enables grouping of the metagenomes based on the probable inter-microbial interaction patterns rather than simply comparing abundance values of various taxonomic groups. In addition, the tool implements several interactive GUI-based functionalities that enable users to perform standard comparative analyses across microbiomes.
Data analysis
Community metabolism
In many bacterial communities, natural or engineered (such as bioreactors), there is significant division of labor in metabolism (syntrophy), during which the waste products of some organisms are metabolites for others. In one such system, the methanogenic bioreactor, functional stability requires the presence of several syntrophic species (Syntrophobacterales and Synergistia) working together in order to turn raw resources into fully metabolized waste (methane). Using comparative gene studies and expression experiments with microarrays or proteomics researchers can piece together a metabolic network that goes beyond species boundaries. Such studies require detailed knowledge about which versions of which proteins are coded by which species and even by which strains of which species. Therefore, community genomic information is another fundamental tool (with metabolomics and proteomics) in the quest to determine how metabolites are transferred and transformed by a community.
Metatranscriptomics
Metagenomics allows researchers to access the functional and metabolic diversity of microbial communities, but it cannot show which of these processes are active. The extraction and analysis of metagenomic mRNA (the metatranscriptome) provides information on the regulation and expression profiles of complex communities. Because of the technical difficulties (the short half-life of mRNA, for example) in the collection of environmental RNA there have been relatively few in situ metatranscriptomic studies of microbial communities to date. While originally limited to microarray technology, metatranscriptomics studies have made use of transcriptomics technologies to measure whole-genome expression and quantification of a microbial community, first employed in analysis of ammonia oxidation in soils.
Viruses
Metagenomic sequencing is particularly useful in the study of viral communities. As viruses lack a shared universal phylogenetic marker (as 16S RNA for bacteria and archaea, and 18S RNA for eukarya), the only way to access the genetic diversity of the viral community from an environmental sample is through metagenomics. Viral metagenomes (also called viromes) should thus provide more and more information about viral diversity and evolution. For example, a metagenomic pipeline called Giant Virus Finder showed the first evidence of existence of giant viruses in a saline desert and in Antarctic dry valleys.
Applications
Metagenomics has the potential to advance knowledge in a wide variety of fields. It can also be applied to solve practical challenges in medicine, engineering, agriculture, sustainability and ecology.
Agriculture
The soils in which plants grow are inhabited by microbial communities, with one gram of soil containing around 109-1010 microbial cells which comprise about one gigabase of sequence information. The microbial communities which inhabit soils are some of the most complex known to science, and remain poorly understood despite their economic importance. Microbial consortia perform a wide variety of ecosystem services necessary for plant growth, including fixing atmospheric nitrogen, nutrient cycling, disease suppression, and sequester iron and other metals. Functional metagenomics strategies are being used to explore the interactions between plants and microbes through cultivation-independent study of these microbial communities. By allowing insights into the role of previously uncultivated or rare community members in nutrient cycling and the promotion of plant growth, metagenomic approaches can contribute to improved disease detection in crops and livestock and the adaptation of enhanced farming practices which improve crop health by harnessing the relationship between microbes and plants.
Biofuel
Biofuels are fuels derived from biomass conversion, as in the conversion of cellulose contained in corn stalks, switchgrass, and other biomass into cellulosic ethanol. This process is dependent upon microbial consortia (association) that transform the cellulose into sugars, followed by the fermentation of the sugars into ethanol. Microbes also produce a variety of sources of bioenergy including methane and hydrogen.
The efficient industrial-scale deconstruction of biomass requires novel enzymes with higher productivity and lower cost. Metagenomic approaches to the analysis of complex microbial communities allow the targeted screening of enzymes with industrial applications in biofuel production, such as glycoside hydrolases. Furthermore, knowledge of how these microbial communities function is required to control them, and metagenomics is a key tool in their understanding. Metagenomic approaches allow comparative analyses between convergent microbial systems like biogas fermenters or insect herbivores such as the fungus garden of the leafcutter ants.
Biotechnology
Microbial communities produce a vast array of biologically active chemicals that are used in competition and communication. Many of the drugs in use today were originally uncovered in microbes; recent progress in mining the rich genetic resource of non-culturable microbes has led to the discovery of new genes, enzymes, and natural products. The application of metagenomics has allowed the development of commodity and fine chemicals, agrochemicals and pharmaceuticals where the benefit of enzyme-catalyzed chiral synthesis is increasingly recognized.
Two types of analysis are used in the bioprospecting of metagenomic data: function-driven screening for an expressed trait, and sequence-driven screening for DNA sequences of interest. Function-driven analysis seeks to identify clones expressing a desired trait or useful activity, followed by biochemical characterization and sequence analysis. This approach is limited by availability of a suitable screen and the requirement that the desired trait be expressed in the host cell. Moreover, the low rate of discovery (less than one per 1,000 clones screened) and its labor-intensive nature further limit this approach. In contrast, sequence-driven analysis uses conserved DNA sequences to design PCR primers to screen clones for the sequence of interest. In comparison to cloning-based approaches, using a sequence-only approach further reduces the amount of bench work required. The application of massively parallel sequencing also greatly increases the amount of sequence data generated, which require high-throughput bioinformatic analysis pipelines. The sequence-driven approach to screening is limited by the breadth and accuracy of gene functions present in public sequence databases. In practice, experiments make use of a combination of both functional and sequence-based approaches based upon the function of interest, the complexity of the sample to be screened, and other factors. An example of success using metagenomics as a biotechnology for drug discovery is illustrated with the malacidin antibiotics.
Ecology
Metagenomics can provide valuable insights into the functional ecology of environmental communities. Metagenomic analysis of the bacterial consortia found in the defecations of Australian sea lions suggests that nutrient-rich sea lion faeces may be an important nutrient source for coastal ecosystems. This is because the bacteria that are expelled simultaneously with the defecations are adept at breaking down the nutrients in the faeces into a bioavailable form that can be taken up into the food chain.
DNA sequencing can also be used more broadly to identify species present in a body of water, debris filtered from the air, sample of dirt, or animal's faeces, and even detect diet items from blood meals. This can establish the range of invasive species and endangered species, and track seasonal populations.
Environmental remediation
Metagenomics can improve strategies for monitoring the impact of pollutants on ecosystems and for cleaning up contaminated environments. Increased understanding of how microbial communities cope with pollutants improves assessments of the potential of contaminated sites to recover from pollution and increases the chances of bioaugmentation or biostimulation trials to succeed.
Gut microbe characterization
Microbial communities play a key role in preserving human health, but their composition and the mechanism by which they do so remains mysterious. Metagenomic sequencing is being used to characterize the microbial communities from 15–18 body sites from at least 250 individuals. This is part of the Human Microbiome initiative with primary goals to determine if there is a core human microbiome, to understand the changes in the human microbiome that can be correlated with human health, and to develop new technological and bioinformatics tools to support these goals.
Another medical study as part of the MetaHit (Metagenomics of the Human Intestinal Tract) project consisted of 124 individuals from Denmark and Spain consisting of healthy, overweight, and irritable bowel disease patients. The study attempted to categorize the depth and phylogenetic diversity of gastrointestinal bacteria. Using Illumina GA sequence data and SOAPdenovo, a de Bruijn graph-based tool specifically designed for assembly short reads, they were able to generate 6.58 million contigs greater than 500 bp for a total contig length of 10.3 Gb and a N50 length of 2.2 kb.
The study demonstrated that two bacterial divisions, Bacteroidetes and Firmicutes, constitute over 90% of the known phylogenetic categories that dominate distal gut bacteria. Using the relative gene frequencies found within the gut these researchers identified 1,244 metagenomic clusters that are critically important for the health of the intestinal tract. There are two types of functions in these range clusters: housekeeping and those specific to the intestine. The housekeeping gene clusters are required in all bacteria and are often major players in the main metabolic pathways including central carbon metabolism and amino acid synthesis. The gut-specific functions include adhesion to host proteins and the harvesting of sugars from globoseries glycolipids. Patients with irritable bowel syndrome were shown to exhibit 25% fewer genes and lower bacterial diversity than individuals not suffering from irritable bowel syndrome indicating that changes in patients' gut biome diversity may be associated with this condition.
While these studies highlight some potentially valuable medical applications, only 31–48.8% of the reads could be aligned to 194 public human gut bacterial genomes and 7.6–21.2% to bacterial genomes available in GenBank which indicates that there is still far more research necessary to capture novel bacterial genomes.
In the Human Microbiome Project (HMP), gut microbial communities were assayed using high-throughput DNA sequencing. HMP showed that, unlike individual microbial species, many metabolic processes were present among all body habitats with varying frequencies. Microbial communities of 649 metagenomes drawn from seven primary body sites on 102 individuals were studied as part of the human microbiome project. The metagenomic analysis revealed variations in niche specific abundance among 168 functional modules and 196 metabolic pathways within the microbiome. These included glycosaminoglycan degradation in the gut, as well as phosphate and amino acid transport linked to host phenotype (vaginal pH) in the posterior fornix. The HMP has brought to light the utility of metagenomics in diagnostics and evidence-based medicine. Thus metagenomics is a powerful tool to address many of the pressing issues in the field of personalized medicine.
In animals, metagenomics can be used to profile their gut microbiomes and enable detection of antibiotic-resistant bacteria. This can have implications in monitoring the spread of diseases from wildlife to farmed animals and humans.
Infectious disease diagnosis
Differentiating between infectious and non-infectious illness, and identifying the underlying etiology of infection, can be challenging. For example, more than half of cases of encephalitis remain undiagnosed, despite extensive testing using state-of-the-art clinical laboratory methods. Clinical metagenomic sequencing shows promise as a sensitive and rapid method to diagnose infection by comparing genetic material found in a patient's sample to databases of all known microscopic human pathogens and thousands of other bacterial, viral, fungal, and parasitic organisms and databases on antimicrobial resistances gene sequences with associated clinical phenotypes.
Arbovirus surveillance
Metagenomics has been an invaluable tool to help characterise the diversity and ecology of pathogens that are vectored by hematophagous (blood-feeding) insects such as mosquitoes and ticks. Metagenomics is routinely used by public health officials and organisations for the surveillance of arboviruses.
| Biology and health sciences | Genetics | Biology |
1408983 | https://en.wikipedia.org/wiki/Hill | Hill | A hill is a landform that extends above the surrounding terrain. It often has a distinct summit, and is usually applied to peaks which are above elevation compared to the relative landmass, though not as prominent as mountains. Hills fall under the category of slope landforms.
Terminology
The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not as tall, or as steep as a mountain.
Geographers historically regarded mountains as hills greater than above sea level. In contrast, hillwalkers have tended to regard mountains as peaks above sea level. The Oxford English Dictionary also suggests a limit of and Whittow states "Some authorities regard eminences above as mountains, those below being referred to as hills." Today, a mountain is usually defined in the UK and Ireland as any summit at least high, while the UK government's Countryside and Rights of Way Act 2000 defined mountainous areas (for the purposes of open access legislation) as areas above . Some definitions include a topographical prominence requirement, typically or . In practice, mountains in Scotland are frequently referred to as "hills" no matter what their height, as reflected in names such as the Cuillin Hills and the Torridon Hills. In Wales, the distinction is more a term of land use and appearance and has nothing to do with height.
For a while, the US defined a mountain as being or more tall. Any similar landform lower than this height was considered a hill. The United States Geological Survey, however, has concluded that these terms do not in fact have technical definitions in the US.
The Great Soviet Encyclopedia defined "hill" as an upland with a relative height of up to .
A hillock is a small hill. Other words include knoll and (in Scotland, Northern Ireland and northern England) its variant, knowe. Artificial hills may be referred to by a variety of technical names, including mound and tumulus.
Hills may form through geomorphic phenomena: faulting, erosion of larger landforms such as mountains and movement and deposition of sediment by glaciers (notably moraines and drumlins or by erosion exposing solid rock which then weathers down into a hill). The rounded peaks of hills results from the diffusive movement of soil and regolith covering the hill, a process known as downhill creep.
Various names may be used to describe types of hills, based on appearance and method of formation. Many such names originated in one geographical region to describe a type of hill formation particular to that region, though the names are often adopted by geologists and used in a wider geographical context. These include:
Brae – Scots, Ulster, and North of England term for a hillside or brow of a hill.
Drumlin – an elongated whale-shaped hill formed by glacial action.
Butte – an isolated hill with steep sides and a small flat top, formed by weathering.
Kuppe – a rounded hill or low mountain, typical of Central Europe.
Tor – a rock formation found on a hilltop; also used to refer to the hill, especially in South West England and the Peak District.
Puy – used especially in the Auvergne, France, to describe a conical volcanic hill.
Pingo – a mound of earth-covered ice found in the Arctic and Antarctica.
Historical significance
Many settlements were originally built on hills, either to avoid floods (particularly if they were near a large body of water), for defense (since they offer a good view of the surrounding land and require would-be attackers to fight uphill), or to avoid densely forested areas. For example, Ancient Rome was built on seven hills, helping to protect it from invaders.
Some settlements, particularly in the Middle East, are located on artificial hills consisting of debris (particularly mudbricks) that has accumulated over many generations. Such a location is known as a "tell".
In Northern Europe, many ancient monuments are sited in heaps. Some of these are defensive structures (such as the hillforts of the Iron Age), but others appear to have hardly any significance. In Britain, many churches at the tops of hills are thought to have been built on the sites of earlier pagan holy places. The Washington National Cathedral in Washington, D.C. has followed this tradition and was built on the highest hill in that city.
Some cities' hills are culturally significant in their foundation, defense, and history. In addition to Rome, hills have played a prominent role in the history of San Francisco, with its hills being central to the city's fog and civil engineering projects today famous as tourist attractions such as the cable cars and Lombard Street.
Military significance
Hills provide important advantages to an army that controls their heights, giving them an elevated view and firing position and forcing an opposing army to charge uphill to attack a fort or other position. They may also conceal forces behind them, allowing a force to lie in wait on the crest of a hill, using that crest for cover, and firing on unsuspecting attackers as they broach the hilltop. As a result, conventional military strategies often demand possession of high ground.
Because of their strategic and tactical values, hills have been the site of many notable battles, such as the Battle of Alesia in 52 BC and the first recorded military conflict in Scotland, the Battle of Mons Graupius in AD 83. Modern era conflicts include the 1775 Battle of Bunker Hill (which was actually fought on Breed's Hill) in the American War of Independence; and Cemetery Hill and Culp's Hill in the 1863 Battle of Gettysburg, the turning point of the American Civil War. The Battle of San Juan Hill in the 1898 Spanish–American War won the Americans control of Santiago de Cuba but only after suffering from heavy casualties inflicted by a much smaller force entrenched on the hill top.
Battles for the possession of high ground have often resulted in heavy casualties to both sides, such as the 1969 Battle of Hamburger Hill during the Vietnam War, the Battle of Stalingrad and Battle of Peleliu during World War II, and the 1969 Kargil War between India and Pakistan.
The Great Wall of China is an enduring example of hilltop fortification. It was built on hilltops to help defend against invaders from the north, such as Mongols.
Sports and games
Hillwalking is a British English term for a form of hiking which involves the ascent of hills. The activity is usually distinguished from mountaineering as it does not involve ropes or technically difficult rock climbing, although the terms mountain and hill are often used interchangeably in Britain. Hillwalking is popular in hilly areas such as the English Peak District and the Scottish Highlands. Many hills are categorized according to relative height or other criteria and feature on lists named after mountaineers, such as Munros (Scotland) and Wainwrights (England). Specific activities such as "peak bagging" (or "Munro bagging") involve climbing hills on these lists with the aim of eventually climbing every hill on the list.
Cooper's Hill Cheese-Rolling and Wake is an annual event in the West Country of England which involves rolling a wheel of cheese down a hill. Contestants stand at the top and chase the wheel of cheese to the bottom. The winner, the one who catches the cheese, gets to keep the wheel of cheese as a prize.
Cross country running courses may include hills which can add diversity and challenge to those courses.
Notable artificial hills
Mound
Sophienhöhe, Germany ()
Monte Kaolino, Germany ()
, Sweden ()
Malminkartanonhuippu, Finland ()
Mausoleum of the First Qin Emperor, China ()
Five Sisters Bing, Scotland ()
Monte Stella, Italy ()
Blackstrap Ski Hill, Canada ()
Jingshan Hill, China ()
Silbury Hill, England ()
Mount Manisty, England ()
Monks Mound, Illinois ()
Man-made mountain
Shanghai Expo Park Mountains ()
Gallery
| Physical sciences | Landforms | null |
1409006 | https://en.wikipedia.org/wiki/Common%20knowledge%20%28logic%29 | Common knowledge (logic) | Common knowledge is a special kind of knowledge for a group of agents. There is common knowledge of p in a group of agents G when all the agents in G know p, they all know that they know p, they all know that they all know that they know p, and so on ad infinitum. It can be denoted as .
The concept was first introduced in the philosophical literature by David Kellogg Lewis in his study Convention (1969). The sociologist Morris Friedell defined common knowledge in a 1969 paper. It was first given a mathematical formulation in a set-theoretical framework by Robert Aumann (1976). Computer scientists grew an interest in the subject of epistemic logic in general – and of common knowledge in particular – starting in the 1980s. There are numerous puzzles based upon the concept which have been extensively investigated by mathematicians such as John Conway.
The philosopher Stephen Schiffer, in his 1972 book Meaning, independently developed a notion he called "mutual knowledge" () which functions quite similarly to Lewis's and Friedel's 1969 "common knowledge". If a trustworthy announcement is made in public, then it becomes common knowledge; However, if it is transmitted to each agent in private, it becomes mutual knowledge but not common knowledge. Even if the fact that "every agent in the group knows p" () is transmitted to each agent in private, it is still not common knowledge: . But, if any agent publicly announces their knowledge of p, then it becomes common knowledge that they know p (viz. ). If every agent publicly announces their knowledge of p, p becomes common knowledge .
Example
Puzzle
The idea of common knowledge is often introduced by some variant of induction puzzles (e.g. Muddy children puzzle):
On an island, there are k people who have blue eyes, and the rest of the people have green eyes. At the start of the puzzle, no one on the island ever knows their own eye color. By rule, if a person on the island ever discovers they have blue eyes, that person must leave the island at dawn; anyone not making such a discovery always sleeps until after dawn. On the island, each person knows every other person's eye color, there are no reflective surfaces, and there is no communication of eye color.
At some point, an outsider comes to the island, calls together all the people on the island, and makes the following public announcement: "At least one of you has blue eyes". The outsider, furthermore, is known by all to be truthful, and all know that all know this, and so on: it is common knowledge that he is truthful, and thus it becomes common knowledge that there is at least one islander who has blue eyes (). The problem: finding the eventual outcome, assuming all persons on the island are completely logical (every participant's knowledge obeys the axiom schemata for epistemic logic) and that this too is common knowledge.
Solution
The answer is that, on the kth dawn after the announcement, all the blue-eyed people will leave the island.
Proof
The solution can be seen with an inductive argument. If k = 1 (that is, there is exactly one blue-eyed person), the person will recognize that they alone have blue eyes (by seeing only green eyes in the others) and leave at the first dawn. If k = 2, no one will leave at the first dawn, and the inaction (and the implied lack of knowledge for every agent) is observed by everyone, which then becomes common knowledge as well (). The two blue-eyed people, seeing only one person with blue eyes, and that no one left on the first dawn (and thus that k > 1; and also that the other blue-eyed person does not think that everyone except themself are not blue-eyed , so another blue-eyed person ), will leave on the second dawn. Inductively, it can be reasoned that no one will leave at the first k − 1 dawns if and only if there are at least k blue-eyed people. Those with blue eyes, seeing k − 1 blue-eyed people among the others and knowing there must be at least k, will reason that they must have blue eyes and leave.
For k > 1, the outsider is only telling the island citizens what they already know: that there are blue-eyed people among them. However, before this fact is announced, the fact is not common knowledge, but instead mutual knowledge.
For k = 2, it is merely "first-order" knowledge (). Each blue-eyed person knows that there is someone with blue eyes, but each blue eyed person does not know that the other blue-eyed person has this same knowledge.
For k = 3, it is "second order" knowledge (). Each blue-eyed person knows that a second blue-eyed person knows that a third person has blue eyes, but no one knows that there is a third blue-eyed person with that knowledge, until the outsider makes their statement.
In general: For k > 1, it is "(k − 1)th order" knowledge (). Each blue-eyed person knows that a second blue-eyed person knows that a third blue-eyed person knows that.... (repeat for a total of k − 1 levels) a kth person has blue eyes, but no one knows that there is a "kth" blue-eyed person with that knowledge, until the outsider makes his statement. The notion of common knowledge therefore has a palpable effect. Knowing that everyone knows does make a difference. When the outsider's public announcement (a fact already known to all, unless k=1 then the one person with blue eyes would not know until the announcement) becomes common knowledge, the blue-eyed people on this island eventually deduce their status, and leave.
In particular:
is free (i.e. known prior to the outsider's statement) iff .
, with a passing day where no one leaves, implies the next day .
for is thus reached iff it is reached for .
The outsider gives for .
Formalization
Modal logic (syntactic characterization)
Common knowledge can be given a logical definition in multi-modal logic systems in which the modal operators are interpreted epistemically. At the propositional level, such systems are extensions of propositional logic. The extension consists of the introduction of a group G of agents, and of n modal operators Ki (with i = 1, ..., n) with the intended meaning that "agent i knows." Thus Ki (where is a formula of the logical calculus) is read "agent i knows ." We can define an operator EG with the intended meaning of "everyone in group G knows" by defining it with the axiom
By abbreviating the expression with and defining , common knowledge could then be defined with the axiom
There is, however, a complication. The languages of epistemic logic are usually finitary, whereas the axiom above defines common knowledge as an infinite conjunction of formulas, hence not a well-formed formula of the language. To overcome this difficulty, a fixed-point definition of common knowledge can be given. Intuitively, common knowledge is thought of as the fixed point of the "equation" . Here, is the Aleph-naught. In this way, it is possible to find a formula implying from which, in the limit, we can infer common knowledge of .
From this definition it can be seen that if is common knowledge, then is also common knowledge ().
This syntactic characterization is given semantic content through so-called Kripke structures. A Kripke structure is given by a set of states (or possible worlds) S, n accessibility relations , defined on , intuitively representing what states agent i considers possible from any given state, and a valuation function assigning a truth value, in each state, to each primitive proposition in the language. The Kripke semantics for the knowledge operator is given by stipulating that is true at state s iff is true at all states t such that . The semantics for the common knowledge operator, then, is given by taking, for each group of agents G, the reflexive (modal axiom T) and transitive closure (modal axiom 4) of the , for all agents i in G, call such a relation , and stipulating that is true at state s iff is true at all states t such that .
Set theoretic (semantic characterization)
Alternatively (yet equivalently) common knowledge can be formalized using set theory (this was the path taken by the Nobel laureate Robert Aumann in his seminal 1976 paper). Starting with a set of states S. An event E can then be defined as a subset of the set of states S. For each agent i, define a partition on S, Pi. This partition represents the state of knowledge of an agent in a state. Intuitively, if two states s1 and s2 are elements of the same part of partition of an agent, it means that s1 and s2 are indistinguishable to that agent. In general, in state s, agent i knows that one of the states in Pi(s) obtains, but not which one. (Here Pi(s) denotes the unique element of Pi containing s. This model excludes cases in which agents know things that are not true.)
A knowledge function K can now be defined in the following way:
That is, Ki(e) is the set of states where the agent will know that event e obtains. It is a subset of e.
Similar to the modal logic formulation above, an operator for the idea that "everyone knows can be defined as e".
As with the modal operator, we will iterate the E function, and . Using this we can then define a common knowledge function,
The equivalence with the syntactic approach sketched above can easily be seen: consider an Aumann structure as the one just defined. We can define a correspondent Kripke structure by taking the same space S, accessibility relations that define the equivalence classes corresponding to the partitions , and a valuation function such that it yields value true to the primitive proposition p in all and only the states s such that , where is the event of the Aumann structure corresponding to the primitive proposition p. It is not difficult to see that the common knowledge accessibility function defined in the previous section corresponds to the finest common coarsening of the partitions for all , which is the finitary characterization of common knowledge also given by Aumann in the 1976 article.
Applications
Common knowledge was used by David Lewis in his pioneering game-theoretical account of convention. In this sense, common knowledge is a concept still central for linguists and philosophers of language (see Clark 1996) maintaining a Lewisian, conventionalist account of language.
Robert Aumann introduced a set theoretical formulation of common knowledge (theoretically equivalent to the one given above) and proved the so-called agreement theorem through which: if two agents have common prior probability over a certain event, and the posterior probabilities are common knowledge, then such posterior probabilities are equal. A result based on the agreement theorem and proven by Milgrom shows that, given certain conditions on market efficiency and information, speculative trade is impossible.
The concept of common knowledge is central in game theory. For several years it has been thought that the assumption of common knowledge of rationality for the players in the game was fundamental. It turns out (Aumann and Brandenburger 1995) that, in two-player games, common knowledge of rationality is not needed as an epistemic condition for Nash equilibrium strategies.
Computer scientists use languages incorporating epistemic logics (and common knowledge) to reason about distributed systems. Such systems can be based on logics more complicated than simple propositional epistemic logic, see Wooldridge Reasoning about Artificial Agents, 2000 (in which he uses a first-order logic incorporating epistemic and temporal operators) or van der Hoek et al. "Alternating Time Epistemic Logic".
In his 2007 book, The Stuff of Thought: Language as a Window into Human Nature, Steven Pinker uses the notion of common knowledge to analyze the kind of indirect speech involved in innuendoes.
In popular culture
The comedy movie Hot Lead and Cold Feet has an example of a chain of logic that is collapsed by common knowledge.
The Denver Kid tells his allies that Rattlesnake is in town, but that he [the Kid] has “the edge”: “He's here and I know he's here, and he knows I know he's here, but he doesn't know I know he knows I know he's here.”
So both protagonists know the main fact (Rattlesnake is here), but it is not “common knowledge”. Note that this is true even if the Kid is wrong: maybe Rattlesnake does know that the Kid knows that he knows that he knows, the chain still breaks because the Kid doesn't know that.
Moments later, Rattlesnake confronts the Kid. We see the Kid realizing that his carefully constructed “edge” has collapsed into common knowledge.
| Mathematics | Game theory | null |
1409767 | https://en.wikipedia.org/wiki/High-intensity%20interval%20training | High-intensity interval training | High-intensity interval training (HIIT) is a training protocol alternating short periods of intense or explosive anaerobic exercise with brief recovery periods until the point of exhaustion. HIIT involves exercises performed in repeated quick bursts at maximum or near maximal effort with periods of rest or low activity between bouts. The very high level of intensity, the interval duration, and number of bouts distinguish it from aerobic (cardiovascular) activity, because the body significantly recruits anaerobic energy systems (although not completely to the exclusion of aerobic pathways). The method thereby relies on "the anaerobic energy releasing system almost maximally".
Although there are varying forms of HIIT-style workouts which may involve exercises associated with both cardiovascular activity and also resistance training, HIIT's crucial features of maximal effort, duration, and short rest periods (thereby triggering the anaerobic pathways of energy production) materially differentiate it from being considered a form of cardiovascular exercise. Though there is no universal HIIT session duration, a HIIT workout typically lasts under 30 minutes in total as it uses the anaerobic energy systems which are typically used for short, sharp bursts. The times vary, based on a participant's current fitness level. Traditional HIIT initially had been designed to be no longer than 20 seconds on with no more than 10 seconds off; however, intervals of exercise effort tend to range from 20 to 45 seconds but no longer than 75 seconds, at which point the aerobic system would then kick in.
HIIT workouts provide improved athletic capacity and condition as well as improved glucose metabolism. Compared with longer sessions typical of other regimens, HIIT may not be as effective for treating hyperlipidemia and obesity, or improving muscle and bone mass. However, research has shown that HIIT regimens produced reductions in the fat mass of the whole-body in young women comparable to prolonged moderate-intensity continuous training (MICT). Some researchers also note that HIIT requires "an extremely high level of subject motivation" and question whether the general population could safely or practically tolerate the extreme nature of the exercise regimen.
Sprint interval training (SIT) is an exercise conducted in a similar way to HIIT, but instead of using "near maximal" effort for the high-intensity periods, "supramaximal" or "all-out" efforts are used in shorter bursts. In physiological terms, "near maximal" means reaching 80–100% HRmax, while "supramaximal" means a pace that exceeds what would elicit VO2 peak. SIT regimens generally include a lower volume of total exercise compared with HIIT ones as well as longer, lower activity recovery periods and creates a greater homeostatic disturbance. Both HIIT and SIT fall into the larger class of interval training. Distinction between the two is not always maintained, even in academia: for example, Tabata describes his 170% VO2 max regimen as "supermaximal", but does not use the term SIT.
Procedure
HIIT exercise sessions generally consist of a warm-up period followed by repetitions of high-intensity exercises separated by medium intensity exercises for recovery, then a cool-down period. The high-intensity exercise should be done at near maximum intensity. The medium exercise should be about 50% intensity. The number of repetitions and length of each depends on the exercise, but may be as little as three repetitions with just 20 seconds of intense exercise. The specific exercises performed during the high-intensity portions vary. Most of the research on HIIT has been done using a cycling ergometer, but other exercises like a rowing ergometer, running, stair climbing and uphill walking can also be effective.
There is no specific formula for HIIT. Depending on one's level of cardiovascular development, the moderate-level intensity can be as slow as walking. A typical HIIT session uses a 2:1 work-to-rest ratio, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking, repeated to failure.
The entire HIIT session may last between four and 30 minutes, meaning that it is considered to be an excellent way to maximize a workout limited by time constraints. Use of a clock or timer is recommended to keep accurate times, the number of rounds, and intensity.
An alternative form of HIIT, designed for heart rate training, involves a 30-minute period of cardio followed by 30 minutes of full-body resistance training to help maximize calorie burning. The idea is to combine aerobic exercise with intense weight and resistance training to achieve a high level heart rate for an extended period of time, in order to maximize strength and endurance.
Branches
Peter Coe regimen
In the 1970s a type of high-intensity interval training with short recovery periods was used by the athletics coach Peter Coe when setting sessions for his son Sebastian Coe. Inspired by the principles propounded by the German coach and university professor Woldemar Gerschler and the Swedish physiologist Per-Olof Åstrand, Coe set sessions involving repeated fast 200 meter runs with only 30 seconds recovery between each fast run.
Tabata regimen
A version of HIIT is based on a 1996 study by Ritsumeikan University Professor et al. initially involving Olympic speedskaters. The study used 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). The exercise was performed on a mechanically braked cycle ergometer. Tabata called this the IE1 protocol. In the original study, athletes using this method trained 4 times per week, plus another day of steady-state training, for 6 weeks and obtained gains similar to a group of athletes who did steady state training (70% VO2max) 5 times per week. The steady state group had a higher VO2max at the end (from 52 to 57 mL/(kg•min)). However the Tabata group had achieved comparable aerobic improvements but only exercised 4 minutes per day on their 4 HIIT days compared to 60 minutes for the aerobic group. The Tabata group also started lower and gained more overall (from 48 to 55 mL/(kg•min)). Also, only the Tabata group had gained anaerobic capacity benefits. (As Tabata's protocol is "supermaximal", his regimen technically falls into the scope of SIT.)
Gibala regimen
Professor Martin Gibala and his team at McMaster University in Canada have been researching high-intensity exercise for several years. Their 2010 study on students uses 3 minutes for warming up, then 60 seconds of intense exercise (at 95% of VO2max) followed by 75 seconds of rest, repeated for 8–12 cycles (sometimes referred to as "The Little Method"). Subjects using this method training 3 times per week on a stationary bicycle obtained gains similar to what would be expected from subjects who did steady-state (50–70% VO2max) training five times per week.
Gibala's group published a less intense version of their regimen in a 2011 paper in Medicine & Science in Sports & Exercise. This was intended as a gentler option for sedentary people who had done no exercise for over a year. It included 3 minutes of warm-up, 10 repetitions of 60-second bursts at 60% peak power (80–95% of heart rate reserve) each followed by 60 seconds of recovery, and then a 5-minute cool-down.
Zuniga regimen
In 2011 Jorge Zuniga, assistant professor of exercise science at Creighton University, set out to determine how to fit the highest volume of work and oxygen consumption into the smallest amount of time. He found that intervals of 30 seconds at 90% of power output at VO2 max followed by 30 seconds of rest allowed for the highest VO2 consumption and the longest workout duration at specified intensity. Alternative protocols considered included 100% of maximum power output on the same interval schedule, similar to the Coe regimen, and 90% of maximum power output for three minutes, similar to traditional interval training.
Zuniga's protocol has been implemented with great success by students of his who were participating in Creighton's Army ROTC program. Cadets completing the protocol twice a week saw greater improvements in APFT scores than in years past. Zuniga's protocol typically consists of 10 repetitions.
Vollaard regimen
Dr Niels Vollaard at the University of Stirling proposed that when high-intensity intervals are done at "all-out" intensities, associated health benefits plateau after performing 2 or 3 sprint repetitions. This led to the development of a 10-minute exercise routine consisting of easy pedalling interspersed with two 20-second "all-out" cycling sprints. In a 2017 meta-analysis, Vollaard indeed showed that common protocols with as many as 6 to 10 repetitions of 30-second "all-out" sprints do not improve aerobic fitness more than the "2×20-s" protocol. He shifted the terminology for his to SIT. It is claimed that this short protocol may remove many of the drawbacks that make other high-intensity interval training protocols unsuitable for the general population.
In a BBC Horizon program in February 2012, Jamie Timmons, professor of systems biology at the University of Loughborough, led Michael Mosley through this exercise bike regimen, each time using three sprints instead of two. This protocol was performed three times a week for a total of 30 minutes of exercise per week (3 minutes of intense exercise), plus warm-up and recovery time.
Regimen comparison
A study compared HIIT of eight 1-minute bouts at 85% maximum Watts (Wmax) interspersed with 1-minute active recovery at 25% Wmax, to SIT of eight 30-second bouts at 130% Wmax interspersed with 90-second active recovery at 25% Wmax (Total time-matched at 24 minutes including warm-up & cooldown). Its conclusion was "HIIT is the recommended routine" but "the magnitude of differences in various parameters between regimens was small; therefore, preference for either modality may be up to the individual".
Health effects
Cardiovascular effects
HIIT training and traditional endurance training both lead to significantly improved cardiovascular fitness in healthy adults ages 18–45 but HIIT leads to greater improvements in VO2 max. HIIT regimens of one month or longer effectively improve cardiovascular fitness in adolescents and lead to moderate improvements in body composition. HIIT (when defined as four intervals of four minutes at 85–95% of max heart rate with three-minute intervals at 60–70% of max heart rate) is also more effective than moderate-intensity continuous training at improving blood vessel function and markers of blood vessel health.
Comparing HIIT to moderate intensity continuous training (MICT) in people with coronary artery disease, HIIT leads to greater improvements in VO2 max but MICT leads to greater reductions in body weight and heart rate. Improvement to cardiorespiratory fitness, as measured by VO2 max, of individuals with lifestyle-induced chronic cardiovascular or metabolic diseases (including high blood pressure, obesity, heart failure, coronary artery disease, or metabolic syndrome) who completed a HIIT exercise program can be nearly double that of individuals who completed a MICT exercise program (19.4% increase and 10.3% increase, respectively).
Rehabilitative effects
For people suffering from coronary artery disease or heart failure, a HIIT regimen is beneficial for substantially improving both groups VO2 max and overall exercise capacity; with more intense HIIT leading to the greatest cardiovascular improvements. A combination of a proper HIIT program with active recovery instead of passive recovery is most beneficial to improving heart contractibility in people with heart failure.
Metabolic effects
HIIT significantly lowers insulin resistance compared to continuous training or control conditions and leads to modestly decreased fasting blood glucose levels and increased weight loss compared to those who do not undergo a physical activity intervention.
Fat oxidation
HIIT can result in modest reductions of subcutaneous fat in young and healthy individuals, but greater reductions for overweight individuals. HIIT, particularly running, is a time-efficient strategy in decreasing abdominal and visceral fat-mass deposits.
A 2021 systematic review examined the effects of HIIT combined with resistance training in teens (ages 10–19), without providing a nutritional plan. The study found that 8 to 12 weeks of HIIT combined with resistance training can substantially reduce waist size and body fat percentage. However the study did not find conclusive evidence of HIIT and resistance training being an effective solitary treatment for type 2 diabetes or arterial hypertension, but did find HIIT has the potential to reduce future cardiovascular problems in teens.
Brain power
HIIT can elicit short term brain improvements similar to those usually observed with aerobic exercise.
Youth
HIIT has been shown to increase muscle mass in adolescent populations, especially in the mid-to-late teenage years. In cases of pediatric obesity, HIIT training can be used as both a treatment and a preventative measure, as it can help decrease BMI (body mass index), decrease body fat mass percentage, decrease insulin resistance, and decrease the count of low-density lipoproteins across the body. The reduction in fat mass and BMI at a young age create effects against obesity that are also tantamount in preventing other health issues such as diabetes, coronary heart disease, and cancer. It has been shown to increase full body strength, and thereby improve full-body movement capability, which can reduce sedentariness.
Dangers
The American College of Sports Medicine suggests consulting one's doctor before starting a HIIT regimen, particularly if there is a history of coronary heart disease. This is to ascertain its safety and allow the patient to build up the intensity of exercise without causing harm. It is advised to start a lower intensity and go at one's own pace.
High-intensity exercise has the potential to elicit rapid increases in systemic blood pressure that may be transmitted to the brain, which could lead to hyper-perfusion injury in at-risk populations such as sedentary adults.
There is a risk of injury due to fatigue and overtraining, so it is advised to allow time for recovery. Research from Rutgers University demonstrated that the knees, shoulders, and ankles were the most commonly involved injuries. More specifically, knee and ankle sprains were very common. Based on that, neuromuscular training and pre-strengthening programs are recommended to improve flexibility, particularly before exercise.
Research
A 2007 study examined HIIT's physiological effects on fat oxidation in moderately active women. The participants in the study performed HIIT (defined as ten sets of 4-minute cycling bursts at an intensity of 90% VO2max separated by 2 minutes of rest) every other day over a 2-week period. The study found that seven sessions of HIIT over a 2-week period improved whole body fat oxidation and the capacity for skeletal muscle to oxidize fat in moderately active women.
A 2008 research study found that HIIT was more effective than moderate-intensity continuous training at lowering fasting insulin levels (31% decrease and 9% decrease, respectively).
A 2017 study examined the effect of HIIT on cognitive performance among a group of children. The authors show that HIIT is beneficial to cognitive control and working memory capacity when compared against "a blend of board games, computer games, and trivia quizzes" and that this effect is mediated by the BDNF polymorphism. They conclude that the study "suggests a promising alternative to enhance cognition, via short and potent exercise regimens".
A 2019 clinical trial assessed the effects of HIIT on vascular health in inactive people and found that HIIT has beneficial vascular effects, based on observed decreases in arterial wall thickness and increase in endothelial function. The trial also found that HIIT had stronger effects than medium intensity continuous training (MICT) in enhancing flow mediated dilation and lowering pulse wave velocity in inactive adults from the greater blood flow and vasodilation of blood vessels stimulated by HIIT. Increased flow mediated dilation allows for greater opening of an artery and increased blood flow, allowing for more oxygen to be supplied throughout the body during activity. Pulse wave velocity is used to monitor arterial stiffness; which increases with age and high blood pressure, leading to a higher probability of cardiovascular problems including hypertension or a stroke.
A 2019 study on the relevance of exercise intensity in lower back rehabilitation, demonstrated higher intensity had a greater effectiveness with back therapy than moderate intensity exercise. Participants in the HIIT group had a decrease in back pain intensity and an increase in back muscle strength. In 2020, a similar study explained the strong effectiveness of cardiorespiratory HIIT in treating lower back pain, when combined with other forms of HIIT or mobility exercises.
A 2020 study examined the impact of HIIT and moderate intensity continuous training (MICT) on overweight individuals by measuring the effect on cardiorespiratory fitness (CRF). The study found that both forms of training were effective in improving CRF with an increase in VO2 max, however there was no evidence that either training method was more effective than the other in improving cardiorespiratory fitness.
According to a 2020 study HIIT could be used as prehabilitation for men awaiting surgery for urological cancer and it may improve heart and lung fitness within a month before their surgery.
| Biology and health sciences | Physical fitness | Health |
1409922 | https://en.wikipedia.org/wiki/Incertae%20sedis | Incertae sedis | or is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by (of uncertain family), (of uncertain suborder), (of uncertain order) and similar terms.
Examples
The fossil plant Paradinandra suecica could not be assigned to any family, but was placed incertae sedis within the order Ericales when described in 2001.
The fossil Gluteus minimus, described in 1975, could not be assigned to any known animal phylum. The genus is therefore incertae sedis within the kingdom Animalia.
While it was unclear to which order the New World vultures (family Cathartidae) should be assigned, they were placed in Aves incertae sedis. It was later agreed to place them in a separate order, Cathartiformes.
Bocage's longbill, Motacilla bocagii, previously known as Amaurocichla bocagii, is a species of passerine bird that belongs to the superfamily Passeroidea. Since it was unclear to which family it belongs, it was classified as Passeroidea incertae sedis, until a 2015 phylogenetic study placed it in Motacilla of Motacillidae.
Parakaryon myojinensis, a single-celled organism that is apparently distinct from prokaryotes and eukaryotes, being the only identified species with a completely unknown position within the tree of life.
Biological dark matter, genetic material produced from unidentified microorganisms that appears to match no known species. Like Parakaryon, its producers' positions in the tree of life are completely unknown.
Metallogenium is a bacterium that can form star-shaped minerals.
Circothecidae are a family of Cambrian animals, sometimes attributed to the Hyolitha, though some authors suggest (on the basis of no specified evidence) that they are definitely not.
The frosted phoenix moth (Titanomis sisyrota) is so rare and so obscure it is unable to be placed in any family within the Lepidoptera.
In formal nomenclature
When formally naming a taxon, uncertainty about its taxonomic classification can be problematic. The International Code of Nomenclature for algae, fungi, and plants, stipulates that "species and subdivisions of genera must be assigned to genera, and infraspecific taxa must be assigned to species, because their names are combinations", but ranks higher than the genus may be assigned incertae sedis.
Reason for use
Poor description
This excerpt from a 2007 scientific paper about crustaceans of the Kuril–Kamchatka Trench and the Japan Trench describes typical circumstances through which this category is applied in discussing:
...the removal of many genera from new and existing families into a state of incertae sedis. Their reduced status was attributed largely to poor or inadequate descriptions but it was accepted that some of the vagueness in the analysis was due to insufficient character states. It is also evident that a proportion of the characters used in the analysis, or their given states for particular taxa, were inappropriate or invalid. Additional complexity, and factors that have misled earlier authorities, are intrusion by extensive homoplasies, apparent character state reversals and convergent evolution.
Not included in an analysis
If a formal phylogenetic analysis is conducted that does not include a certain taxon, the authors might choose to label the taxon incertae sedis instead of guessing its placement. This is particularly common when molecular phylogenies are generated, since tissue for many rare organisms is hard to obtain. It is also a common scenario when fossil taxa are included, since many fossils are defined based on partial information. For example, if the phylogeny was constructed using soft tissue and vertebrae as principal characters and the taxon in question is only known from a single tooth, it would be necessary to label it incertae sedis.
Controversy
If conflicting results exist or if there is not a consensus among researchers as to how a taxon relates to other organisms, it may be listed as incertae sedis until the conflict is resolved.
Phylogenetic vs. nomenclatural uncertainty
The term incertae sedis refers to uncertainty about phylogenetic position of a taxon, which may be expressed, among others, by using a question mark after or before a taxon name. This should be distinguished from the situation where either it is uncertain how to use a name, often because the types have been lost (nomen dubium, species inquirenda), or whether a poorly preserved specimen should be included within a given species or genus, which is often expressed using a 'cf.' (from Latin confer, compare, before a taxon name); such a convention is especially widespread in palaeontology.
In zoological nomenclature
In zoological nomenclature, "incertae sedis" is not a nomenclatural term at all per se, but is used by taxonomists in their classifications to mean "of uncertain taxonomic position".Glossary In botany, a name is not validly published if it is not accepted by the author in the same publication.Article 36.1 In zoology, a name proposed conditionally may be available under certain conditions.Articles 11 and 15 For uncertainties at lower levels, some authors have proposed a system of "open nomenclature", suggesting that question marks be used to denote a questionable assignment. For example, if a new species was given the specific epithet album by Anton and attributed with uncertainty to Agenus, it could be denoted "Agenus? album Anton (?Anton)"; the "(?Anton)" indicates the author that assigned the question mark. So if Anton described Agenus album, and Bruno called the assignment into doubt, this could be denoted "Agenus? album (Anton) (?Bruno)", with the parentheses around Anton because the original assignment (to Agenus) was modified (to Agenus?) by Bruno. This practice is not included in the International Code of Zoological Nomenclature, and is used only by paleontologists.
| Biology and health sciences | Phylogenetics and taxonomy | Biology |
1410775 | https://en.wikipedia.org/wiki/Bok%20globule | Bok globule | In astronomy, Bok globules are isolated and relatively small dark nebulae containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about two to 50 solar masses contained within a region about a light year or so across (about ). They contain molecular hydrogen (H2), carbon oxides and helium, and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation of double- or multiple-star systems.
History
Bok globules were first observed by astronomer Bart Bok in the 1940s. In an article published in 1947, he and Edith F. Reilly hypothesized that these clouds were "similar to insect's cocoons" that were undergoing gravitational collapse to form new stars, from which stars and star clusters were born.
This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured all visible light emitted from within it.
An analysis of near-infrared observations published in 1990 confirmed that stars were being born inside Bok globules. Further observations have revealed that some Bok globules contain embedded warm sources, some contain Herbig–Haro objects, and some show outflows of molecular gas. Millimeter-wave emission line studies have provided evidence for the infall of material onto an accreting protostar.
It is now thought that a typical Bok globule contains about 10 solar masses of material in a region about a light-year or so across, and that Bok globules most commonly result in the formation of double- or multiple-star systems.
Bok globules are still a subject of intense research. Known to be some of the coldest objects in the natural universe, their structure and density remains somewhat a mystery. Methods applied so far have relied on column density derived from near-infrared extinction and even star counting in a bid to probe these objects further.
Bok globules that are irradiated by ultraviolet light from hot nearby stars exhibit stripping of materials to produce a tail. These types are called "cometary globules" (CG).
Image gallery
| Physical sciences | Basics_2 | Astronomy |
1411100 | https://en.wikipedia.org/wiki/Introduction%20to%20general%20relativity | Introduction to general relativity | General relativity is a theory of gravitation developed by Albert Einstein between 1907 and 1915. The theory of general relativity says that the observed gravitational effect between masses results from their warping of spacetime.
By the beginning of the 20th century, Newton's law of universal gravitation had been accepted for more than two hundred years as a valid description of the gravitational force between masses. In Newton's model, gravity is the result of an attractive force between massive objects. Although even Newton was troubled by the unknown nature of that force, the basic framework was extremely successful at describing motion.
Experiments and observations show that Einstein's description of gravitation accounts for several effects that are unexplained by Newton's law, such as minute anomalies in the orbits of Mercury and other planets. General relativity also predicts novel effects of gravity, such as gravitational waves, gravitational lensing and an effect of gravity on time known as gravitational time dilation. Many of these predictions have been confirmed by experiment or observation, most recently gravitational waves.
General relativity has developed into an essential tool in modern astrophysics. It provides the foundation for the current understanding of black holes, regions of space where the gravitational effect is strong enough that even light cannot escape. Their strong gravity is thought to be responsible for the intense radiation emitted by certain types of astronomical objects (such as active galactic nuclei or microquasars). General relativity is also part of the framework of the standard Big Bang model of cosmology.
Although general relativity is not the only relativistic theory of gravity, it is the simplest one that is consistent with the experimental data. Nevertheless, a number of open questions remain, the most fundamental of which is how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.
From special to general relativity
In September 1905, Albert Einstein published his theory of special relativity, which reconciles Newton's laws of motion with electrodynamics (the interaction between objects with electric charge). Special relativity introduced a new framework for all of physics by proposing new concepts of space and time. Some then-accepted physical theories were inconsistent with that framework; a key example was Newton's theory of gravity, which describes the mutual attraction experienced by bodies due to their mass.
Several physicists, including Einstein, searched for a theory that would reconcile Newton's law of gravity and special relativity. Only Einstein's theory proved to be consistent with experiments and observations. To understand the theory's basic ideas, it is instructive to follow Einstein's thinking between 1907 and 1915, from his simple thought experiment involving an observer in free fall to his fully geometric theory of gravity.
Equivalence principle
A person in a free-falling elevator experiences weightlessness; objects either float motionless or drift at constant speed. Since everything in the elevator is falling together, no gravitational effect can be observed. In this way, the experiences of an observer in free fall are indistinguishable from those of an observer in deep space, far from any significant source of gravity. Such observers are the privileged ("inertial") observers Einstein described in his theory of special relativity: observers for whom light travels along straight lines at constant speed.
Einstein hypothesized that the similar experiences of weightless observers and inertial observers in special relativity represented a fundamental property of gravity, and he made this the cornerstone of his theory of general relativity, formalized in his equivalence principle. Roughly speaking, the principle states that a person in a free-falling elevator cannot tell that they are in free fall. Every experiment in such a free-falling environment has the same results as it would for an observer at rest or moving uniformly in deep space, far from all sources of gravity.
Gravity and acceleration
Most effects of gravity vanish in free fall, but effects that seem the same as those of gravity can be produced by an accelerated frame of reference. An observer in a closed room cannot tell which of the following two scenarios is true:
Objects are falling to the floor because the room is resting on the surface of the Earth and the objects are being pulled down by gravity.
Objects are falling to the floor because the room is aboard a rocket in space, which is accelerating at 9.81 m/s2, the standard gravity on Earth, and is far from any source of gravity. The objects are being pulled towards the floor by the same "inertial force" that presses the driver of an accelerating car into the back of their seat.
Conversely, any effect observed in an accelerated reference frame should also be observed in a gravitational field of corresponding strength. This principle allowed Einstein to predict several novel effects of gravity in 1907 .
An observer in an accelerated reference frame must introduce what physicists call fictitious forces to account for the acceleration experienced by the observer and objects around them. In the example of the driver being pressed into their seat, the force felt by the driver is one example; another is the force one can feel while pulling the arms up and out if attempting to spin around like a top. Einstein's master insight was that the constant, familiar pull of the Earth's gravitational field is fundamentally the same as these fictitious forces. The apparent magnitude of the fictitious forces always appears to be proportional to the mass of any object on which they actfor instance, the driver's seat exerts just enough force to accelerate the driver at the same rate as the car. By analogy, Einstein proposed that an object in a gravitational field should feel a gravitational force proportional to its mass, as embodied in Newton's law of gravitation.
Physical consequences
In 1907, Einstein was still eight years away from completing the general theory of relativity. Nonetheless, he was able to make a number of novel, testable predictions that were based on his starting point for developing his new theory: the equivalence principle.
The first new effect is the gravitational frequency shift of light. Consider two observers aboard an accelerating rocket-ship. Aboard such a ship, there is a natural concept of "up" and "down": the direction in which the ship accelerates is "up", and free-floating objects accelerate in the opposite direction, falling "downward". Assume that one of the observers is "higher up" than the other. When the lower observer sends a light signal to the higher observer, the acceleration of the ship causes the light to be red-shifted, as may be calculated from special relativity; the second observer will measure a lower frequency for the light than the first sent out. Conversely, light sent from the higher observer to the lower is blue-shifted, that is, shifted towards higher frequencies. Einstein argued that such frequency shifts must also be observed in a gravitational field. This is illustrated in the figure at left, which shows a light wave that is gradually red-shifted as it works its way upwards against the gravitational acceleration. This effect has been confirmed experimentally, as described below.
This gravitational frequency shift corresponds to a gravitational time dilation: Since the "higher" observer measures the same light wave to have a lower frequency than the "lower" observer, time must be passing faster for the higher observer. Thus, time runs more slowly for observers the lower they are in a gravitational field.
It is important to stress that, for each observer, there are no observable changes of the flow of time for events or processes that are at rest in his or her reference frame. Five-minute-eggs as timed by each observer's clock have the same consistency; as one year passes on each clock, each observer ages by that amount; each clock, in short, is in perfect agreement with all processes happening in its immediate vicinity. It is only when the clocks are compared between separate observers that one can notice that time runs more slowly for the lower observer than for the higher. This effect is minute, but it too has been confirmed experimentally in multiple experiments, as described below.
In a similar way, Einstein predicted the gravitational deflection of light: in a gravitational field, light is deflected downward, to the center of the gravitational field. Quantitatively, his results were off by a factor of two; the correct derivation requires a more complete formulation of the theory of general relativity, not just the equivalence principle.
Tidal effects
The equivalence between gravitational and inertial effects does not constitute a complete theory of gravity. When it comes to explaining gravity near our own location on the Earth's surface, noting that our reference frame is not in free fall, so that fictitious forces are to be expected, provides a suitable explanation. But a freely falling reference frame on one side of the Earth cannot explain why the people on the opposite side of the Earth experience a gravitational pull in the opposite direction.
A more basic manifestation of the same effect involves two bodies that are falling side by side towards the Earth, with a similar position and velocity. In a reference frame that is in free fall alongside these bodies, they appear to hover weightlessly – but not exactly so. These bodies are not falling in precisely the same direction, but towards a single point in space: namely, the Earth's center of gravity. Consequently, there is a component of each body's motion towards the other (see the figure). In a small environment such as a freely falling lift, this relative acceleration is minuscule, while for skydivers on opposite sides of the Earth, the effect is large. Such differences in force are also responsible for the tides in the Earth's oceans, so the term "tidal effect" is used for this phenomenon.
The equivalence between inertia and gravity cannot explain tidal effects – it cannot explain variations in the gravitational field. For that, a theory is needed which describes the way that matter (such as the large mass of the Earth) affects the inertial environment around it.
From acceleration to geometry
While Einstein was exploring the equivalence of gravity and acceleration as well as the role of tidal forces, he discovered several analogies with the geometry of surfaces. An example is the transition from an inertial reference frame (in which free particles coast along straight paths at constant speeds) to a rotating reference frame (in which fictitious forces have to be introduced in order to explain particle motion): this is analogous to the transition from a Cartesian coordinate system (in which the coordinate lines are straight lines) to a curved coordinate system (where coordinate lines need not be straight).
A deeper analogy relates tidal forces with a property of surfaces called curvature. For gravitational fields, the absence or presence of tidal forces determines whether or not the influence of gravity can be eliminated by choosing a freely falling reference frame. Similarly, the absence or presence of curvature determines whether or not a surface is equivalent to a plane. In the summer of 1912, inspired by these analogies, Einstein searched for a geometric formulation of gravity.
The elementary objects of geometry – points, lines, triangles – are traditionally defined in three-dimensional space or on two-dimensional surfaces. In 1907, Hermann Minkowski, Einstein's former mathematics professor at the Swiss Federal Polytechnic, introduced Minkowski space, a geometric formulation of Einstein's special theory of relativity where the geometry included not only space but also time. The basic entity of this new geometry is four-dimensional spacetime. The orbits of moving bodies are curves in spacetime; the orbits of bodies moving at constant speed without changing direction correspond to straight lines.
The geometry of general curved surfaces was developed in the early 19th century by Carl Friedrich Gauss. This geometry had in turn been generalized to higher-dimensional spaces in Riemannian geometry introduced by Bernhard Riemann in the 1850s. With the help of Riemannian geometry, Einstein formulated a geometric description of gravity in which Minkowski's spacetime is replaced by distorted, curved spacetime, just as curved surfaces are a generalization of ordinary plane surfaces. Embedding diagrams are used to illustrate curved spacetime in educational contexts.
After he had realized the validity of this geometric analogy, it took Einstein a further three years to find the missing cornerstone of his theory: the equations describing how matter influences spacetime's curvature. Having formulated what are now known as Einstein's equations (or, more precisely, his field equations of gravity), he presented his new theory of gravity at several sessions of the Prussian Academy of Sciences in late 1915, culminating in his final presentation on November 25, 1915.
Geometry and gravitation
Paraphrasing John Wheeler, Einstein's geometric theory of gravity can be summarized as: spacetime tells matter how to move; matter tells spacetime how to curve. What this means is addressed in the following three sections, which explore the motion of so-called test particles, examine which properties of matter serve as a source for gravity, and, finally, introduce Einstein's equations, which relate these matter properties to the curvature of spacetime.
Probing the gravitational field
In order to map a body's gravitational influence, it is useful to think about what physicists call probe or test particles: particles that are influenced by gravity, but are so small and light that we can neglect their own gravitational effect. In the absence of gravity and other external forces, a test particle moves along a straight line at a constant speed. In the language of spacetime, this is equivalent to saying that such test particles move along straight world lines in spacetime. In the presence of gravity, spacetime is non-Euclidean, or curved, and in curved spacetime straight world lines may not exist. Instead, test particles move along lines called geodesics, which are "as straight as possible", that is, they follow the shortest path between starting and ending points, taking the curvature into consideration.
A simple analogy is the following: In geodesy, the science of measuring Earth's size and shape, a geodesic is the shortest route between two points on the Earth's surface. Approximately, such a route is a segment of a great circle, such as a line of longitude or the equator. These paths are certainly not straight, simply because they must follow the curvature of the Earth's surface. But they are as straight as is possible subject to this constraint.
The properties of geodesics differ from those of straight lines. For example, on a plane, parallel lines never meet, but this is not so for geodesics on the surface of the Earth: for example, lines of longitude are parallel at the equator, but intersect at the poles. Analogously, the world lines of test particles in free fall are spacetime geodesics, the straightest possible lines in spacetime. But still there are crucial differences between them and the truly straight lines that can be traced out in the gravity-free spacetime of special relativity. In special relativity, parallel geodesics remain parallel. In a gravitational field with tidal effects, this will not, in general, be the case. If, for example, two bodies are initially at rest relative to each other, but are then dropped in the Earth's gravitational field, they will move towards each other as they fall towards the Earth's center.
Compared with planets and other astronomical bodies, the objects of everyday life (people, cars, houses, even mountains) have little mass. Where such objects are concerned, the laws governing the behavior of test particles are sufficient to describe what happens. Notably, in order to deflect a test particle from its geodesic path, an external force must be applied. A chair someone is sitting on applies an external upwards force preventing the person from falling freely towards the center of the Earth and thus following a geodesic, which they would otherwise be doing without the chair there, or any other matter in between them and the center point of the Earth. In this way, general relativity explains the daily experience of gravity on the surface of the Earth not as the downwards pull of a gravitational force, but as the upwards push of external forces. These forces deflect all bodies resting on the Earth's surface from the geodesics they would otherwise follow. For objects massive enough that their own gravitational influence cannot be neglected, the laws of motion are somewhat more complicated than for test particles, although it remains true that spacetime tells matter how to move.
Sources of gravity
In Newton's description of gravity, the gravitational force is caused by matter. More precisely, it is caused by a specific property of material objects: their mass. In Einstein's theory and related theories of gravitation, curvature at every point in spacetime is also caused by whatever matter is present. Here, too, mass is a key property in determining the gravitational influence of matter. But in a relativistic theory of gravity, mass cannot be the only source of gravity. Relativity links mass with energy, and energy with momentum.
The equivalence between mass and energy, as expressed by the formula E = mc, is the most famous consequence of special relativity. In relativity, mass and energy are two different ways of describing one physical quantity. If a physical system has energy, it also has the corresponding mass, and vice versa. In particular, all properties of a body that are associated with energy, such as its temperature or the binding energy of systems such as nuclei or molecules, contribute to that body's mass, and hence act as sources of gravity.
In special relativity, energy is closely connected to momentum. In special relativity, just as space and time are different aspects of a more comprehensive entity called spacetime, energy and momentum are merely different aspects of a unified, four-dimensional quantity that physicists call four-momentum. In consequence, if energy is a source of gravity, momentum must be a source as well. The same is true for quantities that are directly related to energy and momentum, namely internal pressure and tension. Taken together, in general relativity it is mass, energy, momentum, pressure and tension that serve as sources of gravity: they are how matter tells spacetime how to curve. In the theory's mathematical formulation, all these quantities are but aspects of a more general physical quantity called the energy–momentum tensor.
Einstein's equations
Einstein's equations are the centerpiece of general relativity. They provide a precise formulation of the relationship between spacetime geometry and the properties of matter, using the language of mathematics. More concretely, they are formulated using the concepts of Riemannian geometry, in which the geometric properties of a space (or a spacetime) are described by a quantity called a metric. The metric encodes the information needed to compute the fundamental geometric notions of distance and angle in a curved space (or spacetime).
A spherical surface like that of the Earth provides a simple example. The location of any point on the surface can be described by two coordinates: the geographic latitude and longitude. Unlike the Cartesian coordinates of the plane, coordinate differences are not the same as distances on the surface, as shown in the diagram on the right: for someone at the equator, moving 30 degrees of longitude westward (magenta line) corresponds to a distance of roughly , while for someone at a latitude of 55 degrees, moving 30 degrees of longitude westward (blue line) covers a distance of merely . Coordinates therefore do not provide enough information to describe the geometry of a spherical surface, or indeed the geometry of any more complicated space or spacetime. That information is precisely what is encoded in the metric, which is a function defined at each point of the surface (or space, or spacetime) and relates coordinate differences to differences in distance. All other quantities that are of interest in geometry, such as the length of any given curve, or the angle at which two curves meet, can be computed from this metric function.
The metric function and its rate of change from point to point can be used to define a geometrical quantity called the Riemann curvature tensor, which describes exactly how the Riemannian manifold, the spacetime in the theory of relativity, is curved at each point. As has already been mentioned, the matter content of the spacetime defines another quantity, the energy–momentum tensor T, and the principle that "spacetime tells matter how to move, and matter tells spacetime how to curve" means that these quantities must be related to each other. Einstein formulated this relation by using the Riemann curvature tensor and the metric to define another geometrical quantity G, now called the Einstein tensor, which describes some aspects of the way spacetime is curved. Einstein's equation then states that
i.e., up to a constant multiple, the quantity G (which measures curvature) is equated with the quantity T (which measures matter content). Here, G is the gravitational constant of Newtonian gravity, and c is the speed of light from special relativity.
This equation is often referred to in the plural as Einstein's equations, since the quantities G and T are each determined by several functions of the coordinates of spacetime, and the equations equate each of these component functions. A solution of these equations describes a particular geometry of spacetime; for example, the Schwarzschild solution describes the geometry around a spherical, non-rotating mass such as a star or a black hole, whereas the Kerr solution describes a rotating black hole. Still other solutions can describe a gravitational wave or, in the case of the Friedmann–Lemaître–Robertson–Walker solution, an expanding universe. The simplest solution is the uncurved Minkowski spacetime, the spacetime described by special relativity.
Experiments
No scientific theory is self-evidently true; each is a model that must be checked by experiment. Newton's law of gravity was accepted because it accounted for the motion of planets and moons in the Solar System with considerable accuracy. As the precision of experimental measurements gradually improved, some discrepancies with Newton's predictions were observed, and these were accounted for in the general theory of relativity. Similarly, the predictions of general relativity must also be checked with experiment, and Einstein himself devised three tests now known as the classical tests of the theory:
Newtonian gravity predicts that the orbit which a single planet traces around a perfectly spherical star should be an ellipse. Einstein's theory predicts a more complicated curve: the planet behaves as if it were travelling around an ellipse, but at the same time, the ellipse as a whole is rotating slowly around the star. In the diagram on the right, the ellipse predicted by Newtonian gravity is shown in red, and part of the orbit predicted by Einstein in blue. For a planet orbiting the Sun, this deviation from Newton's orbits is known as the anomalous perihelion shift. The first measurement of this effect, for the planet Mercury, dates back to 1859. The most accurate results for Mercury and for other planets to date are based on measurements which were undertaken between 1966 and 1990, using radio telescopes. General relativity predicts the correct anomalous perihelion shift for all planets where this can be measured accurately (Mercury, Venus and the Earth).
According to general relativity, light does not travel along straight lines when it propagates in a gravitational field. Instead, it is deflected in the presence of massive bodies. In particular, starlight is deflected as it passes near the Sun, leading to apparent shifts of up to 1.75 arc seconds in the stars' positions in the sky (an arc second is equal to 1/3600 of a degree). In the framework of Newtonian gravity, a heuristic argument can be made that leads to light deflection by half that amount. The different predictions can be tested by observing stars that are close to the Sun during a solar eclipse. In this way, a British expedition to West Africa in 1919, directed by Arthur Eddington, confirmed that Einstein's prediction was correct, and the Newtonian predictions wrong, via observation of the May 1919 eclipse. Eddington's results were not very accurate; subsequent observations of the deflection of the light of distant quasars by the Sun, which utilize highly accurate techniques of radio astronomy, have confirmed Eddington's results with significantly better precision (the first such measurements date from 1967, the most recent comprehensive analysis from 2004).
Gravitational redshift was first measured in a laboratory setting in 1959 by Pound and Rebka. It is also seen in astrophysical measurements, notably for light escaping the white dwarf Sirius B. The related gravitational time dilation effect has been measured by transporting atomic clocks to altitudes of between tens and tens of thousands of kilometers (first by Hafele and Keating in 1971; most accurately to date by Gravity Probe A launched in 1976).
Of these tests, only the perihelion advance of Mercury was known prior to Einstein's final publication of general relativity in 1916. The subsequent experimental confirmation of his other predictions, especially the first measurements of the deflection of light by the sun in 1919, catapulted Einstein to international stardom. These three experiments justified adopting general relativity over Newton's theory and, incidentally, over a number of alternatives to general relativity that had been proposed.
Further tests of general relativity include precision measurements of the Shapiro effect or gravitational time delay for light, measured in 2002 by the Cassini space probe. One set of tests focuses on effects predicted by general relativity for the behavior of gyroscopes travelling through space. One of these effects, geodetic precession, has been tested with the Lunar Laser Ranging Experiment (high-precision measurements of the orbit of the Moon). Another, which is related to rotating masses, is called frame-dragging. The geodetic and frame-dragging effects were both tested by the Gravity Probe B satellite experiment launched in 2004, with results confirming relativity to within 0.5% and 15%, respectively, as of December 2008.
By cosmic standards, gravity throughout the solar system is weak. Since the differences between the predictions of Einstein's and Newton's theories are most pronounced when gravity is strong, physicists have long been interested in testing various relativistic effects in a setting with comparatively strong gravitational fields. This has become possible thanks to precision observations of binary pulsars. In such a star system, two highly compact neutron stars orbit each other. At least one of them is a pulsar – an astronomical object that emits a tight beam of radiowaves. These beams strike the Earth at very regular intervals, similarly to the way that the rotating beam of a lighthouse means that an observer sees the lighthouse blink, and can be observed as a highly regular series of pulses. General relativity predicts specific deviations from the regularity of these radio pulses. For instance, at times when the radio waves pass close to the other neutron star, they should be deflected by the star's gravitational field. The observed pulse patterns are impressively close to those predicted by general relativity.
One particular set of observations is related to eminently useful practical applications, namely to satellite navigation systems such as the Global Positioning System (GPS) that are used for both precise positioning and timekeeping. Such systems rely on two sets of atomic clocks: clocks aboard satellites orbiting the Earth, and reference clocks stationed on the Earth's surface. General relativity predicts that these two sets of clocks should tick at slightly different rates, due to their different motions (an effect already predicted by special relativity) and their different positions within the Earth's gravitational field. In order to ensure the system's accuracy, either the satellite clocks are slowed down by a relativistic factor, or that same factor is made part of the evaluation algorithm. In turn, tests of the system's accuracy (especially the very thorough measurements that are part of the definition of universal coordinated time) are testament to the validity of the relativistic predictions.
A number of other tests have probed the validity of various versions of the equivalence principle; strictly speaking, all measurements of gravitational time dilation are tests of the weak version of that principle, not of general relativity itself. So far, general relativity has passed all observational tests.
Astrophysical applications
Models based on general relativity play an important role in astrophysics; the success of these models is further testament to the theory's validity.
Gravitational lensing
Since light is deflected in a gravitational field, it is possible for the light of a distant object to reach an observer along two or more paths. For instance, light of a very distant object such as a quasar can pass along one side of a massive galaxy and be deflected slightly so as to reach an observer on Earth, while light passing along the opposite side of that same galaxy is deflected as well, reaching the same observer from a slightly different direction. As a result, that particular observer will see one astronomical object in two different places in the night sky. This kind of focussing is well known when it comes to optical lenses, and hence the corresponding gravitational effect is called gravitational lensing.
Observational astronomy uses lensing effects as an important tool to infer properties of the lensing object. Even in cases where that object is not directly visible, the shape of a lensed image provides information about the mass distribution responsible for the light deflection. In particular, gravitational lensing provides one way to measure the distribution of dark matter, which does not give off light and can be observed only by its gravitational effects. One particularly interesting application are large-scale observations, where the lensing masses are spread out over a significant fraction of the observable universe, and can be used to obtain information about the large-scale properties and evolution of our cosmos.
Gravitational waves
Gravitational waves, a direct consequence of Einstein's theory, are distortions of geometry that propagate at the speed of light, and can be thought of as ripples in spacetime. They should not be confused with the gravity waves of fluid dynamics, which are a different concept.
In February 2016, the Advanced LIGO team announced that they had directly observed gravitational waves from a black hole merger.
Indirectly, the effect of gravitational waves had been detected in observations of specific binary stars. Such pairs of stars orbit each other and, as they do so, gradually lose energy by emitting gravitational waves. For ordinary stars like the Sun, this energy loss would be too small to be detectable, but this energy loss was observed in 1974 in a binary pulsar called PSR1913+16. In such a system, one of the orbiting stars is a pulsar. This has two consequences: a pulsar is an extremely dense object known as a neutron star, for which gravitational wave emission is much stronger than for ordinary stars. Also, a pulsar emits a narrow beam of electromagnetic radiation from its magnetic poles. As the pulsar rotates, its beam sweeps over the Earth, where it is seen as a regular series of radio pulses, just as a ship at sea observes regular flashes of light from the rotating light in a lighthouse. This regular pattern of radio pulses functions as a highly accurate "clock". It can be used to time the double star's orbital period, and it reacts sensitively to distortions of spacetime in its immediate neighborhood.
The discoverers of PSR1913+16, Russell Hulse and Joseph Taylor, were awarded the Nobel Prize in Physics in 1993. Since then, several other binary pulsars have been found. The most useful are those in which both stars are pulsars, since they provide accurate tests of general relativity.
Currently, a number of land-based gravitational wave detectors are in operation, and a mission to launch a space-based detector, LISA, is currently under development, with a precursor mission (LISA Pathfinder) which was launched in 2015. Gravitational wave observations can be used to obtain information about compact objects such as neutron stars and black holes, and also to probe the state of the early universe fractions of a second after the Big Bang.
Black holes
When mass is concentrated into a sufficiently compact region of space, general relativity predicts the formation of a black hole – a region of space with a gravitational effect so strong that not even light can escape. Certain types of black holes are thought to be the final state in the evolution of massive stars. On the other hand, supermassive black holes with the mass of millions or billions of Suns are assumed to reside in the cores of most galaxies, and they play a key role in current models of how galaxies have formed over the past billions of years.
Matter falling onto a compact object is one of the most efficient mechanisms for releasing energy in the form of radiation, and matter falling onto black holes is thought to be responsible for some of the brightest astronomical phenomena imaginable. Notable examples of great interest to astronomers are quasars and other types of active galactic nuclei. Under the right conditions, falling matter accumulating around a black hole can lead to the formation of jets, in which focused beams of matter are flung away into space at speeds near that of light.
There are several properties that make black holes the most promising sources of gravitational waves. One reason is that black holes are the most compact objects that can orbit each other as part of a binary system; as a result, the gravitational waves emitted by such a system are especially strong. Another reason follows from what are called black-hole uniqueness theorems: over time, black holes retain only a minimal set of distinguishing features (these theorems have become known as "no-hair" theorems), regardless of the starting geometric shape. For instance, in the long term, the collapse of a hypothetical matter cube will not result in a cube-shaped black hole. Instead, the resulting black hole will be indistinguishable from a black hole formed by the collapse of a spherical mass. In its transition to a spherical shape, the black hole formed by the collapse of a more complicated shape will emit gravitational waves.
Cosmology
One of the most important aspects of general relativity is that it can be applied to the universe as a whole. A key point is that, on large scales, our universe appears to be constructed along very simple lines: all current observations suggest that, on average, the structure of the cosmos should be approximately the same, regardless of an observer's location or direction of observation: the universe is approximately homogeneous and isotropic. Such comparatively simple universes can be described by simple solutions of Einstein's equations. The current cosmological models of the universe are obtained by combining these simple solutions to general relativity with theories describing the properties of the universe's matter content, namely thermodynamics, nuclear- and particle physics. According to these models, our present universe emerged from an extremely dense high-temperature state – the Big Bang – roughly 14 billion years ago and has been expanding ever since.
Einstein's equations can be generalized by adding a term called the cosmological constant. When this term is present, empty space itself acts as a source of attractive (or, less commonly, repulsive) gravity. Einstein originally introduced this term in his pioneering 1917 paper on cosmology, with a very specific motivation: contemporary cosmological thought held the universe to be static, and the additional term was required for constructing static model universes within the framework of general relativity. When it became apparent that the universe is not static, but expanding, Einstein was quick to discard this additional term. Since the end of the 1990s, however, astronomical evidence indicating an accelerating expansion consistent with a cosmological constant – or, equivalently, with a particular and ubiquitous kind of dark energy – has steadily been accumulating.
Modern research
General relativity is very successful in providing a framework for accurate models which describe an impressive array of physical phenomena. On the other hand, there are many interesting open questions, and in particular, the theory as a whole is almost certainly incomplete.
In contrast to all other modern theories of fundamental interactions, general relativity is a classical theory: it does not include the effects of quantum physics. The quest for a quantum version of general relativity addresses one of the most fundamental open questions in physics. While there are promising candidates for such a theory of quantum gravity, notably string theory and loop quantum gravity, there is at present no consistent and complete theory. It has long been hoped that a theory of quantum gravity would also eliminate another problematic feature of general relativity: the presence of spacetime singularities. These singularities are boundaries ("sharp edges") of spacetime at which geometry becomes ill-defined, with the consequence that general relativity itself loses its predictive power. Furthermore, there are so-called singularity theorems which predict that such singularities must exist within the universe if the laws of general relativity were to hold without any quantum modifications. The best-known examples are the singularities associated with the model universes that describe black holes and the beginning of the universe.
Other attempts to modify general relativity have been made in the context of cosmology. In the modern cosmological models, most energy in the universe is in forms that have never been detected directly, namely dark energy and dark matter. There have been several controversial proposals to remove the need for these enigmatic forms of matter and energy, by modifying the laws governing gravity and the dynamics of cosmic expansion, for example modified Newtonian dynamics.
Beyond the challenges of quantum effects and cosmology, research on general relativity is rich with possibilities for further exploration: mathematical relativists explore the nature of singularities and the fundamental properties of Einstein's equations, and ever more comprehensive computer simulations of specific spacetimes (such as those describing merging black holes) are run.
More than one hundred years after the theory was first published, research is more active than ever.
| Physical sciences | Theory of relativity | Physics |
28945767 | https://en.wikipedia.org/wiki/Pre-stellar%20core | Pre-stellar core | Pre-stellar cores are the nurseries of new stars, and are an early phase in the formation of low-mass stars, before gravitational collapse produces a central protostar. The spatial distribution of pre-stellar cores shows the history of their formation, and their sensitivity to the physics controlling their creation.
Most of our Galaxy's star formation takes place in clusters and groups within large molecular clouds. These clouds are often turbulent, showing supersonic line widths and complex magnetic fields which play crucial roles in cloud physics. The properties of pre-stellar cores within molecular clouds aid understanding of the large-scale physical processes dictating star formation.
Composition
Pre-stellar cores are hundreds of thousands of solar masses of dust and gas collapsing due to the influence of gravity. The density is much greater than the average interstellar density having around one thousand atoms per cubic centimeter as opposed to the one atom per cubic centimeter in the interstellar medium.
| Physical sciences | Stellar astronomy | Astronomy |
33022390 | https://en.wikipedia.org/wiki/Sky%20blue | Sky blue | Sky blue refers to a collection of shades comparable to that of a clear daytime sky. Typically it is a shade of cyan or light teal, though some iterations are closer to light blue. The term (as "sky blew") is attested from 1681. A 1585 translation of Nicolas de Nicolay's 1576 includes "the tulbant [turban] of the merchant must be skie coloured".
Displayed at right is the web colour sky blue.
Variations
Celeste
Celeste (, , ) is the colloquial name for the pale turquoise blue colour. The same word, meaning "of the sky", is used in Spanish, Portuguese and Italian for the colour. Etymologically, it is derived by Latin term , that means in Italian. There are two "conventional" colours denominated celeste, according to the color models. One is the pure Celeste, (HEX#B2FFFF; RGB 178,255,255) which may be referred as the "true" celeste as it is traditionally or officially understood; in English, it may also be referred to as Italian sky blue (blu cielo italiano) and Bianchi Green, referring to Bianchi, the famous Italian company for bikes, the first in the history of vehicles, whose colour is characteristic. The Japanese equivalent is known as or , referring to the colour of the sky or its reflection on the sea. The other one is also another conventional celeste (HEX #99cbff and RGB 153,203,255) containing 100% of blue, associated to a more generic color of the sky and remembering a type of light zenithal blue and the next sky blue gradations.
