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The furcula of Oviraptor is very distinct from other oviraptorids in having a midline keel on the anterior surface of the hypocleidium−a downwards directed projection at the center of the furcula. This bone is V-shaped, rounded in cross-section, preserves an elongate spike-like hypocleidium, and the interclavicular angle is about 90°. The scapulocoracoid is fused in the holotype, however, the coracoid is badly damaged. The scapula is slightly bowed and measures in length. Oviraptor had a relatively elongated arm composed of the humerus, radius, ulna, and manus.
The phalangeal formula of Oviraptor was 2-3-4, as seen in most other theropods and oviraptorids. The hand of Oviraptor had three skinny and bird-like fingers with each finger ended in side to side flattened and recurved unguals (claw bone). Unlike some oviraptorids, Oviraptor did not suffer a reduction of the second and third finger relative to the first one. The regarded juvenile Oviraptor AMNH 33092 preserves hindlimb material, comprising a right tibia with metatarsals III and IV. Its tibia is long, indicating a substantially smaller individual than the holotype. The nest AMNH 6508 preserves elongatoolithid eggs, with each egg being long (some are incomplete). Nevertheless, there is the possibility that taphonomical crushing may have compressed them by up to .
Classification
Oviraptor was originally allied with the ornithomimids by Osborn due to its toothless beak. Osborn also found similarities with Chirostenotes, which is still considered a close relative of Oviraptor. In 1976, Barsbold erected a new family to contain Oviraptor and its close kin, making Oviraptor the type genus of the Oviraptoridae. During the redescription of the holotype skull in 2002 by Clark and colleagues, they noted that Oviraptor had a relatively elongated maxilla and dentary. These traits are less pronounced in derived oviraptorids and suggests that Oviraptor belongs to the near base of the Oviraptoridae. | Oviraptor | Wikipedia | 494 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
The cladogram below follows an analysis by Gregory F. Funston and colleagues in 2020:
Paleobiology
Feeding
When first described in 1924 by Osborn, Oviraptor was originally presumed to have been ovivorous—an organism that has an egg-based diet—based on the association of the holotype with a nest thought to belong to Protoceratops. In 1977, Barsbold proposed a crushing jaw hypothesis. He argued that the strength of the robust lower jaws and likely rhamphotheca (horny beak) was strong enough to break the shells of mollusks such as clams, which are found in the same geological formation as Oviraptor. These bones form part of the main upper jaw bone or maxilla, which converge in the middle to form a pair of prongs. The rhamphotheca and lower jaws together with the extension of several bones from the palate, would have made a piercing tool. Barsbold also suggested that oviraptorids could have had a semiaquatic life-style based on the mollusk-based diet, the high location of nasal cavities, an augmented musculature of the tail, and the greater size of the first manual digit. In a 1990 conference abstract, David K. Smith presented an osteological reevaluation of Oviraptor where he rejected the statements made by Barsbold. He found no evidence indicating a forelimb specialized in aquatic locomotion, and the jaws, rather than preserve a crushing mechanism, preserve shearing surfaces. As the skull is toothless, lightly built and lacks several strong muscle insertion areas, Smith suggested that leaves may have been an important part in the diet of Oviraptor. However, in 1995, Norell and colleagues reported the fragmented remains of a lizard in the body cavity of the holotype specimen, suggesting that Oviraptor was partially carnivorous. | Oviraptor | Wikipedia | 392 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
In 2008, Stig Olav K. Jansen compared the skull of several oviraptorid species to those of birds and turtles to investigate which properties can predict a rhamphotheca. He found the lower jaws of oviraptorids to be very similar to those of parrots, and the upper jaws to be more similar to those of turtles. Based on these observations, Jansen suggested that oviraptorids were omnivorous as the sharply-developed rhamphotheca together with the prominent forelimbs would have been adapted to catch and tear small prey. Moreover, the pointed projections of the palate would have contributed in holding prey. Jansen pointed out that a fully herbivorous diet in oviraptorids seems unlikely as they lacked flat and wide tomia (cutting edges of the mandibles) to chew, and were unable to move the lower jaws sideways. However, he considered the lower jaws strong enough to have at least crushed elements like eggs, nuts or other hard seeds. | Oviraptor | Wikipedia | 209 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
Longrich and colleagues in 2010 also rejected a durophagous (animals that practise shell-crushing) hypothesis, given that such animals typically develop teeth with broad crushing surfaces. The pointed shape of the dentary bones in the lower jaws suggests that oviraptorids had a sharp-edged rhamphotheca used for shearing food instead. The symphyseal (bone union) region at the front of the dentary may have given some ability for crushing, but as this was a relatively small area, it was probably not the main function of the jaws. Another argument against them having been eaters of mollusks is the fact that most oviraptorids have been found in sediments that are interpreted to represent mostly arid or semi-arid environments, such as Oviraptor in the Djadokhta Formation. The team also found that oviraptorids and dicynodonts share cranial features such as short, deep, and toothless mandibles; elongated dentary symphyses; elongated mandibular openings; and a pointed palate. Modern animals with jaws that resemble those of oviraptorids include parrots and tortoises; the latter group also has tooth-like projections on the palatal region. Longrich and colleagues concluded that due to the similarities between oviraptorids and herbivorous animals, the bulk of their diet would most likely have been formed by plant material. The jaws of oviraptorids may have been specialised for processing food, such as xerophytic vegetation−a vegetation that is adapted for environments with little water—that would have grown in their arid environments, but this is not possible to demonstrate, as little is known about the paleoflora of the Gobi Desert.
In 2018 however, Funston and colleagues supported the crushing jaw hypothesis. They pointed out that the stocky rostrum and robust lower jaws of oviraptorids suggest, in fact, a strong and nipping bite, which is rather similar to those of parrots. Funston and colleagues considered these anatomical traits of oviraptorids to be consistent with a frugivorous diet that incorporated nuts and seeds.
Reproduction | Oviraptor | Wikipedia | 454 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
Since the description of the embryonic Citipati specimen in 1994, oviraptorids became more understood: instead of having been egg-eating animals, they actually brooded and cared for the nests. This specimen showed that the holotype of Oviraptor was likely a sexually mature individual that perished incubating the associated nest with eggs. This new behavior on oviraptorids became more clear with the report and short description of an adult nesting specimen of Citipati in 1995 by Norell and colleagues. The specimen was found on top of egg clutches, with its hindlimbs crouched symmetrically on each side of the nest and the forelimbs covering the nest perimeter. This brooding posture is found today only in modern avian dinosaurs and supports a behavioral link between the latter group and non-avian dinosaurs. In 1996, Dong and Currie described a new nesting oviraptorid specimen from the Bayan Mandahu Formation. It was found lying atop a nest composed by approximately 6 eggs as preserved, and these were laid in a mound-shaped structure with a circular pattern. As the specimen was found over the nest with its forelimbs covering the eggs and the partially preserved hindfoot near the center of the nest, Dong and Currie suggested that it was caught and buried by a sandstorm during incubation. They ruled out the possibility of oviraptorids being egg-thieves as they would have either consumed or instinctively abandoned the nest long before it was buried by a sandstorm or another meteorological phenomenon.
In 1999 Clark and team described in detail the previously reported Citipati nesting specimen and briefly discussed the holotype specimen of Oviraptor and its association with the nest AMNH 6508. They pointed out that the exact position in which the holotype was found over the nest is unclear as they were separated during preparation, and the nest appears to be not entirely complete with about 15 eggs preserved of which two damaged. Moreover, the semicircular arrangement of the nest indicates that the eggs were laid in pairs and in at least three rings, and this nest was originally circular, similar to a mound. | Oviraptor | Wikipedia | 436 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
Thomas P. Hopp and Mark J. Orsen in 2004 analyzed the brooding behavior of extinct and extant dinosaur species, including oviraptorids, in order to evaluate the reason for the elongation and development of wing and tail feathers. Given that the most complete oviraptorid nesting specimen—at the time, the 1995 Citipati nesting specimen—was found in a very avian-like posture, with the forelimbs in a near-folded posture and the pectoral region, belly, and feet in contact with the eggs, Hopp and Orsen indicated that long pennaceous feathers and a feather covering were most likely present in life. The "wings" and tail of oviraptorids would have granted protection for the eggs and hatchlings against climate factors like the sunlight, wind, and rainfalls. However, the arms of this specimen were not extremely folded as in some modern birds, instead, they are more extended resembling the style of large flightless birds like the ostrich. The extended position of the arm is also similar to the brooding behavior of this bird, which is known to nest in large clutches like oviraptorids. Based on the forelimb position of nesting oviraptorids, Hopp and Orsen proposed brooding as the ancestral reason behind wing and tail feather elongation, as there was a greater need to provide optimal protection for eggs and juveniles. | Oviraptor | Wikipedia | 290 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
In 2005, Tamaki Sato and team reported an unusual oviraptorid specimen from the Nanxiong Formation. This new specimen was found preserving mainly the pelvic region with two eggs inside and thereby indicating a female. The size and position of the eggs suggest that oviraptorids retained two functional oviducts, but had reduced the number of eggs ovulated to one per oviduct. David J. Varricchio and colleagues in 2008 found that the relatively large egg clutch-size of oviraptorids and troodontids is most similar to those of modern birds that practice polygamous mating and extensive male parental care, such as ratite birds, suggesting similar habits. This reproductive system is most likely to represent the ancestral condition for modern birds, with biparental care (where both parents participate) being a later development. In 2014, W. Scott Persons and colleagues suggested that oviraptorosaurs were secondarily flightless and several of the traits in their tails may indicate a propensity for display behaviour, such as courtship display. The tail of several oviraptorosaurs and oviraptorids ended in pygostyles, a bony structure at the end of the tail that, at least in modern birds, is used to support a feather fan. Furthermore, the tail was notably muscular and had a pronounced flexibility, which may have aided in courtship movements.
In 2018, Tzu-Ruei Yang and colleagues identified cuticle layers on several egg-shells of maniraptoran dinosaurs including those of oviraptorids. These particular layers are composed of proteins, polysaccharides and pigments, but mainly of lipids and hydroxyapatite. In modern birds they serve to protect the eggs from dehydration and invasion of microorganisms. As most oviraptorid specimens have been found in formations of caliche-based sedimentation, Yang and colleagues suggested that the cuticle-coated eggs would have been a reproductive strategy adapted for enhancing their hatching success in such arid climates and environments. | Oviraptor | Wikipedia | 430 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
In 2019 Yang and colleagues re-evaluated the hypothesis of thermoregulatory contact incubation using complete oviraptorid nests from the Nanxiong Formation, and provided a detailed reconstruction of the architecture of the oviraptorid clutch. They noted that adult oviraptorid specimens in association with nest were not necessarily incubating the eggs as they could represent a female in the process of laying eggs, and the multi-ring clutch prevented sufficient heat transfer from the parent to the inner rings of eggs. An average oviraptorid nest was built as a gently-inclined mound with a highly organized architecture: the eggs were likely pigmented and arranged in pairs with each pair arranged in three to four elliptical rings. As the parent was likely operating from the nest center, this region was devoid of eggs. Yang and colleagues concluded the oviraptorid nesting style was so unique that they lack modern analogs, therefore, using oviraptorid reproduction may not be the best example to inform about the evolution of bird reproductive strategies. However, the team was unable to determinate if the juvenile Oviraptor AMNH 33092 had hatched from the nest associated with the holotype.
Paleoenvironment
Oviraptor is known from the Bayn Dzak locality of the Djadokhta Formation in Mongolia, a formation that dates back to the Late Cretaceous about 71 million to 75 million years ago. The paleoenvironment of the Djadokhta Formation is interpreted as having a semiarid climate, with sand dune and alluvial settings similar to the modern Gobi Desert. The semiarid steppe landscape was drained by intermittent streams and was sometimes affected by dust and sandstorms, and moisture was seasonal. Though this formation is largely considered to preserved highly arid environments, several short-lived water bodies have been reported from the Ukhaa Tolgod locality, based on fluvial sedimentation. Furthermore, it is thought that later in the Campanian age and into the Maastrichtian, the climate would shift to the more humid fluvial environment seen in the Nemegt Formation. | Oviraptor | Wikipedia | 441 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
The Djadokhta Formation is separated into a lower Bayn Dzak Member and an upper Turgrugyin Member. The known remains of Oviraptor have been produced by the Bayn Dzak member, which has also yielded the dinosaurs Bainoceratops, Pinacosaurus, Protoceratops, Saurornithoides, Velociraptor, and Halszkaraptor. Further dinosaur fauna from this member includes that of the Ukhaa Tolgod locality, composed of Apsaravis, Byronosaurus, Citipati, Gobipteryx, Khaan, Khol, Shuuvuia, Tsaagan, and Minotaurasaurus.
Taphonomy
The pose of the holotype of Oviraptor along with the association of eggs, suggest that it was trapped over the nest during a sandstorm, and burial was relatively rapid given that the body had no opportunity to become fully disarticulated or scavenged by predators. The paleontologist Kenneth Carpenter also agreed in that sandstorms may have been the most likely event that the eggs found in the deposits were buried. Among elements, the skull have become particularly flattened and distorted during the fossilization process. | Oviraptor | Wikipedia | 252 | 581471 | https://en.wikipedia.org/wiki/Oviraptor | Biology and health sciences | Theropods | Animals |
The Crotalinae, commonly known as pit vipers, or pit adders, are a subfamily of vipers found in Asia and the Americas. Like all other vipers, they are venomous. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on both sides of the head. Currently, 23 genera and 155 species are recognized: These are also the only viperids found in the Americas. The groups of snakes represented here include rattlesnakes, lanceheads, and Asian pit vipers. The type genus for this subfamily is Crotalus, of which the type species is the timber rattlesnake, C. horridus.
These snakes range in size from the diminutive hump-nosed viper, Hypnale hypnale, that grows to a typical total length (including tail) of only , to the bushmaster, Lachesis muta, a species known to reach a maximum total length of in length. | Pit viper | Wikipedia | 206 | 581543 | https://en.wikipedia.org/wiki/Pit%20viper | Biology and health sciences | Snakes | Animals |
This subfamily is unique in that all member species share a common characteristic – a deep pit, or fossa, in the loreal area between the eye and the nostril on either side of the head. These loreal pits are the external openings to a pair of extremely sensitive infrared-detecting organs, which in effect give the snakes a sixth sense to help them find and perhaps even judge the size of the small, warm-blooded prey on which they feed. The pit organ is complex in structure and is similar to the thermoreceptive labial pits found in boas and pythons. It is deep and located in a maxillary cavity. The membrane is like an eardrum that divides the pit into two sections of unequal size, with the larger of the two facing forwards and exposed to the environment. The two sections are connected via a narrow tube, or duct, that can be opened or closed by a group of surrounding muscles. By controlling this tube, the snake can balance the air pressure on either side of the membrane. The membrane has many nerve endings packed with mitochondria. Succinic dehydrogenase, lactic dehydrogenase, adenosine triphosphate, monoamine oxidase, generalized esterases, and acetylcholine esterase have also been found in it. When prey comes into range, infrared radiation falling onto the membrane allows the snake to determine its direction. Having one of these organs on either side of the head produces a stereo effect that indicates distance, as well as direction. Experiments have shown, when deprived of their senses of sight and smell, these snakes can strike accurately at moving objects less than warmer than the background. The paired pit organs provide the snake with thermal rangefinder capabilities. Clearly, these organs are of great value to a predator that hunts at night, as well as for avoiding the snake’s own predators.
Among vipers, these snakes are also unique in that they have a specialized muscle, called the muscularis pterigoidius glandulae, between the venom gland and the head of the ectopterygoid. Contraction of this muscle, together with that of the muscularis compressor glandulae, forces venom out of the gland. | Pit viper | Wikipedia | 453 | 581543 | https://en.wikipedia.org/wiki/Pit%20viper | Biology and health sciences | Snakes | Animals |
Evolution
The earliest known fossil pit viper remains are from the Early Miocene of Nebraska. As pit vipers are thought to have had an Asian origin before eventually colonizing the Americas, this suggests that they must have originated and diversified even earlier. During the Late Miocene, they reached as far west as eastern Europe, where they are no longer found; it is thought that they did not expand further into Europe.
Geographic range
The subfamily Crotalinae is found from Central Asia eastward and southward to Japan, China, Indonesia, peninsular India, Nepal, Bangladesh and Sri Lanka. In the Americas, they range from southern Canada southward to Central America to southern South America.
Habitat
Crotalines are a versatile subfamily, with members found in habitats ranging from parched desert (e.g., the sidewinder, Crotalus cerastes) to rainforests (e.g., the bushmaster, Lachesis muta). They may be either arboreal or terrestrial, and at least one species (the cottonmouth, Agkistrodon piscivorus) is semiaquatic. The altitude record is held jointly by Crotalus triseriatus in Mexico and Gloydius strauchi in China, both of which have been found above the treeline at over 4,000 m above sea level.
Behavior
Although a few species of crotalines are highly active by day, such as Trimeresurus trigonocephalus, a bright green pit viper endemic to Sri Lanka, most are nocturnal, preferring to avoid high daytime temperatures and to hunt when their favored prey are also active. The snakes' heat-sensitive pits are also thought to aid in locating cooler areas in which to rest.
As ambush predators, crotalines typically wait patiently somewhere for unsuspecting prey to wander by. At least one species, the arboreal Gloydius shedaoensis of China, is known to select a specific ambush site and return to it every year in time for the spring migration of birds. Studies have indicated these snakes learn to improve their strike accuracy over time. | Pit viper | Wikipedia | 423 | 581543 | https://en.wikipedia.org/wiki/Pit%20viper | Biology and health sciences | Snakes | Animals |
Many temperate species of pit vipers (e.g. most rattlesnakes) congregate in sheltered areas or "dens" to overwinter (brumate, see hibernation), the snakes benefiting from the combined heat. In cool temperatures and while pregnant, pit vipers also bask on sunny ledges. Some species do not mass together in this way, for example the copperhead, Agkistrodon contortrix, or the Mojave rattlesnake, Crotalus scutulatus.
Like most snakes, crotalines keep to themselves and strike only if cornered or threatened. Smaller snakes are less likely to stand their ground than larger specimens. Pollution and the destruction of rainforests have caused many pit viper populations to decline. Humans also threaten pit vipers, as many are hunted for their skins or killed by cars when they wander onto roads.
Reproduction
With few exceptions, crotalines are ovoviviparous, meaning that the embryos develop within eggs that remain inside the mother's body until the offspring are ready to hatch, when the hatchlings emerge as functionally free-living young. In such species, the eggshells are reduced to soft membranes that the young shed, either within the reproductive tract, or immediately after emerging.
Among the oviparous (egg-laying) pit vipers are Lachesis, Calloselasma, and some Trimeresurus species. All egg-laying crotalines are believed to guard their eggs.
Brood sizes range from two for very small species, to as many as 86 for the fer-de-lance, Bothrops atrox, which is among the most prolific of all live-bearing snakes.
Many young crotalines have brightly coloured tails that contrast dramatically with the rest of their bodies. These tails are known to be used by a number of species in a behavior known as caudal luring; the young snakes make worm-like movements with their tails to lure unsuspecting prey within striking distance.
Taxonomy
In the past, the pit vipers were usually classed as a separate family: the Crotalidae. Today, however, the monophyly of the viperines and the crotalines as a whole is undisputed, which is why they are treated here as a subfamily of the Viperidae.
Genera
*) Not including the nominate subspecies.
) Type genus. | Pit viper | Wikipedia | 493 | 581543 | https://en.wikipedia.org/wiki/Pit%20viper | Biology and health sciences | Snakes | Animals |
The mountain gorilla (Gorilla beringei beringei) is one of the two subspecies of the eastern gorilla. It is listed as endangered by the IUCN .
There are two populations: One is found in the Virunga volcanic mountains of Central/East Africa, within three National Parks: Mgahinga, in southwest Uganda; Volcanoes, in northwest Rwanda; and Virunga, in the eastern Democratic Republic of Congo (DRC).
The other population is found in Uganda's Bwindi Impenetrable National Park. Some primatologists speculate the Bwindi population is a separate subspecies, though no description has been finalized. The latest population count, released in 2019, revealed there to be approximately 1060 mountain gorillas in the wild
Evolution, taxonomy, and classification
Mountain gorillas are descendants of ancestral monkeys and apes found in Africa and Arabia during the start of the Oligocene epoch (34–24 million years ago). The fossil record provides evidence of the hominoid primates (apes) found in East Africa approximately 22–32 million years ago. The fossil record of the area where mountain gorillas live is particularly poor and so its evolutionary history is not clear.
It was about 8.8 to 12 million years ago that the group of primates who were to evolve into gorillas split from their common ancestor with humans and chimps; this is when the genus Gorilla emerged. Mountain gorillas have been isolated from eastern lowland gorillas for approximately 10,000 years and these two taxa separated from their western counterparts approximately 1.2 to 3 million years ago. The genus was first referenced as Troglodytes in 1847, but renamed to Gorilla in 1852. It was not until 1967 that the taxonomist Colin Groves proposed that all gorillas be regarded as one species (Gorilla gorilla) with three subspecies Gorilla gorilla gorilla (western lowland gorilla), Gorilla gorilla graueri (lowland gorillas found west of the Virungas) and Gorilla gorilla beringei (mountain gorillas, including Gorilla beringei, found in the Virungas and Bwindi). In 2003, after a review, they were divided into two species (Gorilla gorilla and Gorilla beringei) by The World Conservation Union (IUCN). There is now agreement that there are two species, each with two subspecies.
Characteristics
The fur of the mountain gorilla, often thicker and longer than that of other gorilla species, enables them to live in colder temperatures. Gorillas can be identified by nose prints unique to each individual | Mountain gorilla | Wikipedia | 511 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
Males reach a standing height of , a girth of , an arm span of and a weight of . Females are smaller with a weight of .
This subspecies is smaller than the eastern lowland gorilla, the other subspecies of eastern gorilla. Adult males have more pronounced bony crests on the top and back of their skulls, giving their heads a more conical shape. These crests anchor the powerful temporalis muscles, which attach to the lower jaw (mandible). Adult females also have these crests, but they are less pronounced. Like all gorillas, they feature dark brown eyes framed by a black ring around the iris. Adult males are called silverbacks because a saddle of gray or silver-colored hair develops on their backs with age. The hair on their backs is shorter than on most other body parts, and their arm hair is especially long. Fully erect males average in height, with an arm span of and weigh . The tallest silverback recorded was tall with an arm span of , a chest of , and a weight of , shot in Alimbongo, northern Kivu in May 1938. There is an unconfirmed record of another individual, shot in 1932, that was and weighed . The heaviest silverback recorded was a tall specimen shot in Ambam, Cameroon.
The mountain gorilla is primarily terrestrial and quadrupedal. However, it will climb into fruiting trees if the branches can carry its weight. Like all great apes other than humans, its arms are longer than its legs. It moves by knuckle-walking, supporting its weight on the backs of its curved fingers rather than its palms.
The mountain gorilla is diurnal, spending most of the day eating, as large quantities of food are needed to sustain its massive bulk. It forages in the early morning, rests during the late morning and around midday, and in the afternoon it forages again before resting at night. Each gorilla builds a nest from surrounding vegetation to sleep in, constructing a new one every evening. Only infants sleep in the same nest as their mothers. They leave their sleeping sites when the sun rises at around 6 am, except when it is cold and overcast; then they often stay longer in their nests.
Distribution and habitat | Mountain gorilla | Wikipedia | 450 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
The mountain gorilla inhabits the Albertine Rift montane cloud forest, including the Virunga Mountains, ranging in elevation from . Most groups live on the slopes of three of the dormant volcanoes: Karisimbi, Mikeno, and Visoke. The vegetation is very dense at the bottom of the mountains, becoming more sparse at higher elevations, and the forests are often cloudy, misty and cold. The mountain gorilla also occasionally uses the border habitat with the Rwenzori-Virunga montane moorlands, at elevations higher than the Albertine Rift montane cloud forest.
Behaviour and ecology
The home range used by one group of gorillas during one year is influenced by availability of food sources and usually includes several vegetation zones. George Schaller identified ten distinct zones, including: bamboo forest at ; Hagenia forest at ; and the giant senecio zone at . The mountain gorilla spends most of its time in Hagenia forest, where galium vines are found year-round. All parts of this vine are consumed: leaves, stems, flowers, and berries. It travels to the bamboo forest during the few months of the year when fresh shoots are available, and it climbs into subalpine regions to eat the soft centers of giant senecio trees.
Diet
The mountain gorilla is primarily a herbivore; the majority of its diet is composed of the leaves, shoots, and stems (85.8%) of 142 plant species. It also feeds on bark (6.9%), roots (3.3%), flowers (2.3%), and fruit (1.7%), as well as small invertebrates. (0.1%). In a year long study in Bwindi Impenetrable Forest adult males ate an average of of food a day, while females ate .
Social structure
The mountain gorilla is highly social, and lives in relatively stable, cohesive groups held together by long-term bonds between adult males and females. Relationships among females are relatively weak. These groups are nonterritorial; the silverback generally defends his group rather than his territory. In the Virunga mountain gorillas, the average length of tenure for a dominant silverback is 4.7 years. | Mountain gorilla | Wikipedia | 453 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
61% of groups are composed of one adult male and a number of females and 36% contain more than one adult male. The remaining gorillas are either lone males or exclusively male groups, usually made up of one mature male and a few younger males. Group sizes vary from five to thirty, with an average of ten individuals. A typical group contains: one dominant silverback, who is the group's undisputed leader; another subordinate silverback (usually a younger brother, half-brother, or even an adult son of the dominant silverback); one or two blackbacks, who act as sentries; three to four sexually mature females, who have bonded for life to the dominant silverback; and from three to six juveniles and infants.
Most males and approximately 60% of females leave their natal group. Males leave when they are about eleven years old, and often the separation process is slow: they spend more and more time on the edge of the group until they leave altogether. They may travel alone or with an all-male group for two–five years before they can attract females to join them and form a new group. Females typically emigrate when they are about eight years old, either transferring directly to an established group or beginning a new one with a lone male. Females often transfer to a new group several times before they choose to settle down with a certain silverback male.
The dominant silverback generally determines the movements of the group, leading it to appropriate feeding sites throughout the year. He also mediates conflicts within the group and protects it from external threats. When the group is attacked by humans, leopards, or other gorillas, the silverback will protect them, even at the cost of his own life. He is the center of attention during rest sessions, and young gorillas frequently stay close to him and include him in their games. If a mother dies or leaves the group, the silverback is usually the one who looks after her abandoned offspring, even allowing them to sleep in his nest. Young mountain gorillas have been observed searching for and dismantling poachers' snares. | Mountain gorilla | Wikipedia | 429 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
When the silverback dies or is killed by disease, accident, or poachers, the family group may be disrupted. Unless there is an accepted male descendant capable of taking over his position, the group will either split up or adopt an unrelated male. When a new silverback joins the family group, he may kill all of the infants of the dead silverback. Infanticide has not been observed in stable groups.
Analysis of mountain gorilla genomes by whole genome sequencing indicates that a recent decline in their population size has led to extensive inbreeding. As an apparent result, individuals are typically homozygous for 34% of their genome sequence. Furthermore, homozygosity and the expression of deleterious recessive mutations as consequences of inbreeding have likely resulted in the purging of severely deleterious mutations from the population.
Aggression
Although strong and powerful, mountain gorillas are generally gentle and very shy. Severe aggression is rare in stable groups, but when two mountain gorilla groups meet, sometimes the two silverbacks can engage in a fight to the death, using their canines to cause deep, gaping injuries. Conflicts are most often resolved by displays and other threat behaviors that are intended to intimidate without becoming physical.
A ritualized charge display is unique to gorillas. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms. Jill Donisthorpe has stated that a male charged at her twice. In both cases, the gorilla turned away when she stood her ground.
Affiliation
The midday rest period is an important time for establishing and reinforcing relationships within the group. Mutual grooming reinforces social bonds, and helps keep hair free from dirt and parasites. It is not so common among gorillas as in other primates, although females groom their offspring regularly.
Young gorillas play often and are more arboreal than the large adults. Playing helps them learn how to communicate and behave within the group. Activities include wrestling, chasing, and somersaults. The silverback and his females tolerate and, if encouraged, even participate. | Mountain gorilla | Wikipedia | 483 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
Vocalization
Twenty-five distinct vocalizations are recognized, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members. They also may be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication.
Aversions
Mountain gorillas generally demonstrate aversion to certain reptiles and insects. Infants, whose typical behavior is to chase anything that moves, will go out of their way to avoid chameleons and caterpillars. The gorillas also demonstrate an aversion to water bodies in the environment and will cross streams only if they can do so without getting wet, such as by using fallen logs to cross the stream. They also dislike rain.
Research
In October 1902, Captain Robert von Beringe (1865–1940) shot two large apes during an expedition to establish the boundaries of German East Africa. One of the apes was recovered and sent to the Berlin Zoological Museum, where Professor Paul Matschie (1861–1926) classified the animal as a new form of gorilla and named it Gorilla beringei after the man who shot it. In 1925, Carl Akeley, a hunter from the American Museum of Natural History who wished to study the gorillas, convinced Albert I of Belgium to establish the Albert National Park to protect the animals of the Virunga mountains.
George Schaller began his 20-month observation of the mountain gorillas in 1959, subsequently publishing two books: The Mountain Gorilla and The Year of the Gorilla. Little was known about the life of the mountain gorilla before his research, which described its social organization, life history, and ecology.
Dian Fossey began what would become an 18-year study in 1967. Fossey made new observations, completed the first accurate census, and established active conservation practices, such as anti-poaching patrols. The Digit Fund, which Fossey started, continued her work and was later renamed the Dian Fossey Gorilla Fund International. The Fund's Karisoke Research Center monitors and protects the mountain gorillas of the Virungas. Close monitoring and research of the Bwindi mountain gorillas began in the 1990s. | Mountain gorilla | Wikipedia | 496 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
Conservation
As of 2018, the mountain gorilla was listed as endangered on the IUCN Red List. Conservation efforts have led to an increase in the overall population of the mountain gorilla (Gorilla beringei beringei) in the Virungas and at Bwindi. The overall population is now believed to be at more than 1,000 individuals.
In December 2010, the official website of Virunga National Park announced that "the number of mountain gorillas living in the tri-national forested area of which Virunga forms a part, has increased by 26.3% during the last seven years - an average growth rate of 3.7% per annum." The 2010 census estimated that 480 mountain gorillas inhabited the region. The 2003 census had estimated the Virunga gorilla population to be 380 individuals, which represented a 17% increase in the total population since 1989, when there were 320 individuals. The population has almost doubled since its lowest point in 1981, when a census estimated that only 254 gorillas remained.
The 2006 census at Bwindi indicated a population of 340 gorillas, representing a 6% increase in total population size since 2002 and a 12% increase from 320 individuals in 1997. All of those estimates were based on traditional census methods using dung samples collected at night nests. Conversely, genetic analyses of the entire population during the 2006 census indicated there only were approximately 300 individuals in Bwindi. The discrepancy highlights the difficulty in using imprecise census data to estimate population growth.
According to computer modeling of their population dynamics in both Bwindi and the Virungas, groups of gorillas who were habituated for research and ecotourism have higher growth rates than unhabituated gorillas. Habituation means that through repeated, neutral contact with humans, gorillas exhibit normal behavior when people are in proximity. Habituated gorillas are more closely guarded by field staff and they receive veterinary treatment for snares, respiratory disease, and other life-threatening conditions. Nonetheless, researchers recommended that some gorillas remain unhabituated as a bet-hedging strategy against the risk of human pathogens being transmitted throughout the population.
The main international non-governmental organization involved in conservation of mountain gorillas is the International Gorilla Conservation Programme, which was established in 1991 as a joint effort of the African Wildlife Foundation, Fauna & Flora International, and the World Wide Fund for Nature. Conservation requires work at many levels, from local to international, and involves protection and law enforcement as well as research and education. | Mountain gorilla | Wikipedia | 511 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
Dian Fossey broke down conservation efforts into the following three categories:
Active conservation includes frequent patrols in wildlife areas to destroy poacher equipment and weapons, firm and prompt law enforcement, census counts in regions of breeding and ranging concentration, and strong safeguards for the limited habitat the animals occupy.
Theoretical conservation seeks to encourage growth in tourism by improving existing roads that circle the mountains, by renovating the park headquarters and tourist lodging, and by the habituation of gorillas near the park boundaries for tourists to visit and photograph.
Community-based conservation management involves biodiversity protection by, for, and with the local community.
A collaborative management process has had some success in the Bwindi Impenetrable National Park. The forest was designated a national park in 1991; this occurred with little community consultation and the new status prohibited local people from accessing resources within the park as well as reducing economic opportunities. Subsequently, a number of forest fires were deliberately lit and threats were made to the gorillas. To counteract this, three schemes to provide benefits from the existence of forest communities and involving the local community in park management were developed. They included agreements allowing the controlled harvesting of resources in the park, receipt of some revenue from tourism, and establishment of a trust fund partly for community development. Tension between people and the park has thus been reduced and now there is more willingness to take part in gorilla protection. Surveys of community attitudes conducted by CARE show a steadily increasing proportion of people in favour of the park. Moreover, there have been no cases of deliberate burning and the problem of snares in these areas has been reduced.
While community-based conservation bears out individual analysis, there are significant overlaps between active and theoretical conservation and a discussion of the two as halves of a whole seems more constructive. For example, in 2002, Rwanda's national parks went through a restructuring process. The director of the IGCP, Eugène Rutagarama, stated that "They got more rangers on better salaries, more radios, more patrol cars and better training in wildlife conservation. They also built more shelters in the park, from which rangers could protect the gorillas". The funding for these types of improvements usually comes from tourism - in 2008, approximately 20,000 tourists visited gorilla populations in Rwanda, generating around $8 million in revenue for the parks. | Mountain gorilla | Wikipedia | 471 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
According to the Director of UNESCO, Audrey Azoulay, "As we have seen in Rwanda, species conservation succeeds when local communities are placed at the heart of the conservation strategy. Biodiversity protection measures must go hand in hand with measures that meet the needs of these local communities". In Rwanda, it costs $1,500 per person to come and see the gorillas. Under Rwandan law, 10% of this revenue must be returned to the community, which represents around €10 million invested in building schools, roads and drinking water supplies. As Audrey Azoulay explains, in 1980 there were just 250 mountain gorillas, today there are 1,063 - and 80% of them in Rwanda.
In Uganda too, tourism is seen as a "high value activity that generates enough revenue to cover park management costs and contribute to the national budget of the Uganda Wildlife Authority." Furthermore, tourist visits which are conducted by park rangers also allow censuses of gorilla sub-populations to be undertaken concurrently.
In addition to tourism, other measures for conservation of the sub-population can be taken such as ensuring connecting corridors between isolated areas to make movement between them easier and safer.
Threats
The mountain gorilla is threatened by habitat loss and poaching.
Habitat loss
Loss of habitat is one of the most severe threats to gorilla populations. The forests where mountain gorillas live are surrounded by rapidly increasing human settlement. Through shifting (slash-and-burn) agriculture, pastoral expansion, and logging, villages in forest zones cause fragmentation and degradation of habitat. The late 1960s saw the Virunga Conservation Area (VCA) of Rwanda's national park reduced by more than half of its original size to support the cultivation of Pyrethrum. This led to a massive reduction in mountain gorilla population numbers by the mid-1970s. The resulting deforestation confines the gorillas to isolated deserts. Some groups may raid crops for food, creating further animosity and retaliation.
The impact of habitat loss extends beyond the reduction of suitable living space for gorillas. As gorilla groups are increasingly isolated from one another geographically due to human settlements, the genetic diversity of each group is reduced. Some signs of inbreeding are already appearing in younger gorillas, including webbed hands and feet. | Mountain gorilla | Wikipedia | 454 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
Poaching
Mountain gorillas are not usually hunted for bushmeat, but frequently, they are maimed or killed by traps and snares intended for other animals. They have been killed for their heads, hands, and feet, which are sold to collectors. Infants are sold to zoos, researchers, and people who want them as pets. The abduction of infants generally involves the loss of at least one adult, as members of a group will fight to the death to protect their young. The Virunga gorillas are particularly susceptible to animal trafficking for the illegal pet trade. With young gorillas worth from $1,000 to $5,000 on the black market, poachers seeking infant and juvenile specimens will kill and wound other members of the group in the process. Those of the group that survive often disband. One well-documented case is known as the "Taiping 4". In this situation, a Malaysian Zoo received four wild-born infant gorillas from Nigeria at a cost of US$1.6 million using falsified export documents.
Poaching for meat also is particularly threatening in regions of political unrest. Most of the African great apes survive in areas of chronic insecurity, where there is a breakdown of law and order. The killing of mountain gorillas at Bikenge in Virunga National Park in January 2007 was a well-documented case.
Disease
Despite the protection garnered from being located in national parks, the mountain gorilla is also at risk from people of a more well-meaning nature. Groups subjected to regular visits from tourists and locals are at a continued risk of disease cross-transmission (Lilly et al., 2002) – this is in spite of attempts to enforce a rule that humans and gorillas be separated by a distance of seven metres at all times to prevent this.
With a similar genetic makeup to humans and an immune system that has not evolved to cope with human disease, this poses a serious conservation threat. Indeed, according to some researchers, infectious diseases (predominantly respiratory) are responsible for approximately 20% of sudden deaths in mountain gorilla populations.
With the implementation of a successful ecotourism program in which human-gorilla interaction was minimised, during the period of 1989–2000 four sub-populations in Rwanda experienced an increase of 76%. By contrast, seven of the commonly visited sub-populations in the Democratic Republic of Congo (DRC) saw a decline of almost 20% over only four years (1996–2000). | Mountain gorilla | Wikipedia | 505 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
The risk of disease transmission is not limited to those of a human origin; pathogens from domestic animals and livestock through contaminated water are also a concern. Studies have found that waterborne, gastrointestinal parasites such as Cryptosporidium sp., Microsporidia sp., and Giardia sp. are genetically identical when found in livestock, humans, and gorillas, particularly along the border of the Bwindi Impenetrable Forest, Uganda.
War and civil unrest
Rwanda, Uganda, and the Democratic Republic of Congo have been politically unstable and beleaguered by war and civil unrest during the last decades. Using simulation modeling, Byers et al. (2003) have suggested that times of war and unrest have negative impacts on the habitat and populations of mountain gorillas. Due to the increase in human encounters, both aggressive and passive, this has resulted in a rise in mortality rates and a decrease in reproductive success.
More direct impacts from conflict can also be seen. Kanyamibwa notes that there were reports that mines were placed along trails in the Volcanoes National Park, and that many gorillas were killed as a result. Pressure from habitat destruction in the form of logging also increased as refugees fled the cities and cut down trees for wood. During the Rwandan genocide, some poaching activity also was linked to the general breakdown of law and order and lack of any ramifications. | Mountain gorilla | Wikipedia | 285 | 581632 | https://en.wikipedia.org/wiki/Mountain%20gorilla | Biology and health sciences | Apes | Animals |
In the mathematical discipline of graph theory, a matching or independent edge set in an undirected graph is a set of edges without common vertices. In other words, a subset of the edges is a matching if each vertex appears in at most one edge of that matching. Finding a matching in a bipartite graph can be treated as a network flow problem.
Definitions
Given a graph a matching M in G is a set of pairwise non-adjacent edges, none of which are loops; that is, no two edges share common vertices.
A vertex is matched (or saturated) if it is an endpoint of one of the edges in the matching. Otherwise the vertex is unmatched (or unsaturated).
A maximal matching is a matching M of a graph G that is not a subset of any other matching. A matching M of a graph G is maximal if every edge in G has a non-empty intersection with at least one edge in M. The following figure shows examples of maximal matchings (red) in three graphs.
A maximum matching (also known as maximum-cardinality matching) is a matching that contains the largest possible number of edges. There may be many maximum matchings. The matching number of a graph is the size of a maximum matching. Every maximum matching is maximal, but not every maximal matching is a maximum matching. The following figure shows examples of maximum matchings in the same three graphs.