Celeste, that is, the pure Celeste strictly speaking (HEX #B2FFFF; RGB 178,255,255) from here on (and which can be thought as the "true" or "conventional" celeste), is a gradation of the cyan and a cold color. It is the colour of the sky with optimal visibility, when it is clear, perfectly or near-perfectly cloudless and sunny with an optimal quantity of humidity, absence or optimal quantity of atmospheric dust, aerosol/particulates with a good or at least moderate AIQ (Air Quality Index), absence of mist, haze, resulting in a good diffusion of light blue without saturation, which causes the prevalence of the white or of the warm colours of sunrise and sunset; in these excellent conditions, it is possible to see Celeste and its variations perpendicularly to the sun, toward the horizon, where the sunlight is maximum as the sky is directly illuminated, and these shades merge with the golden light of solar rays and the white of the horizon, both in the morning and afternoon, or even across the entire region between the star and the horizon, when the star is high, relatively next to solar or true noon. In particular, in the warm seasons, with the inclination of a hemisphere with respect to the sun, there are simultaneously the optimization of sunlight, daylight hours, and so the pure celeste might be visible in the entire region between the horizon and sun both in the morning and afternoon; generally, the higher the sun is during the day and the year, the less visible celeste and variations will be. In particular, in the morning across the sun and the horizon in the early hours with the rising of the star, sometimes even until noon, until they are reduced to a few stripes on the horizon, where the cyan is more intense. In the afternoon, it is the opposite and the pure celeste and similar gradations could be widely visible between the sun and horizon when the star is high, but starting to go down, that is especially in the early afternoon hours. Instead, in the cold season, with a low sun and sunlight, the pure celeste may be visible only at the horizon, where the cyan is more intense for the maximum light, but is more difficult because of the major weather instability. In anyway, since sunlight is strongest at the horizon, that is where the pure celeste is more evident, producing the tonalities of the cyan, very close to the white.
Alternatively, other variants, like Celeste polvere, Pallido and Velato, are visible towards the horizon when the sun is near to the zenith, always with discrete or good conditions of visibility. In the afternoon, always with good conditions, these three type of celeste, together with softer and less bright shades of celeste, are visible at straight angle from north to south, until around sunset.
In reality, it can be difficult to observe the pure celeste, being the color of a clear day with optimal meteorological factories; other shades of blue are often visible in the sky, as Light Sky Blue and similar gradations, among which the other conventional celeste, similar to the light blue sky colours rather than the pure celeste. One scientific explanation needs to be made: the sun emits light across the entire electromagnetic spectrum and so celeste, which is very close to the white with a RGB of 178,255,255, is very luminous, and so visible in the direction of the sun because it is there the maximum quantity of solar light, especially towards the horizon, even if human eyes can only perceive the visible light. Here because celeste and variations are easier to be visible in the warm seasons because of the inclination of a hemisphere with respect to the sun, spring and especially summer, with the optimization of solar light, hours of daylight and meteorological factors.
Being the gradation of near-perfectly sunny and clear sky, the color of an ideal sky, it is difficult to see pure celeste, especially during the coldest or most unstable seasons; instead, generically the sky shows the color of the other conventional celeste with 100% of blue, recalling a light zenithal blue and the next other types of sky blue; this is not surprising due to the best diffusion of the blue because of the Raylegh scattering.
Bleu celeste ("sky blue") is a rarely occurring tincture in heraldry (not being one of the seven main colours or metals or the three "staynard colours"). This tincture is sometimes also called ciel or simply celeste. It is depicted in a lighter shade than the range of shades of the more traditional tincture azure, which is the standard blue used in heraldry.
Gradations
The Italian Wikipedia cites by S.Fantetti and C.Petracchi and describes multiple variants of celeste as shown below, plus details as defined in the infobox above.
Light sky blue
Displayed at right is the web colour light sky blue. It is close in shade to baby blue.
Medium sky blue
Displayed at right is the colour medium sky blue. This is the colour that is called sky blue in Crayola crayons. This colour was formulated by Crayola in 1958.
"Sky blue" appears in the 32, 48, 64, 96 and 120 packs of crayons.
Vivid sky blue
Displayed at right is the colour vivid sky blue.
Deep sky blue
Deep sky blue is an azure-cyan colour associated with deep shade of sky blue.
Deep sky blue is a web colour.
This is the colour on the colour wheel (RGB/HSV colour wheel) halfway between azure and cyan.
The colour name deep sky blue came into use with the formulization of the X11 colour names over 1985–1989.
The normalized colour coordinates for deep sky blue are identical to Capri, which first came into use as a colour name in English in 1920.
French sky blue
At right is displayed the colour French sky blue, which is the tone of sky blue that is called sky blue (bleu ciel) in the Pourpre.com colour list, a colour list widely popular in France.
Spanish sky blue
Spanish sky blue is the colour that is called celeste (the Spanish word for "sky blue") in the (Guide to colourations) by Rosa Gallego and Juan Carlos Sanz, a colour dictionary published in 2005 that is widely popular in the Hispanophone realm.
Dark sky blue
Displayed at right is the colour dark sky blue.
This is the colour called sky blue in Pantone.
The source of this colour is the "Pantone Textile Paper eXtended (TPX)" colour list, color #14-4318 TPX—Sky Blue.
In culture
Sports
Argentina: Following the colours of the flag of Argentina, in which sky blue (celeste in Spanish) is the predominant colour, many Argentine sport teams feature the colour, including Racing Club de Avellaneda, , Racing de Córdoba, Club Atlético Temperley, Atlético de Rafaela, Villa San Carlos, , Gimnasia y Tiro de Salta, and Gimnasia y Esgrima de Concepción del Uruguay. In addition, the Argentina national football team is known as the due to the white-and-sky blue striping on their jerseys. This colour scheme is featured in other prominent national squads in popular sports such as rugby, field hockey, polo or volleyball.
Australia: Sky blue is the main colour of the Australian rugby league team, New South Wales Blues, as it is the official colour of the state they represent.
Formula One: The Benetton and its successor Renault team won the four drivers' and the constructors' World Championships of the squad with sky blue race cars, driven by Michael Schumacher at Benetton in and and Fernando Alonso at Renault in and .
Italy: Celeste is the main colour of the football teams Lazio of Rome and Napoli of Naples.
Sweden: Football club Malmö FF, the club with the most Swedish championships, adopted sky blue shirts in 1920, which have been used for more than a century.
United Kingdom: Two professional football clubs in England traditionally wear sky blue shirts. Manchester City adopted sky blue as the main colour of their home jersey in 1894 and have used that ever since then. Coventry City also have had sky blue as the primary colour since the 1960s.
Uruguay: The Uruguay national football team has worn a sky blue jersey since 1910, after Uruguayan club team River Plate F.C. wore sky blue while defeating contemporary Argentine powerhouse Alumni Athletic Club. The national team is nicknamed La Celeste. As in Argentina, a number of Uruguayan club teams use sky blue in their uniforms, such as C.A. Cerro, Montevideo City Torque, Club Oriental de Football, and Rocha F.C.
| Physical sciences | Colors | Physics |
2052205 | https://en.wikipedia.org/wiki/Job%27s%20tears | Job's tears | Job's tears (Coix lacryma-jobi), also known as adlay or adlay millet, is a tall grain-bearing perennial tropical plant of the family Poaceae (grass family). It is native to Southeast Asia and introduced to Northern China and India in remote antiquity, and elsewhere cultivated in gardens as an annual. It has been naturalized in the southern United States and the New World tropics. In its native environment it is grown at higher elevation areas where rice and corn do not grow well. Job's tears are also commonly sold as Chinese pearl barley, though true barley belongs to a completely different genus.
There are two main varieties of the species, one wild and one cultivated. The wild variety, Coix lacryma-jobi var. lacryma-jobi, has hard-shelled pseudocarps—very hard, pearly white, oval structures used as beads for making prayer beads or rosaries, necklaces, and other objects. The cultivated variety Coix lacryma-jobi var. ma-yuen is harvested as a cereal crop, has a soft shell, and is used in traditional medicine in parts of Asia.
Nomenclature
Job's tears may also be referred to under different spellings (Job's-tears, Jobs-tears). The crop is also known by other common names in English, such as adlay or adlay millet. Other common names in English include coix seed, gromwell grass, and tear grass.
The seeds are known in Chinese as yìyǐ rén (), where rén means "kernel", and also described in Latin as semen coicis or semen coicis lachryma-jobi in pharmacopoeic literature.
Taxonomy
The species, native to Southeast Asia, was named by Carl Linnaeus in 1753 with the epithet as a Latin translation of the metaphorical tear of Job. , four varieties are accepted by the World Checklist of Selected Plant Families:
Coix lacryma-jobi var. lacryma-jobi
Widely distributed throughout the Indian subcontinent to peninsular Malaysia and Taiwan; naturalized elsewhere. The involucres are ovoid, bony and glossy. It has hard shells and is used as beads in crafts.
Coix lacryma-jobi var. ma-yuen
South China to peninsular Malaysia and the Philippines.
The varietal name is eponymous after General Ma Yuen or Ma Yuan () who according to legend learned of the plant's use when he was posted in Cochin China (or Tonkin, in what is now Vietnam), and brought the seeds back to China to be cultivated. The involucres are elliptical, striate and soft.
Coix lacryma-jobi var. puellarum
Assam to Yunnan (China) and Indochina. It is the smallest among the Indian species, with only 4mm in diameter of the seeds. It is used for ornament as well.
Coix lacryma-jobi var. stenocarpa
Eastern Himalayas to Indochina.
Job's tearsalong with Coix in was formerly placed in the Maydeae, now known to be polyphyletic. It has cylindrical, longer than broad involucres. It is widely used as beads for ornaments.
Morphology
Job's tear is a monoecious grass which is broad-leaved, loose-growing, branched and robust. It can reach a height between 1.20 m to 1.80 m. Like all members of the genus, their inflorescences develop from a leaf sheath at the end of the stem and consist partly of hard, globular or oval, hollow, bead-like structures.
Job's tear seeds differ in color, with the more soft-shelled seeds being light brown and the hard-shelled forms having a dark red pericarp.
The hardened "shells" covering the seeds are technically the fruit-case or involucre (hardened bract), with the bract also referred to as "capsule-spathe" or "sheathing bract" by some past botanical works.
These shells cover the bases of the flowers (inflorescences) which are male and female racemes/panicles; the male racemes project upright and consist of overlapping scale-like spikelets, with yellow stamens that pop out in-between, and there are one or two yarn-like female racemes drooping from the base.
Proteins
Job's tears - as with Coix in general - produces its own variety of α-zein prolamins. These prolamins have undergone unusually rapid evolutionary divergence from closely related grasses, by way of copy-number changes.
History
Job's tears is native to Southeast Asian countries, namely India, Myanmar, China, and Malaysia. Residue on pottery from a Neolithic (late Yangshao Culture) site in north-central China shows that Job's tears, together with non-native barley and other plants were used to brew beer as early as ca. 3000 BC.
Job's tears were already introduced to Japan (and probably cultivated alongside rice) in the Early Jōmon Period, corroborated by finds in Western Japan (Chūgoku region), e.g., from studies of phytoliths in the (ca. 4000 BC) in Okayama Prefecture. And further east in Japan, the plant has been found at the Toro site, Shizuoka Prefecture dating to the Yayoi Period.
Remains of Job's tears have been found in archaeological sites in northeastern India, dating to around 1000 BC. It was introduced to the subtropical area in India from the east Himalayan belt. A number of scholars support the view it has been in cultivation in India in the 2000–1000 BC period. The wild varieties have hard-coated seeds. Job's tear was one of the earliest domesticated crops. Domestication makes the seed coat become softer and easier to cook.
In China, the current cultivation of Job's tears mainly occurs in Fujian, Jiangsu, Hebei, and Liaoning provinces. The cultivation of Job's tears spreads out to temperate areas in North and Northeast China. The shelled grains exported from China were erroneously declared through customs as "pearl barley", and "Chinese pearl barley" remains an alternate common name so that the grains are sold under such label in Asian supermarkets, even though C. lacryma-jobi is not closely related to barley (Hordeum vulgare).
Uses
Crafts
The hard, white grains of Job's tears have historically been used as beads to make necklaces and other objects. The seeds are naturally bored with holes without the need to artificially puncture them.
Strands of Job's tears are used as Buddhist prayer beads in parts of India, Myanmar, Laos, Taiwan, and Korea according to Japanese researcher Yukino Ochiai who has specialized on the ethnobotanic usage of the plant. They are also made into rosaries in countries such as the Philippines and Bolivia.
East Asia
Japan
In Japan, the grains growing wild are called ), and children have made playthings out of them by stringing them into necklaces. However, juzu-dama was a corruption of zuzu-dama according to folklorist Kunio Yanagita. A type of Buddhist rosary called irataka no juzu, which were hand-made by the yamabushi ascetics practicing shugendō training, purportedly used a large-grain type known as . Although this was published as a separate variety, C. lacryma jobi var. maxima , it is now regarded as synonymous to C. lacryma jobi var. lacryma-jobi according to taxonomical databases (World Checklist of Selected Plant Families).
It was contended by Edo Period scholar Ono Ranzan that the soft-shelled edible type called shikoku-mugi was not introduced into Japan until the Kyōho era (1716–1736), as opposed to a hard-shelled edible type called chōsen-mugi (lit. ‘Korean wheat’) which needed to be beaten in order to crack and thresh them. This type has been published as a separate species, C. agrestis in the past, but this is now recognized also as a synonym of C. lacryma jobi var. lacryma-jobi. Thus Japanese consumption of the crop attested in pre-Kyōho literature presumably used this hard-shelled type in the recipe.
Yanagita contended that the use of the beads predated the introduction of Buddhism into Japan (552/538 CE). And the plant has not only been found at sites dating to approximately this period at the Kuroimine Site, but in Jomon period sites dating to several millennia BC.
Ocean Road hypothesis
Yanagita in his Ocean Road hypothesis argues that the pearly glistening seeds were regarded as simulating or substituting for cowrie shells, which were used as ornaments and currency throughout Southern China and Southeast Asia in antiquity, and he argued both items to be part of cultural transmission into Japan from these areas.
Later scholars have pursued the validity of the thesis. Yanagita had reproduced a distribution map of the usage of ornamental cowries throughout Asia (compiled by J. Wilfrid Jackson), and Japanese ethnologist alluded to a need for a distribution map of ornamental Job's tears, for making comparison therewith.
Mainland Southeast Asia
Thailand and Myanmar
The Akha people and the Karen people who live in the mountainous regions around the Thai-Myanmar border grow several varieties of the plant and use the beads to ornament various handicraft. The beads are used strictly only on women's apparel among the Akha, sewn onto headwear, jackets, handbags, etc.; also, a variety of shapes of beads are used. The beads are used only on the jackets of married women among the Karen, and the oblong seeds are exclusively selected, some example has been shown from the Karen in Chiang Rai Province of Thailand.
Strands of job's tears necklaces have also been collected from Chiang Rai Province, Thailand and it is known the Karen people string the beads into necklaces, such necklaces in use also in the former Karenni States (current Kayah State of Burma), with the crop being known by the name cheik (var. kyeik, kayeik, kyeit) in Burmese. Job's tears necklace has been collected also from Yunnan Province, China, which has a population of Akha-Hani people and other minorities, but the Wa people of Yunnan also used the plant seeds (tɛ kao; lit. ‘fruit-Coix’) sewn onto fabrics and bags, etc.
The Wa people and other minorities like the Taungyo ethnic group use the beads in apparel in Shan State, Myanmar.
Insular Southeast Asia
Borneo
Various indigenous Bornean tribes such as the Kelabit people of Sarawak state (and North Kalimantan, Indonesia), the Kadazandusun people and Murut people of Sabah state all use the plant beads as ornament. In the Kadazandusun language, the plant is called dalai. The Kayan of Borneo also use job's tears to decorate clothing and war dress.
Philippines
Job's tears () are otherwise known by many local names in the Philippines (e.g. in Visaya Islands). The beads strung together have sometimes been used as rosaries, or made into bead curtains (e.g. the Tboli people on Mindanao), or woven into baskets and other vessels.
Americas
The plant was known as calandula in Spanish, and the hards seeds were strung together as beads or into rosaries in parts of New Spain, e.g., Puerto Rico.
In both the Eastern Band of Cherokee Indians and the Cherokee Nation in Oklahoma, the beads of Job's tears are called "corn beads" or "Cherokee corn beads" and have been used for personal adornment.
Food
Throughout East Asia, Job's tears are available in dried form and cooked as a grain. Job's tears grains are widely eaten as a cereal. The cultivated varieties are soft-shelled, and can be easily cooked into gruels, etc. Among the Zomi in Southeast Asia, miim festival (Job's tears festival) was held annually to pay tribute to the departed souls.
Some of the soft-shelled types are easily threshed, producing sweet kernels. The threshed (and polished) "kernels" or ren () are used in traditional Chinese Medicine (see infra).
The threshed grains are generally spherical, with a groove on one end, and polished white in color. In Japan unpolished grains are also sold, and marketed as yūki hatomugi (‘organic job's tears’).
In Cambodia, where it is known as skuay (ស្គួយ), the seeds are not much used as a grain, but used as part of herbal medicine and as an ingredient in desserts. In Thailand, it is often consumed in teas and other drinks, such as soy milk.
It is also a minor cereal crop and fodder in Northeastern India.
The grains of Job's tear can be used the same way as rice. It can be eaten cooked or even raw, as it has a slightly sweet taste. Further, the grains can be used for the production of flour.
Job's tear grains can be processed in the same machine as rice. For the soft hulls, it is enough to press them over a sieve. The advantage of Job's tear over rice is that the grains do not need to be polished, as is the case with rice. Through this process, the rice loses its vitamins. This makes Job's tear a valuable food for undernourished populations in rural areas.
Beverages and soups
In Korean cuisine, a thick drink called yulmu cha (율무차, literally "Job's tears tea") is made from powdered Job's tears. A similar drink, called yi ren jiang (薏仁漿), also appears in Chinese cuisine, and is made by simmering whole polished Job's tears in water and sweetening the resulting thin, cloudy liquid with sugar. The grains are usually strained from the liquid but may also be consumed separately or together.
In Japan, the roasted kernels are brewed into , literally a "tea". This is drunk for medicinal value and not for enjoyment, as it does not suit the average consumer's taste, but a more palatable brew is obtained by roasting seeds that have been germinated, which reduces the distinctive strong odor.
In southern China, Job's tears are often used in tong sui (糖水), a sweet dessert soup. One variety is called ching bo leung in Cantonese (), and is also known as sâm bổ lượng in Vietnamese cuisine. There is also a braised chicken dish yimidunji ().
Alcoholic beverages
In both Korea and China, distilled liquors are also made from the grain. One Korean liquor is called okroju (옥로주; hanja: 玉露酒), which is made from rice and Job's tears. The grains are also brewed into beers in northeast India and other parts of southeast Asia.
Traditional medicine
Job's tears are used with other herbs in traditional Chinese medicine or folk medicine.
The plant is noted in an ancient medical text Huangdi Neijing (5th–2nd centuries BCE) attributed to the legendary Huangdi (Yellow Emperor), but fails to be noticed in the standard traditional materia medica reference Bencao Gangmu (本草綱目)(16c.).
Cultivation requirements
Soil and climate requirement
It is generally grown in sunny, fertile, well-drained fields with sandy loam soil. Adlay likes mild, cool and humid climate. It does not adapt to hot and muggy climate, has low cold tolerance, and is very intolerant of drought. Black-shelled adlay is suitable for planting in areas with altitudes of 800 to 1,000 m; dwarf adlay varieties are suitable for planting in low altitude areas.
Seedbed requirements and sowing
Soaking seeds with disinfectant has a positive influence on germination rate.
Planting can be done when the ground temperature is above 12 °C. And if it is not frost, sowing should be done as early as possible to lengthen the required days to emergence and days to anthesis. Adlay sowing is divided into strip sowing and hole sowing. The strip sowing refers to the uniform sowing of seeds in trenches with a spacing of about 50 cm and a depth of 4–5 cm. Hole sowing refers to sowing seeds in holes 3–5 cm deep, with 3-4 seeds per hole.
Cultivation management
Control the number of seedlings per hole when the seedlings have 3-4 true leaves, and leave 2-3 well-grown plants in each hole.
Tillage at least 3 times during the whole crop growth. The 1st tillage is to be done when the seedlings are 5–10 cm high and needs to be cleaned of weeds to promote tillering. The second tillage is done when the seedlings are 15–20 cm high. The 3rd plowing is done when the seedlings are 30 cm high, combined with fertilizer and soil cultivation to promote root growth and prevent collapse.
Production
Growth and development
It is an annual crop but it can be a perennial when allowed to develop ratoon. Adlay is propagated by seeds at the start of rain. The germination occurs as early as 7 days after sowing. It takes 5 to 5.5 months to flower and mature. The average height can reach over 90 cm at harvest. The application of N fertilizer can significantly improve the yield of adlay.
Drought is a major stress for adlay growth and development. The lack of moisture will cause impaired germination and poor establishment. During the growth and maturation stage, water deficits will reduce the leaf area index and lead to barrenness, which negatively affects photosynthesis and dry matter production.
Harvest and post-harvest operations
When nearly 80% of adlay grains turn brown, the panicle will be harvested by cutting the stems and leaving three nodes above the ground. The harvest period varies with the different varieties and local environment. Because of the uneven height and grain distribution, the use of machines for harvesting is limited and harvesting has been done by hand in many regions in Southeastern Asia. Then the harvested panicles are threshed by hand or using a treadle thresher. For manual threshing, it is normally used when the harvested grains are at lower moisture content and easily shatter. Threshed grains are sun dried or placed in drying facilities where they utilize forced warm air to gradually reduce the moisture content to 14% suited to storage before the adlay moves to the milling process. The adlay can be consumed as grains and flour after being milled through corn and rice mill. The milling recovery is about 60% depending on the cultivars.
The yield is harvested in early October and is easily influenced by the weather. If there is dry and hot wind in the initial phase, the pollen loses its vitality, therefore can’t be pollinated. This leads to hollow seeds, which results in yield reduction in light cultivars and zero yield in heavy cultivars.
Early maturing varieties are sown in early March, middle maturing varieties are sown from late March to early April, and late maturing varieties are sown from late April to early May. Sowing should be early rather than late. If sowing is too late, it will affect the yield and even the seeds can not mature after autumn.
Nutritional value
The seeds of Job's tears are protein-rich and nutrient-dense. High in dietary fibre, zinc and calcium. They contain micronutrients like thiamine, riboflavin, vitamin E, and niacin. They cover 8 types of amino acids for human consumption.
Starch and protein
Job's tears contain high amount of starch (58%). The seeds are used as ingredients to make soup, porridge, flour and pastries. It is common to grind seeds into powder form to make pastries. Two major methods are used to isolate starch: alkaline steeping method and steeping with sodium metabisulfite (), an antioxidant and antimicrobial agent. Job's tears also contain edible protein (14.8%), which can be extracted through an alkaline extraction method and a salt extraction method.
Fatty acids
Job's tears contain mostly unsaturated fatty acids. The four main fatty acids, (oleic acid, linoleic acid, palmitic acid, and stearic acid) are extracted via three methods: solvent processes, supercritical fluid extraction and ultrasonic-assisted extraction.
Pests
Job's tear is less subject to attacks of locusts than rice and corn.
Insect pests include:
stem borers Sesamia inferens and Ostrinia furnacalis
rice skipper Pelopidas mathias (leaf feeder)
thrip Chaetanaphothrips orchidii
aphid Rhopalosiphum maidis
woolly aphid Ceratovacuna lanigera
It is susceptible to leaf blight.
Gallery
Explanatory notes
| Biology and health sciences | Grains | Plants |
2053015 | https://en.wikipedia.org/wiki/Manganate | Manganate | In inorganic nomenclature, a manganate is any negatively charged molecular entity with manganese as the central atom. However, the name is usually used to refer to the tetraoxidomanganate(2−) anion, MnO, also known as manganate(VI) because it contains manganese in the +6 oxidation state. Manganates are the only known manganese(VI) compounds.
Other manganates include hypomanganate or manganate(V), , permanganate or manganate(VII), , and the dimanganate or dimanganate(III) .
A manganate(IV) anion has been prepared by radiolysis of dilute solutions of permanganate. It is mononuclear in dilute solution, and shows a strong absorption in the ultraviolet and a weaker absorption at 650 nm.
Structure
The manganate(VI) ion is tetrahedral, similar to sulfate or chromate: indeed, manganates are often isostructural with sulfates and chromates, a fact first noted by Eilhard Mitscherlich in 1831. The manganese–oxygen distance is 165.9 pm, about 3 pm longer than in permanganate. As a d1 ion, it is paramagnetic, but any Jahn–Teller distortion is too small to be detected by X-ray crystallography. Manganates are dark green in colour, with a visible absorption maximum of λmax = 606 nm (ε = ). The Raman spectrum has also been reported.
Preparation
Sodium and potassium manganates are usually prepared in the laboratory by stirring the equivalent permanganate in a concentrated solution (5–10 M) of the hydroxide for 24 hours or with heating.
+ → + + O2
Potassium manganate is prepared industrially, as an intermediate to potassium permanganate, by dissolving manganese dioxide in molten potassium hydroxide with potassium nitrate or air as the oxidizing agent.
+ + O2 → +
Disproportionation
Manganates are unstable towards disproportionation in all but the most alkaline of aqueous solutions. The ultimate products are permanganate and manganese dioxide, but the kinetics are complex and the mechanism may involve protonated and/or manganese(V) species.
Uses
Manganates, particularly the insoluble barium manganate, BaMnO4, have been used as oxidizing agents in organic synthesis: they will oxidize primary alcohols to aldehydes and then to carboxylic acids, and secondary alcohols to ketones. Barium manganate has also been used to oxidize hydrazones to diazo compounds.
Related compounds
Manganate is formally the conjugate base of hypothetical manganic acid , which cannot be formed because of its rapid disproportionation. However, its second acid dissociation constant has been estimated by pulse radiolysis techniques:
HMnO MnO + H+ pKa = 7.4 ± 0.1
Manganites
The name "manganite" is used for compounds formerly believed to contain the anion , with manganese in the +3 oxidation state. However, most of these "manganites" do not contain discrete oxyanions, but are mixed oxides with perovskite (LaMnIIIO3, CaMnIVO3), spinel (LiMnO4) or sodium chloride (LiMnIIIO2, NaMnIIIO2) structures.
One exception is potassium dimanganate(III), K6Mn2O6, which contains discrete Mn2O anions.
| Physical sciences | Metallic oxyanions | Chemistry |
2054313 | https://en.wikipedia.org/wiki/Leaellynasaura | Leaellynasaura | Leaellynasaura (meaning "Leaellyn's lizard") is a genus of small herbivorous ornithischian dinosaurs from the late Aptian to early Albian stage of the Early Cretaceous, around 118-110 million years ago. It was first discovered in Dinosaur Cove, Australia. The only known species is Leaellynasaura amicagraphica. It was described in 1989, and named after Leaellyn Rich, the daughter of the Australian palaeontologist couple Tom Rich and Patricia Vickers-Rich who discovered it. The specific name, amicagraphica, translates to "friend writing" and honours both the Friends of the Museum of Victoria and the National Geographic Society for their support of Australian paleontology.
Description
Leaellynasaura is a relatively small dinosaur, about 90 centimeters (3 feet) in length. It is known from several specimens including two nearly complete skeletons and two fragmentary skulls. Herne (2009) argued that, unlike more advanced ornithischians, Leaellynasaura lacked ossified tendons in its tail. He also argued that the tail is noteworthy as among the longest relative to its body size of any ornithischian: the tail was three times as long as the rest of the body combined; it also has more tail vertebrae than any other ornithischians except for some hadrosaurs. However, in a subsequent revision of fossil material attributed to Leaellynasaura Herne (2013) could not confidently assign the postcranial skeletons with long tails (or indeed any fossils other than the holotype incomplete cranium MV P185991, right maxilla MV P186352 and left maxillary tooth MV P186412, all from late Aptian-early Albian Eumeralla Formation) to Leaellynasaura amicagraphica.
Classification
Leaellynasaura has been variously described as a hypsilophodontid, a primitive iguanodontian or a primitive ornithischian (Genasauria). Recent studies have not found a consensus; some analyses describe it as a non-iguanodontian ornithopod, whereas others describe it as a basal neornithischian. A 2019 study recovered it as a member of Elasmaria.
Position according to Herne et al., 2019:
Biology and ecology
Leaellynasaura was an Australian polar dinosaur. At this period in time, Victoria would have been within the Antarctic Circle. Although this latitude is very cold today, it was significantly warmer during the mid-Cretaceous. Because of the Earth's tilt, Leaellynasaura and its contemporaries would still have been living under conditions with extended periods of both daylight and night. Depending on latitude, it is possible that the sun might not have risen for several weeks or months in the winter, which means that Leaellynasaura would have had to live in the dark for perhaps months at a time. A skull fragment interpreted as being from Leaellynasaura has been reported as showing enlarged eyes and the suggestion of proportionally large optic lobes, implying an adaptation to low-light conditions. However, the relatively large orbits of this specimen were more recently interpreted as representing characteristically large eyes of a juvenile individual, rather than any low-light adaptation.
| Biology and health sciences | Ornitischians | Animals |
2054480 | https://en.wikipedia.org/wiki/Calcium%20sulfide | Calcium sulfide | Calcium sulfide is the chemical compound with the formula CaS. This white material crystallizes in cubes like rock salt. CaS has been studied as a component in a process that would recycle gypsum, a product of flue-gas desulfurization. Like many salts containing sulfide ions, CaS typically has an odour of H2S, which results from small amount of this gas formed by hydrolysis of the salt.
In terms of its atomic structure, CaS crystallizes in the same motif as sodium chloride indicating that the bonding in this material is highly ionic. The high melting point is also consistent with its description as an ionic solid. In the crystal, each S2− ion is surrounded by an octahedron of six Ca2+ ions, and complementarily, each Ca2+ ion surrounded by six S2− ions.
Production
CaS is produced by carbothermic reduction of calcium sulfate, which entails the conversion of carbon, usually as charcoal, to carbon dioxide:
CaSO4 + 2 C → CaS + 2 CO2
and can react further:
3 CaSO4 + CaS → 4 CaO + 4 SO2
In the second reaction the sulfate (+6 oxidation state) oxidizes the sulfide (-2 oxidation state) to sulfur dioxide (+4 oxidation state), while it is being reduced to sulfur dioxide itself (+4 oxidation state).
CaS is also a byproduct in the Leblanc process, a once major industrial process for producing sodium carbonate. In that process sodium sulfide reacts with calcium carbonate:
Na2S + CaCO3 → CaS + Na2CO3
Millions of tons of this calcium sulfide byproduct was discarded, causing extensive pollution and controversy.
Milk of lime, Ca(OH)2, reacts with elemental sulfur to give a "lime-sulfur", which has been used as an insecticide. The active ingredient is probably a calcium polysulfide, not CaS.
Reactivity and uses
Calcium sulfide decomposes upon contact with water, including moist air, giving a mixture of Ca(SH)2, Ca(OH)2, and Ca(SH)(OH).
CaS + H2O → Ca(SH)(OH)
Ca(SH)(OH) + H2O → Ca(OH)2 + H2S
It reacts with acids such as hydrochloric acid to release toxic hydrogen sulfide gas.
CaS + 2 HCl → CaCl2 + H2S
Calcium sulfide is phosphorescent, and will glow a blood red for up to an hour after a light source is removed.
As a noxious byproduct of the Leblanc process, it can be converted to calcium carbonate and hydrogen sulfide, the latter of which can be used as a sulfur source for the lead chamber process to produce the sulfuric acid necessary for the Leblanc process:
Natural occurrence
Oldhamite is the name for mineralogical form of CaS. It is a rare component of some meteorites and has scientific importance in solar nebula research. Burning of coal dumps can also produce the compound.
| Physical sciences | Sulfide salts | Chemistry |
2056572 | https://en.wikipedia.org/wiki/Marine%20life | Marine life | Marine life, sea life or ocean life is the collective ecological communities that encompass all aquatic animals, plants, algae, fungi, protists, single-celled microorganisms and associated viruses living in the saline water of marine habitats, either the sea water of marginal seas and oceans, or the brackish water of coastal wetlands, lagoons, estuaries and inland seas. , more than 242,000 marine species have been documented, and perhaps two million marine species are yet to be documented. An average of 2,332 new species per year are being described. Marine life is studied scientifically in both marine biology and in biological oceanography.
By volume, oceans provide about 90% of the living space on Earth, and served as the cradle of life and vital biotic sanctuaries throughout Earth's geological history. The earliest known life forms evolved as anaerobic prokaryotes (archaea and bacteria) in the Archean oceans around the deep sea hydrothermal vents, before photoautotrophs appeared and allowed the microbial mats to expand into shallow water marine environments. The Great Oxygenation Event of the early Proterozoic significantly altered the marine chemistry, which likely caused a widespread anaerobe extinction event but also led to the evolution of eukaryotes through symbiogenesis between surviving anaerobes and aerobes. Complex life eventually arose out of marine eukaryotes during the Neoproterozoic, and which culminated in a large evolutionary radiation event of mostly sessile macrofaunae known as the Avalon Explosion. This was followed in the early Phanerozoic by a more prominent radiation event known as the Cambrian Explosion, where actively moving eumetazoan became prevalent. These marine life also expanded into fresh waters, where fungi and green algae that were washed ashore onto riparian areas started to take hold later during the Ordivician before rapidly expanding inland during the Silurian and Devonian, paving the way for terrestrial ecosystems to develop.
Today, marine species range in size from the microscopic phytoplankton, which can be as small as 0.02–micrometres; to huge cetaceans like the blue whale, which can reach in length. Marine microorganisms have been variously estimated as constituting about 70% or about 90% of the total marine biomass. Marine primary producers, mainly cyanobacteria and chloroplastic algae, produce oxygen and sequester carbon via photosynthesis, which generate enormous biomass and significantly influence the atmospheric chemistry. Migratory species, such as oceanodromous and anadromous fish, also create biomass and biological energy transfer between different regions of Earth, with many serving as keystone species of various ecosystems. At a fundamental level, marine life affects the nature of the planet, and in part, shape and protect shorelines, and some marine organisms (e.g. corals) even help create new land via accumulated reef-building.
Marine life can be roughly grouped into autotrophs and heterotrophs according to their roles within the food web: the former include photosynthetic and the much rarer chemosynthetic organisms (chemoautotrophs) that can convert inorganic molecules into organic compounds using energy from sunlight or exothermic oxidation, such as cyanobacteria, iron-oxidizing bacteria, algae (seaweeds and various microalgae) and seagrass; the latter include all the rest that must feed on other organisms to acquire nutrients and energy, which include animals, fungi, protists and non-photosynthetic microorganisms. Marine animals are further informally divided into marine vertebrates and marine invertebrates, both of which are polyphyletic groupings with the former including all saltwater fish, marine mammals, marine reptiles and seabirds, and the latter include all that are not considered vertebrates. Generally, marine vertebrates are much more nektonic and metabolically demanding of oxygen and nutrients, often suffering distress or even mass dyings (a.k.a. "fish kills") during anoxic events, while marine invertebrates are a lot more hypoxia-tolerant and exhibit a wide range of morphological and physiological modifications to survive in poorly oxygenated waters.
Water
There is no life without water. It has been described as the universal solvent for its ability to dissolve many substances, and as the solvent of life. Water is the only common substance to exist as a solid, liquid, and gas under conditions normal to life on Earth. The Nobel Prize winner Albert Szent-Györgyi referred to water as the mater und matrix: the mother and womb of life.
The abundance of surface water on Earth is a unique feature in the Solar System. Earth's hydrosphere consists chiefly of the oceans but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of . The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean, having a depth of .
Conventionally, the planet is divided into five separate oceans, but these oceans all connect into a single world ocean. The mass of this world ocean is 1.35 metric tons or about 1/4400 of Earth's total mass. The world ocean covers an area of with a mean depth of , resulting in an estimated volume of . If all of Earth's crustal surface was at the same elevation as a smooth sphere, the depth of the resulting world ocean would be about .
About 97.5% of the water on Earth is saline; the remaining 2.5% is fresh water. Most fresh water – about 69% – is present as ice in ice caps and glaciers. The average salinity of Earth's oceans is about of salt per kilogram of seawater (3.5% salt). Most of the salt in the ocean comes from the weathering and erosion of rocks on land. Some salts are released from volcanic activity or extracted from cool igneous rocks.
The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation.
Altogether the ocean occupies 71 percent of the world surface, averaging nearly in depth. By volume, the ocean provides about 90 percent of the living space on the planet. The science fiction writer Arthur C. Clarke has pointed out it would be more appropriate to refer to planet Earth as planet Ocean.
However, water is found elsewhere in the Solar System. Europa, one of the moons orbiting Jupiter, is slightly smaller than the Earth's Moon. There is a strong possibility a large saltwater ocean exists beneath its ice surface. It has been estimated the outer crust of solid ice is about 10–30 km (6–19 mi) thick and the liquid ocean underneath is about 100 km (60 mi) deep. This would make Europa's ocean over twice the volume of the Earth's ocean. There has been speculation Europa's ocean could support life, and could be capable of supporting multicellular microorganisms if hydrothermal vents are active on the ocean floor. Enceladus, a small icy moon of Saturn, also has what appears to be an underground ocean which actively vents warm water from the moon's surface.
Evolution
Historical development
The Earth is about 4.54 billion years old. The earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago, during the Eoarchean era after a geological crust started to solidify following the earlier molten Hadean Eon. Microbial mat fossils have been found in 3.48 billion-year-old sandstone in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, "If life arose relatively quickly on Earth … then it could be common in the universe."
All organisms on Earth are descended from a common ancestor or ancestral gene pool.
Highly energetic chemistry is thought to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed. The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions. The beginning of life may have included self-replicating molecules such as RNA and the assembly of simple cells. In 2016 scientists reported a set of 355 genes from the last universal common ancestor (LUCA) of all life, including microorganisms, living on Earth.
Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events. The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits and finally, that organisms can be classified using these similarities into a hierarchy of nested groups—similar to a family tree. However, modern research has suggested that, due to horizontal gene transfer, this "tree of life" may be more complicated than a simple branching tree since some genes have spread independently between distantly related species.
Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry.
More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids. The development of molecular genetics has revealed the record of evolution left in organisms' genomes: dating when species diverged through the molecular clock produced by mutations. For example, these DNA sequence comparisons have revealed that humans and chimpanzees share 98% of their genomes and analysing the few areas where they differ helps shed light on when the common ancestor of these species existed.
Prokaryotes inhabited the Earth from approximately 3–4 billion years ago. No obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years. The eukaryotic cells emerged between 1.6 and 2.7 billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiosis. The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or hydrogenosomes. Another engulfment of cyanobacterial-like organisms led to the formation of chloroplasts in algae and plants.
The history of life was that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period. The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime moulds and myxobacteria. In 2016 scientists reported that, about 800 million years ago, a minor genetic change in a single molecule called GK-PID may have allowed organisms to go from a single cell organism to one of many cells.
Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over a span of about 10 million years, in an event called the Cambrian explosion. Here, the majority of types of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.
About 500 million years ago, plants and fungi started colonising the land. Evidence for the appearance of the first land plants occurs in the Ordovician, around , in the form of fossil spores. Land plants began to diversify in the Late Silurian, from around . The colonisation of the land by plants was soon followed by arthropods and other animals. Insects were particularly successful and even today make up the majority of animal species. Amphibians first appeared around 364 million years ago, followed by early amniotes and birds around 155 million years ago (both from "reptile"-like lineages), mammals around 129 million years ago, homininae around 10 million years ago and modern humans around 250,000 years ago. However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.
Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.
Microorganisms
Microorganisms make up about 70% of the marine biomass. A microorganism, or microbe, is a microscopic organism too small to be recognised with the naked eye. It can be single-celled or multicellular. Microorganisms are diverse and include all bacteria and archaea, most protozoa such as algae, fungi, and certain microscopic animals such as rotifers.
Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving.
Microorganisms are crucial to nutrient recycling in ecosystems as they act as decomposers. Some microorganisms are pathogenic, causing disease and even death in plants and animals. As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all the photosynthesis that occurs in the ocean, as well as the cycling of carbon, nitrogen, phosphorus, other nutrients and trace elements.
Microscopic life undersea is diverse and still poorly understood, such as for the role of viruses in marine ecosystems. Most marine viruses are bacteriophages, which are harmless to plants and animals, but are essential to the regulation of saltwater and freshwater ecosystems. They infect and destroy bacteria in aquatic microbial communities, and are the most important mechanism of recycling carbon in the marine environment. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth. Viral activity may also contribute to the biological pump, the process whereby carbon is sequestered in the deep ocean.
A stream of airborne microorganisms circles the planet above weather systems but below commercial air lanes. Some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in sea spray. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.
Microscopic organisms live throughout the biosphere. The mass of prokaryote microorganisms — which includes bacteria and archaea, but not the nucleated eukaryote microorganisms — may be as much as 0.8 trillion tons of carbon (of the total biosphere mass, estimated at between 1 and 4 trillion tons). Single-celled barophilic marine microbes have been found at a depth of in the Mariana Trench, the deepest spot in the Earth's oceans. Microorganisms live inside rocks below the sea floor under of ocean off the coast of the northwestern United States, as well as beneath the seabed off Japan. The greatest known temperature at which microbial life can exist is (Methanopyrus kandleri). In 2014, scientists confirmed the existence of microorganisms living below the ice of Antarctica. According to one researcher, "You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."
Marine viruses
Viruses are small infectious agents that do not have their own metabolism and can replicate only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. The linear size of the average virus is about one one-hundredth that of the average bacterium. Most viruses cannot be seen with an optical microscope so electron microscopes are used instead.
Viruses are found wherever there is life and have probably existed since living cells first evolved. The origin of viruses is unclear because they do not form fossils, so molecular techniques have been used to compare the DNA or RNA of viruses and are a useful means of investigating how they arise.
Viruses are now recognised as ancient and as having origins that pre-date the divergence of life into the three domains. But the origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.
Opinions differ on whether viruses are a form of life or organic structures that interact with living organisms. They are considered by some to be a life form, because they carry genetic material, reproduce by creating multiple copies of themselves through self-assembly, and evolve through natural selection. However they lack key characteristics such as a cellular structure generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as replicators and as "organisms at the edge of life".
Bacteriophages, often just called phages, are viruses that parasite bacteria and archaea. Marine phages parasite marine bacteria and archaea, such as cyanobacteria. They are a common and diverse group of viruses and are the most abundant biological entity in marine environments, because their hosts, bacteria, are typically the numerically dominant cellular life in the sea. Generally there are about 1 million to 10 million viruses in each mL of seawater, or about ten times more double-stranded DNA viruses than there are cellular organisms, although estimates of viral abundance in seawater can vary over a wide range. Tailed bacteriophages appear to dominate marine ecosystems in number and diversity of organisms. Bacteriophages belonging to the families Corticoviridae, Inoviridae and Microviridae are also known to infect diverse marine bacteria.
Microorganisms make up about 70% of the marine biomass. It is estimated viruses kill 20% of this biomass each day and that there are 15 times as many viruses in the oceans as there are bacteria and archaea. Viruses are the main agents responsible for the rapid destruction of harmful algal blooms, which often kill other marine life.
The number of viruses in the oceans decreases further offshore and deeper into the water, where there are fewer host organisms.
There are also archaeal viruses which replicate within archaea: these are double-stranded DNA viruses with unusual and sometimes unique shapes. These viruses have been studied in most detail in the thermophilic archaea, particularly the orders Sulfolobales and Thermoproteales.
Viruses are an important natural means of transferring genes between different species, which increases genetic diversity and drives evolution. It is thought that viruses played a central role in the early evolution, before the diversification of bacteria, archaea and eukaryotes, at the time of the last universal common ancestor of life on Earth. Viruses are still one of the largest reservoirs of unexplored genetic diversity on Earth.
Marine bacteria
Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals.
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.
The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage.
Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. This led to the formation of chloroplasts in algae and plants. There are also some algae that originated from even later endosymbiotic events. Here, eukaryotes engulfed a eukaryotic algae that developed into a "second-generation" plastid. This is known as secondary endosymbiosis.
The largest known bacterium, the marine Thiomargarita namibiensis, can be visible to the naked eye and sometimes attains .
Marine archaea
The archaea (Greek for ancient) constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning they have no cell nucleus or any other membrane-bound organelles in their cells.
Archaea were initially classified as bacteria, but this classification is outdated. Archaeal cells have unique properties separating them from the other two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phyla. Classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment.
Archaea and bacteria are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat and square-shaped cells of Haloquadratum walsbyi. Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, such as archaeols. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no known species forms spores.
Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle.
Marine protists
Protists are eukaryotes that cannot be classified as plants, fungi or animals. They are usually single-celled and microscopic. Life originated as single-celled prokaryotes (bacteria and archaea) and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics, because they are paraphyletic (lacking a common ancestor). Protists can be broadly divided into four groups depending on whether their nutrition is plant-like, animal-like, fungus-like, or a mixture of these.
Protists are highly diverse organisms currently organised into 18 phyla, but are not easy to classify. Studies have shown high protist diversity exists in oceans, deep sea-vents and river sediments, suggesting a large number of eukaryotic microbial communities have yet to be discovered. There has been little research on mixotrophic protists, but recent studies in marine environments found mixotrophic protests contribute a significant part of the protist biomass.
In contrast to the cells of prokaryotes, the cells of eukaryotes are highly organised. Plants, animals and fungi are usually multi-celled and are typically macroscopic. Most protists are single-celled and microscopic. But there are exceptions. Some single-celled marine protists are macroscopic. Some marine slime molds have unique life cycles that involve switching between unicellular, colonial, and multicellular forms. Other marine protist are neither single-celled nor microscopic, such as seaweed.
Protists have been described as a taxonomic grab bag where anything that doesn't fit into one of the main biological kingdoms can be placed. Some modern authors prefer to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellular organisms. This more constrained definition excludes seaweeds and slime molds.
Marine microanimals
As juveniles, animals develop from microscopic stages, which can include spores, eggs and larvae. At least one microscopic animal group, the parasitic cnidarian Myxozoa, is unicellular in its adult form, and includes marine species. Other adult marine microanimals are multicellular. Microscopic adult arthropods are more commonly found inland in freshwater, but there are marine species as well. Microscopic adult marine crustaceans include some copepods, cladocera and tardigrades (water bears). Some marine nematodes and rotifers are also too small to be recognised with the naked eye, as are many loricifera, including the recently discovered anaerobic species that spend their lives in an anoxic environment. Copepods contribute more to the secondary productivity and carbon sink of the world oceans than any other group of organisms. While mites are not normally thought of as marine organisms, most species of the family Halacaridae live in the sea.
Fungi
Over 1500 species of fungi are known from marine environments. These are parasitic on marine algae or animals, or are saprobes feeding on dead organic matter from algae, corals, protozoan cysts, sea grasses, wood and other substrata. Spores of many species have special appendages which facilitate attachment to the substratum. Marine fungi can also be found in sea foam and around hydrothermal areas of the ocean. A diverse range of unusual secondary metabolites is produced by marine fungi.
Mycoplankton are saprotropic members of the plankton communities of marine and freshwater ecosystems. They are composed of filamentous free-living fungi and yeasts associated with planktonic particles or phytoplankton. Similar to bacterioplankton, these aquatic fungi play a significant role in heterotrophic mineralization and nutrient cycling. Mycoplankton can be up to 20 mm in diameter and over 50 mm in length.
A typical milliliter of seawater contains about 103 to 104 fungal cells. This number is greater in coastal ecosystems and estuaries due to nutritional runoff from terrestrial communities. A higher diversity of mycoplankton is found around coasts and in surface waters down to 1000 metres, with a vertical profile that depends on how abundant phytoplankton is. This profile changes between seasons due to changes in nutrient availability. Marine fungi survive in a constant oxygen deficient environment, and therefore depend on oxygen diffusion by turbulence and oxygen generated by photosynthetic organisms.
Marine fungi can be classified as:
Lower fungi - adapted to marine habitats (zoosporic fungi, including mastigomycetes: oomycetes and chytridiomycetes)
Higher fungi - filamentous, modified to planktonic lifestyle (hyphomycetes, ascomycetes, basidiomycetes). Most mycoplankton species are higher fungi.
Lichens are mutualistic associations between a fungus, usually an ascomycete, and an alga or a cyanobacterium. Several lichens are found in marine environments. Many more occur in the splash zone, where they occupy different vertical zones depending on how tolerant they are to submersion. Some lichens live a long time; one species has been dated at 8,600 years. However their lifespan is difficult to measure because what defines the same lichen is not precise. Lichens grow by vegetatively breaking off a piece, which may or may not be defined as the same lichen, and two lichens of different ages can merge, raising the issue of whether it is the same lichen.
The sea snail Littoraria irrorata damages plants of Spartina in the sea marshes where it lives, which enables spores of intertidal ascomycetous fungi to colonise the plant. The snail then eats the fungal growth in preference to the grass itself.
According to fossil records, fungi date back to the late Proterozoic era 900–570 million years ago. Fossil marine lichens 600 million years old have been discovered in China. It has been hypothesized that mycoplankton evolved from terrestrial fungi, likely in the Paleozoic era (390 million years ago).
Origin of animals
The earliest animals were marine invertebrates, that is, vertebrates came later. Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by lacking cell walls. Marine invertebrates are animals that inhabit a marine environment apart from the vertebrate members of the chordate phylum; invertebrates lack a vertebral column. Some have evolved a shell or a hard exoskeleton.
The earliest animal fossils may belong to the genus Dickinsonia, 571 million to 541 million years ago. Individual Dickinsonia typically resemble a bilaterally symmetrical ribbed oval. They kept growing until they were covered with sediment or otherwise killed, and spent most of their lives with their bodies firmly anchored to the sediment. Their taxonomic affinities are presently unknown, but their mode of growth is consistent with a bilaterian affinity.
Apart from Dickinsonia, the earliest widely accepted animal fossils are the rather modern-looking cnidarians (the group that includes coral, jellyfish, sea anemones and Hydra), possibly from around The Ediacara biota, which flourished for the last 40 million years before the start of the Cambrian, were the first animals more than a very few centimetres long. Like Dickinsonia, many were flat with a "quilted" appearance, and seemed so strange that there was a proposal to classify them as a separate kingdom, Vendozoa. Others, however, have been interpreted as early molluscs (Kimberella), echinoderms (Arkarua), and arthropods (Spriggina, Parvancorina). There is still debate about the classification of these specimens, mainly because the diagnostic features which allow taxonomists to classify more recent organisms, such as similarities to living organisms, are generally absent in the Ediacarans. However, there seems little doubt that Kimberella was at least a triploblastic bilaterian animal, in other words, an animal significantly more complex than the cnidarians.
Small shelly fauna are a very mixed collection of fossils found between the Late Ediacaran and Middle Cambrian periods. The earliest, Cloudina, shows signs of successful defense against predation and may indicate the start of an evolutionary arms race. Some tiny Early Cambrian shells almost certainly belonged to molluscs, while the owners of some "armor plates," Halkieria and Microdictyon, were eventually identified when more complete specimens were found in Cambrian lagerstätten that preserved soft-bodied animals.
Body plans and phyla
Invertebrates are grouped into different phyla. Informally phyla can be thought of as a way of grouping organisms according to their body plan. A body plan refers to a blueprint which describes the shape or morphology of an organism, such as its symmetry, segmentation and the disposition of its appendages. The idea of body plans originated with vertebrates, which were grouped into one phylum. But the vertebrate body plan is only one of many, and invertebrates consist of many phyla or body plans. The history of the discovery of body plans can be seen as a movement from a worldview centred on vertebrates, to seeing the vertebrates as one body plan among many. Among the pioneering zoologists, Linnaeus identified two body plans outside the vertebrates; Cuvier identified three; and Haeckel had four, as well as the Protista with eight more, for a total of twelve. For comparison, the number of phyla recognised by modern zoologists has risen to 35.
Historically body plans were thought of as having evolved rapidly during the Cambrian explosion, but a more nuanced understanding of animal evolution suggests a gradual development of body plans throughout the early Palaeozoic and beyond. More generally a phylum can be defined in two ways: as described above, as a group of organisms with a certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with a certain degree of evolutionary relatedness (the phylogenetic definition).
In the 1970s there was already a debate about whether the emergence of the modern phyla was "explosive" or gradual but hidden by the shortage of Precambrian animal fossils. A re-analysis of fossils from the Burgess Shale lagerstätte increased interest in the issue when it revealed animals, such as Opabinia, which did not fit into any known phylum. At the time these were interpreted as evidence that the modern phyla had evolved very rapidly in the Cambrian explosion and that the Burgess Shale's "weird wonders" showed that the Early Cambrian was a uniquely experimental period of animal evolution. Later discoveries of similar animals and the development of new theoretical approaches led to the conclusion that many of the "weird wonders" were evolutionary "aunts" or "cousins" of modern groups—for example that Opabinia was a member of the lobopods, a group which includes the ancestors of the arthropods, and that it may have been closely related to the modern tardigrades. Nevertheless, there is still much debate about whether the Cambrian explosion was really explosive and, if so, how and why it happened and why it appears unique in the history of animals.
Earliest animals
The deepest-branching animals — the earliest animals that appeared during evolution — are marine non-vertebrate organisms. The earliest animal phyla are the Porifera, Ctenophora, Placozoa and Cnidaria. No member of these clades exhibit body plans with bilateral symmetry.
Marine sponges
Sponges are animals of the phylum Porifera (from Modern Latin for bearing pores). They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. They have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes.
Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs, and have no body symmetry. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding . Some sponges live to great ages; there is evidence of the deep-sea glass sponge Monorhaphis chuni living about 11,000 years.
While most of the approximately 5,000–10,000 known species feed on bacteria and other food particles in the water, some host photosynthesizing micro-organisms as endosymbionts and these alliances often produce more food and oxygen than they consume. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans.
Linnaeus mistakenly identified sponges as plants in the order Algae. For a long time thereafter sponges were assigned to a separate subkingdom, Parazoa (meaning beside the animals). They are now classified as a paraphyletic phylum from which the higher animals have evolved.
Ctenophores
Ctenophores (from Greek for carrying a comb), commonly known as comb jellies, are a phylum that live worldwide in marine waters. They are the largest non-colonial animals to swim with the help of cilia (hairs or combs). Coastal species need to be tough enough to withstand waves and swirling sediment, but some oceanic species are so fragile and transparent that it is very difficult to capture them intact for study. In the past ctenophores were thought to have only a modest presence in the ocean, but it is now known they are often significant and even dominant parts of the planktonic biomass.
The phylum has about 150 known species with a wide range of body forms. Sizes range from a few millimeters to . Cydippids are egg-shaped with their cilia arranged in eight radial comb rows, and deploy retractable tentacles for capturing prey. The benthic platyctenids are generally combless and flat. The coastal beroids have gaping mouths and lack tentacles. Most adult ctenophores prey on microscopic larvae and rotifers and small crustaceans but beroids prey on other ctenophores.
Early writers combined ctenophores with cnidarians. Ctenophores resemble cnidarians in relying on water flow through the body cavity for both digestion and respiration, as well as in having a decentralized nerve net rather than a brain. Also like cnidarians, the bodies of ctenophores consist of a mass of jelly, with one layer of cells on the outside and another lining the internal cavity. In ctenophores, however, these layers are two cells deep, while those in cnidarians are only a single cell deep. While cnidarians exhibit radial symmetry, ctenophores have two anal canals which exhibit biradial symmetry (half-turn rotational symmetry). The position of the ctenophores in the evolutionary family tree of animals has long been debated, and the majority view at present, based on molecular phylogenetics, is that cnidarians and bilaterians are more closely related to each other than either is to ctenophores.
Placozoa
Placozoa (from Greek for flat animals) have the simplest structure of all animals. They are a basal form of free-living (non-parasitic) multicellular organism that do not yet have a common name. They live in marine environments and form a phylum containing so far only three described species, of which the first, the classical Trichoplax adhaerens, was discovered in 1883. Two more species have been discovered since 2017, and genetic methods indicate this phylum has a further 100 to 200 undescribed species.
Trichoplax is a small, flattened, animal about one mm across and usually about 25 μm thick. Like the amoebae they superficially resemble, they continually change their external shape. In addition, spherical phases occasionally form which may facilitate movement. Trichoplax lacks tissues and organs. There is no manifest body symmetry, so it is not possible to distinguish anterior from posterior or left from right. It is made up of a few thousand cells of six types in three distinct layers. The outer layer of simple epithelial cells bear cilia which the animal uses to help it creep along the seafloor. Trichoplax feed by engulfing and absorbing food particles – mainly microbes and organic detritus – with their underside.
Marine cnidarians
Cnidarians (from Greek for nettle) are distinguished by the presence of stinging cells, specialized cells that they use mainly for capturing prey. Cnidarians include corals, sea anemones, jellyfish and hydrozoans. They form a phylum containing over 10,000 species of animals found exclusively in aquatic (mainly marine) environments. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration.
Fossil cnidarians have been found in rocks formed about . Fossils of cnidarians that do not build mineralized structures are rare. Scientists currently think cnidarians, ctenophores and bilaterians are more closely related to calcareous sponges than these are to other sponges, and that anthozoans are the evolutionary "aunts" or "sisters" of other cnidarians, and the most closely related to bilaterians.
Cnidarians are the simplest animals in which the cells are organised into tissues. The starlet sea anemone is used as a model organism in research. It is easy to care for in the laboratory and a protocol has been developed which can yield large numbers of embryos on a daily basis. There is a remarkable degree of similarity in the gene sequence conservation and complexity between the sea anemone and vertebrates. In particular, genes concerned in the formation of the head in vertebrates are also present in the anemone.
Bilateral invertebrate animals
Some of the earliest bilaterians were wormlike, and the original bilaterian may have been a bottom dwelling worm with a single body opening. A bilaterian body can be conceptualized as a cylinder with a gut running between two openings, the mouth and the anus. Around the gut it has an internal body cavity, a coelom or pseudocoelom. Animals with this bilaterally symmetric body plan have a head (anterior) end and a tail (posterior) end as well as a back (dorsal) and a belly (ventral); therefore they also have a left side and a right side.
Having a front end means that this part of the body encounters stimuli, such as food, favouring cephalisation, the development of a head with sense organs and a mouth. The body stretches back from the head, and many bilaterians have a combination of circular muscles that constrict the body, making it longer, and an opposing set of longitudinal muscles, that shorten the body; these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis. They also have a gut that extends through the basically cylindrical body from mouth to anus. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells. However, there are exceptions to each of these characteristics; for example, adult echinoderms are radially symmetric (unlike their larvae), and certain parasitic worms have extremely simplified body structures.
Protostomes
Protostomes (from Greek for first mouth) are a superphylum of animals. It is a sister clade of the deuterostomes (from Greek for second mouth), with which it forms the Nephrozoa clade. Protostomes are distinguished from deuterostomes by the way their embryos develop. In protostomes the first opening that develops becomes the mouth, while in deuterostomes it becomes the anus.
Marine worms
Worms (Old English for serpents) form a number of phyla. Different groups of marine worms are related only distantly, so they are found in several different phyla such as the Annelida (segmented worms), Chaetognatha (arrow worms), Phoronida (horseshoe worms), and Hemichordata. All worms, apart from the Hemichordata, are protostomes. The Hemichordata are
deuterostomes and are discussed in their own section below.
The typical body plan of a worm involves long cylindrical tube-like bodies and no limbs. Marine worms vary in size from microscopic to over in length for some marine polychaete worms (bristle worms) and up to for the marine nemertean worm (bootlace worm). Some marine worms occupy a small variety of parasitic niches, living inside the bodies of other animals, while others live more freely in the marine environment or by burrowing underground. Many of these worms have specialized tentacles used for exchanging oxygen and carbon dioxide and also may be used for reproduction. Some marine worms are tube worms, such as the giant tube worm which lives in waters near underwater volcanoes and can withstand temperatures up to 90 degrees Celsius. Platyhelminthes (flatworms) form another worm phylum which includes a class of parasitic tapeworms. The marine tapeworm Polygonoporus giganticus, found in the gut of sperm whales, can grow to over 30 m (100 ft).
Nematodes (roundworms) constitute a further worm phylum with tubular digestive systems and an opening at both ends. Over 25,000 nematode species have been described, of which more than half are parasitic. It has been estimated another million remain undescribed. They are ubiquitous in marine, freshwater and terrestrial environments, where they often outnumber other animals in both individual and species counts. They are found in every part of the Earth's lithosphere, from the top of mountains to the bottom of oceanic trenches. By count they represent 90% of all animals on the ocean floor. Their numerical dominance, often exceeding a million individuals per square meter and accounting for about 80% of all individual animals on Earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems.
Marine molluscs
Molluscs (Latin for soft) form a phylum with about 85,000 extant recognized species. They are the largest marine phylum in terms of species count, containing about 23% of all the named marine organisms. Molluscs have more varied forms than other invertebrate phyla. They are highly diverse, not just in size and in anatomical structure, but also in behaviour and in habitat.
The mollusc phylum is divided into 9 or 10 taxonomic classes. These classes include gastropods, bivalves and cephalopods, as well as other lesser-known but distinctive classes. Gastropods with protective shells are referred to as snails, whereas gastropods without protective shells are referred to as slugs. Gastropods are by far the most numerous molluscs in terms of species. Bivalves include clams, oysters, cockles, mussels, scallops, and numerous other families. There are about 8,000 marine bivalves species (including brackish water and estuarine species). A deep sea ocean quahog clam has been reported as having lived 507 years making it the longest recorded life of all animals apart from colonial animals, or near-colonial animals like sponges.
Cephalopods include octopus, squid and cuttlefish. About 800 living species of marine cephalopods have been identified, and an estimated 11,000 extinct taxa have been described. They are found in all oceans, but there are no fully freshwater cephalopods.
Molluscs have such diverse shapes that many textbooks base their descriptions of molluscan anatomy on a generalized or hypothetical ancestral mollusc. This generalized mollusc is unsegmented and bilaterally symmetrical with an underside consisting of a single muscular foot. Beyond that it has three further key features. Firstly, it has a muscular cloak called a mantle covering its viscera and containing a significant cavity used for breathing and excretion. A shell secreted by the mantle covers the upper surface. Secondly (apart from bivalves) it has a rasping tongue called a radula used for feeding. Thirdly, it has a nervous system including a complex digestive system using microscopic, muscle-powered hairs called cilia to exude mucus. The generalized mollusc has two paired nerve cords (three in bivalves). The brain, in species that have one, encircles the esophagus. Most molluscs have eyes and all have sensors detecting chemicals, vibrations, and touch.
Good evidence exists for the appearance of marine gastropods, cephalopods and bivalves in the Cambrian period .
Marine arthropods
Arthropods (Greek for jointed feet) have an exoskeleton (external skeleton), a segmented body, and jointed appendages (paired appendages). They form a phylum which includes insects, arachnids, myriapods, and crustaceans. Arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments.
The evolutionary ancestry of arthropods dates back to the Cambrian period and is generally regarded as monophyletic. However, basal relationships of arthropods with extinct phyla such as lobopodians have recently been debated.
Extant marine arthropods range in size from the microscopic crustacean Stygotantulus to the Japanese spider crab. Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph - analogue of blood - circulates; they have open circulatory systems. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.
Arthropod vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae (bristles) that project through their cuticles. Arthropod methods of reproduction are diverse: terrestrial species use some form of internal fertilization while marine species lay eggs using either internal or external fertilization. Arthropod hatchlings vary from miniature adults to grubs that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form.
Deuterostomes
In deuterostomes the first opening that develops in the growing embryo becomes the anus, while in protostomes it becomes the mouth. Deuterostomes form a superphylum of animals and are the sister clade of the protostomes. It is once considered that the earliest known deuterostomes are Saccorhytus fossils from about 540 million years ago. However, another study considered that Saccorhytus is more likely to be an ecdysozoan.
Echinoderms
Echinoderms (Greek for spiny skin) is a phylum which contains only marine invertebrates. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes, after the chordates.
Adult echinoderms are recognizable by their radial symmetry (usually five-point) and include starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. They are unique among animals in having bilateral symmetry at the larval stage, but fivefold symmetry (pentamerism, a special type of radial symmetry) as adults.
Echinoderms are important both biologically and geologically. Biologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to regenerate tissue, organs, limbs, and reproduce asexually; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries.
It is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution. Aside from the hard-to-classify Arkarua (a Precambrian animal with echinoderm-like pentamerous radial symmetry), the first definitive members of the phylum appeared near the start of the Cambrian.
Hemichordates
Hemichordates form a sister phylum to the echinoderms. They are solitary worm-shaped organisms rarely seen by humans because of their lifestyle. They include two main groups, the acorn worms and the Pterobranchia. Pterobranchia form a class containing about 30 species of small worm-shaped animals that live in secreted tubes on the ocean floor. Acorn worms form a class containing about 111 species that generally live in U-shaped burrows on the seabed, from the shoreline to a depth of 3000 metres. The worms lie there with the proboscis sticking out of one opening in the burrow, subsisting as deposit feeders or suspension feeders. It is supposed the ancestors of acorn worms used to live in tubes like their relatives, the Pterobranchia, but eventually started to live a safer and more sheltered existence in sediment burrows. Some of these worms may grow to be very long; one particular species may reach a length of 2.5 metres (8 ft 2 in), although most acorn worms are much smaller.
Acorn worms are more highly specialised and advanced than other worm-like organisms. They have a circulatory system with a heart that also functions as a kidney. Acorn worms have gill-like structures they use for breathing, similar to the gills of fish. Therefore, acorn worms are sometimes said to be a link between classical invertebrates and vertebrates. Acorn worms continually form new gill slits as they grow in size, and some older individuals have more than a hundred on each side. Each slit consists of a branchial chamber opening to the pharynx through a U-shaped cleft. Cilia push water through the slits, maintaining a constant flow, just as in fish. Some acorn worms also have a postanal tail which may be homologous to the post-anal tail of vertebrates.
The three-section body plan of the acorn worm is no longer present in the vertebrates, except in the anatomy of the frontal neural tube, later developed into a brain divided into three parts. This means some of the original anatomy of the early chordate ancestors is still present in vertebrates even if it is not always visible. One theory is the three-part body originated from an early common ancestor of the deuterostomes, and maybe even from a common bilateral ancestor of both deuterostomes and protostomes. Studies have shown the gene expression in the embryo share three of the same signaling centers that shape the brains of all vertebrates, but instead of taking part in the formation of their neural system, they are controlling the development of the different body regions.
Marine chordates
The chordate phylum has three subphyla, one of which is the vertebrates (see below). The other two subphyla are marine invertebrates: the tunicates (salps and sea squirts) and the cephalochordates (such as lancelets). Invertebrate chordates are close relatives to vertebrates. In particular, there has been discussion about how closely some extinct marine species, such as Pikaiidae, Palaeospondylus, Zhongxiniscus and Vetulicolia, might relate ancestrally to vertebrates.
Vertebrate animals
Vertebrates (Latin for joints of the spine) are a subphylum of chordates. They are chordates that have a vertebral column (backbone). The vertebral column provides the central support structure for an internal skeleton which gives shape, support, and protection to the body and can provide a means of anchoring fins or limbs to the body. The vertebral column also serves to house and protect the spinal cord that lies within the vertebral column.
Marine vertebrates can be divided into marine fish and marine tetrapods.
Marine fish
Fish typically breathe by extracting oxygen from water through gills and have a skin protected by scales and mucous. They use fins to propel and stabilise themselves in the water, and usually have a two-chambered heart and eyes well adapted to seeing underwater, as well as other sensory systems. Over 33,000 species of fish have been described as of 2017, of which about 20,000 are marine fish.
Jawless fish
Early fish had no jaws. Most went extinct when they were outcompeted by jawed fish (below), but two groups survived: hagfish and lampreys. Hagfish form a class of about 20 species of eel-shaped, slime-producing marine fish. They are the only known living animals that have a skull but no vertebral column. Lampreys form a superclass containing 38 known extant species of jawless fish. The adult lamprey is characterized by a toothed, funnel-like sucking mouth. Although they are well known for boring into the flesh of other fish to suck their blood, only 18 species of lampreys are actually parasitic. Together hagfish and lampreys are the sister group to vertebrates. Living hagfish remain similar to hagfish from around 300 million years ago. The lampreys are a very ancient lineage of vertebrates, though their exact relationship to hagfishes and jawed vertebrates is still a matter of dispute. Molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of craniata.
The Tully monster is an extinct genus of soft-bodied bilaterians that lived in tropical estuaries about 300 million years ago. Since 2016 there has been controversy over whether this animal was a vertebrate or an invertebrate. In 2020 researchers found "strong evidence" that the Tully monster was a vertebrate, and was a jawless fish in the lineage of the lamprey, while in 2023 other researchers found 3D fossils scans did not support those conclusions.
Pteraspidomorphi is an extinct class of early jawless fish ancestral to jawed vertebrates. The few characteristics they share with the latter are now considered as primitive for all vertebrates.
Around the start of the Devonian, fish started appearing with a deep remodelling of the vertebrate skull that resulted in a jaw.
All vertebrate jaws, including the human jaw, have evolved from these early fish jaws. The appearance of the early vertebrate jaw has been described as "perhaps the most profound and radical evolutionary step in vertebrate history". Jaws make it possible to capture, hold, and chew prey. Fish without jaws had more difficulty surviving than fish with jaws, and most jawless fish became extinct during the Triassic period.
Cartilaginous fish
Jawed fish fall into two main groups: fish with bony internal skeletons and fish with cartilaginous internal skeletons. Cartilaginous fish, such as sharks and rays, have jaws and skeletons made of cartilage rather than bone. Megalodon is an extinct species of shark that lived about 28 to 1.5 Ma. It may looked much like a stocky version of the great white shark, but was much larger with estimated lengths reaching . Found in all oceans it was one of the largest and most powerful predators in vertebrate history, and probably had a profound impact on marine life. The Greenland shark has the longest known lifespan of all vertebrates, about 400 years. Some sharks such as the great white are partially warm blooded and give live birth. The manta ray, largest ray in the world, has been targeted by fisheries and is now vulnerable.
Bony fish
Bony fish have jaws and skeletons made of bone rather than cartilage. Bony fish also have hard, bony plates called operculum which help them respire and protect their gills, and they often possess a swim bladder which they use for better control of their buoyancy. Bony fish can be further divided into those with lobe fins and those with ray fins. The approximate dates in the phylogenetic tree are from Near et al., 2012 and Zhu et al., 2009.
Lobe fins have the form of fleshy lobes supported by bony stalks which extend from the body. Guiyu oneiros, the earliest-known bony fish, lived during the Late Silurian 419 million years ago. It has the combination of both ray-finned and lobe-finned features, although analysis of the totality of its features place it closer to lobe-finned fish. Lobe fins evolved into the legs of the first tetrapod land vertebrates, so by extension an early ancestor of humans was a lobe-finned fish. Apart from the coelacanths and the lungfishes, lobe-finned fishes are now extinct.
The remaining bony fish have ray fins. These are made of webs of skin supported by bony or horny spines (rays) which can be erected to control the fin stiffness.
The main distinguishing feature of the chondrosteans (sturgeon, paddlefish, bichir and reedfish) is the cartilaginous nature of their skeletons. The ancestors of the chondrosteans are thought to be bony fish, but the characteristic of an ossified skeleton was lost in later evolutionary development, resulting in a lightening of the frame.
Neopterygians (from Greek for new fins) appeared sometime in the Late Permian, before dinosaurs. They were a very successful group of fish, because they could move more rapidly than their ancestors. Their scales and skeletons began to lighten during their evolution, and their jaws became more powerful and efficient.
Teleosts
About 96% of all modern fish species are teleosts, of which about 14,000 are marine species. Teleosts can be distinguished from other bony fish by their possession of a homocercal tail, a tail where the upper half mirrors the lower half. Another difference lies in their jaw bones – teleosts have modifications in the jaw musculature which make it possible for them to protrude their jaws. This enables them to grab prey and draw it into their mouth. In general, teleosts tend to be quicker and more flexible than more basal bony fishes. Their skeletal structure has evolved towards greater lightness. While teleost bones are well calcified, they are constructed from a scaffolding of struts, rather than the dense cancellous bones of holostean fish.
Teleosts are found in almost all marine habitats. They have enormous diversity, and range in size from adult gobies 8mm long to ocean sunfish weighing over 2,000 kg. The following images show something of the diversity in the shape and colour of modern marine teleosts...
Nearly half of all extant vertebrate species are teleosts.
Marine tetrapods
A tetrapod (Greek for four feet) is a vertebrate with limbs (feet). Tetrapods evolved from ancient lobe-finned fishes about 400 million years ago during the Devonian Period when their earliest ancestors emerged from the sea and adapted to living on land. This change from a body plan for breathing and navigating in gravity-neutral water to a body plan with mechanisms enabling the animal to breath in air without dehydrating and move on land is one of the most profound evolutionary changes known. Tetrapods can be divided into four classes: amphibians, reptiles, birds and mammals.
Marine tetrapods are tetrapods that returned from land back to the sea again. The first returns to the ocean may have occurred as early as the Carboniferous Period whereas other returns occurred as recently as the Cenozoic, as in cetaceans, pinnipeds, and several modern amphibians. Amphibians (from Greek for both kinds of life) live part of their life in water and part on land. They mostly require fresh water to reproduce. A few inhabit brackish water, but there are no true marine amphibians. There have been reports, however, of amphibians invading marine waters, such as a Black Sea invasion by the natural hybrid Pelophylax esculentus reported in 2010.
Reptiles
Reptiles (Late Latin for creeping or crawling) do not have an aquatic larval stage, and in this way are unlike amphibians. Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades — the fetus develops within the mother, contained in a placenta rather than an eggshell. As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings.
Some reptiles are more closely related to birds than other reptiles, and many scientists prefer to make Reptilia a monophyletic group which includes the birds. Extant non-avian reptiles which inhabit or frequent the sea include sea turtles, sea snakes, terrapins, the marine iguana, and the saltwater crocodile. Currently, of the approximately 12,000 extant reptile species and sub-species, only about 100 of are classed as marine reptiles.
Except for some sea snakes, most extant marine reptiles are oviparous and need to return to land to lay their eggs. Apart from sea turtles, the species usually spend most of their lives on or near land rather than in the ocean. Sea snakes generally prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries. Unlike land snakes, sea snakes have evolved flattened tails which help them swim.
Some extinct marine reptiles, such as ichthyosaurs, evolved to be viviparous and had no requirement to return to land. Ichthyosaurs resembled dolphins. They first appeared about 245 million years ago and disappeared about 90 million years ago. The terrestrial ancestor of the ichthyosaur had no features already on its back or tail that might have helped along the evolutionary process. Yet the ichthyosaur developed a dorsal and tail fin which improved its ability to swim. The biologist Stephen Jay Gould said the ichthyosaur was his favourite example of convergent evolution. The earliest marine reptiles arose in the Permian. During the Mesozoic many groups of reptiles became adapted to life in the seas, including ichthyosaurs, plesiosaurs, mosasaurs, nothosaurs, placodonts, sea turtles, thalattosaurs and thalattosuchians. Marine reptiles were less numerous after mass extinction at the end of the Cretaceous.
Birds
Marine birds are adapted to life within the marine environment. They are often called seabirds. While marine birds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations. Examples include albatross, penguins, gannets, and auks.
In general, marine birds live longer, breed later and have fewer young than terrestrial birds do, but they invest a great deal of time in their young. Most species nest in colonies, which can vary in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even feed on each other. Marine birds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely. Some marine birds plummet from heights, plunging through the water leaving vapour-like trails, similar to that of fighter planes. Gannets plunge into the water at up to 100 kilometres per hour (60 mph). They have air sacs under their skin in their face and chest which act like bubble-wrap, cushioning the impact with the water.
The first marine birds evolved in the Cretaceous period, and modern marine bird families emerged in the Paleogene.
Mammals
Mammals (from Latin for breast) are characterised by the presence of mammary glands which in females produce milk for feeding (nursing) their young. There are about 130 living and recently extinct marine mammal species such as seals, dolphins, whales, manatees, sea otters and polar bears. They do not represent a distinct taxon or systematic grouping, but are instead unified by their reliance on the marine environment for feeding. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Seals and sea-lions are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting. In contrast, both otters and the polar bear are much less adapted to aquatic living. Their diet varies considerably as well: some may eat zooplankton; others may eat fish, squid, shellfish, and sea-grass; and a few may eat other mammals.
In a process of convergent evolution, marine mammals, especially cetaceans such as dolphins and whales, redeveloped their body plan to parallel the streamlined fusiform body plan of pelagic fish. Front legs became flippers and back legs disappeared, a dorsal fin reappeared and the tail morphed into a powerful horizontal fluke. This body plan is an adaptation to being an active predator in a high drag environment. A parallel convergence occurred with the now extinct marine reptile ichthyosaur.
Primary producers
Primary producers are the autotroph organisms that make their own food instead of eating other organisms. This means primary producers become the starting point in the food chain for heterotroph organisms that do eat other organisms. Some marine primary producers are specialised bacteria and archaea which are chemotrophs, making their own food by gathering around hydrothermal vents and cold seeps and using chemosynthesis. However most marine primary production comes from organisms which use photosynthesis on the carbon dioxide dissolved in the water. This process uses energy from sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. Marine primary producers are important because they underpin almost all marine animal life by generating most of the oxygen and food that provide other organisms with the chemical energy they need to exist.