A perfect matching is a matching that matches all vertices of the graph. That is, a matching is perfect if every vertex of the graph is incident to an edge of the matching. A matching is perfect if . Every perfect matching is maximum and hence maximal. In some literature, the term complete matching is used. In the above figure, only part (b) shows a perfect matching. A perfect matching is also a minimum-size edge cover. Thus, the size of a maximum matching is no larger than the size of a minimum edge cover: . A graph can only contain a perfect matching when the graph has an even number of vertices.
A near-perfect matching is one in which exactly one vertex is unmatched. Clearly, a graph can only contain a near-perfect matching when the graph has an odd number of vertices, and near-perfect matchings are maximum matchings. In the above figure, part (c) shows a near-perfect matching. If every vertex is unmatched by some near-perfect matching, then the graph is called factor-critical. | Matching (graph theory) | Wikipedia | 506 | 581797 | https://en.wikipedia.org/wiki/Matching%20%28graph%20theory%29 | Mathematics | Graph theory | null |
Given a matching M, an alternating path is a path that begins with an unmatched vertex and whose edges belong alternately to the matching and not to the matching. An augmenting path is an alternating path that starts from and ends on free (unmatched) vertices. Berge's lemma states that a matching M is maximum if and only if there is no augmenting path with respect to M.
An induced matching is a matching that is the edge set of an induced subgraph.
Properties
In any graph without isolated vertices, the sum of the matching number and the edge covering number equals the number of vertices. If there is a perfect matching, then both the matching number and the edge cover number are .
If and are two maximal matchings, then and . To see this, observe that each edge in can be adjacent to at most two edges in because is a matching; moreover each edge in is adjacent to an edge in by maximality of , hence
Further we deduce that
In particular, this shows that any maximal matching is a 2-approximation of a maximum matching and also a 2-approximation of a minimum maximal matching. This inequality is tight: for example, if is a path with 3 edges and 4 vertices, the size of a minimum maximal matching is 1 and the size of a maximum matching is 2.
A spectral characterization of the matching number of a graph is given by Hassani Monfared and Mallik as follows: Let be a graph on vertices, and be distinct nonzero purely imaginary numbers where . Then the matching number of is if and only if (a) there is a real skew-symmetric matrix with graph and eigenvalues and zeros, and (b) all real skew-symmetric matrices with graph have at most nonzero eigenvalues. Note that the (simple) graph of a real symmetric or skew-symmetric matrix of order has vertices and edges given by the nonozero off-diagonal entries of .
Matching polynomials
A generating function of the number of k-edge matchings in a graph is called a matching polynomial. Let G be a graph and mk be the number of k-edge matchings. One matching polynomial of G is
Another definition gives the matching polynomial as
where n is the number of vertices in the graph. Each type has its uses; for more information see the article on matching polynomials.
Algorithms and computational complexity
Maximum-cardinality matching | Matching (graph theory) | Wikipedia | 493 | 581797 | https://en.wikipedia.org/wiki/Matching%20%28graph%20theory%29 | Mathematics | Graph theory | null |
A fundamental problem in combinatorial optimization is finding a maximum matching. This problem has various algorithms for different classes of graphs.
In an unweighted bipartite graph, the optimization problem is to find a maximum cardinality matching. The problem is solved by the Hopcroft-Karp algorithm in time time, and there are more efficient randomized algorithms, approximation algorithms, and algorithms for special classes of graphs such as bipartite planar graphs, as described in the main article.
Maximum-weight matching
In a weighted bipartite graph, the optimization problem is to find a maximum-weight matching; a dual problem is to find a minimum-weight matching. This problem is often called maximum weighted bipartite matching, or the assignment problem. The Hungarian algorithm solves the assignment problem and it was one of the beginnings of combinatorial optimization algorithms. It uses a modified shortest path search in the augmenting path algorithm. If the Bellman–Ford algorithm is used for this step, the running time of the Hungarian algorithm becomes , or the edge cost can be shifted with a potential to achieve running time with the Dijkstra algorithm and Fibonacci heap.
In a non-bipartite weighted graph, the problem of maximum weight matching can be solved in time using Edmonds' blossom algorithm.
Maximal matchings
A maximal matching can be found with a simple greedy algorithm. A maximum matching is also a maximal matching, and hence it is possible to find a largest maximal matching in polynomial time. However, no polynomial-time algorithm is known for finding a minimum maximal matching, that is, a maximal matching that contains the smallest possible number of edges.
A maximal matching with k edges is an edge dominating set with k edges. Conversely, if we are given a minimum edge dominating set with k edges, we can construct a maximal matching with k edges in polynomial time. Therefore, the problem of finding a minimum maximal matching is essentially equal to the problem of finding a minimum edge dominating set. Both of these two optimization problems are known to be NP-hard; the decision versions of these problems are classical examples of NP-complete problems. Both problems can be approximated within factor 2 in polynomial time: simply find an arbitrary maximal matching M.
Counting problems | Matching (graph theory) | Wikipedia | 454 | 581797 | https://en.wikipedia.org/wiki/Matching%20%28graph%20theory%29 | Mathematics | Graph theory | null |
The number of matchings in a graph is known as the Hosoya index of the graph. It is #P-complete to compute this quantity, even for bipartite graphs. It is also #P-complete to count perfect matchings, even in bipartite graphs, because computing the permanent of an arbitrary 0–1 matrix (another #P-complete problem) is the same as computing the number of perfect matchings in the bipartite graph having the given matrix as its biadjacency matrix. However, there exists a fully polynomial time randomized approximation scheme for counting the number of bipartite matchings. A remarkable theorem of Kasteleyn states that the number of perfect matchings in a planar graph can be computed exactly in polynomial time via the FKT algorithm.
The number of perfect matchings in a complete graph Kn (with n even) is given by the double factorial (n − 1)!!. The numbers of matchings in complete graphs, without constraining the matchings to be perfect, are given by the telephone numbers.
The number of perfect matchings in a graph is also known as the hafnian of its adjacency matrix.
Finding all maximally matchable edges
One of the basic problems in matching theory is to find in a given graph all edges that may be extended to a maximum matching in the graph (such edges are called maximally matchable edges, or allowed edges). Algorithms for this problem include:
For general graphs, a deterministic algorithm in time and a randomized algorithm in time .
For bipartite graphs, if a single maximum matching is found, a deterministic algorithm runs in time .
Online bipartite matching
The problem of developing an online algorithm for matching was first considered by Richard M. Karp, Umesh Vazirani, and Vijay Vazirani in 1990.
In the online setting, nodes on one side of the bipartite graph arrive one at a time and must either be immediately matched to the other side of the graph or discarded. This is a natural generalization of the secretary problem and has applications to online ad auctions. The best online algorithm, for the unweighted maximization case with a random arrival model, attains a competitive ratio of .
Characterizations | Matching (graph theory) | Wikipedia | 467 | 581797 | https://en.wikipedia.org/wiki/Matching%20%28graph%20theory%29 | Mathematics | Graph theory | null |
Kőnig's theorem states that, in bipartite graphs, the maximum matching is equal in size to the minimum vertex cover. Via this result, the minimum vertex cover, maximum independent set, and maximum vertex biclique problems may be solved in polynomial time for bipartite graphs.
Hall's marriage theorem provides a characterization of bipartite graphs which have a perfect matching and the Tutte theorem provides a characterization for arbitrary graphs.
Applications
Matching in general graphs
A Kekulé structure of an aromatic compound consists of a perfect matching of its carbon skeleton, showing the locations of double bonds in the chemical structure. These structures are named after Friedrich August Kekulé von Stradonitz, who showed that benzene (in graph theoretical terms, a 6-vertex cycle) can be given such a structure.
The Hosoya index is the number of non-empty matchings plus one; it is used in computational chemistry and mathematical chemistry investigations for organic compounds.
The Chinese postman problem involves finding a minimum-weight perfect matching as a subproblem.
Matching in bipartite graphs
Graduation problem is about choosing minimum set of classes from given requirements for graduation.
Hitchcock transport problem involves bipartite matching as sub-problem.
Subtree isomorphism problem involves bipartite matching as sub-problem. | Matching (graph theory) | Wikipedia | 264 | 581797 | https://en.wikipedia.org/wiki/Matching%20%28graph%20theory%29 | Mathematics | Graph theory | null |
Tehran Metro () is a rapid transit system serving Tehran, the capital of Iran. It is the largest metro system in the Middle East. The system is owned and operated by Tehran Urban and Suburban Railway. It consists of six operational metro lines (and an additional commuter rail line), with construction under way on seven lines including northwestern extension of line 4, south extension line 6, northwestern and east extension line 7, east extension line 2 and Line 10, Line 8 and 9.
The Tehran Metro carries more than 3 million passengers a day. In 2018, 820 million trips were made on Tehran Metro. , the total system is long, of which is metro-grade rail. It is planned to have a length of with eleven lines once all construction is complete by 2040.
On all days of the week, the Metro service runs from 04:30 to 22:00.
The line uses standard gauge and is mostly underground. Ticket price is 5,300 Iranian Toman for each journey (about US$0.05), regardless of the distance traveled, but using prepaid tickets costs much less. Seniors may travel for free on the metro. On all Tehran metro trains the first and half of the second carriages from each end are reserved for women. Women can still ride other cars freely.
History
Initial plans for the metro system were laid in late 1960s but could not be executed until 1982 because of socio-political issues such as the Iranian Revolution and the Iran-Iraq War. In 1970, the Plan and Budget Organization and the Municipality of Tehran announced an international tender for construction of a metro in Tehran. The French company SOFRETU, affiliated with the state-owned Paris transportation authority RATP, won the tender and in the same year began to conduct preliminary studies on the project. In 1974, a final report with a so-called "street-metro" proposal was tendered. The street-metro system recommended a road network with a loop express way in the central area and two highways for new urban areas and an 8-line metro network which were complemented by bus network and taxi services. Geological surveys commenced in 1976. In 1978, construction on the line was started in northern Tehran by the French company, however this development was short-lived with the advent of the Iranian Revolution and Iran–Iraq War in 1979 and 1980 respectively. SOFRETU ceased operations in Iran in December 1980. On March 3, 1982, the Iranian Cabinet ministers formally announced the stop of Tehran Metro operations by the French company. | Tehran Metro | Wikipedia | 505 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
In 1985, the "Tehran Metro Execution Plan" was re-approved by the Majiles, the Iranian Parliament, on the basis of legal project of "Amendment of Law of Establishment of Tehran Urban and suburban Railway Company" which had been founded on Farvardin 1364 (April 1985). This was a literal continuation of exactly the same project that had been laid out before the revolution. Work proceeded slowly because of the continuing Iran–Iraq War and often ground to a halt. By the summer of 1985, urban pressure from the rapidly urbanising population, and lack of developed public transport system prompted the work to be resumed in earnest. "Line 1" (From Blvd. Shahid Ayatollah Haghani to City of Rey) and its extension to Behesht-e-Zahra Cemetery was made a priority. "Line 2" (From Dardasht in Tehran Pars district to Sadeghiyeh Second Square) and an extending towards the City of Karaj and Mehrshahr district was also made a secondary priority. Studies were also made to establish the previously designed Lines 3 & 4. It was decided that an organisation by the name of the Metro Company should be established in order to handle the future development of the system.
The Metro Company then became managed by Asghar Ebrahimi Asl for eleven years. During that time, hundreds of millions of dollars were spent on the system and the Metro Company was given government concessions for the exploitation of iron ore mines in Bandar Abbas (Hormuzgan Province), exploitation and sale of Moghan Diotomite mine in the Iranian region of Azarbaijan, export of refinery residues from Isfahan oil refinery as well as tar from Isfahan steel mill. The year after Asghar Ebrahimi Asl left the management of the Metro Company and Mohsen Hashemi succeeded him, the first line of the Tehran Metro was launched between Tehran and Karaj.
On 7 March 1999, an overland Tehran-Karaj express electric train started a limited service of between Azadi Square (Tehran) and Malard (Karaj) that called at one intermediate station at Vardavard.
Line 5 of the Tehran metro began operating in 1999. Iran's first metro system, the line was constructed by the Chinese company NORINCO. | Tehran Metro | Wikipedia | 472 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
From 2000 onwards, commercial operation began on Lines 1 and 2. The wagons on these lines are provided by CRV via CNTIC. The railway tracks and points on these lines are provided by the Austrian company Voestalpine.
The Metro uses equipment manufactured by a wide range of international companies: double-deck passenger cars for the Tehran-Karaj regional line are supplied by CRV (although some trains are from SEGC) via CNTIC and assembled by the Wagon Pars factory in Arak.
, approximately $2 billion has been spent on the Metro project. The Tehran Metro transports about 2.5 million passengers daily through its 7 operational lines (Lines 1, 2, 3, 4, 5, 7, and 8). It also has additional one line under construction (Line 6), and an additional two lines in engineering phase. New 80 wagons have been added to the system in September 2012 to ease transportation and reduce rush-hour congestion. Iran is able to produce its need in wagons and trains independently.
A branch line of Line 4 began running to Mehrabad International Airport on 15 March 2016. A express line to Imam Khomeini International Airport was opened in August 2017.
Amidst the COVID-19 cases increasing in Iran, Tehran Metro made wearing masks a requirement to enter the metro network at any station. Law enforcement located in every station were ordered to prevent passengers from entering without masks and such passengers would be led to purchase masks from mask selling desks located at every metro station.
Lines
Line 1
Line 1, coloured red on system maps, is long, of which are underground (from Tajrish station to Shoush-Khayyam crossing) and the rest runs at surface level. There are 5
2 stations along this line of which 23 stations are located underground and 8 above ground. , the total capacity of line 1 is 650,000 passenger per day, with trains stopping at each station for 20 seconds. The trains are each made up of seven wagons, with a nominal capacity of 1,300 seated and standing passengers. The maximum speed of the trains is which is tempered to an average of due to stoppages at stations along the route. | Tehran Metro | Wikipedia | 438 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
Line 1 runs mostly north–south. A , three station extension of the line from Mirdamad station to Qolhak station opened on May 20, 2009. The , four stations second phase of this extension from Qolhak station to Tajrish Square was completed in 2011. Construction was to be completed by March 2007 but faced major issues due to large boulders and rock bed in part of the tunnels as well as water drainage issues. It has also faced major financing issues as the government has refused to release funds earmarked for the project to the municipality.
Since August 2017, one of Line 1's stations, Darvazeh Dowlat is open 24 hours a day, in order to accommodate passengers traveling to and from Imam Khomeini Airport via Line 1.
Line 1 connects Tehran to Imam Khomeini International Airport. Its first phase, to Shahr-e-Aftab station, opened in 2016, and the airport station opened in August 2017. It is the only metro line in Tehran that is completely open 24 hours a day (even if the frequency is only 80 minutes...), in order to accommodate passengers from late night and early morning flights (Line 1's Darvazeh Dowlat station is the only other metro station outside of Line 1 with that classification). A third phase, which is currently operational, will extend Line 1 to the satellite city of Parand and bring the total length of the line to . Its per hour speeds classify it as an express subway line, the first of its kind on the Tehran Metro.
Line 2
This line opened between Sadeghieh and Imam Khomeini in February 2000. Line 2 is long, with underground and elevated. There are 22 stations along the line, of which Imam Khomeini Station was shared by Line 1. Line 2 is coloured blue on system maps and runs mostly east–west through the city.
The line was extended from Imam-Khomeini to Baharestan Metro Station in 2004, and to Shahid Madani, Sarsabz and Elm-o-Sanat University in March 2006 with the intermediate stations, Darvazeh Shemiran and Sabalan, opening in July 2006. It was extended further from Elm-o-Sanat University to Tehran Pars in February 2009, and to Farhangsara in June 2010. The extension phase to new east terminal is under construction.
Line 3 | Tehran Metro | Wikipedia | 495 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
Line 3 travels from northeast to southwest. Line 3 is one of the most important lines as it connects southwest Tehran to northeast, crosses busy parts of the capital city, and can help to alleviate traffic problems. About of Line 3 became operational in December 2012, followed by in April 2014, and finally, the last section of the line which is opened on September 22, 2015, increasing the length of the line to a total of , and serving 25 stations .
Line 4
The line is long with 23 stations. which connects the western part of Tehran to eastern part. This line initially runs through Ekbatan (western Tehran) to Kolahdooz (eastern Tehran). The construction of a western extension to line 4 has been started in 2012 connecting Ekbatan to Chaharbagh Sq. This extension will include 3 stations. A sub-line of this line connects Bimeh station to Mehrabad Airport. This sub-line has 3 stations at Bimeh, Terminal 1&2 and Terminal 4&6.
Section 1, from Ferdowsi Square to Darvazeh Shemiran, opened in April 2008. Section 2 from Darvazeh shemiran to Shohada Square opened in February 2009. On May 24, 2009, Section 3 from Ferdowsi Square to Enghelab Square opened. On July 23, 2012, two more stations were inaugurated, connecting line 4 with line 5.
Currently there are 23 stations in operation on Line 4, coloured yellow on the system maps.
Line 5
Line 5 is coloured green on system maps; it is a commuter rail line and has 13 stations. Entering the area of Karaj with main stations at Karaj and Golshahr and Hashtgerd. It connects with the western end of Line 2 at Tehran (Sadeghiyeh) station, and with the western end of Line 4 at Eram-e Sabz Metro Station.
Line 6
Line 6 is pink coloured on system maps. An initial section between Shohada Square to Dowlat Abad opened on April 7, 2019. This line is long with 13 stations right now. When completed, this line will be long with 31 stations, connecting southeast Tehran to northwest. A tunnel boring machine (TBM) is used to construct the tunnel. TBM is using earth pressure balanced method to pass safely through urban areas without considerable settlement.
Line 7 | Tehran Metro | Wikipedia | 484 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
This line, similar to line 6, and in contrast with line 3, goes from northwest to southeast and was constructed with modern TBM machines. Its first phase, compromising of of line and 7 stations were opened in June 2017. This line has with 20 stations right now.
Future plans
There are several plans to expand Tehran's metro network to over in total. Some plans only concern additional inserted stations, like Vavan on line 1 in the South or Aghdasiyeh on line 3 in the North. Some extensions and completely new lines are under construction, some extensions or new lines are proposals in the moment.
Under construction
Line 3 (formerly named Eslamshahr line)
In the south, line 3 will continue for from the terminus Azadegan with five new stations to Eslamshahr. Originally, the plan was to build a commuter rail-link like line 5 with a new interchange platform at Azadegan under the name "Eslamshahr Line". But until construction began in 2016, the plans were changed into a transfer-free extension of the existing route. The opening is scheduled for 2025.
Line 6
Line 6 extension is on the way in the Northwest, where three new stations are built, and at the East end, where one additional station is under construction.
Line 7
There is an extension of one station each from each recent terminus in the North and in the Southeast under construction.
Line 10
The completely rebuilt line 10, coloured dark blue in the system map, stretching with 35 stations will run along a west–east corridor from Vardavard metro station of line 5 in the west of Tehran towards the area of Kosar aqueduct in the east with an interchange to the extended line 4. Construction started in September 2020.
Further plans
Line 8
Line 8 of Tehran's Metro, coloured brown in the system map, is a planned circular line, surrounding the city center from Fadak station (line 2) in the North, over the West, and ending in the southeastern borough of Shahrak-e-Valfajr. It might have 34 stations, 21 of them newly built, while the others will be expanded existing ones becoming interchange stations to other lines. | Tehran Metro | Wikipedia | 441 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
Line 9
The planned line 9 of the metro network, coloured golden in the system map, is another circular line, starting further west at line 5 station Chitgar, passing the city center in the North, turning south and ending at line 6 station Dowlat Abad. It might have 39 stations all together, 27 of them new constructed, while the others will be expansions of existing stations to become interchanges to other lines.
Line 11
Line 11, coloured light green in the system map, is another planned tangent line, starting from Chitgar station at line 5, connecting the southern parts of Tehran, and ending in the Southeast in the borough of Eslam Abad. It might have 18 stations, most of them newly built, just five to be expanded existing stations to become interchanges with other lines.