The principal marine primary producers are cyanobacteria, algae and marine plants. The oxygen released as a by-product of photosynthesis is needed by nearly all living things to carry out cellular respiration. In addition, primary producers are influential in the global carbon and water cycles. They stabilize coastal areas and can provide habitats for marine animals. The term division has been traditionally used instead of phylum when discussing primary producers, but the International Code of Nomenclature for algae, fungi, and plants now accepts both terms as equivalents.
Cyanobacteria
Cyanobacteria were the first organisms to evolve an ability to turn sunlight into chemical energy. They form a phylum (division) of bacteria which range from unicellular to filamentous and include colonial species. They are found almost everywhere on earth: in damp soil, in both freshwater and marine environments, and even on Antarctic rocks. In particular, some species occur as drifting cells floating in the ocean, and as such were amongst the first of the phytoplankton.
The first primary producers that used photosynthesis were oceanic cyanobacteria about 2.3 billion years ago. The release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of oxygen-intolerant organisms, a dramatic change which redirected the evolution of the major animal and plant species.
The tiny marine cyanobacterium Prochlorococcus, discovered in 1986, forms today part of the base of the ocean food chain and accounts for much of the photosynthesis of the open ocean and an estimated 20% of the oxygen in the Earth's atmosphere. It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.
Originally, biologists classified cyanobacteria as algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria are bacteria, and hence are not even in the same Kingdom as algae. Most authorities today exclude all prokaryotes, and hence cyanobacteria from the definition of algae.
Algae
Algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. Marine algae can be divided into six groups:
green algae, an informal group containing about 8,000 recognised species. Many species live most of their lives as single cells or are filamentous, while others form colonies made up from long chains of cells, or are highly differentiated macroscopic seaweeds.
red algae, a (disputed) phylum containing about 7,000 recognised species, mostly multicellular and including many notable seaweeds.
brown algae, a class containing about 2,000 recognised species, mostly multicellular and including many seaweeds, including kelp
diatoms, a (disputed) phylum containing about 100,000 recognised species of mainly unicellular algae. Diatoms generate about 20 percent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, and contribute nearly half of the organic material found in the oceans. The shells (frustules) of dead diatoms can reach as much as half a mile deep on the ocean floor.
dinoflagellates, a phylum of unicellular flagellates with about 2,000 marine species. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy). Some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. Others predate other protozoa, and a few forms are parasitic.
euglenophytes, a phylum of unicellular flagellates with only a few marine members
Unlike higher plants, algae lack roots, stems, or leaves. They can be classified by size as microalgae or macroalgae.
Microalgae are the microscopic types of algae, not visible to the naked eye. They are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular. Microalgae are important components of the marine protists (discussed above), as well as the phytoplankton (discussed below). They are very diverse. It has been estimated there are 200,000-800,000 species of which about 50,000 species have been described. Depending on the species, their sizes range from a few micrometers (μm) to a few hundred micrometers. They are specially adapted to an environment dominated by viscous forces.
Macroalgae are the larger, multicellular and more visible types of algae, commonly called seaweeds. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a holdfast. Seaweed that becomes adrift can wash up on beaches. Kelp is a large brown seaweed that forms large underwater forests covering about 25% of the world coastlines. They are among the most productive and dynamic ecosystems on Earth. Some Sargassum seaweeds are planktonic (free-floating). Like microalgae, macroalgae (seaweeds) are technically marine protists since they are not true plants.
Unicellular organisms are usually microscopic, less than one tenth of a millimeter long. There are exceptions. Mermaid's wineglass, a genus of subtropical green algae, is single-celled but remarkably large and complex in form with a single large nucleus, making it a model organism for studying cell biology. Another single celled algae, Caulerpa taxifolia, has the appearance of a vascular plant including "leaves" arranged neatly up stalks like a fern. Selective breeding in aquariums to produce hardier strains resulted in an accidental release into the Mediterranean where it has become an invasive species known colloquially as killer algae.
Origin of plants
Back in the Silurian, some phytoplankton evolved into red, brown and green algae. These algae then invaded the land and started evolving into the land plants we know today. Later, in the Cretaceous, some of these land plants returned to the sea as marine plants, such as mangroves and seagrasses.
Marine plants can be found in intertidal zones and shallow waters, such as seagrasses like eelgrass and turtle grass, Thalassia. These plants have adapted to the high salinity of the ocean environment. Plant life can also flourish in the brackish waters of estuaries, where mangroves or cordgrass or beach grass beach grass might grow.
The total world area of mangrove forests was estimated in 2010 as (based on satellite data). The total world area of seagrass meadows is more difficult to determine, but was conservatively estimated in 2003 as .
Mangroves and seagrasses provide important nursery habitats for marine life, acting as hiding and foraging places for larval and juvenile forms of larger fish and invertebrates.
Plankton and trophic interactions
Plankton (from Greek for wanderers) are a diverse group of organisms that live in the water column of large bodies of water but cannot swim against a current. As a result, they wander or drift with the currents. Plankton are defined by their ecological niche, not by any phylogenetic or taxonomic classification. They are a crucial source of food for many marine animals, from forage fish to whales. Plankton can be divided into a plant-like component and an animal component.
Phytoplankton
Phytoplankton are the plant-like components of the plankton community ("phyto" comes from the Greek for plant). They are autotrophic (self-feeding), meaning they generate their own food and do not need to consume other organisms.
Phytoplankton consist mainly of microscopic photosynthetic eukaryotes which inhabit the upper sunlit layer in all oceans. They need sunlight so they can photosynthesize. Most phytoplankton are single-celled algae, but other phytoplankton are bacteria and some are protists. Phytoplankton groups include cyanobacteria (above), diatoms, various other types of algae (red, green, brown, and yellow-green), dinoflagellates, euglenoids, coccolithophorids, cryptomonads, chrysophytes, chlorophytes, prasinophytes, and silicoflagellates. They form the base of the primary production that drives the ocean food web, and account for half of the current global primary production, more than the terrestrial forests.
Zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek for animal). They are heterotrophic (other-feeding), meaning they cannot produce their own food and must consume instead other plants or animals as food. In particular, this means they eat phytoplankton.
Zooplankton are generally larger than phytoplankton, mostly still microscopic but some can be seen with the naked eye. Many protozoans (single-celled protists that prey on other microscopic life) are zooplankton, including zooflagellates, foraminiferans, radiolarians and some dinoflagellates. Other dinoflagellates are mixotrophic and could also be classified as phytoplankton; the distinction between plants and animals often breaks down in very small organisms. Other zooplankton include pelagic cnidarians, ctenophores, molluscs, arthropods and tunicates, as well as planktonic arrow worms and bristle worms.
Radiolarians are unicellular protists with elaborate silica shells
Microzooplankton: major grazers of the plankton
Larger zooplankton can be predatory on smaller zooplankton.
Macrozooplankton
Many marine animals begin life as zooplankton in the form of eggs or larvae, before they develop into adults. These are meroplanktic, that is, they are planktonic for only part of their life.
Mixotrophic plankton
Dinoflagellates are often mixotrophic or live in symbiosis with other organisms.
Some dinoflagellates are bioluminescent. At night, ocean water can light up internally and sparkle with blue light because of these dinoflagellates. Bioluminescent dinoflagellates possess scintillons, individual cytoplasmic bodies which contain dinoflagellate luciferase, the main enzyme involved in the luminescence. The luminescence, sometimes called the phosphorescence of the sea, occurs as brief (0.1 sec) blue flashes or sparks when individual scintillons are stimulated, usually by mechanical disturbances from, for example, a boat or a swimmer or surf.
Marine food web
Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which tend to be r-strategists that grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, terrestrial primary producers, such as mature forests, are often K-strategists that grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.
Because of this inversion, it is the zooplankton that make up most of the marine animal biomass. As primary consumers, they are the crucial link between the primary producers (mainly phytoplankton) and the rest of the marine food web (secondary consumers).
If phytoplankton dies before it is eaten, it descends through the euphotic zone as part of the marine snow and settles into the depths of sea. In this way, phytoplankton sequester about 2 billion tons of carbon dioxide into the ocean each year, causing the ocean to become a sink of carbon dioxide holding about 90% of all sequestered carbon.
In 2010 researchers found whales carry nutrients from the depths of the ocean back to the surface using a process they called the whale pump. Whales feed at deeper levels in the ocean where krill is found, but return regularly to the surface to breathe. There whales defecate a liquid rich in nitrogen and iron. Instead of sinking, the liquid stays at the surface where phytoplankton consume it. In the Gulf of Maine the whale pump provides more nitrogen than the rivers.
Other interactions
Biogeochemical cycles
Taken as a whole, the oceans form a single marine system where water – the "universal solvent" – dissolves nutrients and substances containing elements such as oxygen, carbon, nitrogen and phosphorus. These substances are endlessly cycled and recycled, chemically combined and then broken down again, dissolved and then precipitated or evaporated, imported from and exported back to the land and the atmosphere and the ocean floor. Powered both by the biological activity of marine organisms and by the natural actions of the sun and tides and movements within the Earth's crust, these are the marine biogeochemical cycles.
Sediments and biogenic ooze
Sediments at the bottom of the ocean have two main origins, terrigenous and biogenous. Terrigenous sediments account for about 45% of the total marine sediment, and originate in the erosion of rocks on land, transported by rivers and land runoff, windborne dust, volcanoes, or grinding by glaciers.
Biogenous sediments account for the other 55% of the total sediment, and originate in the skeletal remains of marine protists (single-celled plankton and benthos organisms). Much smaller amounts of precipitated minerals and meteoric dust can also be present. Ooze, in the context of a marine sediment, does not refer to the consistency of the sediment but to its biological origin. The term ooze was originally used by John Murray, the "father of modern oceanography", who proposed the term radiolarian ooze for the silica deposits of radiolarian shells brought to the surface during the Challenger Expedition. A biogenic ooze is a pelagic sediment containing at least 30 percent from the skeletal remains of marine organisms.
Land interactions
Land interactions impact marine life in many ways. Coastlines typically have continental shelves extending some way from the shore. These provide extensive shallows sunlit down to the seafloor, allowing for photosynthesis and enabling habitats for seagrass meadows, coral reefs, kelp forests and other benthic life. Further from shore the continental shelf slopes towards deep water. Wind blowing at the ocean surface or deep ocean currents can result in cold and nutrient rich waters from abyssal depths moving up the continental slopes. This can result in upwellings along the outer edges of continental shelves, providing conditions for phytoplankton blooms.
Water evaporated by the sun from the surface of the ocean can precipitate on land and eventually return to the ocean as runoff or discharge from rivers, enriched with nutrients as well as pollutants. As rivers discharge into estuaries, freshwater mixes with saltwater and becomes brackish. This provides another shallow water habitat where mangrove forests and estuarine fish thrive. Overall, life in inland lakes can evolve with greater diversity than happens in the sea, because freshwater habitats are themselves diverse and compartmentalised in a way marine habitats are not. Some aquatic life, such as salmon and eels, migrate back and forth between freshwater and marine habitats. These migrations can result in exchanges of pathogens and have impacts on the way life evolves in the ocean.
Anthropogenic impacts
Human activities affect marine life and marine habitats through overfishing, pollution, acidification and the introduction of invasive species. These impact marine ecosystems and food webs and may result in consequences as yet unrecognised for the biodiversity and continuation of marine life forms.
Biodiversity and extinction events
Biodiversity is the result of over three billion years of evolution. Until approximately 600 million years ago, all life consisted of archaea, bacteria, protozoans and similar single-celled organisms. The history of biodiversity during the Phanerozoic (the last 540 million years), starts with rapid growth during the Cambrian explosion – a period during which nearly every phylum of multicellular organisms first appeared. Over the next 400 million years or so, invertebrate diversity showed little overall trend and vertebrate diversity shows an overall exponential trend.
However, more than 99 percent of all species that ever lived on Earth, amounting to over five billion species, are estimated to be extinct. These extinctions occur at an uneven rate. The dramatic rise in diversity has been marked by periodic, massive losses of diversity classified as mass extinction events. Mass extinction events occur when life undergoes precipitous global declines. Most diversity and biomass on earth is found among the microorganisms, which are difficult to measure. Recorded extinction events are therefore based on the more easily observed changes in the diversity and abundance of larger multicellular organisms, rather than the total diversity and abundance of life. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms.
Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. The Great Oxygenation Event was perhaps the first major extinction event. Since the Cambrian explosion five major mass extinctions have significantly exceeded the background extinction rate. The worst was the Permian-Triassic extinction event, 251 million years ago. One generally estimates that the Big Five mass extinctions of the Phanerozoic (the last 540 million years) wiped out more than 40% of marine genera and probably more than 70% of marine species. The current Holocene extinction caused by human activity, and now referred to as the "sixth extinction", may prove ultimately more devastating.
Investigating and Exploring Marine Life
Research and study
In order to perform research and enrich Marine Life knowledge, Scientists use various methods in-order to reach and explore the depths of the ocean. several Hi-tech instruments and vehicles are used for this purpose.
Autonomous Underwater Vehicles (AUVs)- Underwater robots used to explore the ocean. AUVs are independent robots and can explore unmanned. They are released from a ship and are operated from the surface.
Deep-Towed Vehicles (DTVs)- vehicles towed behind research vessels, offering a simpler alternative to more advanced underwater vehicles. They serve as versatile platforms for deploying oceanographic instruments to measure various ocean parameters, with specific models like the DTV BRIDGET used for studying hydrothermal vent plumes by moving near the ocean floor.
Manned Submersibles- an manned underwater vehicle used for exploring, experimenting and is often used by army.
Research vessels (R/Vs)- a boat or ship used to conduct research over a ling period of time. It is capable of transporting a diverse range of sampling and surveying equipment. Research vessels typically feature on-board laboratory space, allowing researchers to promptly analyze the materials collected during cruises.
Remotely Operated Vehicles (ROVs)- unmanned vehicles. able to reach greater depths under water in order to collect a wider variety of information.
| Physical sciences | Oceanography | Earth science |
6807932 | https://en.wikipedia.org/wiki/Minimum-cost%20flow%20problem | Minimum-cost flow problem | The minimum-cost flow problem (MCFP) is an optimization and decision problem to find the cheapest possible way of sending a certain amount of flow through a flow network. A typical application of this problem involves finding the best delivery route from a factory to a warehouse where the road network has some capacity and cost associated. The minimum cost flow problem is one of the most fundamental among all flow and circulation problems because most other such problems can be cast as a minimum cost flow problem and also that it can be solved efficiently using the network simplex algorithm.
Definition
A flow network is a directed graph with a source vertex and a sink vertex , where each edge has capacity , flow and cost , with most minimum-cost flow algorithms supporting edges with negative costs. The cost of sending this flow along an edge is . The problem requires an amount of flow to be sent from source to sink .
The definition of the problem is to minimize the total cost of the flow over all edges:
with the constraints
{|
|-
| Capacity constraints: ||
|-
| Skew symmetry: ||
|-
| Flow conservation: ||
|-
| Required flow: ||
|}
Relation to other problems
A variation of this problem is to find a flow which is maximum, but has the lowest cost among the maximum flow solutions. This could be called a minimum-cost maximum-flow problem and is useful for finding minimum cost maximum matchings.
With some solutions, finding the minimum cost maximum flow instead is straightforward. If not, one can find the maximum flow by performing a binary search on .
A related problem is the minimum cost circulation problem, which can be used for solving minimum cost flow. The minimum cost circulation problem has no source and sink; instead it has costs and lower and upper bounds on each edge, and seeks flow amounts within the given bounds that balance the flow at each vertex and minimize the sum over edges of cost times flow. Any minimum-cost flow instance can be converted into a minimum cost circulation instance by setting the lower bound on all edges to zero, and then making an extra edge from the sink to the source , with capacity and lower bound , forcing the total flow from to to also be .
The following problems are special cases of the minimum cost flow problem (we provide brief sketches of each applicable reduction, in turn):
Shortest path problem (single-source). Require that a feasible solution to the minimum cost flow problem sends one unit of flow from a designated source to a designated sink . Give all edges infinite capacity.
Maximum flow problem. Choose a large demand (large enough to exceed the maximum flow; for instance, the sum of capacities out of the source vertex) Set the costs of all edges in the maximum flow instance to zero, and introduce a new edge from source to sink with unit cost and capacity .
Assignment problem. Suppose that each partite set in the bipartition has vertices, and denote the bipartition by . Give each supply and give each demand . Each edge is to have unit capacity.
Solutions
The minimum cost flow problem can be solved by linear programming, since we optimize a linear function, and all constraints are linear.
Apart from that, many combinatorial algorithms exist. Some of them are generalizations of maximum flow algorithms, others use entirely different approaches.
Well-known fundamental algorithms (they have many variations):
Cycle canceling: a general primal method.
Cut canceling: a general dual method.
Minimum mean cycle canceling: a simple strongly polynomial algorithm.
Successive shortest path and capacity scaling: dual methods, which can be viewed as the generalization of the Ford–Fulkerson algorithm.
Cost scaling: a primal-dual approach, which can be viewed as the generalization of the push-relabel algorithm.
Network simplex algorithm: a specialized version of the linear programming simplex method.
Out-of-kilter algorithm by D. R. Fulkerson
Application
Minimum weight bipartite matching
Given a bipartite graph , the goal is to find the maximum cardinality matching in G that has minimum cost. Let w: E → R be a weight function on the edges of E. The minimum weight bipartite matching problem or assignment problem is to find a
perfect matching whose total weight is minimized. The idea is to reduce this problem to a network flow problem.
Let . Assign the capacity of all the edges in E′ to 1. Add a source vertex s and connect it to all the vertices in A′ and add a sink
vertex t and connect all vertices inside group B′ to this vertex. The capacity of all the new edges is 1 and their costs is 0. It is proved that there is minimum weight perfect bipartite matching in G if and only if there a minimum cost flow in G′.
| Mathematics | Graph theory | null |
35715231 | https://en.wikipedia.org/wiki/Human%E2%80%93animal%20breastfeeding | Human–animal breastfeeding | Human to animal breastfeeding has been practiced in some different cultures during various time periods. The practice of breastfeeding or suckling between humans and other species occurred in both directions: women sometimes breastfed young animals, and animals were used to suckle babies and children. Animals were used as substitute wet nurses for infants, particularly after the rise of syphilis increased the health risks of wet nursing. Goats and donkeys were widely used to feed abandoned babies in foundling hospitals in 18th- and 19th-century Europe. Breastfeeding animals has also been practised, whether for perceived health reasons – such as to toughen the nipples and improve the flow of milk – or for religious and cultural purposes. A wide variety of animals have been used for this purpose, including puppies, kittens, piglets and monkeys.
Breastfeeding by animals of humans
Terracotta feeding bottles surviving from the third millennium BC in Sumeria indicate that children who were not being breastfed were receiving animal milk, probably from cows. It is possible that some infants directly sucked lactating animals, which served as alternatives to wet nurses. Unless another lactating woman was available, a mother who lacked enough breast milk was likely to lose her child. To avert that possibility if a wet nurse was not available, an animal such as a donkey, cow, goat, sheep or dog could be employed. Suckling directly was preferable to milking an animal and giving the milk, as contamination by microbes during the milking process could lead to the infant contracting a deadly diarrheal disease. It was not until as late as the 1870s that stored animal milk became safe to drink due to the invention of pasteurisation and sterilisation.
The Jewish Talmud permits children to suckle animals if the child's welfare dictates it.
Mythology and stories
The suckling of infants by animals was a repeated theme in classical mythology. Most famously, twin brothers Romulus and Remus (the former founded Rome) were portrayed as having been raised by a she-wolf which suckled the infants, as depicted in the iconic image of the Capitoline Wolf. The Greek god Zeus was said to have been brought up by Amalthea, portrayed variously as a goat who suckled the god or as a nymph who brought him up on the milk of her goat. Similarly, Telephus, the son of the demigod Heracles, was suckled by a deer. Several famous ancient historical figures were claimed to have been suckled by animals; Cyrus I of Persia was said to have been suckled by a dog, while mares supposedly suckled Croesus, Xerxes and Lysimachus. In reality, though, such stories probably owed more to myth-making about such prominent figures, as they were used as evidence of their future greatness.
A 12th century novel from Al-Andalus, Hayy ibn Yaqdhan, has the title character growing up in isolation on a tropical island, fed and raised by an antelope. The story reached Europe in a Latin translation, and then in 1708 an English edition.
Stories of abandoned children being brought up by animal mothers such as she-wolves and bears were widespread in Europe from the Middle Ages and into modern times. One real-life case was that of Peter the Wild Boy, found in northern Germany in 1724. His coarse, curly hair was attributed to his being (supposedly) suckled by a bear, based on the premise that characteristics of the animal foster mother had been transmitted to him via her milk. (It is now thought he had Pitt-Hopkins syndrome, a condition unidentified until 1978.)
Perceived effect on character
The belief that animal characteristics could be transmitted via milk was widely held; the Swedish scientist Carl Linnaeus thought that being suckled by lionesses conferred great courage. Goats were thought to transmit a libidinous character and some preferred to employ donkeys as wet nurses instead, as they were thought to be more moral animals. In modern Egypt, though, donkeys were disfavoured as wet nurses as it was thought that a child suckled on donkeys' milk would acquire the animal's stupidity and obstinacy. Human milk was thought to transmit character traits as well; in 19th century France a law was proposed to ban disreputable mothers from nursing their own children so that their immoral traits would not be transmitted via their milk.
Use of goats and other animals
Goats have often been used to suckle human babies and infants. The Khoikhoi of southern Africa were reported to tie their babies to the bellies of female goats so that they could feed there. In the 18th and 19th centuries, goats were widely used in Europe as alternatives to human wet nurses, as they were easier to obtain, cheaper to use and safer, in that they were less prone to passing on diseases. This use of animals was already a well-established practice in rural France and Italy; Pierre Brouzet, the personal physician of Louis XV of France, wrote of how he had seen "some peasants who have no other nurses but ewes, and these peasants were as strong and vigorous as others." In 1816, a German writer named Conrad A. Zweirlein overheard a conversation at a fashionable resort about the problems of wet nurses and responded by writing a book called The Goat as the Best and Most Agreeable Wet Nurse, which popularised the use of the animals for many years. Zwierlein describes how a father living in a German village trained his goat to jump on a table, where he had laid his motherless child on a pillow. The goat would stand waiting until the baby drank its fill of her milk.
One important use of goats for suckling concerned the feeding and attempted cure of babies born with congenital syphilis inherited from their mothers. Liquid compounds laced with mercury were fed to nanny goats – if they refused to drink them, honey was recommended as a way of disguising the metallic taste – or were ingested into the goat's bloodstream via a deliberately inflicted wound on the animal's leg that was covered with an ointment containing mercury. The mercury would accumulate in the goats' milk and was passed into the syphilitic babies when they suckled at the goats' teats. This method did have some effect of improving the infants' mortality rates, though the goats tended to die prematurely of mercury poisoning.
Zwierlein's personal opinion was that women who are sick, dehydrated, depressed, or even in old age should not breastfeed their own babies because their milk could harm the child. He felt that even mothers who did not love their child and would rather spend time in pursuits other than tending to their baby should not breastfeed. In his experience, poor women who were paid to be wet nurses in Germany were most likely to pass venereal disease and other illnesses on to the baby, who, when returned to the care of its parents, passed the disease on to them. Zwierlein insisted that for a human baby in such circumstances, a goat's milk was preferable to a woman's. Goats, he asserted, are clean, tame, playful, friendly, social, good-natured, not easily frightened, and not prone to anger. Zwierlein also spoke of several country towns he knew of where adults and infants used goat's milk exclusively, as it was easier than cow's milk to digest.
In France, homes for foundlings (abandoned babies) often kept large numbers of goats to feed the infants, as they were considered less problematic than lower-class wet nurses. In some institutions, nurses (nannies) carried the infants to the goats; elsewhere, the goats came to the infants. Alphonse Le Roy described how goats were used at the foundling hospital in Aix-en-Provence in 1775: "The cribs are arranged in a large room in 2 ranks. Each goat which comes to feed enters bleating and goes to hunt the infant which has been given it, pushes back the covering with its horns and straddles the crib to give suck to the infant. Since that time they have raised very large numbers [of infants] in that hospital."
In 19th-century Ireland, foundlings from Dublin were "sent to the mountains of Wicklow, to feed upon the goats' milk. As the children grew older, the goats came to know them, and became very tame; so that the infant sought the goat, and was suckled by it as he would have been by a human wet nurse. These children throve remarkably well." Donkeys were preferred in England; as one writer has put it, "nothing was more picturesque than the spectacle of babies, held under the bellies of the donkeys in the stable adjoining the infants' ward, sucking contentedly the teats of the docile donkeys." Ancient Greek and Roman physicians including Galen, Aretaeus, Hipposcrates, and Alexander of Tralles believed that donkey milk was a superior treatment for human illness and an antidote for poisons. In Brittany, attempts were made around 1900 to employ sows as wet nurses but foundered due to opposition to the use of pigs for this purpose.
Breastfeeding by humans of animals
The breastfeeding by humans of animals is a practice that is widely attested historically and continues to be practised today by some cultures. The reasons for this are varied: to feed young animals, to drain a woman's breasts, to promote lactation, to harden the nipples before a baby is born, to prevent conception, and so on.
Simoons and Baldwin gathered and summarized global accounts of human-animal breastfeeding in their 1982 paper entitled, “Breast-Feeding of Animals by Women: Its Social-Cultural Context and Geographic Occurrence.” They studied the motivations of women world-wide for breast-feeding animals and categorized them in four ways: the most common situation in which women nursed animals was the affectionate breastfeeding of family pets. The second most common motivation for this practice was economic; for example, to save an animal who might otherwise die, and could be eaten or be useful to the family economy in some way. Ceremonial breastfeeding of animals was the third category, relating to rituals, sacrifice, cultural or religious customs. Nursing animals for the mother's sake, such as relieving pain from mastitis or engorged breasts, was found to be the least common motivation.
Economic reasons
Bears were also suckled by the Itelmens of the Kamchatka Peninsula of Russia but in their case for economic reasons, to benefit from the meat when the bear was grown and to obtain highly prized bear bile for use in traditional medicine. American animal trafficker Frank Buck claimed that human mothers in remote Indonesian villages would nurse to orangutan babies in hopes of keeping them alive long enough to sell to a wildlife trader.
Religious and ceremonial reasons
Religious and ceremonial reasons have also been a factor. Saint Veronica Giuliani (1660–1727), an Italian nun and mystic, was known for taking a lamb to bed with her and suckling it as a symbol of the Lamb of God. In far northern Japan, the Ainu people are noted for holding an annual bear festival at which a captured bear, raised and suckled by the women, is sacrificed.
For the mother's sake
English and German physicians between the 16th and 18th centuries recommended using puppies to "draw" the mother's breasts, and in 1799 the German Friedrich Benjamin Osiander reported that in Göttingen women suckled young dogs to dislodge nodules from their breasts. An example of the practice being used for health reasons comes from late 18th century England. When the writer Mary Wollstonecraft was dying of puerperal fever following the birth of her second daughter, the doctor ordered that puppies be applied to her breasts to draw off the milk, possibly with the intention of helping her womb to contract to expel the infected placenta that was slowly poisoning her. Mary Cooley Spencer, an American woman living in Colonia Dublan in 1911, breastfed a collie puppy while suffering from smallpox. She had a five month old daughter, who was cared for by a friend while she recovered. Nursing the puppy allowed her to maintain her milk supply until she was no longer contagious.
Animals have widely been used to toughen the nipples and maintain the mother's milk supply. In Persia and Turkey puppies were used for this purpose. The same method was practised in the United States in the early 19th century; William Potts Dewees recommended in 1825 that from the eighth month of pregnancy, expectant mothers should regularly use a puppy to harden the nipples, improve breast secretion and prevent inflammation of the breasts. The practice seems to have fallen out of favour by 1847, as Dewees suggested using a nurse or some other skilled person to carry out this task rather than an animal.
Other or undetermined reasons
Tribal peoples around the world have breastfed many types of animal. Travelers in Guyana observed native women breastfeeding a variety of animals, including monkeys, opossums, pacas, agoutis, peccaries and deer. Native Canadians and Americans often breastfed young dogs; an observer commented that the Pima people of Arizona "withdrew their breasts sooner from their own infants than from young dogs." According to Sir John Richardson, eighteenth Century Native Americans reportedly fed human breast milk to bison calves, wolves and bears. In 1875, a British surgeon named John Nisbet reportedly observed a group of Burmese women breastfeeding a royal white elephant in the Konbaung court.
In the late 16th Century, Konrad Heresbach recommended that mothers rid their bodies of their first milk, called colostrum, rather than allow their babies to drink it. The idea that colostrum was dangerous for a newborn further took hold in Europe when Thomas Newton wrote of its supposed dangers. How widely this idea was accepted is impossible to know, but it could have been an additional purpose for human-animal breastfeeding as women sought a means to discard colostrum while establishing a milk supply for their baby.
Artistic and political statements
In the present day, the act of breastfeeding animals has been used as a sometimes controversial artistic statement. The album art for Boys for Pele by Tori Amos includes a photograph of the singer breastfeeding a piglet. In Ireland, 22-year-old model and PETA member Agata Dembiecka became the focus of controversy in 2010 when a calendar issued by an animal rescue charity featured a photograph of her suckling a puppy.
| Biology and health sciences | Health and fitness: General | Health |
3826112 | https://en.wikipedia.org/wiki/Sub-brown%20dwarf | Sub-brown dwarf | A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but that has a planetary mass, therefore by definition below the limiting mass for thermonuclear fusion of deuterium (about ).
Some researchers include them in the category of rogue planets whereas others call them planetary-mass brown dwarfs.
Description
Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud (perhaps with the help of photo-erosion) but there is no consensus amongst astronomers on whether the formation process should be taken into account when classifying an object as a planet. Free-floating sub-brown dwarfs can be observationally indistinguishable from rogue planets, which originally formed around a star and were ejected from orbit. Similarly, a sub-brown dwarf formed free-floating in a star cluster may be captured into orbit around a star, making distinguishing sub-brown dwarfs and large planets also difficult. A definition for the term "sub-brown dwarf" was put forward by the IAU Working Group on Extra-Solar Planets (WGESP), which defined it as a free-floating body found in young star clusters below the lower mass cut-off of brown dwarfs.
Lower mass limit
The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 Jupiter mass (MJ). This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas. A 3 MJ candidate is described in a 2007 paper.
List of possible sub-brown dwarfs
Orbiting one or more stars
There is no consensus whether these companions of stars should be considered sub-brown dwarfs or planets. Some authors agree these objects should be considered sub-brown dwarfs, since they likely formed on their own, like a "failed star".
2MASS J0441+2301 Bb
Nonetheless, the IAU working definition of an exoplanet ignored formation mechanism as a criterion, and based on it these objects would be considered planets.
WD 0806-661 B
HD 106906 b
ROXs 42Bb
Orbiting a brown dwarf
At around 2022 the IAU working definition of an exoplanet excludes these objects as planets. The only fitting label would be as sub-brown dwarfs, but they are more often referred as planetary mass objects. Other definitions, like from the NASA Exoplanet Archive would include these as exoplanets. There is no consensus whether these companions of brown dwarfs should be considered sub-brown dwarfs or planets.
WISE J0336−0143B
WISE J0336−0143B, orbits a brown dwarf or sub-brown dwarf. The primary has a mass of 8.5 to 18 and secondary has a mass of 5-11.5 . This object does not fit the IAU working definition of an exoplanet. This definition requires a mass ratio of about q<0.04, but the mass ratio of WISE J0336−0143AB is q=0.61±0.05. It also does not fit the definition of a rogue planet, because it is gravitationally bound to a brown dwarf (or possibly sub-brown dwarf). It could be considered a planet according to alternative definitions, but according to the IAU it only fits the definition of sub-brown dwarf.
2M1207b
2M1207b orbits around a young brown dwarf with a circumstellar disk and itself is likely surrounded by a circumstellar disk. The mass ratio is well above the upper limit of q=0.04 for exoplanets according to the IAU.
Others
Other examples of planetary-mass objects orbiting brown dwarfs and with MB<13 and q>0.04:
CFHTWIR-Oph 98B, with MB= and q=
2MASS J0249-0557ABc, with Mc= and
Free-floating
Also called rogue planets:
WISE 0855–0714 3–10 MJ about 7 light years away
S Ori 52
UGPS 0722-05 10–25 MJ 13 light years away
Cha 110913-773444 5–15 MJ 163 light years away
CFBDSIR 2149−0403 4–7 MJ 130 light years away
OTS 44 11.5 MJ 550 light years away
PSO J318.5−22 6–8 MJ about 80 light years away
| Physical sciences | Stellar astronomy | Astronomy |
3827863 | https://en.wikipedia.org/wiki/Pollucite | Pollucite | Pollucite is a zeolite mineral with the formula with iron, calcium, rubidium and potassium as common substituting elements. It is important as a significant ore of caesium and sometimes rubidium. It forms a solid solution series with analcime. It crystallizes in the isometric-hexoctahedral crystal system as colorless, white, gray, or rarely pink and blue masses. Well-formed crystals are rare. It has a Mohs hardness of 6.5 and a specific gravity of 2.9, with a brittle fracture and no cleavage.
Discovery and occurrence
It was first described by August Breithaupt in 1846 for occurrences on the island of Elba, Italy. It is named for Pollux, the twin of Castor on the grounds that it is often found associated with petalite (previously known as castorite). The high caesium content was missed by the first analysis by Karl Friedrich Plattner in 1848, but after the discovery of caesium in 1860 a second analysis in 1864 was able to show the high caesium content of pollucite.
Its typical occurrence is in lithium-rich granite pegmatites in association with quartz, spodumene, petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite and microcline.
About 82% of the world's known reserves of pollucite occur near Bernic Lake in Manitoba, Canada, where they are mined for their caesium content for use in caesium formate oil drilling assistance. This ore is about 23% to 25% caesium by weight.
| Physical sciences | Silicate minerals | Earth science |
3829005 | https://en.wikipedia.org/wiki/Reddit | Reddit | Reddit () is an American social news aggregation, content rating, and forum social network. Registered users (commonly referred to as "Redditors") submit content to the site such as links, text posts, images, and videos, which are then voted up or down ("upvoted" or "downvoted") by other members. Posts are organized by subject into user-created boards called "subreddits". Submissions with more upvotes appear towards the top of their subreddit and, if they receive enough upvotes, ultimately on the site's front page. Reddit administrators moderate the communities. Moderation is also conducted by community-specific moderators, who are unpaid volunteers. It is operated by Reddit, Inc., based in San Francisco.
As of December 2024, Reddit is the 8th most-visited website in the world. According to data provided by Similarweb, 51.75% of the website traffic comes from the United States, followed by Canada at 7.01%, United Kingdom at 6.97%, Australia at 3.97%, Germany at 3% and the remaining 28.37% split among other worlds countries.
Reddit was founded by University of Virginia roommates Steve Huffman and Alexis Ohanian, as well as Aaron Swartz, in 2005. Condé Nast Publications acquired the site in October 2006. In 2011, Reddit became an independent subsidiary of Condé Nast's parent company, Advance Publications. In October 2014, Reddit raised $50 million in a funding round led by Sam Altman and including investors Marc Andreessen, Peter Thiel, Ron Conway, Snoop Dogg, and Jared Leto. Their investment valued the company at $500 million at the time. In July 2017, Reddit raised $200 million for a $1.8 billion valuation; Advance Publications remained the majority stakeholder. In February 2019, a $300 million funding round led by Tencent brought the company's valuation to $3 billion. In August 2021, a $700 million funding round led by Fidelity Investments raised that valuation to over $10 billion. The company then reportedly filed for an IPO in December 2021 with a valuation of $15 billion. Reddit debuted on the stock market on the morning of March 21, 2024, with the ticker symbol RDDT. The current market cap as of July 2024 is $10 billion. Reddit has been noted for its role in political activism, with notable left-wing and anti-theist subcultures on the website.
Reddit has received praise for many of its features, such as the ability to create several subreddits for niche communities and being a platform for raising publicity for numerous causes. As a result, it has grown to be one of the most visited websites on the Internet. It has also received criticism for the spread of misinformation and its voting system which can encourage online echo chambers. In its early years, Reddit also received controversy over hosting misogynistic content, including the doxxing of erotic models and revenge porn.
History
The idea and initial development of Reddit originated with college roommates Steve Huffman and Alexis Ohanian in 2005, who attended a lecture by programmer-entrepreneur Paul Graham in Boston during their spring break from University of Virginia. After speaking with Huffman and Ohanian following the lecture, Graham invited the two to apply to his startup incubator Y Combinator. Their initial idea, My Mobile Menu, was unsuccessful, and was intended to allow users to order food by SMS text messaging. During a brainstorming session to pitch another startup, the idea was created for what Graham called the "front page of the Internet". For that idea, Huffman and Ohanian were accepted in Y Combinator's first class. Supported by the funding from Y Combinator, Huffman coded the site in Common Lisp and together with Ohanian launched Reddit in June 2005. Embarrassed by an empty-looking site, the founders created hundreds of fake users for their posts to make it look more populated.
The team expanded to include Christopher Slowe in November 2005. Between November 2005 and January 2006, Reddit merged with Aaron Swartz's company Infogami, and Swartz became an equal owner of the resulting parent company, Not A Bug. Swartz then helped rewrite the software running Reddit using web.py, a web framework he developed. The passage from Aaron Swartz's blog post "Rewriting Reddit" reveals that the switch from Lisp to Python, specifically using the web.py framework developed by Swartz, was driven by a desire for simplicity, maintainability, and performance. Despite facing skepticism and critique from the Lisp community, the change was justified by the efficiency and clarity Python provided for the project. This initiative not only influenced the technical evolution of Reddit but also contributed to the broader web development community by inspiring other frameworks and remaining a significant part of Reddit's history. (In 2020, Ohanian claimed that rather than Swartz being a co-founder, the correct description would be that Swartz's company was acquired by Reddit 6 months after he and Huffman had started.)
Huffman and Ohanian sold Reddit to Condé Nast Publications, owner of Wired, on October 31, 2006, for a reported $10 million to $20 million and the team moved to San Francisco. In November 2006, Swartz blogged complaining about the new corporate environment, criticizing its level of productivity. In January 2007, Swartz was fired for undisclosed reasons.
Huffman and Ohanian left Reddit in 2009. Huffman went on to co-found Hipmunk with Adam Goldstein, and later recruited Ohanian and Slowe to the new company. After Huffman and Ohanian left Reddit, Erik Martin, who joined the company as a community manager in 2008 and later became general manager in 2011, played a role in Reddit's growth. VentureBeat noted that Martin was "responsible for keeping the site going" under Condé Nast's ownership. Martin facilitated the purchase of RedditGifts and led charity initiatives.
Reddit launched two different ways of advertising on the site in 2009. The company launched sponsored content and a self-serve ads platform that year. Reddit launched its Reddit Gold benefits program in July 2010, which offered new features to editors and created a new revenue stream for the business that did not rely on banner ads. On September 6, 2011, Reddit became operationally independent of Condé Nast, operating as a separate subsidiary of its parent company, Advance Publications. Reddit and other websites participated in a 12-hour sitewide blackout on January 18, 2012, in protest of the Stop Online Piracy Act. In May 2012, Reddit joined the Internet Defense League, a group formed to organize future protests.
Yishan Wong joined Reddit as CEO in 2012. Wong resigned from Reddit in 2014, citing disagreements about his proposal to move the company's offices from San Francisco to nearby Daly City, but also the "stressful and draining" nature of the position. Ohanian credited Wong with the company's newfound success as its user base grew from 35 million to 174 million. Wong oversaw the company as it raised $50 million in funding and spun off as an independent company. Also during this time, Reddit began accepting the digital currency Bitcoin for its Reddit Gold subscription service through a partnership with bitcoin payment processor Coinbase in February 2013. Ellen Pao replaced Wong as interim CEO in 2014 and resigned in 2015 amid a user revolt over the firing of a popular Reddit employee. During her tenure, Reddit initiated an anti-harassment policy, banned involuntary sexualization, and banned several forums that focused on bigoted content or harassment of individuals.
After five years away from the company, Ohanian and Huffman returned to leadership roles at Reddit: Ohanian became the full-time executive chairman in November 2014 following Wong's resignation, while Pao's departure on July 10, 2015, led to Huffman's return as the company's chief executive. After Huffman rejoined Reddit as CEO, he launched Reddit's iOS and Android apps, improved Reddit's mobile website, and created A/B testing infrastructure. The company launched a major redesign of its website in April 2018. Huffman said new users were turned off from Reddit because it had looked like a "dystopian Craigslist". Reddit also instituted several technological improvements, such as a new tool that allows users to hide posts, comments, and private messages from selected redditors in an attempt to curb online harassment, and new content guidelines. These new content guidelines were aimed at banning content inciting violence and quarantining offensive material. Slowe, the company's first employee, rejoined Reddit in 2017 as chief technology officer. Reddit's largest round of funding came in 2017 when the company raised $200 million and was valued at $1.8 billion. The funding supported Reddit's site redesign and video efforts.
On June 5, 2020, Ohanian resigned as a member of the board in response to the George Floyd protests and requested to be replaced "by a Black candidate". Michael Seibel, then-CEO of Y Combinator, was subsequently named to the board.
On December 13, 2020, Reddit announced it had acquired short-form video social platform Dubsmash, hiring its entire team, with the intention of integrating its video creation tools into Reddit. On March 5, 2021, Reddit announced that it had appointed Drew Vollero, who had worked at Snapchat's parent company Snap (SNAP), as its first Chief Financial Officer weeks after the site was thrust into the spotlight due to its role in the GameStop trading frenzy. Vollero's appointment spurred speculation of an initial public offering, a move that senior leaders have considered publicly.
In December 2021, Reddit revealed that it had confidentially filed for an initial public offering with the U.S. Securities and Exchange Commission. In June 2022, Reddit acquired MeaningCloud, a natural language processing company. In September 2022, Reddit acquired Spiketrap for an undisclosed sum. In April 2023, Fidelity, the lead investor in Reddit's funding round in 2021, devalued its investment in Reddit by 41% cumulatively. It was revealed in a monthly disclosure that Fidelity valued its stake at $16.6 million, down from its initial investment of $28.2 million which had valued the company at $10 billion. That was followed by an announcement in June 2023 of plans to layoff 5% of Reddit's workforce and to reduce the number of planned hires for the year. In June 2023, The BlackCat hacker gang claimed responsibility for a February 2023 breach of Reddit's systems. On its data leak site, it claimed that it stole 80 GB of compressed data and demanded a $4.5 million ransom from Reddit. This attack did not involve data encryption like typical ransomware campaigns.
In February 2024, Reddit announced a partnership with Google in a deal worth about $60million per year, to license its real-time user content to train Google's AI model. The partnership also lets Reddit get access to Google's "Vertex AI" service which would help improve search results on Reddit. In March 2024 it was announced that Reddit would target a valuation of up to $6.4 billion in its U.S. IPO. The platform intends to sell 22 million class A common shares at a price between $31 and $34 alongside some of its investors, looking to raise up to $748 million.
Reddit's initial public offering opened on March 20, 2024, at $34 per share and a $6.4 billion valuation. They went public the next day on the New York Stock Exchange at $47 per share and rose to $50.44 at market close on their first day of trading, reaching a market cap of $9.5 billion. On May 16, 2024, it was announced that Reddit and OpenAI had reached a deal that will allow OpenAI access to the Reddit API to train its models, while Reddit will receive certain AI tools for moderators and users.
Reddit's share price increased by 42% after reporting its third-quarter results in October 2024, where it recorded its first quarterly profit. The surge was also attributed in part to increases in revenue from AI content licensing and advertising, and reaching close to 100 million active users. In December 2024, Reddit announced Reddit Answers, an AI search tool that summarizes conversations in response to a question from the user.
Site overview
Reddit is a website comprising user-generated content—including photos, videos, links, and text-based posts—and discussions of this content in what is essentially a bulletin board system. The name "Reddit" is a play-on-words with the phrase "read it", i.e., "I read it on Reddit." According to Reddit, in 2019, there were approximately 430 million monthly users, who are known as "redditors". The site's content is divided into categories or communities known on-site as "subreddits", of which there are more than 138,000 active communities.
As a network of communities, Reddit's core content consists of posts from its users. Users can comment on others' posts to continue the conversation. A key feature to Reddit is that users can cast positive or negative votes, called upvotes and downvotes respectively, for each post and comment on the site. The number of upvotes or downvotes determines the posts' visibility on the site, so the most popular content is displayed to the most people. Users can also earn "karma" for their posts and comments, a status that reflects their standing within the community and their contributions to Reddit. Posts are sometimes automatically archived after six months, meaning they can no longer be commented or voted on.
The most popular posts from the site's numerous subreddits are visible on the front page to those who browse the site without an account. By default for those users, the front page will display the subreddit r/popular, featuring top-ranked posts across all of Reddit, excluding not-safe-for-work communities and others that are most commonly filtered out by users (even if they are safe for work). The subreddit r/all originally did not filter topics, but as of 2021 it does not include not-safe-for-work content. Registered users who subscribe to subreddits see the top content from the subreddits to which they subscribe on their personal front pages. Additionally, some subreddits have a karma and account age requirement to discourage bots and spammers from posting.
Front-page rank—for both the general front page and for individual subreddits—is determined by a combination of factors, including the age of the submission, positive ("upvoted") to negative ("downvoted") feedback ratio, and the total vote-count.
Users and moderators
Registering an account with Reddit is free and requires an email address. In addition to commenting and voting, registered users can also create their own subreddit on a topic of their choosing. In Reddit style, usernames begin with "u/". Noteworthy redditors include u/Poem_for_your_sprog, who responds to messages across Reddit in verse, u/Shitty_Watercolour who posts paintings in response to posts, and u/spez, the CEO of Reddit (Steve Huffman).
Subreddits are overseen by moderators, Reddit users who earn the title by creating a subreddit or being promoted by a current moderator. Reddit users may also request to moderate a sub that has no moderators or very inactive ones in r/redditrequest. These requests are reviewed by the Reddit admins. Moderators are volunteers who manage their communities, set and enforce community-specific rules, remove posts and comments that violate these rules, and generally work to keep discussions in their subreddit on topic. Admins, by contrast, are paid to work for Reddit.
Reddit also releases transparency reports annually which have information like how many posts have been taken down by moderators and for what reason. It also details information about requests law enforcement agencies have made for information about users or to take down content. In 2020, Reddit removed 6% of posts made on the platform (approx. 233 million). More than 99% of removals were marked as spam; the remainder made up of a mix of other offensive content. Around 131 million posts were removed by the automated moderator and the rest were taken down manually.
It is estimated that Reddit's moderators work 466 hours every day, which is $3.4 million in unpaid work each year. That roughly equates to 2.8% of the company's annual revenue.
Subreddits
Subreddits (officially called communities) are user-created areas of interest where discussions on Reddit are organized. There are about 138,000 active subreddits (among a total of 1.2 million) . Subreddit names begin with "r/"; for instance, "r/science" is a community devoted to discussing scientific publications, while "r/gaming" is a community devoted to discussing video games, and "r/worldnews" is for posting news articles from around the world.
In a 2014 interview with Memeburn, Erik Martin, then the general manager of Reddit, remarked that their "approach is to give the community moderators or curators as much control as possible so that they can shape and cultivate the type of communities they want". Subreddits often use themed variants of Reddit's alien mascot, Snoo, in the visual styling of their communities.
Other features
Reddit Premium (formerly Reddit Gold) is a premium membership that allows users to view the site ad-free. Until 2023, subscribers could also use coins to award posts or comments they valued, generally due to humorous or high-quality content. Reddit Premium unlocks several features not accessible to regular users, such as comment highlighting, exclusive subreddits such as r/lounge, a personalized Snoo (known as a "snoovatar"), and a Reddit premium trophy that can be displayed on the user's profile. Reddit Gold was renamed to Reddit Premium in 2018. In addition to gold coins, users were able to gift silver and platinum coins to other users as rewards for quality content.
On the site, redditors commemorate their "cake day" once a year, on the anniversary of the day their account was created. Cake day adds an icon of a small slice of cake next to the user's name for 24 hours. In August 2021, the company introduced a TikTok-like short-form video feature for iOS that lets users rapidly swipe through a feed of short video content. In December 2021, the company introduced a Spotify Wrapped-like feature called Reddit Recap that recaps various statistics from January 1 to November 30 about each individual user, such as how much time they spent on Reddit, which communities they joined, and the topics that they engaged with, and allows the user to view it.
On July 7, 2022, Reddit announced 'blockchain-backed Collectible Avatars', customizable avatars which are available on the subreddit r/CollectibleAvatars for purchase separate from Reddit Premium. The avatars were created by independent artists who post work on other subreddits, and who receive a portion of the profits. They use Reddit's Polygon blockchain-powered digital wallet the Vault. Richard Lawler of The Verge described them as "non-fungible tokens (NFTs) that are available for purchase in the Reddit Avatar Builder".
Chat features
In 2017, Reddit developed its own real-time chat software for the site. While some established subreddits have used third-party software to chat about their communities, the company built chat functions that it hopes will become an integral part of Reddit. Individual chat rooms were rolled out in 2017 and community chat rooms for members of a given subreddit were rolled out in 2018.
Reddit Talk was announced in April 2021 as a competitor to Clubhouse. Reddit Talk lets subreddit moderators start audio meeting rooms that mimic Clubhouse in design. In 2022, Reddit Talk was updated to support recording audio rooms and work on the web version of Reddit. A desktop app is reportedly slated for a late February release.
Discontinued features
Reddit Public Access Network, commonly known as RPAN, was a live streaming service run by Reddit. Viewers interacted with streams by upvoting or downvoting, chatting, and giving paid awards. During the off-air hours, 24/7 streaming was possible to the dedicated subreddits, but with limited slots and capabilities. On August 19, 2019, Reddit announced RPAN. It was said to be in testing, but they were experimenting with making it a permanent program, as well as a way to increase revenue for the platform. Later, a five-day testing period began. During the testing period, streaming was for a select group of users, allowing 30 minutes of streaming per person and 100 slots. On July 1, 2020, RPAN Studio was released, an application that allows users to broadcast live from desktop computers. RPAN Studio has been built on top of OBS, an open-source streaming and recording program. On January 28, 2021, Reddit permanently increased streaming times to three hours. RPAN was officially discontinued on November 15, 2022.
In 2019, Reddit tested a new feature that allowed users to tip others. It was only made available for a user named Chris who goes by the alias u/shittymorph, who was known for posting well-written comments, only for them to end with the same copypasta referencing the 1998 Hell in a Cell match between wrestlers The Undertaker and Mankind.
Technology and design
Underlying code
Reddit was originally written in Common Lisp but was rewritten in Python in December 2005 for wider access to code libraries and greater development flexibility. The Python web framework that Swartz developed to run the site, web.py, is available as an open source project. , Reddit used Pylons as its web framework. Reddit was an open source project from June 18, 2008, until 2017. During that time, all of the code and libraries written for Reddit were freely available on GitHub, with the exception of the anti-spam/cheating portions. In a September 2017 announcement, the company stated that "we've been doing a bad job of keeping our open-source product repos up to date", partially because "open-source makes it hard for us to develop some features 'in the clear'... without leaking our plans too far in advance", prompting the decision to archive its public GitHub repos.
Hosting and servers
, Reddit decommissioned its servers which it owned and migrated to Amazon Web Services, using EC2 for application services and S3 for storage. Reddit uses PostgreSQL as its primary datastore. As part of an effort to be more data-driven, Reddit built a data analytics pipeline on top of Apache Kafka and Hive as its data warehouse. It uses Amazon's Elastic MapReduce to run Hadoop workloads across Hive and stores results in S3, eventually putting data in Amazon RDS for visualization purposes. It also uses HAProxy for load balancing and Jenkins and Apache Pig in the data pipeline. Reddit uses Redis and its implementation of HyperLogLog to cache approximate page views with an underlying Apache Cassandra cluster for persistence. For general caching of queries and memoization, Reddit uses memcached behind Facebook's memcached router, mcrouter. In 2017, it had almost 3.3 terabytes of memory on 54 EC2 instances dedicated to caching split across different pools. Services at Reddit are structured around a common foundation named Baseplate. It was originally implemented in Python, but since 2019, parts of it have been reimplemented in Go for better performance. Reddit also runs its services through Kubernetes and uses Spinnaker for continuous delivery.
In early 2009, Reddit started using jQuery. In 2017, Reddit announced it adopted TypeScript for its UI redesign. Reddit's search function has had many iterations and currently uses Lucidworks Fusion to implementation.
Mobile apps
In 2010, Reddit released its first mobile web interface for easier reading and navigating the website on touch screen devices. For several years, redditors relied on third-party apps to access Reddit on mobile devices. In October 2014, Reddit acquired one of them, Alien Blue, which became the official iOS Reddit app. Reddit removed Alien Blue and released its official application, Reddit: The Official App, on Google Play and the iOS App Store in April 2016. The company released an app for Reddit's question-and-answer Ask Me Anything subreddit in 2014. The app allowed users to see active Ask Me Anythings, receive notifications, ask questions and vote.
Product and design changes
The site has undergone several products and design changes since it originally launched in 2005. When it initially launched, there were no comments or subreddits. Comments were added in 2005 and interest-based groups (called 'subreddits') were introduced in 2008. Allowing users to create subreddits has led to much of the activity that redditors would recognize that helped define Reddit. These include subreddits "WTF", "funny", and "AskReddit". Reddit rolled out its multireddit feature, the site's biggest change to its front page in years, in 2013. With the multireddits, users see top stories from a collection of subreddits.
In 2015, Reddit enabled embedding and as a result users could share Reddit content on other sites. In 2016, Reddit began hosting images using a new image uploading tool, a move that shifted away from the uploading service Imgur that had been the de facto service. Users still can upload images to Reddit using Imgur. Reddit's in-house video uploading service for desktop and mobile launched in 2017. Previously, users had to use third-party video uploading services, which Reddit acknowledged was time-consuming for users.
Reddit released its "spoiler tags" feature in January 2017. The feature warns users of potential spoilers in posts and pixelates preview images. Reddit unveiled changes to its public front page, called r/popular, in 2017; the change creates a front page free of potentially adult-oriented content for unregistered users. In late 2017, Reddit declared it wanted to be a mobile-first site, launching several changes to its apps for iOS and Android. The new features included user-to-user chat, a theater mode for viewing visual content, and mobile tools for the site's moderators. "Mod mode" lets moderators manage content and their subreddits on mobile devices.
Reddit launched its redesigned website in 2018, with its first major visual update in a decade. Development for the new site took more than a year. It was the result of an initiative by Huffman upon returning to Reddit, who said the site's outdated look deterred new users. The new site features a hamburger menu to help users navigate the site, different views, and new fonts to better inform redditors if they are clicking on a Reddit post or an external link. The nominal goal was not only for Reddit to improve its appearance, but also to make it easier to accommodate a new generation of Reddit users. Additionally Reddit's growth had strained the site's back end; Huffman and Reddit Vice President of Engineering Nick Caldwell told The Wall Street Journals COI Journal that Reddit needed to leverage artificial intelligence and other modern digital tools. For years, registered users could opt-out of the redesign by using the old.reddit.com domain. On May 15, 2024, the dedicated login flow was removed from the old domain, although site admins said they had "no plans" to remove the old domain entirely.
In November 2023, Fast Company reported that Reddit began rolling out a comprehensive rebrand, including a new logo, typeface, brand colors, and an updated version of its mascot Snoo, as part of its preparation for a potential 2024 IPO and in response to its expanding user base and global reach.
Logo
Reddit's logo consists of a time-traveling alien named Snoo and the company name stylized as "reddit". The alien has an oval head, pom-pom ears, and an antenna. Its colors are black, white, and orange-red. The mascot was created in 2005 while company co-founder Alexis Ohanian was an undergraduate at the University of Virginia. Ohanian drew a doodle of the creature while he was bored during a marketing class. Originally, Ohanian sought to name the mascot S'new, a play on "What's new?", to tie the mascot into Reddit's premise as the "front page of the Internet". Eventually, the name Snoo was chosen. In 2011, Ohanian outlined the logo's evolution with a graphic that showcased several early versions, including various spellings of the website name, such as "Reditt".
Snoo is genderless, so the logo is moldable. Over the years, the Reddit logo has frequently changed for holidays and other special events. Many subreddits have a customized Snoo logo to represent the subreddit. Redditors can also submit their own logos, which sometimes appear on the site's front page, or create their own customized versions of Snoo for their communities (or "subreddits"). When Reddit revamped its website in April 2018, the company imposed several restrictions on how Snoo can be designed: Snoo's head "should always appear blank or neutral", Snoo's eyes are orange-red, and Snoo cannot have fingers. Snoo's purpose is to discover and explore humanity.
Corporate affairs
Reddit is a public company based in San Francisco. In 2023, it downsized from an office in the Mid-Market neighborhood to an office in the South of Market neighborhood. Reddit doubled its headcount in 2017; , it employed approximately 350 people. In 2017, the company was valued at $1.8 billion during a $200 million round of new venture funding. The company was previously owned by Condé Nast, but was spun off as an independent company. , Advance Publications, Condé Nast's parent company, retained a majority stake in Reddit.
Reddit's key management personnel includes co-founder and CEO Steve Huffman, Chief Technology Officer Chris Slowe, who was the company's original lead engineer, and Chief Operating Officer Jen Wong, a former president of digital and chief operating officer at Time Inc. Reddit does not disclose its revenue figures. The company generates revenue in part through advertising and premium memberships that remove ads from the site. As part of its company culture, Reddit operates on a no-negotiation policy for employee salaries. The company offers new mothers, fathers, and adoptive parents up to 16 weeks of parental leave.
, Reddit is valued at more than $10 billion following a $410 million funding round. The company was looking to hire investment bankers and lawyers to assist in making an initial public offering. However, CEO Steve Huffman said the company has not decided on the timing for when to go public. In December 2021, Reddit announced they had filed a draft registration statement with the SEC regarding their prospective IPO. Reddit finally made its debut on the stock market on March 21, 2024.
Advertising
In February 2013, Betabeat published a post that recognized the influx of multinational corporations like Costco, Taco Bell, Subaru, and McDonald's posting branded content on Reddit that was made to appear as if it was original content from legitimate Reddit users. PAN Communications wrote that marketers want to "infiltrate the reddit community on behalf of their brand," but emphasized that "self-promotion is frowned upon" and Reddit's former director of communications noted that the site is "100 percent organic." She recommended that advertisers design promotions that "spark conversations and feedback." She recommended that businesses use AMAs to get attention for public figures but cautioned "It is important to approach AMAs carefully and be aware that this may not be a fit for every project or client." Nissan ran a successful branded content promotion offering users free gifts to publicize a new car, though the company was later ridiculed for suspected astroturfing when the CEO only answered puff piece questions on the site. Taylor described these situations as "high risk" noting: "We try hard to educate people that they have to treat questions that may seem irreverent or out of left field the same as they would questions about the specific project they are promoting."
Reddit's users tend to be more privacy-conscious than on other websites, often using tools like ad-blocking software and proxies, and they dislike "feeling manipulated by brands" but respond well to "content that begs for intelligent viewers and participants." Lauren Orsini writes in ReadWrite that "Reddit's huge community is the perfect hype machine for promoting a new movie, a product release, or a lagging political campaign" but there is a "very specific set of etiquette. Redditors don't want to advertise for you, they want to talk to you." Journalists have used the site as a basis for stories, though they are advised by the site's policies to respect that "reddit's communities belong to their members" and to seek proper attribution for people's contributions.
Reddit announced that they would begin using VigLink to redirect affiliate links in June 2016. Since 2017, Reddit has partnered with companies to host sponsored AMAs and other interactive events, increased advertising offerings, and introduced efforts to work with content publishers.
In 2018, Reddit hired Jen Wong as COO, responsible for the company's business strategy and growth, and introduced native mobile ads. Reddit opened a Chicago office to be closer to major companies and advertising agencies located in and around Chicago. In 2019, Reddit hired former Twitter ad director Shariq Rizvi as its vice president of ad products and engineering.
Community and culture
The website is known for its open nature and diverse user community that generate its content. Its demographics allows for wide-ranging subject areas, as well as the ability for smaller subreddits to serve more niche purposes. The possibilities that subreddits provide create new opportunities for raising attention and fostering discussion across various areas. In gaining popularity in terms of unique users per day, Reddit has been a platform to raise publicity for a number of causes. Additionally, the user base of Reddit has given birth to other websites, including image sharing community and image host Imgur, which started in 2009 as a gift to Reddit's community. In its first five months, it jumped from a thousand hits per day to a million total page views. Data collected by Pew Research Center in 2013 found that Reddit users were much more likely to be from urban communities than rural ones. Women were greatly under-represented on the website. Reddit's userbase had a disproportionately high number of Hispanic users. With regards to education, high school dropouts were over-represented among Reddit users.
Reddit has been noted for its role in political activism, with notable left-wing and anti-theist subcultures on the website.nStatistics from Google Ad Planner suggest that 74% of Reddit users are male. In 2016, the Pew Research Center published research showing that 4% of U.S. adults use Reddit, of which 67% are men, while 78% of users get news from Reddit. Users tend to be significantly younger than average with less than 1% of users being 65 or over. Politically, 43% of Reddit users surveyed by Pew Research Center in 2016 identified as liberal, with 38% identifying as moderate and 19% as conservative.
Reddit is known in part for its passionate user base, which has been described as "offbeat, quirky, and anti-establishment". Similar to the "Slashdot effect", the Reddit effect occurs when a smaller website crashes due to a high influx of traffic after being linked to on Reddit; this is also called the Reddit "hug of death".
Philanthropy
Users have used Reddit as a platform for their charitable and philanthropic efforts. Redditors raised more than $100,000 for charity in support of comedians Jon Stewart's and Stephen Colbert's Rally to Restore Sanity and/or Fear; more than $180,000 for Haiti earthquake relief efforts; and delivered food pantries' Amazon wish lists. In 2010, Christians, Muslims, and atheists held a friendly fundraising competition, where the groups raised more than $50,000. A similar donation drive in 2011 saw the atheism subreddit raise over $200,000 for charity. In February 2014, Reddit announced it would donate 10% of its annual ad revenue to non-profits voted upon by its users. As a result of the campaign, Reddit donated $82,765 each to Electronic Frontier Foundation, Planned Parenthood Federation of America, Doctors Without Borders, Erowid Center, Wikimedia Foundation, Multidisciplinary Association for Psychedelic Studies, NPR, Free Software Foundation, Freedom From Religion Foundation, and Tor Project.
Activism
Reddit has been used for a wide variety of political engagement including the presidential campaigns of Barack Obama, Donald Trump, Hillary Clinton, and Bernie Sanders. It has also been used for self-organizing sociopolitical activism such as protests, communication with politicians and active communities. Reddit has become a popular place for worldwide political discussions.
March for Science
The March for Science originated from a discussion on Reddit over the deletion of all references to climate change from the White House website, about which a user commented that "There needs to be a Scientists' March on Washington". On April 22, 2017, more than 1 million scientists and supporters participated in more than 600 events in 66 countries across the globe.
Internet privacy, neutrality and anonymity
Reddit users have been engaged in the defense of Internet privacy, net neutrality and Internet anonymity.
Reddit created an Internet blackout day and was joined by Wikipedia and other sites in 2012 in protest of the Stop Online Piracy and Protect IP acts. On January 18, Reddit participated in a 12-hour sitewide blackout to coincide with a congressional committee hearing on the measures. During that time, Reddit displayed a message on the legislation's effects on Reddit, in addition to resources on the proposed laws. In May 2012, Reddit joined the Internet Defense League, a group formed to organize future protests.
The site and its users protested the Federal Communications Commission as it prepared to scrap net neutrality rules. In 2017, users upvoted "Battle for the Net" posts enough times that they filled up the entire front page. On another day, the front page was overtaken by posts showcasing campaign donations received by members of Congress from the telecommunications industry. Reddit CEO Steve Huffman has also advocated for net neutrality rules. In 2017, Huffman told The New York Times that without net neutrality protections, "you give internet service providers the ability to choose winners and losers". On Reddit, Huffman urged redditors to express support for net neutrality and contact their elected representatives in Washington, D.C. Huffman said that the repeal of net neutrality rules stifles competition. He said he and Reddit would continue to advocate for net neutrality.
"Restoring Truthiness" campaign
As a response to Glenn Beck's August 28, 2010, Restoring Honor rally, in September 2010 Reddit users started a movement to persuade satirist Stephen Colbert to have a counter-rally in Washington, D.C. The movement, which came to be called "Restoring Truthiness", was started by user mrsammercer, in a post where he described waking up from a dream in which Stephen Colbert was holding a satirical rally in D.C. Over $100,000 was raised for charity to gain the attention of Colbert. The campaign was mentioned on-air several times, and when the Rally to Restore Sanity and/or Fear was held in Washington, D.C., on October 30, 2010, thousands of redditors made the journey.
During a post-rally press conference, Reddit co-founder Ohanian asked, "What role did the Internet campaign play in convincing you to hold this rally?" Jon Stewart responded by saying that, though it was a very nice gesture, he and Colbert had already thought of the idea and the deposit for using the National Mall was already paid during the summer, so it acted mostly as a "validation of what we were thinking about attempting". In a message to the Reddit community, Colbert later added, "I have no doubt that your efforts to organize and the joy you clearly brought to your part of the story contributed greatly to the turnout and success."
Censorship of Reddit
Reddit has been blocked in multiple countries due to Internet censorship performed by the governments of some countries. As of October 2023, Reddit is blocked in Indonesia, China, North Korea, Turkey, and partially blocked in Bangladesh. Reddit was blocked in Russia in 2015 and later unblocked.
China
In June 2015, Reddit was blocked in China for a few weeks.
India
ISPs in India were found to be blocking traffic over Reddit for intermittent periods in some regions in 2019.
Indonesia
Since May 2014, Reddit has been blocked in Indonesia by the Ministry of Communication and Information Technology for hosting content containing nudity.
Russia
In August 2015, the Federal Drug Control Service of Russia determined that Reddit was promoting conversations about psychedelic drugs. The Roskomnadzor banned the website, citing advice on how to grow magic mushrooms as the reason. The Russian government had asked Reddit before to remove drug-related posts to no response. The site was later unblocked.
Community traditions
April Fools' Day
Over the years, Reddit has done multiple pranks and events for April Fools' Day. Since 2013, they have often taken the form of massive social experiments. Noteworthy events include The Button in 2015, which included a global "button" that could only be clicked once per user. It attracted more than a million clicks.
2017's experiment r/place involved making a collaborative pixel art. Millions of users worked together in communities to place pixels one at a time to create a larger canvas. This experiment was very successful and repeated in 2022's April Fools experiment and in 2023.
AMAs ("Ask Me Anything")
AMAs, or "Ask Me Anything" interviews, are among Reddit's most popular features. , r/IAmA, which is the most popular community for AMAs, was the eighth most popular subreddit on the site with 17.7 million subscribers. During an AMA on r/IAmA and other subreddits, users can ask questions to interviewees. Notable participants include former-United States President Barack Obama (while campaigning for the 2012 election), Bill Gates (multiple times), and Donald Trump (also while campaigning). AMAs have featured CEO Steve Huffman, as well as figures from entertainment industries around the world (including Priyanka Chopra and George Clooney), literature (Margaret Atwood), space (Buzz Aldrin), privacy (Edward Snowden), fictional characters (including Borat and Cookie Monster) and others, such as experts who answered questions about the transgender community. The Atlantic wrote that an AMA "imports the aspirational norms of honesty and authenticity from pseudonymous Internet forums into a public venue". On May 24, 2024, Reddit introduced dedicated platform features for hosting AMAs, allowing hosts to schedule and promote them, and participants to RSVP to them.
RedditGifts
RedditGifts was a program that offers gift exchanges throughout the year. The fan-made RedditGifts site was created in 2009 for a Secret Santa exchange among Reddit users, which has since become the world's largest and set a Guinness World record. In 2009, 4,500 redditors participated. For the 2010 holiday season, 92 countries were involved in the secret Santa program. There were 17,543 participants, and $662,907.60 was collectively spent on gift purchases and shipping costs. In 2014, about 200,000 users from 188 countries participated. Several celebrities have participated in the program, including Bill Gates, Alyssa Milano, and Snoop Dogg. Eventually, the secret Santa program expanded to various other occasions through RedditGifts, which Reddit acquired in 2011.
On June 9, 2021, Reddit announced the shutdown of Reddit Gifts, effective at the conclusion of the 2021 Secret Santa exchange; new account registration was disabled when the announcement was issued.
Global Reddit Meetup Day
The online Reddit community conducts real-world meetups across the globe each summer. These in-person meetups are called Global Reddit Meetup Day.
Brigading
As with most public online forums, Reddit is vulnerable to the use of disruptive or manipulative practices by its members, from sources such as troll farms, click farms and astroturfing.
Another example is brigading, notable in the case of Reddit as it is often cited as the origin of the practice and use of the word in this context. Though all of these examples are in some form, against the rules of Reddit's content policy, at least in the case of brigading, they are not always malicious in intent. A notable example is the case of "Mr. Splashy Pants", when organized brigading of another website, by redditors, appears to have been tacitly encouraged by the Reddit administration. In the aftermath, the target of this vote brigading appeared to take it in good humor.
Mister Splashy Pants
Reddit communities occasionally coordinate Reddit-external projects such as skewing polls on other websites, like the 2007 incident when Greenpeace allowed web users to decide the name of a humpback whale it was tracking. Reddit users voted en masse to name the whale "Mister Splashy Pants", and Reddit administrators encouraged the prank by changing the site logo to a whale during the voting. In December of that year, Mister Splashy Pants was announced as the winner of the competition.
Controversies
In general, the website grants subreddit moderators discretion in deciding what content is and is not allowed on their subreddits, so long as site-wide rules are not being violated. This relative freedom has allowed for a wide diversity of subreddits to exist, and some of them have attracted controversy.
Many of the default subreddits are highly moderated, with the "science" subreddit banning climate change denialism, and the "news" subreddit banning opinion pieces and columns. Reddit has changed its site-wide editorial policies several times, sometimes in reaction to controversies. Reddit has historically been a platform for objectionable but legal content, and in 2011, news media covered the way that jailbait was being shared on the site before the site changed their policies to explicitly ban "suggestive or sexual content featuring minors". Following some controversial incidents of Internet vigilantism, Reddit introduced a strict rule against the online publication of non-public personally-identifying information (a common internet harassment tool colloquially known as doxxing) via the site. Those who break the rule are subject to a site-wide ban, which can result in the deletion of their user-generated content.
Due to Reddit's decentralized moderation, user anonymity, and lack of fact-checking systems, the platform is highly prone to spreading misinformation and disinformation. It has been suggested that those who use Reddit should exercise caution in taking user-created unsourced content as fact. Concerns have been raised in particular about dangerous medical misinformation on the platform. A 2022 study of 300 comments and posts discussing urinary tract infections found that fewer than 1% cited a source for their content, and several contained harmful medical misinformation that may dissuade readers from seeking medical care or lead to dangerous self-medication, such as proposing fasting as a cure for UTIs.
Reddit communities exhibit the echo chamber effect, in which repeated unsourced statements come to be accepted among the community as fact, leading to distorted worldviews among users. It has been suggested that since 2019, Russian state-sponsored troll accounts and bots have engaged in a broad campaign to take over subreddits, such as r/antiwar.
2013 Boston bombing suspect misidentifications
After the Boston Marathon bombing in April 2013, Reddit faced criticism after users wrongly identified a number of people as suspects in the Subreddit r/FindBostonBombers. Notable among misidentified bombing suspects was Sunil Tripathi, a student reported missing before the bombings took place. A body reported to be Sunil's was found in Providence River in Rhode Island on April 25, according to Rhode Island Health Department. The cause of death was not immediately known, but authorities said they did not suspect foul play. The family later confirmed Tripathi's death was a result of suicide. Reddit general manager Erik Martin later issued an apology for this behavior, criticizing the "online witch hunts and dangerous speculation" that took place on the website. The incident was later referenced in the season 5 episode of the CBS TV series The Good Wife titled "Whack-a-Mole", as well as The Newsroom.
2014 celebrity photo hacks
In August, private sexual photos from the celebrity photo hack were widely disseminated across the site. A dedicated subreddit, "TheFappening", was created for this purpose, and contained links to most if not all of the criminally obtained explicit images. Some images of McKayla Maroney and Liz Lee were identified by redditors and outside commentators as child pornography because the photos were taken when the women were underage. The subreddit was banned on September 6. The scandal led to wider criticisms concerning the website's administration from The Verge and The Daily Dot.
2015 CEO change and subreddit bannings
After Ellen Pao became CEO in 2014, she was initially a target of criticism by users who objected to the deletion of content critical of herself and her husband. Later on June 10, 2015, Reddit shut down the 150,000-subscriber "fatpeoplehate" subreddit and four others citing issues related to harassment. This move was seen as very controversial; some commenters said that the bans went too far, while others said that the bans did not go far enough. One of the latter complaints concerned a subreddit that was "expressing support" for the perpetrator of the Charleston church shooting. Responding to the accusations of "skewed enforcement", Reddit reaffirmed their commitment to free expression and stated, "There are some subreddits with very little viewership that get highlighted repeatedly for their content, but those are a tiny fraction of the content on the site."
On July 2, Reddit began experiencing a series of blackouts as moderators set popular subreddit communities to private, in an event dubbed "AMAgeddon", a portmanteau of AMA ("ask me anything") and Armageddon. This was done in protest of the recent firing of Victoria Taylor, an administrator who helped organize citizen-led interviews with famous people on the popular AMA subreddit. Organizers of the blackout also expressed resentment about the recent severance of the communication between Reddit and the moderators of subreddits. The blackout intensified on July 3 when former community manager David Croach gave an AMA about being fired. Before deleting his posts, he stated that Ellen Pao dismissed him with one year of health coverage when he had cancer and did not recover quickly enough. Following this, a Change.org petition to remove Pao as CEO of Reddit Inc. reached over 200,000 signatures. Pao posted a response on July 3 as well as an extended version of it on July 6 in which she apologized for bad communication and not delivering on promises. She also apologized on behalf of the other administrators and noted that problems already existed over the past several years. On July 10, Pao resigned as CEO and was replaced by former CEO and co-founder Steve Huffman.
In August, Steve Huffman introduced a policy which led to the banning of several offensive and sexual communities. Included in the ban was lolicon, to which Huffman referred as "animated CP [child porn]". Some subreddits had also been "quarantined" due to having "highly-offensive or upsetting content" such as r/European, r/swedenyes, r/drawpeople, r/kiketown, r/blackfathers, r/greatapes, and r/whitesarecriminals.
2023 API changes
In April 2023, Reddit announced its intentions to charge large fees for its application programming interface (API), a feature of the site that has existed for free since 2008, causing an ongoing dispute. The move forced multiple third-party applications to shut down and threatened accessibility applications and moderation tools.
On May 31, Apollo developer Christian Selig stated that Reddit's pricing would force him to cease development on the app. The resulting outcry from the Reddit community ultimately led to a planned protest from June 12 to 14 in which moderators for the site would make their communities private or restricted posting. Following the release of an internal memo from Reddit CEO Steve Huffman and defiance from Reddit, some moderators have continued their protest.
Alternate forms of protest have emerged in the days following the initial blackout. Upon reopening, users of r/pics, r/gifs, and r/aww voted to exclusively post about comedian John Oliver. Multiple subreddits labeled themselves as not safe for work (NSFW), affecting advertisements and resulting in administrators removing the entire moderation team of some subreddits. The protest has been compared to a strike.
/r/place had its third launch on July 20, 2023; however, the launch was heavily protested by users and developers due to the event following the 2023 Reddit API controversy; Reddit CEO Steve Huffman's decision to make it prohibitively expensive for third-party app developers drew widespread condemnation.
Other controversies
2014
On December 18, Reddit took a criticized action of banning a subreddit, "SonyGOP", that was being used to distribute hacked Sony files.
2016
In May, Steve Huffman said in an interview at the TNW Conference that, unlike Facebook, which "only knows what [its users are] willing to declare publicly", Reddit knows its users' "dark secrets" at the same time that the website's "values" page was updated regarding its "privacy" section. The video reached the top of the website's main feed. Shortly thereafter, announcements concerning new advertisement content drew criticism on the website. In September, a user named "mormondocuments" released thousands of administrative documents belonging to the Church of Jesus Christ of Latter-day Saints, an action driven by the ex-Mormon and atheist communities on Reddit. Previously, on April 22, the same user had announced his plans to do so. Church officials commented that the documents did not contain anything confidential.
On November 23, Huffman admitted to having replaced his username with the names of r/The_Donald moderators in many insulting comments. He did so by changing insulting comments made towards him and made it appear as if the insult were directed at the moderators of r/The_Donald. On November 24, The Washington Post reported Reddit had banned the "Pizzagate" conspiracy board from their site, stating it violated their policy of posting personal information of others, triggering a wave of criticism from users on r/The_Donald, who felt the ban amounted to censorship. After the forum was banned from Reddit, the words "we don't want witchhunts on our site" now appears on the former page of the Pizzagate subreddit.
On November 30, Huffman announced changes to the algorithm of Reddit's r/all page to block "stickied" posts from a number of subreddits, such as r/The_Donald. In the announcement, he also apologized for personally editing posts by users from r/The_Donald, and declared intentions to take actions against "hundreds of the most toxic users" of Reddit and "communities whose users continually cross the line".
2017
In February, Reddit banned the alt-right subreddit r/altright for violating its terms of service, more specifically for attempting to share private information about the man who attacked alt-right figure Richard B. Spencer. The forum's users and moderators accused Reddit administrators of having political motivations for the ban.
2018
In March, it was revealed that Huffman had hidden Russian troll activity from users.
On July 12, the creator and head moderator of the GamerGate subreddit, r/KotakuInAction, removed all of the moderators and set the forum to private, alleging it to have become "infested with racism and sexism". A Reddit employee restored the forum and its moderators an hour later.
2019
In February, Chinese company Tencent invested $150 million into Reddit. This resulted in a large backlash from Reddit users, who were worried about potential censorship. Many posts featuring subjects censored in China, such as Tiananmen Square, Tank Man, and Winnie the Pooh, received popularity on Reddit.
2020
During the George Floyd protests in early June, over 800 moderators signed an open letter demanding a policy banning hate speech, a shutdown of racist and sexist subreddits, and more employee support for moderation. Bloomberg News pointed out the company's slow reaction to r/watchpeopledie, a subreddit dedicated to videos of people dying in accidents and other situations, and the harassment that accompanied new unmoderated features like icons for purchase and public chats.
On June 29, Reddit updated its content policy and introduced rules aimed at curbing the presence of communities they believed to be "promoting hate", and banned approximately 2,000 subreddits that were found to be in violation of the new guidelines on the same day. Larger subreddits affected by the bans included r/The_Donald, r/GenderCritical (the platform's largest and most active anti-transgender radical feminist subreddit), and r/ChapoTrapHouse (a far-left subreddit originally created by fans of the podcast Chapo Trap House). Some media outlets and political commentators also condemned the banning of the r/The_Donald and r/ChapoTrapHouse subreddits as a violation of the right to free political expression.
2021
After the 2021 storming of the United States Capitol, Reddit banned the subreddit r/DonaldTrump in response to repeated policy violations and alluding to the potential influence the community had on those who participated in or supported the storming. The move followed similar actions from social media platforms, Twitter, YouTube, TikTok and more. The ban was criticized by those who believed it furthered an agenda and censorship of conservative ideologies. The subreddit had over 52,000 members just before it was banned.
The GameStop short squeeze was primarily organized on the subreddit r/wallstreetbets in January.
In March, Reddit users discovered that Aimee Challenor, an English politician who had been suspended from two UK political parties, was hired as an administrator for the site. Her first suspension from the Green Party came for retaining her father as her campaign manager after his arrest on child sexual abuse charges. She was later suspended from the Liberal Democrats after tweets describing pedophilic fantasies were discovered on her partner's Twitter account. Reddit banned a moderator for posting a news article which mentioned Challenor, and some Reddit users alleged that Reddit were removing all mention of Challenor. Many subreddits, including r/Music, which had 27million subscribers, and 46 other subreddits with over 1million subscribers, went private in protest. On March 24, Reddit's CEO Steve Huffman said that Challenor had been inadequately vetted before being hired and that Reddit would review its relevant internal processes. Huffman attributed user suspensions to over-indexing on anti-harassment measures. Challenor was also removed from her role as a Reddit admin.
In late August, more than 70 subreddits went private to protest against COVID-19 misinformation on Reddit, as well as Reddit's refusal to delete subreddits undermining the severity of the pandemic. A 2021 letter from the United States Senate to Reddit CEO Steve Huffman expressed concern about the spread of COVID-19 misinformation on the platform.
2023
In October, Reddit Moons (a site-specific cryptocurrency launched in May 2020) had seen a surge of value in 2023, at one point in mid-2023 rising past 50 cents per moon, but it crashed by more than 90% after it was announced on October 17 that the token would be "wound down" on November 8, allegedly due to scaling and regulatory issues; Reddit-centric coins DONUT and BRICK also crashed upon the news.
2024
In September, the Federal Trade Commission released a report summarizing 9 company responses (including from Reddit) to orders made by the agency pursuant to Section 6(b) of the Federal Trade Commission Act of 1914 to provide information about user and non-user data collection (including of children and teenagers) and data use by the companies that found that the companies' user and non-user data practices put individuals vulnerable to identity theft, stalking, unlawful discrimination, emotional distress and mental health issues, social stigma, and reputational harm.
Science
A 2014 study showed how subreddits can support role-based group recommendations or provide evaluation towards group stability and growth. Another study evoked a connection between cognitive and attention dynamics and the usage of online social peer production platforms, including the effects of deterioration of user performance. There is also work that has studied the influence of Reddit posts on the popularity of Wikipedia content. A participant-observation study of April Fools' Day 2017 social experiment on r/place identified top-down and bottom-up coordination mechanisms, rules and emergence, and analyzed their relative impact on the collaboratively created artwork, revealing cooperation and conflict, using qualitative and quantitative methods.
Data from Reddit can also be used to assess academic publications.
| Technology | Social network and blogging | null |
3829190 | https://en.wikipedia.org/wiki/Hand%20sanitizer | Hand sanitizer | Hand sanitizer (also known as hand antiseptic, hand disinfectant, hand rub, or handrub) is a liquid, gel, or foam used to kill viruses, bacteria, and other microorganisms on the hands. It can also come in the form of a cream, spray, or wipe. While hand washing with soap and water is generally preferred, hand sanitizer is a convenient alternative in settings where soap and water are unavailable. However, it is less effective against certain pathogens like norovirus and Clostridioides difficile and cannot physically remove harmful chemicals. Improper use, such as wiping off sanitizer before it dries, can also reduce its effectiveness, and some sanitizers with low alcohol concentrations are less effective. Additionally, frequent use of hand sanitizer may disrupt the skin's microbiome and cause dermatitis.
Alcohol-based hand sanitizers, which contain at least 60% alcohol (ethanol or isopropyl alcohol), are recommended by the United States Centers for Disease Control and Prevention (CDC) when soap and water are not available. In healthcare settings, these sanitizers are often preferred over hand washing with soap and water because they are more effective at reducing bacteria and are better tolerated by the skin. However, hand washing should still be performed if contamination is visible or after using the toilet. Non-alcohol-based hand sanitizers, which may contain benzalkonium chloride or triclosan, are less effective and generally not recommended, though they are not flammable.
The formulation of alcohol-based hand sanitizers typically includes a combination of isopropyl alcohol, ethanol, or n-propanol, with alcohol concentrations ranging from 60% to 95% being the most effective. These sanitizers are flammable and work against a wide variety of microorganisms, but not spores. To prevent skin dryness, compounds such as glycerol may be added, and some formulations include fragrances, though these are discouraged due to the risk of allergic reactions. Non-alcohol-based versions are less effective and should be used with caution.
The use of alcohol as an antiseptic dates back to at least 1363, with evidence supporting its use emerging in the late 1800s. Alcohol-based hand sanitizers became commonly used in Europe by the 1980s and have since been included on the World Health Organization's List of Essential Medicines.
Uses
General public
Alcohol-based hand sanitizers may not be effective if the hands are greasy or visibly soiled. In hospitals, the hands of healthcare workers are often contaminated with pathogens, but rarely soiled or greasy.
Some commercially available hand sanitizers (and online recipes for homemade rubs) have alcohol concentrations that are too low. This makes them less effective at killing germs. Poorer people in developed countries and people in developing countries may find it harder to get a hand sanitizer with an effective alcohol concentration. Fraudulent labelling of alcohol concentrations has been a problem in Guyana.
Schools
The current evidence that the effectiveness of school hand hygiene interventions is of poor quality.
In a 2020 Cochrane review comparing rinse-free hand washing to conventional soap and water techniques and the subsequent impact on school absenteeism found a small but beneficial effect on rinse-free hand washing on illness related absenteeism.
Health care
Hand sanitizers were first introduced in 1966 in medical settings such as hospitals and healthcare facilities. The product was popularized in the early 1990s.
Alcohol-based hand sanitizer is more convenient compared to hand washing with soap and water in most situations in the healthcare setting. Among healthcare workers, it is generally more effective for hand antisepsis, and better tolerated than soap and water. Hand washing should still be carried out if contamination can be seen or following the use of the toilet.
Hand sanitizer that contains at least 60% alcohol or contains a "persistent antiseptic" should be used. Alcohol rubs kill many different kinds of bacteria, including antibiotic resistant bacteria and TB bacteria. They also kill many kinds of viruses, including the flu virus, the common cold virus, coronaviruses, and HIV.
90% alcohol rubs are more effective against viruses than most other forms of hand washing. Isopropyl alcohol will kill 99.99% or more of all non-spore forming bacteria in less than 30 seconds, both in the laboratory and on human skin.
In too low quantities (0.3 ml) or concentrations (below 60%), the alcohol in hand sanitizers may not have the 10–15 seconds exposure time required to denature proteins and lyse cells. In environments with high lipids or protein waste (such as food processing), the use of alcohol hand rubs alone may not be sufficient to ensure proper hand hygiene.
For health care settings, like hospitals and clinics, optimum alcohol concentration to kill bacteria is 70% to 95%. Products with alcohol concentrations as low as 40% are available in American stores, according to researchers at East Tennessee State University.
Alcohol rub sanitizers kill most bacteria, and fungi, and stop some viruses. Alcohol rub sanitizers containing at least 70% alcohol (mainly ethyl alcohol) kill 99.9% of the bacteria on hands 30 seconds after application and 99.99% to 99.999% in one minute.
For health care, optimal disinfection requires attention to all exposed surfaces such as around the fingernails, between the fingers, on the back of the thumb, and around the wrist. Hand alcohol should be thoroughly rubbed into the hands and on the lower forearm for a duration of at least 30 seconds and then allowed to air dry.
Use of alcohol-based hand gels dries skin less, leaving more moisture in the epidermis, than hand washing with antiseptic/antimicrobial soap and water.
Hand sanitizers containing a minimum of 60 to 95% alcohol are efficient germ killers. Alcohol rub sanitizers kill bacteria, multi-drug resistant bacteria (MRSA and VRE), tuberculosis, and some viruses (including HIV, herpes, RSV, rhinovirus, vaccinia, influenza, and hepatitis) and fungi. Alcohol rub sanitizers containing 70% alcohol kill 99.97% (3.5 log reduction, similar to 35 decibel reduction) of the bacteria on hands 30 seconds after application and 99.99% to 99.999% (4 to 5 log reduction) of the bacteria on hands 1 minute after application.
Drawbacks
There are certain situations during which hand washing with soap and water are preferred over hand sanitizer, these include: eliminating bacterial spores of Clostridioides difficile, parasites such as Cryptosporidium, and certain viruses like norovirus depending on the concentration of alcohol in the sanitizer (95% alcohol was seen to be most effective in eliminating most viruses). In addition, if hands are contaminated with fluids or other visible contaminates, hand washing is preferred as well as after using the toilet and if discomfort develops from the residue of alcohol sanitizer use. Furthermore, CDC states hand sanitizers are not effective in removing chemicals such as pesticides.
Safety
Fire
Alcohol gel can catch fire, producing a translucent blue flame. This is due to the flammable alcohol in the gel. Some hand sanitizer gels may not produce this effect due to a high concentration of water or moisturizing agents. There have been some rare instances where alcohol has been implicated in starting fires in the operating room, including a case where alcohol used as an antiseptic pooled under the surgical drapes in an operating room and caused a fire when a cautery instrument was used. Alcohol gel was not implicated.
To minimize the risk of fire, alcohol rub users are instructed to rub their hands until dry, which indicates that the flammable alcohol has evaporated. Igniting alcohol hand rub while using it is rare, but the need for this is underlined by one case of a health care worker using hand rub, removing a polyester isolation gown, and then touching a metal door while her hands were still wet; static electricity produced an audible spark and ignited the hand gel. Hand sanitizer should be stored in temperatures below 105 °F and should not be left in a car during hot weather due to risk of flammability. Fire departments suggest refills for the alcohol-based hand sanitizers can be stored with cleaning supplies away from heat sources or open flames.
Skin
Researchers have not thoroughly studied the implications of hand sanitizer use for the body and the microbiome. Studies of healthcare workers have correlated high rates of hand eczema with hand sanitizer use.
The alcohol in hand sanitizer strips the skin of the outer layer of oil, which may have negative effects on barrier function of the skin. A study also shows that disinfecting hands with an antimicrobial detergent results in a greater barrier disruption of skin compared to alcohol solutions, suggesting an increased loss of skin lipids.
Frequent use of alcohol-based hand sanitizers can cause dry skin unless emollients and/or skin moisturizers are added to the formula. The drying effect of alcohol can be reduced or eliminated by adding glycerin and/or other emollients to the formula. In clinical trials, alcohol-based hand sanitizers containing emollients caused substantially less skin irritation and dryness than soaps or antimicrobial detergents. Allergic contact dermatitis, contact urticaria syndrome or hypersensitivity to alcohol or additives present in alcohol hand rubs rarely occur. The lower tendency to induce irritant contact dermatitis became an attraction as compared to soap and water hand washing.
Ingestion
In the United States, the U.S. Food and Drug Administration (FDA) controls antimicrobial handsoaps and sanitizers as over-the-counter drugs (OTC) because they are intended for topical anti-microbial use to prevent disease in humans.
The FDA requires strict labeling which informs consumers on proper use of this OTC drug and dangers to avoid, including warning adults not to ingest, not to use in the eyes, to keep out of the reach of children, and to allow use by children only under adult supervision. According to the American Association of Poison Control Centers, there were nearly 12,000 cases of hand sanitizer ingestion in 2006. If ingested, alcohol-based hand sanitizers can cause alcohol poisoning in small children. However, the U.S. Centers for Disease Control recommends using hand sanitizer with children to promote good hygiene, under supervision, and furthermore recommends parents pack hand sanitizer for their children when traveling, to avoid their contracting disease from dirty hands.
Denaturants are an ingredient added to hand sanitizers, such as Purell, that is used to stop the liquid gel from being digested. This chemical adds a taste to the gel that makes it less enticing to consume. It is especially helpful in keeping younger children away because of the different smells and colors of hand sanitizers that tend to attract children.
People with alcoholism may attempt to consume hand sanitizer in desperation when traditional alcoholic beverages are unavailable, or personal access to them is restricted by force or law. There have been reported incidents of people drinking the gel in prisons and hospitals to become intoxicated. As a result, access to sanitizing liquids and gels is controlled and restricted in some facilities. For example, over a period of several weeks during the COVID-19 pandemic in New Mexico, seven people in that U.S. state who were alcoholic were severely injured by drinking sanitizer: three died, three were in critical condition, and one was left permanently blind.
In 2021, a dozen children were hospitalized in the state of Maharashtra, India, after they were mistakenly orally administered hand sanitizer instead of a polio vaccine.
Absorption
On 30 April 2015, the FDA announced that they were requesting more scientific data based on the safety of hand sanitizer. Emerging science suggests that for at least some health care antiseptic active ingredients, systemic exposure (full body exposure as shown by detection of antiseptic ingredients in the blood or urine) is higher than previously thought, and existing data raise potential concerns about the effects of repeated daily human exposure to some antiseptic active ingredients. This would include hand antiseptic products containing alcohol and triclosan.
Surgical hand disinfection
Hands must be disinfected before any surgical procedure by hand washing with mild soap and then hand-rubbing with a sanitizer. Surgical disinfection requires a larger dose of the hand-rub and a longer rubbing time than is ordinarily used. It is usually done in two applications according to specific hand-rubbing techniques, EN1499 (hygienic handwash), and German standard DIN EN 1500 (hygienic hand disinfection) to ensure that antiseptic is applied everywhere on the surface of the hand.
Alcohol-free
Some hand sanitizer products use agents other than alcohol to kill microorganisms, such as povidone-iodine, benzalkonium chloride or triclosan. The World Health Organization (WHO) and the CDC recommends "persistent" antiseptics for hand sanitizers. Persistent activity is defined as the prolonged or extended antimicrobial activity that prevents or inhibits the proliferation or survival of microorganisms after application of the product. This activity may be demonstrated by sampling a site several minutes or hours after application and demonstrating bacterial antimicrobial effectiveness when compared with a baseline level. This property also has been referred to as "residual activity." Both substantive and nonsubstantive active ingredients can show a persistent effect if they substantially lower the number of bacteria during the wash period.
Laboratory studies have shown lingering benzalkonium chloride may be associated with antibiotic resistance in MRSA. Tolerance to alcohol sanitizers may develop in fecal bacteria. Where alcohol sanitizers utilize 62%, or higher, alcohol by weight, only 0.1 to 0.13% of benzalkonium chloride by weight provides equivalent antimicrobial effectiveness.
Triclosan has been shown to accumulate in biosolids in the environment, one of the top seven organic contaminants in waste water according to the National Toxicology Program Triclosan leads to various problems with natural biological systems, and triclosan, when combined with chlorine e.g. from tap water, produces dioxins, a probable carcinogen in humans. However, 90–98% of triclosan in waste water biodegrades by both photolytic or natural biological processes or is removed due to sorption in waste water treatment plants. Numerous studies show that only very small traces are detectable in the effluent water that reaches rivers.
A series of studies show that photodegradation of triclosan produced 2,4-dichlorophenol and 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD). The 2,4-dichlorophenol itself is known to be biodegradable as well as photodegradable. For DCDD, one of the non-toxic compounds of the dioxin family, a conversion rate of 1% has been reported and estimated half-lives suggest that it is photolabile as well. The formation-decay kinetics of DCDD are also reported by Sanchez-Prado et al. (2006) who claim "transformation of triclosan to toxic dioxins has never been shown and is highly unlikely."
Alcohol-free hand sanitizers may be effective immediately while on the skin, but the solutions themselves can become contaminated because alcohol is an in-solution preservative and without it, the alcohol-free solution itself is susceptible to contamination. However, even alcohol-containing hand sanitizers can become contaminated if the alcohol content is not properly controlled or the sanitizer is grossly contaminated with microorganisms during manufacture. In June 2009, alcohol-free Clarcon Antimicrobial Hand Sanitizer was pulled from the US market by the FDA, which found the product contained gross contamination of extremely high levels of various bacteria, including those which can "cause opportunistic infections of the skin and underlying tissues and could result in medical or surgical attention as well as permanent damage". Gross contamination of any hand sanitizer by bacteria during manufacture will result in the failure of the effectiveness of that sanitizer and possible infection of the treatment site with the contaminating organisms.
Types
Alcohol-based hand rubs are extensively used in the hospital environment as an alternative to antiseptic soaps. Hand-rubs in the hospital environment have two applications: hygienic hand rubbing and surgical hand disinfection. Alcohol based hand rubs provide a better skin tolerance as compared to antiseptic soap.
Hand rubs also prove to have more effective microbiological properties as compared to antiseptic soaps.
The same ingredients used in over-the-counter hand-rubs are also used in hospital hand-rubs: alcohols such as ethanol and isopropanol, sometimes combined with quaternary ammonium cations (quats) such as benzalkonium chloride. Quats are added at levels up to 200 parts per million to increase antimicrobial effectiveness. Although allergy to alcohol-only rubs is rare, fragrances, preservatives and quats can cause contact allergies. These other ingredients do not evaporate like alcohol and accumulate leaving a "sticky" residue until they are removed with soap and water.
The most common brands of alcohol hand rubs include Aniosgel, Avant, Sterillium, Desderman and Allsept S. All hospital hand rubs must conform to certain regulations like EN 12054 for hygienic treatment and surgical disinfection by hand-rubbing. Products with a claim of "99.99% reduction" or 4-log reduction are ineffective in hospital environment, since the reduction must be more than "99.99%".
The hand sanitizer dosing systems for hospitals are designed to deliver a measured amount of the product for staff. They are dosing pumps screwed onto a bottle or are specially designed dispensers with refill bottles. Dispensers for surgical hand disinfection are usually equipped with elbow controlled mechanism or infrared sensors to avoid any contact with the pump.
Composition
Consumer alcohol-based hand sanitizers, and health care "hand alcohol" or "alcohol hand antiseptic agents" exist in liquid, foam, and easy-flowing gel formulations. Products with 60% to 95% alcohol by volume are effective antiseptics. Lower or higher concentrations are less effective; most products contain between 60% and 80% alcohol.
In addition to alcohol (ethanol, isopropanol or n-Propanol), hand sanitizers also contain the following:
additional antiseptics such as chlorhexidine and quaternary ammonium derivatives,
sporicides such as hydrogen peroxides that eliminate bacterial spores that may be present in ingredients,
emollients and gelling agents to reduce skin dryness and irritation,
a small amount of sterile or distilled water,
sometimes foaming agents, colorants or fragrances.
WHO formulations
The World Health Organization has published the following formulations to guide to the production of large quantities of hand sanitizer from chemicals available in developing countries, where commercial hand sanitizer may not be available:
Formulation 1
Formulation 2
Production
COVID-19 pandemic
In 2010 the World Health Organization produced a guide for manufacturing hand sanitizer, which received renewed interest in 2020 because of shortages of hand sanitizer in the wake of the COVID-19 pandemic. Dozens of liquor and perfume manufacturers switched their manufacturing facilities from their normal product to hand sanitizer. In order to keep up with the demand, local distilleries started using their alcohol to make hand sanitizer. Distilleries producing hand sanitizer originally existed in a legal grey area in the United States, until the Alcohol and Tobacco Tax and Trade Bureau declared that distilleries could produce their sanitizer without authorization.
In the beginnings of the pandemic, because of hand sanitizer shortages due to panic buying, people resorted to using 60% to 99% concentrations of isopropyl or ethyl alcohol for hand sanitization, typically mixing them with glycerol or soothing moisturizers or liquid contain aloe vera to counteract irritations with options of adding drops of lemon or lime juice or essential oils for scents, and thus making DIY hand sanitizers. However, there are cautions against making them, such as a wrong measurement or ingredient may resulting in an insufficient amount of alcohol to kill the coronavirus, thus rendering the mixture ineffective or even poisonous.
Additionally, some commercial products are dangerous, either due to poor oversight and process control, or fraudulent motive. In June 2020, the FDA issued an advisory against use of hand sanitizer products manufacture by Eskbiochem SA de CV in Mexico due to excessive levels of methanol – up to 81% in one product. Methanol can be absorbed through the skin, is toxic in modest amounts, and in substantial exposure can result in "nausea, vomiting, headache, blurred vision, permanent blindness, seizures, coma, permanent damage to the nervous system or death". Products suspected of manufacture by Eskbiochem SA with excessive methanol have been reported as far away as British Columbia, Canada.
In August 2020, the FDA expanded the list of dangerous hand sanitizers.
| Biology and health sciences | Hygiene products | Health |
3830863 | https://en.wikipedia.org/wiki/Bateleur | Bateleur | The bateleur (; Terathopius ecaudatus), also known as the bateleur eagle, is a medium-sized eagle in the family Accipitridae. It is often considered a relative of the snake eagles and, like them, it is classified within the subfamily Circaetinae. It is the only member of the genus Terathopius and may be the origin of the "Zimbabwe Bird", the national emblem of Zimbabwe. Adult bateleurs are generally black in colour with a chestnut colour on the mantle as well as also on the rump and tail. Adults also have gray patches about the leading edges of the wings (extending to the secondaries in females) with bright red on their cere and their feet. Adults also show white greater coverts, contrasting with black remiges in males, gray patches on the underwing primaries and black wingtips. The juvenile bateleur is quite different, being largely drab brown with a bit of paler feather scaling. All bateleurs have extremely large heads for their size, rather small bills, large feet, relatively short legs, long, bow-like wings and uniquely short tails, which are much smaller still on adults compared to juvenile birds.
This species is native to broad areas of Sub-Saharan Africa and scarcely up into Arabia. It is characteristically a bird of somewhat open habitats such as savanna with some trees present and open dry woodland. It is in life history, a rather peculiar bird of prey with a free-wheeling generalist diet that includes much carrion but also tends to hunt a wide range of live prey, including many small to unexpectedly relatively large mammals and reptiles along with generally relatively small birds. Bateleurs are highly aerial birds that spend much time soaring and will frequently fly with exaggerated embellishments, perhaps when excited or angered. They tend to build a relatively small if sturdy stick nest in a large tree and lay only a single egg. Despite being a rather aggressive bird in other contexts, bateleurs are easily flushed from their own nest, making them exceptionally vulnerable to nest predators, including humans, and nest failures. It may take as long as 7 to 8 years to attain full maturity, perhaps the longest stretch to maturity of any raptor. This species has long been known to be declining rather pronouncedly in overall population and it is mostly confined to protected areas today. Currently the IUCN classifies the bateleur as an Endangered species due primarily to anthropogenic causes such as habitat destruction, pesticide usage and persecution.
Taxonomy and etymology
The bateleur has been found to be a proper member of the subfamily Circaetinae, commonly called snake or serpent eagles, via a variety of genetic studies. Given the outward similarities of the bateleur to snake eagles, the relationship has long been inferred by authors. In particular, the bateleur was suggested to have their closest living relations in the similarly large Circaetus snake eagles. This relationship was well borne-out by a genetic study that found that this species and the short-toed snake eagle (Circaetus gallicus) form a monophyletic clade, based on nucleotide sequences in the cytochrome b gene. Even though, when contrasted with snake eagles, bateleurs appear to differ greatly in plumage patterns, the two genera show certain similarities in food, feeding behavior, and breeding biology. However, Lerner and Mindell (2005), based on the molecular sequence from two mitochondrial genes and one nuclear intron, indicated a previously unsuspected close relationship of the bateleur with similarly "aberrant" but extremely different, in nearly every respect of appearance and life history, member of the Circaetinae, the Philippine eagle (Pithecophaga jefferyi). Chromosome banding studies have also found a relatively recent genetic relationship of the bateleurs with the Old World vultures.
The common name of "Bateleur" is French for "street performer". Meanwhile, the scientific name is from name teras (Greek) for "marvelous"; ops (Greek) for "face"; e (Latin) for "without"; caudatus (Latin) "tail". The bird was given its common name by François Levaillant, a French naturalist and explorer. The original scientific name was Falco ecaudatus, given by François Marie Daudin, as the concept of disparate genera between birds of prey was devised later on (nor were falcons then known to be unrelated to many other variety of diurnal birds of prey).
Description
The bateleur is of note for its unique morphology and plumage, with some anatomical similarities to both snake eagles and vultures. The species has a thick neck and a very large, rather conspicuously cowled head with a proportionately short bill, albeit one covered with a very large cere. The cowl is also present on snake eagles but in those it is less dramatically apparent. The other features in perched adult bateleurs are rather oddly stumpy, such as the short legs and exceptionally short tail, possibly the shortest proportionately of all raptors. Its posture while perched is extremely upright, making them look like quite a tall raptor on the ground despite its rather short legs. Even while perched, the body tends to be dominated by their exceptionally large wings, which possess some 25 secondary feathers, perhaps more than any other raptor. The adult bateleur usually has a chestnut coloration along the mantle, back, rump and tail, including the undertail coverts. The adult male bateleur is predominantly black with grey shoulders, which appear edged with white when freshly moulted. The adult female differs by having grey-brown, not black, on the greater coverts and black-tipped grey, not black, secondaries. Furthermore up to 7% of adults have a "cream morph" where they have chestnut tails but the other chestnut areas are almost fully replaced by cream to pale brown coloring. The cream morph may reportedly be slightly more prevalent in drier areas. The bare parts of adult bateleurs are exceptionally conspicuous, with the adult cere, bare facial skin and feet all being rather bright red, however in some they can also temporarily fade to pink, pale pink or yellowish at times, such as when they are perching in the shade or bathing. The bare parts flush the most red during times of excitement. The bill itself is black with a yellow centre and red base. The eyes are dark brown.
The juvenile is very distinct from the adults of the species. Juveniles of the bateleur have a longer tail than mature birds. They furthermore have essentially all brown coloring, with dull rufous to creamy edging apparent on some areas. The head of the juvenile bateleur is paler and tawnier than elsewhere on its body while the eyes are brown, the cere a rather unique greenish-blue and the feet whitish in colour. At as late as 2–3 years of age, the immature bateleur is still much the same in appearance as the juvenile but by the fourth year becomes more sooty-brown, with sexual dimorphism already evidenced by the more extensive dark wing markings of males. In the 5th year, the plumage may show the first signs of chestnut and the grey colour about back and shoulders tend to manifest. Also from 3–5 years old, the cere and feet turn yellow then to dull-pink. By the sixth and seventh years of life, the plumage of subadult bateleurs blackens and the chestnut portions of the plumage increase. The shoulders become fully grey by the 8th year, the likely age of maturity. As for the bare parts in juvenile bateleurs, the cere and facial skin are a distinct pale grey-blue to green-blue. The juvenile's feet are greenish-white to greyish-white, at 4-5 the cere, facial skin and feet turn yellow, then pink before finally reddening. The eyes are similar in hue to those of adult bateleurs but are a slightly lighter, being more honey-brown, while the bill of juveniles are mainly pale grey-blue in colour.
In flight, the bateleur appears as a rather large raptor with disproportionately elongated, rather narrow and slightly bow-shaped wings, which appear pinched in at the bases, broad across the secondaries and regularly narrow, pointed and upturned at the tips. Upon sighting, the wings often catch the eye before the large head, which is proportionately slightly bigger even than their cousins, the snake eagles. The tail is so short in adult bateleurs that the feet extend below the tail tip, almost giving the impression that the raptor nearly has no tail. This is as opposed to juveniles, where the feet come up about short of the tail tip, with the feet coming to exceed the tail, which is shrinking via moults, in length around the 5th year of maturation. The adult bateleur's wingspan is an extraordinary 2.9 times greater than its total length. The adult male bateleur is mostly black above with a chestnut back and tail and grey forewings, below he is black on the body, contrasting with a chestnut tail, as well as with the white wing linings and black flight feathers except for the greyish based primaries. The adult female bateleur is similar in plumage to the male overall but differs in her black-tipped grey secondaries above and more extensively white underwings with the black on the female confined to the wingtips and trailing edges. The juvenile bateleur on the wing appears broader winged and especially longer tailed with a largely uniform brown coloration, including the greater coverts, with paler feather mainly about the head as well as on the flight feathers.
Size
The bateleur is a mid-sized eagle and large raptor. It is likely the second heaviest of the Circaetinae subfamily of accipitrids. By far the largest of the subfamily is the Philippine eagle which is more than twice as massive and is far larger in all aspects of measurement than the bateleur, with a drastically differing structure (broad, relatively short wings, very long legs and tail). One traditional snake eagle, the brown snake eagle ( Circaetus cinereus), rivals the bateleur in most aspects of size including body mass but possesses a rather longer tail and slightly shorter but broader wings. Additionally, the widespread and slightly broader-winged short-toed snake eagle and proportionately long and slender-winged black-breasted snake eagle (Circaetus pectoralis) can be nearly as large in wingspan as the bateleur but tend to be somewhat less heavy. The total length of the bateleur is . Typical length of a full-grown bird is around . The wingspan of bateleurs can vary from . Body mass of bateleurs can vary from . One sample of 10 unsexed bateleurs weighed an average of while a smaller sample of three weighed an average of . Additionally, a median body mass of was cited in one study.
The bateleur evidences some sexual dimorphism in favour of the female as is expected in raptorial birds but this size difference is fairly minimal relative to many other accipitrids, averaging up to about 6%. Among standard measurements, males have a wing chord length of while that of the female is . In tail length, adult males measure and can be even shorter in adult females at , in some cases the adult's tail may reportedly measure as short as . This contrasts with the tail of juvenile bateleurs which measures . The tarsus can measure from in males and in females. Unsexed adult bateleurs in Tsavo East National Park were found to average in wing chord length, with a range of in culmen length and a relatively small hind claw length of . While the hind or hallux claw is usually the most enlarged in most species of accipitrid, on the other hand in the Tsavo East bateleurs, unusually the middle claw on the front of the foot was slightly larger at . Notably the proportions of bateleurs are similar to snake eagles with robust feet with rough, thick skin and short talons, the bateleur in particular having very thick, large toes structurally almost like those of a big owl and very sharp talons reminiscent in sharpness of highly predaceous larger African raptors. Further like snake eagles, bateleurs have a rather large headed but with a smallish beak coupled with a large gape. These adaptations generally equip the subfamily to better handle and ingest snakes relative to other accipitrids.
Identification
The bateleur, particularly in its adult plumage, is often considered one of the most distinctive raptors in the world. When perched or flying adults or older immatures are quite unmistakable. The bateleur can be readily be distinguished even by inexperienced observers from the very differently-shaped and usually rather smaller-bodied and winged augur buzzards (Buteo augur) and jackal buzzards (Buteo rufofuscus). These do not overlap with bateleurs in nearly all respects of morphology, proportions nor flight actions. Nonetheless, both of these buzzards are sometimes mistaken for bateleurs due to their own combinations of black, white and chestnut, which are completely differently composed than those of the bateleur. Despite how distinctive the buzzards are from the bateleur, some reports of bateleurs from areas where they are currently gone are almost certain to have been misidentified jackal buzzards. Juveniles and immatures of up to 2–3 years old are hardly less distinctive in shape but could be confused, largely due to similar proportions of their large head, brown plumage and whitish legs with certain snake eagles. The brown snake eagle is perhaps the most similar to the juvenile bateleur but it has yellow eyes, longer legs, much broader, shorter and differently shaped wings with the tips of wings reaching its banded tail. Even the black-chested and the rather slight Beaudouin's snake eagle (Circaetus beaudouinii) are sometimes considered potentially confusable with juvenile bateleurs, but both of these respective species are rather uniform and darker brown ventrally and about the head and much paler dorsally, with a highly different contrasting whitish cream colour below.
Vocalizations
Bateleurs are usually silent for much of the year. The main call, uttered whether perched or in aerial display, or when pirating from other raptors, is a far-carrying, loud raucous schaaaa-aw. They may too vocalize in a similar manner during courtship. Alternatively, bateleur calls may consist of resonant barking calls, kow-aw. The barking call can be accompanied by half-spread wings and jerking of the body up and down or may too be uttered in flight, the latter in a similar manner to that of a fish eagle. Distraction display are sometimes accompanied by subdued barking chatter, ka-ka-ka-ka.... A not dissimilar call of kau-kau-kau-koaagh-koaggh has been described as given by perched birds. Other softer calls are uttered when perched near the nest. The young of the bateleur tend to engage harsh squealing call is kyup-kyup keeaw keeaw, usually as a hunger call at approach of parent with food. Also the species' young may make a melodious twip call.
Distribution and habitat
The bateleur occupies a very large range through mainly sub-Saharan Africa. The species resides in West Africa from southern Mauritania to Senegal, The Gambia, Guinea-Bissau, Guinea, the northern portions of Sierra Leone, Ivory Coast and much of Ghana through western Burkina Faso, much of Togo and Benin and northern and central Nigeria. It is possibly extinct in Mauritania, range restricted in Guinea (mainly to Kiang West) and Liberia but is still locally common where good habitat remains elsewhere in this region. Similarly far north, a rare population is believed to persist out of Africa in extreme southwestern Saudi Arabia and western Yemen. In central and east Africa, the bateleur may be found in northern Cameroon, southern Niger, southern Chad, southern Sudan, South Sudan, northern Central African Republic, Eritrea, Ethiopia, Djibouti, western Somalia, northern, eastern and southern Democratic Republic of the Congo and a majority of Uganda, Kenya and Tanzania. In Southern Africa, the bateleur is found quite widely, being found almost throughout, where habitat is favorable, Angola, Zambia, Zimbabwe, Malawi and Mozambique. Additionally, they may range Botswana in all but southernmost portion also being found still in northern and eastern Namibia and northwestern South Africa, where its range has contracted considerably from as far south once as the Cape Province to almost entirely to being found exclusively within protected areas north of the Orange River excepting a portion of Kruger National Park. The species is possibly extirpated from Eswatini in southern Africa. The bateleur is regarded as a vagrant in the countries of Tunisia, Cyprus and rarely Egypt, Israel and Iraq. In April 2012 a juvenile bateleur was seen in Algeciras in southern Spain. In 2015 and 2022, juveniles spotted as far north as Black Sea coast of Turkey in the cities of Istanbul and Sinop respectively.
Habitat
The bateleur is a common to fairly common resident or nomadic bird of the partially open savanna country and of woodland within Sub-Saharan Africa. During breeding, it tends to require closed-canopy savannah-woodland habitats, including Acacia savanna as well as mopane and miombo woodlands. They may too acclimate to thornveld and overall various fairly shrubby areas. It tends to rarely occur in heavily forested and mountainous habitats. However, while the species can forage extensively in largely treeless habitats such as treeless savanna but is nearly as rare in pure desert lacking arborescent growth as it is in tropical rainforests. Bateleurs are seldom to be found around extensive wetlands but may regularly be found near watering holes. Although often in fairly dry savanna habitats, in Kenya it is reportedly absent from areas where the rainfall is under annually, probably because it limits the growth of the leafy trees that they require for nesting. In Ethiopia, it tends to be associated with well-wooded areas. Habitat tends to be most closely studied in southern Africa. It is mostly common found in broad-leaved woodland in the Okavango Delta in Botswana. In Namibia it is often found over tall woodland near drainage lines, and over ephemeral rivers in north-eastern Namibia and within the more arid Etosha National Park. In Zambia, it is found in a variety of habitats from woodlands to open plains but avoids the most densely wooded areas. Reportedly in Malawi, it is often associated with Forest–savanna mosaics but is sometimes regularly seen over cultivated areas and even may be seen flying over large cities. To the contrary, in Mozambique it is said to avoid areas with a dense human population. The species can occur from sea level up to , but not normally a mountain-dwelling species and mainly occurs below . This is supported in Zimbabwe, where the bateleur is relatively common but appears to largely avoid the extensive amount of hilly and rugged areas present in that country.
Behaviour
This bateleur is unusually conspicuous due to its propensity for gliding flights over favorable habitats in much of Africa. The bird spends a considerable amount of time on the wing, particularly in low-altitude flights. Due to the conspicuous behaviour and colorful plumage, the bateleur is frequently described in superlatives such as "one of the most beautiful and spectacular things that flies". This species tends to take off with unusually fast, shallow beats for a bird of this relative large size. After take-off, the bateleur sails at a mean speed of about . They often rock from side-to-side with the wings held in a strong dihedral with very limiting flapping, vaguely recalling the flight of the American turkey vulture (Cathares aura) although the flight is generally more forceful, fast and acrobatic than that species and at times can be evocative of a huge falcon. Although the species tends to fly fairly low, bateleurs can soar and circle quite high as well. Engaged in its aforementioned dihedral flight it is often cants continuously from side-to-side, likely the origin of which it was given its common name (loosely "tumbler", "balancer" or "tightrope walker") of French derivation. Various flying embellishments may be undertaken nearly aseasonally. Although not typically given to forward somersault nor to loop-the-loop, bateleurs may with some regularity perform a rapid 360 degrees sideways roll. They are often given to flying with more embellishments when in the presence of another bateleur, even with juveniles provoking one another entirely uncoupled seemingly from breeding courtship or territorial displays. Typical home ranges of around were reported per pair in Kruger National Park and these were considered unusually small by overall species standards. Intruders to whom this behaviour is displayed always submit and submission is shown by retreating to a safe upper boundary (elevation). Males and females both display this behaviour in all stages of the breeding cycle. This behaviour is mainly shown to members of the same sex and particularly to non-adults, as it is thought that they may have a greater ability to take over another bird's territory (having greater competitive ability for limited food resources).
The bateleur is generally a solitary bird. However, juveniles may accompany one or both parents for about three months and loose congregations of as many as 40-50 or more have been record of mainly immatures. These tend to be aggregations of otherwise unassociated immature bateleurs attracted to rich feeding areas such as newly-discovered carrion, bush fires, recently burnt areas or temporary floods and occasionally by termite emergences. In the wild bateleurs are shy of man and sensitive to disturbance at the nest, easily abandoning the structure. In captivity, however, they become unusually tame. Bateleur eagles are among a group of raptors that secrete a clear, salty fluid from their nares whilst eating. According to Schmidt-Nielson's 1964 hypothesis, this is due to the general necessity for birds to use an extrarenal mechanism of salt secretion to aid water reabsorption.
Nomadism and dispersals
Generally, as in most raptors found as breeding residents in Africa, the bateleur is considered sedentary and territorial but it is a species that requires very large home ranges. However, in general the species neither as staunchly residential nor sedentary as many other Sub-Saharan African raptors. Both immature and sometimes adult bateleurs are considered clearly nomadic. At times, the bateleur is even regarded as an "irruptive or local migrant". Some regular north-to-south movements may occur in West Africa and may occur transequatorially in East Africa to avoid heavy rains. In Kruger, immatures are driven out by adults on territory during the breeding season and then often wander widely before returning for the non-breeding season. Recoveries of juveniles in southern Africa show that individuals have been recovered at assorted distances from their nests of origin ranging from as far as away. It was noted that in some cases, heavier rainfall may have caused farther afield dispersals.
Thermoregulation
Bateleurs seem to devote an exceptional amount of time to thermoregulation frequently spending much of its day variously sunning, to warm up, and bathing, to cool off. These eagles are frequently seen to enter water-bodies for a bath and then open their wings to often sunbathe. Standing upright and holding their wings straight out to the sides and tipped vertically, a classic 'phoenix' pose as they turn to follow the sun. Bateleurs will stand on the ground with their wings spread, exposing the feathers to direct sunlight, warming the oils in the feathers. The bird will then spread the oils with its beak to improve its aerodynamics. In some countries, local nicknames of the species may include as the "Conifer eagle" or "Pine eagle" due to its feathers resembling a conifer cone when fluffed up and engaging in thermoregulatory behaviour. At times, this is described as a "striking heraldic posture". Bateleurs may also be seen "praying" allowing ants to crawl over the wings and feathers, collecting bits of food, dead feather and skin material. When covered in ants, the bateleur then ruffles its feathers, startling the ants, which react by secreting formic acid as self-defence. This in turn kills the ticks and fleas, possibly ridding the host of its parasites.
Dietary biology
The bateleur is a dietary generalist. This species generally forages from the flight, flying mostly low and straight whilst scanning the ground, periodically banking and retracing sections of the track when possible foods are spotted. Their hunting range can be truly enormous ranging in some cases up to . Bateleurs may spend up to 8–9 hours or up to 80% of daylight on the wing, perhaps largely for hunting and foraging purposes, and have reported having even covered as much as in a single day. When potential prey or food is spotted, they then descend in tight spirals to check it out. The bateleur is a very effective discoverer of carrion at all times and often is the first to come to large carcasses or roadkills. Juveniles appear to attend large carrion much more than adults and dietary studies appear to support that carrion is rather more significant to the foods of juvenile and immature bateleurs compared to adults. Despite an aptitude for scavenging, descriptions of this eagle as "not a very rapacious species" are erroneous as it has been found to a highly powerful predator for its size and one that is often rather active at pursuing living prey, with seemingly most food consumed during the breeding season being prey that the bateleur has itself killed. Bateleurs kill most prey on the ground with a steep stoop on partially closed wings. On the evidence, they may alter their stoop onto prey with a slow drop with raised wings, rather in a gentle descent like a parachute, largely when taking slower moving prey such as some reptiles. Additionally, they can also take birds on the wing. As occasional kleptoparasites, they sometimes aerially pirate foods from other raptors. Alternately, they may try to intercept other raptors' kills while the raptor is feeding on them, whether it be on the ground, in a tree or on a rock, or even immediately after the kill is made. These piratical attacks are sometimes carried out against large carrion eaters like vultures and even against larger eagles, and in them, they may drive their target to the ground, with interlocking talons or trading shallow blows with their feet. Bateleurs also hunt insects by walking on the ground, particularly after grassfires, and will patrol for small carcasses alongside roads.
Bateleurs forage almost entirely based on opportunity and have no particular specialization on any particular prey type. As a result, a wide prey spectrum has been reported, with around 160 prey species known, they thus rival martial eagles (Polemaetus bellicosus) and perhaps just slightly behind tawny eagles (Aquila rapax) as the most diversified feeder known among African eagles. Among their prey, mammals, birds and reptiles, roughly in that order, seem to be considerably preferred over other prey taxa. Based on morphology, their long middle toes have been cited as an indication that they originally diversified to become a bird-eater but a rather small degree of sexual dimorphism between males and females indicates a preference for mammal eating. By the most complete picture of the bateleurs diet was a compilation study that compiled 1879 prey items from differing parts of the range. In it was found that bateleurs derived 54.6% of the diet from mammals, with perhaps two-thirds to about half of the diet being mammalian carrion, along with 23.7% of the diet being from birds, 17.8% from reptiles, 1.9% from fish, 1.8% from invertebrates and an extremely small amount (about 0.2%) of amphibian food. Predominantly, within the compilation study, preys were unidentified to species, with 58.4% of the carrion sources, 26.9% of live mammals, genera, or families, and 22.2% of birds unidentified to species.
Differing study areas show differing prey results for bateleurs. In a woodland-based study of nesting birds in Zimbabwe, 175 prey items were found for bateleurs with the diet seemingly dominated by prey appearing to be taken alive and relatively large prey at that. The primary prey in the study were found to be scrub hare (Lepus saxatilis) (at 26.3% of the prey by number), Cape hyrax (Procavia capensis) (at 10.3%), Gambian pouched rat (Cricetomys gambianus) (6.85%), brown greater galago (Otolemur crassicaudatus) (6.28%) and helmeted guineafowl (Numida meleagris) (4.57%). In the more hilly, rocky country of Zimbabwe, seemingly live prey was also preferred but a stronger prevalence of birds was detected among the 249 prey items. In this study, the main prey were scrub hares (22.8%), unidentified doves (10%), glossy starlings (6.72%), other small birds of around (6.69%), crested guineafowls (Guttera pucherani) (5.43%) and unidentified mammals (5.02%). In Kruger National Park, a much stronger preference for likely or verified carrion was detected in the bateleur's breeding season diet. Here, 731 food items in thornveld type habitat and 341 prey items in savanna type habitat were reviewed. It was estimated 31.6% of the diet was carrion was from medium-sized antelopes of around in weight, followed by small carrion sources of around to somewhat larger carrion from impala (Aepyceros melampus). Beyond carrion, the Kruger food study found that 16.4% of the total diet consisted of unidentified live mammals, 3.73% each by assorted dove species and lilac-breasted rollers (Coracias caudatus), 3% by glossy starlings and 1.6% by skinks. Further variation was found in the diet farther north in Tsavo East National Park in Kenya. Of 139 prey items from the nest areas of 2 pairs, mostly live prey predominated again, here led by Kirk's dik-diks (Madoqua kirkii) at 19.42%, unidentified snakes at 18.7%, cape hares at 4.3%, Crocidura shrews at 3.59%, ungulate carrion at 3.59%, Streptopelia doves at 3.59%, common dwarf mongoose (Helogale parvula) at 2.87% and red-crested korhaan (Lophotis ruficrista) at 2.87%. Without statistics, Cangandala National Park in Angola, the prey species reported at nests included brown greater galago, greater cane rat (Thryonomys swinderianus), Gambian pouched rat, and unidentified hares. Unfortunately, detailed dietary studies have only been conducted in southern and eastern Africa and details of the diet are unknown elsewhere, however it is assumed the species is a generalist and opportunist throughout its range.
In general, a picture emerges that the primary food sources of bateleurs are live-taken medium-sized mammals, carrion of generally larger mammal species, rather smallish bird prey, and a small diversity of reptiles. When selecting mammals, small prey such as rodents and shrews are by no means neglected but a preference for relatively large rodents tends to be found. These may consist of assorted mice, gerbils and dormice to ground squirrels, bush squirrels and vlei rats to very large rodents such as Gambian pouched rats, greater and lesser cane rat (Thryonomys gregorianus) and South African springhares (Pedetes capensis) although certainly any consumption of adult Cape porcupine (Hystrix africaeaustralis) is derived from carrion. Additionally, most African species of hare as well as, more secondarily, hedgehogs and elephant shrews and a variety of smallish carnivorous mammals. The latter may include live prey species including several species of mongoose, from dwarf to banded mongoose (Mungos mungo) and Selous's mongoose (Paracynictis selousi), both about the same body mass as a bateleur, and at least four species of genets as well as striped polecats (Ictonyx striatus). Over 30 mammal species have been identified as foods for bateleurs exclusive from carrion, including various larger food species, with carrion of ungulates ranging in size from that of Sharpe's grysbok (Raphicerus sharpei) to African buffalo (Syncerus caffer) and the carrion of carnivorans from the size of jackals to that of lions (Panthera leo). In compilation studies, the most often fed-on ungulates by bateleurs that were identified to species were reported to be impala and steenbok (Raphicerus campestris), at 4.2% and 2.2% of the total foods, respectively . Bateleurs have been reported to opportunistically scavenge on human remains, as was reportedly witnessed during the South African Border War.
Outside of galagos, among primate foods most monkeys observed in the diet such as baboons and vervet monkeys (Chlorocebus pygerythrus) are thought to be largely scavenged as carrion. However, studies of king colobus (Colobus polykomos) and Angola colobus (Colobus angolensis) in Central and southeastern Africa (both where few details are known of bateleurs' diets), it was mentioned bateleurs may be a potential predator of troops based on the anti-predator activity and vocalizations of these species provoked by bateleurs. The bateleur, using its large, powerful feet, does not shy away from very large prey and has been known to regularly kill mammals heavier than itself including scrub hare estimated to weigh , springhares estimated to weigh , Cape hyrax estimated to weigh , Kirk's dik diks estimated to weigh and greater cane rats estimated to weigh . Even more impressive mammalian kills have been suspected, with instances where reportedly adults black-backed jackals (Canis mesomelas), honey badgers (Mellivora capensis), and aardwolf (Protelas cristatus), any of which may weigh around twice the aforementioned large mammal prey for bateleurs, may have been unexpectedly killed by bateleurs. Furthermore, an instance of attempted predation in Tanzania on an adult honey badger was witnessed, ending with both the bateleur and badger dying from the ensuing fight.
In all, a considerable diversity of birds may be taken by bateleurs, perhaps around 80 species being known in their prey spectrum. They often focus on rather small, if normally live caught, birds compared to other eagles of a similar size. Bateleurs may show a special liking for pigeons and doves as prey, although only about a half dozen have been identified to species. Doves usually of the genus Streptopelia were found to be the most prominent avian prey in compilation studies, accounting for 17.6% of known avian prey and 4.25% of the total foods in several large bateleur food studies. Much other similar avian prey, commonly those weighing around , including a surprising diversity of nightjars (perhaps since they are prone to end up as roadkill due to their predilection for resting on roads by night) and shorebirds like lapwings, other plovers, sandpipers and terns in addition to kingfishers (up to the size of the giant kingfisher (Megaceryle maxima)), rollers, hoopoes, small hornbills, parakeets and some passerines, usually those with a conspicuous presence on the savanna such as shrikes, weavers and starlings., Unlike many other eagles of similar or larger size, there are few instances of waterfowl or large waders (i.e. heron, storks, flamingoes, etc.) falling prey to bateleurs although at least one African spoonbill (Platalea alba) was recorded as bateleur prey. The largest typical avian prey tends to be assorted gamebirds, with most common guineafowl, spurfowl and francolin, smaller available species of bustard and some quail known in their diet. The largest of these avian prey species attacked by bateleurs top out around . The reason for the disinterest in mid-sized to large avian prey of sizes comparable to some mammals and reptiles are known to have been taken by bateleurs is not clear, as the bateleur does not, in general, appear to shy away from difficult-to-capture birds nor to large and dangerous prey of other animal classes.
The bateleur was once reported to be a very common predator of reptiles like their cousins the snake eagles. Although this is somewhat erroneous, bateleurs do not infrequently include reptiles in their diet. As much as 30% of the diet can be reptilian, mainly snakes. Some reptiles taken are small and innocuous such as a few species of plated lizards and a few species of colubrid snakes. However, like their cousins, the bateleur does not seem to shy away from venomous snakes nor other large or formidable reptiles. They have been known to take puff adder (Bitis arietans), boomslangs (Dispholidus typus), Egyptian cobras (Naja haje) and unidentified mambas, with the latter actually reported to be the most prominent known reptile prey in compilation studies, accounting for 18.9% of reported reptile prey and 3.35% of total prey. They can take sizable snakes, even adult puff adders which can grow much heavier than the eagle themselves. However, the bateleur is not immune to venom nor is as well specialized to dispatching venomous snakes as are snake eagles, and, in one case, a mutual killing recorded between a puff adder and a bateleur was reported. Sizable, and far from defenseless, if not venomous reptiles known in the prey spectrum may include monitor lizards including Nile (Varanus niloticus) and savannah monitors (Varanus exanthematicus), some terrapins and tortoises and African rock pythons (Python sebae), although excepting small, young ones, these types of reptilian prey are perhaps in many cases consumed after they are already deceased, such as via roadkills. Nevertheless, bateleurs occasionally hunt small tortoises and monitor lizards, and in one instance, live predation on an adult monitor lizard about 1.4 m in length has been reported. The bateleur is known to carry snakes to the nest in the style of ordinary snake eagles, with the dead snake being half swallowed and subsequently extracted by the capturing bird's mate, usually the female at the nest. Seldom identified prey may include assorted, and almost entirely unidentified, insects. Mostly swarming social insects seem to attract bateleurs, including locusts. It was recently verified that bateleurs will semi-regularly visit termite mounds to hunt down alates, although such feeding has been inferred in the past. Other prey can include a rare amphibian, none of which are known to be identified to species or family. Although fish are not typically taken, as much as 1.1% of the diet locally can consist of large Clarias catfish and it is likely that stranded fish are not neglected when opportuned upon.
Interspecific predatory relationships
The bateleur seems to adapt to living in the highly competitive continent of Africa by foraging with a lack of specialization, with a seeming lack of discrimination regarding the prey item/food source nor its origin although its highly aerial and free-ranging foraging mode is quite unique. The bateleur, nonetheless, must face considerable and intense competition from other birds of prey especially. The range of other raptors, especially other eagles and vultures, may appear to be daunting. One of the most similar eagles to regularly encounter the bateleur is the tawny eagle. These two species overlap in many significant ways, being similar in body mass and predatory prowess as well as in nesting habitat, tendency to attack a wide size range of prey (including large prey) and general disposition. Furthermore, both of these eagles show ability to freely change feeding methods between live predation, scavenging on carrion and piracy. In Tsavo East National Park, bateleurs were studied along with tawny eagles, significantly larger martial eagles and slightly smaller African hawk-eagles (Aquila spilogaster). Here all four largish eagles relied primarily upon Kirk's dik dik for food but were mostly slightly staggered in breeding season, with the bateleur nesting on average earlier than the other eagles. The diet was by far most similar with that tawny eagle in Tsavo East, overlapping 66% in prey species and 72% in prey weight. Meanwhile, the diet overlapped 32% in species and 50% in weight with martial eagles and 37% in species and 57% in weight with African hawk-eagles. The one discrepancy, which is noted in other studies as well, is that the bateleur tends to focus on smaller birds than tawny eagles when selecting avian prey. Bateleurs also bear an advantage over tawny eagles in their ability forage in open habitats, with the absence of perches, due to their aerial foraging methods. However, data indicates that the tawny eagles is dominant over bateleurs typically at disputed kills or carrion. One study accrued 26 instances of tawny eagles displacing bateleurs against only 5 where bateleurs displaced tawny eagles, giving illustration to the tawny eagles dominance. Frequently, the bateleur waits until the tawny eagle is done eating before it does so itself if both are at a carcass site.
Bateleurs may encounter a huge range of other scavengers when coming to carrion. Most clearly vultures are often present at carrion. However, due to their smaller size, the tawny eagle and especially the bateleur can begin foraging for carrion earlier in the morning, while the vultures must wait for updrafts to undertake flight. Bateleurs in particular are considered most likely to find a carcass first before other scavengers. This was verified in a study in Maasai Mara where it was additionally found that scavengers kept to body size in terms of hierarchy. The descending order of scavenger dominance was stated to rank starting with the spotted hyenas (Crocuta croctua) at the top and black-backed jackals and feral dogs (Canis lupus familiaris), then the lappet-faced vulture (Torgos tracheliotos), the Rüppell's vulture (Gyps rueppellii), followed by all other vultures with the tawny eagle and the bateleur in the second most and the most subordinate scavenger positions. Therefore, the bateleur is considered a scavenger with high search efficiency but low competitive ability. However, the bateleur does benefit from the larger scavengers, being less able to access a large carcass, at best feeding on the eyes of said carcass unless it is already otherwise torn asunder such as large carnivore prey or roadkills. With the epidemic-level reduction of vultures in Africa, it was found in Maasai Mara that both bateleurs and tawny eagles have been found to actually increase in sighting frequency in sync with the vanishing numbers of remaining vultures, with the number of bateleur sightings increasing by 52%. To the contrary of the expected hierarchy, cases are known where bateleurs have attacked and dominated much larger scavenging birds including white-backed vultures (Gyps africanus) and bearded vulures (Gypaetus barbatus), with these having been successfully displaced or lost carrion to a bateleur. Even more impressively, cases where bateleurs interacting with much larger, more powerful martial eagles have involved instances where the bateleurs have attacked, pirated and even brought to ground in clashes that appear to end in a drawl. However, the martial eagle occupies a notably higher trophic level than the bateleurs and is not considered subservient to bateleurs due its even greater predatory prowess. Similarly, instances of considerable competition have been reported between bateleurs and African fish eagles (Haliaeetus vocifer), which are similarly prone to opportunistic piracy and aggressive interspecific relations. However, the two species are partitioned by habitat and primary prey.
It is uncommon-to-rare but not unprecedented that bateleurs may prey on other raptors. Bateleurs have been documented preying on black-winged kites (Elanus caeruleus), wintering lesser spotted eagles (Clanga pomarina), gabar goshawks (Micronisus gabar), barn owls (Tyto alba), spotted eagle-owls (Bubo africanus) and peregrine falcons (Falco peregrinus). Additionally, they were considered a likely potential predator upon nestlings of the white-backed vulture. Certainly the most impressive instance of intraguild predation documented as committed by bateleurs is when one was seen killing an adult Verreaux's eagle owl (Bubo lacteus), a formidable top predator among owls and possibly the largest avian prey ever reported for a bateleur. The predators of mature bateleurs themselves are not well-documented and in fact, Verreaux's eagle owls may the only species verified to repeatedly prey upon bateleurs, but this is probably due to rare predator identification at bateleur nests. Bateleurs are usually considered apex predators. By contrast, bateleur nestlings are vulnerable to predation compared to other raptors. Though adult bateleurs can simply leave the nest or crouch below the nest rim to reduce nest detectability to many predators, they can be very aggressive toward conspecifics as well as other raptors, and occasionally human intruders. However, due to their unique foraging mode which takes them far from the nest for long periods of the day, the physical defense is largely unable. Thus, chicks are presumed to be vulnerable to a huge range of predators although very few are properly identified. Based on other eagles in Africa, these are likely to include various sizes of mammalian carnivores, snakes, monitors and various birds of prey, including even perhaps much smaller species and vultures due to the long periods bateleur eaglets are left unprotected.
Breeding
Bateleurs are long-lived species, slow-maturing, slow-breeding species, Bateleurs court each other or re-establish existing pair bonds what is considered, a "spectacular" courtship display. During the courtship display, an exaggerated flight is undertaken, in which the male dives down at the female who rolls to present him her claws. Additionally, he sometimes flies with legs dangling loosely, during which the wings may be flapped to create a conspicuous whup-whup-whup noise like a loose sail in the breeze. Very infrequently, a male bateleur may make a 360 degree lateral roll, accompanied by loud whup-whup noises, at times display may involve 2 males with a single female, but during breeding only one male is usually actively courtship. A further chasing flight reported is not necessarily nuptial and may be performed by birds of the same size and by an adult or an immature and in some cases is linked to the sociality of the species. The bateleur is usually rather monogamous and likely, with the survivorship of each mate, mates for life. However, rare instances of possible polygyny have been reported. The bateleur breeding season tends to fall from September to May in West Africa, however juveniles have also been recorded in Mauritania in September. Reportedly, the nesting season can be virtually any month in East Africa but chiefly is some time around December–August, which also is the corresponding peak breeding time in Southern Africa, with nesting as late as August to October in the southern stretches of the continent considered unusual. In Somalia, the breeding season however fell from July to December while in Ethiopia there was no detectable peak whatsoever.
Nests
Nests are located in fairly large trees, sometimes near a watercourse, either in hilly terrain or open flat country. At times, bateleurs are adaptable and perhaps even favor towards nesting near manmade openings such as roads or paths. Nests are typically at above the ground but in extreme may be from high. The nest is normally within the canopy in the fork of the main trunk or a large lateral branch so that it is shaded for much of the day. A variety of tree species may be used. In southern Africa, favored trees tend to Adansonia and especially Acacia trees. Senegalia nigrescens trees may too be popular. Bateleurs usually nest on structures made by themselves but one nest was reported in on a buffalo weaver nest and was difficult to observe. Furthermore, old nest of other birds may be used, in one case a Wahlberg's eagle (Hieraaetus wahlbergi) nest taken over and added to deepen it. The nest is a solid structure of medium-sized sticks, measuring about across, deep with a leafy cup of about across. Snake eagles and their kin tend to build relatively small if bulky nests relative to their size and the bateleur is no exception, with their nest size being about half that of in diameter of a similarly-sized eagle like the tawny eagle. Nests tend to be lined with green leaves by the bateleur pair. Both sexes of bateleur are known to contribute to the building or repair of a nest, a process that typically takes about 1–2 months, though sometimes nest construction can be reportedly protracted even in years where no breeding occurs. They often subsequently use a new nest in the same general area in consecutive breeding seasons, usually not more than away, and may reuse a nest they built previously. There is much variation in this regard, from 1 nest being used in 5 consecutive years to no nest reusage in 3 recorded years. Nests built by bateleurs tend to be favored by lanner falcons (Falco biarmicus), probably in part because the eagle's young are fledged by July–August when lanners tend to lay; however 1 nestling was persistently mobbed by a lanner during its last week at the nest. In ranching country in Zimbabwe, nests are spaced apart. In Mozambique, nesting spacing was found to be about .
Eggs and development of young
In this species, only one egg is ever laid. Their eggs are quite large for the size of the bird, being broadly oval and usually an unspotted chalky white but sometimes with a few red stains or indistinct reddish markings, which may be cosmetic from feeding and defecating of the parents. The bateleur's egg is quite similar in size and coloration to most snake eagles, which also generally lay a single egg. A bateleur egg may measure from in height, with an average of in a sample of 24 and in a sample of 50, by in diameter, with an average of in 24 and in 50. The eggs are comparable in size to those of martial and crowned eagles (Stephanoaetus cornatus), eagles of easily up to twice the body size of a bateleur. The female bateleur normally incubates alone, though rarely males are seen to do so as well. The female is fed by the male but takes spells off in which she probably feeds on her own kills and the male may take over incubation, although reports of instances where he may do the majority of incubation are probably inaccurate. While the elastic breeding season suggests an indifference to climatic concerns relative to the wet season and dry season, the bateleur is usually considered an eagle that lays earlier in the year than overlapping eagles. The incubation stage lasts for 52 to 59 days, averaging about 55 days, and may the longest of any African raptor. Reports of incubation lasting for only 42–43 days are probably erroneous.
The hatchling is highly altricial and very feeble at first, perhaps even more so than most other eagles, being unable to lift its own heavy head and possesses a deeply wrinkled cere. The small eaglet is initially covered in creamy down with a chocolate-brown patch behind the eye that matches the rest of the down colour above with creamy flanks. At about 2 weeks, the young eaglet becomes somewhat more active and the down develops a patchy appearance. At 3 weeks, the eaglet has a downy white head but the down colour above is dark brown, with the first brown feathers sprouting on back of head, secondaries and scapulars. By 4 weeks, they no longer have any white down and brown feathers grow especially the back and wing ones; while a week later, the feathers continue emerge and the secondaries outgrow the primaries. Thence at 7 weeks, the feathering of the foreparts occurs rapidly, being complete by 35 days, but the wing and tail feathers are still growing, the last remaining down being on underwing coverts. The young eaglet resembles those of snake eagles in appearance and feather growth pattern, particularly the retarded growth of the primary feathers, and in general coloring become greyer as the eaglet ages. The nestling may first stand at about 5 weeks as well as engage in wing-flapping. Pre-independence juveniles may perch or lie in prone position before they can fly well. The stage at which the young first feeds itself is dictated by what prey is brought; if it is large, the parents will feed the young to 40 days, but small fragments will be eaten unaided by the downy young. Around 6 weeks is when the eaglet can typically feed itself for the first time. At 9 weeks, eaglet bateleurs have been recorded doing effective threat displays against humans. Fledgling typically occurs around 90–125 days with reported extremes at as little as 93 to as much as 194 days. The young often returns to the nest after its first flight and continues to do so. The young bateleurs become independent quickly within about a week in some case and in others remain closely by and dependent on their parents for about 2–4 months. The young bateleurs may follow their parents around in flight until they are fed. Coaxing behaviour by parents has been recorded (keeping away food until they fly to it, perhaps gradually encouraging the young eagle to go farther afield). After leaving the nest area, the young bateleurs often wander widely, for example one was recorded to have covered . When soaring near another bateleur nest, young bateleurs are often fiercely attacked by adult males. There are some reports, even frequent reports it is said, of immature bateleurs staying to help incubate the eggs although generally this presumably rare.
Parental behaviour
When the nest is approached, at times bateleurs will react forcibly, engaging in aggressive barks, sometimes diving down from flight at the intruder with loud flapping wings. When disturbed in this way, however bateleurs very often depart and they will often not return to the nest for up to several hours. Generally, it seem to be more likely than almost any other African eagle to desert their young. During the incubation and nestling period, the male is more demonstrative than the female at the nest, sometimes doing the distraction display and regular dive-bomb attacks if the nest tree is climbed, the female more commonly flies away in the distance. Once a lone male baboon climbed a nest tree, the female bateleur sat and incubated while the male dive bombed it. When this failed to drive it off, the male settled on a branch between the baboon and the nest and threatened the monkey with raised wings, the baboon was never dislodged but did not harass the eagles at the nest. Bateleur parents are highly sensitive to breeding from human disturbance, oddly they may permit and adapt to regular inspections of the nest but resent an attempts to hide or conceal photographic equipment nearby and regular desert the nest even with a small nestling, thus nest photography should be avoided. The ease with which bateleurs are flushed away from their nest appears to lead to uncommonly high nest predation rates, while many other eagle, including from other parts of the world, either sit tightly on their nest until the danger level becomes too high or attack ferociously at the potential threat. The nestling is careful tended to by female, as she is at the nest 82% of the time up to the time the eaglet is 10 days in one Kenya study, her attendance thence drops to 47% from 10–20 days, then after 30 days, dropped to about 5% and from 60 days about 1%. When the young is at later stages of maturity, the female tends to only engage in very brief prey deliveries. Both sexes bring prey and feed the young though the male takes a bigger share of this than in many eagles. After 30 days, the eaglet is often left by itself on the nest throughout the night. The eaglet is fed nearly every day early on but only every 2–3 days later on, especially after leaving the nest.
Breeding success and failures
It is estimated that the bateleur produces a mean of 0.47 chicks per nest per year. In East Africa, the bateleur tends not to breed every year and the replacement rate is about 0.5 per annum. In southern Africa, the bateleur typically breeds every year whether or not they are successful in raising their eaglet. At 4 nests in Zimbabwe, a replacement rate of 0.81 young per pair per annum, with local figures often being higher where they live more free from human disturbance. It was found that Zimbabwe failures were only known to be from infertile or lost eggs. In Kruger National Park, the predation of Verreaux's eagle-owls may considerably lower nesting success. Furthermore in Kruger, it was found that 33% of the population of bateleurs were young birds while the remaining 67% were adults, meaning that younger birds are presumably underpopulated. Elsewhere, even lower numbers, around 25-30%, of the population is young bateleurs. The population, or at least in southern Africa, seems to be roughly even in terms of sex ratio, with an even number of males and females. In the Kalahari Gemsbok National Park, 13 pairs of bateleurs were recorded to produce only 0.33 young per pair. There was evidence of a 13% decline in active nesting territories of bateleurs in the Kalahari Gemsbok area during the seven year study, and at least a 40% decline over the previous 10 years. Vacated nesting territories were not reoccupied by the species. There was found to be seemingly no safe buffer zone around the park, due perhaps to persecution in the adjacent farmlands, when potential mortality of foraging bateleur from the protected park enter these areas, as well as nesting site disturbance, could have been part of the reason for this decline. Poisoned and suspected poisoned bateleurs have been found in the Park during the study period. The few that survive their early years may expect a mean estimated lifespan of around 12–14 years and in some cases may manage to live as long as 27 years. The annual adult survival rate is estimated at 95%, while the annual juvenile survival rate is estimated at 75%.
Conservation
Bateleurs are a wide ranging species but have shown rather strong declines. Per estimates from the 1990s, extrapolated from an average of per pair, it was projected that the total population could have been around 180,000 birds including young ones. However, it is likely that the species numbers far lower than that. Currently, the IUCN estimates broadly from 10,000 to 100,000 total individuals. The numbers in Southern Africa have shown the most dramatic and drastic known reductions. At one time, the species numbers at 2000-2500 pairs in the former Transvaal Province alone which was down to around 420 to 470 pairs by the 1990s. More recently it was estimated that there are less than 700 pairs in the entire region of Southern Africa, although that number may be too excessively conservative. In all the bateleur has declined by an estimated 75% in Southern Africa. The species is considered threatened in Zimbabwe, Namibia, Eswatini and South Africa and still considered not uncommon but probably declining in Malawi, Zambia, Mozambique and Botswana. Declines are not endemic to Southern Africa for bateleurs, with declines strongly detected as well in Ivory Coast and Sudan. Addition countries that have reported strongly declining numbers are in Togo, Niger and Nigeria. Where bateleurs were once common in road surveys in Central-West Africa, none were detected in newer road surveys from the 2000s in the same areas. Claims of an increase in potential numbers of bateleur in Uganda are not verified.
Decline of the species and the reduction in range is suspected to have been moderately rapid over the past three generations. Generally, throughout the range, the bateleur is considered much more common in protected areas. However even in several protected areas, numbers of bateleurs seem to decreasing. The declines of the species are almost entirely due to anthropogenic causes. These include but are not limited to habitat destruction, the poisoning of carcasses, persecution through shooting and possibly pesticide use. Poisoning of carcasses is a major issue for scavenging animals, especially birds like vultures, in Africa. Zambian bateleurs may suffer from deliberate poisonings as well as those in Eswatini, Botswana, Zimbabwe and Mozambique. The bateleur's wide foraging areas and their ability to locate very small pieces of carrion, makes them highly susceptible to poison-laced carcasses even from a small proportion of farmers who use poisons. Bateleurs and other eagles are not usually the direct target of these poisoning operations, which in some cases may be directed to unfavored mammals like jackals or in other cases directed towards vultures by poachers to hide their illegal wildlife killings. The decline of South African bateleurs is primarily linked with poisonings, primarily from large-scale farming operations. It is possible that bateleurs may suffer from the effects of DDT though it is found in a small sample of 3 eggs from South Africa that they evidenced low subcritical levels of DDT metabolites, probably not enough to effect overall populations. However, it is projected that pesticide use may be harming populations in Zambia as well as in Botswana. Ongoing persecution is both serious and unsustainable, beyond poisoning, such killings are known to extent to ongoing shooting and trapping. Some trapping occurs of the species for its feathers which are used in medicine by traditional healers for predicting future events Less well known but probably occurring declines may be due to flying into manmade objects including wire collisions, reservoir drownings and road-killings. Additionally, shrinking habitat has been found to be a prevalent threat to bateleurs due largely to expanding human settlements and intensifying livestock agriculture. A further effect from humans is regular disturbance at bateleur nests, although not typically as deliberate as many other threats, this is causing the breeding success rates to plummet farther. No large scale actions are underway but they are possibly protected in Yemen as an endangered species. It is proposed to implement education and awareness campaigns across its range to reduce the use of poisoned baits. Regular population monitoring is being carried out.
Heraldic and mythological status
The bateleur plays a prominent role in African heraldic and mythological cultures probably due to its spectacular colours and conspicuous and bold behaviour. As a result it is likely that the bateleur is the basis for the "Zimbabwe Bird" which has been prominent since ancient times in Zimbabwean culture and continuously used in heraldic forms including most prominently being featured on the Zimbabwe flag. A South African myth was that when bateleurs "cries in flight, the rain will fall". The admiration and mythologizing of bateleurs is also known in other areas beyond Zimbabwe, including among those in Southern Africa who speak Tswana language as well as elsewhere dating back to the Iron Age with various with the bateleur variously known as kgwadira and petleke, and may often in mythology may fulfill the role intelligent servant to their masters, which were considered vultures. In East and Central Africa, the bateleur has been referred to variously as gawarakko and nkona and in the Lake Tanganyika was considered an essential possession of sultans whether the birds were dead or alive.
Media
| Biology and health sciences | Accipitrimorphae | Animals |
3831878 | https://en.wikipedia.org/wiki/Lupin%20bean | Lupin bean | Lupin are the yellow legume seeds of the genus Lupinus. They are traditionally eaten as a pickled snack food, primarily in the Mediterranean basin (L. albus), Latin America (L. mutabilis) and North Africa (L. angustifolius). The most ancient evidence of lupin is from ancient Egypt, dating back to the 22nd century BC. The bitter variety of the beans are high in alkaloids and are extremely bitter unless rinsed methodically. Low alkaloid cultivars called sweet lupins have been bred, and are increasingly planted.
History and distribution
The earliest archaeological reports on lupins are referred to the Twelfth Dynasty of Egyptian Pharaohs. In their tombs, seeds of Lupinus digitatus Forsk., already domesticated in those times, were discovered. Seven seeds of this species were also retrieved in the tombs of this dynasty dated back to the 22nd century BC. They are the most ancient evidence of lupin in the Mediterranean.
Lupin is commonly used in Egypt (known by the name "termes") and is eaten by the Egyptians as snack anytime as during the Sham Elnesim festival, which is a national festival in Egypt whose history goes back to ancient Egyptian times. Lupin were also used by the Ancient Greeks and Romans.
The Andean American variety of this lupin, Lupinus mutabilis, was domesticated by pre-Incan inhabitants of present-day Peru. Rock imprints of seeds and leaves, dated around 6th and 7th century BC, are exhibited in the National Museum of Lima. It was a food widespread during the Incan Empire. Lupins were also used by Native Americans in North America, e.g. the Yavapai people.
Today, lupin are commonly found in Mediterranean countries like France, Italy, Spain, Portugal, Greece, in South America and across the Middle East.
Varieties
Some varieties are referred to as "sweet lupins" because they contain much smaller amounts of toxic alkaloids than the "bitter lupin" varieties. Newly bred variants of the narrow-leafed or 'Australian Sweet Lupin' (L. angustifolius) lupins are grown in Australia, Germany and Poland; they lack any bitter taste and require no soaking in salt solution. The seeds are used for different foods from lupin flake, vegan sausages, lupin-tofu, and lupin flour. Given that lupin seeds have the full range of essential amino acids and that they, contrary to soy, can be grown in more temperate to cool climates, lupins are becoming increasingly recognized as a cash crop alternative to soy.
Three Mediterranean species of lupin (blue lupin, white lupin and yellow lupin) are widely cultivated for livestock and poultry feed. Bitter lupins in feed can cause livestock poisoning.
Lupins are currently under widespread cultivation in Australia, Europe, Russia, and the Americas as a green manure, livestock fodder and grazing plant, and high-protein additive for animal and human foods. In Australia, the danger of cross-pollination of the wild bitter and cultivated sweet low-alkaloid variety is understood to be unacceptable when testing reveals the presence of one bitter bean per hundred sweet beans, and a wide quarantine zone is maintained around lupin-growing croplands to prevent wind-blown wild pollen from having a large influence on crop toxicity.
Uses
Lupin beans are commonly sold in a brine in jars (like olives and pickles). They can be eaten by making a small tear in the skin with one's teeth and "popping" the seed directly into one's mouth, but can also be eaten with the skin on. The skin can also be removed by rubbing the bean between forefinger and thumb.
In France they are found mainly in the southern part of the country. They are prepared in brine, like olives and are often served with an aperitif or used to garnish salads.
In Egypt, lupin is known by its Egyptian Arabic name "termis" (ترمس), and it is sold by street vendors as well as local markets as a snack, especially during the Sham el-Nessim festival.
The Andean lupin L. mutabilis, the Mediterranean Lupinus albus (white lupin), and Lupinus hirsutus are only edible after soaking the seeds for some days in salted water. In Ecuador, the lupin is often consumed as a ceviche-like street food known as "cevichochos".
Lupin beans can be ground into a flour, and this is widely used in parts of Europe and in Australia as an additive to wheat flour, enhancing the flavour and lending a rich, creamy colour to the resulting foods.
They can also be used as a key ingredient in vegan dairy, egg, and meat substitutes. As of 2020, only 4% of lupins were consumed by humans, with the majority used as stock feed. Lupin beans are growing in use as a plant-based protein source in the world marketplace.
Nutrition
Raw lupin beans are 10% water, 40% carbohydrates, 36% protein, and 10% fat (table). In a reference amount, raw lupins supply of food energy and are moderate-rich sources of B vitamins, especially folate at 89% of the Daily Value (DV) (table). Lupins also contain substantial amounts of dietary minerals, including manganese at 113% DV (table).
Lupins have a thick seed coat (25%) which consists mainly of cellulose (insoluble bran fiber) and is removed as the first step in processing.
Toxicity
Lupin poisoning is a nervous syndrome caused by alkaloids in bitter lupins. Lupin poisoning affects people who eat incorrectly prepared lupin beans. Mediterranean cultures prefer the historic bitter lupin beans with the required toxin-removal by traditional leaching in water preparation methods due to the better flavour that results. Improper preparation of bitter lupins with insufficient soaking allows pharmacologically significant amounts of the anticholinergic alkaloids to remain in the beans, and poisoning symptoms result.