LRT Lines
3 LRT (Tram) lines are proposed along with the Metro lines.
Express Commuter Railway
3 other commuter Rail lines are planned along with Line 5 (Tehran-Karaj-Hashtgerd Commuter Rail) bringing the total Metro Commuter Rails to 4 Lines . | Tehran Metro | Wikipedia | 219 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
Interchange stations
1- Darvazeh Shemiran; Lines 2 & 4
2- Shahid Beheshti; Lines 1 & 3
3- Darvazeh Dowlat; Lines 1 & 4
4- Imam Khomeini; Lines 1 & 2
5- Theatr-e Shahr; Lines 3 & 4
6- Shademan; Lines 2 & 4
7- (Tehran) Sadeghiyeh; Lines 2 & 5
8- Eram-e Sabz; Lines 4 & 5
9- Shahid Navvab-e Safavi; Lines 2 & 7
10- Mahdiyeh; Lines 3 & 7
11- Meydan-e Shohada; Lines 4 & 6
12- Meydan-e Mohammadiyeh; Lines 1 & 7
13- Imam Hossein; Lines 2 & 6
14- Daneshgah-e Tarbiat Modares; Lines 6 & 7
15- Towhid; Lines 4 & 7
16- Shohada-ye Haftom-e Tir; Lines 1 & 6
17- Meydan-e Vali Asr; Lines 3 & 6
18- Shohada-ye Hefdah-e Shahrivar; Lines 6 & 7 (under construction on line 6, operational on line 7)
19- Daneshgah-e Emam Ali; Lines 2 & 3 (operational on line 2, planned on line 3)
20- Ayatollah Kashani; Lines 4 & 6 (under construction on line 4, operational on line 6)
21- Shahr-e-Rey; Lines 1 & 6 (operational on line 1, under construction on line 6)
Network map
Safety
All routes have been equipped with automatic train protection (ATP), automatic train stop (ATS), centralized traffic control (CTC), and SCADA. More and more residents use the metro due to the improvement in the peak-hour headways, the opening of more stations and overall improvement with new escalators, elevators, and air-conditioning in the trains. | Tehran Metro | Wikipedia | 423 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
On 18 July 2007, a twenty square metres area immediately adjacent to the entrance of the Toupkhaneh metro station caved in. There were no casualties, but the station had to undergo numerous repairs.
On 15 April 2012, safety walls of Mianrood River broke due to heavy rain in Tehran, and consequently, 300,000 cubic meters of water entered metro tunnel of Line 4. The two nearest stations were still under construction, so Metro operators had enough time to evacuate other stations from passengers. Nobody was killed, but water depth in the Habib-o-llah station, the deepest station on Line 4, was estimated to be near 18 meters. It took nearly two weeks to reopen the flooded stations which were previously in operation.
Complaints
The Cultural Heritage Organization of Iran has complained that the vibrations caused by the Metro were having a significant and highly adverse effect on the Masoudieh Palace in the Baharestan neighbourhood of central Tehran. The Cultural Heritage Organisation has also complained about vibrations near other historic sites such as the Golestan Palace and the National Museum of Iran.
Tickets
Regular single table tickets
You can only use the subway once with this ticket. This ticket costs 12,000 Rials. If you plan to take a round trip, you need to get two single tickets.
Suburban single table tickets
This is the ticket from the 5th metro line that reaches Sadeghieh station from Karaj station. This ticket costs 12,000 Rials.
International Airport Single Ticket
This ticket is used for the subway line of Imam Khomeini Airport. This ticket costs 90,000 Rials.
Electronic ticket
You can use the subway as many times as you want by charging it. The cost of each of these e-cards is 30,000 Rials or 50,000 Rials and you can charge up to 500,000 Rials after purchase. You can charge your e-card using various booths and wall-mounted electronic charging devices at the bus and subway stations, either by cash or by bank credit card and with non-attendance methods such as my Tehran app
Tehran Metro Snapshot
Gallery | Tehran Metro | Wikipedia | 423 | 2174399 | https://en.wikipedia.org/wiki/Tehran%20Metro | Technology | Asia_2 | null |
A microbial cyst is a resting or dormant stage of a microorganism, that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. Many groups of single-celled, microscopic organisms, or microbes, possess the ability to enter this dormant state.
Encystment, the process of cyst formation, can function as a method for dispersal and as a way for an organism to survive in unfavorable environmental conditions. These two functions can be combined when a microbe needs to be able to survive harsh conditions between habitable environments (such as between hosts) in order to disperse. Cysts can also be sites for nuclear reorganization and cell division, and in parasitic species they are often the infectious stage between hosts. When the encysted microbe reaches an environment favorable to its growth and survival, the cyst wall breaks down by a process known as excystation.
Environmental conditions that may trigger encystment include, but are not limited to: lack of nutrients or oxygen, extreme temperatures, desiccation, adverse pH, and presence of toxic chemicals which are not conducive for the growth of the microbe.
History and terminology
The idea that microbes could temporarily assume an alternate state of being to withstand changes in environmental conditions began with Antonie van Leeuwenhoek’s 1702 study on Animalcules, currently known as rotifers:
“'I have often placed the Animalcules I have before described out of the water, not leaving the quantity of a grain of sand adjoining to them, in order to see whether when all the water about them was evaporated and they were exposed to the air their bodies would burst, as I had often seen in other Animalcules. But now I found that when almost all the water was evaporated, so that the creature could no longer be covered with water, nor move itself as usual, it then contracted itself into an oval figure, and in that state it remained, nor could I perceive that the moisture evaporated from its body, for it preserved its oval and round shape, unhurt." | Microbial cyst | Wikipedia | 452 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
Leeuwenhoek later continued his work with rotifers to discover that when he returned the dried bodies to their preferred aquatic conditions, they resumed their original shape and began swimming again. These observations did not gain traction with the general microbiological community of the time, and the phenomena as Leeuwenhoek observed it was never given a name.
In 1743, John Turberville Needham observed the revival of the encysted larval stage of the wheat parasite, Anguillulina tritici and later published these findings in New Microscopal Discoveries (1745). Several others repeated and expanded upon this work, informally referring to their studies on the “phenomenon of reviviscence.”
In the late 1850s, reviviscence became embroiled in the debate surrounding the theory of spontaneous generation of life, leading two highly involved scientists on either side of the issue to call upon the Biological Society of France for an independent review of their opposing conclusions on the matter. Doyere, who believed rotifers could be desiccated and revitalized, and Pouchet, who believed they could not, allowed independent observers of various scientific backgrounds to observe and attempt to replicate their findings. The resulting report leaned toward the arguments made by Pouchet, with notable dissension from the main author who blamed his framing of the issue in the report on fear of religious retribution. Despite the attempt by Doyere and Pouchet to conclude debate on the topic of resurrection, investigations continued.
In 1872, Wilhelm Preyer introduced the term ‘anabiosis’ (return to life) to describe the revitalization of viable, lifeless organisms to an active state. This was quickly followed by Schmidt’s 1948 proposal of the term ‘abiosis,’ leading to some confusion between terms describing the beginning of life from non-living elements, viable lifelessness, and nonliving components that are necessary for life.
As part of his 1959 review of Leeuwenhoek’s original findings and the evolution of the science surrounding microbial cysts and other forms of metabolic suspension, D. Keilin proposed the term ‘cryptobiosis’ (latent life) to describe:
“...the state of an organism when it shows no visible signs of life and when its metabolic activity becomes hardly measurable, or comes reversibly to a standstill.” | Microbial cyst | Wikipedia | 483 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
As microbial research began to gain popularity exponentially, details about ciliated protist physiology and cyst formation led to increased curiosity about the role of encystment in the life cycle of ciliates and other microbes. The realization that no one category of microscopic organism ‘owns’ the ability to form metabolically dormant cysts necessitates the term ‘microbial cyst’ to describe the physical object as it exists in all its forms. Also important in the generation of the term, is the delineation of endospores and microbial cysts as different forms of cryptobiosis or dormancy. Endospores exhibit more extreme isolation from their environment in terms of cell wall thickness, impermeability to substrates, and presence of dipicolinic acid, a compound known to confer resistance to extreme heat. Microbial cysts have been likened to modified vegetative cells with the addition of a specialized capsule. Importantly, encystment is a process observed to precede cell division, while the formation of an endospore involves non-reproductive cellular division. The study of the encystment process was mostly confined to the 1970s and '80s, resulting in the lack of understanding of genetic mechanisms and additional defining characteristics, though they are generally thought to follow a different formation sequence than endospores.
Formation and composition of the cyst wall
Indicators of cyst formation in ciliated protists include varying degrees of ciliature resorption, with some ciliates losing both cilia and the membranous structures supporting them while others maintain kinetosomes and/or microtubular structures. De novo synthesis of cyst wall precursors in the endoplasmic reticulum also frequently indicate a ciliate is undergoing encystment. | Microbial cyst | Wikipedia | 373 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
The composition of the cyst wall is variable in different organisms.
The cyst walls of bacteria are formed by the thickening of the normal cell wall with added peptidoglycan layers.
The walls of protozoan cysts are made of chitin, a type of glycopolymer.
The cyst wall of some ciliated protists is composed of four layers, ectocyst, mesocyst, endocyst, and the granular layer. The ectocyst is the outer layer and contains a plug-like structure through which the vegetative cell reemerges during excystation. Interior to the ectocyst, the thick mesocyst is compact yet stratified in density. Chitinase treatments indicate the presence of chitin in the mesocyst of some ciliate species, but this compositional characteristic appears to be highly heterogeneous. The thin endocyst, interior to the mesocyst, is less dense than the ectocyst and is believed to be composed of proteins. The innermost granular layer lies directly outside the pellicle and is composed of de novo synthesized precursors of granular material.
Cyst formation across species
In bacteria
In bacteria (for instance, Azotobacter sp.), encystment occurs by changes in the cell wall; the cytoplasm contracts and the cell wall thickens. Various members of the Azotobacteraceae family have been shown to survive in an encysted form for up to 24 years. The extremophile Rhodospirillum centenum, an anoxygenic, photosynthetic, nitrogen-fixing bacterium that grows in hot springs was found to form cysts in response to desiccation as well. Bacteria do not always form a single cyst. Varieties of cysts formation events are known. Rhodospirillum centenum can change the number of cysts per cell, usually ranging from four to ten cells per cyst depending on the environment. | Microbial cyst | Wikipedia | 428 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
Some species of filamentous cyanobacteria have been known to form heterocysts to escape levels of oxygen concentration detrimental to their nitrogen fixing processes. This process is distinct from other types of microbial cysts in that the heterocysts are often produced in a repeating pattern within a filament composed of several vegetative cells, and once formed, heterocysts cannot return to a vegetative state.
In protists
Protists, especially protozoan parasites, are often exposed to very harsh conditions at various stages in their life cycle. For example, Entamoeba histolytica, a common intestinal parasite that causes dysentery, has to endure the highly acidic environment of the stomach before it reaches the intestine and various unpredictable conditions like desiccation and lack of nutrients while it is outside the host. An encysted form is well suited to survive such extreme conditions, although protozoan cysts are less resistant to adverse conditions compared to bacterial cysts. Cytoplasmic dehydration, high autophagic activity, nuclear condensation, and decrease of cell volume are all indicators of encystment initiation in ciliated protists. In addition to survival, the chemical composition of certain protozoan cyst walls may play a role in their dispersal. The sialyl groups present in the cyst wall of Entamoeba histolytica confer a net negative charge to the cyst which prevents its attachment to the intestinal wall thus causing its elimination in the feces. Other protozoan intestinal parasites like Giardia lamblia and Cryptosporidium also produce cysts as part of their life cycle (see oocyst). Due to the hard outer shell of the cyst, Cryptosporidium and Giardia are resistant to common disinfectants used by water treatment facilities such as chlorine. In some protozoans, the unicellular organism multiplies during or after encystment and releases multiple trophozoites upon excystation.
Many additional species of protists have been shown to exhibit encystment when confronted with unfavorable environmental conditions.
In rotifers | Microbial cyst | Wikipedia | 463 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
Rotifers also produce diapause cysts, which are different from quiescent (environmentally triggered) cysts in that the process of their formation begins before environmental conditions have deteriorated to unfavorable levels and the dormant state may extend past the restoration of ideal conditions for microbial life. Food limited females of some Synchaeta pectinata strains produce unfertilized diapausing eggs with a thicker shell. Fertilized diapausing eggs can be produced in both food limited and non-food limited conditions, indicative of a bet-hedging mechanism for food availability or perhaps an adaptation to variation in food levels throughout a growing season.
Pathology
While the cyst component itself is not pathogenic, the formation of a cyst is what gives Giardia its primary tool of survival and its ability to spread from host to host. Ingestion of contaminated water, foods, or fecal matter gives rise to the most commonly diagnosed intestinal disease, giardiasis.
Whereas it was previously believed that encystment only served a purpose for the organism itself, it has been found that protozoan cysts have a harboring effect. Common pathogenic bacteria can also be found taking refuge in the cyst of free-living protozoa. Survival times for bacteria in these cysts range from a few days to a few months in harsh environments. Not all bacteria are guaranteed to survive in the cyst formation of a protozoan; many species of bacteria are digested by the protozoan as it undergoes cystic growth. | Microbial cyst | Wikipedia | 317 | 14469976 | https://en.wikipedia.org/wiki/Microbial%20cyst | Biology and health sciences | Biological reproduction | null |
The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaii to the edge of the Aleutian Trench, near the eastern coast of Russia.
While some volcanoes are created by geologic processes near tectonic plate convergence and subduction zones, the Hawaii hotspot is located far from plate boundaries. The classic hotspot theory, first proposed in 1963 by John Tuzo Wilson, proposes that a single, fixed mantle plume builds volcanoes that then, cut off from their source by the movement of the Pacific Plate, this causes less lava to erupt from these volcanoes and eventually erode below sea level over millions of years. According to this theory, the nearly 60° bend where the Emperor and Hawaiian segments within the seamounts was caused by shift in the movement of the Pacific Plate. Studies on tectonic movement have shown that several plates have changed their direction of plate movement because of differential subduction rates, breaking off of suducting slabs, and drag forces. In 2003, new investigations of this irregularity led to the proposal of a mobile hotspot hypothesis, suggesting that hotspots are prone to movement instead of the previous idea that hotspots are fixed in place, and that the 47-million-year-old bend was caused by a shift in the hotspot's motion rather than the plate's. According to this 2003 study, this could occur through plume drag taking parts of the plume in the direction of plate movement while the main plume could remain stationary. Many other hot spot tracks move in almost parallel so current thinking is a combination of these ideas. | Hawaii hotspot | Wikipedia | 411 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Ancient Hawaiians were the first to recognize the increasing age and weathered state of the volcanoes to the north as they progressed on fishing expeditions along the islands. The volatile state of the Hawaiian volcanoes and their constant battle with the sea was a major element in Hawaiian mythology, embodied in Pele, the deity of volcanoes. After the arrival of Europeans on the island, in 1880–1881 James Dwight Dana directed the first formal geological study of the hotspot's volcanics, confirming the relationship long observed by the natives. The Hawaiian Volcano Observatory was founded in 1912 by volcanologist Thomas Jaggar, initiating continuous scientific observation of the islands. In the 1970s, a mapping project was initiated to gain more information about the complex geology of Hawaii's seafloor.
The hotspot has since been tomographically imaged, showing it to be wide and up to deep, and olivine and garnet-based studies have shown its magma chamber is approximately . In its at least 85 million years of activity the hotspot has produced an estimated of rock. The chain's rate of drift has slowly increased over time, causing the amount of time each individual volcano is active to decrease, from 18 million years for the 76-million-year-old Detroit Seamount, to just under 900,000 for the one-million-year-old Kohala; on the other hand, eruptive volume has increased from per year to about . Overall, this has caused a trend towards more active but quickly-silenced, closely spaced volcanoes — whereas volcanoes on the near side of the hotspot overlap each other (forming such superstructures as Hawaii Island and the ancient Maui Nui), the oldest of the Emperor seamounts are spaced as far as apart.
Theories
Tectonic plates generally focus deformation and volcanism at plate boundaries. However, the Hawaii hotspot is more than from the nearest plate boundary; while studying it in 1963, Canadian geophysicist J. Tuzo Wilson proposed the hotspot theory to explain these zones of volcanism so far from regular conditions, a theory that has since come into wide acceptance.
Wilson's stationary hotspot theory | Hawaii hotspot | Wikipedia | 441 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Wilson proposed that mantle convection produces small, hot, buoyant upwellings under the Earth's surface; these thermally active mantle plumes supply magma which in turn sustains long-lasting volcanic activity. This "mid-plate" volcanism builds peaks that rise from relatively featureless sea floor, initially as seamounts and later as fully-fledged volcanic islands. The local tectonic plate (in the case of the Hawaii hotspot, the Pacific Plate) gradually passes over the hotspot, carrying its volcanoes with it without affecting the plume. Over hundreds of thousands of years, the magma supply for an individual volcano is slowly cut off, eventually causing its extinction. No longer active enough to overpower erosion, the volcano slowly recedes beneath the waves, becoming a seamount once again. As the cycle continues, a new volcanic center pierces the crust, and a volcanic island arises anew. The process continues until the mantle plume itself collapses.
This cycle of growth and dormancy strings together volcanoes over millions of years, leaving a trail of volcanic islands and seamounts across the ocean floor. According to Wilson's theory, the Hawaiian volcanoes should be progressively older and increasingly eroded the further they are from the hotspot, and this is easily observable; the oldest rock in the main Hawaiian islands, that of Kauai, is about 5.5 million years old and deeply eroded, while the rock on Hawaii Island is a comparatively young 0.7 million years of age or less, with new lava constantly erupting at Kīlauea, the hotspot's present center. Another consequence of his theory is that the chain's length and orientation serves to record the direction and speed of the Pacific Plate's movement. A major feature of the Hawaiian trail is a "sudden" 60-degree bend at a 40- to 50-million-year-old section of its length, and according to Wilson's theory, this is evidence of a major change in plate direction, one that would have initiated subduction along much of the Pacific Plate's western boundary. This part of the theory has recently been challenged, and the bend might be attributed to the movement of the hotspot itself. | Hawaii hotspot | Wikipedia | 455 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Geophysicists believe that hotspots originate at one of two major boundaries deep in the Earth, either a shallow interface in the lower mantle between an upper mantle convecting layer and a lower non-convecting layer, or a deeper D'' ("D double-prime") layer, approximately thick and immediately above the core-mantle boundary. A mantle plume that would initiate melt is generated through partial melting of mantle material, reduction in melting point through addition of volatiles by subduction of hydrated slabs, and decrease in pressure due to erosional processes. This heated, buoyant, and less-viscous portion of the upper layer would become less dense due to thermal expansion, and rise towards the surface as a Rayleigh-Taylor instability. When the mantle plume reaches the base of the lithosphere, the plume heats it and produces melt. This magma then makes its way to the surface, where it is erupted as lava.
Arguments for the validity of the hotspot theory generally center on the steady age progression of the Hawaiian islands and nearby features: a similar bend in the trail of the Macdonald hotspot, the Austral–Marshall Islands seamount chain, located just south; other Pacific hotspots following the same age-progressed trend from southeast to northwest in fixed relative positions; and seismologic studies of Hawaii which show increased temperatures at the core–mantle boundary, showing further evidence for a mantle plume forming.
Shallow hotspot hypothesis | Hawaii hotspot | Wikipedia | 301 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Another hypothesis is that melting anomalies form as a result of lithospheric extension, which allows pre-existing melt to rise to the surface. These melting anomalies are normally called "hotspots", but under the shallow-source hypothesis the mantle underlying them is not anomalously hot. In the case of the Hawaiian–Emperor seamount chain, the Pacific plate boundary system was very different around 80 Mya, when the Emperor seamount chain began to form. There is evidence that the chain started on a spreading ridge (the Pacific-Kula Ridge) that has now been subducted at the Aleutian trench. The locus of melt extraction may have migrated off the ridge and into the plate interior, leaving a trail of volcanism behind it. This migration may have occurred because this part of the plate was extending in order to accommodate intraplate stress. Thus, a long-lived region of melt escape could have been sustained. Supporters of this hypothesis argue that the wavespeed anomalies seen in seismic tomographic studies cannot be reliably interpreted as hot upwellings originating in the lower mantle.
Moving hotspot theory
The most heavily challenged element of Wilson's theory is whether hotspots are indeed fixed relative to the overlying tectonic plates. Drill samples, collected by scientists as far back as 1963, suggest that the hotspot may have drifted over time, at the relatively rapid pace of about per year during the late Cretaceous and early Paleogene eras (81–47 Mya); in comparison, the Mid-Atlantic Ridge spreads at a rate of per year. In 1987, a study published by Peter Molnar and Joann Stock found that the hotspot does move relative to the Pacific Ocean; however, they interpreted this as the result of the relative motions of the North American and Pacific plates rather than that of the hotspot itself. | Hawaii hotspot | Wikipedia | 387 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
In 2021 researchers proposed a three stage Hawaii hotspot model. The first stage has ridge plume interaction in which the Hawaii hotspot either fed the Izanagi-Pacific or Kula-Pacific ridge. This period involved the creation of young oceanic crust and the formation of the Meji and Detroit seamounts. The second stage involved the mutual movements of the Pacific plate and the Hawaii hotspot. It is possible, as supported by gravitational modelling, that during this period that the Hawaii hotspot drifted about 4-9 degrees to the south, in contrast to the northward Pacific Plate movement. The third stage has continued movement of the Pacific plate, with stagnation of the Hawaii hotspot.
In 2001 the Ocean Drilling Program (since merged into the Integrated Ocean Drilling Program), an international research effort to study the world's seafloors, funded a two-month expedition aboard the research vessel JOIDES Resolution to collect lava samples from four submerged Emperor seamounts. The project drilled Detroit, Nintoku, and Koko seamounts, all of which are in the far northwest end of the chain, the oldest section. These lava samples were then tested in 2003, suggesting a mobile Hawaiian hotspot and a shift in its motion as the cause of the bend. Lead scientist John Tarduno told National Geographic:
The Hawaii bend was used as a classic example of how a large plate can change motion quickly. You can find a diagram of the Hawaii–Emperor bend entered into just about every introductory geological textbook out there. It really is something that catches your eye." | Hawaii hotspot | Wikipedia | 323 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Despite the large shift, the change in direction was never recorded by magnetic declinations, fracture zone orientations or plate reconstructions; nor could a continental collision have occurred fast enough to produce such a pronounced bend in the chain. To test whether the bend was a result of a change in direction of the Pacific Plate, scientists analyzed the lava samples' geochemistry to determine where and when they formed. Age was determined by the radiometric dating of radioactive isotopes of potassium and argon. Researchers estimated that the volcanoes formed during a period 81 million to 45 million years ago. Tarduno and his team determined where the volcanoes formed by analyzing the rock for the magnetic mineral magnetite. While hot lava from a volcanic eruption cools, tiny grains within the magnetite align with the Earth's magnetic field, and lock in place once the rock solidifies. Researchers were able to verify the latitudes at which the volcanoes formed by measuring the grains' orientation within the magnetite. Paleomagnetists concluded that the Hawaiian hotspot had drifted southward sometime in its history, and that, 47 million years ago, the hotspot's southward motion greatly slowed, perhaps even stopping entirely.
History of study
Ancient Hawaiians
The possibility that the Hawaiian Islands became older as one moved to the northwest was suspected by ancient Hawaiians long before Europeans arrived. During their voyages, seafaring Hawaiians noticed differences in erosion, soil formation, and vegetation, allowing them to deduce that the islands to the northwest (Niihau and Kauai) were older than those to the southeast (Maui and Hawaii). The idea was handed down the generations through the legend of Pele, the Hawaiian goddess of volcanoes. | Hawaii hotspot | Wikipedia | 346 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Pele was born to the female spirit Haumea, or Hina, who, like all Hawaiian gods and goddesses, descended from the supreme beings, Papa, or Earth Mother, and Wakea, or Sky Father. According to the myth, Pele originally lived on Kauai, when her older sister Nāmaka, the Goddess of the Sea, attacked her for seducing her husband. Pele fled southeast to the island of Oahu. When forced by Nāmaka to flee again, Pele moved southeast to Maui and finally to Hawaii, where she still lives in Halemaʻumaʻu at the summit of Kīlauea. There she was safe, because the slopes of the volcano are so high that even Nāmaka's mighty waves could not reach her. Pele's mythical flight, which alludes to an eternal struggle between volcanic islands and ocean waves, is consistent with geologic evidence about the ages of the islands decreasing to the southeast.
Modern studies
Three of the earliest recorded observers of the volcanoes were the Scottish scientists Archibald Menzies in 1794, James Macrae in 1825, and David Douglas in 1834. Just reaching the summits proved daunting: Menzies took three attempts to ascend Mauna Loa, and Douglas died on the slopes of Mauna Kea. The United States Exploring Expedition spent several months studying the islands in 1840–1841. American geologist James Dwight Dana was on that expedition, as was Lieutenant Charles Wilkes, who spent most of the time leading a team of hundreds that hauled a Kater's pendulum to the summit of Mauna Loa to measure gravity. Dana stayed with missionary Titus Coan, who would provide decades of first-hand observations. Dana published a short paper in 1852. | Hawaii hotspot | Wikipedia | 355 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Dana remained interested in the origin of the Hawaiian Islands, and directed a more in-depth study in 1880 and 1881. He confirmed that the islands' age increased with their distance from the southeasternmost island by observing differences in their degree of erosion. He also suggested that many other island chains in the Pacific showed a similar general increase in age from southeast to northwest. Dana concluded that the Hawaiian chain consisted of two volcanic strands, located along distinct but parallel curving pathways. He coined the terms "Loa" and "Kea" for the two prominent trends. The Kea trend includes the volcanoes of Kīlauea, Mauna Kea, Kohala, Haleakalā, and West Maui. The Loa trend includes Lōihi, Mauna Loa, Hualālai, Kahoolawe, Lānai, and West Molokai. Dana proposed that the alignment of the Hawaiian Islands reflected localized volcanic activity along a major fissure zone. Dana's "great fissure" theory served as the working hypothesis for subsequent studies until the mid-20th century.
Dana's work was followed up by the 1884 expedition of geologist C. E. Dutton, who refined and expanded Dana's ideas. Most notably, Dutton established that the island of Hawaii actually harbored five volcanoes, whereas Dana counted three. This is because Dana had originally regarded Kīlauea as a flank vent of Mauna Loa, and Kohala as part of Mauna Kea. Dutton also refined others of Dana's observations, and is credited with the naming of 'a'ā and pāhoehoe-type lavas, although Dana had also noted a distinction. Stimulated by Dutton's expedition, Dana returned in 1887, and published many accounts of his expedition in the American Journal of Science. In 1890 he published the most detailed manuscript of its day, which remained the definitive guide to Hawaiian volcanism for decades. In 1909 two major books about Hawaii's volcanoes were published ("The volcanoes of Kilauea and Mauna Loa" by W.T. Brigham and "Hawaii and its volcanoes" by C.H. Hitchcock). | Hawaii hotspot | Wikipedia | 431 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
In 1912 geologist Thomas Jaggar founded the Hawaiian Volcano Observatory. The facility was taken over in 1919 by the National Oceanic and Atmospheric Administration and in 1924 by the United States Geological Survey (USGS), which marked the start of continuous volcano observation on Hawaii Island. The next century was a period of thorough investigation, marked by contributions from many top scientists. The first complete evolutionary model was first formulated in 1946, by USGS geologist and hydrologist Harold T. Stearns. Since that time, advances (e.g. improved rock dating methods and submarine volcanic stages) have enabled the study of previously limited areas of observation.
In the 1970s, the Hawaiian seafloor was mapped using ship-based sonar. Computed SYNBAPS (Synthetic Bathymetric Profiling System) data filled gaps between the ship-based sonar bathymetric measurements. From 1994 to 1998 the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) mapped Hawaii in detail and studied its ocean floor, making it one of the world's best-studied marine features. The JAMSTEC project, a collaboration with USGS and other agencies, employed manned submersibles, remotely operated underwater vehicles, dredge samples, and core samples. The Simrad EM300 multibeam side-scanning sonar system collected bathymetry and backscatter data.
Characteristics
Position
The Hawaii hotspot has been imaged through seismic tomography, and is estimated to be wide. Tomographic images show a thin low-velocity zone extending to a depth of , connecting with a large low-velocity zone extending from a depth of to the core-mantle boundary. These low seismic velocity zones often indicate hotter and more buoyant mantle material, consistent with a plume originating in the lower mantle and a pond of plume material in the upper mantle. The low-velocity zone associated with the source of the plume is north of Hawaii, showing that the plume is tilted to a certain degree, deflected toward the south by mantle flow. Uranium decay-series disequilibria data has shown that the actively flowing region of the melt zone is km wide at its base and at the upper mantle upwelling, consistent with tomographic measurements. | Hawaii hotspot | Wikipedia | 445 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Temperature
Indirect studies found that the magma chamber is located about underground, which matches the estimated depth of the Cretaceous Period rock in the oceanic lithosphere; this may indicate that the lithosphere acts as a lid on melting by arresting the magma's ascent. The magma's original temperature was found in two ways, by testing garnet's melting point in lava and by adjusting the lava for olivine deterioration. Both USGS tests seem to confirm the temperature at about ; in comparison, the estimated temperature for mid-ocean ridge basalt is about .
The surface heat flow anomaly around the Hawaiian Swell is only of the order of 10 mW/m2, far less than the continental United States range of 25–150 mW/m2. This is unexpected for the classic model of a hot, buoyant plume in the mantle. However, it has been shown that other plumes display highly variable surface heat fluxes and that this variability may be due to variable hydrothermal fluid flow in the Earth's crust above the hotspots. This fluid flow advectively removes heat from the crust, and the measured conductive heat flow is therefore lower than the true total surface heat flux. The low heat across the Hawaiian Swell indicates that it is not supported by a buoyant crust or upper lithosphere, but is rather propped up by the upwelling hot (and therefore less-dense) mantle plume that causes the surface to rise through a mechanism known as "dynamic topography".
Movement
Hawaiian volcanoes drift northwest from the hotspot at a rate of about a year. The hotspot has migrated south by about relative to the Emperor chain. Paleomagnetic studies support this conclusion based on changes in Earth's magnetic field, as captured in the orientation of magnetically susceptible mineral grains imprinted on igneous rocks during crystallization of the different rock bodies, showing that these seamounts formed at higher latitudes than present-day Hawaii. Prior to the bend, the hotspot migrated an estimated per year; the rate of movement changed at the time of the bend to about per year. The Ocean Drilling Program provided most of the current knowledge about the drift. The 2001 expedition drilled six seamounts and tested the samples to determine their original latitude, and thus the characteristics and speed of the hotspot's drift pattern in total. | Hawaii hotspot | Wikipedia | 479 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Each successive volcano spends less time actively attached to the plume. The large difference between the youngest and oldest lavas between Emperor and Hawaiian volcanoes indicates that the hotspot's velocity is increasing. For example, Kohala, the oldest volcano on Hawaii island, is one million years old and last erupted 120,000 years ago, a period of just under 900,000 years; whereas one of the oldest, Detroit Seamount, experienced 18 million or more years of volcanic activity.
The oldest volcano in the chain, Meiji Seamount, perched on the edge of the Aleutian Trench, formed 85 million years ago. At its current velocity, the seamount will be destroyed within a few million years, as the Pacific Plate slides under the Eurasian Plate. It is unknown whether the seamount chain has been subducting under the Eurasian Plate, and whether the hotspot is older than Meiji Seamount, as any older seamounts have since been destroyed by the plate margin. It is also possible that a collision near the Aleutian Trench had changed the velocity of the Pacific Plate, explaining the hotspot chain's bend; the relationship between these features is still being investigated.
Magma
The composition of the volcanoes' magma has changed significantly according to analysis of the strontium–niobium–palladium elemental ratios. The Emperor Seamounts were active for at least 46 million years, with the oldest lava dated to the Cretaceous Period, followed by another 39 million years of activity along the Hawaiian segment of the chain, totaling 85 million years. Data demonstrate vertical variability in the amount of strontium present in both the alkalic (early stages) and tholeiitic (later stages) lavas. The systematic increase slows drastically at the time of the bend. | Hawaii hotspot | Wikipedia | 360 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Almost all magma created by the hotspot is igneous basalt; the volcanoes are constructed almost entirely of this or the similar in composition but coarser-grained gabbro and diabase. Other igneous rocks such as nephelinite are present in small quantities; these occur often on the older volcanoes, most prominently Detroit Seamount. Most eruptions are runny because basaltic magma is less viscous than magmas characteristic of more explosive eruptions such as the andesitic magmas that produce spectacular and dangerous eruptions around Pacific Basin margins. Volcanoes fall into several eruptive categories. Hawaiian volcanoes are called "Hawaiian-type". Hawaiian lava spills out of craters and forms long streams of glowing molten rock, flowing down the slope, covering acres of land and replacing ocean with new land.
Eruptive frequency and scale
There is significant evidence that lava flow rates have been increasing. Over the last six million years they have been far higher than ever before, at over per year. The average for the last million years is even higher, at about . In comparison, the average production rate at a mid-ocean ridge is about for every of ridge. The rate along the Emperor seamount chain averaged about per year. The rate was almost zero for the initial five million or so years in the hotspot's life. The average lava production rate along the Hawaiian chain has been greater, at per year. In total, the hotspot has produced an estimated of lava, enough to cover California with a layer about thick.
The distance between individual volcanoes has shrunk. Although volcanoes have been drifting north faster and spending less time active, the far greater modern eruptive volume of the hotspot has generated more closely spaced volcanoes, and many of them overlap, forming such superstructures as Hawaii island and the ancient Maui Nui. Meanwhile, many of the volcanoes in the Emperor seamounts are separated by or even as much as . | Hawaii hotspot | Wikipedia | 392 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Topography and geoid
A detailed topographic analysis of the Hawaiian–Emperor seamount chain reveals the hotspot as the center of a topographic high, and that elevation falls with distance from the hotspot. The most rapid decrease in elevation and the highest ratio between the topography and geoid height are over the southeastern part of the chain, falling with distance from the hotspot, particularly at the intersection of the Molokai and Murray fracture zones. The most likely explanation is that the region between the two zones is more susceptible to reheating than most of the chain. Another possible explanation is that the hotspot strength swells and subsides over time.
In 1953, Robert S. Dietz and his colleagues first identified the swell behavior. It was suggested that the cause was mantle upwelling. Later work pointed to tectonic uplift, caused by reheating within the lower lithosphere. However, normal seismic activity beneath the swell, as well as lack of detected heat flow, caused scientists to suggest dynamic topography as the cause, in which the motion of the hot and buoyant mantle plume supports the high surface topography around the islands. Understanding the Hawaiian swell has important implications for hotspot study, island formation, and inner Earth. | Hawaii hotspot | Wikipedia | 256 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Seismicity
The Hawaii hotspot is a highly active seismic zone with thousands of earthquakes occurring on and near Hawaii island every year. Most are too small to be felt by people but some are large enough to result in minor to moderate devastation. The most destructive recorded earthquake was the 2 April 1868 earthquake which had a magnitude of 7.9 on the Richter scale. It triggered a landslide on Mauna Loa, north of Pahala, killing 31 people. A tsunami claimed 46 more lives. The villages of Punaluu, Nīnole, Kaaawa, Honuapo, and Keauhou Landing were severely damaged. The tsunami reportedly rolled over the tops of the coconut trees up to high and it reached inland a distance of a quarter of a mile (400 m) in some places. The lower magnitude earthquakes are believed to occur through local stresses caused by spreading through the seepage of lava into fractures in the overlying rocks (wedging the rocks apart further) or the buoyancy of the underlying mantle plume upheaving the surrounding rocks. These local stresses would only produce lower energy earthquakes because of the lower tensile strength of basalt comparatively to its higher compressive strength. The higher magnitude earthquakes are derived from the basal (decollement) layer being influenced by deformities caused by the increased weight of the Hawaiian islands. These deformities could cause more compressive stresses, allowing for higher magnitude earthquakes. Such modelling to explain observed eathquake patterns suggests the concept that a soft center hole exists under the island of Hawaii where the lithospheric Pacific plate is broken.
Volcanoes
Over its 85 million year history, the Hawaii hotspot has created at least 129 volcanoes, more than 123 of which are extinct volcanoes, seamounts, and atolls, four of which are active volcanoes, and two of which are dormant volcanoes. They can be organized into three general categories: the Hawaiian archipelago, which comprises most of the U.S. state of Hawaii and is the location of all modern volcanic activity; the Northwestern Hawaiian Islands, which consist of coral atolls, extinct islands, and atoll islands; and the Emperor Seamounts, all of which have since eroded and subsided to the sea and become seamounts and guyots (flat-topped seamounts).
Volcanic characteristics | Hawaii hotspot | Wikipedia | 467 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
Hawaiian volcanoes are characterized by frequent rift eruptions, their large size (thousands of cubic kilometers in volume), and their rough, decentralized shape. Rift zones are a prominent feature on these volcanoes, and account for their seemingly random volcanic structure. The tallest mountain in the Hawaii chain, Mauna Kea, rises above mean sea level. Measured from its base on the seafloor, it is the world's tallest mountain, at ; Mount Everest rises above sea level. Hawaii is surrounded by a myriad of seamounts; however, they were found to be unconnected to the hotspot and its volcanism. Kīlauea erupted continuously from 1983 to 2018 through Puʻu ʻŌʻō, a minor volcanic cone, which has become an attraction for volcanologists and tourists alike.
Landslides
The Hawaiian islands are carpeted by a large number of landslides sourced from volcanic collapse. Bathymetric mapping has revealed at least 70 large landslides on the island flanks over in length, and the longest are long and over in volume. These debris flows can be sorted into two broad categories: slumps, mass movement over slopes which slowly flatten their originators, and more catastrophic debris avalanches, associated with flank and sector collapse, which fragment volcanic slopes and scatter volcanic debris past their slopes. These slides have caused massive tsunamis and earthquakes, fractured volcanic massifs, and scattered debris hundreds of miles away from their source. Active slumping is currently taking place on the south flank of the Big Island, where the Hilina Slump comprises a mobile portion of the island’s mass south of Kīlauea.
Slumps tend to be deeply rooted in their originators, moving rock up to deep inside the volcano. Forced forward by the mass of newly ejected volcanic material, slumps may creep forward slowly, or surge forward in spasms that have caused the largest of Hawaii's historical earthquakes, in 1868 and 1975. Debris avalanches, meanwhile, are thinner and longer, and are defined by volcanic amphitheaters at their head and hummocky terrain at their base. Rapidly moving avalanches carried blocks tens of kilometers away, disturbing the local water column and causing a tsunami. Evidence of these events exists in the form of marine deposits high on the slopes of many Hawaiian volcanoes, and has marred the slopes of several Emperor seamounts, such as Daikakuji Guyot and Detroit Seamount. | Hawaii hotspot | Wikipedia | 488 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
GPS measurements on the eastern flank of Hawaii Island over a 5 year epoch show the pattern of collapse with velocities of up to relative to the Pacific Plate
Evolution and construction
Hawaiian volcanoes follow a well-established life cycle of growth and erosion. After a new volcano forms, its lava output gradually increases. Height and activity both peak when the volcano is around 500,000 years old and then rapidly decline. Eventually it goes dormant, and eventually extinct. Weathering and erosion gradually reduce the height of the volcano until it again becomes a seamount.
This life cycle consists of several stages. The first stage is the submarine preshield stage, currently represented solely by Kama‘ehuakanaloa. During this stage, the volcano builds height through increasingly frequent eruptions. The sea's pressure prevents explosive eruptions. The cold water quickly solidifies the lava, producing the pillow lava that is typical of underwater volcanic activity.
As the seamount slowly grows, it goes through the shield stages. It forms many mature features, such as a caldera, while submerged. The summit eventually breaches the surface, and the lava and ocean water "battle" for control as the volcano enters the explosive subphase. This stage of development is exemplified by explosive steam vents. This stage produces mostly volcanic ash, a result of the waves dampening the lava. This conflict between lava and sea influences Hawaiian mythology.