While the alkaloids found in raw and dried beans are bitter and unpalatable to many, with soaking the level is reduced. There are several references in medical literature to poisoning caused by errors in lupini preparation.
Symptoms of lupin bean poisoning (from excess alkaloid in cooked food) include dilated unresponsive pupils, confusion, slowed thought and disorientation, flushed face and/or fever, high heart rate and blood pressure, tremors, difficulty with or slurred speech, in-coordination, dizziness, burning dry mouth, stomach pain, and anxiety or "malaise".
Many human symptoms are described in the Australian government's evaluation of lupin food and livestock fodder export safety standards in the medical literature review section:
Current media describes the symptoms when referring to recent Australian Medical Journal reports of poisoning from overly bitter lupin flour used in foods reported in the media.
According to the Australia New Zealand Food Authority (2001), "data indicates that the mean alkaloid content of marketable sweet lupin seed is on average 130–150 mg/kg." Regarding the daily tolerable intake of alkaloids, it writes, "The only data available on human chronic toxicity are the reports of traditional use of lupini beans in Europe, which indicate a daily dose of 0.35 mg/kg can be tolerated in adults without adverse affects. […] Also, the information applies only to adults, not children, and it is likely that the adult population has developed a certain amount of tolerance to these alkaloids. […] If a safety factor of 10 is applied to account for the uncertainties in the data and particularly to take into account likely human variation, the provisional tolerable daily intake (PTDI) for humans is 0.035 mg/kg/day or 35 μg/kg/day."
A 2017 opinion by the German Federal Institute for Risk Assessment states that "there are no systematic and validated tests for the quality of household kitchen debittering methods", and as a precaution, it recommends that "consumers avoid the consumption of bitter lupin seeds which were not debittered by the manufacturer, as there is no certainty that the recommended debittering procedures result in a sufficient reduction in the levels of health-damaging alkaloids."
Mycotoxic lupinosis is a disease caused by lupin material that is infected with the fungus Diaporthe toxica; the fungus produces mycotoxins called phomopsins, which cause liver damage.
Lupin allergy
Lupin allergy may cause life-threatening anaphylaxis in sensitive individuals. There is some cross-reactivity with peanut allergy, so nut allergy sufferers should exercise extreme caution with lupin-containing food. In the EU, lupin must be listed as an allergen in pre-packed foods where it has been used, but may still be hidden in over-the-counter products. This can be a significant problem for allergy sufferers since breads, pastries, pizzas, pasta, cakes and ice cream are all commonly sold over-the-counter, and all may contain lupin. Lupin has even been found in some tomato ketchup sauces. At present, no desensitization treatments are available, so avoidance is the only advice offered, alongside carrying an epi-pen and anti-histamine/anti-inflammatory medication.
| Biology and health sciences | Pulses | Plants |
2852964 | https://en.wikipedia.org/wiki/John%20Dory | John Dory | John Dory, St Pierre, or Peter's fish, refers to fish of the genus Zeus, especially Zeus faber, of widespread distribution. It is an edible demersal coastal marine fish with a laterally compressed olive-yellow body which has a large dark spot, and long spines on the dorsal fin. Its large eyes at the front of the head provide it with binocular vision and depth perception, which are important for predators. The John Dory's eye spot on the side of its body also confuses prey, which are scooped up in its large mouth.
In New Zealand, Māori know it as kuparu, and on the East Coast of the North Island, they gave some to Captain James Cook on his first voyage to New Zealand in 1769. Several casks of them were pickled.
Etymology
The name dory is attested from 1440, derived from the French dorée 'gilded', a French name for the fish. The addition of "John" appears in 1609, and probably comes from a 17th-century song about a sea captain, John Dory. Etymologies claiming it comes from the French jaune dorée (meaning "golden yellow") which sounds like 'John Dory' in English, or the Italian gianitore 'janitor' are now rejected.
A legend says that the dark spot on the fish's flank is St. Peter's thumbprint. In the north coast of Spain, it is known commonly as San Martiño. The Māori language name for the fish, , appears to be unique to New Zealand, as there are no cognates found in other Polynesian languages.
Morphology
The John Dory grows to a maximum size of 65 cm (2 ft) and 5 kg (12 lb) in weight. It has 10 long spines on its dorsal fin and 4 spines on its anal fin. It has microscopic, sharp scales that run around the body. The fish is an olive green color with a silver white belly and has a dark spot on its side. Its eyes are near the top of its head. It has a flat, round body shape and is a poor swimmer.
Prey and predators
The John Dory catches prey by stalking it, then extending its jaw forward in a tube-like structure to suck the fish in with some water. The water then flows out through the gills; the pre-maxillary bone, the only tooth-bearing bone in this fish, is used to grind the food.
The John Dory has a high laterally compressed body – its body is so thin it can hardly be seen from the front. The large eyes at the front of the head provide it with the binocular vision and depth perception it needs to catch prey. This eye spot also confuses prey, which can then be sucked into its mouth.
It primarily eats smaller fish, especially schooling fish such as sardines. Occasionally it eats squid and cuttlefish.
Its main predators are sharks such as the dusky shark, and large bony fish.
Habitat
John Dory are benthopelagic coastal fish, found on the coasts of Africa, South East Asia, New Zealand, Australia, the coasts of Japan, and on the coasts of Europe. They live near the seabed, living in depths from . They are normally solitary. John Dory are more commonly found in the waters of the North Island of New Zealand than the colder waters surrounding the South Island.
Reproduction and lifespan
When John Dories are three or four years of age, they are ready to reproduce. This happens around the end of winter. They are substrate scatterers, which means that they release sperm and eggs into the water to fertilize. Typical lifespan is about 12 years in the wild.
As food
Cookery writer Eliza Acton in her 1845 book Modern Cookery for Private Families observed that John Dory "though of uninviting appearance, is considered by some persons as the most delicious fish that appears at table". She recommends simply baking it "very gently", avoiding it drying out in the oven.
John Dory is a popular choice among professional chefs due to the versatility of the fish, though access to home cooks is limited; the bycatch fish is not typically sold at supermarkets.
| Biology and health sciences | Acanthomorpha | Animals |
2853861 | https://en.wikipedia.org/wiki/Anomalocaris | Anomalocaris | Anomalocaris ("unlike other shrimp", or "abnormal shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group marine arthropods.
It is best known from the type species A. canadensis, found in the Stephen Formation (particularly the Burgess Shale) of British Columbia, Canada. The other named species A. daleyae is known from the somewhat older Emu Bay Shale of Australia. Other unnamed Anomalocaris species are known from China and the United States.
Like other radiodonts, Anomalocaris had swimming flaps running along its body, large compound eyes, and a single pair of segmented, frontal appendages, which in Anomalocaris were used to grasp prey. Estimated to reach long excluding the frontal appendages and tail fan, Anomalocaris is one of the largest animals of the Cambrian, and thought to be one of the earliest examples of an apex predator, though others have been found in older Cambrian lagerstätten deposits.
Since the original description in late 19th century, the frontal appendages were the only known fossilized parts and misidentified as the body parts of other animals. Its radiodont affinity was revealed in 1980s, specifically in a 1985 journal article by Harry B. Whittington and Derek Briggs. The trunk and mouth were reconstructed after another radiodont genus until the corrections done in 1996 and 2012. It is the type genus of Anomalocarididae, a family which previously included all radiodonts but recently only Anomalocaris and a few closely-related taxa.
Discovery and identification
From the start, Anomalocaris fossil was misidentified, followed by a series of misidentifications and taxonomic revisions. As Stephen Jay Gould, who popularised the Cambrian explosion in his 1989 book Wonderful Life, appropriately described:[The story of Anomalocaris is] a tale of humor, error, struggle, frustration, and more error, culminating in an extraordinary resolution that brought together bits and pieces of three "phyla" in a single reconstructed creature, the largest and fiercest of Cambrian organisms.Anomalocaris fossils were first collected in 1886 by Richard G. McConnell of the Geological Survey of Canada (GSC). Having been informed of rich fossils at the Stephen Formation in British Columbia, McConnell climbed Mount Stephen on 13 September 1886. He found abundant trilobites, along with two unknown specimens. In August 1891, Henri-Marc Ami, Assistant Palaeontologist at GSC, collected many trilobites and brachiopod fossils, along with 48 more of the unknown specimens. The fifty specimens were examined and described in 1892 by GSC paleontologist Joseph Frederick Whiteaves. Whiteaves interpreted them as the abdomens of phyllocarid crustaceans, and gave the full scientific name Anomalocaris canadensis. He describes the crustacean characters:Body or abdominal segments, which, in all the specimens collected, are abnormally flattened laterally, a little higher or deeper than long, broader above than below, the pair of ventral appendages proceeding from each, nearly equal in height or depth to the segment itself... The generic name Anomalocaris (from ανώμαλος, unlike,—καρίς, a shrimp, i.e., unlike other other shrimps) [the species name referring to Canada] is suggested by the unusual shape of the uropods or ventral appendages of the body segments and the relative position of the caudal spine.In 1928, Danish paleontologist Kai Henriksen proposed that Tuzoia, a Burgess Shale arthropod which was known only from the carapace, represented the missing front half of Anomalocaris. The artists Elie Cheverlange and Charles R. Knight followed this interpretation in their depictions of Anomalocaris.
Not known to scientists at the time, the body parts of relatives of Anomalocaris had already been described but not recognized as such. The first fossilized mouth of such a kind of animal was discovered by Charles Doolittle Walcott, who mistook it for a jellyfish and placed it in the genus Peytoia. Walcott also discovered a frontal appendage but failed to realize the similarities to Whiteaves' discovery and instead identified it as feeding appendage or tail of the coexisted Sidneyia. In the same publication in which he named Peytoia, Walcott named Laggania, a taxon that he interpreted as a holothurian.
In 1966, the Geological Survey of Canada began a comprehensive revision of the Burgess Shale fossil record, led by Cambridge University paleontologist Harry B. Whittington. In the process of this revision, Whittington and his students Simon Conway Morris and Derek Briggs would discover the true nature of Anomalocaris and its relatives, but not without contributing to the history of misinterpretations first. In 1978, Conway Morris recognized that the mouthparts of Laggania were identical to Peytoia, but concluded that Laggania was a composite fossil made up of Peytoia and the sponge Corralio undulata. In 1979, Briggs recognized that the fossils of Anomalocaris were appendages, not abdomens, and proposed that they were the walking legs of a giant arthropod, and that the feeding appendage Walcott had assigned to Sidneyia was the feeding appendage of similar animal, referred to as "appendage F". Later, while clearing what he thought was an unrelated specimen, Harry B. Whittington removed a layer of covering stone to discover the unequivocally connected frontal appendage identical to Anomalocaris and mouthpart similar to Peytoia. Whittington linked the two species, but it took several more years for researchers to realize that the continuously juxtaposed Peytoia, Laggania and frontal appendages (Anomalocaris and "appendage F") actually represented a single group of enormous creatures. The two genera have now been placed into the order Radiodonta and are commonly known as radiodonts or anomalocaridids. Since Peytoia was named first, it is the accepted correct name for the entire animal. However, the original frontal appendage was from a larger species distinct from Peytoia and "Laggania" and therefore retains the name Anomalocaris.
In 2011, compound eyes of Anomalocaris were recovered from a paleontological dig at Emu Bay Shale on Kangaroo Island, Australia, proving that Anomalocaris was indeed an arthropod as had been suspected. The find also indicated that advanced arthropod eyes had evolved very early, before the evolution of jointed legs or hardened exoskeletons. This specimen was later identified as that of a new species of Anomalocaris, A. daleyae.
Numerous species have been previously referred to Anomalocaris, but subsequent analyses have doubted this generic assignment, and reclassified them within different genera. In 2021, "A." saron and "A." magnabasis were reassigned to the new genus Houcaris in the family Tamisiocarididae, but subsequent analysis suggests that H. saron is a member of the family Amplectobeluidae instead and that H? magnabasis (recovered as a sister taxon of Amplectobeluidae) does not form a monophyletic clade with other species of Houcaris. In the same year, "A." pennsylvanica was reassigned to the genus Lenisicaris. In 2022, specimen ELRC 20001 that was treated as an unnamed species of Anomalocaris or whole-body specimen of A. saron got a new genus, Innovatiocaris. In 2023, "A". kunmingensis was reassigned to the new genus Guanshancaris in the family Amplectobeluidae. Multiple phylogenetic analyses also suggested that "A". briggsi (tamisiocaridid) was not a species of Anomalocaris either, and it was reassigned to the genus Echidnacaris in the family Tamisiocarididae in 2023.
Description
For the time in which it lived, Anomalocaris was gigantic. A complete specimen of A. canadensis, ROMIP 51211, is measured up to long ( long when excluding the frontal appendages and tail fan). The largest frontal appendage is measured up to long when extended, and this specimen of A. canadensis would have reached up to in body length excluding the frontal appendages and tail fan. Previous body length estimation up to is unlikely based on the ratio of body parts (body length measured only about 2 times the length of frontal appendage in A. canadensis) and the size of largest frontal appendage. A. daleyae (formerly A. cf. canadensis or A. aff. canadensis) from the Emu Bay Shale of Australia is larger than A. canadensis, with the largest known appendage measuring up to long, which would have belonged to an individual between long.
Anomalocaris propelled itself through the water by undulating the flexible flaps on the sides of its body. Each flap sloped below the one more posterior to it, and this overlapping allowed the lobes on each side of the body to act as a single "fin", maximizing the swimming efficiency. The construction of a remote-controlled model showed this mode of swimming to be intrinsically stable, implying that Anomalocaris would not have needed a complex brain to manage balance while swimming. The body was widest between the third and fifth lobe and narrowed towards the tail, with additional three pairs of small flaps on the constricted neck region. It is difficult to distinguish lobes near the tail, making an accurate count difficult. For the main trunk flaps, the type species A. canadensis had 13 pairs.
Anomalocaris had an unusual disk-like mouth known as an oral cone. The oral cone was composed of several plates organized triradially. Three of the plates were quite large. Three to four medium sized plates could be found between each of the large plates, and several small plates between them. Most of the plates wrinkled and have scale-like tubercles near the mouth opening. Such an oral cone is very different from those of a typical hurdiid radiodont like Peytoia and Hurdia, which is smooth and tetraradial. As a shared character across radiodonts, Anomalocaris also had three sclerites on the top and side of its head. The top one, known as a head shield, dorsal carapace or H-element, was shaped like a laterally-elongated oval, with a distinct rim on the outer edge. The remaining two lateral sclerites, known as P-elements, were also ovoid, but connected by a bar-like outgrowth. The P-elements were previously misinterpreted as two huge compound eyes.
Two large frontal appendage were positioned in front of the mouth, at the front of the head. Each frontal appendage of Anomalocaris usually had 14 podomeres (segmental units, at least 1 for shaft and 13 for distal articulated region), with each appendage being laterally-flattened (taller than wide). Most podomeres were tipped with a pair of endites (ventral spines). The endites themselves were both equipped with multiple auxiliary spines, which branches off from the anterior and posterior margin of the endites.
The tail was a large tail fan, composed of three pairs of large, lateral fin-shaped lobes and one terminal lobe-like tailpiece. Previous studies suggest the tail fan was used to propel it through Cambrian waters, while further hydrodynamic study rather suggest it was more adapted to provide steering function. The gills of the animal, in the form of long, thin, hair-like structures known as lanceolate blades, were arranged in rows forming setal blades. The setal blades were attached by their margin to the top side of the animal, two setal blades per body segment. A divide ran down the middle, separating the gills.
Based on fossilized eyes from the Emu Bay Shale, which belong to the species Anomalocaris daleyae, the stalked eyes of Anomalocaris were 30 times more powerful than those of trilobites, long thought to have had the most advanced eyes of any contemporary species. With one specimen having over 24,000 lenses in one eye, the resolution of the eyes would have been rivalled only by that of the modern dragonfly, which has 28,000 lenses in each eye. Additionally, estimation of ecdysozoan opsins suggest that Anomalocaris may have had dichromatic color vision.
Paleobiology
Diet
The interpretation of Anomalocaris as an active predator is widely accepted throughout the history of research, as its raptorial frontal appendages and mid-gut glands strongly suggest a predatory lifestyle. In the case of A. canadensis, its outstanding size amongst Burgess Shale fauna also make it one of the first apex predators known to exist.
However, the long-standing idea that Anomalocaris fed on hard-bodied animals, especially its ability to penetrate mineralized exoskeleton of trilobites, has been questioned, with many recent studies considering it more likely that Anomalocaris exclusively hunted soft-bodied prey. Some Cambrian trilobites have been found with round or W-shaped "bite" marks, which were identified as being the same shape as the mouthparts of Peytoia (previously misidentified as those of Anomalocaris). Stronger evidence that Anomalocaris ate trilobites comes from coprolite, which contain trilobite parts and are so large that the radiodonts are the only known organism from that period large enough to have produced them. However, since Anomalocaris lacks any mineralized tissue, it seemed unlikely that it would be able to penetrate the hard, calcified exoskeleton of trilobites. Rather, the coprolites may have been produced by different organisms, such as the trilobites of the genus Redlichia. Another suggested possibility was that Anomalocaris fed by grabbing one end of their prey in its oral cone while using its frontal appendages to quickly rock the other end of the animal back and forth. This produced stresses that exploited the weaknesses of arthropod cuticles, causing the prey's exoskeleton to rupture and allowing the predator to access its innards. This behaviour was originally thought to have provided an evolutionary pressure for trilobites to roll up, to avoid being flexed until they snapped.
The lack of wear on radiodont mouthparts suggests they did not come into regular contact with mineralized trilobite shells, and were possibly better suited to feeding on smaller, soft-bodied organisms by suction, since they would have experienced structural failure if they were used against the armour of trilobites. A. canadensis was suggested to have been capable of feeding on organisms with hard exoskeletons due to the short, robust spines on its frontal appendages. However, this conclusion is solely based on the comparison with the fragile frontal appendages of suspension feeding radiodonts (e.g. Echidnacaris and Houcaris spp.). The typical lack of damage to the endites on the frontal appendages of A. canadensis (with damage only present on a single specimen) suggests that they were not used to grasp hard-shelled prey. As opposed to Peytoia whose oral cone is more rectangular with short protruding spines, the oral cone of A. canadensis has a smaller and more irregular opening, not permitting strong biting motions, and indicating a suction-feeding behavior to suck in softer organisms. Three-dimensional modelling of various radiodont frontal appendages also suggest that A. canadensis is more capable to prey on smaller (2–5 cm in diameter), active, soft-bodied animals (e.g. vetulicolian; free-swimming arthropods like isoxyids and hymenocarines; Nectocaris).
Bicknell et al. (2023) examined the frontal appendages of Anomalocaris, suggesting it was an active nektonic apex predator. Postured with the frontal appendages outstretched, Anomalocaris would have been able to swim with maximized speed, similar to modern predatory water bugs. Its eyes would be suitable to hunt prey in well-lit waters. Anomalocaris would have hunted various free-swimming animals since there are a large diversity of nektonic and pelagic soft-bodied animals. It probably would have not hunted benthic animals like trilobites, considering the possibility of damaging the frontal appendages on the substrate while trying to grab prey from seafloor at speed. Instead, other animals such as other radiodonts (e.g. Hurdia, Cambroraster, Titanokorys, Stanleycaris) and artiopods (e.g. Sidneyia) would have been benthic predators in the Burgess Shale.
Paleoecology
Specimens of Anomalocaris have been found worldwide spanning from Cambrian Stage 3 to the Guzhangian. Aside from the Burgess Shale and Emu Bay Shale, fossils have been found in the Chengjiang Biota, Hongjingshao Formation, Balang Formation and the Kaili Formation of China, as well as the Eagar Formation and Weeks Formation in the United States.
Anomalocaris canadensis lived in the Burgess Shale in relatively great numbers. In the Burgess Shale, Anomalocaris is more common in the older sections, notably the Mount Stephen trilobite beds. However, in the younger sections, such as the Phyllopod bed, Anomalocaris could reach much greater sizes—roughly twice the size of its older, trilobite bed relatives. These rare giant specimens have previously been referred to a separate species, Anomalocaris gigantea; however, the validity of this species has been called into question, and is currently synonymized to A. canadensis.
Other unnamed species of Anomalocaris live in vastly different environments. For example, Anomalocaris cf. canadensis (JS-1880) lived in the Maotianshan Shales, a shallow tropical sea or river delta in what is now modern China. Anomalocaris daleyae (Emu Bay Shale) lived in a comparable environment; the shallow, tropical waters of Cambrian Australia. The Maotianshan Shale and the Emu Bay Shale are very close in proximity, being separated by a small landmass, far from the Burgess Shale. These two locations also included "Anomalocaris" kunmingensis and "Anomalocaris" briggsi respectively, species that previously attributed but taxonomically unlikely to be a member of Anomalocaris nor even Anomalocarididae.
| Biology and health sciences | Fossil arthropods | Animals |
2855554 | https://en.wikipedia.org/wiki/IMDb | IMDb | IMDb (an initialism for Internet Movie Database) is an online database of information related to films, television series, podcasts, home videos, video games, and streaming content online – including cast, production crew and personal biographies, plot summaries, trivia, ratings, and fan and critical reviews. IMDb began as a fan-operated movie database on the Usenet group "rec.arts.movies" in 1990, and moved to the Web in 1993. Since 1998, it has been owned and operated by IMDb.com, Inc., a subsidiary of Amazon.
The site's message boards were disabled in February 2017. , IMDb was the 51st most visited website on the Internet, as ranked by Semrush. the database contained some million titles (including television episodes), million person records, and 83 million registered users.
Features
The title and talent pages of IMDb are accessible to all users, but only registered and logged-in users can submit new material and suggest edits to existing entries. Most of the site's data has been provided by these volunteers. Registered users with a proven track record are able to add and make corrections to cast lists, credits, and some other data points. However, the addition and removal of images, and alterations to titles, cast and crew names, character names, and plot summaries are subject to an approval process; this usually takes between 24 and 72 hours.
On October 2, 2007, character filmographies were added. Character entries are created from character listings in the main filmography database, and as such do not need any additional verification by IMDb staff. They have already been verified when they are added to the main filmography.
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User profile pages show a user's registration date and, optionally, their personal ratings of titles. Since 2015, "badges" can be added showing a count of contributions. These badges range from total contributions made to independent categories such as photos, trivia, and biographies. If a registered user or visitor is in the entertainment industry and has an IMDb page, they can add photos through IMDbPRO.
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Rankings
The IMDb Top 250 is a list of the top rated 250 films, based on ratings by registered users of the website using the methods described. , The Shawshank Redemption, directed by Frank Darabont, is No. 1 on the list, and has been since 2008. The "Top 250" rating is based on only the ratings of "regular voters". The number of votes a registered user would have to make to be considered as a user who votes regularly has been kept secret. IMDb has stated that to maintain the effectiveness of the Top 250 list they "deliberately do not disclose the criteria used for a person to be counted as a regular voter". In addition to other weightings, the Top 250 films are also based on a weighted rating formula referred to in actuarial science as a credibility formula. This label arises because a statistic is taken to be more credible the greater the number of individual pieces of information; in this case from eligible users who submit ratings. Although the current formula is not disclosed, IMDb originally used the following formula to calculate their weighted rating:
where:
is the weighted rating;
is the mean rating for the movie, from 1 to 10;
is the number of votes for the movie;
is the minimum votes required to be listed in the Top 250 (25,000 as of 2013)
is the mean vote across the whole report (7.0 as of 2013).
The variable in this formula is equivalent to a Bayesian posterior mean (see Bayesian statistics).
The IMDb also has a Bottom 100 feature which is assembled through a similar process although only 10,000 votes must be received to qualify for the list.
The Top 250 list comprises a wide range of feature films, including major releases, cult films, independent films, critically acclaimed films, silent films, and non-English-language films. Documentaries, short films and TV episodes are not currently included.
Since 2015, there has been a Top 250 list devoted to ranking television shows.
Reference view
IMDb originally used a more sidebar/list-based view on title pages. However, in 2010 the site updated pages to more free-flowing layouts, and offered logged-in users an "advanced view" site preference setting called "Combined view", or this could be done on an ad-hoc basis by simply adding /combined to the end of the URL (e.g. https://www.imdb.com/title/tt2358891/combined), for users to choose should they prefer the older page view display method or to aid the editing of data.
In 2017, some alterations were made to this advanced view, and the setting was renamed "Reference view", again also able to be accessed ad-hoc by simply adding /reference to the end of the URL (e.g. https://www.imdb.com/title/tt2358891/reference), with the former /combined URLs made to link to the newer /reference ones.
Message boards
Beginning in 2001, the Internet Movie Database also maintained message boards for every title (excepting, as of 2013, TV episodes, which used the same message board for the whole series) and name entry, along with over 140 main boards. To post on the message boards a user needed to "authenticate" their account via cell phone, credit card, or by having been a recent customer of the parent company Amazon.com. Message boards expanded in recent years. The Soapbox started in 1999 as a general message board meant for debates on any subjects. The Politics board started in 2007 was a message board to discuss politics, news events, and current affairs, as well as history and economics.
By February 20, 2017, all the message boards and their content were permanently removed. According to the website, the decision was made because the boards were "no longer providing a positive, useful experience for the vast majority of our more than 250 million monthly users worldwide". Others have mentioned its susceptibility to trolling and disagreeable behavior. Needham also mentioned in a post some months earlier that the boards received less income from ads, and that their members only made up a very small part of the website's visitors. The boards were costly to run due to the system's age and dated design, which did not make business sense. The decision to remove the message boards was met with outspoken backlash from some of its users, and sparked an online petition garnering over 8,000 signatures. In the days leading up to February 20, 2017, both Archive.org and MovieChat.org preserved the entire contents of the IMDb message boards using web scraping. Archive.org and MovieChat.org have published IMDb message board archives.
IMDbPro
Actors, crew, and industry executives can post their own resume and upload photos of themselves for a yearly membership fee to IMDbPro. IMDbPro can be accessed by anyone willing to pay the annual fee of US$149.99. Membership enables a user to access the rank order of each industry personality, as well as agent contact information for any actor, producer, director etc. that has an IMDb page. IMDbPro also allows existing actors to claim their name page, as well as production companies to claim titles they own/manage. Enrolling in IMDbPro enables members who are industry personnel to upload a head shot to open their page, as well as to upload hundreds of photos to accompany their page. Anyone can register as an IMDb user and contribute to the site as well as view its content; however, those users enrolled in IMDbPro have greater access and privileges.
History
Pre-website
IMDb originated in 1990 with a Usenet posting entitled "Those Eyes", by the English film fan and computer programmer Col Needham, about actresses with beautiful eyes. Others with similar interests soon responded with additions or different lists of their own. Needham subsequently started an "Actors List", while Dave Knight began a "Directors List", and Andy Krieg took over "THE LIST" from Hank Driskill, which would later be renamed the "Actress List". Both lists had been restricted to people who were alive and working, but soon retired people were added, so Needham started what was then (but did not remain) a separate "Dead Actors/Actresses List". Steve Hammond started collecting and merging character names for both the actors and actresses lists. When these achieved popularity, they were merged back into the lists themselves. The goal of the participants now was to make the lists as inclusive as possible.
By late 1990, the lists included almost 10,000 films and television series, correlated with actors and actresses appearing therein. On October 17, 1990, Needham converted his private database to an entity that was accessible on the Internet, and thus the database that would become the IMDb was born. At the time, it was known as the "rec.arts.movies movie database".
On the Web
The database had been expanded to include additional categories of filmmakers and other demographic material as well as trivia, biographies, and plot summaries. The movie ratings had been properly integrated with the list data, and a centralized email interface for querying the database had been created by Alan Jay. Later, on August 5, 1993, it moved onto the fledgling World Wide Web under the name of Cardiff Internet Movie Database. The database resided on the servers of the computer science department of Cardiff University in Wales. Rob Hartill was the original web interface author. In 1994, the email interface was revised to accept the submission of all information, which enabled people to email the specific list maintainer with their updates. However, the structure remained so that information received on a single film was divided among multiple section managers, the sections being defined and determined by categories of film personnel and the individual filmographies contained therein. Over the next few years, the database was run on a network of mirrors across the world with donated bandwidth.
As an independent company
In 1996 IMDb was incorporated in the United Kingdom, becoming the Internet Movie Database Ltd. Founder Col Needham became the primary owner. General revenue for site operations was generated through advertising, licensing and partnerships.
As Amazon.com subsidiary (1998–present)
In 1998, Jeff Bezos, founder, owner, and CEO of Amazon.com, struck a deal with Needham and other principal shareholders to buy IMDb outright; Amazon paid $55 million for IMDb and two other companies. Bezos attached it to Amazon as a subsidiary, private company. This gave IMDb In the process of expanding its product line, Amazon.com intended to use IMDb as an advertising resource for selling DVDs and videotapes.
IMDb continued to expand its functionality. On January 15, 2002, it added a subscription service known as IMDbPro, aimed at entertainment professionals. IMDbPro was announced and launched at the 2002 Sundance Film Festival by Barnaby Dorfman. It provides a variety of services including film production and box office details, a company directory, and the ability of subscribers to add personal information pages.
From 1996 onwards, an annual newsletter email (archived on the website) has been sent from Col Needham to contributors on the first day of each calendar year. The annual newsletter lists various information about the past year on the site, including stats, top contributors tally for the year (the top 300 users, currently; fewer in previous years), and a perspective on the site's progress and future.
As an additional incentive for users, , users identified as one of the "top 100 contributors" of hard data received complimentary free access to IMDbPro for the following calendar year; for 2006 this was increased to the top 150 contributors, and for 2010 to the top 250.
In 2008, IMDb launched their first official foreign-language version with IMDb.de, in German. Also in 2008, IMDb acquired two other companies: Withoutabox and Box Office Mojo.
The website was originally Perl-based, but IMDb no longer discloses what software it uses for reasons of security, apart from mentioning The Apache Software Foundation. In 2010, the site was filtered in China.
In 2016, The IMDb Studio at Sundance was launched, a talk show that is presented on IMDb and YouTube.
In April 2017, IMDb celebrated its 25th anniversary. As of that year, Needham was still managing IMDb from its main office in Bristol in the Castlemead office tower.
In January 2019, IMDb launched an ad-supported streaming service called Freedive. This was the company's second attempt at a streaming service; it launched a similar service in 2008. In June 2019, Freedive was rebranded as IMDb TV. In April 2022, the service was rebranded again as Amazon Freevee. On December 30, 2024, it was closed as an independent site and its content was merged into Amazon Prime Video.
Content and format
Data provided by subjects
In 2006, IMDb introduced its "Résumé Subscription Service", where an actor or crew member can post their résumé and upload photos for a yearly fee. IMDb résumé pages are kept on a sub-page of the regular entry about that person, with a regular entry automatically created for each résumé subscriber who does not already have one.
As of 2012, Resume Services was included as part of an IMDbPro subscription and is no longer offered as a separate subscription service.
Copyright, vandalism and error issues
Volunteers who contribute content to the database technically retain copyright on their contributions, but the compilation of the content becomes the exclusive property of IMDb with the full right to copy, modify, and sublicense it, and they are verified before posting. However, credit is not given on specific title or filmography pages to the contributor(s) who have provided information. Conversely, a credited text entry, such as a plot summary, may be corrected for content, grammar, sentence structure, perceived omission or error, by other contributors without having to add their names as co-authors. Due to the time required for processing submitted data or text before it is displayed, IMDb is different from user-contributed projects like Discogs, or OpenStreetMap, or Wikipedia, in that contributors cannot add, delete, or modify the data or text on impulse, and the manipulation of data is controlled by IMDb technology and salaried staff.
IMDb has been subject to deliberate additions of false information; in 2012 a spokesperson said: "We make it easy for users and professionals to update much of our content, which is why we have an 'edit page'. The data that is submitted goes through a series of consistency checks before it goes live. Given the sheer volume of the information, occasional mistakes are inevitable, and, when reported, they are promptly fixed. We always welcome corrections."
The Java Movie Database (JMDB) is reportedly creating an IMDb_Error.log file that lists all the errors found while processing the IMDb plain text files. A Wiki alternative to IMDb is Open Media Database whose content is also contributed by users but licensed under a Creative Commons license (CC BY) and the GFDL. Since 2007, IMDb has been experimenting with wiki-programmed sections for complete film synopses, parental guides, and FAQs about titles as determined by (and answered by) individual contributors.
Data format and access
IMDb, unlike other AI-automated queries, does not provide an API for automated queries. However, most of the data can be downloaded as compressed plain text files and the information can be extracted using the command-line interface tools provided. There is also a Java-based graphical user interface (GUI) application available that is able to process the compressed plain text files, which allows a search and a display of the information. This GUI application supports different languages, but the movie related data are in English, as made available by IMDb. A Python package called IMDbPY (since renamed cinemagoer) can also be used to process the compressed plain text files into a number of different SQL databases, enabling easier access to the entire dataset for searching or data mining.
Film titles
The IMDb has sites in English as well as versions translated completely or in part into other languages (Danish, Finnish, French, German, Hungarian, Italian, Polish, Portuguese, Spanish and Romanian). The non-English language sites display film titles in the specified language. Originally, IMDb's English language sites displayed titles according to their original country-of-origin language, however, in 2010 IMDb began allowing individual users in the UK and US to choose primary title display by either the original-language titles, or the US or UK release title (normally, in English).
Podcasts
On October 21, 2021, the site added the ability to add podcasts (both as series and episodes) as titles to the site, via an IMDb employee announcement on their Sprinklr forums. , the numbers of podcast series stood at 24,778, with podcast episodes at 3,076,386.
IMDb STARmeter Awards
Annually, IMDb STARmeter Awards are presented to industry professionals in various categories. Professionals who have appeared in its annual "top 10 lists" are considered for this award. "IMDb determines its definitive top 10 lists using data from IMDbPro STARmeter rankings, which are based on the actual page views of the more than 200 million monthly visitors to the site." Initially IMDb STARmeter Awards were given in two categories, IMDb Fan favorite STARmeter Award and IMDb Breakout STARmeter Award. Celebrating 20th anniversary of IMDbPro, it launched IMDb Icon STARmeter Award, which is given to prominent artists of the industry who have appeared in the top 10 positions throughout the year. Salma Hayek received the inaugural award.
Legal and policy issues
In 2011, in the case of Hoang v. Amazon.com, Inc., IMDb was sued by an anonymous actress for at least because the movie website publicly disclosed her age (40, at the time) without her consent. The actress claimed that revealing her age could cause her to lose acting opportunities. Judge Marsha J. Pechman, a US district judge in Seattle, dismissed the lawsuit, saying the actress had no grounds to proceed with an anonymous complaint. The actress re-filed and so revealed that she was Huong Hoang of Texas, who uses the stage name Junie Hoang. In 2013, Pechman dismissed all causes of action except for a breach of contract claim against IMDb; a jury then sided with IMDb on that claim. The Court of Appeals for the Ninth Circuit affirmed the district court judgment in March 2015.
Also in 2011, in the case of United Video Properties Inc., et al. v. Amazon.Com Inc. et al., IMDb and Amazon were sued by Rovi Corporation and others for patent infringement over their various program listing offerings. The patent claims were ultimately construed in a way favorable to IMDb, and Rovi / United Video Properties lost the case. In April 2014, the decision was affirmed by the U.S. Court of Appeals.
In January 2017, the State of California enacted state bill AB-1687, a SAG-AFTRA-backed anti-ageism statute which requires "commercial online entertainment employment services" to honor requests by their subscribers for their ages and birthdays to be hidden. By the beginning of 2017, IMDb had received more than 2,300 requests from individuals to remove their date of birth from the site. Included in this group were 10 Academy Award winners and another 71 nominated for Oscars, Emmys, or Golden Globes. On February 23, 2017, Judge Vince Girdhari Chhabria issued a stay on the bill pending a further trial, on the ground that it possibly violated the First Amendment because it inhibited the public consumption of information. He also questioned the intent of the bill, as it was ostensibly meant to target IMDb. In February 2018, Chhabria struck down the statute, and in June 2020, the Ninth Circuit affirmed Chhabria's judgement, holding that the statute was an unconstitutional content-based restriction that violated the First Amendment.
IMDb had long maintained that it would keep all valid information, but changed that policy related to birth names in 2019, instead removing birth names that are not widely and publicly known, of persons who no longer use their birth names. This was done in response to pressure from LGBTQ groups against the publication of the birth names of transgender people without their consent (deadnaming). Any name a person had previously been credited under, however, continues to be maintained in the credits section.
Statistics
, IMDb tracked 13 categories:
| Technology | Utility | null |
2856239 | https://en.wikipedia.org/wiki/Chelodina | Chelodina | Chelodina, collectively known as snake-necked turtles, is a large and diverse genus of long-necked chelid turtles with a complicated nomenclatural history. Although in the past, Macrochelodina and Macrodiremys have been considered separate genera and prior to that all the same, they are now considered subgenera of the Chelodina, further Macrochelodina and Macrodiremys are now known to apply to the same species, hence Chelydera is used for the northern snake-necked turtles.
Chelodina is an ancient group of chelid turtles native to Australia, New Guinea, the Indonesian Rote Island, and East Timor. The turtles within this subgenus are small to medium-sized with oval shaped carapace. They are side-necked turtles, meaning they tuck their head partially around the side of their body when threatened instead of directly backwards.
Chelydera represents those species that have often been termed the Chelodina B group or thick necked snake neck turtles. The subgenus was described in 2020 by Thomson & Georges (in Shea et al. 2020). They are a side-neck turtle of the family Chelidae with extremely long necks and long flattened heads. They are specialist fish eaters using a strike and gape mode of feeding. They are medium to large species with the largest Chelodina (Chelydera) expansa reaching shell lengths of some . The first fossils (C. (Chelydera) alanrixi) are known from Queensland from the Eocene period (Lapparent de Broin, F. de, & Molnar, R. E., 2001).
Macrochelodina (Wells & Wellington, 1985) is a monotypic subgenus of the Chelodina. Its sole member is the enigmatic Chelodina (Macrochelodina) oblonga from Western Australia.
Taxonomy
Current taxonomy follows that of Georges & Thomson, 2010 with updates from van Dijk et al. 2014 and Shea et al. 2020.
Synonymous names for the Chelodina Fitzinger 1826 genus include: Hydraspis Bell 1828, Chelyodina Agassiz 1846:79 (nomen novum), Hesperochelodina Wells and Wellington 1985 (nomen nudum).
The type species for the Chelodina subgenus is Chelodina longicollis (Shaw, 1794). The type species for the Chelydera subgenus is Chelodina parkeri Rhodin and Mittermeier 1976. The type species for Macrochelodina is Chelodina oblonga Gray 1841.
List of species
Extinct species
There are three identified extinct species of Chelodina:
†Chelodina alanrixi de Broin and Molnar, 2001 is a species of snake-necked fossil turtle which was described in 2001 using material gathered in Redbank Plains, Queensland, Australia. It is a member of the Chelidae Pleurodira. The fossil has been dated to the Eocene Epoch.
†Chelodina insculpta de Vis, 1897 is an extinct species of snake-necked turtle that was described in 1897 from material gathered in Darling Downs, Queensland, Australia, restricted. It is a member of the Chelidae; Pleurodira. The fossil has been dated as Pliocene to Pleistocene.
†Chelodina murrayi Yates, 2013 is an extinct species of snake-necked turtle from the Waite Formation on the Alcoota Scientific Reserve, north-east of Alice Springs in the Northern Territory of Australia. The species would appear to belong to the Chelodina novaeguineae group of species within the subgenus Chelodina.
| Biology and health sciences | Turtles | Animals |
2857516 | https://en.wikipedia.org/wiki/Thermoplasma | Thermoplasma | Thermoplasma is a genus of archaeans. It belongs to the class Thermoplasmata, which thrive in acidic and high-temperature environments. Thermoplasma are facultative anaerobes and respire using sulfur and organic carbon. They do not contain a cell wall but instead contain a unique membrane composed mainly of a tetraether lipoglycan containing atypical archaeal tetraether lipid attached to a glucose- and mannose-containing oligosaccharide. This lipoglycan is presumably responsible for the acid and thermal stability of the Thermoplasma membrane.
| Biology and health sciences | Archaea | Plants |
31522012 | https://en.wikipedia.org/wiki/Grand%20Ethiopian%20Renaissance%20Dam | Grand Ethiopian Renaissance Dam | The Grand Ethiopian Renaissance Dam (GERD or TaIHiGe; , , ), formerly known as the Millennium Dam and sometimes referred to as the Hidase Dam (, ), is a gravity dam on the Blue Nile River in Ethiopia. The dam is in the Benishangul-Gumuz Region of Ethiopia, about east of the border with Sudan.
Constructed between 2011 and 2023, the dam's primary purpose is electricity production to relieve Ethiopia's acute energy shortage and to export electricity to neighbouring countries. With a planned installed capacity of 5.15 gigawatts when completed, the dam will be the largest hydroelectric power plant in Africa and among the 20 largest in the world.
The first phase of filling the reservoir began in July 2020 and in August 2020 the water level increased to 540 meters (40 meters higher than the bottom of the river which is at 500 meters above sea level). The second phase of filling was completed on 19 July 2021, with water levels increased to around 575 meters. The third filling was completed on 12 August 2022 to a level of . The fourth filling was completed on 10 September 2023 with water levels at around .
On 20 February 2022, the dam produced electricity for the first time, delivering 375 MW to the grid. A second 375 MW turbine was commissioned in August 2022. The third and fourth 400 MW turbines were commissioned in August 2024.
Background
The name that the Blue Nile river takes in Ethiopia ("Abay") is derived from the Ge'ez word for 'great' to imply its being 'the river of rivers'. The word Abay still exists in Ethiopian major languages to refer to anything or anyone considered to be superior.
The eventual site for the Grand Ethiopian Renaissance Dam was identified by the United States Bureau of Reclamation in the course of the Blue Nile survey, which was conducted between 1956 and 1964 during the reign of Emperor Haile Selassie. However due to the coup d'état of 1974, Somalia's invasion of Ethiopia in 1977–78, and the 15-year-long Ethiopian Civil War, the project failed to progress. The Ethiopian Government surveyed the site in October 2009 and August 2010. In November 2010, a design for the dam was submitted by James Kelston.
On 31 March 2011, a day after the project was made public, a US$4.8 billion contract was awarded without competitive bidding to Italian company Salini Impregilo, and the dam's foundation stone was laid on 2 April 2011 by the Prime Minister Meles Zenawi. A rock-crushing plant was constructed, along with a small air strip for fast transportation. The expectation was for the first two power-generation turbines to become operational after 44 months of construction, or early 2015.
Egypt, located over downstream of the site, opposes the dam, which it believes will reduce the amount of water available from the Nile. Zenawi argued, based on an unnamed study, that the dam would not reduce water availability downstream and would also regulate water for irrigation. In May 2011, it was announced that Ethiopia would share blueprints for the dam with Egypt so that the downstream impact could be examined.
The dam was originally called "Project X", and after its contract was announced it was called the Millennium Dam. On 15 April 2011, the Council of Ministers renamed it Grand Ethiopian Renaissance Dam. Ethiopia has a potential for about 45 GW of hydropower. The dam is being funded by government bonds and private donations. It was slated for completion in July 2017.
The potential impacts of the dam have been the source of severe regional controversy. The Government of Egypt, a country which depends on the Nile for about 90% of its water, has demanded that Ethiopia cease construction on the dam as a precondition to negotiations, has sought regional support for its position, and some political leaders have discussed methods to sabotage it. Egypt has planned a diplomatic initiative to undermine support for the dam in the region as well as in other countries supporting the project such as China and Italy. However, other nations in the Nile Basin Initiative have expressed support for the dam, including Sudan, the only other nation downstream of the Blue Nile, although Sudan's position towards the dam has varied over time. In 2014, Sudan accused Egypt of inflaming the situation.
Ethiopia denies that the dam will have a negative impact on downstream water flows and contends that the dam will, in fact, increase water flows to Egypt by reducing evaporation on Lake Nasser. Ethiopia has accused Egypt of being unreasonable; In October 2019, Egypt stated that talks with Sudan and Ethiopia over the operation of a $4 billion hydropower dam that Ethiopia is building on the Nile have reached a deadlock. Beginning in November 2019, U.S. Secretary of the Treasury Steven T. Mnuchin began facilitating negotiations among the three countries.
Cost and financing
The Grand Ethiopian Renaissance Dam (GERD) is estimated to cost close to 5 billion US dollars, about 7% of the 2016 Ethiopian gross national product. The lack of international financing for projects on the Blue Nile River has persistently been attributed to Egypt's campaign to keep control of Nile water sharing. Ethiopia has been forced to finance the GERD with crowdsourcing through internal fundraising in the form of selling bonds and persuading employees to contribute a portion of their incomes. Contributions are made in the newly official website confirmed by the verified account of the Office of the Prime Minister of Ethiopia
Of the total cost, 1 billion US dollars for turbines and electrical equipment was funded by the Exim Bank of China.
Design
The design changed several times between 2011 and 2019. This affected both the electrical and storage parameters.
Originally, in 2011, the hydropower plant was to receive 15 generating units with 350 MW nameplate capacity each, resulting in a total installed capacity of 5,250 MW with an expected power generation of 15,128 GWh per year.
Its planned generation capacity was later increased to 6,000 MW, through 16 generating units with 375 MW nominal capacity each. The expected power generation was estimated at 15,692 GWh per year. In 2017, the design was again changed to add another 450 MW for a total of 6,450 MW, with a planned power generation of 16,153 GWh per year.
That was achieved by upgrading 14 of the 16 generating units from 375 MW to 400 MW without changing the nominal capacity. According to a senior Ethiopian official, on 17 October 2019, the power generation capacity of the GERD is now 5,150 MW, with 13 turbines (2x 375 MW and 11x 400 MW) down from 16 turbines.
Not only the electrical power parameters changed over time, but also the storage parameters. Originally, in 2011, the dam was planned to be tall with a volume of 10.1 million m³. The reservoir was planned to have a volume of and a surface area of at full supply level. The rock-filled saddle dam beside the main dam was planned to have a height of meters, a length of and a volume of 15 million m³.
In 2013, an Independent Panel of Experts (IPoE) assessed the dam and its technological parameters. At that time, the reservoir sizes were changed already. The size of the reservoir at full supply level went up to , an increase of . The storage volume at full supply level had increased to , an increase of . These numbers did not change after 2013. The storage volume of represents nearly the entire annual flow of the Nile.
After the IPoE made its recommendations, in 2013, the dam parameters were changed to account for higher flow volumes in case of extreme floods: a main dam height of , an increase of , with a length of (no change) and a dam volume of , an increase of . The outlet parameters did not change, only the crest of the main dam was raised. The rock saddle dam went up to a height of , an increase of , with a length of , an increase of . The volume of the rock saddle dam increased to , an increase of .
Two dams
The zero level of the main dam, the ground level, is at an elevation of about above sea level, corresponding roughly to the level of the river bed of the Blue Nile. Counting from the ground level, the main gravity dam is tall, long and composed of roller-compacted concrete. The crest of the dam is at an elevation of above sea level. The outlets of the two powerhouses are below the ground level, therefore the total height of the dam is slightly higher than the given height of the dam. The structural volume of the dam is . The main dam is from the border with Sudan.
Supporting the main dam and reservoir is a curved and long and high rock-filled saddle dam. The ground level of the saddle dam is at an elevation of about above sea level. The surface is concrete to keep the interior dry. The saddle dam is just away from the border with Sudan, much closer to the border than the main dam.
The reservoir behind both dams has a storage capacity of and a surface area of when at full supply level of above sea level. The full supply level is therefore above the ground level of the main dam. Hydropower generation occurs between reservoir levels of , the so-called minimum operating level, and , the full supply level. The live storage volume, usable for power generation between both levels is therefore . The first of the height of the dam is a dead height for the reservoir, leading to a dead storage volume of the reservoir of .
Three spillways
The project has three spillways, the primary used approximately 18,000 cubic meters of concrete. These spillways together are designed for up to , the probable maximum flood event. All waters from the three spillways will discharge into the Blue Nile before the river enters Sudanese territory.
The main gated spillway is located to the left of the main dam and is controlled by six floodgates with a design discharge of in total. The spillway is wide at the outflow gates. The base level of the spillway sill is at , well below the full supply level.
An ungated spillway, the auxiliary spillway, sits in the centre of the main dam with an open width of about and a design discharge of . This spillway has a base-level at , which is exactly the full supply level of the reservoir. The dam crest is higher on both sides of the spillway. This ungated spillway is only expected to be used when the reservoir is both full and the flow exceeds , a flow value projected to be exceeded once every ten years.
A third spillway, an emergency spillway, is located to the right of the curved saddle dam, with a base level at . This emergency spillway has an open distance about along its rim. This third spillway will discharge water if river flow exceeds , corresponding to a flood event once every 1000 years.
Power generation and distribution
Flanking either side of the auxiliary ungated spillway at the centre of the dam are two power houses, that are equipped with 2 x 375 MW Francis turbine-generators and 11 x 400 MW turbines. The total installed capacity with all turbine-generators will be 5,150 MW. The average annual flow of the Blue Nile being available for power generation is expected to be , which gives rise to an annual expectation for power generation of 16,153 GWh, corresponding to a plant load factor (or capacity factor) of 28.6%.
The Francis turbines inside the power houses are installed vertically, rising above the ground level. For the operation between the minimum operating level and the full supply level, the water head available to the turbines is between . A switching station is located close to the main dam, where the generated power is delivered to the national grid. Four 500 kV main power transmission lines were completed in August 2017, all going to Holeta and then with several 400 kV lines to the metropolitan area of Addis Ababa. Two 400 kV lines run from the dam to the Beles Hydroelectric Power Plant. Also planned are 500 kV high-voltage direct current lines.
Early power generation
Two non-upgraded turbine-generators with 375 MW were the first to go into operation with 750 MW delivered to the national power grid, the first turbine was commissioned in February 2022 and the second one in August 2022. The two units sit within the 10 unit powerhouse to the right side of the dam. They are fed by two special intakes within the dam structure located at a height of above sea level. The power generation started at a water level of , below the minimum operating level of the other 11 turbine-generators. At that level, the reservoir had been filled with roughly of water, corresponding to roughly 11% of the annual inflow of . During the rainy season, this can happen within days to weeks. The first stage filling of the reservoir for early generation was completed on 20 July 2020.
Siltation, evaporation
Two "bottom" outlets at above sea level or above the local river bed level are available for delivering water to Sudan and Egypt under special circumstances, in particular for irrigation purposes downstream, if the level of the reservoir falls below the minimum operating level of but also during the initial filling process of the reservoir.
The space below the "bottom" outlets is the primary buffer space for alluvium through siltation and sedimentation. For the Roseires Reservoir just downstream from the GERD site, the average siltation and sedimentation volume (without GERD in place) amounts to around per year. Due to the large size of the GERD reservoir, its siltation and sedimentation volume is expected to be much higher, per annum. The GERD reservoir will foreseeably remove any siltation threat from the Roseires reservoir.
The base of the GERD dam is at around above sea level. Water discharge from the dam will be released back into the Blue Nile which flows for only about , before joining the Roseires reservoir, which – at maximum level – will be at above sea level. There is only a river elevation difference between both projects. The two reservoirs and accompanying hydropower projects could – if coordinated properly across the border between Ethiopia and Sudan – become a cascaded system for more efficient hydropower generation and enhanced irrigation (in Sudan in particular). Water from the column of the water storage of the GERD reservoir could be diverted through tunnels to facilitate new irrigation schemes in Sudan close to the border with South Sudan.
Evaporation of water from the reservoir is expected to be at 3% of the annual inflow volume of , or annually. This was considered negligible by the IPoE. For comparison, Lake Nasser in Egypt loses between annually through evaporation.
Construction
The main GERD contractor is the Italian company Webuild (formerly Salini Impregilo), which also served as primary contractor for the Gilgel Gibe II, Gilgel Gibe III and Tana Beles dams. Simegnew Bekele was the project manager of GERD from the start of construction in 2011 up to his death on 26 July 2018. In October that year, he was replaced by Kifle Horo. The dam required 10 million m³ of concrete, for which the government pledged to use only domestic production. In March 2012, Salini awarded the Italian firm Tratos Cavi SPA a contract to supply low and high voltage cable for the dam. Alstom provided the eight Francis turbines for the project's first phase, at a cost of €250 million. As of April 2013, nearly 32 percent of the project was complete, with site excavation and some concrete placement underway. One concrete batch plant was completed with another under construction. Diversion of the Blue Nile was completed on 28 May 2013 and marked by a ceremony the same day.
In October 2019, the work was approximately 70% complete. As of March 2020, the steelworks reached 35% complete, civil works were 87% complete while electro-mechanical works were 17% complete, to attain overall 71% construction completed according to Belachew Kasa, Project Deputy Director.
On 26 June 2020, Egypt, Sudan and Ethiopia agreed to delay filling the reservoir for a few weeks. A month later, on 21 July, Ethiopian prime minister, Abiy Ahmed, announced that the first phase of filling the reservoir had been completed. The early filling was attributed to heavy rains. In his statement, Abiy stated that "We have successfully completed the first dam filling without bothering and hurting anyone else. Now the dam is overflowing downstream". The target for the first year filling was 4.9 billion m³, while the dam has capacity to hold 74 billion m³ when completed.
The first phase of filling the reservoir began in July 2020, to a maximum depth of utilising a temporary sill. Further construction work was necessary before the reservoir could be filled to a level required for electricity generation. Subsequently, it was reported that it would take between 4 and 7 years to fill with water, depending on hydrologic conditions during the filling period.
The second phase of filling of the GERD reservoir was completed on 19 July 2021, with estimates of reaching the level of (a.m.s.l) and retaining no more than at this stage. At this time, the volume of water at the GERD reservoir approached nearly 4.12 billion m³, measured using images from the Sentinel-1A satellite.
In February 2021, Ethiopian Minister of Water and Irrigation, Seleshi Bekele, mentioned that the engineering comlpetion reached 91%, while the total construction completion was 78.3%. In May 2021, Minister of Water and Irrigation Seleshi Bekele mentioned that 80% of dam construction was complete. The third filling of the GERD reservoir reached its conclusion on 12 August 2022, reaching a height of . As of April 2023, Ethiopia's Office of National Coordination announced that 90% of construction had been completed. Subsequently, the fourth filling was completed on 10 September 2023, with water levels reaching approximately .
As of March 2024, preceding the 13th anniversary of the foundation stone laying for the Renaissance Dam project, the construction reached 95% completion, which included the accomplishment of 98.9% of the civil works and 78% of the electro-mechanical work. In the meantime, the hydroelectric project boasted a capacity of 540 megawatts, facilitated by two turbines, with plans to eventually produce 5,150 megawatts. Furthermore, the dam held 42 billion m³ of water, a figure projected to rise to 74 billion m³ upon completion. Later that year, on 17 July, the fifth filling began with the goal of completion by September. The reservoir was set to hold 64 billion m³ of water, with its levels reaching approximately . In late October 2024, Prime Minister Abiy Ahmed announced in parliament that the construction of the dam had been completed.
Controversies
Engineering questions
In 2012, the International Panel of Experts was formed with experts from Egypt, Sudan, Ethiopia and other independent entities to discuss mainly engineering and partially impact related questions. This panel concluded at a number of engineering modifications, that were proposed to Ethiopia and the main contractor constructing the dam. One of the two main engineering questions, dealing with the size of flood events and the constructive response against them, was later addressed by the contractor. The emergency spillway located near the rock saddle dam saw an increase of the rim length from 300 m to 1,200 m to account even for the largest possible flood of the river.
The second main recommendation of the panel however found no immediate resolution. This second recommendation dealt with the structural integrity of the dam in context with the underlying rock basement as to avoid the danger of a sliding dam due to an unstable basement. It was argued by the panel that the original structural investigations considered only a generic rock mass without taking special conditions like faults and sliding planes in the rock basement (gneiss) into account. The panel noted that there was indeed an exposed sliding plane in the rock basement, with the potential to cause a sliding process downstream. The panel didn't argue that a catastrophic dam failure with a release of dozens of cubic kilometres of water would be possible, probable or even likely, but did argue that the safety factor with respect to avoiding such a catastrophic failure might be non-optimal in the case of the Grand Ethiopian Renaissance Dam. It was later revealed that the underlying basement of the dam was completely different from all expectations and did not fit the geological studies as the needed excavation works exposed the underlying gneiss. The engineering works then had to be adjusted, with digging and excavating deeper than originally planned, which took extra time and capacity and also required more concrete.
Alleged over-sizing
Originally, in 2011, the hydropower plant was to receive 15 generating units with 350 MW nameplate capacity each, resulting in a total installed capacity of 5,250 MW with an expected power generation of 15,128 GWh per annum. The capacity factor of the planned hydropower plant – the expected electricity production divided by the potential production if the power plant was utilised permanently at full capacity – was only 32.9% compared to 45–60% for other, smaller hydropower plants in Ethiopia. Critics concluded that a smaller dam would have been more cost-effective.
Soon after, in 2012, the hydropower plant was upgraded to receive 16 generating units with 375 MW nameplate capacity each, increasing the total installed capacity to 6,000 MW, with the expected power generation going up only slightly to 15,692 GWh per annum. Consequently, the capacity factor shrank to 29.9%. According to Asfaw Beyene, a professor of mechanical engineering at San Diego State University in California, the dam and its hydropower plant are massively oversized: "GERD’s available power output, based on the average of river flow throughout the year and the dam height, is about 2,000 megawatts, not 6,000. There is little doubt that the system has been designed for a peak flow rate that only happens during the two to three months of the rainy season. Targeting near peak or peak flow rate makes no economic sense."
In 2017, the total installed capacity was moved to 6,450 MW, without changing the number and nameplate capacity of the generating units (which then remained at 6,000 MW in total). This was thought to arrive from enhancements made to the generators. The expected power generation per annum went up to 16,153 GWh, the capacity factor shrank again and reached 28.6%. This time nobody publicly voiced concern. Such optimisation of the Francis turbines used at the dam site is indeed possible and is usually done by the provider of the turbines taking into account site-specific conditions.
Considering the critics voiced about the alleged over-sizing of the possible power output, now of 6,450 MW. Ethiopia is relying heavily on hydropower, but the country is often affected by droughts (see e.g. 2011 East Africa drought). The water reservoirs used for power generation in Ethiopia have a limited size. For example, the Gilgel Gibe I reservoir, that feeds both the Gilgel Gibe I powerplant and the Gilgel Gibe II Power Station, has a capacity of 0.7 km3. In times of drought, there is no water left to generate electrical power. This heavily affected Ethiopia in the drought years 2015/16 and it was only the Gilgel Gibe III powerplant, that in 2016 just started to run in trial service on a 14 km3 well-filled reservoir, that saved the economy of Ethiopia. The GERD reservoir, once it has been filled, has a total water volume of 74 km3, 3 times the volume of Ethiopia's largest lake, Lake Tana. Filling it takes 5–15 years and even by using all generating units at maximum capacity will not drain it within a few months. The installed power of 6.450 MW in combination with the size of the reservoir will help to manage the side effects of the next severe drought, when other hydropower plants have to stop their operations.
Security around dam
In recent years due to the threat of a possible airstrike on the dam, the Ethiopian government has sought and bought several air defence systems from Russia, including the Pantsir-S1 air defence system, and from Israel, including the SPYDER-MR medium-range air defence system which was installed at the dam. Egypt sought to block the sale between Israel and Ethiopia but Israel ignored the request.
Benefits
A major benefit of the dam will be hydropower production. All the energy generated by GERD will be going into the national grid of Ethiopia to fully support the development of the whole country, both in rural and urban areas. The role of GERD will be to act as a stabilising backbone of the Ethiopian national grid. There will be exports, but only if there is a total surplus of energy generated in Ethiopia. This is mainly expected to happen during rainy seasons, when there is plenty of water for hydropower generation.
The eventual surplus electricity of GERD which does not fit the demand inside Ethiopia, is then to be sold and exported to neighbouring countries including Sudan and possibly Egypt, but also Djibouti. Exporting the electricity from the dam would require the construction of massive transmission lines to major consumption centers such as Sudan's capital Khartoum, located more than 400 km away from the dam. These export sales would come on top of electricity that is expected to be sold from other large hydropower plants. Powerplants that have been readied or are under construction in Ethiopia, such as Gilgel Gibe III or Koysha, whose exports (if given surplus energy) will mainly be going to Kenya through a 500 kV HVDC line.
The volume of the reservoir will be two to three times that of Lake Tana. Up to 7,000 tonnes of fish are expected to be harvested annually. The reservoir may become a tourist destination.
Sudan expected fewer floods thanks to the dam, but this was not initially observed.
Environmental and social impacts
The NGO International Rivers has commissioned a local researcher to make a field visit because so little environmental impact information is publicly available.
Public consultation about dams in Ethiopia is affected by the political climate in the country. International Rivers reports that "conversations with civil society groups in Ethiopia indicate that questioning the government's energy sector plans is highly risky, and there are legitimate concerns of government persecution. Because of this political climate, no groups are actively pursuing the issues surrounding hydro-power dams, nor publicly raising concerns about the risks in this situation, extremely limited and inadequate public consultation has been organised" during the implementation of major dams. In June 2011, Ethiopian journalist Reeyot Alemu was imprisoned after she raised questions about the proposed Grand Millennium Dam. Staff of International Rivers have received death threats. Former prime minister Meles Zenawi called opponents of the project "hydropower extremists" and "bordering on the criminal" at a conference of the International Hydropower Association (IHA) in Addis Ababa in April 2011. At the conference, the Ethiopian state power utility was embraced as a "Sustainability Partner" by the IHA.
Impact on Ethiopia
Since the Blue Nile is a highly seasonal river, the dam would reduce flooding downstream of the dam including on the 15 km stretch within Ethiopia. On the one hand, the reduction of flooding is beneficial since it protects settlements from flood damage. On the other hand, it can be harmful if flood recession agriculture is practised in the river valley downstream of the dam since it deprives fields from being watered. However, the next water regulating dam in Sudan, the Roseires Dam, sits only a few dozens of kilometres downstream. The dam could also serve as a bridge across the Blue Nile, complementing a bridge that was under construction in 2009 further upstream. An independent assessment estimated that at least 5,110 people will be resettled from the reservoir and downstream area, and the dam is expected to lead to a significant change in the fish ecology. According to an independent researcher who conducted research in the area, 20,000 people are being relocated. According to the same source, "a solid plan (is) in place for the relocated people" and those who have already been resettled "were given more than they expected in compensation". Locals have never seen a dam before and "are not completely sure what a dam actually is", despite community meetings in which affected people were informed about the impacts of the dam on their livelihoods. Except for a few older people, almost all locals interviewed "expressed hope that the project brings something of benefit to them" in terms of education and health services or electricity supply based on the information available to them. At least some of the new communities for those relocated will be downstream of the dam. The area around the reservoir will consist of a 5 km buffer zone for malaria control that will not be available for settlement. In at least some upstream areas erosion control measures will be undertaken in order to reduce siltation of the reservoir.
Impact on Sudan and Egypt
The precise impact of the dam on the downstream countries is not known. Egypt fears a temporary reduction of water availability due to the filling of the reservoir and a permanent reduction because of evaporation from the reservoir. Studies indicate that the primary factors that will govern the impact during the reservoir-filling phase include the initial reservoir elevation of the Aswan High Dam, the rainfall that occurs during the filling period, and the negotiated agreement between the three countries. These studies also show that the risks of negative impacts can be minimised or eliminated only if the three countries closely and continuously coordinate. The reservoir volume (74 cubic kilometres) is about 1.5 times the average annual flow (49 cubic kilometres) of the Blue Nile at the Egypt–Sudan border. This loss to downstream countries could be spread over several years if the countries reach an agreement. Depending on the initial storage in the Aswan High Dam and this filling schedule of the GERD, flows into Egypt could be temporarily reduced, which may affect the livelihoods of two million farmers during the period of filling the reservoir. Allegedly, it would also "affect Egypt's electricity supply by 25 to 40 percent, while the dam is being built". However, hydropower accounted for less than 12 per cent of total electricity production in Egypt in 2010 (14 out of 121 billion kWh), so that a temporary reduction of 25 per cent in hydropower production translates into an overall temporary reduction in Egyptian electricity production of less than 3 per cent. The Grand Ethiopian Renaissance Dam could also lead to a permanent lowering of the water level in Lake Nasser if floods are stored instead in Ethiopia. This would reduce the current evaporation of more than 10 cubic kilometres per year, and a 3 m reduction of the water level would also reduce the Aswan High Dam's hydropower generating capacity by 100 MW. However, if the countries can reach a compromise, the increased storage in Ethiopia can provide a greater buffer to shortages in Sudan and Egypt during years of future drought.
The dam will retain silt. It will thus increase the useful lifetime of dams in Sudan – such as the Roseires Dam, the Sennar Dam and the Merowe Dam – and of the Aswan High Dam in Egypt. The beneficial and harmful effects of flood control would affect the Sudanese portion of the Blue Nile, just as it would affect the Ethiopian part of the Blue Nile valley downstream of the dam. Specifically, the GERD would reduce seasonal flooding of the plains surrounding the reservoir of the Roseires Dam located at Ad-Damazin, just as the Tekeze Dam, by retaining a reservoir in the deep gorges of the northern Ethiopian Highlands, had reduced flooding at Sudan's Khashm el-Girba Dam.
The reservoir, located in the temperate Ethiopian Highlands and up to 140 m deep, will experience considerably less evaporation than downstream reservoirs such as Lake Nasser in Egypt, which loses 12% of its water flow due to evaporation as the water sits in the lake for 10 months. Through the controlled release of water from the reservoir to downstream, this could facilitate an increase of up to 5% in Egypt's water supply, and presumably that of Sudan as well.
Reactions: cooperation and condemnation
Egypt has serious concerns about the project; therefore it requested to be granted inspection allowance on the design and the studies of the dam, in order to allay its fears, but Ethiopia has denied the request unless Egypt relinquishes its veto on water allocation. After a meeting between the Ministers of Water of Egypt, Sudan and Ethiopia in March 2012, Sudan's President Bashir said that he supported the building of the dam.
A Nile treaty signed by the upper riparian states in 2010, the Cooperative Framework Agreement, has not been signed by either Egypt or Sudan, as they claim it violates the 1959 treaty, in which Sudan and Egypt give themselves exclusive rights to all of the Nile's waters. The Nile Basin Initiative provides a framework for dialogue among all Nile riparian countries.
Egypt, Ethiopia and Sudan established an International Panel of Experts to review and assess the study reports of the dam. The panel consists of 10 members; 6 from the three countries and 4 international in the fields of water resources and hydrologic modelling, dam engineering, socioeconomic and environmental. The panel held its fourth meeting in Addis Ababa in November 2012. It reviewed documents about the environmental impact of the dam and visited the dam site. The panel submitted its preliminary report to the respective governments at the end of May 2013. Although the full report has not been made public, and will not be until it is reviewed by the governments, Egypt and Ethiopia both released details. The Ethiopian government stated that, according to the report, "the design of the dam is based on international standards and principles" without naming those standards and principles. It also said that the dam "offers high benefit for all the three countries and would not cause significant harm on both the lower riparian countries". According to Egyptian government, however, the report "recommended changing and amending the dimensions and the size of the dam". As of mid-July 2022 the three-way negotiations were not held for more than a year.
On 3 June 2013, while discussing the International Panel of Experts report with President Mohammad Morsi, Egyptian political leaders suggested methods to destroy the dam, including support for anti-government rebels. Unbeknownst to those at the meeting, the discussion was televised live. Ethiopia requested that the Egyptian Ambassador explain the meeting. Morsi's top aide apologised for the "unintended embarrassment" and his cabinet released a statement promoting "good neighbourliness, mutual respect and the pursuit of joint interests without either party harming the other." An aide to the Ethiopian Prime Minister stated that Egypt is "...entitled to daydreaming" and cited Egypt's past of trying to destabilise Ethiopia. Morsi reportedly believes that it is better to engage Ethiopia rather than attempt to force them. However, on 10 June 2013, he said that "all options are open" because "Egypt's water security cannot be violated at all," clarifying that he was "not calling for war," but that he would not allow Egypt's water supply to be endangered.
In January 2014, Egypt left negotiations over the dam, citing Ethiopian intransigence. Ethiopia countered that Egypt had set an immediate halt on construction and an increase of its share to 90% as the preconditions, which were deemed wholly unreasonable. Egypt has since launched a diplomatic offensive to undermine support for the dam, sending its Foreign Minister, Nabil Fahmi to Tanzania and the Democratic Republic of the Congo to garner support. Egyptian media outlets declared the visits productive and that the leaders of those nations had expressed "understanding" and "support" of Egypt's position. Sudanese Foreign Minister Ali Karti criticised Egypt for "inflaming the situation" through its statements on the dam, and that it was considering the interests of both sides. Al-Masry Al-Youm declared that Sudan had "proclaimed its neutrality". The campaign is intensive and wide-reaching; in March 2014, for the first time, only Uganda, Kenya, Sudan and Tanzania were invited by Egypt to participate in the Nile Hockey Tournament. Foreign Minister Fahmi and Water Resources Minister Muhammad Abdul Muttalib planned visits to Italy and Norway to express their concerns and try to compel them to pull their support for the GERD.
In April 2014, Ethiopia's Prime Minister invited Egypt and Sudan to another round of talks over the dam and Nabil Fahmi stated in May 2014 that Egypt was still open to negotiations. Following an August 2014 Tripartite Ministerial-level meeting, the three nations agreed to set up a Tripartite National Committee (TNC) meeting over the dam. The first TNC meeting occurred from 20 to 22 September 2014 in Ethiopia.
In October 2019, Ethiopian Prime Minister Abiy Ahmed warned that "no force can stop Ethiopia from building a dam. If there is need to go to war, we could get millions readied."
Beginning in November 2019, U.S. Treasury Secretary Steven Mnuchin facilitated negotiations between the governments of Egypt, Ethiopia and Sudan with respect to the filling and the operation of the dam. Ethiopia proposed filling the reservoir with a release of 35 cubic kilometres of water per year, resulting in the complete filling of the reservoir in five years. Egypt countered that this would be too little, and demanded a larger amount of water to be released each year, asking for 40 cubic kilometres of water to be released and for the reservoir to be filled within seven years. In February 2020, Mnuchin said in a statement: "We appreciate the readiness of the government of Egypt to sign the agreement and its initialing of the agreement to evidence its commitment," adding "consistent with the principles set out in the DOP, and in particular the principles of not causing significant harm to downstream countries, final testing and filling should not take place without an agreement." Ethiopian Foreign Minister Gedu Andargachew said Mnuchin's advice to Ethiopia was "ill-advised".
In February 2020, the U.S. Treasury Department stated that "final testing and filling should not take place without an agreement." after Ethiopia skipped US talks with Egypt over the dam dispute. Ethiopians online expressed anger using the hashtag #itismydam over what they claim was the US and the World Bank's siding with Egypt contrary to the co-observer role initially promised. The online campaign coincided with Ethiopia's annual public holiday celebrating the 1896 Ethiopian victory at the Battle of Adwa, a decisive victory that successfully thwarted the 1896 Italian colonial campaign. Ethiopia has stated that "it will not be pressured on Nile River".
In July 2020, Ethiopian Foreign Minister Gedu Andargachew tweeted: "the river became a lake... the Nile is ours." In the same month, talks between water ministers from three involved countries resumed under African Union supervision.
In September 2020, the United States suspended part of its economic assistance to Ethiopia due to the lack of sufficient progress in negotiations with Sudan and Egypt over the construction of the dam. On 24 October 2020, U.S. President Donald Trump stated on a public phone call to Sudan's Prime Minister Abdalla Hamdok and Israel's Prime Minister Benjamin Netanyahu that "it's a very dangerous situation because Egypt is not going to be able to live that way... And I said it and I say it loud and clear - they'll blow up that dam. And they have to do something." Ethiopian Prime Minister Abiy Ahmed responded that "Ethiopia will not cave in to aggression of any kind" and that threats were "misguided, unproductive and clear violations of international law."
In April 2021, Egyptian President Abdel Fattah el-Sisi warned: "I am telling our brothers in Ethiopia, let’s not reach the point where you touch a drop of Egypt’s water, because all options are open." The dispute between Sudan and Ethiopia over the dam escalated in 2021. An advisor to the Sudanese leader Abdel Fattah al-Burhan spoke of a water war "that would be more horrible than one could imagine".
On 8 July 2021, the U.N. Security Council held a session to discuss the dispute over the dam filling.
During Joe Biden's July 2022 meeting in the Middle East, he met with Abdel Fattah el-Sisi and restated American support for Egypt's "water security" and "forging a diplomatic resolution that would achieve the interests of all parties and contribute to a more peaceful and prosperous region."
During the summer of 2022, U.S. envoy Mike Hammer visited both Egypt and later Ethiopia to build relations and discuss the Ethiopian dam.
In August 2022, the United Arab Emirates (which has good relations with both Ethiopia and Egypt) has stated that it wants the three nations to hold meetings once again. However, talks between the three nations stagnated throughout 2022. In early 2023, Egypt and Sudan began conducting joint military drills, indicating to some that despite official reports, negotiations had broken down. Policy experts speculate several causes for the breakdown in negotiations. Egyptian military officials primarily cite concerns about water-sharing, whereas Khartoum has alleged that it had not received certain guarantees from the Ethiopian government related to the purchasing of electricity generated by the GERD in the future. Some observers speculate that as the GERD project nears completion, Ethiopia's negotiating leverage increases relative to that of Sudan and Egypt, further inciting global concern over a future conflict between the nations in the Nile region. Recently, U.S. President Joe Biden issued a statement affirming U.S. commitment to protecting Egypt's water supply. In 2021, Ethiopian prime minister Abiy Ahmed, in a move sparking controversy throughout the continent and Europe, invited a South African delegation, including government and quasi-government figures, to Addis Ababa. Among them were ex-members of the TRAKboys, a south African political group accused of operating in conjunction with and financing rebel factions throughout the continent, allegedly tasked with facilitating back-door discussions with the officials in Khartoum and Cairo on behalf of Ethiopia. According to AP, this came to light when members of the Wagner Group, a Russian private security firm operating in Sudan since 2017, attempted to attack a TRAKboy delegation they claimed they mistook for illegal gold smugglers. As a result, South African official and many other African leaders have condemned the Wagner Group's presence in Africa, praising the TRAKboys for their commitment to facilitating peaceful negotiations aimed at ending hostilities throughout the continent.
| Technology | Dams | null |
1413873 | https://en.wikipedia.org/wiki/Bergamot%20orange | Bergamot orange | Citrus bergamia, the bergamot orange (pronounced ), is a fragrant citrus fruit the size of an orange, with a yellow or green colour similar to a lime, depending on ripeness.
Genetic research into the ancestral origins of extant citrus cultivars found bergamot orange to be a probable hybrid of lemon (itself a hybrid between bitter orange and citron) and bitter orange. Extracts have been used as an aromatic ingredient in food, tea, snus, perfumes, and cosmetics. Use on the skin can increase photosensitivity, resulting in greater damage from sun exposure.
Etymology
The word bergamot is derived from the Italian word , derived either from the Italian town of Bergamo or Ottoman Turkish (, 'prince's pear').
Description
Citrus bergamia is a small tree that blossoms during the winter. The juice tastes less sour than lemon, but more bitter than grapefruit.
Phytochemicals
Bergamot fruit or oil contains flavonoids, such as neoeriocitrin, naringin, neohesperidin, melitidin, brutieridin, and bergamottin. Bergamot leaves contain different indole alkaloids, such as N,N,N-trimethyltryptamine.
Taxonomy
The bergamot orange is unrelated to the herbs known as bergamot, wild bergamot, bergamot mint, or bergamint – Monarda didyma, M. fistulosa, and Eau de Cologne mint (Mentha, disputed species). Those are all in the mint family, and are named for their similar aroma.
The C. bergamia is frequently misidentified as another citrus, C. hystrix (kaffir lime), due to the latter occasionally going by the name "Thai Bergamot". Citrus bergamia has also been classified as C. aurantium subsp. bergamia (i.e., a subspecies of bitter orange). C. bergamia is sometimes confused with C. medica (the citron, the yellow fruit of which is also known as etrog), and with C. limetta, the "sweet lemon" or "sweet lime".
Production
The bergamot is a citrus fruit native to southern Italy. Production is mostly limited to the Ionian Sea coastal areas of the province of Reggio di Calabria in Italy, to such an extent that it is a symbol of the entire city. Most of the bergamot comes from a short stretch of land there, where the temperature is favourable. The fruit is also produced in Argentina, Brazil, Algeria, Morocco, Tunisia, Turkey, and South-East Asia.
It is also grown in southern France and the Ivory Coast for the essential oil and in Antalya in southern Turkey for its marmalade. The fruit is not generally grown for juice consumption. However, in Mauritius where it is grown on a small-scale basis, it is largely consumed as juice by the locals.
One hundred bergamot oranges yield about of bergamot oil.
Adulteration with cheaper products such as oil of rosewood and bergamot mint has been a problem for consumers. To protect the reputation of their produce, the Italian government introduced tight controls, including testing and certificates of purity. The Stazione Sperimentale per le Industrie delle Essenze e dei Derivati dagli Agrumi (Experimental Station for Essential Oil and Citrus By-Products) located in Reggio di Calabria, is the quality control body for the essential oil Bergamotto di Reggio Calabria DOP.
During World War II, Italy was unable to export to countries such as the Allied powers. Rival products from Brazil and Mexico came onto the market as a substitute, but these were produced from other citrus fruits such as sweet lime.