The volcano enters the subaerial subphase once it is tall enough to escape the water. Now the volcano puts on 95% of its above-water height over roughly 500,000 years. Thereafter eruptions become much less explosive. The lava released in this stage often includes both pāhoehoe and ʻaʻā, and the currently active Hawaiian volcanoes, Mauna Loa and Kīlauea, are in this phase. Hawaiian lava is often runny, blocky, slow, and relatively easy to predict; the USGS tracks where it is most likely to run, and maintains a tourist site for viewing the lava.
Mechanical collapse, indicated by large submarine landslides adjacent to landslide scars on the islands, is an ongoing process that shapes the early phases of volcano construction for each of the islands. | Hawaii hotspot | Wikipedia | 441 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
After the subaerial phase the volcano enters a series of postshield stages involving mechanical collapse creating subsidence and erosion, becoming an atoll and eventually a seamount. Once the Pacific Plate moves it out of the tropics, the reef mostly dies away, and the extinct volcano becomes one of an estimated 10,000 barren seamounts worldwide. Every Emperor seamount is a dead volcano.
Coral reef development on Hawaiian Hotspot islands
Reef growth and morphology often show the progression from underwater volcano to subaerial shield to seamount. The process of reef building around the margins of a volcanic island once it is formed, relates to both local island subsidence and global sea level increase. Other local factors such as water temperature and topography are important in reef formation. These fringing reefs gradually accrete vertically and seaward as an inactive volcano subsides, coinciding with a rise in relative sea level. A modern example, Kailua Bay off Oahu Hawaii, has been studied extensively to understand reef carbonate generation, sediment production and deposition. It is estimated that gross carbonate production is approximately 1.22 kg m−2 y−1 while sediment production via bio erosion is 0.33 kg m−2 y−1 resulting in an average vertical accretion of . This rate is considerably lower than worldwide averages for fringing reef accretion . Researchers are investigating the connections between strong wave action, reef biodiversity, rising sea levels and anthropogenic influence. As island subsidence progresses, fringing reefs develop into barrier reefs and once the volcano becomes a seamount, barrier reefs form atolls. Midway Atoll is a good example of the final stage of the evolution of a hotspot volcanic island. | Hawaii hotspot | Wikipedia | 348 | 13309470 | https://en.wikipedia.org/wiki/Hawaii%20hotspot | Physical sciences | Geologic features | Earth science |
A therapy or medical treatment is the attempted remediation of a health problem, usually following a medical diagnosis. Both words, treatment and therapy, are often abbreviated tx, Tx, or Tx.
As a rule, each therapy has indications and contraindications. There are many different types of therapy. Not all therapies are effective. Many therapies can produce unwanted adverse effects.
Treatment and therapy are often synonymous, especially in the usage of health professionals. However, in the context of mental health, the term therapy may refer specifically to psychotherapy.
Semantic field
The words care, therapy, treatment, and intervention overlap in a semantic field, and thus they can be synonymous depending on context. Moving rightward through that order, the connotative level of holism decreases and the level of specificity (to concrete instances) increases. Thus, in health-care contexts (where its senses are always noncount), the word care tends to imply a broad idea of everything done to protect or improve someone's health (for example, as in the terms preventive care and primary care, which connote ongoing action), although it sometimes implies a narrower idea (for example, in the simplest cases of wound care or postanesthesia care, a few particular steps are sufficient, and the patient's interaction with the provider of such care is soon finished). In contrast, the word intervention tends to be specific and concrete, and thus the word is often countable; for example, one instance of cardiac catheterization is one intervention performed, and coronary care (noncount) can require a series of interventions (count). At the extreme, the piling on of such countable interventions amounts to interventionism, a flawed model of care lacking holistic circumspection—merely treating discrete problems (in billable increments) rather than maintaining health. Therapy and treatment, in the middle of the semantic field, can connote either the holism of care or the discreteness of intervention, with context conveying the intent in each use. Accordingly, they can be used in both noncount and count senses (for example, therapy for chronic kidney disease can involve several dialysis treatments per week).
The words aceology and are obscure and obsolete synonyms referring to the study of therapies. | Therapy | Wikipedia | 477 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
The English word therapy comes via Latin therapīa from and literally means "curing" or "healing". The term is a somewhat archaic doublet of the word therapy.
Types of therapies
By chronology, priority, or intensity | Therapy | Wikipedia | 48 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
Levels of care
Levels of care classify health care into categories of chronology, priority, or intensity, as follows:
Urgent care handles health issues that need to be handled today but are not necessarily emergencies; the urgent care venue can send a patient to the emergency care level if it turns out to be needed.
In the United States (and possibly various other countries), urgent care centers also serve another function as their other main purpose: U.S. primary care practices have evolved in recent decades into a configuration whereby urgent care centers provide portions of primary care that cannot wait a month, because getting an appointment with the primary care practitioner is often subject to a waitlist of 2 to 8 weeks.
Emergency care handles medical emergencies and is a first point of contact or intake for less serious problems, which can be referred to other levels of care as appropriate.
Intensive care, also called critical care, is care for extremely ill or injured patients. It thus requires high resource intensity, knowledge, and skill, as well as quick decision making.
Ambulatory care is care provided on an outpatient basis. Typically patients can walk into and out of the clinic under their own power (hence "ambulatory"), usually on the same day.
Home care is care at home, including care from providers (such as physicians, nurses, and home health aides) making house calls, care from caregivers such as family members, and patient self-care.
Primary care is meant to be the main kind of care in general, and ideally a medical home that unifies care across referred providers.
Secondary care is care provided by medical specialists and other health professionals who generally do not have first contact with patients, for example, cardiologists, urologists and dermatologists. A patient reaches secondary care as a next step from primary care, typically by provider referral although sometimes by patient self-initiative. According to a systematic review, fields for development secondary care from patients’ viewpoint may be classified into four domains that should usefully guide future improvement of this care stage: “barriers to care, communication, coordination, and relationships and personal value”.
Tertiary care is specialized consultative care, usually for inpatients and on referral from a primary or secondary health professional, in a facility that has personnel and facilities for advanced medical investigation and treatment, such as a tertiary referral hospital.
Follow-up care is additional care during or after convalescence. Aftercare is generally synonymous with follow-up care. | Therapy | Wikipedia | 502 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
End-of-life care is care near the end of one's life. It often includes the following:
Palliative care is supportive care, most especially (but not necessarily) near the end of life.
Hospice care is palliative care very near the end of life when cure is very unlikely. Its main goal is comfort, both physical and mental. | Therapy | Wikipedia | 74 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
Lines of therapy
Treatment decisions often follow formal or informal algorithmic guidelines. Treatment options can often be ranked or prioritized into lines of therapy: first-line therapy, second-line therapy, third-line therapy, and so on. First-line therapy (sometimes referred to as induction therapy, primary therapy, or front-line therapy) is the first therapy that will be tried. Its priority over other options is usually either: (1) formally recommended on the basis of clinical trial evidence for its best-available combination of efficacy, safety, and tolerability or (2) chosen based on the clinical experience of the physician. If a first-line therapy either fails to resolve the issue or produces intolerable side effects, additional (second-line) therapies may be substituted or added to the treatment regimen, followed by third-line therapies, and so on.
An example of a context in which the formalization of treatment algorithms and the ranking of lines of therapy is very extensive is chemotherapy regimens. Because of the great difficulty in successfully treating some forms of cancer, one line after another may be tried. In oncology the count of therapy lines may reach 10 or even 20.
Often multiple therapies may be tried simultaneously (combination therapy or polytherapy). Thus combination chemotherapy is also called polychemotherapy, whereas chemotherapy with one agent at a time is called single-agent therapy or monotherapy.
Adjuvant therapy is therapy given in addition to the primary, main, or initial treatment, but simultaneously (as opposed to second-line therapy). Neoadjuvant therapy is therapy that is begun before the main therapy. Thus one can consider surgical excision of a tumor as the first-line therapy for a certain type and stage of cancer even though radiotherapy is used before it; the radiotherapy is neoadjuvant (chronologically first but not primary in the sense of the main event). Premedication is conceptually not far from this, but the words are not interchangeable; cytotoxic drugs to put a tumor "on the ropes" before surgery delivers the "knockout punch" are called neoadjuvant chemotherapy, not premedication, whereas things like anesthetics or prophylactic antibiotics before dental surgery are called premedication. | Therapy | Wikipedia | 472 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
Step therapy or stepladder therapy is a specific type of prioritization by lines of therapy. It is controversial in American health care because unlike conventional decision-making about what constitutes first-line, second-line, and third-line therapy, which in the U.S. reflects safety and efficacy first and cost only according to the patient's wishes, step therapy attempts to mix cost containment by someone other than the patient (third-party payers) into the algorithm. Therapy freedom and the negotiation between individual and group rights are involved.
By intent
By therapy composition
Treatments can be classified according to the method of treatment: | Therapy | Wikipedia | 126 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
By matter
by drugs: pharmacotherapy, chemotherapy (also, medical therapy often means specifically pharmacotherapy)
by medical devices: implantation
cardiac resynchronization therapy
by specific molecules: molecular therapy (although most drugs are specific molecules, molecular medicine refers in particular to medicine relying on molecular biology)
by specific biomolecular targets: targeted therapy
molecular chaperone therapy
by chelation: chelation therapy
by specific chemical elements:
by metals:
by heavy metals:
by gold: chrysotherapy (aurotherapy)
by platinum-containing drugs: platin therapy
by biometals
by lithium: lithium therapy
by potassium: potassium supplementation
by magnesium: magnesium supplementation
by chromium: chromium supplementation; phonemic neurological hypochromium therapy
by copper: copper supplementation
by nonmetals:
by diatomic oxygen: oxygen therapy, hyperbaric oxygen therapy (hyperbaric medicine)
transdermal continuous oxygen therapy
by triatomic oxygen (ozone): ozone therapy
by fluoride: fluoride therapy
by other gases: medical gas therapy
by water:
hydrotherapy
aquatic therapy
rehydration therapy
oral rehydration therapy
water cure (therapy)
by biological materials (biogenic substances, biomolecules, biotic materials, natural products), including their synthetic equivalents: biotherapy
by whole organisms
by viruses: virotherapy
by bacteriophages: phage therapy
by animal interaction: see animal interaction section
by constituents or products of organisms
by plant parts or extracts (but many drugs are derived from plants, even when the term phytotherapy is not used)
scientific type: phytotherapy
traditional (prescientific) type: herbalism
by animal parts: quackery involving shark fins, tiger parts, and so on, often driving threat or endangerment of species
by genes: gene therapy
gene therapy for epilepsy
gene therapy for osteoarthritis
gene therapy for color blindness
gene therapy of the human retina
gene therapy in Parkinson's disease
by epigenetics: epigenetic therapy
by proteins: protein therapy (but many drugs are proteins despite not being called protein therapy)
by enzymes: enzyme replacement therapy
by hormones: hormone therapy
hormonal therapy (oncology)
hormone replacement therapy
estrogen replacement therapy
androgen replacement therapy
hormone replacement therapy (menopause)
transgender hormone therapy
feminizing hormone therapy
masculinizing hormone therapy
antihormone therapy | Therapy | Wikipedia | 511 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
androgen deprivation therapy
by whole cells: cell therapy (cytotherapy)
by stem cells: stem cell therapy
by immune cells: see immune system products below
by immune system products: immunotherapy, host modulatory therapy
by immune cells:
T-cell vaccination
cell transfer therapy
autologous immune enhancement therapy
TK cell therapy
by humoral immune factors: antibody therapy
by whole serum: serotherapy, including antiserum therapy
by immunoglobulins: immunoglobulin therapy
by monoclonal antibodies: monoclonal antibody therapy
by urine: urine therapy (some scientific forms; many prescientific or pseudoscientific forms)
by food and dietary choices:
medical nutrition therapy
grape therapy (quackery)
by salts (but many drugs are the salts of organic acids, even when drug therapy is not called by names reflecting that)
by salts in the air
by natural dry salt air: "taking the cure" in desert locales (especially common in prescientific medicine; for example, one 19th-century way to treat tuberculosis)
by artificial dry salt air:
low-humidity forms of speleotherapy
negative air ionization therapy
by moist salt air:
by natural moist salt air: seaside cure (especially common in prescientific medicine)
by artificial moist salt air: water vapor forms of speleotherapy
by salts in the water
by mineral water: spa cure ("taking the waters") (especially common in prescientific medicine)
by seawater: seaside cure (especially common in prescientific medicine)
by aroma: aromatherapy
by other materials with mechanism of action unknown
by occlusion with duct tape: duct tape occlusion therapy | Therapy | Wikipedia | 353 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
By energy
by electric energy as electric current: electrotherapy, electroconvulsive therapy
Transcranial magnetic stimulation
Vagus nerve stimulation
by magnetic energy:
magnet therapy
pulsed electromagnetic field therapy
magnetic resonance therapy
by electromagnetic radiation (EMR):
by light: light therapy (phototherapy)
ultraviolet light therapy
PUVA therapy
photodynamic therapy
photothermal therapy
cytoluminescent therapy
blood irradiation therapy
by darkness: dark therapy
by lasers: laser therapy
low level laser therapy
by gamma rays: radiosurgery
Gamma Knife radiosurgery
stereotactic radiation therapy
cobalt therapy
by radiation generally: radiation therapy (radiotherapy)
intraoperative radiation therapy
by EMR particles:
particle therapy
proton therapy
electron therapy
intraoperative electron radiation therapy
Auger therapy
neutron therapy
fast neutron therapy
neutron capture therapy of cancer
by radioisotopes emitting EMR:
by nuclear medicine
by brachytherapy
quackery type: electromagnetic therapy (alternative medicine)
by mechanical: manual therapy as massotherapy and therapy by exercise as in physical therapy
inversion therapy
by sound:
by ultrasound:
ultrasonic lithotripsy
extracorporeal shockwave therapy
sonodynamic therapy
by music: music therapy
by temperature
by heat: heat therapy (thermotherapy)
by moderately elevated ambient temperatures: hyperthermia therapy
by dry warm surroundings: Waon therapy
by dry or humid warm surroundings: sauna, including infrared sauna, for sweat therapy
by cold:
by extreme cold to specific tissue volumes: cryotherapy
by ice and compression: cold compression therapy
by ambient cold:
hypothermia therapy for neonatal encephalopathy (in newborns)
targeted temperature management (therapeutic hypothermia, protective hypothermia)
by hot and cold alternation: contrast bath therapy
By procedure and human interaction
Surgery
by counseling, such as psychotherapy (see also: list of psychotherapies)
systemic therapy
by group psychotherapy
by cognitive behavioral therapy
by cognitive therapy
by behaviour therapy
by dialectical behavior therapy
by cognitive emotional behavioral therapy
by cognitive rehabilitation therapy
by family therapy
by education
by psychoeducation
by information therapy
by speech therapy, physical therapy, occupational therapy, vision therapy, massage therapy, chiropractic or acupuncture
by lifestyle modifications, such as avoiding unhealthy food or maintaining a predictable sleep schedule
by coaching | Therapy | Wikipedia | 473 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
By animal interaction
by pets, assistance animals, or working animals: animal-assisted therapy
by horses: equine therapy, hippotherapy
by dogs: pet therapy with therapy dogs, including grief therapy dogs
by cats: pet therapy with therapy cats
by fish: ichthyotherapy (wading with fish), aquarium therapy (watching fish)
by maggots: maggot therapy
by worms:
by internal worms: helminthic therapy
by leeches: leech therapy
by immersion: animal bath
By meditation
by mindfulness: mindfulness-based cognitive therapy
By reading
by bibliotherapy
By creativity
by expression: expressive therapy
by writing: writing therapy
journal therapy
by play: play therapy
by art: art therapy
sensory art therapy
comic book therapy
by gardening: horticultural therapy
by dance: dance therapy
by drama: drama therapy
by recreation: recreational therapy
by music: music therapy
By sleeping and waking
by deep sleep: deep sleep therapy
by sleep deprivation: wake therapy | Therapy | Wikipedia | 197 | 13311819 | https://en.wikipedia.org/wiki/Therapy | Biology and health sciences | Medical procedures | null |
In electromagnetism, the impedance of free space, , is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. That is,
where is the electric field strength, and is the magnetic field strength. Its presently accepted value is
,
where Ω is the ohm, the SI unit of electrical resistance. The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability and the speed of light in vacuum . Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value of the impedance of free space was therefore likewise taken to be exact. However, with the revision of the SI that came into force on 20 May 2019, the impedance of free space as expressed with an SI unit is subject to experimental measurement because only the speed of light in vacuum retains an exactly defined value.
Terminology
The analogous quantity for a plane wave travelling through a dielectric medium is called the intrinsic impedance of the medium and designated (eta). Hence is sometimes referred to as the intrinsic impedance of free space, and given the symbol . It has numerous other synonyms, including:
wave impedance of free space,
the vacuum impedance,
intrinsic impedance of vacuum,
characteristic impedance of vacuum,
wave resistance of free space.
Relation to other constants
From the above definition, and the plane wave solution to Maxwell's equations,
where
H/m is the magnetic constant, also known as the permeability of free space,
F/m is the electric constant, also known as the permittivity of free space,
is the speed of light in free space,
The reciprocal of is sometimes referred to as the admittance of free space and represented by the symbol .
Historical exact value
Between 1948 and 2019, the SI unit the ampere was defined by choosing the numerical value of to be exactly . Similarly, since 1983 the SI metre has been defined relative to the second by choosing the value of to be . Consequently, until the 2019 revision,
exactly,
or
exactly,
or
This chain of dependencies changed when the ampere was redefined on 20 May 2019.
Approximation as 120π ohms | Impedance of free space | Wikipedia | 474 | 7001745 | https://en.wikipedia.org/wiki/Impedance%20of%20free%20space | Physical sciences | Physical constants | Physics |
It is very common in textbooks and papers written before about 1990 to substitute the approximate value 120 ohms for . This is equivalent to taking the speed of light to be precisely in conjunction with the then-current definition of as . For example, Cheng 1989 states that the radiation resistance of a Hertzian dipole is
(result in ohms; not exact).
This practice may be recognized from the resulting discrepancy in the units of the given formula. Consideration of the units, or more formally dimensional analysis, may be used to restore the formula to a more exact form, in this case to | Impedance of free space | Wikipedia | 121 | 7001745 | https://en.wikipedia.org/wiki/Impedance%20of%20free%20space | Physical sciences | Physical constants | Physics |
Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat. The resulting value, η (eta), ranges between 0 and 1.
Overview
Energy conversion efficiency depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle. Energy converter is an example of an energy transformation. For example, a light bulb falls into the categories energy converter.
Even though the definition includes the notion of usefulness, efficiency is considered a technical or physical term. Goal or mission oriented terms include effectiveness and efficacy.
Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0% to 100%. Efficiencies cannot exceed 100%, which would result in a perpetual motion machine, which is impossible.
However, other effectiveness measures that can exceed 1.0 are used for refrigerators, heat pumps and other devices that move heat rather than convert it. It is not called efficiency, but the coefficient of performance, or COP. It is a ratio of useful heating or cooling provided relative to the work (energy) required. Higher COPs equate to higher efficiency, lower energy (power) consumption and thus lower operating costs. The COP usually exceeds 1, especially in heat pumps, because instead of just converting work to heat (which, if 100% efficient, would be a COP of 1), it pumps additional heat from a heat source to where the heat is required. Most air conditioners have a COP of 2.3 to 3.5.
When talking about the efficiency of heat engines and power stations the convention should be stated, i.e., HHV ( Gross Heating Value, etc.) or LCV (a.k.a. Net Heating value), and whether gross output (at the generator terminals) or net output (at the power station fence) are being considered. The two are separate but both must be stated. Failure to do so causes endless confusion. | Energy conversion efficiency | Wikipedia | 458 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
Related, more specific terms include
Electrical efficiency, useful power output per electrical power consumed;
Mechanical efficiency, where one form of mechanical energy (e.g. potential energy of water) is converted to mechanical energy (work);
Thermal efficiency or Fuel efficiency, useful heat and/or work output per input energy such as the fuel consumed;
'Total efficiency', e.g., for cogeneration, useful electric power and heat output per fuel energy consumed. Same as the thermal efficiency.
Luminous efficiency, that portion of the emitted electromagnetic radiation is usable for human vision.
Chemical conversion efficiency
The change of Gibbs energy of a defined chemical transformation at a particular temperature is the minimum theoretical quantity of energy required to make that change occur (if the change in Gibbs energy between reactants and products is positive) or the maximum theoretical energy that might be obtained from that change (if the change in Gibbs energy between reactants and products is negative). The energy efficiency of a process involving chemical change may be expressed relative to these theoretical minima or maxima.The difference between the change of enthalpy and the change of Gibbs energy of a chemical transformation at a particular temperature indicates the heat input required or the heat removal (cooling) required to maintain that temperature.
A fuel cell may be considered to be the reverse of electrolysis. For example, an ideal fuel cell operating at a temperature of 25 °C having gaseous hydrogen and gaseous oxygen as inputs and liquid water as the output could produce a theoretical maximum amount of electrical energy of 237.129 kJ (0.06587 kWh) per gram mol (18.0154 gram) of water produced and would require 48.701 kJ (0.01353 kWh) per gram mol of water produced of heat energy to be removed from the cell to maintain that temperature.
An ideal electrolysis unit operating at a temperature of 25 °C having liquid water as the input and gaseous hydrogen and gaseous oxygen as products would require a theoretical minimum input of electrical energy of 237.129 kJ (0.06587 kWh) per gram mol (18.0154 gram) of water consumed and would require 48.701 kJ (0.01353 kWh) per gram mol of water consumed of heat energy to be added to the unit to maintain that temperature. It would operate at a cell voltage of 1.24 V. | Energy conversion efficiency | Wikipedia | 490 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
For a water electrolysis unit operating at a constant temperature of 25 °C without the input of any additional heat energy, electrical energy would have to be supplied at a rate equivalent of the enthalpy (heat) of reaction or 285.830 kJ (0.07940 kWh) per gram mol of water consumed. It would operate at a cell voltage of 1.48 V. The electrical energy input of this cell is 1.20 times greater than the theoretical minimum so the energy efficiency is 0.83 compared to the ideal cell.
A water electrolysis unit operating with a higher voltage that 1.48 V and at a temperature of 25 °C would have to have heat energy removed in order to maintain a constant temperature and the energy efficiency would be less than 0.83.
The large entropy difference between liquid water and gaseous hydrogen plus gaseous oxygen accounts for the significant difference between the Gibbs energy of reaction and the enthalpy (heat) of reaction.
Fuel heating values and efficiency
In Europe the usable energy content of a fuel is typically calculated using the lower heating value (LHV) of that fuel, the definition of which assumes that the water vapor produced during fuel combustion (oxidation) remains gaseous, and is not condensed to liquid water so the latent heat of vaporization of that water is not usable. Using the LHV, a condensing boiler can achieve a "heating efficiency" in excess of 100% (this does not violate the first law of thermodynamics as long as the LHV convention is understood, but does cause confusion). This is because the apparatus recovers part of the heat of vaporization, which is not included in the definition of the lower heating value of a fuel. In the U.S. and elsewhere, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor, and thus the thermodynamic maximum of 100% efficiency cannot be exceeded.
Wall-plug efficiency, luminous efficiency, and efficacy
In optical systems such as lighting and lasers, the energy conversion efficiency is often referred to as wall-plug efficiency. The wall-plug efficiency is the measure of output radiative-energy, in watts (joules per second), per total input electrical energy in watts. The output energy is usually measured in terms of absolute irradiance and the wall-plug efficiency is given as a percentage of the total input energy, with the inverse percentage representing the losses. | Energy conversion efficiency | Wikipedia | 511 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
The wall-plug efficiency differs from the luminous efficiency in that wall-plug efficiency describes the direct output/input conversion of energy (the amount of work that can be performed) whereas luminous efficiency takes into account the human eye's varying sensitivity to different wavelengths (how well it can illuminate a space). Instead of using watts, the power of a light source to produce wavelengths proportional to human perception is measured in lumens. The human eye is most sensitive to wavelengths of 555 nanometers (greenish-yellow) but the sensitivity decreases dramatically to either side of this wavelength, following a Gaussian power-curve and dropping to zero sensitivity at the red and violet ends of the spectrum. Due to this the eye does not usually see all of the wavelengths emitted by a particular light-source, nor does it see all of the wavelengths within the visual spectrum equally. Yellow and green, for example, make up more than 50% of what the eye perceives as being white, even though in terms of radiant energy white-light is made from equal portions of all colors (i.e.: a 5 mW green laser appears brighter than a 5 mW red laser, yet the red laser stands-out better against a white background). Therefore, the radiant intensity of a light source may be much greater than its luminous intensity, meaning that the source emits more energy than the eye can use. Likewise, the lamp's wall-plug efficiency is usually greater than its luminous efficiency. The effectiveness of a light source to convert electrical energy into wavelengths of visible light, in proportion to the sensitivity of the human eye, is referred to as luminous efficacy, which is measured in units of lumens per watt (lm/w) of electrical input-energy. | Energy conversion efficiency | Wikipedia | 357 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
Unlike efficacy (effectiveness), which is a unit of measurement, efficiency is a unitless number expressed as a percentage, requiring only that the input and output units be of the same type. The luminous efficiency of a light source is thus the percentage of luminous efficacy per theoretical maximum efficacy at a specific wavelength. The amount of energy carried by a photon of light is determined by its wavelength. In lumens, this energy is offset by the eye's sensitivity to the selected wavelengths. For example, a green laser pointer can have greater than 30 times the apparent brightness of a red pointer of the same power output. At 555 nm in wavelength, 1 watt of radiant energy is equivalent to 683 lumens, thus a monochromatic light source at this wavelength, with a luminous efficacy of 683 lm/w, would have a luminous efficiency of 100%. The theoretical-maximum efficacy lowers for wavelengths at either side of 555 nm. For example, low-pressure sodium lamps produce monochromatic light at 589 nm with a luminous efficacy of 200 lm/w, which is the highest of any lamp. The theoretical-maximum efficacy at that wavelength is 525 lm/w, so the lamp has a luminous efficiency of 38.1%. Because the lamp is monochromatic, the luminous efficiency nearly matches the wall-plug efficiency of < 40%. | Energy conversion efficiency | Wikipedia | 277 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
Calculations for luminous efficiency become more complex for lamps that produce white light or a mixture of spectral lines. Fluorescent lamps have higher wall-plug efficiencies than low-pressure sodium lamps, but only have half the luminous efficacy of ~ 100 lm/w, thus the luminous efficiency of fluorescents is lower than sodium lamps. A xenon flashtube has a typical wall-plug efficiency of 50–70%, exceeding that of most other forms of lighting. Because the flashtube emits large amounts of infrared and ultraviolet radiation, only a portion of the output energy is used by the eye. The luminous efficacy is therefore typically around 50 lm/w. However, not all applications for lighting involve the human eye nor are restricted to visible wavelengths. For laser pumping, the efficacy is not related to the human eye so it is not called "luminous" efficacy, but rather simply "efficacy" as it relates to the absorption lines of the laser medium. Krypton flashtubes are often chosen for pumping Nd:YAG lasers, even though their wall-plug efficiency is typically only ~ 40%. Krypton's spectral lines better match the absorption lines of the neodymium-doped crystal, thus the efficacy of krypton for this purpose is much higher than xenon; able to produce up to twice the laser output for the same electrical input. All of these terms refer to the amount of energy and lumens as they exit the light source, disregarding any losses that might occur within the lighting fixture or subsequent output optics. Luminaire efficiency refers to the total lumen-output from the fixture per the lamp output. | Energy conversion efficiency | Wikipedia | 339 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
With the exception of a few light sources, such as incandescent light bulbs, most light sources have multiple stages of energy conversion between the "wall plug" (electrical input point, which may include batteries, direct wiring, or other sources) and the final light-output, with each stage producing a loss. Low-pressure sodium lamps initially convert the electrical energy using an electrical ballast, to maintain the proper current and voltage, but some energy is lost in the ballast. Similarly, fluorescent lamps also convert the electricity using a ballast (electronic efficiency). The electricity is then converted into light energy by the electrical arc (electrode efficiency and discharge efficiency). The light is then transferred to a fluorescent coating that only absorbs suitable wavelengths, with some losses of those wavelengths due to reflection off and transmission through the coating (transfer efficiency). The number of photons absorbed by the coating will not match the number then reemitted as fluorescence (quantum efficiency). Finally, due to the phenomenon of the Stokes shift, the re-emitted photons will have a longer wavelength (thus lower energy) than the absorbed photons (fluorescence efficiency). In very similar fashion, lasers also experience many stages of conversion between the wall plug and the output aperture. The terms "wall-plug efficiency" or "energy conversion efficiency" are therefore used to denote the overall efficiency of the energy-conversion device, deducting the losses from each stage, although this may exclude external components needed to operate some devices, such as coolant pumps.
Example of energy conversion efficiency | Energy conversion efficiency | Wikipedia | 313 | 7005062 | https://en.wikipedia.org/wiki/Energy%20conversion%20efficiency | Physical sciences | Thermodynamics | Physics |
Theoretical computer science is a subfield of computer science and mathematics that focuses on the abstract and mathematical foundations of computation.
It is difficult to circumscribe the theoretical areas precisely. The ACM's Special Interest Group on Algorithms and Computation Theory (SIGACT) provides the following description:
History
While logical inference and mathematical proof had existed previously, in 1931 Kurt Gödel proved with his incompleteness theorem that there are fundamental limitations on what statements could be proved or disproved.
Information theory was added to the field with a 1948 mathematical theory of communication by Claude Shannon. In the same decade, Donald Hebb introduced a mathematical model of learning in the brain. With mounting biological data supporting this hypothesis with some modification, the fields of neural networks and parallel distributed processing were established. In 1971, Stephen Cook and, working independently, Leonid Levin, proved that there exist practically relevant problems that are NP-complete – a landmark result in computational complexity theory.
Modern theoretical computer science research is based on these basic developments, but includes many other mathematical and interdisciplinary problems that have been posed, as shown below:
Topics
Algorithms
An algorithm is a step-by-step procedure for calculations. Algorithms are used for calculation, data processing, and automated reasoning.
An algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Starting from an initial state and initial input (perhaps empty), the instructions describe a computation that, when executed, proceeds through a finite number of well-defined successive states, eventually producing "output" and terminating at a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate random input.
Automata theory
Automata theory is the study of abstract machines and automata, as well as the computational problems that can be solved using them. It is a theory in theoretical computer science, under discrete mathematics (a section of mathematics and also of computer science). Automata comes from the Greek word αὐτόματα meaning "self-acting".
Automata Theory is the study of self-operating virtual machines to help in the logical understanding of input and output process, without or with intermediate stage(s) of computation (or any function/process).
Coding theory | Theoretical computer science | Wikipedia | 464 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Coding theory is the study of the properties of codes and their fitness for a specific application. Codes are used for data compression, cryptography, error correction and more recently also for network coding. Codes are studied by various scientific disciplines – such as information theory, electrical engineering, mathematics, and computer science – for the purpose of designing efficient and reliable data transmission methods. This typically involves the removal of redundancy and the correction (or detection) of errors in the transmitted data.
Computational complexity theory
Computational complexity theory is a branch of the theory of computation that focuses on classifying computational problems according to their inherent difficulty, and relating those classes to each other. A computational problem is understood to be a task that is in principle amenable to being solved by a computer, which is equivalent to stating that the problem may be solved by mechanical application of mathematical steps, such as an algorithm.
A problem is regarded as inherently difficult if its solution requires significant resources, whatever the algorithm used. The theory formalizes this intuition, by introducing mathematical models of computation to study these problems and quantifying the amount of resources needed to solve them, such as time and storage. Other complexity measures are also used, such as the amount of communication (used in communication complexity), the number of gates in a circuit (used in circuit complexity) and the number of processors (used in parallel computing). One of the roles of computational complexity theory is to determine the practical limits on what computers can and cannot do.
Computational geometry
Computational geometry is a branch of computer science devoted to the study of algorithms that can be stated in terms of geometry. Some purely geometrical problems arise out of the study of computational geometric algorithms, and such problems are also considered to be part of computational geometry.
The main impetus for the development of computational geometry as a discipline was progress in computer graphics and computer-aided design and manufacturing (CAD/CAM), but many problems in computational geometry are classical in nature, and may come from mathematical visualization.
Other important applications of computational geometry include robotics (motion planning and visibility problems), geographic information systems (GIS) (geometrical location and search, route planning), integrated circuit design (IC geometry design and verification), computer-aided engineering (CAE) (mesh generation), computer vision (3D reconstruction).
Computational learning theory | Theoretical computer science | Wikipedia | 468 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Theoretical results in machine learning mainly deal with a type of inductive learning called supervised learning. In supervised learning, an algorithm is given samples that are labeled in some
useful way. For example, the samples might be descriptions of mushrooms, and the labels could be whether or not the mushrooms are edible. The algorithm takes these previously labeled samples and
uses them to induce a classifier. This classifier is a function that assigns labels to samples including the samples that have never been previously seen by the algorithm. The goal of the supervised learning algorithm is to optimize some measure of performance such as minimizing the number of mistakes made on new samples.
Computational number theory
Computational number theory, also known as algorithmic number theory, is the study of algorithms for performing number theoretic computations. The best known problem in the field is integer factorization.
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties (called adversaries). More generally, it is about constructing and analyzing protocols that overcome the influence of adversaries and that are related to various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation. Modern cryptography intersects the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.
Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in practice by any adversary. It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means. These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in integer factorization algorithms, and faster computing technology require these solutions to be continually adapted. There exist information-theoretically secure schemes that cannot be broken even with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to implement than the best theoretically breakable but computationally secure mechanisms.
Data structures
A data structure is a particular way of organizing data in a computer so that it can be used efficiently.
Different kinds of data structures are suited to different kinds of applications, and some are highly specialized to specific tasks. For example, databases use B-tree indexes for small percentages of data retrieval and compilers and databases use dynamic hash tables as look up tables. | Theoretical computer science | Wikipedia | 496 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Data structures provide a means to manage large amounts of data efficiently for uses such as large databases and internet indexing services. Usually, efficient data structures are key to designing efficient algorithms. Some formal design methods and programming languages emphasize data structures, rather than algorithms, as the key organizing factor in software design. Storing and retrieving can be carried out on data stored in both main memory and in secondary memory.
Distributed computation
Distributed computing studies distributed systems. A distributed system is a software system in which components located on networked computers communicate and coordinate their actions by passing messages. The components interact with each other in order to achieve a common goal. Three significant characteristics of distributed systems are: concurrency of components, lack of a global clock, and independent failure of components. Examples of distributed systems vary from SOA-based systems to massively multiplayer online games to peer-to-peer applications, and blockchain networks like Bitcoin.
A computer program that runs in a distributed system is called a distributed program, and distributed programming is the process of writing such programs. There are many alternatives for the message passing mechanism, including RPC-like connectors and message queues. An important goal and challenge of distributed systems is location transparency.
Information-based complexity
Information-based complexity (IBC) studies optimal algorithms and computational complexity for continuous problems. IBC has studied continuous problems as path integration, partial differential equations, systems of ordinary differential equations, nonlinear equations, integral equations, fixed points, and very-high-dimensional integration.
Formal methods
Formal methods are a particular kind of mathematics based techniques for the specification, development and verification of software and hardware systems. The use of formal methods for software and hardware design is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analysis can contribute to the reliability and robustness of a design.
Formal methods are best described as the application of a fairly broad variety of theoretical computer science fundamentals, in particular logic calculi, formal languages, automata theory, and program semantics, but also type systems and algebraic data types to problems in software and hardware specification and verification.
Information theory | Theoretical computer science | Wikipedia | 427 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Information theory is a branch of applied mathematics, electrical engineering, and computer science involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and communicating data. Since its inception it has broadened to find applications in many other areas, including statistical inference, natural language processing, cryptography, neurobiology, the evolution and function of molecular codes, model selection in statistics, thermal physics, quantum computing, linguistics, plagiarism detection, pattern recognition, anomaly detection and other forms of data analysis.
Applications of fundamental topics of information theory include lossless data compression (e.g. ZIP files), lossy data compression (e.g. MP3s and JPEGs), and channel coding (e.g. for Digital Subscriber Line (DSL)). The field is at the intersection of mathematics, statistics, computer science, physics, neurobiology, and electrical engineering. Its impact has been crucial to the success of the Voyager missions to deep space, the invention of the compact disc, the feasibility of mobile phones, the development of the Internet, the study of linguistics and of human perception, the understanding of black holes, and numerous other fields. Important sub-fields of information theory are source coding, channel coding, algorithmic complexity theory, algorithmic information theory, information-theoretic security, and measures of information.
Machine learning
Machine learning is a scientific discipline that deals with the construction and study of algorithms that can learn from data. Such algorithms operate by building a model based on inputs and using that to make predictions or decisions, rather than following only explicitly programmed instructions.
Machine learning can be considered a subfield of computer science and statistics. It has strong ties to artificial intelligence and optimization, which deliver methods, theory and application domains to the field. Machine learning is employed in a range of computing tasks where designing and programming explicit, rule-based algorithms is infeasible. Example applications include spam filtering, optical character recognition (OCR), search engines and computer vision. Machine learning is sometimes conflated with data mining, although that focuses more on exploratory data analysis. Machine learning and pattern recognition "can be viewed as two facets of
the same field."
Natural computation
Parallel computation | Theoretical computer science | Wikipedia | 476 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved "in parallel". There are several different forms of parallel computing: bit-level, instruction level, data, and task parallelism. Parallelism has been employed for many years, mainly in high-performance computing, but interest in it has grown lately due to the physical constraints preventing frequency scaling. As power consumption (and consequently heat generation) by computers has become a concern in recent years, parallel computing has become the dominant paradigm in computer architecture, mainly in the form of multi-core processors.
Parallel computer programs are more difficult to write than sequential ones, because concurrency introduces several new classes of potential software bugs, of which race conditions are the most common. Communication and synchronization between the different subtasks are typically some of the greatest obstacles to getting good parallel program performance.
The maximum possible speed-up of a single program as a result of parallelization is known as Amdahl's law.
Programming language theory and program semantics
Programming language theory is a branch of computer science that deals with the design, implementation, analysis, characterization, and classification of programming languages and their individual features. It falls within the discipline of theoretical computer science, both depending on and affecting mathematics, software engineering, and linguistics. It is an active research area, with numerous dedicated academic journals.
In programming language theory, semantics is the field concerned with the rigorous mathematical study of the meaning of programming languages. It does so by evaluating the meaning of syntactically legal strings defined by a specific programming language, showing the computation involved. In such a case that the evaluation would be of syntactically illegal strings, the result would be non-computation. Semantics describes the processes a computer follows when executing a program in that specific language. This can be shown by describing the relationship between the input and output of a program, or an explanation of how the program will execute on a certain platform, hence creating a model of computation.
Quantum computation | Theoretical computer science | Wikipedia | 421 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
A quantum computer is a computation system that makes direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data. Quantum computers are different from digital computers based on transistors. Whereas digital computers require data to be encoded into binary digits (bits), each of which is always in one of two definite states (0 or 1), quantum computation uses qubits (quantum bits), which can be in superpositions of states. A theoretical model is the quantum Turing machine, also known as the universal quantum computer. Quantum computers share theoretical similarities with non-deterministic and probabilistic computers; one example is the ability to be in more than one state simultaneously. The field of quantum computing was first introduced by Yuri Manin in 1980 and Richard Feynman in 1982. A quantum computer with spins as quantum bits was also formulated for use as a quantum space–time in 1968.
Experiments have been carried out in which quantum computational operations were executed on a very small number of qubits. Both practical and theoretical research continues, and many national governments and military funding agencies support quantum computing research to develop quantum computers for both civilian and national security purposes, such as cryptanalysis.