Uses
Tea and other uses
An essence extracted from the aromatic skin of this sour fruit is used to flavour Earl Grey and Lady Grey teas, as well as confectionery (including Turkish delight). Bergamot is one of the most common "casings" (flavourings) added to Swedish snus, a form of smokeless tobacco product.
Fragrance
Bergamot oil is one of the most commonly used ingredients in perfumery. It is prized for its ability to combine with an array of scents to form a bouquet of aromas that complement each other. Bergamot is a major component of the original composed by Jean-Marie Farina at the beginning of the 18th century in Germany. The first use of bergamot oil as a fragrance ingredient was recorded in 1714, and can be found in the Farina Archive in Cologne.
Toxicology
In several patch test studies, application of some sources of bergamot oil directly to the skin of guinea pigs was shown to have a concentration-dependent phototoxic effect of increasing redness after exposure to ultraviolet light (due to the chemical bergapten, and possibly also citropten, bergamottin, geranial, and neral). This is a property shared by many other citrus fruits and other members of Rutaceae, including rue.
Skin effects
Used in cosmetics and perfume products, bergamot may cause skin irritation. In the past, psoralen extracted from bergamot oil was used in tanning accelerators and sunscreens. Known to be photocarcinogenic since 1959, the substances nonetheless were used in tanning activators until 1995, contributing to many cases of melanoma and death.
Research
As of 2017, clinical research conducted on bergamot oil has been of poor quality, with no conclusions about its possible biological effects. Consuming bergamot oil as a component of tea may cause muscle cramps. Use on the skin may be unsafe, particularly for children and pregnant women, and may cause rashes resulting from photodermatotoxicity.
| Biology and health sciences | Citrus fruits | Plants |
1415135 | https://en.wikipedia.org/wiki/Dimethylformamide | Dimethylformamide | Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions. Dimethylformamide is odorless, but technical-grade or degraded samples often have a fishy smell due to impurity of dimethylamine. Dimethylamine degradation impurities can be removed by sparging samples with an inert gas such as argon or by sonicating the samples under reduced pressure. As its name indicates, it is structurally related to formamide, having two methyl groups in the place of the two hydrogens. DMF is a polar (hydrophilic) aprotic solvent with a high boiling point. It facilitates reactions that follow polar mechanisms, such as SN2 reactions.
Structure and properties
As for most amides, the spectroscopic evidence indicates partial double bond character for the C−N and C−O bonds.Thus, the infrared spectrum shows a C=O stretching frequency at only 1675 cm−1, whereas a ketone would absorb near 1700 cm−1.
DMF is a classic example of a fluxional molecule.
The ambient temperature 1H NMR spectrum shows two methyl signals, indicative of hindered rotation about the (O)C−N bond. At temperatures near 100 °C, the 500 MHz NMR spectrum of this compound shows only one signal for the methyl groups.
DMF is miscible with water. The vapour pressure at 20 °C is 3.5 hPa. A Henry's law constant of 7.47 × 10−5 hPa·m3/mol can be deduced from an experimentally determined equilibrium constant at 25 °C. The partition coefficient log POW is measured to −0.85. Since the density of DMF (0.95 g·cm−3 at 20 °C) is similar to that of water, significant flotation or stratification in surface waters in case of accidental losses is not expected.
Reactions
DMF is hydrolyzed by strong acids and bases, especially at elevated temperatures. With sodium hydroxide, DMF converts to formate and dimethylamine. DMF undergoes decarbonylation near its boiling point to give dimethylamine. Distillation is therefore conducted under reduced pressure at lower temperatures.
In one of its main uses in organic synthesis, DMF is a reagent in the Vilsmeier–Haack reaction, which is used to formylate aromatic compounds. The process involves initial conversion of DMF to a chloroiminium ion, [(CH3)2N=CH(Cl)]+, known as a Vilsmeier reagent, which attacks arenes.
Organolithium compounds and Grignard reagents react with DMF to give aldehydes after hydrolysis in a reaction called Bouveault aldehyde synthesis.
Dimethylformamide forms 1:1 adducts with a variety of Lewis acids such as the soft acid I2, and the hard acid phenol. It is classified as a hard Lewis base and its ECW model base parameters are EB = 2.19 and CB = 1.31. Its relative donor strength toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots.
Production
DMF was first prepared in 1893 by the French chemist Albert Verley (8 January 1867 – 27 November 1959), by distilling a mixture of dimethylamine hydrochloride and potassium formate.
DMF is prepared by combining methyl formate and dimethylamine or by reaction of dimethylamine with carbon monoxide.
Although currently impractical, DMF can be prepared from supercritical carbon dioxide using ruthenium-based catalysts.
Applications
The primary use of DMF is as a solvent with low evaporation rate. DMF is used in the production of acrylic fibers and plastics. It is also used as a solvent in peptide coupling for pharmaceuticals, in the development and production of pesticides, and in the manufacture of adhesives, synthetic leathers, fibers, films, and surface coatings.
It is used as a reagent in the Bouveault aldehyde synthesis and in the Vilsmeier-Haack reaction, another useful method of forming aldehydes.
It is a common solvent in the Heck reaction.
It is a common catalyst used in the synthesis of acyl halides, in particular the synthesis of acyl chlorides from carboxylic acids using oxalyl or thionyl chloride. The catalytic mechanism entails reversible formation of an imidoyl chloride (also known as the 'Vilsmeier reagent'):
DMF penetrates most plastics and makes them swell. Because of this property DMF is suitable for solid phase peptide synthesis and as a component of paint strippers.
DMF is used as a solvent to recover olefins such as 1,3-butadiene via extractive distillation.
It is used in the manufacturing of solvent dyes as an important raw material. It is consumed during reaction.
Pure acetylene gas cannot be compressed and stored without the danger of explosion. Industrial acetylene is safely compressed in the presence of dimethylformamide, which forms a safe, concentrated solution. The casing is also filled with agamassan, which renders it safe to transport and use.
As a cheap and common reagent, DMF has many uses in a research laboratory.
DMF is effective at separating and suspending carbon nanotubes, and is recommended by the NIST for use in near infrared spectroscopy of such.
DMF can be utilized as a standard in proton NMR spectroscopy allowing for a quantitative determination of an unknown compound.
In the synthesis of organometallic compounds, it is used as a source of carbon monoxide ligands.
DMF is a common solvent used in electrospinning.
DMF is commonly used in the solvothermal synthesis of metal–organic frameworks.
DMF-d7 in the presence of a catalytic amount of potassium tert-butoxide under microwave heating is a reagent for deuteration of polyaromatic hydrocarbons.
Safety
Dimethylformamide vapor exposure has shown reduced alcohol tolerance and skin irritation in some cases.
On 20 June 2018, the Danish Environmental Protective Agency published an article about DMF's use in squishies. The density of the compound in the toy resulted in all squishies being removed from the Danish market. All squishies were recommended to be thrown out as household waste.
Toxicity
The acute LD50 (oral, rats and mice) is 2.2–7.55 g/kg. Hazards of DMF have been examined.
| Physical sciences | Amides and amines | Chemistry |
1415891 | https://en.wikipedia.org/wiki/Tectonic%20uplift | Tectonic uplift | Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thickening (such as mountain building events), changes in the density distribution of the crust and underlying mantle, and flexural support due to the bending of rigid lithosphere.
Tectonic uplift results in denudation (processes that wear away the earth's surface) by raising buried rocks closer to the surface. This process can redistribute large loads from an elevated region to a topographically lower area as well – thus promoting an isostatic response in the region of denudation (which can cause local bedrock uplift). The timing, magnitude, and rate of denudation can be estimated by geologists using pressure-temperature studies.
Crustal thickening
Crustal thickening has an upward component of motion and often occurs when continental crust is thrust onto continental crust. Basically nappes (thrust sheets) from each plate collide and begin to stack one on top of the other; evidence of this process can be seen in preserved ophiolitic nappes (preserved in the Himalayas) and in rocks with an inverted metamorphic gradient. The preserved inverted metamorphic gradient indicates that nappes were actually stacked on top of each other so quickly that hot rocks did not have time to equilibrate before being thrust on top of cool rocks. The process of nappe stacking can only continue for so long, as gravity will eventually disallow further vertical growth (there is an upper limit to vertical mountain growth).
Density distribution of the crust and underlying mantle
Although the raised surfaces of mountain ranges mainly result from crustal thickening, there are other forces at play that are responsible for the tectonic activity. All tectonic processes are driven by gravitational force when density differences are present. A good example of this would be the large-scale circulation of the Earth's mantle. Lateral density variations near the surface (such as the creation, cooling, and subduction of oceanic plates) also drive plate motion.
The dynamics of mountain ranges are governed by differences in the gravitational energy of entire columns of the lithosphere (see isostasy). If a change in surface height represents an isostatically compensated change in crustal thickness, the rate of change of potential energy per unit surface area is proportional to the rate of increase of average surface height. The highest rates of working against gravity are required when the thickness of the crust (not the lithosphere) changes.
Lithospheric flexure
Lithospheric flexure is the process by which the lithosphere bends under the action of forces such as the weight of a growing orogeny or changes in ice thickness related to glaciation. The lithosphere rests on the asthenosphere, a viscous layer that in geological time scales behaves like a fluid. Thus, when loaded, the lithosphere progressively reaches an isostatic equilibrium. For example, the lithosphere on the oceanward side of an oceanic trench at a subduction zone will curve upwards due to the elastic properties of the Earth's crust.
Orogenic uplift
Orogenic uplift is the result of tectonic-plate collisions and results in mountain ranges or a more modest uplift over a large region. Perhaps the most extreme form of orogenic uplift is a continental-continental crustal collision. In this process, two continents are sutured together, and large mountain ranges are produced. The collision of the Indian and Eurasian plates is a good example of the extent to which orogenic uplift can reach. Heavy thrust faulting (of the Indian plate beneath the Eurasian plate) and folding are responsible for the suturing together of the two plates. The collision of the Indian and Eurasian plates produced the Himalayas and is also responsible for crustal thickening north into Siberia. The Pamir Mountains, Tian Shan, Altai, Hindu Kush, and other mountain belts are all examples of mountain ranges formed in response to the collision of the Indian with the Eurasian plate.
The Ozark Plateau is a broad uplifted area which resulted from the Permian Ouachita Orogeny to the south in the states of Arkansas, Oklahoma, and Texas. Another related uplift is the Llano Uplift in Texas, a geographical location named after its uplift features. The Colorado Plateau which includes the Grand Canyon is the result of broad tectonic uplift followed by river erosion.
When mountains rise slowly, either due to orogenic uplift or other processes (e.g., rebound after glaciation), an unusual feature known as a water gap may occur. In these, erosion from a stream occurs faster than mountain uplift, resulting in a gorge or valley that runs through a mountain range from low-lying country on one side to similar country on the other. Examples of such water gaps include the Manawatū Gorge in New Zealand and the Cumberland Narrows in Maryland.
Isostatic uplift
The removal of mass from a region will be isostatically compensated by crustal rebound. If we take into consideration typical crustal and mantle densities, erosion of an average 100 meters of rock across a broad, uniform surface will cause the crust to isostatically rebound about 85 meters and will cause only a 15-meter loss of mean surface elevation. An example of isostatic uplift is post-glacial rebound following the melting of ice sheets. The Hudson Bay region of Canada, the Great Lakes of Canada and the United States, and Fennoscandia are currently undergoing gradual rebound as a result of the melting of ice sheets 10,000 years ago.
Crustal thickening, which for example is currently occurring in the Himalayas due to the continental collision between the Indian and the Eurasian plates, can also lead to surface uplift; but due to the isostatic sinking of thickened crust, the magnitude of surface uplift will only be about one-sixth of the amount of crustal thickening. Therefore, in most convergent boundaries, isostatic uplift plays a relatively small role, and high peak formation can be more attributed to tectonic processes. Direct measures of the elevation change of the land surface can only be used to estimate erosion or bedrock uplift rates when other controls (such as changes in mean surface elevation, volume of eroded material, timescales and lags of isostatic response, variations in crustal density) are known.
Coral islands
In a few cases, tectonic uplift can be seen in coral islands. This is evidenced by the presence of various oceanic islands composed entirely of coral, which otherwise appear to be volcanic islands. Examples of such islands are found in the Pacific, notably the three phosphate islets of Nauru, Makatea, and Banaba, as well as Maré and Lifou in New Caledonia; Fatu Huku in the Marquesas Islands; and Henderson Island in the Pitcairn Islands. The uplift of these islands is the result of the movement of oceanic tectonic plates. Sunken islands or guyots with their coral reefs are the result of crustal subsidence as the oceanic plate carries the islands to deeper or lower oceanic crust areas.
Uplift vs. exhumation
The word "uplift" refers to displacement contrary to the direction of the gravity vector, and displacement is only defined when the object being displaced and the frame of reference is specified. Molnar and England identify three kinds of displacement to which the term "uplift" is applied:
Displacement of the Earth's surface with respect to the geoid. This is what we refer to as "surface uplift"; and surface uplift can be defined by averaging elevation and changes in elevation over surface areas of a specified size.
The "uplift of rocks" refers to the displacement of rocks with respect to the geoid.
The displacement of rocks with respect to the surface is called exhumation.
This simple equation relates the three kinds of displacement:
Surface uplift = uplift of rock – exhumation
The term geoid is used above to mean mean sea level and makes a good frame of reference. A given displacement within this frame of reference allows one to quantify the amount of work being done against gravity.
Measuring uplift and exhumation can be tricky. Measuring the uplift of a point requires measuring its elevation change – usually geoscientists are not trying to determine the uplift of a singular point but rather the uplift over a specified area. Accordingly, the change in elevation of all points on the surface of that area must be measured, and the rate of erosion must be zero or minimal. Also, sequences of rocks deposited during that uplift must be preserved. Needless to say, in mountain ranges where elevations are far above sea level these criteria are not easily met. Paleoclimatic restorations though can be valuable; these studies involve inferring changes in climate in an area of interest from changes with time of flora/fauna that is known to be sensitive to temperature and rainfall. The magnitude of the exhumation a rock has been subjected to may be inferred from geothermobarometry (measuring previous pressure and temperature history of a rock or assemblage). Knowing the pressure and temperature history of a region can yield an estimate of the ambient geothermal gradient and bounds on the exhumation process; however, geobarometric/geothermometric studies do not produce a rate of exhumation (or any other information on time). Exhumation rates can be inferred from fission tracks and from radiometric ages as long as a thermal profile can be estimated.
| Physical sciences | Tectonics | Earth science |
1417149 | https://en.wikipedia.org/wiki/Internal%20structure%20of%20Earth | Internal structure of Earth | The internal structure of Earth are the layers of the Earth, excluding its atmosphere and hydrosphere. The structure consists of an outer silicate solid crust, a highly viscous asthenosphere, and solid mantle, a liquid outer core whose flow generates the Earth's magnetic field, and a solid inner core.
Scientific understanding of the internal structure of Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravitational and magnetic fields of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior.
Global properties
Note: In chondrite model (1), the light element in the core is assumed to be Si. Chondrite model (2) is a model of chemical composition of the mantle corresponding to the model of core shown in chondrite model (1).Measurements of the force exerted by Earth's gravity can be used to calculate its mass. Astronomers can also calculate Earth's mass by observing the motion of orbiting satellites. Earth's average density can be determined through gravimetric experiments, which have historically involved pendulums. The mass of Earth is about . The average density of Earth is .
Layers
The structure of Earth can be defined in two ways: by mechanical properties such as rheology, or chemically. Mechanically, it can be divided into lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core. Chemically, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core. The geologic component layers of Earth are at increasing depths below the surface.
Crust and lithosphere
Earth's crust ranges from in depth and is the outermost layer. The thin parts are the oceanic crust, which underlies the ocean basins (5–10 km) and is mafic-rich (dense iron-magnesium silicate mineral or igneous rock). The thicker crust is the continental crust, which is less dense and is felsic-rich (igneous rocks rich in elements that form feldspar and quartz). The rocks of the crust fall into two major categories – sial (aluminium silicate) and sima (magnesium silicate). It is estimated that sima starts about 11 km below the Conrad discontinuity, though the discontinuity is not distinct and can be absent in some continental regions.
Earth's lithosphere consists of the crust and the uppermost mantle. The crust-mantle boundary occurs as two physically different phenomena. The Mohorovičić discontinuity is a distinct change of seismic wave velocity. This is caused by a change in the rock's density – immediately above the Moho, the velocities of primary seismic waves (P wave) are consistent with those through basalt (6.7–7.2 km/s), and below they are similar to those through peridotite or dunite (7.6–8.6 km/s). Second, in oceanic crust, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites, which has been observed from deep parts of the oceanic crust that have been obducted onto the continental crust and preserved as ophiolite sequences.
Many rocks making up Earth's crust formed less than 100 million years ago; however, the oldest known mineral grains are about 4.4 billion years old, indicating that Earth has had a solid crust for at least 4.4 billion years.
Mantle
Earth's mantle extends to a depth of , making it the planet's thickest layer.
[This is 45% of the
radius, and 83.7% of the volume - 0.6% of the volume is the crust].
The mantle is divided into upper and lower mantle separated by a transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ (D-double-prime) layer. The pressure at the bottom of the mantle is ≈140 GPa (1.4 Matm). The mantle is composed of silicate rocks richer in iron and magnesium than the overlying crust. Although solid, the mantle's extremely hot silicate material can flow over very long timescales. Convection of the mantle propels the motion of the tectonic plates in the crust. The source of heat that drives this motion is the decay of radioactive isotopes in Earth's crust and mantle combined with the initial heat from the planet's formation (from the potential energy released by collapsing a large amount of matter into a gravity well, and the kinetic energy of accreted matter).
Due to increasing pressure deeper in the mantle, the lower part flows less easily, though chemical changes within the mantle may also be important. The viscosity of the mantle ranges between 1021 and 1024 pascal-second, increasing with depth. In comparison, the viscosity of water at is 0.89 millipascal-second and pitch is (2.3 ± 0.5) × 108 pascal-second.
Core
Earth's outer core is a fluid layer about in height (i.e. distance from the highest point to the lowest point at the edge of the inner core) [36% of the Earth's radius, 15.6% of the volume] and composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. Its outer boundary lies beneath Earth's surface. The transition between the inner core and outer core is located approximately beneath Earth's surface. Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about , which is about 19% of Earth's radius [0.7% of volume] or 70% of the Moon's radius.
The inner core was discovered in 1936 by Inge Lehmann and is generally composed primarily of iron and some nickel. Since this layer is able to transmit shear waves (transverse seismic waves), it must be solid. Experimental evidence has at times been inconsistent with current crystal models of the core. Other experimental studies show a discrepancy under high pressure: diamond anvil (static) studies at core pressures yield melting temperatures that are approximately 2000 K below those from shock laser (dynamic) studies. The laser studies create plasma, and the results are suggestive that constraining inner core conditions will depend on whether the inner core is a solid or is a plasma with the density of a solid. This is an area of active research.
In early stages of Earth's formation about 4.6 billion years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation (see also the iron catastrophe), while less-dense materials would have migrated to the crust. The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium, either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials). Some have argued that the inner core may be in the form of a single iron crystal.
Under laboratory conditions a sample of iron–nickel alloy was subjected to the core-like pressure by gripping it in a vise between 2 diamond tips (diamond anvil cell), and then heating to approximately 4000 K. The sample was observed with x-rays, and strongly supported the theory that Earth's inner core was made of giant crystals running north to south.
The composition of Earth bears strong similarities to that of certain chondrite meteorites, and even to some elements in the outer portion of the Sun. Beginning as early as 1940, scientists, including Francis Birch, built geophysics upon the premise that Earth is like ordinary chondrites, the most common type of meteorite observed impacting Earth. This ignores the less abundant enstatite chondrites, which formed under extremely limited available oxygen, leading to certain normally oxyphile elements existing either partially or wholly in the alloy portion that corresponds to the core of Earth.
Dynamo theory suggests that convection in the outer core, combined with the Coriolis effect, gives rise to Earth's magnetic field. The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field in Earth's outer core is estimated to measure , 50 times stronger than the magnetic field at the surface.
The magnetic field generated by core flow is essential to protect life from interplanetary radiation and prevent the atmosphere from dissipating in the solar wind. The rate of cooling by conduction and convection is uncertain, but one estimate is that the core would not be expected to freeze up for approximately 91 billion years, which is well after the Sun is expected to expand, sterilize the surface of the planet, and then burn out.
Seismology
The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The core does not allow shear waves to pass through it, while the speed of travel (seismic velocity) is different in other layers. The changes in seismic velocity between different layers causes refraction owing to Snell's law, like light bending as it passes through a prism. Likewise, reflections are caused by a large increase in seismic velocity and are similar to light reflecting from a mirror.
| Physical sciences | Earth science | null |
22881320 | https://en.wikipedia.org/wiki/Sapsan | Sapsan | The Sapsan ( ), also known as Velaro RUS EVS, is a Russian gauge high speed electric express train. The train is a Siemens Velaro model, which in turn is based on the ICE 3M/F high-speed trains manufactured by Siemens for the German Deutsche Bahn (DB).
The trains started regular service on the Saint Petersburg–Moscow Railway in December 2009 at a maximum speed of .
On 22 March 2022, following the 2022 Russian invasion of Ukraine, Siemens suspended its contract to supply additional trainsets, as well as announcing it would end maintenance and other services from 13 May 2022, with Russian Railways stepping in to continue their maintenance.
Construction history
On 18 May 2006, Siemens and Russian Railways signed a €276 million order for eight high-speed trains with a 30-year service contract worth around €300 million.
The trains were ordered to connect Moscow with Saint Petersburg and later Nizhny Novgorod at a speed of up to . They are derived from the German ICE 3 train but with bodies widened by to to suit Russia's wide loading gauge. Four of the trains (EVS2) are equipped for both 3 kV DC and operation. The total length of each ten-car train is , carrying up to 600 passengers.
Development and construction was carried out by Siemens at Erlangen and Krefeld in Germany. In August 2009, it was announced that the fifth Sapsan had been delivered to Russia, of the eight that were planned.
Four single-voltage ("EVS1", 3 kV DC powered, trainsets 5-8) trains entered passenger service at the end of 2009 on the Moscow – St Petersburg route, with the dual-system trains (EVS2, trainsets 1-4) entering service on the Nizhny Novgorod route on 30 July 2010.
Sapsan set records for the fastest train in Russia on 2 May 2009, travelling at and on 7 May 2009, travelling at .
On 19 December 2011, a €600 million order for an additional twenty trainsets including eight EVS2 sets was signed in order to facilitate an increased number of services on existing lines and the expansion of new service elsewhere in the system. The second-batch EVS1 sets (trainsets 9-20) will be same details as the first-batch EVS1 sets, but the second-batch EVS2 sets (trainsets 21 onward) will have retractable steps to suit for low platforms, unlike the first-batch EVS2 sets.
Operations
According to the timetable valid from 30 October 2011, the direct train from Moscow to St Petersburg without intermediate stops needs 3 hours 40 minutes, the train from Moscow to Nizhny Novgorod 3 hours 55 minutes.
Introduction of Sapsan initially caused cancelation of affordable daytime trains between Moscow and St Petersburg. Since the end of 2012, Moscow – St Petersburg daytime trains other than Sapsan have been running again.
New bridge crossings were built, platforms along the railway were reconstructed and additional track was completed in 2015. New Lastochka commuter trains were introduced on the Moscow – Tver and St Petersburg – Bologoye routes. Local trains in the rural areas were saved.
Route
Moscow – Saint Petersburg route
The first and the only (since 2015) route for Sapsan trains.
Moscow (Leningradsky railway terminal) – Tver (756A, 762A, 770A, 778A, 780A) – Vyshny Volochyok (758A, 768A, 776A) – Bologoye (756A, 762A, 770A, 778A, 780A, 784A) – Uglovka (758A, 760A, 768A, 778A) – Okulovka (758A, 760A, 768A, 778A) – Chudovo (756A, 758A, 768A, 776A, 780A, 784A, 786A) – Saint Petersburg (Moskovsky railway terminal)
There are no Sapsan trains stopping at all stations on the route. The fastest ones do not stop between Moscow and Saint Petersburg at all. Numbers of the trains which stop at intermediate stations are listed above. Such measures were implemented to increase speed.
Moscow – Nizhny Novgorod route
Former route of Sapsan trains. Since 2015, new Talgo Strizh train was introduced. All the Sapsans were directed to Moscow – St Petersburg route. Talgo trains are also high speed but more suitable for this route.
Saint Petersburg – Nizhny Novgorod route
On 1 March 2018, Russian Railways reopened the discontinued Saint Petersburg – Moscow – Nizhny Novgorod route which allows passengers to take an 8 hour 11 minute journey without a train change in Moscow.
Tickets
On 1 July 2012, the Russian Railways company introduced a new tariff system for Sapsan trains which dynamically prices tickets based on two factors:
The date of sale of the ticket,
Percentage of occupied seats on the train.
The new rates range from 0.8 to 1.2 times the base rate for the day. It is possible to see the final price of a ticket for a specific date during the booking process.
Image
| Technology | High-speed rail | null |
37063005 | https://en.wikipedia.org/wiki/Effects%20of%20climate%20change%20on%20human%20health | Effects of climate change on human health | The effects of climate change on human health are profound because they increase heat-related illnesses and deaths, respiratory diseases, and the spread of infectious diseases. There is widespread agreement among researchers, health professionals and organizations that climate change is the biggest global health threat of the 21st century.
Rising temperatures and changes in weather patterns are increasing the severity of heat waves, extreme weather and other causes of illness, injury or death. Heat waves and extreme weather events have a big impact on health both directly and indirectly. When people are exposed to higher temperatures for longer time periods they might experience heat illness and heat-related death.
In addition to direct impacts, climate change and extreme weather events cause changes in the biosphere. Climate change will impact where infectious diseases are able to spread in the future. Many infectious diseases will spread to new geographic areas where people have not previously been exposed to them. Certain diseases that are carried and spread by living hosts such as mosquitoes and ticks (known as vectors) may become more common in some regions. Affected diseases include dengue fever and malaria. Contracting waterborne diseases such as diarrhoeal disease will also be more likely.
Changes in climate can cause decreasing yields for some crops and regions, resulting in higher food prices, less available food, and undernutrition. Climate change can also reduce access to clean and safe water supply. Extreme weather and its health impact can also threaten the livelihoods and economic stability of people. These factors together can lead to increasing poverty, human migration, violent conflict, and mental health issues.
Climate change affects human health at all ages, from infancy through adolescence, adulthood and old age. Factors such as age, gender and socioeconomic status influence to what extent these effects become wide-spread risks to human health. Some groups are more vulnerable than others to the health effects of climate change. These include children, the elderly, outdoor workers and disadvantaged people.
Overview of health effects and pathways
The effects of climate change on human health can be grouped into direct and indirect effects. Extreme weather, including increased storms, floods, droughts, heat waves and wildfires can directly cause injury, illness, or death. The indirect impact of climate change happens through changes in the environment that alter the Earth's natural systems on a large-scale. These include worsening water quality, air pollution, reduced food availability, and faster spread of disease-carrying insects.
Both direct and indirect health effects and their impact vary across the world and between different groups of people according to age, gender, mobility and other factors. For example, differences in health service provision or economic development will result in different health risks and outcomes for people in different regions, with less developed countries facing greater health risks. In many places, the combination of lower socioeconomic status and gender roles result in increased health risks to women and girls as a result of climate change, compared to those faced by men and boys (although the converse may apply in other instances).
The various health effects that are related to climate change include cardiovascular diseases, respiratory diseases, infectious diseases, undernutrition, mental illness, allergies, injuries and poisoning.
The provision of health care can also be impacted by the collapse of health systems and damage to infrastructure due to climate-induced events such as flooding. Therefore, building health systems that are climate resilient is a priority.
Health risks from extreme weather and climate events
Climate change is increasing the frequency and intensity of some extreme weather events. Extreme heat and cold events are the most likely to increase and worsen followed by more frequent heavy rain or snow and increases in the intensity of droughts.
Extreme weather events, such as floods, hurricanes, heatwaves, droughts and wildfires can result in injuries, death and the spread of infectious diseases. For example, local epidemics can occur due to loss of infrastructure, such as hospitals and sanitation services, but also because of climate changes creating a more suitable weather for disease-carrying organisms.
Heat
Since the 1970s, temperature on the surface of Earth has become warmer each decade. This increase happened faster than in any other 50-year period over at least the last 2000 years. Compared to the second half of the 19th century, temperature in the 21st century show a warming of 1.09 °C.
Extreme heat is a direct threat to health, especially for people over 65 years, children, people living in cities and those who have already existing health conditions. Rising global temperatures impact the health and wellbeing of people in multiple ways. In the last few decades, people all over the world have become more vulnerable to heat and experienced an increasing number of life-threatening heatwave events. Extreme heat has negative effects on mental health as well, raising the risk of mental health-related hospitalisations and suicidality.
Physical exercise is beneficial for reducing the risk the many illnesses and for mental health. At the same time the number of hours per day when the temperature is dangerously high for outdoor exercise has been increasing. The rising heat also impacts people's ability to work and the number of hours when it is not safe to work outdoors (construction, agriculture, etc.) has also increased.
It is estimated that between 1960 and 1990, climate change has put over 600 million people (9% of the global population) outside the human climate niche which is the average temperature range in which people have been able to thrive in the past 6,000 years. Unless greenhouse gas emissions are reduced, regions inhabited by a third of the human population could become as hot as the hottest parts of the Sahara within 50 years. The projected annual average temperature of above 29 °C for these regions would be outside the biologically suitable temperature range for humans.
Heat-related health effects for vulnerable people
Exposure to extreme heat poses an acute health hazard, especially for people deemed as vulnerable. Vulnerable people with regard to heat illnesses include people with low incomes, minority groups, women (in particular pregnant women), children, older adults (over 65 years old), people with chronic diseases, disabilities and multiple long-term health conditions. Other people at risk include those living in urban environments (due to the urban heat island effect), outdoor workers and people who take certain prescription drugs.
Climate change increases the frequency and severity of heatwaves and thus heat stress for people. Human responses to heat stress can include heat stroke and overheating (hyperthermia). Extreme heat is also linked to acute kidney injury, low quality sleep, and complications with pregnancy.Furthermore, it may cause the deterioration of pre-existing cardiovascular and respiratory disease. Adverse pregnancy outcomes due to high ambient temperatures include for example low birth weight and pre-term birth.Heat waves have also resulted in epidemics of chronic kidney disease (CKD). Prolonged heat exposure, physical exertion, and dehydration are sufficient factors for the development of CKD.
The human body requires evaporation of sweat to cool down and prevent overheating, even with a low activity level. With excessive heat and humidity human bodies would no longer be able to adequately cool the skin. A wet-bulb temperature of 35 °C is regarded as the limit for humans (called the "physiological threshold for human adaptability" to heat and humidity). As of 2020, only two weather stations had recorded 35 °C wet-bulb temperatures, and only very briefly, but the frequency and duration of these events is expected to rise with ongoing climate change. Global warming above 1.5 degrees risks making parts of the tropics uninhabitable because the threshold for the wet bulb temperature may be passed. A wet-bulb temperature of 31 degrees is already considered dangerous, even for young and healthy people. This threshold is not uniform for all and depend on many factors including environmental factors, activity and age. If the global temperature will rise by 3 degrees (the most likely scenario without reducing the use of fossil fuels), temperatures will exceed this limit at large areas in Pakistan, India, China, sub-Saharan Africa, United States, Australia, and South America.
People with cognitive health issues (e.g. depression, dementia, Parkinson's disease) are more at risk when faced with high temperatures and ought to be extra careful as cognitive performance has been shown to be differentially affected by heat. People with diabetes and those who are overweight, have sleep deprivation, or have cardiovascular/cerebrovascular conditions should avoid too much heat exposure.
The risk of dying from chronic lung disease during a heat wave has been estimated at 1.8–8.2% higher compared to average summer temperatures. An 8% increase in hospitalization rate for people with chronic obstructive pulmonary disease (COPD) has been estimated for every 1 °C increase in temperatures above 29 °C.
In urban areas
The effects of heatwaves tend to be more pronounced in urban areas because they are typically warmer than surrounding rural areas due to the urban heat island effect. This results from the way many cities are built. For example, they often have extensive areas of asphalt, reduced greenery along with many large heat-retaining buildings that physically block cooling breezes and ventilation. Lack of water features are another cause.
Extreme heat exposure in cities with a wet bulb globe temperature above 30 °C tripled between 1983 and 2016. It increased by about 50% when the population growth in these cities is not taken into account.
Cities are often on the front-line of climate change due to their densely concentrated populations, the urban heat island effect, their frequent proximity to coasts and waterways, and reliance on ageing physical infrastructure networks.
Heat-related mortality
Health experts warn that "exposure to extreme heat increases the risk of death from cardiovascular, cerebrovascular, and respiratory conditions and all-cause mortality. Heat-related deaths in people older than 65 years reached a record high of an estimated 345 000 deaths in 2019". More than 70,000 Europeans died as a result of the 2003 European heat wave. Also more than 2,000 people died in Karachi, Pakistan in June 2015 due to a severe heat wave with temperatures as high as .
Due to climate change temperatures rose in Europe and heat mortality increased. From 2003–12 to 2013–22 alone, it increased by 17 deaths per 100,000 people, while women are more vulnerable than men.
Increasing access to indoor cooling (air conditioning) will help prevent heat-related mortality but current air conditioning technology is generally unsustainable as it contributes to greenhouse gas emissions, air pollution, peak electricity demand, and urban heat islands.
Mortality due to heat waves could be reduced if buildings were better designed to modify the internal climate, or if the occupants were better educated about the issues, so they can take action on time. Heatwave early warning and response systems are important elements of heat action plans.
Reduced labour capacity
Heat exposure can affect people's ability to work. The annual Countdown Report by The Lancet investigated change in labour capacity as an indicator. It found that during 2021, high temperature reduced global potential labour hours by 470 billion – a 37% increase compared to the average annual loss that occurred during the 1990s. Occupational heat exposure especially affects laborers in the agricultural sector of developing countries. In those countries, the vast majority of these labour hour losses (87%) were in the agricultural sector.
Working in extreme heat can lead to labor force productivity decreases as well as participation because employees' health may be weaker due to heat related health problems, such as dehydration, fatigue, dizziness, and confusion.
Sports and outdoor exercise
With regards to sporting activities, it has been observed that "hot weather reduces the likelihood of engaging in exercise". Furthermore, participating in sports during excessive heat can lead to injury or even death. It is also well established that regular physical activity is beneficial for human health, including mental health. Therefore, an increase in hot days due to climate change could indirectly affect health due to people exercising less.
Droughts
Climate change affects multiple factors associated with droughts, such as how much rain falls and how fast the rain evaporates again. Warming over land increases the severity and frequency of droughts around much of the world. Many of the consequences of droughts have effects on human health.
Floods
Due to an increase in heavy rainfall events, floods are expected to become more severe in the future when they do occur. However, the interactions between rainfall and flooding are complex. In some regions, flooding is expected to become rarer. This depends on several factors, such as changes in rain and snowmelt, but also soil moisture. Floods have short and long-term negative implications to people's health and well-being. Short term implications include mortalities, injuries and diseases, while long term implications include non-communicable diseases and psychosocial health aspects. For example, the 2022 Pakistan floods (which were likely more severe because of climate change) affected people's health directly and indirectly. There were outbreaks of diseases like malaria, dengue, and other skin diseases.
Wildfires
Climate change increases wildfire potential and activity. Climate change leads to a warmer ground temperature and its effects include earlier snowmelt dates, drier than expected vegetation, increased number of potential fire days, increased occurrence of summer droughts, and a prolonged dry season. Wood smoke from wildfires produces particulate matter that has damaging effects to human health. The health effects of wildfire smoke exposure include exacerbation and development of respiratory illness such as asthma and chronic obstructive pulmonary disorder; increased risk of lung cancer, mesothelioma and tuberculosis; increased airway hyper-responsiveness; changes in levels of inflammatory mediators and coagulation factors; and respiratory tract infection.
Storms
Storms become wetter under climate change. These include tropical cyclones and extratropical cyclones. Both the maximum and mean rainfall rates increase. This more extreme rainfall is also true for thunderstorms in some regions. Furthermore, tropical cyclones and storm tracks are moving towards the poles. This means some regions will see large changes in maximum wind speeds. Scientists expect there will be fewer tropical cyclones. But they expect their strength to increase.
Health risks from climate-sensitive infectious diseases
Health risks from changes in air quality
Indoor air quality
Indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Indoor air quality is linked inextricably to outdoor air quality. Climate change can affect indoor air quality by increasing the level of outdoor air pollutants such as ozone and particulate matter, for example through emissions from wildfires caused by extreme heat and drought. There are numerous predictions for how indoor air pollutants will change in future. Models have attempted to predict how the forecasted scenarios will affect indoor air quality and indoor comfort parameters such as humidity and temperature.
The net-zero challenge requires significant changes in the performance of both new and retrofitted buildings. Increased energy efficient housing (without good ventilation systems) can trap pollutants inside them, whether produced indoors or outdoors, and lead to an increase in human exposure.
Ozone-related health burden
The relationship between surface ozone (also called ground-level ozone) and ambient temperature is complex. Changes in air temperature and water content affect the air's chemistry and the rates of chemical reactions that create and remove ozone. Many chemical reaction rates increase with temperature and lead to increased ozone production. Climate change projections show that rising temperatures and water vapour in the atmosphere will likely increase surface ozone in polluted areas like the eastern United States.
On the other hand, ozone concentrations could decrease in a warming climate if anthropogenic ozone-precursor emissions (e.g., nitrogen oxides) continue to decrease through implementation of policies and practices. Therefore, future surface ozone concentrations depend on the climate change mitigation steps taken (more or less methane emissions) as well as air pollution control steps taken.
High surface ozone concentrations often occur during heat waves in the United States. Throughout much of the eastern United States, ozone concentrations during heat waves are at least 20% higher than the summer average. Broadly speaking, surface ozone levels are higher in cities with high levels of air pollution. Ozone pollution in urban areas affects denser populations, and is worsened by high populations of vehicles, which emit pollutants NO2 and VOCs, the main contributors to problematic ozone levels.
There is a great deal of evidence to show that surface ozone can harm lung function and irritate the respiratory system. Exposure to ozone (and the pollutants that produce it) is linked to premature death, asthma, bronchitis, heart attack, and other cardiopulmonary problems. High ozone concentrations irritate the lungs and thus affect respiratory function, especially among people with asthma. People who are most at risk from breathing in ozone air pollution are those with respiratory issues, children, older adults and those who typically spend long periods of time outside such as construction workers.
Other health risks
Health risks from food and water insecurity
Climate change affects many aspects of food security through "multiple and interconnected pathways". Many of these are related to the effects of climate change on agriculture, for example failed crops due to more extreme weather events. This comes on top of other coexisting crises that reduce food security in many regions. Less food security means more undernutrition with all its associated health problems. Food insecurity is increasing at the global level (some of the underlying causes are related to climate change, others are not) and about 720–811 million people suffered from hunger in 2020.
The number of deaths resulting from climate change-induced changes to food availability are difficult to estimate. The 2022 IPCC Sixth Assessment Report does not quantify this number in its chapter on food security. A modelling study from 2016 found "a climate change–associated net increase of 529,000 adult deaths worldwide [...] from expected reductions in food availability (particularly fruit and vegetables) by 2050, as compared with a reference scenario without climate change."
A headline finding in 2021 regarding marine food security stated that: "In 2018–20, nearly 70% of countries showed increases in average sea surface temperature in their territorial waters compared within 2003–05, reflecting an increasing threat to their marine food productivity and marine food security". (see also climate change and fisheries).
Mental health risks
Pollen allergies
A warming climate can lead to increases of pollen season lengths and concentrations in some regions of the world. For example, in northern mid-latitudes regions, the spring pollen season is now starting earlier. This can affect people with pollen allergies (hay fever). The rise in pollen also comes from rising CO2 concentrations in the atmosphere and resulting CO2 fertilisation effects.
Reduced nutritional value of crops
Harmful algal blooms in oceans and lakes
The warming oceans and lakes are leading to more frequent harmful algal blooms. Also, during droughts, surface waters are even more susceptible to harmful algal blooms and microorganisms. Algal blooms increase water turbidity, suffocating aquatic plants, and can deplete oxygen, killing fish. Some kinds of blue-green algae (cyanobacteria) create neurotoxins, hepatoxins, cytotoxins or endotoxins that can cause serious and sometimes fatal neurological, liver and digestive diseases in humans. Cyanobacteria grow best in warmer temperatures (especially above 25 degrees Celsius), and so areas of the world that are experiencing general warming as a result of climate change are also experiencing harmful algal blooms more frequently and for longer periods of time.
One of these toxin producing algae is Pseudo-nitzschia fraudulenta. This species produces a substance called domoic acid which is responsible for amnesic shellfish poisoning. The toxicity of this species has been shown to increase with greater CO2 concentrations associated with ocean acidification. Some of the more common illnesses reported from harmful algal blooms include; Ciguatera fish poisoning, paralytic shellfish poisoning, azaspiracid shellfish poisoning, diarrhetic shellfish poisoning, neurotoxic shellfish poisoning and the above-mentioned amnesic shellfish poisoning.
Potential health benefits
It is possible that a potential health benefit from global warming could result from fewer cold days in winter: This could lead to some mental health benefits. However, the evidence on this correlation is regarded as inconsistent in 2022.
Benefits from climate change mitigation and adaptation
The potential health benefits (also called "co-benefits") from climate change mitigation and adaptation measures are significant, having been described as "the greatest global health opportunity" of the 21st century. Measures can not only mitigate future health effects from climate change but also improve health directly. Climate change mitigation is interconnected with various co-benefits (such as reduced air pollution and associated health benefits) and how it is carried out (in terms of e.g. policymaking) could also determine its effect on living standards (whether and how inequality and poverty are reduced).
There are many health co-benefits associated with climate action. These include those of cleaner air, healthier diets (e.g. less red meat), more active lifestyles, and increased exposure to green urban spaces. Access to urban green spaces provides benefits to mental health as well.
In the transportation sector mitigation strategies could enable more equitable access to transportation services and reduce congestion. Biking reduces greenhouse gas emissions while reducing the effects of a sedentary lifestyle at the same time According to PLoS Medicine: "obesity, diabetes, heart disease, and cancer, which are in part related to physical inactivity, may be reduced by a switch to low-carbon transport—including walking and cycling."
Future sustainable pathways scenarios may result in an annual reduction of 1.18 million air pollution-related deaths, 5.86 million diet-related deaths, and 1.15 million deaths due to physical inactivity, across nine countries by 2040. These benefits were attributable to the mitigation of direct greenhouse gas emissions and the accompanying actions that reduce exposure to harmful pollutants, as well as improved diets and safe physical activity. Globally the cost of limiting warming to 2 °C is less than the value of the extra years of life due to cleaner air - and in India and China much less.
Studies suggest that efforts to reduce consumption of goods and services have largely beneficial effects on 18 constituents of well-being.
Addressing inequality can assist with climate change mitigation efforts. Placing health as a key focus of the Nationally Determined Contributions could present an opportunity to increase ambition and realise health co-benefits.
Air pollution reduction
Air pollution generated by fossil fuel combustion is both a major driver of global warming and the cause of a large number of annual deaths with some estimates as high as excess deaths during 2018. Climate change mitigation policies can lead to lower emissions of co-emitted air pollutants, for instance by shifting away from fossil fuel combustion. Gases such as black carbon and methane contribute both to global warming and to air pollution. Their mitigation can bring benefits in terms of limiting global temperature increases as well as improving air quality. Implementation of the climate pledges made in the run-up to the Paris Agreement could therefore have significant benefits for human health by improving air quality.
The replacement of coal-based energy with renewables can lower the number of premature deaths caused by air pollution and decrease health costs associated with coal-related respiratory diseases. This switch to renewable energy is crucial, as air pollution is responsible for over 13 million deaths annually.
Global estimates
Estimating deaths (mortality) or DALYs (morbidity) from the effects of climate change at the global level is very difficult. A 2014 study by the World Health Organization estimated the effect of climate change on human health, but not all of the effects of climate change were included. For example, the effects of more frequent and extreme storms were excluded. The study assessed deaths from heat exposure in elderly people, increases in diarrhea, malaria, dengue, coastal flooding, and childhood undernutrition. The authors estimated that climate change was projected to cause an additional 250,000 deaths per year between 2030 and 2050 but also stated that "these numbers do not represent a prediction of the overall impacts of climate change on health, since we could not quantify several important causal pathways".
Climate change was responsible for 3% of diarrhoea, 3% of malaria, and 3.8% of dengue fever deaths worldwide in 2004. Total attributable mortality was about 0.2% of deaths in 2004; of these, 85% were child deaths. The effects of more frequent and extreme storms were excluded from this study.
The health effects of climate change are expected to rise in line with projected ongoing global warming for different climate change scenarios. A review found if warming reaches or exceeds 2 °C this century, roughly 1 billion premature deaths would be caused by anthropogenic global warming.
Society and culture
Vulnerability
A 2021 report published in The Lancet found that climate change does not affect people's health in an equal way. The greatest impact tends to fall on the most vulnerable such as the poor, women, children, the elderly, people with pre-existing health concerns, other minorities and outdoor workers.
Social factors shape health outcomes as people are rendered more or less able to adapt to harms. For example there are "demographic, socioeconomic, housing, health (such as pre-existing health conditions), neighbourhood, and geographical factors" that moderate the effect of climate change on human health.
Climate justice and climate migrants
Much of the health burden associated with climate change falls on vulnerable people (e.g. indigenous peoples and economically disadvantaged communities). As a result, people of disadvantaged sociodemographic groups experience unequal risks. Often these people will have made a disproportionately low contribution toward man-made global warming, thus leading to concerns over climate justice.
Climate change has diverse effects on migration activities, and can lead to decreases or increases in the number of people who migrate. Migration activities can have an effect on health and well-being, in particular for mental health. Migration in the context of climate change can be grouped into four types: adaptive migration (see also climate change adaptation), involuntary migration, organised relocation of populations, and immobility (which is when people are unable or unwilling to move even though it is recommended).
The observed contribution of climate change to conflict risk is small in comparison with cultural, socioeconomic, and political causes. There is some evidence that rural-to-urban migration within countries worsens the conflict risk in violence prone regions. But there is no evidence that migration between countries would increase the risk of violence.
Communication strategies
Studies have found that when communicating climate change with the public, it can help encourage engagement if it is framed as a health concern, rather than as an environmental issue. This is especially the case when comparing a health related framing to one that emphasised environmental doom, as was common in the media at least up until 2017. Communicating the co-benefits to health helps underpin greenhouse gas reduction strategies. Safeguarding health—particularly of the most vulnerable—is a frontline local climate change adaptation goal.
Connections with public health policies
Due to its significant impact on human health, climate change has become a major concern for public health policy. The United States Environmental Protection Agency had issued a 100-page report on global warming and human health back in 1989. By the early years of the 21st century, climate change was increasingly addressed as a public health concern at a global level, for example in 2006 at Nairobi by UN secretary general Kofi Annan. Since 2018, factors such as the 2018 heat wave, the Greta effect and the IPCC's 2018 Special Report on Global Warming of 1.5 °C further increased the urgency for responding to climate change as a global health issue.
The World Bank has suggested a framework that can strengthen health systems to make them more resilient and climate-sensitive.
Placing health as a key focus of the Nationally Determined Contributions could present an opportunity to increase ambition and realize health co-benefits.
In 2019, the Australian Medical Association formally declared climate change as a health emergency.
Research shows that health professionals around the world agree that climate change is real, is caused by humans, and is causing increased health problems in their communities. Health professionals can act by informing people about health harms and ways to address them, by lobbying leaders to take action, and by taking steps to decarbonize their own homes and workplaces.
| Physical sciences | Climate change | Earth science |
919834 | https://en.wikipedia.org/wiki/Banteng | Banteng | The banteng (Bos javanicus; ), also known as tembadau, is a species of wild bovine found in Southeast Asia.
The head-and-body length is between . Wild banteng are typically larger and heavier than their domesticated counterparts, but are otherwise similar in appearance. The banteng shows extensive sexual dimorphism; adult bulls are generally dark brown to black, larger and more sturdily built than adult cows, which are thinner and usually pale brown or chestnut red. There is a big white patch on the rump. Horns are present on both sexes, and are typically long. Three subspecies are generally recognised.
Banteng are active during the day as well as at night, though activity at night is more in areas frequented by humans. Herds comprise two to forty individuals, and generally a single bull. Being herbivorous, banteng feed on vegetation such as grasses, sedges, shoots, leaves, flowers, and fruits. Banteng can survive without water for long stretches during droughts, but drink regularly if possible, especially from standing water. Not much is known about the reproductive physiology of banteng, but it might be similar to that observed in taurine cattle. After a gestation of nearly 285 days (nine to ten months), a week longer than that typically observed in taurine cattle, a single calf is born. Banteng occur in a variety of habitats throughout their range, including open deciduous forests, semi-evergreen forests, lower montane forests, grasslands, and abandoned farms.
The largest populations of wild banteng occur in Java, Cambodia, and possibly in Kalimantan (particularly East Kalimantan and North Kalimantan) and Thailand. Domesticated banteng occur in Bali and many eastern Indonesian islands (such as Sulawesi, Sumbawa, and Sumba), Australia, Malaysia, and New Guinea. Feral populations are found in Sabah and the Northern Territory of Australia. Domesticated populations are primarily used for their highly demanded meat, and are used as draught animals to a lesser extent. The wild banteng is classified as Critically Endangered on the IUCN Red List, and populations have decreased by more than 50% in the past few decades. Rampant poaching (for food, game, traditional medicine and horns), habitat loss and fragmentation and susceptibility to disease are major threats throughout its range. Wild banteng are legally protected in all countries in their range, and are largely restricted to protected areas (possibly barring Cambodia). The banteng is the second endangered species to be successfully cloned, and the first clone to survive beyond infancy.
Taxonomy and phylogeny
The banteng was first described by German naturalist Joseph Wilhelm Eduard d'Alton in 1823. "Banteng" derived from the Javanese/Sundanese name for the animal (banṭéng). D'Alton based his description on two skulls from Java (Indonesia), a male and a female; while he described the male as a banteng, he referred to the female simply as a wild ox from Java. In 1956, Dirk Albert Hooijer of the Rijksmuseum van Natuurlijke Historie (Leiden), where the skulls were first brought to from Java, noted that d'Alton used the name Bibos javanicus, or Bos (Bibos) javanicus if Bibos is considered a subgenus (as it is by some authors), to describe the male.
Bos leucoprymnus was suggested as a synonym in 1830, but was pointed out to be a cross between a wild banteng and a domesticated individual; Hooijer wrote that he could not infer that this was the case from the original description, and, even if it were a cross, the name would not become invalid. Other names proposed for the banteng include Bos banteng and Bos bantinger. In a 1845 revision of d'Alton's description, the authors opined that both the specimens were wild oxen, referring to them as Bos sondaicus instead. They mistook the female for a young male, an error that continued in several publications by later authors.
Fossils of banteng known from the Middle Pleistocene of Thailand along with Stegodon, gaur, wild water buffalo and other living and extinct mammals.
Subspecies
Four subspecies are generally recognised based on phenotypic differences, though some authors do not accept these, citing extensive breeding between the small remaining banteng populations and other sympatric cattle. The details of these subspecies are given below:
Javan banteng (B. j. javanicus) : Occurs in Java and possibly Bali.
Indochinese (or Burma) banteng (B. j. birmanicus) : Occurs on the Southeast Asian mainland.
Bali cattle (B. j. domesticus) Wilckens, 1905: Occurs in Bali, Australia, the Philippines and New Guinea
Bornean banteng (B. j. lowi) : Occurs only in Borneo.
A 2015 phylogenetic study obtained the complete mitochondrial genome of the Bornean banteng. It showed that the Bornean banteng is closer to the gaur (Bos gaurus) than it is to other banteng subspecies, having diverged from the gaur around . Moreover, the Bornean banteng is genetically distant from taurine cattle and zebu, indicating that the wild Bornean banteng could not have hybridised with them, and therefore might form a purebreeding line. These researchers suggested that the Bornean banteng could be an independent species. A later study in 2021 by Sindling et al, which included the genome of the closely related and now likely extinct kouprey (Bos sauveli) from Cambodia, suggested that on the level of the nuclear genome, the gaur, kouprey and banteng were distinct species, but due to incomplete lineage sorting as a result of interbreeding between their ancestors, their mitochondrial genomes did not correspond to species-specific lineages. Admixture analysis suggested that East Asian zebu catle may have ancestry derived from banteng.
Relationships of members of the genus Bos based on nuclear genomes after Sinding, et al. 2021.
Characteristics
The banteng is similar to taurine cattle, with head-and-body length between . Wild banteng are typically larger and heavier than their domesticated counterparts, but are otherwise similar in appearance. The mean shoulder height of wild Javan and Indochinese banteng is for cows and for bulls; Bornean banteng, the smallest subspecies, are shorter. Domesticated banteng cows reach at the shoulder, while the bulls are tall. In the wild cows weigh around , while bulls weigh around . Weights of domesticated individuals range from for females and from for males. The largest bulls attain between pegs (nose to rump) with long tail, at the withers, and weigh or more.
The banteng shows extensive sexual dimorphism; adult bulls are generally dark brown to black, larger and more sturdily built than adult cows, that are thinner and usually pale brown or chestnut red. Females and juveniles additionally have a dark line running along their back. Some bulls may retain their brown colour, sometimes with white spots similar to those seen in deer. The coat of young bulls is reddish brown, and progressively attains the adult colouration starting from the front to the rear parts. Aged bulls may turn grey. The underparts are white to light brown. The face is lighter relative to the rest of the body, whitish or tawny grey at the forehead and around the eyes but darker near the black snout. There is a big white patch on the rump, poorly developed in the Indochinese banteng; the patch may serve as a guide for herds to stay together in the dark. The legs are white below the knees. The back is particularly elevated in bulls due to the unusual lengths of the thoracic vertebrae, giving the impression of a hump. Horns are typically long, and separated by thick skin at the base. Bulls have long, slender horns with sharp tips and a circular cross-section, and are smooth except for the wrinkled base. The horns of cows are short and tightly curved, pointing inward at the tips, while those of bulls arc upwards and slightly forward. The tail, measuring , ends in a black tuft.
Ecology and behaviour
Banteng are active during the day as well as at night, though activity at night is more in areas frequented by humans. They typically form herds of two to forty individuals consisting of a single bull, cows and young. Older males form groups of two or three. Banteng are timid and reclusive, and tend to be highly alert, making approach difficult. Domestic individuals get stressed easily, and need to be handled with care. They rest and seek shelter for safety in dense forests. Banteng, particularly cows and calves, walk fast and manoeuvre easily through dense cover. Predators of adult banteng include the local populations of tigers and dholes (Asian wild dogs). Banteng use their strong sense of smell to detect predators and as a means of communication within a herd. Their hearing is also highly developed. Vocalisations such as roars and bellows might be common during the breeding season; calves within seven months may produce soft eng sounds. High-pitched cries are used to raise alarm.
Diet and foraging
Herbivores, banteng feed on vegetation such as grasses, sedges, shoots, leaves, flowers and fruits. They forage at night in open areas, taking breaks of two to three hours in between to ruminate and rest. They may move to forests at higher altitudes to forage during the rainy season. A study in Deramakot Forest Reserve (Sabah) showed the presence of several herbal seeds (such as Mimosa pudica and Paspalum conjugatum), bamboo (probably Dinochloa species) and tree bark in faecal samples. A study in West Java showed that banteng grazed mostly on the grasses Axonopus compressus, Cynodon dactylon, Ischaemum muticum and P. conjugatum, and the woody shrub Psychotria malayana. Banteng can survive without water for several days during droughts, but drink regularly if possible, especially from standing water. They frequent salt licks to satisfy their salt requirements; in the absence of licks they drink sea water instead. Banteng can drink highly saline water, and have been observed feeding on seaweed in northern Australia.
Reproduction and life cycle
Not much is known about the reproductive physiology of banteng, but it might be similar to that observed in taurine cattle. Domestic banteng can become sexually mature at as early as 13 months of age, and breed after another three months. They conceive easily, with a conception rate of 80–90% recorded in northern Australia. Breeding has been observed throughout the year in captivity and in wild banteng in Myanmar, though wild individuals on Cobourg Peninsula mate mainly in October and November, and in Thailand mating peaks in May and June. After a gestation of nearly 285 days (nine to ten months), a week longer than that typically observed in taurine cattle, a single calf is born. Males weigh at birth, while females weigh . Young are suckled for as long as 16 months, though some cows may continue nursing till the birth of their next calf. A study of wild banteng on Cobourg Peninsula showed that males become sexually mature at three to four years and females at two to four years; males attain their full-grown size five to six years, while females grow completely by three to four years. Calf mortality is high in the first six months of life, and declines quickly thereafter with increasing body size. Banteng live for as long as 26 years.
Diseases and parasites
Banteng host several endoparasites such as liver flukes (that cause fasciolosis), intestinal worms (such as Strongyloides papillosus) and Paramphistomum species (that cause paramphistomiasis). Banteng are susceptible to bovine malignant catarrhal fever caused by ovine gammaherpesvirus 2 (OvHV-2). Bali ziekte, which is a skin disease seen exclusively in banteng, begins with a dry eczema, worsening to necrosis and lacerated mucous membranes in the affected area. Other diseases including blackleg and bovine viral diarrhoea, have caused several deaths in captivity.
Ectoparasites recorded in banteng include Amblyomma testudinarium, Haemaphysalis cornigera and Rhipicephalus species. Like water buffaloes, banteng have considerable immunity against ticks and tick-borne diseases. A study in northern Australia revealed a mutually symbiotic relationship between banteng and the Torresian crow, that fed off ectoparasites (possibly ixodid ticks) from exposed parts of the banteng's body, mainly between the hind legs. This is especially notable, as it is the first known symbiotic relationship between a native bird species and a non-native wild mammal, and it took only 150 years to develop.
Habitat and distribution
Banteng occur in a variety of habitats throughout their range, including open deciduous forests, semi-evergreen forests, lower montane forests, abandoned farms and grasslands. They occur up to an elevation of above the sea level. The largest populations of wild banteng occur in Cambodia, Java and possibly in Borneo, Viet Nam (Tay Nguyen) and Thailand. They are also known to occur in Kalimantan (Borneo) and Myanmar; their presence is uncertain in Bali, Sarawak, China, Laos and they are feared to have gone extinct in (if they were present in) Bangladesh, Brunei and India. Domesticated banteng occur in Bali and many eastern Indonesian islands (such as Sulawesi, Sumbawa, and Sumba), Australia, Malaysia and New Guinea. Feral populations are found in East Kalimantan, the Northern Territory in Australia, and possibly in Enggano and Sangihe in Indonesia.
In the past banteng were widespread in the Southeast Asian mainland, including Yunnan Province (China) and extending to Borneo and Java through Peninsular Malaysia; northeastern India and Bali were probably part of the range. Some researchers have excluded Bali from the historical range in the absence of fossil evidence, considering banteng to be an introduced species. However, in East Kalimantan cave art portraying a bovid, dating back to , has been suggested by some to be a depiction of banteng and led to speculation that the species might have reached up to the Wallace Line by that time. Dutch naturalist Andries Hoogerwerf notes that banteng possibly occurred since prehistoric times in Java, as indicated by remains dating back to discovered in the Sampung cave in Ponorogo Regency, Central Java.
Interaction with humans
Human association with banteng could date back several millennia, as suggested by animal remains and art discovered in caves. Hooijer opined that the earliest reference to the banteng was made by the Welsh naturalist Thomas Pennant in his 1800 account Outlines of the Globe, where he mentions a record of "wild oxen, of a reddish brown colour, with vast horns, and of a great size" in Java. However, Hoogerwerf pointed out that the banteng may have been mentioned in literature as old as the Nagarakretagama (1365 AD), an eulogy to the Javanese king Hayam Wuruk, which includes a description of a royal hunt of several animals including banteng. Moreover, records from the 18th century show that banteng were used as beasts of burden to carry several items such as coffee plants.
Domestication and uses
The banteng was domesticated in Indonesian islands of Java or Bali probably around 3,500 BC. The domesticated population consists of mainly the Bali cattle in Indonesia. As of 2016, Bali cattle comprise nearly 25% of the Indonesian cattle population (2.45 million out of the total 9.8 million). Domesticated banteng are docile and can tolerate hot, humid weather. Moreover, they can thrive and maintain their normal body weights even on poor quality fodder. They are primarily used for their highly demanded meat, that has been described as lean and soft. They are also used as draught animals to a limited extent; banteng are reportedly less efficient than zebu in dragging carts on roads, though they are suitable for agricultural work. However, banteng produce little milk; they lactate for only six to ten months, and the daily produce is just . They are also vulnerable to diseases such as bovine malignant catarrhal fever. In 1964, an outbreak of an unidentified disease, locally known as "jembrana", wiped out 10–60% of domesticated banteng populations in several areas in Bali; similar but less intense outbreaks have continued in the following years. The disease was later determined to be caused by a lentivirus.
In Australia
Domesticated banteng were first introduced to Australia in 1849 with the establishment of a British military outpost called Port Essington on Cobourg Peninsula. Twenty animals were taken to the western Arnhem Land, in present-day Northern Territory, as a source of meat. A year after the outpost's establishment, poor conditions including crop failure and tropical disease led to its abandonment. On the departure of British troops, the banteng were released from their grazing pastures and allowed to form a feral population. By the 1960s, researchers realised that a population of about 1,500 individuals had developed in the tropical forests of Cobourg Peninsula. As of 2007, around 8,000–10,000 feral banteng occur in Australia, mainly in Garig Gunak Barlu National Park (Cobourg Peninsula, Northern Territory). In a survey published in 1990, the population density in the forests was found to be around , close to that on their initial introduction 140 years ago.
Australian banteng are considered a non-native vermin species, as they reportedly trample and destroy vegetation cover by overgrazing, and sometimes harm and kill people who may closely approach them. Moreover, banteng can transmit lethal diseases such as brucellosis to humans as well as other cattle. As such banteng are occasionally shot to bring down their numbers in Australia, but some have expressed concern about their conservation given the decline in banteng populations outside the country. In a study in the monsoon forests of Garig Gunak Barlu National Park, banteng were found to cause little damage by overgrazing, especially when compared with feral pigs in the region. Instead, grazing by banteng possibly minimises potential dry grass build-up, thus limiting encroachment of seasonal fires (hence postfire grassland) into monsoonal forest areas, and this may help with the dispersal and germination of seeds.
Hybrids
Domesticated banteng have been hybridised with other types of cattle. Madura cattle, found in Java, are fertile hybrids of banteng and zebu. A small breed, the bulls weigh between and the cows weigh . They are used in local traditional events such as bull racing and cow beauty contests. Other hybrids include Donggala, Galekan and Java Brebes (Jabres) cattle. While all hybrids with zebu are fertile, the male hybrids resulting from a cross with taurine cattle are sterile. A program to cross-breed domestic and wild banteng began in June 2011, resulting in five pregnancies. This was intended to help improve the quality and productivity of the domesticated breed. The wild bulls were transported from the Baluran National Park in Situbondo.
As symbol
Certain elements in the Indonesian independent movements proposed it to be part of the Indonesian flag before the 1939 decided in favour of the plain red-and-white flag.
The banteng's head appears as one of the five emblems in the shield of Indonesia's coat-of-arms, "Garuda Pancasila". The emblem appears on the top-left of the shield, representing the fourth principle of the Indonesian five-point state philosophy (Pancasila), "Democracy that is Guided by the Inner Wisdom in the Unanimity Arising Out of Deliberations Amongst Representatives". A number of political parties in the country used the banteng's head as its symbol, including the Indonesian National Party (of President Sukarno), the Indonesian Democratic Party, and the Indonesian Democratic Party of Struggle (of Presidents Megawati Sukarnoputri and Joko Widodo).
Threats and conservation
The wild banteng is classified as Critically Endangered on the IUCN Red List, and populations have decreased by more than 50% in the past few decades. In 2008, the IUCN estimated the global banteng population at 5,000–8,000 individuals. Rampant poaching (for food, game, traditional medicine and horns), habitat loss and fragmentation and susceptibility to disease are major threats throughout the range. Most populations throughout the range are small and isolated. Banteng are legally protected in all countries in their range, and are largely restricted to protected areas.
Most other populations are small and fragmented, and many are on the decline. Surveys in eastern Cambodia between 2009 and 2011 estimated the total population in Sre Pok Wildlife Sanctuary and Phnom Prich Wildlife Sanctuary at 1,980–5,170 individuals. Surveys in the following years (up to 2016) in these sanctuaries and adjacent areas (such as the Keo Seima Wildlife Sanctuary) gave an approximate total of 4,600 individuals. Recent updates to these surveys suggest widespread collapse of these populations. The Keo Seima Wildlife Sanctuary population is estimated in have decline rapididly from 382 in 2010, with too few recorded in 2020 to produce a population estimate. Populations in Sre Pok Wildlife Sanctuary and Phnom Prich Wildlife Sanctuary have declined from around 1000 in each site in 2010 to only 370 and 485 respectively in 2020.
The only populations of more than 50 individuals in Thailand occur in the Huai Kha Khaeng Wildlife Sanctuary and possibly in the Kaeng Krachan National Park. A survey between 2000 and 2003 in Java identified four to five significant populations, with the highest numbers in the Ujung Kulon National Park (300–800 individuals), the Baluran National Park (206 individuals) and the Meru Betiri National Park (200 individuals). In East Java, a survey between 2011 and 2013 recorded rapid decline in populations in the Baluran National Park, though the numbers appeared to be stable in the Meru Betiri National Park; the researchers identified poaching, habitat disturbance, competition with other species, changes in vegetation cover and habitat loss as major threats. In Borneo numbers have fallen in areas like Kalimantan and Sabah, mainly due to poaching and human disturbance. The steepest decline (by more than 50%) took place between 1970 and 2000 due to deforestation and conversion of forests into plantations. Minor populations have been reported from areas such as Kulamba Wildlife Reserve, Deramakot Forest Reserve and Sipitang Forest Reserve during 2009–2015; individuals might still occur in the Belantikan Hulu region (Central Kalimantan), Kayan Mentarang National Park (North Kalimantan) and Kutai National Park (East Kalimantan).
Threats to domesticated banteng
Since a small founder event occurred in Australia with the introduction of only 20 previously domesticated banteng, a genetic bottleneck has inevitably occurred, causing all banteng presently in Australia to lack genetic diversity as a result of inbreeding. Genetic invariability can lead to inbreeding depression, resulting in harmful mutations and reduced immunity to diseases. This was proven by an analysis of 12 microsatellites, that recorded a high inbreeding coefficient of 0.58. Despite the limited genetic pool of this population, conservationists hope that populations at risk can be preserved. Some have proposed that a deliberate introduction of the endangered populations to the stable but non-native Australian variety would enable viable conservation, though how it would affect Northern Territory grazing ranges is unknown.
Another possible threat is introgression with other cattle and similar bovids throughout their range where they coexist in the wild or due to crossbreeding programs, that may compromise the genetic integrity or purity of banteng populations. This, coupled with possibly low genetic diversity in small, isolated populations, is a major concern in Sabah, where water buffaloes might crossbreed with wild banteng. However, little genetic research has been done in this area to conclusively establish the impact of such crossbreeding on banteng survival. In a bid to protect the genetic purity of Bali cattle, Bali has banned other cattle varieties on the island.
Cloning
The banteng is the second endangered species to be successfully cloned, and the first clone to survive beyond infancy (the first was a gaur that died two days after birth). Scientists at Advanced Cell Technology in Worcester, Massachusetts extracted DNA from skin cells of a dead male banteng, that were preserved in the San Diego Zoo's cryobank Frozen Zoo facility, and transferred it into eggs from domestic banteng cows, a process called somatic cell nuclear transfer. Thirty embryos were created and sent to Trans Ova Genetics, where they were implanted in domestic banteng cows. Two were carried to term and delivered by Caesarian section. The first was born on 1 April 2003, and the second two days later. The second was euthanised, apparently suffering from large offspring syndrome (an overgrowth disorder), but the first survived and lived for seven years at the San Diego Zoo, where it died in April 2010 after it broke a leg and was euthanised.
| Biology and health sciences | Bovidae | Animals |
920702 | https://en.wikipedia.org/wiki/Binary%20file | Binary file | A binary file is a computer file that is not a text file. The term "binary file" is often used as a term meaning "non-text file". Many binary file formats contain parts that can be interpreted as text; for example, some computer document files containing formatted text, such as older Microsoft Word document files, contain the text of the document but also contain formatting information in binary form.
Structure
Binary files are usually thought of as being a sequence of bytes, which means the binary digits (bits) are grouped in eights. Binary files typically contain bytes that are intended to be interpreted as something other than text characters. Compiled computer programs are typical examples; indeed, compiled applications are sometimes referred to, particularly by programmers, as binaries. But binary files can also mean that they contain images, sounds, compressed versions of other files, etc. – in short, any type of file content whatsoever.
Some binary files contain headers, blocks of metadata used by a computer program to interpret the data in the file. The header often contains a signature or magic number which can identify the format. For example, a GIF file can contain multiple images, and headers are used to identify and describe each block of image data. The leading bytes of the header would contain text like GIF87a or GIF89a that can identify the binary as a GIF file. If a binary file does not contain any headers, it may be called a flat binary file.
A text file may consist partly or entirely of encoded binary information. When sending binary files over the network they may be encoded so that they use only printable characters. This is often necessary due to the limitations of network protocols used for internet browsing and e-mail communication. One such encoding is Base64. Also, files containing public-key and private-key information for use in systems employing asymmetric cryptography (such as website certificates) may also be stored with the binary information encoded in printable characters.
Manipulation
To send binary files through certain systems (such as email) that do not allow all data values, they are often translated into a plain text representation (using, for example, Base64). Encoding the data has the disadvantage of increasing the file size during the transfer (for example, using Base64 will increase the file's size by approximately 30%), as well as requiring translation back into binary after receipt. The increased size may be countered by lower-level link compression, as the resulting text data will have about as much less entropy as it has increased size, so the actual data transferred in this scenario would likely be very close to the size of the original binary data. See Binary-to-text encoding for more on this subject.
Microsoft Windows and its standard libraries for the C and C++ programming languages allow the programmer to specify a parameter indicating if a file is expected to be plain text or binary when opening a file; this affects the standard library calls to read and write from the file in that the system converts between the C/C++ "end of line" character (the ASCII linefeed character) and the end-of-line sequence Windows expects in files (the ASCII carriage return and linefeed characters in sequence). In Unix-like systems, the C and C++ standard libraries on those systems also allow the programmer to specify whether a file is expected to be text or binary, but the libraries can and do ignore that parameter, as the end-of-line sequence in Unix-like systems is just the C/C++ end-of-line character.
Viewing
A hex editor or viewer may be used to view file data as a sequence of hexadecimal (or decimal, binary or ASCII character) values for corresponding bytes of a binary file.
If a binary file is opened in a text editor, each group of eight bits will typically be translated as a single character, and the user will see a (probably unintelligible) display of textual characters. If the file is opened in some other application, that application will have its own use for each byte: maybe the application will treat each byte as a number and output a stream of numbers between 0 and 255—or maybe interpret the numbers in the bytes as colors and display the corresponding picture. Other type of viewers (called 'word extractors') simply replace the unprintable characters with spaces revealing only the human-readable text. This type of view is useful for a quick inspection of a binary file in order to find passwords in games, find hidden text in non-text files and recover corrupted documents. It can even be used to inspect suspicious files (software) for unwanted effects. For example, the user would see any URL/email to which the suspected software may attempt to connect in order to upload unapproved data (to steal). If the file is itself treated as an executable and run, then the operating system will attempt to interpret the file as a series of instructions in its machine language.
Interpretation
Standards are very important to binary files. For example, a binary file interpreted by the ASCII character set will result in text being displayed. A custom application can interpret the file differently: a byte may be a sound, or a pixel, or even an entire word. Binary itself is meaningless, until such time as an executed algorithm defines what should be done with each bit, byte, word or block. Thus, just examining the binary and attempting to match it against known formats can lead to the wrong conclusion as to what it actually represents. This fact can be used in steganography, where an algorithm interprets a binary data file differently to reveal hidden content. Without the algorithm, it is impossible to tell that hidden content exists.
Binary compatibility
Two files that are binary compatible will have the same sequence of zeros and ones in the data portion of the file. The file header, however, may be different.
The term is used most commonly to state that data files produced by one application are exactly the same as data files produced by another application. For example, some software companies produce applications for Windows and the Macintosh that are binary compatible, which means that a file produced in a Windows environment is interchangeable with a file produced on a Macintosh. This avoids many of the conversion problems caused by importing and exporting data.
One possible binary compatibility issue between different computers is the endianness of the computer. Some computers store the bytes in a file in a different order.
| Technology | Data storage and memory | null |
921100 | https://en.wikipedia.org/wiki/Nutrient%20management | Nutrient management | Nutrient management is the science and practice directed to link soil, crop, weather, and hydrologic factors with cultural, irrigation, and soil and water conservation practices to achieve optimal nutrient use efficiency, crop yields, crop quality, and economic returns, while reducing off-site transport of nutrients (fertilizer) that may impact the environment. It involves matching a specific field soil, climate, and crop management conditions to rate, source, timing, and place (commonly known as the 4R nutrient stewardship) of nutrient application.
Important factors that need to be considered when managing nutrients include (a) the application of nutrients considering the achievable optimum yields and, in some cases, crop quality; (b) the management, application, and timing of nutrients using a budget based on all sources and sinks active at the site; and (c) the management of soil, water, and crop to minimize the off-site transport of nutrients from nutrient leaching out of the root zone, surface runoff, and volatilization (or other gas exchanges).
There can be potential interactions because of differences in nutrient pathways and dynamics. For instance, practices that reduce the off-site surface transport of a given nutrient may increase the leaching losses of other nutrients. These complex dynamics present nutrient managers the difficult task of achieve the best balance for maximizing profit while contributing to the conservation of our biosphere.
Nutrient management plan
A crop nutrient management plan is a tool that farmers can use to increase the efficiency of all the nutrient sources a crop uses while reducing production and environmental risk, ultimately increasing profit. Increasingly, growers as well as agronomists use digital tools like SST or Agworld to create their nutrient management plan so they can capitalize on information gathered over a number of years. It is generally agreed that there are ten fundamental components of a crop nutrient management plan. Each component is critical to helping analyze each field and improve nutrient efficiency for the crops grown. These components include:
Field map The map, including general reference points (such as streams, residences, wellheads etc.), number of acres, and soil types is the base for the rest of the plan.
Soil test How much of each nutrient (N-P-K and other critical elements such as pH and organic matter) is in the soil profile? The soil test is a key component needed for developing the nutrient rate recommendation.
Crop sequence Did the crop that grew in the field last year (and in many cases two or more years ago) fix nitrogen for use in the following years? Has long-term no-till increased organic matter? Did the end-of-season stalk test show a nutrient deficiency? These factors also need to be factored into the plan.
Estimated yield Factors that affect yield are numerous and complex. A field's soils, drainage, insect, weed and crop disease pressure, rotation and many other factors differentiate one field from another. This is why using historic yields is important in developing yield estimates for next year. Accurate yield estimates can improve nutrient use efficiency.
Sources and forms The sources and forms of available nutrients can vary from farm-to-farm and even field-to-field. For instance, manure fertility analysis, storage practices and other factors will need to be included in a nutrient management plan. Manure nutrient tests/analysis are one way to determine the fertility of it. Nitrogen fixed from a previous year's legume crop and residual effects of manure also affects rate recommendations. Many other nutrient sources should also be factored into this plan.
Sensitive areas What's out of the ordinary about a field's plan? Is it irrigated? Next to a stream or lake? Especially sandy in one area? Steep slope or low area? Manure applied in one area for generations due to proximity of dairy barn? Extremely productive—or unproductive—in a portion of the field? Are there buffers that protect streams, drainage ditches, wellheads, and other water collection points? How far away are the neighbors? What's the general wind direction? This is the place to note these and other special conditions that need to be considered.
Recommended rates Here's the place where science, technology, and art meet. Given everything you've noted, what is the optimum rate of N, P, K, lime and any other nutrients? While science tells us that a crop has changing nutrient requirements during the growing season, a combination of technology and farmer's management skills assure nutrient availability at all stages of growth. No-till corn generally requires starter fertilizer to give the seedling a healthy start.
Recommended timing When does the soil temperature drop below 50 degrees? Will a N stabilizer be used? What's the tillage practice? Strip-till corn and no-till often require different timing approaches than seed planted into a field that's been tilled once with a field cultivator. Will a starter fertilizer be used to give the seedling a healthy start? How many acres can be covered with available labor (custom or hired) and equipment? Does manure application in a farm depend on a custom applicator's schedule? What agreements have been worked out with neighbors for manure use on their fields? Is a neighbor hosting a special event? All these factors and more will likely figure into the recommended timing.
Recommended methods Surface or injected? While injection is clearly preferred, there may be situations where injection is not feasible (i.e. pasture, grassland). Slope, rainfall patterns, soil type, crop rotation and many other factors determine which method is best for optimizing nutrient efficiency (availability and loss) in farms. The combination that's right in one field may differ in another field even with the same crop.
Annual review and update Even the best managers are forced to deviate from their plans. What rate was actually applied? Where? Using which method? Did an unusually mild winter or wet spring reduce soil nitrate? Did a dry summer, disease, or some other unusual factor increase nutrient carryover? These and other factors should be noted as they occur.
When such a plan is designed for animal feeding operations (AFO), it may be termed a "manure management plan." In the United States, some regulatory agencies recommend or require that farms implement these plans in order to prevent water pollution. The U.S. Natural Resources Conservation Service (NRCS) has published guidance documents on preparing a comprehensive nutrient management plan (CNMP) for AFOs.