Symbolic computation
Computer algebra, also called symbolic computation or algebraic computation is a scientific area that refers to the study and development of algorithms and software for manipulating mathematical expressions and other mathematical objects. Although, properly speaking, computer algebra should be a subfield of scientific computing, they are generally considered as distinct fields because scientific computing is usually based on numerical computation with approximate floating point numbers, while symbolic computation emphasizes exact computation with expressions containing variables that have not any given value and are thus manipulated as symbols (therefore the name of symbolic computation).
Software applications that perform symbolic calculations are called computer algebra systems, with the term system alluding to the complexity of the main applications that include, at least, a method to represent mathematical data in a computer, a user programming language (usually different from the language used for the implementation), a dedicated memory manager, a user interface for the input/output of mathematical expressions, a large set of routines to perform usual operations, like simplification of expressions, differentiation using chain rule, polynomial factorization, indefinite integration, etc.
Very-large-scale integration | Theoretical computer science | Wikipedia | 465 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. VLSI allows IC makers to add all of these circuits into one chip.
Organizations
European Association for Theoretical Computer Science
SIGACT
Simons Institute for the Theory of Computing
Journals and newsletters
Discrete Mathematics and Theoretical Computer Science
Information and Computation
Theory of Computing (open access journal)
Formal Aspects of Computing
Journal of the ACM
SIAM Journal on Computing (SICOMP)
SIGACT News
Theoretical Computer Science
Theory of Computing Systems
TheoretiCS (open access journal)
International Journal of Foundations of Computer Science
Chicago Journal of Theoretical Computer Science (open access journal)
Foundations and Trends in Theoretical Computer Science
Journal of Automata, Languages and Combinatorics
Acta Informatica
Fundamenta Informaticae
ACM Transactions on Computation Theory
Computational Complexity
Journal of Complexity
ACM Transactions on Algorithms
Information Processing Letters
Open Computer Science (open access journal)
Conferences
Annual ACM Symposium on Theory of Computing (STOC)
Annual IEEE Symposium on Foundations of Computer Science (FOCS)
Innovations in Theoretical Computer Science (ITCS)
Mathematical Foundations of Computer Science (MFCS)
International Computer Science Symposium in Russia (CSR)
ACM–SIAM Symposium on Discrete Algorithms (SODA)
IEEE Symposium on Logic in Computer Science (LICS)
Computational Complexity Conference (CCC)
International Colloquium on Automata, Languages and Programming (ICALP)
Annual Symposium on Computational Geometry (SoCG)
ACM Symposium on Principles of Distributed Computing (PODC)
ACM Symposium on Parallelism in Algorithms and Architectures (SPAA)
Annual Conference on Learning Theory (COLT)
International Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM)
Symposium on Theoretical Aspects of Computer Science (STACS)
European Symposium on Algorithms (ESA)
Workshop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX)
Workshop on Randomization and Computation (RANDOM)
International Symposium on Algorithms and Computation (ISAAC)
International Symposium on Fundamentals of Computation Theory (FCT)
International Workshop on Graph-Theoretic Concepts in Computer Science (WG) | Theoretical computer science | Wikipedia | 505 | 323392 | https://en.wikipedia.org/wiki/Theoretical%20computer%20science | Mathematics | Discrete mathematics | null |
The common wood pigeon (Columba palumbus), also known as simply wood pigeon, is a large species in the dove and pigeon family (Columbidae), native to the western Palearctic. It belongs to the genus Columba, which includes closely related species such as the rock dove (Columba livia). It has a flexible diet, predominantly feeding on vegetable matter, including cereal crops, leading to them being regarded as an agricultural pest. Wood pigeons are extensively hunted over large parts of their range, but this does not seem to have a great impact on their population.
Taxonomy
The common wood pigeon was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae. He placed it with all the other pigeons in the genus Columba and coined the binomial name Columba palumbus. The specific epithet palumbus is an alternate form of the Latin palumbes for a wood pigeon.
Five subspecies are recognised, one of which is now extinct:
C. p. palumbus Linnaeus, 1758 – Europe to western Siberia and Iraq; Northwest Africa
† C. p. maderensis Tschusi, 1904 – Madeira (extinct)
C. p. azorica Hartert, 1905 – the eastern and central Azores
C. p. iranica (Zarudny, 1910) – southwestern and northern Iran to southwestern Turkmenistan
C. p. casiotis (Bonaparte, 1854) – southeastern Iran and Kazakhstan to western China, northwestern India and Nepal
† = extinct
Fossil records of the species are known from the early Middle Pleistocene of Sicily.
Description
The three Western European Columba pigeons, common wood pigeon, stock dove and rock dove, though superficially alike, have very distinctive characteristics; the common wood pigeon may be identified at once by its larger size at and weight , and the white on its neck and wing. It is otherwise a basically grey bird, with a pinkish breast. The wingspan can range from and the wing chord measures . The tail measures , the bill is and the tarsus is . Adult birds bear a series of green and white patches on their necks, and a pink patch on their chest. The eye colour is a pale yellow, in contrast to that of rock doves, which is orange-red, and the stock dove, which is black. | Common wood pigeon | Wikipedia | 479 | 323559 | https://en.wikipedia.org/wiki/Common%20wood%20pigeon | Biology and health sciences | Columbimorphae | Animals |
Juvenile birds do not have the white patches on either side of the neck. When they are about 6 months old (about three months out of the nest) they gain small white patches on both sides of the neck, which gradually enlarge until they are fully formed when the bird is about 6–8 months old. Juvenile birds also have a greyer beak and an overall lighter grey appearance than adult birds.
Distribution and habitat
In the colder northern and eastern parts of Europe and western Asia the common wood pigeon is a migrant, but in southern and western Europe it is a well distributed and often abundant resident. In Great Britain wood pigeons are commonly seen in parks and gardens and are seen with increasing numbers in towns and cities.
Behaviour
Its flight is quick, performed by regular beats, with an occasional sharp flick of the wings, characteristic of pigeons in general. It takes off with a loud clattering. It perches well, and in its nuptial display walks along a horizontal branch with swelled neck, lowered wings, and fanned tail. During the display flight the bird climbs, the wings are smartly cracked like a whiplash, and the bird glides down on stiff wings. The common wood pigeon is gregarious, often forming very large flocks outside the breeding season. Like many species of pigeon, wood pigeons take advantage of trees and buildings to gain a vantage point over the surrounding area, and their distinctive call means that they are usually heard before they are seen.
Wood pigeons are known to fiercely defend their territory, and will fight each other to gain access to nesting and roosting locations. Male wood pigeons will typically attempt to drive competitors off by threat displays and pursuit, but will also directly fight, jumping and striking their rival with both wings.
This species can be an agricultural pest, and it is often shot, being a legal quarry species in most European countries. It is wary in rural areas, but often quite tame where it is not persecuted.
Breeding
It breeds in trees in woods, parks and gardens, laying two white eggs in a simple stick nest which hatch after 17 to 19 days. Wood pigeons seem to have a preference for trees near roadways and rivers. Males exhibit aggressive behaviour towards each other during the breeding season by jumping and flapping wings at each other. Their plumage becomes much darker, especially the head, during hot summer periods. Breeding can happen year round if there is food abundant however breeding season most commonly occurs between April and October. | Common wood pigeon | Wikipedia | 496 | 323559 | https://en.wikipedia.org/wiki/Common%20wood%20pigeon | Biology and health sciences | Columbimorphae | Animals |
The nests are vulnerable to attack, particularly by crows. The young usually fly at 33 to 34 days; however, if the nest is disturbed, some young may be able to survive having left the nest as early as 20 days from hatching.
In a study carried out using ring-recovery data, the survival rate for juveniles in their first year was 52 per cent, and the adult annual survival rate was 61 per cent. For birds that survive the first year the typical lifespan is thus only three years, but the maximum recorded age is 17 years and 8 months for a bird ringed and recovered on the Orkney Islands.
Diet
Most of its diet is vegetable, round and fleshy leaves from Caryophyllaceae, Asteraceae, and cruciferous vegetables taken from open fields or gardens and lawns; young shoots and seedlings are favoured, and it will take grain, pine nuts, and certain fruits and berries. In the autumn they also eat figs and acorns, and in winter buds of trees and bushes. They will also eat larvae, ants, and small worms. They need open water to drink and bathe in. Young common wood pigeons swiftly become fat, as a result of the crop milk they are fed by their parents. This is an extremely rich fluid that is produced in the adult birds' crops during the breeding season.
Calls
The call of the wood pigeon is a loud and sustained characteristic cooing phrase, coo-COO-COO-coo-coo. In Ireland and the UK, the traditional mnemonic for the distinctive call of the bird has been interpreted as "Take two cows, Teddy", or "Take two cows, Taffy". Other interpretations for the birdsong include "I am a pigeon", "My toe bleeds, Betty", and "I don't want to go".
Predators
Predators of the wood pigeon typically consist of the Eurasian sparrowhawk, Eurasian goshawk and domestic cat. The eggs and babies of wood pigeons are also often predated by magpies and crows.
Hunting
The wood pigeon is widely hunted over large parts of its range, with millions of birds being shot annually, in part because it has been regarded as an agricultural pest, especially of cereal crops. In 1953, the British Government introduced a subsidy for the cost of cartridges to sport-hunters of wood pigeons, which was later abolished in 1969. | Common wood pigeon | Wikipedia | 490 | 323559 | https://en.wikipedia.org/wiki/Common%20wood%20pigeon | Biology and health sciences | Columbimorphae | Animals |
In culture
The wood pigeon is mentioned several times in the Eclogues written by the ancient Roman poet Virgil. Referring to its distinctive husky call, Virgil writes in Eclogue 1;
Here beneath high rocks
The gatherers of leaves, with cheerful songs
Fill the high winds. Meanwhile thy turtle doves
And hoarse wood pigeons from the lofty elms
Make endless moan. | Common wood pigeon | Wikipedia | 73 | 323559 | https://en.wikipedia.org/wiki/Common%20wood%20pigeon | Biology and health sciences | Columbimorphae | Animals |
Eublepharis is a genus of terrestrial geckos native to eastern and southwestern Asia. The genus was first described by the British zoologist John Edward Gray in 1827. The etymology of their name is 'eu' = good (=true) |'blephar' = eyelid, and all have fully functional eyelids. Members of this genus are found in eastern and southwestern Asia. These geckos are sturdily built. Their tail is shorter than their snout–vent length, and their body is covered with numerous wart-like bumps. The toes do not have adhesive lamellae or membranes (Eublepharis cannot climb like their other gecko cousins). Like all members of Eublepharidae, they are primarily nocturnal. Included in this group is the popular pet leopard gecko Eublepharis macularius.
Species of the genus Eublepharis
The members of the Goniurosaurus kuroiwae superspecies were formerly considered members of the genus Eublepharis. | Eublepharis | Wikipedia | 211 | 323654 | https://en.wikipedia.org/wiki/Eublepharis | Biology and health sciences | Lizards and other Squamata | Animals |
Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Skinks are characterized by their smaller legs in comparison to typical lizards and are found in different habitats except arctic and subarctic regions.
Etymology
The word skink, which entered the English language around 1580–1590, comes from classical Greek and Latin , names that referred to various specific lizards.
Description
Skinks look like lizards of the family Lacertidae (sometimes called true lizards), but most species of skinks have no pronounced neck and relatively small legs. Several genera (e.g., Typhlosaurus) have no limbs at all. This is not true for all skinks, however, as some species such as the red-eyed crocodile skink have a head that is very distinguished from the body. These lizards also have legs that are relatively small proportional to their body size.
Skinks' skulls are covered by substantial bony scales, usually matching up in shape and size, while overlapping. Other genera, such as Neoseps, have reduced limbs and fewer than five toes (digits) on each foot. In such species, their locomotion resembles that of snakes more than that of lizards with well-developed limbs. As a general rule, the longer the digits, the more arboreal the species is likely to be. A biological ratio can determine the ecological niche of a given skink species. The Scincidae ecological niche index (SENI) is a ratio based on anterior foot length at the junction of the ulna/radius-carpal bones to the longest digit divided by the snout-to-vent length.
Most species of skinks have long, tapering tails they can shed if predators grab onto them. Such species generally can regenerate the lost part of a tail, though imperfectly. A lost tail can grow back within around three to four months. Species with stumpy tails have no special regenerative abilities. | Skink | Wikipedia | 431 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
Some species of skinks are quite small; Scincella lateralis typically ranges from , more than half of which is the tail. Most skinks, though, are medium-sized, with snout-to-vent lengths around , although some grow larger; the Solomon Islands skink (Corucia zebrata) is the largest known extant species and may attain a snout-to-vent length of some .
Skinks can often hide easily in their habitat because of their protective colouring (camouflage).
Blood color
Skinks in the genus Prasinohaema have green blood because of a buildup of the waste product biliverdin.
Evolutionary history
The oldest known skink is Electroscincus zedi described from the mid-Cretaceous (late Albian to early Cenomanian) Burmese amber from Myanmar, dating to around . Based on the presence of osteoderms, Electroscincus appears to belong to the Scincidae crown group, indicating that some divergence among the extant skink subfamilies must have already occurred by 100 million years ago. Other definitive skink fossils are known from the Miocene.
Skink genera known from fossils include the following:
Behavior
A trait apparent in many species of skink is digging and burrowing. Many spend their time underground where they are mostly safe from predators, sometimes even digging out tunnels for easy navigation. They also use their tongues to sniff the air and track their prey. When they encounter their prey, they chase it down until they corner it or manage to land a bite and then swallow it whole. Despite being voracious hunters at times, all species pose no threat to humans and will generally avoid interaction in the wild. Being neither poisonous nor venomous, their bites are also mild and minor.
Diet
Skinks are generally carnivorous and in particular insectivorous. Typical prey include flies, crickets, grasshoppers, beetles, and caterpillars. Various species also eat earthworms, millipedes, centipedes, snails, slugs, isopods (woodlice etc), moths, small lizards (including geckos), and small rodents. Some species, particularly those favored as home pets, are omnivorous and have more varied diets and can be maintained on a regimen of roughly 60% vegetables/leaves/fruit and 40% meat (insects and rodents). Species of the genus Tristiidon are mainly frugivorous, but occasionally eat moss and insects.
Breeding | Skink | Wikipedia | 505 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
Although most species of skinks are oviparous, laying eggs in clutches, some 45% of skink species are viviparous in one sense or another. Many species are ovoviviparous, the young (skinklets) developing lecithotrophically in eggs that hatch inside the mother's reproductive tract, and emerging as live births.
In some genera, however, such as Tiliqua and Corucia, the young developing in the reproductive tract derive their nourishment from a mammal-like placenta attached to the female – unambiguous examples of viviparous matrotrophy. Furthermore, an example recently described in Trachylepis ivensi is the most extreme to date: a purely reptilian placenta directly comparable in structure and function, to a eutherian placenta.
Clearly, such vivipary repeatedly has developed independently in the evolutionary history of the Scincidae and the different examples are not ancestral to the others. In particular, placental development of whatever degree in lizards is phylogenetically analogous, rather than homologous, to functionally similar processes in mammals.
Nesting
Skinks typically seek out environments protected from the elements, such as thick foliage, underneath man-made structures, and ground-level buildings such as garages and first-floor apartments. When two or more skinks are seen in a small area, it is typical to find a nest nearby. Skinks are considered to be territorial and often are seen standing in front of or "guarding" their nest area. If a nest is nearby, one can expect to see 10-30 lizards within the period of a month. In parts of the southern United States, nests are commonly found in houses and apartments, especially along the coast. The nest is where the skink lays its small white eggs, up to 4-8 at a time.
Habitat
Skinks are very specific in their habitat as some can depend on vegetation while others may depend on land and the soil. As a family, skinks are cosmopolitan; species occur in a variety of habitats worldwide, apart from boreal and polar regions. Various species occur in ecosystems ranging from deserts and mountains to grasslands. | Skink | Wikipedia | 450 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
Many species are good burrowers. More species are terrestrial or fossorial (burrowing) than arboreal (tree-climbing) or aquatic species. Some are "sand swimmers", especially the desert species, such as the mole skink or sand skink in Florida. Some use a very similar action in moving through grass tussocks. Most skinks are diurnal (day-active) and typically bask on rocks or logs during the day.
Predators
Raccoons, foxes, possums, snakes, coatis, weasels, crows, cats, dogs, herons, hawks, lizards, and other predators of small land vertebrates also prey on various skinks. This can be troublesome, given the long gestation period for some skinks, making them an easy target to predators such as the mongoose, which often threaten the species to at least near extinction, such as the Anguilla Bank skink. Invasive rodents are a major threat to skinks that have been overlooked, especially tropical skinks.
Skinks are also hunted for food by indigenous peoples in New Guinea, including by the Kalam people in the highlands of Madang Province, Papua New Guinea.
Genetics
Genomic architecture
Despite making up 15% of reptiles, skinks have a relatively conserved chromosome number, between 11 and 16 pairs. Skink genomes are typically about 1.5 Gb, approximately one-half the size of the human genome. The Christmas Island blue-tailed skink (Cryptoblepharus egeriae) was sequenced in 2022, representing the first skink reference genome.
Sex determination systems
Skinks were long thought to have both genetic sex determination (GSD) and temperature-dependent sex determination (TSD). Despite having sex chromosomes that are not distinguishable with a microscope, all major skink lineages share an old XY system that is over 80 million years old. These X and Y specific regions are highly divergent and contain multiple chromosomal rearrangements and repetitive sequences.
Genera
Many genera, Mabuya for example, are still insufficiently studied, and their systematics are at times controversial, see for example the taxonomy of the western skink, Plestiodon skiltonianus. Mabuya in particular, is being split, many species being allocated to new genera such as Trachylepis, Chioninia, and Eutropis.
Subfamily Acontinae (limbless skinks; 30 species in 2 genera) | Skink | Wikipedia | 510 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
Acontias (25 species)
Typhlosaurus (5 species)
Subfamily Egerniinae (social skinks; 63 species in 9 genera)
Bellatorias (3 species)
Corucia (1 species)
Cyclodomorphus (9 species)
Egernia (17 species)
Liopholis (12 species)
Lissolepis (2 species)
Tiliqua (7 species)
Tribolonotus (10 species)
Subfamily Eugongylinae (eugongylid skinks; 455 species in 50 genera) | Skink | Wikipedia | 113 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
Ablepharus (18 species)
Acritoscincus (3 species)
Alpinoscincus (2 species)
Anepischetosia (1 species)
Austroablepharus (3 species)
Caesoris (1 species)
Caledoniscincus (14 species)
Carinascincus (8 species)
Carlia (46 species)
Celatiscincus (2 species)
Cophoscincopus (4 species)
Cryptoblepharus (53 species)
Emoia (78 species)
Epibator (3 species)
Eroticoscincus (1 species)
Eugongylus (5 species)
Geomyersia (2 species)
Geoscincus (1 species)
Graciliscincus (1 species)
Harrisoniascincus (1 species)
Kanakysaurus (2 species)
Kuniesaurus (1 species)
Lacertaspis (5 species)
Lacertoides (1 species)
Lampropholis (14 species)
Leiolopisma (4 species)
Leptosiaphos (18 species)
Liburnascincus (4 species)
Lioscincus (2 species)
Lobulia (8 species)
Lygisaurus (14 species)
Marmorosphax (5 species)
Menetia (5 species)
Morethia (8 species)
Nannoscincus (12 species)
Nubeoscincus (2 species)
Oligosoma (53 species)
Panaspis (21 species)
Phaeoscincus (2 species)
Phasmasaurus (2 species)
Phoboscincus (2 species)
Proablepharus (2 species)
Pseudemoia (6 species)
Pygmaeascincus (3 species)
Saproscincus (12 species)
Sigaloseps (6 species)
Simiscincus (1 species)
Tachygia (1 species)
Techmarscincus (1 species)
Tropidoscincus (3 species)
Subfamily Lygosominae (lygosomid skinks; 56 species in 6 genera)
Haackgreerius (1 species)
Lamprolepis (3 species)
Lygosoma (16 species)
Mochlus (18 species)
Riopa (9 species)
Subdoluseps (8 species)
Subfamily Mabuyinae (mabuyid skinks; 226 species in 25 genera) | Skink | Wikipedia | 490 | 323825 | https://en.wikipedia.org/wiki/Skink | Biology and health sciences | Reptiles | null |
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