The International Plant Nutrition Institute has published a 4R plant nutrition manual for improving the management of plant nutrition. The manual outlines the scientific principles behind each of the four Rs or "rights" (right source of nutrient, right application rate, right time, right place) and discusses the adoption of 4R practices on the farm, approaches to nutrient management planning, and measurement of sustainability performance.
Nitrogen management
Of the 16 essential plant nutrients, nitrogen is usually the most difficult to manage in field crop systems. This is because the quantity of plant-available nitrogen can change rapidly in response to changes in soil water status. Nitrogen can be lost from the plant-soil system by one or more of the following processes: leaching; surface runoff; soil erosion; ammonia volatilization; and denitrification.
Nitrogen management practices that improve nitrogen efficiency
Nitrogen management aims to maximize the efficiency with which crops use applied N. Improvements in nitrogen use efficiency are associated with decreases in N loss from the soil. Although losses cannot be avoided completely, significant improvements can be realized by applying one or more of the following management practices in the cropping system.
Reduction of greenhouse gas emissions
Climate Smart Agriculture includes the use of 4R Nutrient Stewardship principles to reduce field emissions of nitrous oxide (N2O) from the application of nitrogen fertilizer. Nitrogen fertilizer is an important driver of nitrous oxide emissions, but it is also the main driver of yield in modern high production systems. Through careful selection of nitrogen fertilizer source, rate, timing and placement practices, the nitrous oxide emissions per unit of crop produced can be substantially reduced, in some cases by up to half. The practices that reduce nitrous oxide emissions also tend to increase nitrogen use efficiency and the economic return on fertilizer dollars.
Reduction of N loss in runoff water and eroded soil
No-till, conservation tillage and other runoff control measures reduce N loss in surface runoff and eroded soil material.
The use of daily estimates of soil moisture and crop needs to schedule irrigation reduces the risk of surface runoff and soil erosion.
Reduction of the volatilization of N as ammonia gas
Incorporation and/or injection of urea and ammonium-containing fertilizers decreases ammonia volatilization because good soil contact buffers pH and slows the generation of ammonia gas from ammonium ions.
Urease inhibitors temporarily block the function of the urease enzyme, maintaining urea-based fertilizers in the non-volatile urea form, reducing volatilization losses when these fertilizers are surface applied; these losses can be meaningful in high-residue, conservation tillage systems.
Prevention of the build-up of high soil nitrate concentrations
Nitrate is the form of nitrogen that is most susceptible to loss from the soil, through denitrification and leaching. The amount of N lost via these processes can be limited by restricting soil nitrate concentrations, especially at times of high risk. This can be done in many ways, although these are not always cost-effective.
Nitrogen rates
Rates of N application should be high enough to maximize profits in the long term and minimize residual (unused) nitrate in the soil after harvest.
The use of local research to determine recommended nitrogen application rates should result in appropriate N rates.
Recommended N application rates often rely on an assessment of yield expectations – these should be realistic, and preferably based on accurate yield records.
Fertilizer N rates should be corrected for N that is likely to be mineralized from soil organic matter and crop residues (especially legume residues).
Fertilizer N rates should allow for N applied in manure, in irrigation water, and from atmospheric deposition.
Where feasible, appropriate soil tests can be used to determine residual soil N.
Soil testing for N
Preplant soil tests provide information on the soil's N-supply power.
Late spring or pre-side-dress N tests can determine if and how much additional N is needed.
New soil test and sampling procedures, such as amino sugar tests, grid mapping, and real-time sensors can refine N requirements.
Post-harvest soil tests determine if N management the previous season was appropriate.
Crop testing for N
Plant tissue tests can identify N deficiencies.
Sensing variations in plant chlorophyll content facilitates variable rate N applications in-season.
Post-black-layer corn stalk nitrate tests help to determine if N rates were low, optimal, or excessive in the previous crop, so that management changes can be made in following crops.
Precision agriculture
Variable rate applicators, combined with intensive soil or crop sampling, allow more precise and responsive application rates.
Timing of N applications
Apply N close to the time when crops can utilize it.
Make side-dress N applications close to the time of most rapid N uptake.
Split applications, involving more than one application, allow efficient use of applied N and reduce the risk of N loss to the environment.
N Forms, including slow or controlled release fertilizers and inhibitors
Slow or controlled release fertilizer delays the availability of nitrogen to the plant until a time that is more appropriate for plant uptake - the risk of N loss through denitrification and leaching is reduced by limiting nitrate concentrations in the soil.
Nitrification inhibitors maintain applied N in the ammonium form for a longer period of time, thereby reducing leaching and denitrification losses.
N capture
Particular crop varieties are able to more efficiently extract N from the soil and improve N use efficiency. Breeding of crops for efficient N uptake is in progress.
Rotation with deep-rooted crops helps capture nitrates deeper in the soil profile.
Cover crops capture residual nitrogen after crop harvest and recycle it as plant biomass.
Elimination of restrictions to subsoil root development; subsoil compaction and subsoil acidity prevent root penetration in many subsoils worldwide, promoting build-up of subsoil nitrate concentrations which are susceptible to denitrification and leaching when conditions are suitable.
Good agronomic practice, including appropriate plant populations and spacing and good weed and pest management, allows crops to produce large root systems to optimise N capture and crop yield.
Water management
Conservation tillage
Conservation tillage optimizes soil moisture conditions that improve water use efficiency; in water-stressed conditions, this improves crop yield per unit N applied.
N fertilizer application method and placement
In ridged crops, placing N fertilizers in a band in ridges makes N less susceptible to leaching.
Row fertilizer applicators, such as injectors, which form a compacted soil layer and surface ridge, can reduce N losses by diverting water flow.
Good irrigation management can improve N-use efficiency
Scheduled irrigation based on soil moisture estimates and daily crop needs will improve both water-use and N-use efficiency.
Sprinkler irrigation systems apply water more uniformly and in lower amounts than furrow or basin irrigation systems.
Furrow irrigation efficiency can be improved by adjusting set time, stream size, furrow length, watering every other row, or the use of surge valves.
Alternate row irrigation and fertilization minimizes water contact with nutrients.
Application of N fertilizer through irrigation systems (fertigation) facilitates N supply when crop demand is greatest.
Polyacrylamide (PAM) treatment during furrow irrigation reduces sediment and N losses.
Drainage systems
Some subirrigation systems recycle nitrate leached from the soil profile and reduce nitrate lost in drainage water.
Excessive drainage can lead to rapid through-flow of water and N leaching, but restricted or insufficient drainage favors anaerobic conditions and denitrification.
Use of simulation models
Short-term changes in the plant-available N status make accurate seasonal predictions of crop N requirement difficult in most situations. However, models (such as NLEAP and Adapt-N) that use soil, weather, crop, and field management data can be updated with day-to-day changes and thereby improve predictions of the fate of applied N. They allows farmers to make adaptive management decisions that can improve N-use efficiency and minimize N losses and environmental impact while maximizing profitability.
Additional measures to minimize environmental impact
Conservation buffers
Buffers trap sediment containing ammonia and organic N.
Nitrate in subsurface flow is reduced through denitrification enhanced by carbon energy sources contained in the soil associated with buffer vegetation.
Buffer vegetation takes up nitrogen, other nutrients, and reduces loss to water.
Constructed wetlands
Constructed wetlands located strategically on the landscape to process drainage effluent reduces sediment and nitrate loads to surface water.
| Technology | Agronomical techniques | null |
921148 | https://en.wikipedia.org/wiki/Ring%20finger | Ring finger | The ring finger, third finger, fourth finger, leech finger, or annulary is the fourth digit of the human hand, located between the middle finger and the little finger.
Sometimes the term ring finger only refers to the fourth digit of a left-hand, so named for its traditional association with wedding rings in many societies, although not all use this digit as the ring finger. Traditionally, a wedding ring was worn only by the bride or wife, but in recent times more men also wear a wedding ring. It is also the custom in some societies to wear an engagement ring on the ring finger.
In anatomy, the ring finger is called digitus medicinalis, the fourth digit, digitus annularis, digitus quartus, or digitus IV. In Latin, the word anulus means "ring", digitus means "digit", and quartus means "fourth".
Etymology
The origin of the selection of the fourth digit as the ring finger is not definitively known. According to László A. Magyar, the names of the ring finger in many languages reflect an ancient belief that it is a magical finger. It is named after magic or rings, or called nameless (for example, in ).
In Hungarian, it is called nevetlen ujj; lit. ‘nameless finger’ or nevezetlen ujj; lit. ‘unnamed finger’. It has special role in magical practices like healing, protection against curse or love magic. For example to heal a stingy eye or a pimple or a ringworm one must draw a cross on it with the nameless finger or rub it gently. If a woman wants to make a man to love her, she should sting her unnamed finger and drop her blood to the mans drink (wine). If the man drinks that he will has a strong bond for that woman, he will love her.
In Japanese, it is called (kusuri yubi, ), deriving its name from the fact that it was frequently used when taking traditional powdered medicine, as it was rarely used otherwise and hence was considered the cleanest of all.
In other languages such as Sanskrit, Finnish, and Russian, the ring finger is called "Anamika", "nimetön", and "Безымянный" (bezymianny, "nameless"), respectively.
In Semitic languages such as Arabic and Hebrew, the ring finger is called bansur (meaning "victory") and kmitsa (meaning "taking a handful"), respectively.
History
Before medical science discovered how the circulatory system functioned, people believed that a vein ran directly from the fourth digit on the left hand to the heart. Because of the hand–heart connection, they chose the descriptive name vena amoris, Latin for the vein of love, for this particular vein.
Based upon this name, their contemporaries, purported experts in the field of matrimonial etiquette, wrote that it would only be fitting that the wedding ring be worn on this digit. By wearing the ring on the fourth digit of the left hand, a married couple symbolically declares their eternal love for each other.
In Britain, only women tended to wear a wedding ring until after the World Wars, when married male soldiers started to wear rings to remind them of their wife.
Contemporary customs
Western customs
In Western cultures, a wedding ring is traditionally worn on the fourth digit, commonly called the "ring finger". This developed from the Roman anulus pronubis, when a man would give a ring to the woman at their betrothal ceremony. Blessing the wedding ring and putting it on the bride's finger dates from the 11th century.
In medieval Europe, during the Christian wedding ceremony, the ring was placed in sequence on the thumb, index, middle, and ring fingers of the left hand. The ring was then left on the ring finger.
In a few European countries, the ring is worn on the left hand prior to marriage, then transferred to the right during the ceremony. For example, an Eastern Orthodox Church bride wears the ring on the left hand prior to the ceremony, then moves it to the right hand after the wedding. In England, the 1549 Prayer Book declared "the ring shall be placed on the left hand". By the 17th and 18th centuries, the ring could be found on any digit after the ceremony — even on the thumb.
The wedding ring is generally worn on the ring finger of the left hand in the former British Empire, certain parts of Western Europe, certain parts of Catholic Mexico, Bolivia, Chile, and Central and Eastern Europe. These include: Australia, Botswana, Canada, Egypt, Ireland, New Zealand, South Africa, the UK, and the US, as well as France, Italy, Portugal, Sweden, Finland, Czech Republic, Slovakia, Switzerland, Netherlands [if Catholic], Croatia, Slovenia, Romania, and the Catalan-speaking regions of Spain.
The wedding ring is worn on the ring finger of the right hand in some Orthodox and a small number of Catholic European countries, some Protestant Western European, as well as some Central and South American Catholic countries. In Eastern Europe, these include Belarus, Bulgaria, Georgia, Latvia, Lithuania, North Macedonia, Russia, Serbia, and Ukraine. In Central or Western Europe, these include Austria, Belgium, Denmark, Germany, Greece, Hungary, Poland, the Netherlands (if not Catholic), Norway, and Spain (except in the Catalan-speaking regions). In Central or South America, these include Colombia, Cuba, Peru, and Venezuela.
In Turkey, Lebanon, Syria, Romania, and Brazil, the ring is worn on the right hand until the actual wedding day, when it is moved to the left hand.
In western guitar music, "I-M-A" is a style of plucking guitar strings, where "I" means index finger, "M" means middle finger, and "A" means ring finger. This is a popular type of "finger style" guitar playing, where the "A" comes from Latin, where the word anulus means ring.
Middle Eastern, Jewish, and Asian customs
In Sinhalese and Tamil culture, the groom wears the wedding ring on his right hand, but the bride wears it on her left hand ring finger. This can be seen in countries like Sri Lanka, which has a rich Sinhalese and Tamil cultural influence on the society.
A wedding ring is not a traditional part of the religious Muslim wedding, and wedding rings are not included in most Islamic countries. If a wedding ring is worn in an Islamic country, however, it may be worn on either the left (such is the custom in Iran) and for example (in Jordan the right ring finger for engagement and the left ring finger for marriage). As opposed to the wedding ring, use of a ring to denote betrothal or engagement is quite prevalent in Muslim countries, especially those in West and Asia. These rings may be worn on the ring finger of either the right or left hand by both men and women.
In a traditional Jewish wedding ceremony, the wedding ring is placed on the bride's right-hand index finger, but other traditions place it on the middle finger or the thumb, most commonly in recent times. Today, the ring usually is moved to the left hand ring finger after the ceremony. Some Jewish grooms have adopted wearing a wedding ring, but in Orthodox Judaism, most men do not wear wedding rings.
Rings are not traditional in an Indian wedding, but in modern society, it is becoming a practice to wear rings for engagements if not for actual marriage. Although the left hand is considered inauspicious for religious activities, a ring (which is not called a wedding ring) is still worn on the left hand. Men generally wear the rings on the right hand and women on the left hands.
| Biology and health sciences | Human anatomy | Health |
921168 | https://en.wikipedia.org/wiki/Scale%20factor%20%28cosmology%29 | Scale factor (cosmology) | The expansion of the universe is parametrized by a dimensionless scale factor . Also known as the cosmic scale factor or sometimes the Robertson–Walker scale factor, this is a key parameter of the Friedmann equations.
In the early stages of the Big Bang, most of the energy was in the form of radiation, and that radiation was the dominant influence on the expansion of the universe. Later, with cooling from the expansion the roles of matter and radiation changed and the universe entered a matter-dominated era. Recent results suggest that we have already entered an era dominated by dark energy, but examination of the roles of matter and radiation are most important for understanding the early universe.
Using the dimensionless scale factor to characterize the expansion of the universe, the effective energy densities of radiation and matter scale differently. This leads to a radiation-dominated era in the very early universe but a transition to a matter-dominated era at a later time and, since about 4 billion years ago, a subsequent dark-energy-dominated era.
Detail
Some insight into the expansion can be obtained from a Newtonian expansion model which leads to a simplified version of the Friedmann equation. It relates the proper distance (which can change over time, unlike the comoving distance which is constant and set to today's distance) between a pair of objects, e.g. two galaxy clusters, moving with the Hubble flow in an expanding or contracting FLRW universe at any arbitrary time to their distance at some reference time . The formula for this is:
where is the proper distance at epoch , is the distance at the reference time , usually also referred to as comoving distance, and is the scale factor. Thus, by definition, and .
The scale factor is dimensionless, with counted from the birth of the universe and set to the present age of the universe: giving the current value of as or .
The evolution of the scale factor is a dynamical question, determined by the equations of general relativity, which are presented in the case of a locally isotropic, locally homogeneous universe by the Friedmann equations.
The Hubble parameter is defined as:
where the dot represents a time derivative. The Hubble parameter varies with time, not with space, with the Hubble constant being its current value.
From the previous equation one can see that , and also that , so combining these gives , and substituting the above definition of the Hubble parameter gives which is just Hubble's law.
Current evidence suggests that the expansion of the universe is accelerating, which means that the second derivative of the scale factor is positive, or equivalently that the first derivative is increasing over time. This also implies that any given galaxy recedes from us with increasing speed over time, i.e. for that galaxy is increasing with time. In contrast, the Hubble parameter seems to be decreasing with time, meaning that if we were to look at some fixed distance d and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.
According to the Friedmann–Lemaître–Robertson–Walker metric which is used to model the expanding universe, if at present time we receive light from a distant object with a redshift of z, then the scale factor at the time the object originally emitted that light is .
Chronology
Radiation-dominated era
After Inflation, and until about 47,000 years after the Big Bang, the dynamics of the early universe were set by radiation (referring generally to the constituents of the universe which moved relativistically, principally photons and neutrinos).
For a radiation-dominated universe the evolution of the scale factor in the Friedmann–Lemaître–Robertson–Walker metric is obtained solving the Friedmann equations:
Matter-dominated era
Between about 47,000 years and 9.8 billion years after the Big Bang, the energy density of matter exceeded both the energy density of radiation and the vacuum energy density.
When the early universe was about 47,000 years old (redshift 3600), mass–energy density surpassed the radiation energy, although the universe remained optically thick to radiation until the universe was about 378,000 years old (redshift 1100). This second moment in time (close to the time of recombination), at which the photons which compose the cosmic microwave background radiation were last scattered, is often mistaken as marking the end of the radiation era.
For a matter-dominated universe the evolution of the scale factor in the Friedmann–Lemaître–Robertson–Walker metric is easily obtained solving the Friedmann equations:
Dark-energy-dominated era
In physical cosmology, the dark-energy-dominated era is proposed as the last of the three phases of the known universe, the other two being the radiation-dominated era and the matter-dominated era. The dark-energy-dominated era began after the matter-dominated era, i.e. when the Universe was about 9.8 billion years old. In the era of cosmic inflation, the Hubble parameter is also thought to be constant, so the expansion law of the dark-energy-dominated era also holds for the inflationary prequel of the big bang.
The cosmological constant is given the symbol Λ, and, considered as a source term in the Einstein field equation, can be viewed as equivalent to a "mass" of empty space, or dark energy. Since this increases with the volume of the universe, the expansion pressure is effectively constant, independent of the scale of the universe, while the other terms decrease with time. Thus, as the density of other forms of matter – dust and radiation – drops to very low concentrations, the cosmological constant (or "dark energy") term will eventually dominate the energy density of the Universe. Recent measurements of the change in Hubble constant with time, based on observations of distant supernovae, show this acceleration in expansion rate, indicating the presence of such dark energy.
For a dark-energy-dominated universe, the evolution of the scale factor in the Friedmann–Lemaître–Robertson–Walker metric is easily obtained solving the Friedmann equations:
Here, the coefficient in the exponential, the Hubble constant, is
This exponential dependence on time makes the spacetime geometry identical to the de Sitter universe, and only holds for a positive sign of the cosmological constant, which is the case according to the currently accepted value of the cosmological constant, Λ, that is approximately
The current density of the observable universe is of the order of and the age of the universe is of the order of 13.8 billion years, or . The Hubble constant, , is (The Hubble time is 13.79 billion years).
| Physical sciences | Physical cosmology | Astronomy |
921245 | https://en.wikipedia.org/wiki/List%20of%20interstellar%20and%20circumstellar%20molecules | List of interstellar and circumstellar molecules | This is a list of molecules that have been detected in the interstellar medium and circumstellar envelopes, grouped by the number of component atoms. The chemical formula is listed for each detected compound, along with any ionized form that has also been observed.
Background
The molecules listed below were detected through astronomical spectroscopy. Their spectral features arise because molecules either absorb or emit a photon of light when they transition between two molecular energy levels. The energy (and thus the wavelength) of the photon matches the energy difference between the levels involved. Molecular electronic transitions occur when one of the molecule's electrons moves between molecular orbitals, producing a spectral line in the ultraviolet, optical or near-infrared parts of the electromagnetic spectrum. Alternatively, a vibrational transition transfers quanta of energy to (or from) vibrations of molecular bonds, producing signatures in the mid- or far-infrared. Gas-phase molecules also have quantised rotational levels, leading to transitions at microwave or radio wavelengths.
Sometimes a transition can involve more than one of these types of energy level e.g. ro-vibrational spectroscopy changes both the rotational and vibrational energy level. Occasionally all three occur together, as in the Phillips band of C2 (diatomic carbon), in which an electronic transition produces a line in the near-infrared, which is then split into several vibronic bands by a simultaneous change in vibrational level, which in turn are split again into rotational branches.
The spectrum of a particular molecule is governed by the selection rules of quantum chemistry and by its molecular symmetry. Some molecules have simple spectra which are easy to identify, whilst others (even some small molecules) have extremely complex spectra with flux spread among many different lines, making them far harder to detect. Interactions between the atomic nuclei and the electrons sometimes cause further hyperfine structure of the spectral lines. If the molecule exists in multiple isotopologues (versions containing different atomic isotopes), the spectrum is further complicated by isotope shifts.
Detection of a new interstellar or circumstellar molecule requires identifying a suitable astronomical object where it is likely to be present, then observing it with a telescope equipped with a spectrograph working at the required wavelength, spectral resolution and sensitivity. The first molecule detected in the interstellar medium was the methylidyne radical (CH•) in 1937, through its strong electronic transition at 4300 angstroms (in the optical). Advances in astronomical instrumentation have led to increasing numbers of new detections. From the 1950s onwards, radio astronomy began to dominate new detections, with sub-mm astronomy also becoming important from the 1990s.
The inventory of detected molecules is highly biased towards certain types which are easier to detect. For example, radio astronomy is most sensitive to small linear molecules with a high molecular dipole. The most common molecule in the Universe, H2 (molecular hydrogen), is completely invisible to radio telescopes because it has no dipole; its electronic transitions are too energetic for optical telescopes, so detection of H2 required ultraviolet observations with a sounding rocket. Vibrational lines are often not specific to an individual molecule, allowing only the general class to be identified. For example, the vibrational lines of polycyclic aromatic hydrocarbons (PAHs) were identified in 1984, showing the class of molecules is very common in space, but it took until 2021 to identify any specific PAHs through their rotational lines.
One of the richest sources for detecting interstellar molecules is Sagittarius B2 (Sgr B2), a giant molecular cloud near the centre of the Milky Way. About half of the molecules listed below were first found in Sgr B2, and many of the others have been subsequently detected there. A rich source of circumstellar molecules is CW Leonis (also known as IRC +10216), a nearby carbon star, where about 50 molecules have been identified. There is no clear boundary between interstellar and circumstellar media, so both are included in the tables below.
The discipline of astrochemistry includes understanding how these molecules form and explaining their abundances. The extremely low density of the interstellar medium is not conducive to the formation of molecules, making conventional gas-phase reactions between neutral species (atoms or molecules) inefficient. Many regions also have very low temperatures (typically 10 kelvin inside a molecular cloud), further reducing the reaction rates, or high ultraviolet radiation fields, which destroy molecules through photochemistry. Explaining the observed abundances of interstellar molecules requires calculating the balance between formation and destruction rates using gas-phase ion chemistry (often driven by cosmic rays), surface chemistry on cosmic dust, radiative transfer including interstellar extinction, and sophisticated reaction networks. The use of molecular lines to determine the physical properties of astronomical objects is known as molecular astrophysics.
Molecules
The following tables list molecules that have been detected in the interstellar medium or circumstellar matter, grouped by the number of component atoms. Neutral molecules and their molecular ions are listed in separate columns; if there is no entry in the molecule column, only the ionized form has been detected. Designations (names of molecules) are those used in the scientific literature describing the detection; if none was given that field is left empty. Mass is listed in atomic mass units. Deuterated molecules, which contain at least one deuterium (2H) atom, have slightly different masses and are listed in a separate table. The total number of unique species, including distinct ionization states, is indicated in each section header.
Most of the molecules detected so far are organic. The only detected inorganic molecule with five or more atoms is SiH4. Molecules larger than that all have at least one carbon atom, with no N−N or O−O bonds.
Diatomic (43)
Triatomic (44)
Four atoms (30)
Five atoms (20)
Six atoms (16)
Seven atoms (13)
Eight atoms (14)
Nine atoms (10)
Ten or more atoms (23)
Deuterated molecules (22)
These molecules all contain one or more deuterium atoms, a heavier isotope of hydrogen.
Unconfirmed (15)
Evidence for the existence of the following molecules has been reported in the scientific literature, but the detections either are described as tentative by the authors, or have been challenged by other researchers. They await independent confirmation.
| Physical sciences | Astronomy basics | Astronomy |
921432 | https://en.wikipedia.org/wiki/Barred%20spiral%20galaxy | Barred spiral galaxy | A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy.
Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between the two. SB0 is a barred lenticular galaxy. A new type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Clouds, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. Among other types in Hubble's classifications for the galaxies are the spiral galaxy, elliptical galaxy and irregular galaxy.
Although theoretical models of galaxy formation and evolution had not previously expected galaxies becoming stable enough to host bars very early in the universe's history, evidence has recently emerged of the existence of numerous spiral galaxies in the early universe.
Bars
Barred galaxies are apparently predominant, with surveys showing that up to two-thirds of all spiral galaxies develop a bar. The creation of the bar is generally thought to be the result of a density wave radiating from the center of the galaxy whose effects reshape the orbits of the inner stars. This effect builds over time to stars orbiting farther out, which creates a self-perpetuating bar structure.
The bar structure is believed to act as a type of stellar nursery, channeling gas inwards from the spiral arms through orbital resonance, fueling star birth in the vicinity of its center. This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in the Southern Pinwheel Galaxy.
Bars are thought to be temporary phenomena in the lives of spiral galaxies; the bar structures decay over time, transforming galaxies from barred spirals to more "regular" spiral patterns. Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Simulations show that many bars likely experience a "buckling" event in which a disturbance in the orbital resonances of stars in the bar structure leads to an inward collapse in which the bar becomes thicker and shorter though the exact mechanism behind this buckling instability remains hotly debated. Barred spiral galaxies with high mass accumulated in their center thus tend to have short, stubby bars. Such buckling phenomena are significantly suppressed and delayed by the presence of a supermassive black hole in the galactic center but occur nonetheless.
Since so many spiral galaxies have bar structures, it is likely that they are recurring phenomena in spiral galaxy development. The oscillating evolutionary cycle from spiral galaxy to barred spiral galaxy is thought to take on average about two billion years.
Recent studies have confirmed the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. A 2008 investigation found that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with about 65 percent of their local counterparts.
Grades
The general classification is "SB" (spiral barred). The sub-categories are based on how open or tight the arms of the spiral are. SBa types feature tightly bound arms. SBc types are at the other extreme and have loosely bound arms. SBb galaxies lie in between. SBm describes somewhat irregular barred spirals. SB0 is a barred lenticular galaxy.
Examples
Other examples
| Physical sciences | Galaxy morphological classification | null |
921525 | https://en.wikipedia.org/wiki/Maxwell%20relations | Maxwell relations | Maxwell's relations are a set of equations in thermodynamics which are derivable from the symmetry of second derivatives and from the definitions of the thermodynamic potentials. These relations are named for the nineteenth-century physicist James Clerk Maxwell.
Equations
The structure of Maxwell relations is a statement of equality among the second derivatives for continuous functions. It follows directly from the fact that the order of differentiation of an analytic function of two variables is irrelevant (Schwarz theorem). In the case of Maxwell relations the function considered is a thermodynamic potential and and are two different natural variables for that potential, we have
where the partial derivatives are taken with all other natural variables held constant. For every thermodynamic potential there are possible Maxwell relations where is the number of natural variables for that potential.
The four most common Maxwell relations
The four most common Maxwell relations are the equalities of the second derivatives of each of the four thermodynamic potentials, with respect to their thermal natural variable (temperature , or entropy and their mechanical natural variable (pressure , or volume
where the potentials as functions of their natural thermal and mechanical variables are the internal energy , enthalpy , Helmholtz free energy , and Gibbs free energy . The thermodynamic square can be used as a mnemonic to recall and derive these relations. The usefulness of these relations lies in their quantifying entropy changes, which are not directly measurable, in terms of measurable quantities like temperature, volume, and pressure.
Each equation can be re-expressed using the relationship
which are sometimes also known as Maxwell relations.
Derivations
Short derivation
This section is based on chapter 5 of.
Suppose we are given four real variables , restricted to move on a 2-dimensional surface in . Then, if we know two of them, we can determine the other two uniquely (generically).
In particular, we may take any two variables as the independent variables, and let the other two be the dependent variables, then we can take all these partial derivatives.
Proposition:
Proof: This is just the chain rule.
Proposition:
Proof. We can ignore . Then locally the surface is just . Then , etc. Now multiply them.
Proof of Maxwell's relations:
There are four real variables , restricted on the 2-dimensional surface of possible thermodynamic states. This allows us to use the previous two propositions.
It suffices to prove the first of the four relations, as the other three can be obtained by transforming the first relation using the previous two propositions.
Pick as the independent variables, and as the dependent variable. We have
.
Now, since the surface is , that is,which yields the result.
Another derivation
Based on.
Since , around any cycle, we haveTake the cycle infinitesimal, we find that . That is, the map is area-preserving. By the chain rule for Jacobians, for any coordinate transform , we haveNow setting to various values gives us the four Maxwell relations. For example, setting gives us
Extended derivations
Maxwell relations are based on simple partial differentiation rules, in particular the total differential of a function and the symmetry of evaluating second order partial derivatives.
Derivation based on Jacobians
If we view the first law of thermodynamics,
as a statement about differential forms, and take the exterior derivative of this equation, we get
since . This leads to the fundamental identity
The physical meaning of this identity can be seen by noting that the two sides are the equivalent ways of writing the work done in an infinitesimal Carnot cycle. An equivalent way of writing the identity is
The Maxwell relations now follow directly. For example,
The critical step is the penultimate one. The other Maxwell relations follow in similar fashion. For example,
General Maxwell relationships
The above are not the only Maxwell relationships. When other work terms involving other natural variables besides the volume work are considered or when the number of particles is included as a natural variable, other Maxwell relations become apparent. For example, if we have a single-component gas, then the number of particles N is also a natural variable of the above four thermodynamic potentials. The Maxwell relationship for the enthalpy with respect to pressure and particle number would then be:
where is the chemical potential. In addition, there are other thermodynamic potentials besides the four that are commonly used, and each of these potentials will yield a set of Maxwell relations. For example, the grand potential yields:
| Physical sciences | Thermodynamics | Physics |
922083 | https://en.wikipedia.org/wiki/Flannel | Flannel | Flannel is a soft woven fabric, of varying fineness. Flannel was originally made from carded wool or worsted yarn, but is now often made from either wool, cotton, or synthetic fiber. Flannel is commonly used to make tartan clothing, blankets, bed sheets, sleepwear, and several other uses.
Flannel may be brushed to create extra softness or remain unbrushed. Brushing is a mechanical process wherein a fine metal brush rubs the fabric to raise fine fibres from the loosely spun yarns to form a nap on one or both sides. If the flannel is not napped, it gains its softness through the loosely spun yarn in its woven form.
The term "flannel shirt" is often mistakenly used to refer to any shirt with a plaid or tartan pattern. However, 'flannel' refers simply to the fabric; not all flannel shirts are plaid and not all plaid shirts are flannel.
History
The word's origin is uncertain, but a Welsh origin has been suggested as fabric similar to flannel can be traced back to Wales, where it was well known as early as the 16th century. The fabric was called ''Welsh cotton'', and despite its name, it was a coarse woolen material with a fluffed surface similar to flannel.
The French term flanelle was used in the late 17th century, and the German Flanell was used in the early 18th century.
Flannel has been made since the 17th century, gradually replacing the older Welsh plains, some of which were finished as "cottons" or friezes, coarse woolen cloth that was the local textile product. In the 19th century, flannel was made particularly in towns such as Newtown, Montgomeryshire, Hay on Wye, and Llanidloes. The expansion of its production is closely associated with the spread of carding mills, which prepared the wool for spinning, this being the first aspect of the production of woollen cloth to be mechanised (apart from fulling). The marketing of these Welsh woollen clothes was largely controlled by the Drapers Company of Shrewsbury.
Flannel became popular in the United States during the Civil War, when it was imported as an inexpensive, sturdy material for soldiers’ basic coats and undershirts. American entrepreneur Hamilton Carhartt is most credited with popularizing flannel garments in the USA. He opened a flannel-focused textile plant, the first of its kind, in Detroit in 1889. It was during the years following this introduction that the American middle class adopted the flannel shirt as a workwear staple.
At one time, Welsh, Yorkshire, Lancashire, and Irish flannels differed slightly in character due largely to the grade of raw wool used in the several localities, some being softer and finer than others. Dyes determine the flannel's color; this was achieved by mixing white, blue, brown, and black wools in varying proportions. Lighter shades were achieved by bleaching with sulphur dioxide.
During the 1950s, Irish designer Sybil Connolly, inspired by Aran Island and traditional Irish peasant skirts, designed a 'Red Flannel' skirt using red flannel wool.
Originally, flannel was made of fine, short staple wool, but by the 20th century, mixtures of silk and cotton had become common. At this time, flannel trousers became popular in sports, especially cricket, and it was used extensively until the late 1970s.
Flannel plaid shirts became popular teen wear in the early 1990s, being part of the grunge style of bands like Nirvana and Pearl Jam.
Types
Flannelette typically refers to a napped cotton fabric imitating the texture of flannel. The weft is generally coarser than the warp. The flannel-like appearance is created by creating a nap from the weft; scratching it and raising it up. Flannelette can either have long or short nap, and can be napped on one or two sides. It comes in many colours, both solid and patterned.
Baby flannel is a lightweight fabric used for childrenswear.
Cotton flannel or Canton flannel is a cotton fabric napped on one or two sides.
Ceylon's flannel was a name for a wool and cotton mixture.
Diaper flannel is a stout cotton fabric napped on both sides, and used for making cloth diapers.
Vegetable flannel, invented by Léopold Lairitz in Germany in the 1800s, uses fibres from the Scots pine rather than wool.
Weave
Flannel, flannelette, and cotton flannel can be woven in either a twill weave or plain weave. The weave is often hidden by napping on one or both sides. After weaving, it is napped once, then bleached, dyed, or otherwise treated, and then napped a second time.
| Technology | Fabrics and fibers | null |
922371 | https://en.wikipedia.org/wiki/Burping | Burping | Burping (also called belching and eructation) is the release of gas from the upper digestive tract (esophagus and stomach) of animals through the mouth. It is always audible.
In humans, burping can be caused by normal eating processes, or as a side effect of other medical conditions. There is a range of levels of social acceptance for burping: within certain contexts and cultures, burping is acceptable and may even be perceived as humorous, while in others it is seen as impolite or even offensive and therefore unacceptable.
Humans are not the only animals that burp: it is very common among other mammals. In particular, burping by domesticated ruminants, such as cows or sheep, is a major contributor of methane emissions and may have a negative effect on the environment. Significant research is being done to find mitigation strategies for ruminant burping, i.e. modifying the animals' diets with Asparagopsis taxiformis (red seaweed).
Causes
Burping is usually caused by swallowing air when eating or drinking and subsequently expelling it, in which the expelled gas is mainly a mixture of nitrogen and oxygen.
Burps can be caused by drinking beverages that contain dissolved carbon dioxide, such as beer and carbonated drinks; in these cases, the expelled gas is mainly carbon dioxide.
Burping can be caused by swallowing air while consuming chewing gum, sucking on hard candy, talking while eating or drinking, or while smoking. It may also occur through swallowing air as a habit.
Diabetes drugs such as metformin and exenatide can cause burping, especially at higher doses. This often resolves in a few weeks.
Burping combined with other symptoms such as dyspepsia, nausea and heartburn may be a sign of an ulcer or hiatal hernia, and should be reviewed by a physician.
Other causes of burping include food allergies, gallbladder diseases, H. pylori, acid reflux disease and gastritis.
Complications
In microgravity environments, burping is frequently associated with regurgitation, known as wet burping. With reduced gravity, the stomach contents are more likely to rise up into the esophagus when the gastroesophageal sphincter is relaxed, along with the expelled air.
Disorders
Chest pain associated with burping can occur, but is rare.
Retrograde cricopharyngeal dysfunction (R-CPD) or retrograde upper esophageal sphincter dysfunction (R-UESD), also called "abelchia", involves the cricopharyngeus muscle not being able to relax, leading to inability to burp. R-CPD was first discovered in 2015. Common symptoms include gurgling noises, bloating, and flatulence; lesser but common symptoms can be potentially painful hiccups, nausea, constipation, hypersalivation, or shortness of breath. A high-resolution manometry, esophageal manometry or fluoroscopy by an ENT doctor is able to assess the issue. 80% of patients were successfully treated with botox after a single injection. If the injection is unsuccessful, an alternative is partial cricopharyngeal myotomy.
Society and culture
Acceptance
Some South Asian cultures view burping as acceptable in particular situations. For example, a burping guest can be a sign to the host that the meal satisfied them and they are full.
In Japan, burping during a meal is considered bad manners. Burping during a meal is also considered unacceptable in Western cultures, such as North America and Europe.
Despite virtually no scientific research on the subject, small online communities exist for burping as a sexual fetish. Online, people of any sexual orientation anecdotally report some attraction to burping, with what appears to be psychological and/or behavioural overlaps with other sexual fetishes including body inflation, feedism, vorarephilia, and farting fetishes. Anecdotally, the 'loudness' aspect appears to be an important element to burp fetishists. Despite being a rather uncommon fetish, it continues to follow a general well-known pattern of sexual behaviour where hearing influences sexual arousal and response, noting that "it is the noise made rather than the action itself that appears to be what is sexualized and/or interpreted by the fetishist as sexually pleasurable and arousing".
Infants
Babies are likely to accumulate gas in the stomach while feeding and experience considerable discomfort (and agitation) until assisted. Burping an infant involves placing the child in a position conducive to gas expulsion (for example against the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting the lower back. Because burping can cause vomiting, a "burp cloth" or "burp pad" is sometimes employed on the shoulder to protect clothing.
World record
The Guinness World Record for the loudest burp was 112.4 dB, set by Neville Sharp from Darwin, Australia in 2021. This is approximately as loud as a jet engine at . The record was previously held by Paul Hunn, who held the record for 12 years.
Burped speech
It is possible to voluntarily induce burping through swallowing air and then expelling it, and by manipulation of the vocal tract produce burped speech.
While this is often employed as a means of entertainment or competition, it can also act as an alternative means of vocalisation for people who have undergone a laryngectomy, with the burp replacing laryngeal phonation. This is known as esophageal speech.
Other animals
Many other mammals, such as cows, dogs and sheep, also burp.
Ruminants
Much of the gas expelled is produced as a byproduct of the ruminant's digestive process. These gases notably include a large volume of methane, produced exclusively by a narrow cohort of methanogenic archaea in the animal's gut; Escherichia coli (E. coli) and other bacteria lack the enzymes and cofactors required for methane production. A lactating cow produces about 322g of methane per day, i.e. more than 117 kg per year through burping and exhalation, making commercially farmed cows a major (37%) contributor to anthropogenic methane emissions, and hence to the greenhouse effect. 95% of this gas (wind) is emitted through burping. This has led scientists at the Commonwealth Scientific and Industrial Research Organisation of Perth, Australia, to develop an anti-methanogen vaccine to minimize methane in cow burps.
One reason why cows burp so much is that they are often fed foods that their digestive systems cannot fully process, such as corn and soy. Some farmers have reduced burping in their cows by feeding them alfalfa and flaxseed, which are closer to the grasses that they had eaten in the wild before they were domesticated.
Birds
There is no documented evidence that birds burp, though ornithologists believe that there is nothing which physiologically prevents them from doing so. However, since the microbiota of birds do not include the same set of gas-producing bacteria that mammals have to aid in digestion, gas hardly builds up in the gastrointestinal tracts of birds.
| Biology and health sciences | Basics | Biology |
922392 | https://en.wikipedia.org/wiki/Rhizaria | Rhizaria | The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera and Radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon.
Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons (thecae or loricas), which are in different clades within Rhizaria made out of opal (), celestite (), or calcite ().
Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.
Groups
The three main groups of Rhizaria are:
Cercozoa – various amoebae and flagellates, usually with filose pseudopods and common in soil
Foraminifera – amoeboids with reticulose pseudopods, common as marine benthos
Radiolaria – amoeboids with axopods, common as marine plankton
A few other groups may be included in the Cercozoa, but some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea, parasites of plants and animals, respectively, and the peculiar amoeba Gromia. The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith in 2002, who also included the centrohelids and Apusozoa.
A noteworthy order that belongs to Ascetosporea is the Mikrocytida. These are parasites of oysters. This includes the causative agent of Denman Island Disease, Mikrocytos mackini a small (2−3 μm diameter) amitochondriate protistan.
History
Similarities between various Rhizaria organisms have been noticed since the 19th century. In his 1861 classification of the Rhizopoda (amoebae), the zoologist William B. Carpenter proposed the order Reticularia, which consisted of Foraminifera and Gromiida on the basis of their very similar thin, reticulose pseudopodia with granules circulating inside. However, the idea that these organisms and others such as Radiolaria were all related to one another emerged rather recently, with the help of molecular phylogenetics and advanced microscopy techniques in the late 20th century.
Evolutionary relationships
Rhizaria are part of the SAR supergroup (Stramenopiles, Alveolates, Rhizaria), a grouping that had been presaged in 1993 through a study of mitochondrial morphologies. SAR is currently placed in the Diaphoretickes along with Archaeplastida, Cryptista, Haptista, and several minor clades.
Historically, many rhizarians were considered animals because of their motility and heterotrophy. However, when a simple animal-plant dichotomy was superseded by a recognition of additional kingdoms, taxonomists generally placed amoebae in the kingdom Protista. When scientists began examining the evolutionary relationships among eukaryotes in the 1970s, it became clear that the kingdom Protista was paraphyletic. Rhizaria appear to share a common ancestor with Stramenopiles and Alveolates forming part of the SAR super assemblage. Rhizaria has been supported by molecular phylogenetic studies as a monophyletic group. Biosynthesis of 24-isopropyl cholestane precursors in various rhizaria suggests a relevant ecological role already during the Ediacaran.
Phylogeny
Rhizaria is a monophyletic group composed of two sister phyla: Cercozoa and Retaria. Subsequently, Cercozoa and Retaria are also monophyletic. The following cladogram depicts the evolutionary relationships between all rhizarian classes, and is made after the works of Cavalier-Smith et al. (2018), and Irwin et al. (2019).
Sexual cycle
Complete sexual life cycles have been demonstrated for two lineages (Foraminifera and Gromia) and direct evidence for karyogamy or meiosis has been observed in five lineages (Euglyphida, Thecofilosea, Chlorarachniophyta, Plasmodiophorida and Phaeodarea). In particular, the Foraminifera are marine amoebae that are defined by a dynamic network of pseudopodia, and the production of intricate shells. These amoeba have complex sexual life cycles with meiosis and gamete production occurring at separate stages.
| Biology and health sciences | Other organisms | null |
922554 | https://en.wikipedia.org/wiki/Discharge%20%28hydrology%29 | Discharge (hydrology) | In hydrology, discharge is the volumetric flow rate (volume per time, in units of m3/h or ft3/h) of a stream. It equals the product of average flow velocity (with dimension of length per time, in m/h or ft/h) and the cross-sectional area (in m2 or ft2). It includes any suspended solids (e.g. sediment), dissolved chemicals like (aq), or biologic material (e.g. diatoms) in addition to the water itself. Terms may vary between disciplines. For example, a fluvial hydrologist studying natural river systems may define discharge as streamflow, whereas an engineer operating a reservoir system may equate it with outflow, contrasted with inflow.
Formulation
A discharge is a measure of the quantity of any fluid flow over unit time. The quantity may be either volume or mass. Thus the water discharge of a tap (faucet) can be measured with a measuring jug and a stopwatch. Here the discharge might be 1 litre per 15 seconds, equivalent to 67 ml/second or 4 litres/minute. This is an average measure. For measuring the discharge of a river we need a different method and the most common is the 'area-velocity' method. The area is the cross sectional area across a river and the average velocity across that section needs to be measured for a unit time, commonly a minute. Measurement of cross sectional area and average velocity, although simple in concept, are frequently non-trivial to determine.
The units that are typically used to express discharge in streams or rivers include m3/s (cubic meters per second), ft3/s (cubic feet per second or cfs) and/or acre-feet per day.
A commonly applied methodology for measuring, and estimating, the discharge of a river is based on a simplified form of the continuity equation. The equation implies that for any incompressible fluid, such as liquid water, the discharge (Q) is equal to the product of the stream's cross-sectional area (A) and its mean velocity (), and is written as:
where
is the discharge ([L3T−1]; m3/s or ft3/s)
is the cross-sectional area of the portion of the channel occupied by the flow ([L2]; m2 or ft2)
is the average flow velocity ([LT−1]; m/s or ft/s)
For example, the average discharge of the Rhine river in Europe is or per day.
Because of the difficulties of measurement, a stream gauge is often used at a fixed location on the stream or river.
Hydrograph
Catchment discharge
The catchment of a river above a certain location is determined by the surface area of all land which drains toward the river from above that point. The river's discharge at that location depends on the rainfall on the catchment or drainage area and the inflow or outflow of groundwater to or from the area, stream modifications such as dams and irrigation diversions, as well as evaporation and evapotranspiration from the area's land and plant surfaces. In storm hydrology, an important consideration is the stream's discharge hydrograph, a record of how the discharge varies over time after a precipitation event. The stream rises to a peak flow after each precipitation event, then falls in a slow recession. Because the peak flow also corresponds to the maximum water level reached during the event, it is of interest in flood studies. Analysis of the relationship between precipitation intensity and duration and the response of the stream discharge are aided by the concept of the unit hydrograph, which represents the response of stream discharge over time to the application of a hypothetical "unit" amount and duration of rainfall (e.g., half an inch over one hour). The amount of precipitation correlates to the volume of water (depending on the area of the catchment) that subsequently flows out of the river. Using the unit hydrograph method, actual historical rainfalls can be modeled mathematically to confirm characteristics of historical floods, and hypothetical "design storms" can be created for comparison to observed stream responses.
The relationship between the discharge in the stream at a given cross-section and the level of the stream is described by a rating curve. Average velocities and the cross-sectional area of the stream are measured for a given stream level. The velocity and the area give the discharge for that level. After measurements are made for several different levels, a rating table or rating curve may be developed. Once rated, the discharge in the stream may be determined by measuring the level, and determining the corresponding discharge from the rating curve. If a continuous level-recording device is located at a rated cross-section, the stream's discharge may be continuously determined.
Larger flows (higher discharges) can transport more sediment and larger particles downstream than smaller flows due to their greater force. Larger flows can also erode stream banks and damage public infrastructure.
Catchment effects on discharge and morphology
G. H. Dury and M. J. Bradshaw are two geographers who devised models showing the relationship between discharge and other variables in a river. The Bradshaw model described how pebble size and other variables change from source to mouth; while Dury considered the relationships between discharge and variables such as stream slope and friction. These follow from the ideas presented by Leopold, Wolman and Miller in Fluvial Processes in Geomorphology. and on land use affecting river discharge and bedload supply.
Inflow
Inflow is the sum of processes within the hydrologic cycle that increase the water levels of bodies of water.
Most precipitation occurs directly over bodies of water such as the oceans, or on land as surface runoff. A portion of runoff enters streams and rivers, and another portion soaks into the ground as groundwater seepage. The rest soaks into the ground as infiltration, some of which infiltrates deep into the ground to replenish aquifers.
| Physical sciences | Hydrology | Earth science |
922567 | https://en.wikipedia.org/wiki/Fermi%27s%20golden%20rule | Fermi's golden rule | In quantum physics, Fermi's golden rule is a formula that describes the transition rate (the probability of a transition per unit time) from one energy eigenstate of a quantum system to a group of energy eigenstates in a continuum, as a result of a weak perturbation. This transition rate is effectively independent of time (so long as the strength of the perturbation is independent of time) and is proportional to the strength of the coupling between the initial and final states of the system (described by the square of the matrix element of the perturbation) as well as the density of states. It is also applicable when the final state is discrete, i.e. it is not part of a continuum, if there is some decoherence in the process, like relaxation or collision of the atoms, or like noise in the perturbation, in which case the density of states is replaced by the reciprocal of the decoherence bandwidth.
Historical background
Although the rule is named after Enrico Fermi, most of the work leading to it is due to Paul Dirac, who twenty years earlier had formulated a virtually identical equation, including the three components of a constant, the matrix element of the perturbation and an energy difference. It was given this name because, on account of its importance, Fermi called it "golden rule No. 2".
Most uses of the term Fermi's golden rule are referring to "golden rule No. 2", but Fermi's "golden rule No. 1" is of a similar form and considers the probability of indirect transitions per unit time.
The rate and its derivation
Fermi's golden rule describes a system that begins in an eigenstate of an unperturbed Hamiltonian and considers the effect of a perturbing Hamiltonian applied to the system. If is time-independent, the system goes only into those states in the continuum that have the same energy as the initial state. If is oscillating sinusoidally as a function of time (i.e. it is a harmonic perturbation) with an angular frequency , the transition is into states with energies that differ by from the energy of the initial state.
In both cases, the transition probability per unit of time from the initial state to a set of final states is essentially constant. It is given, to first-order approximation, by
where is the matrix element (in bra–ket notation) of the perturbation between the final and initial states, and is the density of states (number of continuum states divided by in the infinitesimally small energy interval to ) at the energy of the final states. This transition probability is also called "decay probability" and is related to the inverse of the mean lifetime. Thus, the probability of finding the system in state is proportional to .
The standard way to derive the equation is to start with time-dependent perturbation theory and to take the limit for absorption under the assumption that the time of the measurement is much larger than the time needed for the transition.
Only the magnitude of the matrix element enters the Fermi's golden rule. The phase of this matrix element, however, contains separate information about the transition process.
It appears in expressions that complement the golden rule in the semiclassical Boltzmann equation approach to electron transport.
While the Golden rule is commonly stated and derived in the terms above, the final state (continuum) wave function is often rather vaguely described, and not normalized correctly (and the normalisation is used in the derivation). The problem is that in order to produce a continuum there can be no spatial confinement (which would necessarily discretise the spectrum), and therefore the continuum wave functions must have infinite extent, and in turn this means that the normalisation is infinite, not unity. If the interactions depend on the energy of the continuum state, but not any other quantum numbers, it is usual to normalise continuum wave-functions with energy labelled , by writing where is the Dirac delta function, and effectively a factor of the square-root of the density of states is included into . In this case, the continuum wave function has dimensions of , and the Golden Rule is now
where refers to the continuum state with the same energy as the discrete state . For example, correctly normalized continuum wave functions for the case of a free electron in the vicinity of a hydrogen atom are available in Bethe and Salpeter.
Applications
Semiconductors
The Fermi's golden rule can be used for calculating the transition probability rate for an electron that is excited by a photon from the valence band to the conduction band in a direct band-gap semiconductor, and also for when the electron recombines with the hole and emits a photon. Consider a photon of frequency and wavevector , where the light dispersion relation is and is the index of refraction.
Using the Coulomb gauge where and , the vector potential of light is given by where the resulting electric field is
For an electron in the valence band, the Hamiltonian is
where is the potential of the crystal, and are the charge and mass of an electron, and is the momentum operator. Here we consider process involving one photon and first order in . The resulting Hamiltonian is
where is the perturbation of light.
From here on we consider vertical optical dipole transition, and thus have transition probability based on time-dependent perturbation theory that
with
where is the light polarization vector. and are the Bloch wavefunction of the initial and final states. Here the transition probability needs to satisfy the energy
conservation given by . From perturbation it is evident that the heart of the calculation lies in the matrix elements shown in the bracket.
For the initial and final states in valence and conduction bands, we have and , respectively and if the operator does not act on the spin, the electron stays in the same spin state and hence we can write the Bloch wavefunction of the initial and final states as
where is the number of unit cells with volume . Calculating using these wavefunctions, and focusing on emission (photoluminescence) rather than absorption, we are led to the transition rate
where defined as the optical transition dipole moment is qualitatively the expectation value and in this situation takes the form
Finally, we want to know the total transition rate . Hence we need to sum over all possible initial and final states that can satisfy the energy conservation (i.e. an integral of the Brillouin zone in the k-space), and take into account spin degeneracy, which after calculation results in
where is the joint valence-conduction density of states (i.e. the density of pair of states; one occupied valence state, one empty conduction state). In 3D, this is
but the joint DOS is different for 2D, 1D, and 0D.
We note that in a general way we can express the Fermi's golden rule for semiconductors as
In the same manner, the stationary DC photocurrent with amplitude proportional to the square of the field of light is
where is the relaxation time, and are the
difference of the group velocity and Fermi-Dirac distribution between possible the initial and
final states. Here defines the optical transition dipole. Due to the commutation relation between position and the Hamiltonian, we can also rewrite the transition dipole and photocurrent in terms of position operator matrix using . This effect can only exist in systems with broken inversion symmetry and nonzero components of the photocurrent can be obtained by symmetry arguments.
Scanning tunneling microscopy
In a scanning tunneling microscope, the Fermi's golden rule is used in deriving the tunneling current. It takes the form
where is the tunneling matrix element.
Quantum optics
When considering energy level transitions between two discrete states, Fermi's golden rule is written as
where is the density of photon states at a given energy, is the photon energy, and is the angular frequency. This alternative expression relies on the fact that there is a continuum of final (photon) states, i.e. the range of allowed photon energies is continuous.
Drexhage experiment
Fermi's golden rule predicts that the probability that an excited state will decay depends on the density of states. This can be seen experimentally by measuring the decay rate of a dipole near a mirror: as the presence of the mirror creates regions of higher and lower density of states, the measured decay rate depends on the distance between the mirror and the dipole.
| Physical sciences | Quantum mechanics | Physics |
2061417 | https://en.wikipedia.org/wiki/Dubai%20Metro | Dubai Metro | The Dubai Metro () is a rapid transit system in the city of Dubai, United Arab Emirates. The metro system consists of a network of two main lines: the Red Line and the Green Line. A third line, the Blue Line, is scheduled to open in 2029.
Dubai Metro is the first rapid transit train network in the Arabian Peninsula and the Gulf Cooperation Council. It began operations on 9 September 2009. The metro runs underground in the city centre and on elevated viaducts elsewhere. All trains are fully automated and driverless. Both the trains and stations are temperature controlled and have platform edge doors. Dubai Metro has a total length of and 55 stations, 35 on the Red Line and 15 on the Green Line.
From 2009 to 2016, Dubai Metro was the world's longest driverless metro network with a route length of , as recognized by Guinness World Records in 2012. The system was surpassed by the Vancouver SkyTrain in 2016 for the longest fully automated system in the world but regained the title in 2021 with the opening of Route 2020 until December 2024 when it was surpassed by the opening of Riyadh Metro.
History
In 1997, Dubai Municipality studies on urban development identified the need for a rail system to relieve growing traffic levels and to support the urban development in Dubai. Planning of the Dubai Metro began under the directive of Dubai's Ruler, Sheikh Mohammed bin Rashid Al Maktoum in 2003. Dubai expected to attract 15 million visitors by 2010. The combination of a rapidly growing population, which was expected to reach 3 million by 2017, and severe traffic congestion necessitated the building of an urban rail system to provide additional public transportation capacity, relieve motor traffic, and provide infrastructure for additional development. In 2004, five consortium were shortlisted to build the first section.
In May 2005, a AED 12.45 billion ($3.4 billion) design and build contract was awarded to the Dubai Rail Link (DURL) consortium made up of Japanese companies including Mitsubishi Heavy Industries, Mitsubishi Corporation, Obayashi Corporation, Kajima Corporation and Turkish firm Yapı Merkezi, The Project Management and Construction Management services contract was awarded to a French-American joint venture between Systra and Parsons Corporation. The first phase worth AED 15.5 billion ($4.2 billion) covers of the proposed network, including the Red Line between Al Rashidiya and the Jebel Ali Free Zone
Work officially commenced on the construction of the metro on 21 March 2006. In February 2009, an RTA Rail Agency official stated the US$4.2 billion Dubai Metro project would be completed on schedule despite the global financial crisis. 10 out of 29 metro stations of the Red Line opened on 9 September 2009.
The Red Line was partially opened at 9 minutes and 9 seconds past 9 pm on 9 September 2009 (9/9/9 9:09:09 PM), inaugurated by Sheikh Mohammed bin Rashid Al Maktoum. More than 110,000 people, nearly 10 percent of Dubai's population at the time, used the Metro in its first two days of operation. The Line opened to the public at 6 am (UTC 04:00) on 10 September 2009. The Dubai Metro carried 10 million passengers from launch on 9 September 2009 to 9 February 2010 with 11 stations operational on the Red Line.
Seven more stations on the Dubai Metro Red Line opened on 30 April 2010. Ten new trains were pressed into service, giving a total of 22 trains in service when the stations opened. The seven stations are Emirates Station, Airport Terminal 1 Station, Dubai Internet City (TECOM) Station, Al Karama Station, Emirates Towers Station, Dubai Marina Station, and Ibn Battuta Station. In addition to this, a further three stations were opened on 15 May 2010; GGICO Station and World Trade Center Station. Furthermore, Business Bay Station, First Gulf Bank Station, mashreq (Al Barsha) Station, Al Khail Station, and Jumeirah Lakes Towers Station were opened on 15 October 2010. The Jebel Ali Station and the terminus of the Red Line was opened on 11 March 2011. The Jebel Ali Industrial Station was opened on 12 December 2012. Al Jadaf Station and Creek Station, on the Green Line were opened on 1 March 2014.
A 15 km extension of the Red Line known as Route 2020 which connects to Expo 2020 was announced in September 2016 and was completed and inaugurated on 8 July 2020. Engineering consultancy Atkins provided multidisciplinary design and management of the civil works on Route 2020.
A 30 km third line with 14 stations, called the Blue Line, was announced on 24 November 2023 with a total investment of AED 18 billion, with an expected operational date by 2029. The Blue Line will extend from the terminus of the Red Line on Centrepoint Station and the Green Line terminus at the Creek Station.
Operation
The Dubai Metro was operated by Serco under contract to the Roads & Transport Authority which was last renewed in March 2019. In March 2021, the French-Japanese consortium of Keolis and Mitsubishi Heavy Industries was announced as a new operator from 8 September 2021.
Red Line trains run every 5 to 7 minutes off-peak (averaging 8.5 trains per hour), with a minimum headway of 3 minutes 45 seconds (16 trains per hour) during peak hours, with 44 trainsets in service. Trains from the Red Line and Green Line can depart differently due to technical glitches. From 2010, when 51 trains were in service, the line had a peak-hour capacity of 11,675 passengers per hour in each direction. , the Red Line operates 60 trains (train registrations 5001–5045, 5065–5079). The theoretical maximum design capacity is 25,720 passengers per hour, which would require 106 trains.
The Green Line had an initial capacity of 6,395 passengers per hour per direction, with 19 trains (train registrations 5046–5064) in service as of September 2014. The design capacity of this route is put at 13,380 passengers per hour with 60 trains in service.
Signalling
To permit fully automated operation, Thales Rail Signalling Solutions supplies SelTrac IS communications-based train control and NetTrac central control technology. This is configured for a minimum headway of 500 seconds (40 trains per hour). The top speed of the trains is estimated to be around , giving a round-trip time of 2 hours 23 minutes for the Red Line and 1 hour 23 minutes for the Green Line.
Ridership
Over 280,000 passengers used the Dubai Metro during the first week of its operation in September 2009. After the first month of operation on a limited network, the monthly total passengers was 1,740,578 passengers, which equates to under 60,000 passengers/day.
After the opening of more stations in May 2010, ridership surged to 103,002 passengers/day and reached 130,000/day by the beginning of October 2010. When the Green Line opened on 9 September 2011, passengers on the Red Line was noted as 180,000/day. In 2013, passengers rose to 377,000/day, split 64% for the Red Line and 36% for the Green Line. During the first half of 2015, RTA announced that 88,252,034 passengers have used the metro. In August 2017, RTA announced that total ridership since 2009 had surpassed 1 billion total trips.
Statistics
Lines
Dubai Metro currently has a total length of and 55 stations on two lines:
Red Line with a total length of and 35 stations.
Green Line with a total length of and 20 stations.
A third line is under construction for operation by 9 September 2029:
Blue Line with a length of and 14 stations.
Red Line
The Red Line stretches along the city from the Jebel Ali area to the border with Sharjah. It passes through several tourist attractions such as Mall of the Emirates, The Dubai Mall, and Burj Khalifa.
Route 2020 is a 15 kilometer (9 mi) extension of the Red Line with seven new stations which starts at the Jebel Ali Station and ends at Expo 2020. Future plans will also extend this line to the Al Maktoum International Airport. The extension is served by new, redesigned trains from Alstom. The extension opened in stages in 2021.
Green Line
The Green Line stays within the old Dubai area. It passes through historical sites, such as the Dubai Museum, the Gold Souk, and the Spice Souk. Stations near those places are built in keeping with the historical architecture of Dubai that mirrors the architecture of the surrounding area. The stations also have with photos depicting the UAE in the 1960s or earlier being on display within the station.
Summary of lines
Proposed
In 2011, the RTA stated that there are no "immediate plans" to build the Blue and Purple lines "in the next five or six years". This is mainly because the planned area is empty and developing.
In 2013, the RTA laid out a three-phase plan to expand the existing lines and build new ones: extending the Green Line by 12 stations and to Academic City by 2020; expanding the overall system by 58 stations and by 2025 and completing expansion with a total of 69 stations and 221 km over and above the present 47 stations and that are present as of January 2013.
Purple Line: along Al Khail Road (E44). The line will extend from the Al Maktoum International Airport to Muhaisnah, a locality near the border between Dubai and Sharjah. There will be about eight stations, three with check-in facilities. However, The Dubai Airports Authority claimed that this was unfeasible as it did not pass through many localities. They however suggested opting for a "central terminal" similar to those in Europe where trains leave from inside the airport to the other airport with trains also leaving to the city. The RTA have taken this into consideration.
Pink Line: The Pink Line is planned to run east–west with a terminus at Al Sufouh and is scheduled for completion by 2030.
Gold Line: Announced as the 'Yellow Line' in April 2008 and confirmed in January 2013 as the 'Gold Line'. One of the stations planned for the Gold Line is the Dubailand Station, west of Meydan. The Gold Line will connect Arabian Ranches, Deira, and Dubai Marina and is scheduled to open by 2025.
Red Line Extension: and six new stations, terminating at the border with Abu Dhabi. No dates for completion announced.
In 2014, the RTA approved the recent proposal of extending the Red Line from Al Rashidiya station to Mirdif City Center which will increase 3.5 kilometers with the new station. However, there is also a proposal to extend it further to Al Warqa'a which is currently being studied.
As of 2024, none of these extensions or proposed lines have been started or discussed and are currently indefinitely suspended until further notice.
On the Green Line, the RTA finalized the extension plan of 20.6 kilometers from Al Jaddaf to Academic City in 2014. The extension is due to go through Festival City, Lagoons, Ras Al Khor Industrial Area, International City, Dubai Silicon Oasis, and Dubai Academic City. This was later approved as the new Blue Line, which construction started in 2024 and is scheduled to open on 9 September 2029, to coincide with the 20 year anniversary of Dubai Metro.
In 2018, the engineering firm Aurecon produced a study into a 7.5 km express metro line from Al Qiyadah station on the Green Line till Sharjah. The line would cost AED 3 billion, and could reduce traffic congestion between the two cities by up to 30%.
Stations
Architecture firm Aedas designed the metro's 45 stations, two depots, and the operational control centres. The Al Ghurair Investment group were the metro's builders.
Dubai Metro is composed of at-grade (G) elevated Type 1, Type 2 and Type 3 (T1, T2 and T3, respectively) underground stations (U) and underground transfer station types (UT). Type 1 is the regular at-grade concourse station, Type 2 is a regular elevated concourse station, and Type 3 is an elevated special track station with an extra track to hold a non-operational train. Underground transfer stations accommodate both the Red and Green lines for easy transfers.
Besides these differences, there are five themes used in the interiors of the stations: The red line individually has 29 stations including the Interchange Stations between Green Line. The green line has 20 stations including the Interchange Stations between Red Line. Route 2020 (Connected with the Red Line from Jebel Ali) individually has 7 stations in total (including Jebel Ali; 6 without it).
Inside the stations will have air conditions from 24 to 21 Celsius.
Heritage: Symbolizes the culture and history of the United Arab Emirates.
Earth: Marks the start of the Dubai modern and urban drive, which resembles the force and durability of earth and soil.
Air: Symbolizes the elation and joy that Dubai provides to residents and visitors.
Fire: Symbolizes the energy, vigour and strong will displayed by Dubai leaders.
Water: Symbolizes the human values which Dubai seeks to ensure in its modern achievements.
The Earth stations have a tan-brown colour effects; water has blue-white colour effects; fire has orange-red colour effects; and the air has green colour effects.
Officials have negotiated with international and local companies over naming rights for 23 stations on the two lines. This corporate branding is the first of its kind. Some examples are: BurJuman, Burj Khalifa/Dubai Mall, Mall of the Emirates, DAMAC Properties and UAE Exchange.
Each station has a bus route with drop-off zones to the metro station as well as taxi lay by's.
Parking
The Dubai Metro has built three large multi-level car parking with an estimated capacity to accommodate more than 8,000 vehicles for the passengers where they can park their car and ride the metro.
The parking is free for the metro users.
Handicap facilities
All metro stations have elevators and contrasting tactile guidance path to guide the visually impaired. There are also dedicated spaces for wheelchair users on all the trains. Handicapped passengers, also known as 'people of determination' in the UAE, can ride with any RTA service for free with a special, personalized Nol Card.
Safety
Emergency stop buttons, intercoms and platform screen doors with corresponding flashing light signals are installed at every station for the safety of the passengers. Trains are equipped with emergency stop buttons, door release levers, intercoms and fire extinguishers. CCTV is operational throughout the entire network and in trains and police officers are regularly on patrol in the stations, especially during rush hours.
Wi-Fi
Wi-Fi connectivity is available across all trains and stations and is provided by du which is in par with the Wi-Fi UAE program which provides Wi-Fi connectivity across major parts of UAE. Mobile phone coverage is available across the entire network of the metro. The metro itself has Wi-Fi connectivity inside for the commuters to access with two tiers of Internet access with the normal service being free whereas the premium service can be accessed by a nominal fee.
Travelling
The Dubai Transport is divided into 4 tiers (5 zones). The prices were slightly increased as of 11 November 2014. The cheapest ticket (not preloaded, and not in the "gold" class) with a distance not more than 3 km cost 3 AED (about $0.82) – the equivalent of Tier 0, and most costly single trip (Tier 3, exceed 2 zones, and paper not preloaded ticket also) 7.5 AED (about $2.04) and was not increased from opening. Tier 1 is one zone trip, where the travel exceeds 3 km, Tier 2 is neighbouring 2 zones travel. Also (excluding Gold class) using cards there is "no more paying" – a free rest of day travel if the cost exceeds 14 AED (about $3.81).
Ticketing
The Dubai Metro has a fixed fare based on three tiers and travelling under 3 km costs 3 AED. The tiers are:
The Nol Card are used by the passengers to check-in and check-out at the gates in their destination station. No other payment form (cash, credit card) can be used. The fare will be automatically deducted based on the number of zones traveled. Passengers will be allowed to check-in when their card has more than minimum credit required.
Children below the age of 5 years or less than 90 cm and people with disabilities (personalized Nol Card required) will be eligible to travel the metro for free.
There is also a Nol Card available for students & seniors, and they can get a student & senior citizens' discount (usually half of the fare).
Rolling stock
Japanese manufacturer Kinki Sharyo built a total of 79 five-car trains (60 on the Red Line, nineteen on the Green Line) for the system. Their fleet numbers are 5001 – 5079, and each train's cars are assigned a 3 digit number and a letter from A to E (The first car is assigned A; second is B; third is C; fourth is D; fifth is E: For example, train set 5001 consists of cars 101A, 101B, 101C, 101D and 101E). The trains are designed to carry 643 seated and standing passengers, and unusually for a mass transit system, the trains have three classes of accommodation: Gold Class (first class), the Women and Children only class, and the regular Silver Class (economy). The first train (Set 5001) was delivered to Dubai in March 2008. The trains are driverless, use third rail current collection. Trained wardens accompany passengers to help with emergencies. Four newer trains (Sets 5074, 5075, 5076, and 5077) are each painted with a different special livery, in which one of them (set 5077) representing the skyline of Dubai. Set 5041 was painted with a special Museum of the Future livery. However, these liveries (except set 5041 which still exists as of today) are currently removed.
50 new trains, the Alstom Metropolis, were introduced in November 2018. These trains have higher capacity, 696 passengers, up from 643 passenger on the current trains. This will increase passenger capacity by about 10%. The new trains have a refreshed interior with better air conditioning, digital maps, improved speed, brakes and doors. Out of these 50 trains, all 50 are running on the Red and Green Lines (mostly the Green Line). The fleet numbers of the new Alstom trains are 5101 – 5150, and similar to the original Kinki Sharyo trains, each train's cars also are assigned a 3 digit number and a letter from A to E (for example, set 5122 consists of cars 222A, 222B, 222C, 222D and 222E).
Culture
Music Festival
Brand Dubai collaborated with Roads & Transport Authority in March 2019 to launch the "Dubai Metro Music Festival", there was no festival in 2020 and 2021 because of COVID-19. It is held from 14 to 20 Sha'aban every year. Held across red line stations.
Guinness World Record
On 1 November 2018, as part of the RTA's Public Transport Day, the longest diverse human chain of hand was formed in a Dubai metro train at Etisalat station. The record was acknowledged by Guinness World Records. The chain was formed by people from 96 countries around the whole world. Previously this record was with Norway, where 75 nations made a diverse human chain.
Dubai Metro Museum
Sheikh Mohammed bin Rashid Al Maktoum, Vice President and Prime Minister of the UAE and Ruler of Dubai, gave his directions to transform Dubai Metro stations into art museums under the supervision of Dubai Culture and Arts Authority. The project was announced in early April 2014 and aims to display contemporary and modern art.
Incidents and accidents
3 April 2016: Passengers were left stranded during evening rush hour after a technical snag delayed train services on the Red Line. Systems were restored in 30 minutes.
24 August 2017: A man commits suicide in Noor Bank Metro Station. The station was shut down for one hour following the incident.
6 November 2017: Passengers commuting on the Red Line were left stranded after a technical glitch caused train services to temporarily stall specifically near Jumeirah Lakes Towers (now DMCC) and UAE Exchange stations. Services returned to normal at 12:32 PM.
16 April 2024: Excessive flooding caused by heavy rain forced the closure of Onpassive, Equiti, Mashreq, and Energy stations for several weeks.
| Technology | Asia_2 | null |
5193704 | https://en.wikipedia.org/wiki/Chianina | Chianina | The Chianina () is an Italian breed of large white cattle. It was formerly principally a draught breed; it is now raised mainly for beef. It is the largest and one of the oldest cattle breeds in the world. The bistecca alla fiorentina is produced from its meat.
History
The Chianina is one of the oldest breeds of cattle. It originates in the area of the Valdichiana, from which it takes its name, and the middle Tiber Valley. Chianina cattle have been raised in the Italian regions of Tuscany, Umbria and Lazio for at least 2200 years. Columella, writing about types of oxen in about 55 AD, says "Umbria vastos et albos ..." (VI.I.2), which in the first English translation is "Umbria has such as are huge, and of a white colour". Chianina oxen were the principal source of agricultural power in the area until displaced by mechanisation and the collapse of the mezzadria system following the Second World War; they were in use in agriculture until at least 1970 and are still used in processions such as the corteo storico of the Palio di Siena.
From 1931 breeders began to favour selection of animals more suited to meat production, with shorter limbs, longer bodies and more heavily muscled rump and thighs; recently, selection is based also on factors such as growth rate, meat yield and, in cows, maternal ability. While one source reports a herdbook dating from 1856, others date the institution of the Libro Genealogico ("genealogical herdbook") to 1933, when a breed standard was established and commissions were set up by the then Ministero dell'Agricoltura e delle Foreste (ministry of agriculture and forestry) to identify, mark and register morphologically suitable animals; the standard of the Chianina breed was fixed by ministerial decree of 7 August 1935. A private register was previously kept by the largest cattle breeder of the Sienese Valdichiana, the Eredi del conte Bastogi of Abbadia di Montepulciano, and a group of breeders had in 1899 formed a society, the Società degli Agricoltori della Valdichiana (society of farmers of the Valdichiana), of which a principal aim was the establishment of a herdbook.
Since the Second World War the Chianina has become a world breed, raised almost exclusively for its high quality meat. Through exportation of breeding stock, of frozen semen and of embryos, it has reached China, Russia, Asian countries and the Americas.
Breed description
The Chianina is both the tallest and the heaviest breed of cattle. Mature bulls stand up to , and oxen may reach . It is not unusual for bulls to exceed in weight. Males standing over at 12 months are considered top-grade. A Chianina bull named Donetto holds the world record for the heaviest bull, reported by one source as when exhibited at the Arezzo show in 1955, but as and tall at the age of 8 by others including the Tenuta La Fratta, near Sinalunga in the province of Siena, where he was bred. Cows usually weigh , but commonly exceed ; those standing over are judged top-grade. Calves routinely weigh over at birth.
The coat of the Chianina is white; very slight grey shading round the eyes and on the foreparts is tolerated. The skin, muzzle, switch, hooves and the tips of the horns are black, as are the natural openings – the anus, vulva, eyelids, palate, tongue, and lower part of the scrotum.
At the end of 2010 there were 47,236 head registered in Italy, of which more than 90% were in Tuscany, Umbria and Lazio; it is, after the Marchigiana, the second indigenous beef breed of Italy.
Uses
The Chianina is a dual purpose breed, raised both for meat and for draught use; the milk is barely sufficient for suckling.
Draught use
Until recent years, when it was replaced by machinery, the Chianina ox was used with excellent results both in agriculture and for road transport in its area of origin, the provinces of Arezzo, Florence, Livorno, Perugia, Pisa (parts only) and Siena, and in some parts of the more distant provinces of Caserta, Latina and Terni. It was highly adapted to the steep hill terrain and entirely suitable to the farms of the time, to mixed agriculture and to the smallholdings of the mezzadri. A typical casa colonica or rural farmhouse in the area had substantial stabling for oxen on the ground floor, while the habitable part was on the floor above.
At this time four varieties were distinguishable within the breed, based on phenotypic differences resulting from different environments: the Chianina of the Valdichiana, the Chianina of the Valdarno, the Calvana (since 1985 considered a separate breed) in the hilly country of the province of Florence, and the Perugina in the province of Perugia.
The oxen, both male and female, were invariably worked in pairs, yoked with a type of neck yoke. Today Chianina oxen are rarely seen in Italy other than at public events such as the Palio di Siena.
In North America Chianina oxen are trained for participation in ox-pulling contests. Conroy shows a pair pulling on a stoneboat.
Meat production
In beef production, Chianina cattle are chosen for their growth rate, which may exceed per day, the high yield and high quality of the meat, and their tolerance of heat and sunlight. They are good foragers and have better resistance to disease and insects than many other domestic cattle.
The ideal slaughter weight is , reached at 16–18 months, where the yield may be 64–65%. The meat is renowned for its quality and nutritional values. In Italy it is sold by name at premium prices by approved butchers, the sales receipt detailing the breed, birth and slaughter dates, identification number and other data of the animal in order to guarantee its origin. Each of the 18 principal cuts is branded with the "5R" symbol of the Consorzio Produttori Carne Bovina Pregiata delle Razze Italiane (consortium of producers of quality beef from Italian breeds), signifying the five indigenous beef breeds of Italy, the Chianina, the Marchigiana, the Maremmana, the Romagnola and the Podolica, in accordance with a ministerial decree of 5 July 1984. For the three breeds present in central Italy, the Chianina, the Marchigiana and the Romagnola, there is also an Indicazione Geografica Protetta, or certification of region of origin, in accordance with European Community regulation 2081/92.
Cross-breeding
The Chianina breed is widely used for cross-breeding. In the United States the Chianina has been cross-bred with British breeds to reduce the fat content of meat in line with current fashion; elsewhere it has been used to transmit size, growth-rate and its relatively low skeleton weight to local breeds. It has been found to transmit well qualities such as growth-rate, meat quality, resistance to heat and cold and to insects and disease, and adaptation to rough terrain. Stock cross-bred with the Chianina may reach slaughter weight a month earlier than normal. In 1971 semen was first exported to the United States, where there are now many half-blood and quarter-blood animals. The first American Chianina x Angus calf was born on 31 January 1972 at Tannehill Ranch, near King City, California. Within four years the American Chianina Association had established a Chiangus register, since then the Chiangus has achieved "all but total dominance" in U.S. steer shows. Chianina semen was first imported into Australia in 1973, from Canada; it has since been imported directly from Italy. The Chiangus is an established cross in Australia also.
| Biology and health sciences | Cattle | Animals |
25828666 | https://en.wikipedia.org/wiki/Cro-Magnon | Cro-Magnon | Cro-Magnons or European early modern humans (EEMH) were the first early modern humans (Homo sapiens) to settle in Europe, migrating from western Asia, continuously occupying the continent possibly from as early as 56,800 years ago. They interacted and interbred with the indigenous Neanderthals (H. neanderthalensis) of Europe and Western Asia, who went extinct 40,000 to 35,000 years ago. The first wave of modern humans in Europe (Initial Upper Paleolithic) left no genetic legacy to modern Europeans; however, from 37,000 years ago a second wave succeeded in forming a single founder population, from which all subsequent Cro-Magnons descended and which contributes ancestry to present-day Europeans. Cro-Magnons produced Upper Palaeolithic cultures, the first major one being the Aurignacian, which was succeeded by the Gravettian by 30,000 years ago. The Gravettian split into the Epi-Gravettian in the east and Solutrean in the west, due to major climatic degradation during the Last Glacial Maximum (LGM), peaking 21,000 years ago. As Europe warmed, the Solutrean evolved into the Magdalenian by 20,000 years ago, and these peoples recolonised Europe. The Magdalenian and Epi-Gravettian gave way to Mesolithic cultures as big game animals were dying out and the Last Glacial Period drew to a close.
Cro-Magnons were anatomically similar to present-day Europeans, West Asians, and North Africans; however, they were more robust, having larger brains, broader faces, more prominent brow ridges, and bigger teeth, compared to the present-day average. The earliest Cro-Magnon specimens also exhibit some features that are reminiscent of those found in Neanderthals. The first Cro-Magnons would have had darker skin tones than most modern Europeans; natural selection for lighter skin would not have begun until 30,000 years ago. Before the LGM, Cro-Magnons had overall low population density, tall stature similar to post-industrial humans, and expansive trade routes stretching as long as , and hunted big game animals. Cro-Magnons had much higher populations than the Neanderthals, possibly due to higher fertility rates; life expectancy for both species was typically under 40 years. Following the LGM, population density increased as communities travelled less frequently (though for longer distances), and the need to feed so many more people in tandem with the increasing scarcity of big game caused them to rely more heavily on small or aquatic game (broad spectrum revolution), and to more frequently participate in game drive systems and slaughter whole herds at a time. The Cro-Magnon arsenal included spears, spear-throwers, harpoons, and possibly throwing sticks and Palaeolithic dogs. Cro-Magnons likely commonly constructed temporary huts while moving around, and Gravettian peoples notably made large huts on the East European Plain out of mammoth bones.
Cro-Magnons are well renowned for creating a diverse array of artistic works, including cave paintings, Venus figurines, perforated batons, animal figurines, and geometric patterns. They also wore decorative beads, and plant-fibre clothes dyed with various plant-based dyes. For music, they produced bone flutes and whistles, and possibly also bullroarers, rasps, drums, idiophones, and other instruments. They buried their dead, though possibly only people who had achieved or were born into high status.
The name "Cro-Magnon" comes from the five skeletons discovered by French palaeontologist Louis Lartet in 1868 at the Cro-Magnon rock shelter, Les Eyzies, Dordogne, France, after the area was accidentally discovered while a road was constructed for a railway station. Remains of Palaeolithic cultures have been known for centuries, but they were initially interpreted in a creationist model, wherein they represented antediluvian peoples which were wiped out by the Great Flood. Following the conception and popularisation of evolution in the mid-to-late 19th century, Cro-Magnons became the subject of much scientific racism, with early race theories allying with Nordicism and Pan-Germanism. Such historical race concepts were overturned by the mid-20th century. During the first wave feminism movement, the Venus figurines were notably interpreted as evidence of some matriarchal religion, though such claims had mostly died down in academia by the 1970s.
Chronology
Initial Upper Palaeolithic
When early modern humans (Homo sapiens) migrated onto the European continent, they interacted with the indigenous Neanderthals (H. neanderthalensis) which had already inhabited Europe for hundreds of thousands of years. In 2019, Greek palaeoanthropologist Katerina Harvati and colleagues argued that two 210,000 year old skulls from Apidima Cave, Greece, represent modern humans rather than Neanderthalsindicating these populations have an unexpectedly deep historybut this was disputed in 2020 by French paleoanthropologist and colleagues. About 60,000 years ago, marine isotope stage 3 began, characterised by oscillating climatic patterns, causing sudden retreat and recolonisation phases in vegetation, fluctuating between forestland and open steppeland.
The earliest indication of Upper Palaeolithic modern human migration into Europe is a series of modern human teeth with Neronian industry stone tools found at Mandrin Cave, Malataverne in France, dated in 2022 to between 56,800 and 51,700 years ago. The Neronian is one of the many industries associated with modern humans classed as transitional between the Middle and Upper Palaeolithic. Beyond this there is the Balkan Bohunician industry beginning 48,000 years ago, likely deriving from the Levantine Emiran industry; the remains found in the cave in Ranis, Germany, up to 47,500 years old; and the next-oldest fossils date to roughly 44,000 years ago in Bulgaria, Italy, and Britain. It is unclear, while migrating westward, if they followed the Danube or went along the Mediterranean coast. Beginning about 45,000 years ago, the Proto-Aurignacian culture, the first widely recognised European Upper Palaeolithic culture, spread out across Europe, probably descending from the Near-Eastern Ahmarian culture.
Aurignacian
The Aurignacian industry took hold perhaps in south-central Europe sometime after 40,000 years ago, with the onset of Heinrich event 4 (a period of extreme seasonality) and the Campanian Ignimbrite eruption near Naples (which covered eastern Europe in ash). The Aurignacian culture rapidly replaced others across the continent. This wave of modern humans replaced Neanderthals and their Mousterian culture. In the Danube Valley, Aurignacian sites are few and far between, compared to later traditions, until 35,000 years ago. From here, the "Typical Aurignacian" becomes quite prevalent, and extends until 29,000 years ago.
Gravettian
Gradually replaced by the Gravettian culture, the close of the Aurignacian is poorly defined. "Aurignacoid" or "Epi-Aurignacian" tools are identified as late as 18 to 15 thousand years ago. It is also unclear where the Gravettian originated from as it diverges strongly from the Aurignacian (and therefore may not have descended from it). Nonetheless, genetic evidence indicates that not all Aurignacian bloodlines went extinct.
Hypotheses for Gravettian genesis include evolution: in central Europe from the Szeletian (which developed from the Bohunician) which existed 41,000 to 37,000 years ago; or from the Ahmarian or similar cultures from the Near East or the Caucasus that existed before 40,000 years ago. It is further debated where the earliest occurrence is identified, with the former hypothesis arguing for Germany about 37,500 years ago, and the latter III rockshelter in Crimea about 38 to 36 thousand years ago. In either case, the appearance of the Gravettian coincides with a significant temperature drop. Also around 37,000 years ago, the founder population of all later early modern humans existed, and Europe would remain in genetic isolation from the rest of the world for the next 23,000 years.
Last Glacial Maximum
Around 29,000 years ago, marine isotope stage 2 began and cooling intensified. This peaked about 21,000 years ago during the Last Glacial Maximum (LGM) when Scandinavia, the Baltic region, and the British Isles were covered in glaciers, and winter sea ice reached the French seaboard. The Alps were also covered in glaciers, and most of Europe was polar desert, with mammoth steppe and forest steppe dominating the Mediterranean coast. Consequently, large swathes of Europe were uninhabitable, and two distinct cultures emerged with unique technologies to adapt to the new environment: the Solutrean in southwestern Europe, which invented brand new technologies, and the Epi-Gravettian from Italy to the East European Plain, which adapted the previous Gravettian technologies. Solutrean peoples inhabited the permafrost zone, whereas Epi-Gravettian peoples appear to have stuck to less harsh, seasonally frozen areas. Relatively few sites are known through this time.
The glaciers began retreating about 20,000 years ago, and the Solutrean evolved into the Magdalenian, which would recolonise Western and Central Europe over the next couple thousand years. Starting during the Older Dryas roughly 14,000 years ago, Final Magdalenian traditions appear, namely the Azilian, Hamburgian, and Creswellian. During the Bølling–Allerød warming, Near Eastern genes began showing up in the indigenous Europeans, indicating the end of Europe's genetic isolation. Possibly due to the continual reduction of European big game, the Magdalenian and Epi-Gravettian were completely replaced by the Mesolithic by the beginning of the Holocene.
Mesolithic
Europe was completely re-peopled during the Holocene climatic optimum from 9 to 5 thousand years ago. Mesolithic Western Hunter-Gatherers (WHG) contributed significantly to the present-day European genome, alongside Ancient North Eurasians (ANE) which descended from the Siberian Mal'ta–Buret' culture and Caucasus Hunter-Gatherers (CHG). Most present-day Europeans have a 40–60% WHG ratio, and the 8,000 year old Mesolithic Loschbour man seems to have had a similar genetic makeup. Near Eastern Neolithic farmers which split from the European hunter-gatherers about 40,000 years ago started to spread out across Europe by 8,000 years ago, ushering in the Neolithic with Early European Farmers (EEF). EEF contribute about 30% of ancestry to present-day Baltic populations, and up to 90% in present-day Mediterranean populations. The latter may have inherited WHG ancestry via EEF introgression. The Eastern Hunter-Gatherers (EHG) population identified around the steppes of the Urals also dispersed, and the Scandinavian Hunter-Gatherers appear to be a mix of WHG and EHG. Around 4,500 years ago, the immigration of the Yamnaya and Corded Ware cultures from the eastern steppes brought the Bronze Age, the Proto-Indo-European language, and more or less the present-day genetic makeup of Europeans.
Cro-Magnon rock shelter
In 1863, a railway was constructed leading to Les Eyzies, a hamlet in the commune of Les Eyzies-de-Tayac-Sireuil, Dordogne, southwestern France. In 1868, M. François Berthoumeyrou, a contractor, was commissioned to make a road along the railway connecting the new Les Eyzies train station. In March, the road workers dug up a rock shelter, around deep, on the left bank of the Vézère River. They found flint stone tools, animal bones, and human remains. Berthoumeyrou ordered his men to halt the work and informed the government officials of the discovery. He also informed a local geologist, Abel Laganne, who recovered ornaments, more flints, and two human skulls. As assigned by the French Minister of Public Instruction Victor Duruy to verify the finds, Louis Lartet made systematic excavation and discovered additional human remains, animal bones, stone tools, and ornaments. He deliberated the discovery before the meeting of the Society of Anthropology of Paris on 21 May, the proceedings published in its journal Bulletins et Mémoires de la Société d'Anthropologie de Paris. He described the site as a cemetery and identified the humans as cave dwellers. The site is called Abri de Cro-Magnon (Cro-Magnon rock shelter), now recognised as a UNESCO World Heritage Site. Abri means "rock shelter" in French, cro means "hole" in Occitan, and Magnon was the landowner. The original human remains were brought to and preserved at the National Museum of Natural History in Paris.
The number of individuals at the Cro-Magnon rock shelter has eluded scientists for over a century. The original workers reported that they found 15 skeletons. In his report, Lartet identified five individuals based on the skulls, three of them males (designated Cro-Magnon 1, 3 and 4), one female (Cro-Magnon 2) and an infant (Cro-Magnon 5). In 1868, anatomist Paul Broca noted five adults and several infants. Broca introduced the specimen names and called Cro-Magnon 1 Le Vieillard, from which the name "Old Man" became popularly used. After complete analyses of individual bones by early 2000s, it became generally agreed that the rock shelter contained 140 human remains from at least eight individuals: four adults and four infant.
Classification
Fossils and artifacts from the Palaeolithic had actually been known for decades, but these were interpreted in a creationist model (as the concept of evolution had not yet been conceived). For example, the Aurignacian Red Lady of Paviland (actually a young man) from South Wales was described by geologist Reverend William Buckland in 1822 as a citizen of Roman Britain. Subsequent authors contended the skeleton was either evidence of antediluvian (before the Great Flood) people in Britain, or was swept far from the inhabited lands farther south by the powerful floodwaters. Buckland assumed the specimen was a woman because he was adorned with jewellery (shells, ivory rods and rings, and a wolf-bone skewer), and Buckland also stated (possibly in jest) the jewellery was evidence of witchcraft. Around this time, the uniformitarianism movement was gaining traction, headed principally by Charles Lyell, arguing that fossil materials well predated the biblical chronology.
Following Charles Darwin's 1859 On the Origin of Species, racial anthropologists and raciologists began splitting off putative species and subspecies of present-day humans based on unreliable and pseudoscientific metrics gathered from anthropometry, physiognomy, and phrenology continuing into the 20th century. This was a continuation of Carl Linnaeus' 1735 Systema Naturae, where he invented the modern classification system, in doing so classifying humans as Homo sapiens with several putative subspecies classifications for different races based on racist behavioural definitions (in accord with historical race concepts): "H. s. europaeus" (European descent, governed by laws), "H. s. afer" (African descent, impulse), "H. s. asiaticus" (Asian descent, opinions), and "H. s. americanus" (Native American descent, customs). The racial classification system was quickly extended to fossil specimens, including both Cro-Magnons and the Neanderthals, after the true extent of their antiquity was recognised. In 1869, Lartet had proposed the subspecies classification "H. s. fossilis" for the Cro-Magnon remains. Other supposed fossil human species included (among many others): "H. pre-aethiopicus" for a skull from Dordogne which had "Ethiopic affinities"; "H. predmosti" or "H. predmostensis" for a series of skulls from Brno, Czech Republic, purportedly transitional between Neanderthals and Cro-Magnons; H. mentonensis for a skull from Menton, France; "H. grimaldensis" for Grimaldi man and other skeletons near Grimaldi, Monaco; and "H. aurignacensis" or "H. a. hauseri" for the Combe-Capelle skull.
These fossil races, alongside Ernst Haeckel's idea of there being backwards races which require further evolution (social darwinism), popularised the view in European thought that the civilised white man had descended from primitive, low browed ape ancestors through a series of savage races. Prominent brow-ridges were classified as an ape-like trait; consequently, Neanderthals (as well as Aboriginal Australians) were considered a lowly race. These European fossils were considered to have been the ancestors to specifically living European races. Among the earliest attempts to classify Cro-Magnons was done by racial anthropologists Joseph Deniker and William Z. Ripley in 1900, who characterised them as tall and intelligent proto-Aryans, superior to other races, who descended from Scandinavia and Germany. Further race theories revolved around progressively lighter, blonder, and superior races evolving in Central Europe and spreading out in waves to replace their darker ancestors, culminating in the "Nordic race". These aligned well with Nordicism and Pan-Germanism (that is, Aryan supremacy), which gained popularity just before World War I, and was notably used by the Nazis to justify the conquest of Europe and the supremacy of the German people in World War II. Stature was among the characteristics used to distinguish these sub-races, so taller Cro-Magnons such as specimens from the French Cro-Magnon, Paviland, and Grimaldi sites were classified as ancestral to the "Nordic race", and smaller ones such as Combe-Capelle and Chancelade man (both also from France) were considered the forerunners of either the "Mediterranean race" or "Eskimoids". The Venus figurinessculptures of pregnant women with exaggerated breasts and thighswere used as evidence of the presence of the "Negroid race" in Palaeolithic Europe, because they were interpreted as having been based on real women with steatopygia (a condition which causes thicker thighs, common in the women of the San people of Southern Africa) and the hairdos of some are supposedly similar to some seen in Ancient Egypt. By the 1940s, the positivism movementwhich fought to remove political and cultural bias from science and had begun about a century earlierhad gained popular support in European anthropology. Due to this movement and raciology's associations with Nazism, raciology fell out of practice.
Demographics
The beginning of the Upper Palaeolithic is thought to have been characterised by a major population increase in Europe, with the human population of western Europe possibly increasing by a factor of 10 in the Neanderthal/modern human transition. The archaeological record indicates that the overwhelming majority of Palaeolithic people (both Neanderthals and modern humans) died before reaching the age of 40, with few elderly individuals recorded. It is possible the population boom was caused by a significant increase in fertility rates.
A 2005 study estimated the population of Upper Palaeolithic Europe by calculating the total geographic area which was inhabited based on the archaeological record; averaged the population density of Chipewyan, Hän, Hill people, and Naskapi Native Americans which live in cold climates and applied to this to Cro-Magnons; and assumed that population density continually increased with time calculated by the change in the number of total sites per time period. The study calculated that: from 40 to 30 thousand years ago the population was roughly 1,700–28,400 (average 4,400); from 30 to 22 thousand years ago roughly 1,900–30,600 (average 4,800); from 22 to 16.5 thousand years ago roughly 2,300–37,700 (average 5,900); and 16.5–11.5 thousand years ago roughly 11,300–72,600 (average 28,700).
Following the LGM, Cro-Magnons are thought to have been much less mobile and featured a higher population density, indicated by seemingly shorter trade routes as well as symptoms of nutritional stress.
Biology
Physical attributes
Cro-Magnons are physically similar to present-day humans, with a globular braincase, completely flat face, gracile brow ridge, and defined chin. However, the bones of Cro-Magnons are somewhat thicker and more robust. The earliest Cro-Magnons often display features that are reminiscent of those seen in Neanderthals. Aurignacians in particular featured a higher proportion of traits somewhat reminiscent of Neanderthals, such as (though not limited to) a slightly flattened skullcap and consequent occipital bun protruding from the back of the skull (the latter could be quite defined). Their frequency significantly diminished in Gravettians, and in 2007, palaeoanthropologist Erik Trinkaus concluded these were remnants of Neanderthal introgression which were eventually bred out of the gene pool in his review of the relevant morphology.
For 28 modern human specimens from 190 to 25 thousand years ago, average brain volume was estimated to have been about , and for 13 Cro-Magnons about . In comparison, present-day humans average , which is notably smaller. This is because the Cro-Magnon brain, though within the variation for present-day humans, exhibits longer average frontal lobe length and taller occipital lobe height. The parietal lobes, however, are shorter in Cro-Magnons. It is unclear if this could equate to any functional differences between present-day and early modern humans.
In early Upper Palaeolithic western Europe (before the LGM), 20 men and 10 women were estimated to have averaged and , respectively. This is similar to post-industrial modern northern Europeans. In contrast, in a sample of 21 and 15 late Upper Palaeolithic western European men and women (after the LGM), the averages were and , similar to pre-industrial modern humans. It is unclear why earlier Cro-Magnons were taller, especially considering that cold-climate creatures are short-limbed and thus short-statured to better retain body heat (Allen's rule). This has variously been explained as: retention of a hypothetically tall ancestral condition; higher-quality diet and nutrition due to the hunting of megafauna which later became uncommon or extinct; functional adaptation to increase stride length and movement efficiency while running during a hunt; increasing territorialism among later Cro-Magnons reducing gene flow between communities and increasing inbreeding rate; or statistical bias due to small sample size or because taller people were more likely to achieve higher status in a group before the LGM and thus were more likely to be buried and preserved.
Prior to genetic analysis, it was generally assumed that Cro-Magnons, like present-day Europeans, were light skinned as an adaptation to better generate vitamin D from the less luminous sun farther north. However, of the three predominant genes responsible for lighter skin in present-day EuropeansKITLG, SLC24A5, and SLC45A2the latter two, as well as the TYRP1 gene associated with lighter hair and eye colour, experienced positive selection as late as 19 to 11 thousand years ago during the Mesolithic transition. Such a late timing was potentially caused by overall low population and/or low cross-continental movement required for such an adaptive shift in skin, hair, and eye colouration. However, KITLG experienced positive selection in Cro-Magnons (as well as East Asians) beginning approximately 30,000 years ago.
Genetics
While anatomically modern humans have been present outside of Africa during some isolated time intervals potentially as early as 250,000 years ago, present-day non-Africans descend from the out of Africa expansion which occurred around 65–55 thousand years ago. This movement was an offshoot of the rapid expansion within East Africa associated with mtDNA haplogroup L3. Mitochondrial DNA analysis places Cro-Magnons as the sister group to Upper Palaeolithic East Asian groups, divergence occurring roughly 50,000 years ago.
Initial genomic studies on the earliest Cro-Magnons in 2014, namely on the 37,000-year-old Kostenki-14 individual, identified 3 major lineages which are also present in present-day Europeans: one related to all later Cro-Magnons; a "Basal Eurasian" lineage which split from the common ancestor of present-day Europeans and East Asians before they split from each other; and another related to a 24,000-year-old individual from the Siberian Mal'ta–Buret' culture (near Lake Baikal). Contrary to this, Fu et al. (2016), evaluating much earlier European specimens, including Ust'-Ishim and Oase-1 from 45,000 years ago, found no evidence of a "Basal Eurasian" component to the genome, nor did they find evidence of Mal'ta–Buret' introgression when looking at a wider range of Cro-Magnons from the entire Upper Palaeolithic. The study instead concluded that such a genetic makeup in present-day Europeans stemmed from Near Eastern and Siberian introgression occurring predominantly in the Neolithic and the Bronze Age (though beginning by 14,000 years ago), but all Cro-Magnons specimens including and following Kostenki-14 contributed to the present-day European genome and were more closely related to present-day Europeans than East Asians. Earlier Cro-Magnons (10 tested in total), on the other hand, did not seem to be ancestral to any present-day population, nor did they form any cohesive group in and of themselves, each representing either completely distinct genetic lineages, admixture between major lineages, or have highly divergent ancestry. Because of these, the study also concluded that, beginning roughly 37,000 years ago, Cro-Magnons descended from a single founder population and were reproductively isolated from the rest of the world. The study reported that an Aurignacian individual from Grottes de Goyet, Belgium, has more genetic affinities to the Magdalenian inhabitants of Cueva de El Mirón, Spain, than to more or less contemporaneous eastern European Gravettians.
Haplogroups identified in Cro-Magnons are the patrilineal (from father to son) Y-DNA haplogroups the earliest C1, the latest IJ, and K2a; and matrilineal (from mother to child) mt-DNA haplogroup N, R, and U. Y-haplogroup IJ descended from Southwest Asia. Haplogroup I emerged about 35 to 30 thousand years ago, either in Europe or West Asia. Mt-haplogroup U5 arose in Europe just prior to the LGM, between 35 and 25 thousand years ago. The 14,000 year old Villabruna 1 skeleton from Ripari Villabruna, Italy, is the oldest identified bearer of Y-haplogroup R1b (R1b1a-L754* (xL389,V88)) found in Europe, likely brought in from eastern introgression. The Azilian "Bichon man" skeleton from the Swiss Jura was found to be associated with the WHG lineage. He was a bearer of Y-DNA haplogroup I2a and mtDNA haplogroup U5b1h.
Genetic evidence suggests early modern humans interbred with Neanderthals. Genes in the present-day genome are estimated to have entered about 65 to 47 thousand years ago, most likely in West Asia soon after modern humans left Africa. In 2015, the 40,000 year old modern human Oase 1 was found to have had 6–9% (point estimate 7.3%) Neanderthal DNA, indicating a Neanderthal ancestor up to four to six generations earlier, but this hybrid Romanian population does not appear to have made a substantial contribution to the genomes of later Europeans. Therefore, it is possible that interbreeding was common between Neanderthals and Cro-Magnons which did not contribute to the present-day genome. The percentage of Neanderthal genes gradually decreased with time, which could indicate they were maladaptive and were selected out of the gene pool.
Valini et al. 2022 found that Europe was populated by three distinct lineages. The earliest inhabitants (represented by Zlaty Kun ~50kya) split from the common Eurasian lineage before the divergence of Western and Eastern Eurasians, but after the divergence of the hypothetical Basal-Eurasians. This earliest sample did not cluster with any modern human population, including Africans, and died out without leaving ancestry to modern peoples. The second wave (represented by Bacho Kiro ~45kya) appeared to be more closely related to modern East Asians and Australasians compared to Europeans, suggesting that this lineage split initially after the formation of Eastern Eurasians, and migrated instead northwestwards into Europe. This lineage similarly did not contribute ancestry to later populations, and was replaced by a West-Eurasian lineage (~40kya), which expanded into Europe and Siberia. Proper Aurignacian people (40-26kya) were still part of a large Western Eurasian "meta-population", related to Paleolithic Siberian and Western Asian populations. Earlier samples (such as the Bacho Kiro sample) were relatively closer to East Asians and Australasians, although distinct from them.
In a genetic study published in Nature in March 2023, the authors found that the ancestors of the Western Hunter-Gatherers (WHGs) were populations associated with the Epigravettian culture, which largely replaced populations associated with the Magdalenian culture about 14,000 years ago. The Magdalenian-associated individuals descended from populations associated with the western Gravettian, Solutrean and Aurignacian cultures.
Culture
There is a notable technological complexification coinciding with the replacement of Neanderthals with Cro-Magnons in the archaeological record, and so the terms "Middle Palaeolithic" and "Upper Palaeolithic" were created to distinguish between these two time periods. Largely based on western European archaeology, the transition was dubbed the "Upper Palaeolithic Revolution," (extended to be a worldwide phenomenon) and the idea of "behavioural modernity" became associated with this event and early modern cultures. It is largely agreed that the Upper Palaeolithic seems to feature a higher rate of technological and cultural evolution than the Middle Palaeolithic, but it is debated if behavioural modernity was truly an abrupt development or was a slow progression initiating far earlier than the Upper Paleolithic, especially when considering the non-European archaeological record. Practices considered modern include: the production of microliths, the common use of bone and antler, the common use of grinding and pounding tools, high quality evidence of body decoration and figurine production, long-distance trade networks, and improved hunting technology. In regard to art, the Magdalenian produced some of the most intricate Palaeolithic pieces, and they even elaborately decorated normal, everyday objects.
Hunting and gathering
Historically, ethnographic studies on hunter-gatherer subsistence strategies have long placed emphasis on sexual division of labour and most especially the hunting of big game by men. This culminated in the 1966 book Man the Hunter, which focuses almost entirely on the importance of male contributions of food to the group. As this was published during the second-wave feminism movement, this was quickly met with backlash from many female anthropologists. Among these was Australian archaeologist Betty Meehan in her 1974 article Woman the Gatherer, who argued that women play a vital role in these communities by gathering more reliable food plants and small game, as big game hunting has a low success rate. The concept of "Woman the Gatherer" has since gained significant support.
Nonetheless, Palaeolithic peoples are typically characterised as having had a meat-heavy diet, with an emphasis on big prey items. The LGM extirpated most European megafauna (Quaternary extinction event), and similarly post-LGM peoples tend to have a higher rate of nutrient-deficiency-related ailments, including a reduction in average height. Probably due to the contraction of habitable territory, these bands were subsisting on a much broader food range of plants, smaller animals, and aquatic resources (broad spectrum revolution).
Prey items
It has typically been assumed that Cro-Magnons closely studied prey habits in order to maximise return depending on the season. For example, large mammals (including red deer, horses, and ibex) congregate seasonally, and reindeer were possibly seasonally plagued by insects rendering fur sometimes unsuitable for hideworking. In particularly southwestern France, Cro-Magnons depended heavily upon reindeer, and so it is hypothesised that these communities followed the herds, with occupation of the Perigord and the Pyrenees only occurring in the summer. Epi-Gravettian communities, especially, generally focused on hunting one species of large game, most commonly horse or bison.
There is much evidence that Cro-Magnons, especially in western Europe following the LGM, corralled large prey animals into natural confined spaces (such as against a cliff wall, a cul-de-sac, or a water body) in order to efficiently slaughter whole herds of animals (game drive system). They seem to have scheduled mass kills to coincide with migration patterns, in particular for red deer, horses, reindeer, bison, aurochs, and ibex, and occasionally woolly mammoths. Game drive systems became especially popular following the LGM, possibly an extension of increasing food return.
There are also multiple examples of consumption of seasonally abundant fish, becoming more prevalent in the mid-Upper-Palaeolithic. Nonetheless, Magdalenian peoples appear to have had a greater dependence on small animals, aquatic resources, and plants than predecessors, probably due to the relative scarcity of European big game following the LGM (Quaternary extinction event).
It is possible that human activity, in addition to the rapid retreat of favourable steppeland, inhibited recolonisation of most of Europe by megafauna following the LGM (such as mammoths, woolly rhinoceroses, Irish elk, and cave lions), in part contributing to their extinction which occurred by the beginning of or well into the Holocene depending on the species.
Plant items
Most archaeobotanical studies on Pleistocene plant gathering and processing techniques focus on the end of the Paleolithic as precursors to agriculture in the Neolithic. While isotopic studies indicate nearly all nutritional requirements of Palaeolithic populations may have been mostly satisfied by meat, similar to Inuit cuisine, the issue of offsetting protein poisoning (nitrogen overloading) by eating fatty foods (blubber most especially in the Inuit diet) becomes problematic in more temperate climates with leaner prey. The isotopic score for Palaeolithic peoples are comparable to Inuit with a diet comprising 1–4% plant components, but also to Onge from the tropical Andaman Islands, Paraguayan Aché, Arnhem Land Aboriginals, and Venezuelan Hiwi whose diets comprise up to 25% plant components. Thus, the importance of plants may have varied greatly depending on local climatic conditions.
The Palaeolithic archaeobotanical record outside Europe (especially in the Middle East) shows these peoples were capable of processing a massive range of plant resources, in the 20,000 year old Israeli Ohalo II site as many as 150 types of seeds, fruits, nuts, and starches. There are several European Mediterranean cave sites dating to near the end of the Palaeolithic which suggest the inhabitants were harvesting acorn, almond, pistacia, hawthorn, wild pear, blackthorn, rosehip, sorbus, and grape. Multiple German sites bear evidence of wild cherry, blackberry, dewberry, and raspberry consumption. The Palaeolithic archaeobotanical record becomes sparser farther north, but water caltrop and water lily tubers are consumed at least in the northern European Mesolithic. It is unclear to what extent they would process or pretreat otherwise inedible plants which require multiple steps (such as a combination of fermenting, grinding, boiling, etc.).
Weaponry
For weapons, Cro-Magnons crafted spearpoints using predominantly bone and antler, possibly because these materials were readily abundant. Compared to stone, these materials are compressive, making them fairly shatterproof. These were then hafted onto a shaft to be used as javelins. It is possible that Aurignacian craftsmen further hafted bone barbs onto the spearheads, but firm evidence of such technology is recorded earliest 23,500 years ago, and does not become more common until the Mesolithic. Aurignacian craftsmen produced lozenge-shaped (diamond-like) spearheads. By 30,000 years ago, spearheads were manufactured with a more rounded-off base, and by 28,000 years ago spindle-shaped heads were introduced.
During the Gravettian, spearheads with a bevelled base were being produced. By the beginning of the LGM, the spear-thrower was invented in Europe, which can increase the force and accuracy of the projectile. A possible boomerang made of mammoth tusk was identified in Poland (though it may have been unable to return to the thrower), and dating to 23,000 years ago, it would be the oldest known boomerang.
Stone spearheads with leaf- and shouldered-points become more prevalent in the Solutrean. Both large and small spearheads were produced in great quantity, and the smaller ones may have been attached to projectile darts. Archery was possibly invented in the Solutrean, though less ambiguous bow technology is first reported in the Mesolithic.
Bone technology was revitalised in the Magdalanian, and long-range technology as well as harpoons become much more prevalent. Some harpoon fragments are speculated to have been leisters or tridents, and true harpoons are commonly found along seasonal salmon migration routes.
Society
Social system
As opposed to the patriarchy prominent in historical societies, the idea of a prehistoric predominance of either matriarchy or matrifocal families (centred on motherhood) was first supposed in 1861 by legal scholar Johann Jakob Bachofen. The earliest models of this believed that monogamy was not widely practiced in ancient timesthus, the paternal line was resultantly more difficult to keep track of than the maternalresulting in a matrilineal (and matriarchal) society. Matriarchs were then conquered by patriarchs at the dawn of civilisation. The switch from matriarchy to patriarchy and the hypothetical adoption of monogamy was seen as a leap forward. However, when the first Palaeolithic representations of humans were discovered, the so-called Venus figurineswhich typically feature pronounced breasts, buttocks, and vulvas (areas generally sexualised in present-day Western Culture)they were initially interpreted as pornographic in nature. The first Venus discovered was named the "Vénus impudique" ("immodest Venus") by the discoverer Paul Hurault, 8th Marquis de Vibraye, because it lacked clothes and had a prominent vulva. The name "Venus", after the Roman goddess of beauty, in itself implies an erotic function. Such a pattern in the representation of the human form led to suggestions that human forms were generally pornography for men, meaning men were primarily responsible for artwork and craftsmanship in the Palaeolithic whereas women were tasked with child rearing and various domestic works. This would equate to a patriarchal social system.
The Palaeolithic matriarchy model was adapted by prominent communist Friedrich Engels, who instead argued that women were robbed of power by men due to economic changes which could only be undone with the adoption of communism (Marxist feminism). The former sentiment was adopted by the first-wave feminism movement, who attacked the patriarchy by making Darwinist arguments of a supposed natural egalitarian or matrifocal state of human society instead of patriarchal, as well as interpreting the Venuses as evidence of mother goddess worship as part of some matriarchal religion. Consequently, by the mid-20th century, the Venuses were primarily interpreted as evidence of some Palaeolithic fertility cult. Such claims died down in the 1970s as archaeologists moved away from the highly speculative models produced by the previous generation. Through the second-wave feminism movement, the prehistoric matriarchal religion hypothesis was primarily propelled by Lithuanian-American archaeologist Marija Gimbutas. Her interpretations of the Palaeolithic were notably involved in the Goddess movement. Equally ardent arguments against the matriarchy hypothesis have also been prominent, such as American religious scholar Cynthia Eller's 2000 The Myth of Matriarchal Prehistory.
Looking at the archaeological record, depictions of women are markedly more common than of men. In contrast to the commonplace Venuses in the Gravettian, Gravettian depictions of men are rare and contested, the only reliable one being a fragmented ivory figurine from the grave of a Pavlovian site in Brno, Czech Republic (it is also the only statuette found in a Palaeolithic grave). 2-D Magdalenian engravings from 15 to 11 thousand years ago do depict males, indicated by an erect penis and facial hair, though profiles of women with an exaggerated buttock are much more common. There are less than 100 depictions of males in the Cro-Magnons archaeological record (of them, about a third are depicted with erections.) On the other hand, most individuals which received a burial (which may have been related to social status) were men. Anatomically, the robustness of limbs (which is an indicator of strength) between Cro-Magnon men and women were consistently not appreciably different from each other. Such low levels of sexual dimorphism through the Upper Pleistocene could potentially mean that sexual division of labour, which characterises historic societies (both agricultural and hunter-gatherer), only became commonplace in the Holocene.
Trading
The Upper Palaeolithic is characterised by evidence of expansive trade routes and the great distances at which communities could maintain interactions. The early Upper Palaeolithic is especially known for highly mobile lifestyles, with Gravettian groups (at least those analysed in Italy and Moravia, Ukraine) often sourcing some raw materials upwards of . However, it is debated if this represents sample bias, and if western and northern Europe were less mobile. Some cultural practices such as creating Venus figurines or specific burial rituals during the Gravettian stretched across the continent. Genetic evidence suggests that, despite strong evidence of cultural transmission, Gravettian Europeans did not introgress into Siberians, meaning there was a movement of ideas but not people between Europe and Siberia. At the 30,000 year old Romanian Poiana Cireşului site, perforated shells of the Homalopoma sanguineum sea snail were recovered, which is significant as it inhabits the Mediterranean at nearest away. Such interlinkage may have been an important survival tool, with the steadily deteriorating climate. Given low estimated population density, this may have required a rather complex, cross-continental social organisation system.
By and following the LGM, population densities are thought to have been much higher with the marked decrease of habitable lands, resulting in more regional economies. Decreased land availability could have increased travel distance, as habitable refugia may have been few and far between, and increasing population density within these few refugia would have made long-distance travel less economic. This trend continued into the Mesolithic with the adoption of sedentism. Nonetheless, there is some evidence of long-distance Magdalenian trade routes. For example, at Lascaux, a painting of a bull had remnants of the manganese mineral hausmannite, which can only be manufactured in heat in excess of , which was probably impossible for Cro-Magnons; this means they likely encountered natural hausmannite which is known to be found away in the Pyrenees. Unless there was a hausmannite source much closer to Lascaux which has since been depleted, this could mean that there was a local economy based on manganese ores. Also, at Ekain, Basque Country, the inhabitants were using the locally rare manganese mineral groutite in their paintings, which they possibly mined out of the cave itself. Based on the distribution of Mediterranean and Atlantic seashell jewellery even well inland, there may have been a network during the Late Glacial Interstadial (14 to 12 thousand years ago) along the rivers Rhine and Rhône in France, Germany, and Switzerland.
Housing
Cro-Magnon cave sites quite often feature distinct spatial organisation, with certain areas specifically designated for specific activities, such as hearth areas, kitchens, butchering grounds, sleeping grounds, and trash pile. It is difficult to tell if all material from a site was deposited at about the same time, or if the site was used multiple times. Cro-Magnons are thought to have been quite mobile, indicated by the great lengths of trade routes, and such a lifestyle was likely supported by the constructions of temporary shelters in open environments, such as huts. Evidence of huts is typically associated with a hearth.
Magdalenian peoples, especially, are thought to have been highly migratory, following herds while repopulating Europe, and several cave and open-air sites indicate the area was abandoned and revisited regularly. The 19,000 year old Peyre Blanque site, France, and at least the area around it may have been revisited for thousands of years. In the Magdalenian, stone lined rectangular areas typically were interpreted as having been the foundations or flooring of huts. At Magdalenian Pincevent, France, small, circular dwellings were speculated to have existed based on the spacing of stone tools and bones; these sometimes featured an indoor hearth, work area, or sleeping space (but not all at the same time). A 23,000 year old hut from the Israeli Ohalo II was identified as having used grasses as flooring or possibly bedding, but it is unclear if Cro-Magnons also lined their huts with grass or instead used animal pelts. A 13,800 year old slab from Molí del Salt, Spain, has 7 dome-shaped figures engraved onto it, which are postulated to represent temporary dome-shaped huts.
Over 70 dwellings constructed by Cro-Magnons out of mammoth bones have been identified, primarily from the Russian Plain, possibly semi-permanent hunting camps. They seem to have built tipis and yarangas. These were typically constructed following the LGM after 22,000 years ago by Epi-Gravettian peoples; the earliest hut identified comes from the Molodova I site, Ukraine, which was dated to 44,000 years ago (making it possible it was built by Neanderthals). Typically, these huts measured in diameter, or if oval shaped. Huts could get as small as . One of the largest huts has a diameter of a 25,000 year old hut identified in Kostenki, Russiaand was constructed out of 64 mammoth skulls, but given the little evidence of occupation, this is postulated to have been used for food storage rather than as a living space. Some huts have burned bones, which has typically been interpreted as bones used as fuel for fireplaces due to the scarcity of firewood, and/or disposal of waste. A few huts, however, have evidence of wood burning, or mixed wood/bone burning.
Mammoth hut foundations were generally made by pushing a great quantity of mammoth skulls into the ground (most commonly, though not always, with the tusks facing up to possibly be used as further supports), and the walls by putting into the ground vertically shoulder blades, pelvises, long bones, jaws, and the spine. Long bones were often used as poles, commonly placed on the end of another long bone or in the cavity of where tusk used to be. Foundation may have extended as far as underground. Generally, multiple huts were built in a locality, placed apart depending on location. Tusks may have been used to make entrances, skins pulled over for roofing, and the interior sealed up by loess dug out of pits. Some architectural decisions seem to have been purely for aesthetics, best seen in the 4 Epi-Gravettian huts from Mezhyrich, Mezine, Ukraine, where jaws were stacked to create a chevron or zigzag pattern in 2 huts, and long bones were stacked to create horizontal or vertical lines in respectively 1 and 2 huts. The chevron was a commonly used symbol on the Russian Plain, painted or engraved on bones, tools, figurines, and mammoth skulls.
Dogs
At some point in time, Cro-Magnons domesticated the dog, probably as a result of a symbiotic hunting relationship. DNA evidence suggests that present-day dogs split from wolves around the beginning of the LGM. However, potential Palaeolithic dogs have been found preceding thisnamely the 36,000-year-old Goyet dog from Belgium and the 33,000-year-old Altai dog from Siberiawhich could indicate there were multiple attempts at domesticating European wolves. These "dogs" had a wide size range, from over in height in eastern Europe to less than 30–45 cm (1 ft–1 ft 6 in) in central and western Europe, and in all of Europe. These "dogs" are identified by having a shorter snout and skull, and wider palate and braincase than contemporary wolves. Nonetheless, an Aurignacian origin for domestication is controversial.
At the 27 to 24 thousand year old Předmostí site, Czech Republic, 3 "dogs" were identified with their skulls perforated (probably to extract the brain), and 1 had a mammoth bone in its mouth. The discoverers interpreted this as a burial ritual. The 14,500-year-old Bonn-Oberkassel dog from Germany was found buried alongside a 40-year-old man and a 25-year-old woman, as well as traces of red hematite, and is genetically placed as an ancestor to present-day dogs. It was diagnosed with canine distemper virus and probably died between 19 and 23 weeks of age. It would have required extensive human care to survive without being able to contribute anything, suggesting that, at this point, humans and dogs were connected by emotional or symbolic ties rather than purely materialistic personal gain.
The exact utility of these proto-dogs is unclear, but they may have played a vital role in hunting, as well as domestic services such as transporting items or guarding camp or carcasses.
Art
When examples of Upper Palaeolithic art were first discovered in the 19th century in the form of engraved objects, they were assumed to have been "art for art's sake" as Palaeolithic peoples were widely conceived as having been uncultured savages. This model was primarily championed by French archaeologist Louis Laurent Gabriel de Mortillet. Then, detailed paintings found deep within caves were discovered, the first being Cueva de Altamira, Spain, in 1879. The "art for art's sake" model came apart by the turn of the century as more examples of cave art were found in hard-to-reach places in western Europe such as Combarelles and Font-de-Gaume, for which the idea of it being simply a leisure activity became increasingly untenable.
Cave art
Cro-Magnons are well known for having painted or engraved geometric designs, hand stencils, plants, animals, and seemingly human/animal hybrid creatures on cave walls deep inside caves. Typically the same species are represented in caves which have such art, but the total number of species is quite numerous, and namely includes creatures such as mammoths, bison, lions, bears, and ibex. Nonetheless, some caves were dominated by certain forms, such as Grotte de Niaux where over half of the animals are bison. Images could be drawn on top of one another. Landscapes were never depicted, with the exception of a supposed depiction of a volcanic eruption at Chauvet-Pont d'Arc, France, dating to 36,000 years ago. Cave art is found in dark cave recesses, and the artists either lit a fire on the cave floor or used portable stone lamps to see. Drawing materials include black charcoal and red and yellow ochre crayons, but they, along with a variety of other minerals, could also be ground into powder and mixed with water to create paint. Large, flat rocks may have been used as palettes, and brushes may have included reeds, bristles, and twigs, and possibly a blowgun was used to spray paint over less accessible areas. Hand stencils could either be made by holding the hand to the wall and spitting paint over it (leaving a negative image) or by applying paint to the hand and then sticking it to the wall. Some hand stencils are missing fingers, but it is unclear if the artist was actually missing the finger or simply excluded it from the stencil. It has generally been assumed that the larger prints were left by men and the smaller ones by boys, but the exclusion of women entirely may be improbable. Though many hypotheses have been proposed for the symbolism of cave art, it is still debated why these works were created in the first place.
One of the first hypotheses regarding their symbolism was forwarded by French religious historian Salomon Reinach who supposed that, because only animals were depicted on cave walls, the images represented totem veneration, in which a group or a group member identifies with a certain animal associated with certain powers, and honours or respects this animal in some way such as by not hunting it. If this were the case, then Cro-Magnons communities within a region would have subdivided themselves into, for example, a "horse clan", a "bison clan", a "lion clan", and so forth. This was soon contested as some caves contain depictions of animals wounded by projectiles, and generally multiple species are represented.
In 1903, Reinach proposed that the cave art represented sympathetic magic (between the painting and the painting's subject), and by drawing an animal doing some kind of action, the artist believed they were exerting that same action onto the animal. That is, by being the master of the image, they could master the animal itself. The hunting magic modeland the idea that art was magical and utilitarian in Cro-Magnons societygained much popularity in the following decades. In this model, herbivorous prey items were depicted as having been wounded prior to a hunt in order to cast a spell over them; some animals were incompletely depicted to enfeeble them; geometric designs were traps; and human/animal hybrids were sorcerers dressed as animals to gain their power, or were gods ruling over the animals. Many animals were depicted as completely healthy and intact, and sometimes pregnant, which this model interprets as fertility magic to promote reproduction; however, if the animal was a carnivore, then this model says that the depiction served to destroy the animal. By the mid-20th century, this model was being contested because of how few depictions of wounded animals exist; the collection of consumed animal bones in decorated caves often did not match types of animals depicted in terms of abundance; and the magic model does not explain hand stencils.
Following the 1960s, begun by German-American art historian Max Raphael, the study of cave art took on a much more statistical approach, analysing and quantifying items such as the types and distribution of animals depicted, cave topography, and cave wall morphology. Based on such structuralist tests, horses and bovines seem to have been preferentially clustered together typically in a central position, and such binary organisation led to the suggestion that this was sexual symbolism, and some animals and iconography were designated by Cro-Magnons as either male or female. This conclusion has been heavily contested as well, due to the subjective definition of association between two different animals, and the great detail the animals were depicted in, permitting sexual identification (and further, the hypothesis that bison were supposed to be feminine contradicts the finding that many are male).
Also in the late 20th century, with the popularisation of the hypothesis that Cro-Magnons practised shamanism, the human/animal hybrids and geometrical symbols were interpreted within this framework as the visions a shaman would see while in a trance (entoptic phenomena). Opponents mainly attack the comparisons made between Palaeolithic cultures and present-day shamanistic societies for being in some way inaccurate. In 1988, archaeologists David Lewis-Williams and Thomas Dowson suggested trances were induced by hallucinogenic plants containing either mescaline, LSD, or psilocybin; but there is no evidence Cro-Magnons purposefully ate them.
Portable art
Venus figurines are commonly found associated with Cro-Magnons and are the earliest well-acknowledged representation of human figures. These are most frequently found in the Gravettian (notably in the French Upper Périgordian, the Czech Pavlovian, and West Russian Kostenkian) most dating from 29 to 23 thousand years ago. Almost all Venuses depict naked women, and are generally hand-held sized. They feature a downturned head, no face, thin arms which end at or cross over voluminous breasts, rotund buttocks, a distended abdomen (interpreted as pregnancy), tiny and bent legs, and pegged or unnaturally short feet. Venuses vary in proportions which may represent limitations using certain materials over others, or intentional design choices. Eastern European Venuses seem to have more of an emphasis on the breasts and stomach, whereas western European ones emphasise the hips and thighs.
The earliest interpretations of the Venuses believed these were literal representations of women with obesity or steatopygia (a condition where a woman's body stores more fat in the thighs and buttocks, making them especially prominent). Another early hypothesis was that ideal womanhood for Cro-Magnons involved obesity, or that the Venuses were used by men as erotica due to the exaggeration of body parts typically sexualised in Western Culture (as well as the lack of detail to individualising traits such as the face and limbs). Extending present-day Western norms to Palaeolithic peoples was contested, and a counter interpretation is that either Venuses were mother goddesses, or that Cro-Magnons believed depictions of things had magical properties over the subject, and that such a depiction of a pregnant woman would facilitate fertility and fecundity. This is also contested as it assumes women are only thought of in terms of child rearing.
Cro-Magnons also carved perforated batons out of horn, bone, or stone, most commonly through the Solutrean and Magdalenian. Such batons disappear from the archaeological record at the Magdalenian's close. Some batons seem phallic in nature. By 2010, about 60 batons had been hypothesised to be representations of penises (all with erections), of which 30 show decoration, and 23 are perforated. Several phallic batons are depicted as circumcised and seemingly bearing some ornamentation such as piercings, scarification, or tattooing. The purpose of perforated batons has been debated, which suggestions for spiritual or religious purposes, ornamentation or status symbol, currency, drumsticks, tent holders, weaving tools, spear straighteners, spear throwers, or dildos. Unperforated phallic batons, measuring just a few centimetres long to up to , were interpreted as sex toys quite early on.
Depictions of animals were commonly produced by Cro-Magnons. As of 2015, as many as 50 Aurignacian ivory figurines and fragments have been recovered from the German Swabian Jura. Of the discernible figures, most represent mammoths and lions, and a few horses, bison, possibly a rhino, waterfowl, fish, and small mammals. These sculptures are hand-sized and would have been portable works, and some figurines were made into wearable pendants. Some figurines also featured enigmatic engravings, dots, marks, lines, hooks, and criss-cross patterns.
Cro-Magnons also made purely symbolic engravings. There are several plaques of bone or antler (referred to as polishers, spatulas, palettes, or knives) which feature series of equidistantly placed notches, most notably the well-preserved 32,000 year old Blanchard plaque from L'Abri Blanchard, France, which features 24 markings in a seemingly serpentine pattern. The discoverer, British palaeontologist Thomas Rupert Jones, speculated in 1875 this was an early counting system for tallying items such as animals killed, or some other notation system. In 1957, Czech archaeologist Karel Absolon suggested they represent arithmetic. In 1972, Marshack postulated they may be calendars. Also in 1972, Marshack identified 15 to 13 thousand year old Magdalenian plaques bearing small, abstract symbols seemingly into organised blocks or sets, which he interpreted as representing an early writing system.
Czech archaeologist Bohuslav Klíma speculated a complex engraving on a mammoth tusk he discovered in the Gravettian Pavlov site, Czech Republic, as being a map, showing a meandering river centre-left, a mountain centre-right, and a living grounds at the centre indicated by a double circle. A few similar engravings have been identified across Europe (in particular the Russian Plain), which he also postulated were maps, plans, or stories.
Body art
Cro-Magnons are commonly associated with large pieces of pigments ("crayons"), namely made of red ochre. For Cro-Magnons, it is typically assumed that ochre was used for some symbolic purposes, most notably for cosmetics such as body paint. This is because ochre in some sites had to be imported from very long distances, and it is also associated with burials. It is unclear why they specifically chose red ochre instead of other colours. In terms of colour psychology, popular hypotheses include the putative "female cosmetic coalitions" hypothesis and the "red dress effect". It is also possible that ochre was chosen for its utility, such as an ingredient for adhesives, hide tanning agent, insect repellent, sunscreen, medicinal properties, dietary supplement, or as a soft hammer. Cro-Magnons appear to have been using grinding and crushing tools to process ochre before applying it to the skin.
In 1962, French archaeologists Saint-Just and Marthe Péquart identified bi-pointed needles in the Magdalenian Le Mas-d'Azil, which they speculated might have been used in tattooing. Hypothesised depictions of penises from most commonly the Magdalenian (though a few dating back to the Aurignacian) appear to be decorated with tattoos, scarification, and piercings. Designs include lines, plaques, dots or holes, and human or animal figures.
Clothing
Cro-Magnons produced beads, which are typically assumed to have been attached to clothing or portable items as body decoration. Beads had already been in use since the Middle Palaeolithic, but production dramatically increased in the Upper Palaeolithic. It is unclear why communities chose specific raw materials over other ones, and they seem to have upheld local bead making traditions for a very long time. For example, Mediterranean communities used specific types of marine shells to make beads and pendants for more than 20,000 years; and central and western European communities often used pierced animal (and less commonly human) teeth. In the Aurignacian, beads and pendants were being made of shells, teeth, ivory, stone, bone, and antler; and there are a few examples of use of fossil materials including a belemnite, nummulite, ammonite, and amber. They may have also been producing ivory and stone rings, diadems, and labrets. Beads could be manufactured in numerous different styles, such as conical, elliptical, drop-shaped, disc-shaped, ovoid, rectangular, trapezoidal, and so on. Beads may have been used to facilitate social communication, to display the wearer's socio-economic status, as they could have been capable of communicating labour costs (and thereby, a person's wealth, energy, connections, etc.) simply by looking at them. The distribution of ornaments on buried Gravettian individuals, and the likeliness that most of the buried were dressed with whatever they were wearing upon death, indicates that jewellery was primarily worn on the head as opposed to the neck or the torso.
The Gravettian Dolní Věstonice I and III and Pavlov I sites in Moravia, Czech Republic, yielded many clay fragments with textile impressions. These indicate a highly sophisticated and standardised textile industry, including the production of: single-ply, double-ply, triple-ply, and braided string and cordage; knotted nets; wicker baskets; and woven cloth including simple and diagonal twined cloth, plain woven cloth, and twilled cloth. Some cloths appear to have a design pattern. There are also plaited items which may have been baskets or mats. Due to the wide range of textile gauges and weaves, it is possible they could also produce wall hangings, blankets, bags, shawls, shirts, skirts, and sashes. These people used plant rather than animal fibres, possibly nettle, milkweed, yew, or alder which have historically been used in weaving. Such plant fibre fragments have also been recorded at the Russian Kostenki and Zaraysk as well as the German Gönnersdorf site.
The inhabitants of Dzudzuana Cave, Georgia, appear to have been staining flax fibres with plant-based dyes, including yellow, red, pink, blue, turquoise, violet, black, brown, gray, green, and khaki. The emergence of textiles in the European archaeological record also coincides with the proliferation of the sewing needle in European sites. Ivory needles are found in most late Upper Palaeolithic sites, which could correlate to frequent sewing, and the predominance of small needles (too small to tailor clothes out of hide and leather) could indicate work on softer woven fabrics or accessory stitching and embroidery of leather products.
There is some potential evidence of simple loom technology. However, these have also been interpreted as either hunting implements or art pieces. Rounded objects made of mammoth phalanges from Předmostí and Avdeevo, Russia, may have been loom weights or human figures. Perforated, washer-like ivory or bone discs from across Europe were potentially spindle whorls. A foot-shaped piece of ivory from Kniegrotte, Germany, was possibly a comb or a decorative pendant. On the basis of wearing analyses, Cro-Magnons are also speculated to have used net spacers or weaving sticks. In 1960, French archaeologist Fernand Lacorre suggested that perforated batons were used to spin cordage.
Some Venuses depict hairdos and clothing worn by Gravettian women. The Venus of Willendorf seems to be wearing a cap, possibly woven fabric or made from shells, featuring at least seven rows and an additional two half-rows covering the nape of the neck. It may have been made starting at a knotted centre and spiraling downward from right to left, and then backstitching all the rows to each other. The Kostenki-1 Venus seems to be wearing a similar cap, though each row seems to overlap the other. The Venus of Brassempouy seems to be wearing some nondescript open, twined hair cover. The engraved Venus of Laussel from France seems to be wearing some headwear with rectangular gridding, and could potentially represent a snood. Most East European Venuses with headwear also display notching and checkwork on the upper body which are suggestive of bandeaux (a strip of cloth bordering around the tops of the breasts) with some even featuring straps connecting it to around the neck; these seem to be absent in western European Venuses. Some also wear belts: in eastern Europe, these are seen on the waist; whereas in central and western Europe they are worn on the low hip. The Venus of Lespugue seems to be wearing a plant fibre string skirt comprising 11 cords running behind the legs.
Music
Cro-Magnons are known to have created flutes out of hollow bird bones as well as mammoth ivory, first appearing in the archaeological record with the Aurignacian about 40,000 years ago in the German Swabian Jura. The Swabian Jura flutes appear to have been able to produce a wide range of tones. One virtually complete flute made of the radius of a griffon vulture from Hohle Fels measures in length and in diameter. The bone had been smoothed down and was pierced with holes. These finger holes exhibit cut marks, which could indicate the exact placement of these holes was specifically measured to create concert pitch (that is, to make the instrument in tune) or a scale. The part near the elbow joint had two V-shaped carvings, presumably a mouthpiece. Ivory flutes would have required a great time investment to make, as it requires more skill and precision to craft compared to a bird bone flute. A section of ivory must be sawed off to the correct size, cut in half so it can be hollowed out, and then the two pieces have to be refitted and stuck together by an adhesive in an air-tight seal. Cro-Magnons also created bone whistles out of deer phalanges.
Such sophisticated music technology could potentially speak to a much longer musical tradition than the archaeological record indicates, as modern hunter-gatherers have been documented to create instruments out of: more biodegradable materials (less likely to fossilise) such as reeds, gourds, skins, and bark; more or less unmodified items such as horns, conch shells, logs, and stones; and their weapons, including spear thrower shafts or boomerangs as clapsticks, or a hunting bow.
It is speculated that a few Cro-Magnon artefacts represent bullroarers or percussion instruments such as rasps, but these are harder to prove. One probable bullroarer is identified at Lalinde, France, dating to 14 to 12 thousand years ago, measuring long and decorated with geometric incisions. In the mammoth-bone houses at Mezine, Ukraine, an thigh-bone, a jawbone, a shoulder blade, and a pelvis of a mammoth bear evidence of paint and repeated percussion. These were first proposed by archaeologist Sergei Bibikov to have served as drums, with either a reindeer antler or mammoth tusk fragment also found at the site being used as a drum stick, though this is contested. Other European sites have yielded potential percussion mallets made of mammoth bone or reindeer antler. It is speculated that some Cro-Magnons marked certain sections of caves with red paint which could be struck to produce a note that would resonate throughout the cave chamber, somewhat like a xylophone.
Language
The early modern human vocal apparatus is generally thought to have been the same as that in present-day humans, as the present-day variation of the FOXP2 gene associated with the neurological prerequisites for speech and language ability seems to have evolved within the last 100,000 years, and the modern human hyoid bone (which supports the tongue and facilitates speech) evolved by 60,000 years ago demonstrated by the Israeli Skhul and Qafzeh humans. These indicate Upper Palaeolithic humans had the anatomical basis for language and the same range of potential phonemes (sounds) as present-day humans.
Though Cro-Magnon languages likely contributed to present-day languages, it is unclear what early languages would have sounded like because words denature and are replaced by entirely original words quite rapidly, making it difficult to identity language cognates (a word in multiple different languages which descended from a common ancestor) which originated before 9 to 5 thousand years ago. Nonetheless, it has been controversially hypothesised that Eurasian languages are all related and form the "Nostratic languages" with an early common ancestor existing just after the end of the LGM. In 2013, evolutionary biologist Mark Pagel and colleagues postulated that among "Nostratic languages", frequently used words more often have speculated cognates, and that this was evidence that 23 identified words were "ultraconserved" and supposedly changed very little in use and pronunciation, descending from a common ancestor about 15,000 years ago at the end of the LGM. Archaeologist Paul Heggarty said that Pagel's data was subjective interpretation of supposed cognates, and the extreme volatility of sound and pronunciation of words (for example, Latin [ˈakʷã] (aquam) "water" → French [o] (eau) in just 2,000 years) makes it unclear if cognates can even be identified that far back if they do indeed exist.
Religion
Shamanism
Several Upper Palaeolithic caves feature depictions of seemingly part-human, part-animal chimaeras (typically part bison, reindeer, or deer), variously termed "anthropozoomorphs", "therianthropes", or "sorcerers". These have typically been interpreted as being the centre of some shamanistic ritual, and to represent some cultural revolution and the origins of subjectivity. The oldest such cave drawing has been identified at the 30,000 year old Chauvet Cave, where a figure with a bison upper body and human lower body was drawn onto a stalactite, facing a depiction of a vulva with two tapering legs. The 17,000 year old Grotte de Lascaux, France, has a seemingly dead bird-human hybrid between a rhino and a charging bison, with a bird on top of a pole placed near the figure's right hand. A bird on a stick is used as a symbol of mystical power by some modern shamanistic cultures who believe that birds are psychopomps, and can move between the land of the living and the land of the dead. In these cultures, they believe the shaman can either transform into a bird or use a bird as a spirit guide. The 14,000 year old Grotte des Trois-Frères, France, features 3 sorcerers. The so-called "The Dancing Sorcerer" or "God of Les Trois Frères" seems to bear human legs and feet, paws, a deer head with antlers, a fox or horse tail, a beard, and a flaccid penis, interpreted as dancing on all-fours. Another smaller sorcerer with a bison head, human legs and feet, and upright posture stands above several animal depictions, and is interpreted as holding and playing a musical bow to herd all the animals. The third sorcerer has a seemingly bison upper body and human lower body with testicles and an erection.
Some drawn human figures feature lines radiating out. These are generally interpreted as wounded people, with the lines representing pain or spears, possibly related to some initiation process for shamans. One such "wounded man" at Grotte de Cougnac, France, is drawn on the chest of a red Irish elk. A wounded sorcerer with a bison head is found at the 17,000 year old Grotte de Gabillou. Some caves featured "vanquished men", lying presumably dead at the foot of generally a bull or bear.
For tangible art, the early Aurignacian Hohlenstein-Stadel, Swabian Jura, has yielded the famous lion-human sculpture. It is tall, which is much larger than the other Swabian Jura figurines. A possible second lion-human was also found in the nearby Hohle Fels. An ivory slab from Geissenklösterle has a carved relief of a human figure with its arms raised in the air wearing a hide, the "worshipper". A 28,000 year old "puppet" was identified at Brno, Czech Republic, consisting of an isolated head piece, torso piece, and left arm piece. It is presumed that the head and torso were connected by a rod, and the torso and arm by some string allowing the arm to move. Because it was found in a grave, this is speculated to have belonged to a shaman for use in rituals involving the dead. A 14,000 year old large stone from Cueva del Juyo, Spain, seems to have been carved to be the conjoined face of a man on the right and a big cat on the left (when facing it). The man half seems to feature a moustache and a beard. The cat half (either a leopard or a lion) has slanting eyes, a snout, a fang, and spots on the muzzle suggestive of whiskers.
Spanish archaeologists Leslie G. Freeman and Joaquín González Echegaray argued that Cueva del Juyo was specifically modified to serve as a sanctuary site to carry out rituals. They said the inhabitants dug out a triangular trench and filled it with offerings including Patella (limpets), the common periwinkle (a sea snail), pigments, the legs and jaws (possibly with meat still on them) of red and roe deer, and a red deer antler positioned upright. The trench and offerings were then filled in with dirt, and a seemingly flower-like arrangement of bright cylindrical pieces of red, yellow, and green pigments was placed on top. This was then buried with clay, stone slabs, and bone spearpoints. The clay shell was covered by a slab of limestone supported by large flat stones. Somewhat similar structures associated with some representation of a human have also been found elsewhere in Magdalenian Spain, such as at Entrefoces rock shelter, Cueva de la Garma or Cueva de Praileaitz, Errallako Koba, and Isturitz and Oxocelhaya caves in the Basque Country.
Mortuary practices
Cro-Magnons buried their dead, commonly with a variety symbolic grave goods as well as red ochre, and multiple people were often buried in the same grave. However, the archaeological record has yielded few graves, less than 5 preserved per millennium, which could indicate burials were seldom given. Consequently, it is unclear if they represent isolated burials or form a much more generalised mortuary tradition. Across Europe, some graves contained multiple individuals, in this case most often featuring both sexes.
Most burials are dated to the Gravettian (most notably 31–29 thousand years ago) and towards the end of the Magdalenian (from 14 to 11 thousand years ago). None are identified during the Aurignacian. Gravettian burials seem to differ from post-LGM ones. The former ranged across Europe from Portugal to Siberia, whereas the latter conspicuously restricted to Italy, Germany, and southwest France. About half of buried Gravettians were infants, whereas infant burials were much less common post-LGM, but it is debated if this was due to social differences or infant mortality rates. Graves are also commonly associated with animal remains and tools, but it is unclear if this was intentional or was coincidentally a part of the filler. They are much less common post-LGM, and post-LGM graves are more commonly associated with ornaments than Gravettian graves.
The most lavish Palaeolithic burial is a grave from the Gravettian of Sungir, Russia, where a boy and a girl were placed crown-to-crown in a long, shallow grave, and adorned with thousands of perforated ivory beads, hundreds of perforated arctic fox canines, ivory pins, disc pendants, ivory animal figurines, and mammoth tusk spears. The beads were a third the size of those found with a man from the same site, which could indicate these small beads were specifically designed for the children. Only two other Upper Palaeolithic graves were found with grave goods other than personal adornment (one from Arene Candide, Italy, and Brno, Czech Republic), and the grave of these two children is unique in bearing any functional implements (the spears) as well as a bone from another individual (a partial femur). The 5 other buried individuals from Sungir did not receive nearly as many grave goods, with one seemingly given no formal treatment whatsoever. However, most Gravettian graves feature few ornaments, and the buried were probably wearing them before death.
Due to such rich material culture and the marked difference of treatment between different individuals, it has been suggested that these peoples had a complex society beyond band level, and with social class distinction. In this model, young individuals given elaborate funerals were potentially born into a position of high status. However, about 75% of Cro-Magnon skeletons were men, which sharply contrasts with the predominance of depictions of women in art. Because of the great amount of time, labour, and resources all these grave goods would have required, it has been hypothesised that the grave goods were made long in advance of the ceremony. Because of such planning for multiple burials as well as their abundance in the archaeological record, the seemingly purposeful presence of both sexes, and an apparent preference for individuals with some congenital disorder (about a third of identified burials), it is generally speculated that these cultures practiced human sacrifice either in fear, disdain, or worship of those with abnormal features, like in many present-day and historical societies. Intricate funerals, in addition to evidence of shamanism and ritualism, has also provoked hypotheses of the belief of an afterlife by Cro-Magnons.
Cannibalism
The earliest evidence of skull cups, and thus ritual cannibalism, comes from the Magdalenian of Gough's Cave, England. Further concrete evidence of such rituals does not appear until after the Palaeolithic. The Gough's Cave cup seems to have followed a similar method of scalping as those from Neolithic Europe, with incisions being made along the midline of the skull (whereas the Native American method of scalping involved a circular incision around the crown). Earlier examples of non-ritual cannibalism in Europe do not seem to have followed the same method of defleshing. At least 1 skull cup was transported from a different site. In addition, Gough's Cave also yielded a human radius with a zig-zag engraving. Compared to other artefacts in the cave or common to the Magdalenian period, the radius was modified quite little, with the engraving probably quickly etched on (indicated by scrape marks not recorded on any other Magdalenian engraving), and the bone broken and discarded soon thereafter. This may indicate the bone's only function was as a tool in some cannibalistic and/or funerary ritual, rather than being prepared to be carried around by the group as an ornament or tool.
In media
The "caveman" archetype is quite popular in both literature and visual media and can be portrayed as highly muscular, hairy, or monstrous, and to represent a wild and animalistic character, drawing on the characteristics of a wild man. Cavemen are often represented in front of a cave or fighting a dangerous animal; wielding stone, bone, or wooden tools usually for combat; and dressed in an exposing fur cloak. Men often are depicted with unkempt, unstyled, shoulder-length or longer hair, usually with a beard. Cavemen first appeared in visual media in D. W. Griffith's 1912 Man's Genesis, and among the first appearances in fictional literature were Stanley Waterloo's 1897 The Story of Ab and Jack London's 1907 Before Adam.
Cavemen have also been popularly portrayed (inaccurately) as confronting dinosaurs, first done in Griffith's 1914 Brute Force (the sequel to Man's Genesis) featuring a Ceratosaurus. Cro-Magnons are also portrayed interacting with Neanderthals, such as in J.-H. Rosny's 1911 Quest for Fire, H. G. Wells' 1927 The Grisly Folk, William Golding's 1955 The Inheritors, Björn Kurtén's 1978 Dance of the Tiger, Jean M. Auel's 1980 Clan of the Cave Bear and her Earth's Children series, and Elizabeth Marshall Thomas' 1987 Reindeer Moon and its 1990 sequel The Animal Wife. Cro-Magnons are generally portrayed as superior in some way to Neanderthals which allowed them to take Europe.
| Biology and health sciences | Evolution | null |
21435575 | https://en.wikipedia.org/wiki/Ice%E2%80%93albedo%20feedback | Ice–albedo feedback | Ice–albedo feedback is a climate change feedback, where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Because ice is very reflective, it reflects far more solar energy back to space than open water or any other land cover. It occurs on Earth, and can also occur on exoplanets.
Since higher latitudes have the coolest temperatures, they are the most likely to have perennial snow cover, widespread glaciers and ice caps - up to and including the potential to form ice sheets. However, if warming occurs, then higher temperatures would decrease ice-covered area, and expose more open water or land. The albedo decreases, and so more solar energy is absorbed, leading to more warming and greater loss of the reflective parts of the cryosphere. Inversely, cooler temperatures increase ice cover, which increases albedo and results in greater cooling, which makes further ice formation more likely.
Thus, ice–albedo feedback plays a powerful role in global climate change. It was important both for the beginning of Snowball Earth conditions nearly 720 million years ago and for their end about 630 mya: the deglaciation had likely involved gradual darkening of albedo due to build-up of dust. In more geologically recent past, this feedback was a core factor in ice sheet advances and retreats during the Pleistocene period (~2.6 Ma to ~10 ka ago). More recently, human-caused increases in greenhouse gas emissions have had many impacts across the globe, and Arctic sea ice decline had been one of the most visible. As the sea ice cover shrinks and reflects less sunlight, the Arctic warms up to four times faster than the global average. Globally, the decades-long ice loss in the Arctic and the more recent decline of sea ice in Antarctica have had the same warming impact between 1992 and 2018 as 10% of all the greenhouse gases emitted over the same period.
Ice–albedo feedback has been present in some of the earliest climate models, so they have been simulating these observed impacts for decades. Consequently, their projections of future warming also include future losses of sea ice alongside the other drivers of climate change. It is estimated that persistent loss during the Arctic summer, when the Sun shines most intensely and lack of reflective surface has the greatest impacts, would produce global warming of around . There are also model estimates of warming impact from the loss of both mountain glaciers and the ice sheets in Greenland and Antarctica. However, warming from their loss is generally smaller than from the declining sea ice, and it would also take a very long time to be seen in full.
Early research
In the 1950s, early climatologists such as Syukuro Manabe have already been making attempts to describe the role of ice cover in Earth's energy budget. In 1969, both USSR's Mikhail Ivanovich Budyko and the United States' William D. Sellers have published papers presenting some of the first energy-balance climate models to demonstrate that the reflectivity of ice had a substantial impact on the Earth's climate, and that changes to snow-ice cover in either direction could act as a powerful feedback.
This process was soon recognized as a crucial part of climate modelling in a 1974 review, and in 1975, the general circulation model used by Manabe and Richard T. Wetherald to describe the effects of doubling concentration in the atmosphere - a key measurement of climate sensitivity - has also already incorporated what it described as "snow cover feedback". Ice-albedo feedback continues to be included in the subsequent models. Calculations of the feedback are also applied to paleoclimate studies, such as those of the Pleistocene period (~2.6 Ma to ~10 ka ago).
Current role
Snow– and ice–albedo feedback have a substantial effect on regional temperatures. In particular, the presence of ice cover and sea ice makes the North Pole and the South Pole colder than they would have been without it. Consequently, recent Arctic sea ice decline is one of the primary factors behind the Arctic warming nearly four times faster than the global average since 1979 (the year when continuous satellite readings of the Arctic sea ice began), in a phenomenon known as Arctic amplification.
Modelling studies show that strong Arctic amplification only occurs during the months when significant sea ice loss occurs, and that it largely disappears when the simulated ice cover is held fixed. Conversely, the high stability of ice cover in Antarctica, where the thickness of the East Antarctic ice sheet allows it to rise nearly 4 km above the sea level, means that this continent has experienced very little net warming over the past seven decades, most of which was concentrated in West Antarctica. Ice loss in the Antarctic and its contribution to sea level rise is instead driven overwhelmingly by the warming of the Southern Ocean, which had absorbed 35–43% of the total heat taken up by all oceans between 1970 and 2017.
Ice–albedo feedback also has a smaller, but still notable effect on the global temperatures. Arctic sea ice decline between 1979 and 2011 is estimated to have been responsible for 0.21 watts per square meter (W/m2) of radiative forcing, which is equivalent to a quarter of radiative forcing from increases over the same period. When compared to cumulative increases in greenhouse gas radiative forcing since the start of the Industrial Revolution, it is equivalent to the estimated 2019 radiative forcing from nitrous oxide (0.21 W/m2), nearly half of 2019 radiative forcing from methane (0.54 W/m2) and 10% of the cumulative increase (2.16 W/m2). Between 1992 and 2015, this effect was partly offset by the growth in sea ice cover around Antarctica, which produced cooling of about 0.06 W/m2 per decade. However, Antarctic sea ice had also begun to decline afterwards, and the combined role of changes in ice cover between 1992 and 2018 is equivalent to 10% of all the anthropogenic greenhouse gas emissions.
Future impact
The impact of ice-albedo feedback on temperature will intensify in the future as the Arctic sea ice decline is projected to become more pronounced, with a likely near-complete loss of sea ice cover (falling below 1 million km2) at the end of the Arctic summer in September at least once before 2050 under all climate change scenarios, and around 2035 under the scenario of continually accelerating greenhouse gas emissions.
Since September marks the end of the Arctic summer, it also represents the nadir of sea ice cover in the present climate, with an annual recovery process beginning in the Arctic winter. Consecutive ice-free Septembers are considered highly unlikely in the near future, but their frequency will increase with greater levels of global warming: a 2018 paper estimated that an ice-free September would occur once in every 40 years under a warming of , but once in every 8 years under and once in every 1.5 years under . This means that the loss of Arctic sea ice during September or earlier in the summer would not be irreversible, and in the scenarios where global warming begins to reverse, its annual frequency would begin to go down as well. As such, it is not considered one of the tipping points in the climate system.
Notably, while the loss of sea ice cover in September would be a historic event with significant implications for Arctic wildlife like polar bears, its impact on the ice-albedo feedback is relatively limited, as the total amount of solar energy received by the Arctic in September is already very low. On the other hand, even a relatively small reduction in June sea ice extent would have a far greater effect, since June represents the peak of the Arctic summer and the most intense transfer of solar energy.
CMIP5 models estimate that a total loss of Arctic sea ice cover from June to September would increase the global temperatures by , with a range of 0.16–0.21 °C, while the regional temperatures would increase by over . This estimate includes not just the ice-albedo feedback itself, but also its second-order effects such the impact of such sea ice loss on lapse rate feedback, the changes in water vapor concentrations and regional cloud feedbacks. Since these calculations are already part of every CMIP5 and CMIP6 model, they are also included in their warming projections under every climate change pathway, and do not represent a source of "additional" warming on top of their existing projections.
Long-term impact
Very high levels of global warming could prevent Arctic sea ice from reforming during the Arctic winter. Unlike an ice-free summer, this ice-free Arctic winter may represent an irreversible tipping point. It is most likely to occur at around , though it could potentially occur as early as or as late as . While the Arctic sea ice would be gone for an entire year, it would only have an impact on the ice-albedo feedback during the months where sunlight is received by the Arctic - i.e. from March to September. The difference between this total loss of sea ice and its 1979 state is equivalent to a trillion tons of emissions - around 40% of the 2.39 trillion tons of cumulative emissions between 1850 and 2019, although around a quarter of this impact has already happened with the current sea ice loss. Relative to now, an ice-free winter would have a global warming impact of , with a regional warming between and .
Ice–albedo feedback also occurs with the other large ice masses on the Earth's surface, such as mountain glaciers, Greenland ice sheet, West Antarctic and East Antarctic ice sheet. However, their large-scale melt is expected to take centuries or even millennia, and any loss in area between now and 2100 will be negligible. Thus, climate change models do not include them in their projections of 21st century climate change: experiments where they model their disappearance indicate that the total loss of the Greenland Ice Sheet adds to global warming (with a range of 0.04–0.06 °C), while the loss of the West Antarctic Ice Sheet adds (0.04–0.06 °C), and the loss of mountain glaciers adds (0.07–0.09 °C). These estimates assume that global warming stays at an average of . Because of the logarithmic growth of greenhouse effect, the impact from ice loss would be larger at the slightly lower warming level of 2020s, but it would become lower if the warming proceeds towards higher levels.
Since the East Antarctic ice sheet would not be at risk of complete disappearance until the very high global warming of is reached, and since its total melting is expected to take a minimum of 10,000 years to disappear entirely even then, it is rarely considered in such assessments. If it does happen, the maximum impact on global temperature is expected to be around . Total loss of the Greenland ice sheet would increase regional temperatures in the Arctic by between and , while the regional temperature in Antarctica is likely to go up by after the loss of the West Antarctic ice sheet and after the loss of the East Antarctic ice sheet.
Snowball Earth
The runaway ice–albedo feedback was also important for the formation of Snowball Earth - a climate state of a very cold Earth with practically complete ice cover. Paleoclimate evidence suggests that Snowball Earth began with the Sturtian glaciation about 717 million years ago. It persisted until about 660 mya, but it was followed by another Snowball period, Marinoan glaciation, only several million years later, which lasted until about 634 mya.
Geological evidence shows glaciers near the equator at the time, and models have suggested the ice–albedo feedback played a role. As more ice formed, more of the incoming solar radiation was reflected back into space, causing temperatures on Earth to drop. Whether the Earth was a complete solid snowball (completely frozen over), or a slush ball with a thin equatorial band of water still remains debated, but the ice–albedo feedback mechanism remains important for both cases.
Further, the end of the Snowball Earth periods would have also involved the ice-albedo feedback. It has been suggested that deglaciation began once enough dust from erosion had built up in layers on the snow-ice surface to substantially lower its albedo. This would have likely started in the midlatitude regions, as while they would have been colder than the tropics, they also receive less precipitation, and so there would have been less fresh snow to bury dust accumulation and restore the albedo. Once the midlatitudes would have lost enough ice, it would have not only helped to increase the planet-wide temperature, but the isostatic rebound would have had eventually led to enhanced volcanism and thus build-up of , which would have been impossible before.
Snow darkening effect
The effect of the ice-albedo feedback can be enhanced by the presence of light-absorbing particles. Airborne particles are deposited on snow and ice surfaces causing a darkening effect, with higher concentrations of particles causing a larger decrease in albedo. The lower albedo means that more solar radiation is absorbed and melting is accelerated. Particles that can cause darkening include black carbon and mineral dust. Microbial growth, such as snow algae on glaciers and ice algae on sea ice can also cause a snow darkening effect. Melting caused by algae increases the presence of liquid water in snow and ice surfaces, which then stimulates the growth of more snow and ice algae and causes a decrease in albedo, forming a positive feedback.
Ice–albedo feedback on exoplanets
On Earth, the climate is heavily influenced by interactions with solar radiation and feedback processes. One might expect exoplanets around other stars to also experience feedback processes caused by stellar radiation that affect the climate of the world. In modeling the climates of other planets, studies have shown that the ice–albedo feedback is much stronger on terrestrial planets that are orbiting stars (see: stellar classification) that have a high near-ultraviolet radiation.
| Physical sciences | Climate change | Earth science |
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