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7139731 | https://en.wikipedia.org/wiki/Dwarf%20crocodile | Dwarf crocodile | The dwarf crocodile (Osteolaemus tetraspis), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile) or bony crocodile, is an African crocodile that is also the smallest extant (living) species of crocodile.
Description
Dwarf crocodiles attain a medium adult length of , though the maximum recorded length for this species is . Adult specimens typically weigh between , with the largest females weighing up to and the largest males weighing . This makes it the smallest living crocodile species, although the Cuvier's dwarf caiman (Paleosuchus palpebrosus), a member of the family Alligatoridae, is smaller at up to about . If the Congo dwarf crocodile (O. osborni) is recognized as a valid species, it would be both the smallest crocodile and the smallest crocodilian since it does not surpass . Adults are all dark above and on their sides, while the underside is yellowish with black patches.
Some individuals living in the caves of Abanda, Gabon, displayed orange patches, apparently due to alkaline bat guano that erodes the skin of the crocodile. Juveniles have a lighter brown banding on body and tails and yellow patterns on the head.
As a result of its small size and heightened vulnerability to predation, this species of crocodile has a heavily armoured neck, back, and tail and also has osteoderms on its belly and underside of neck.
Osteolaemus has a blunt short snout, as long as it is wide, similar to that of a Cuvier's dwarf caiman, probably a result of occupying a similar ecological niche. The dentition consists of four premaxillary teeth, 12 to 13 on the maxilla, and 14 to 15 on the dentary bone.
O. t. tetraspis has lighter colours, a more pointed, upturned snout, and more body armour than O. t. osborni.
Distribution and habitat
Dwarf crocodiles range across tropical regions of Sub-Saharan West Africa and Central Africa. Such a distribution greatly overlaps with that of the slender-snouted crocodile, encompassing countries as far west as Senegal, reaching Uganda in the east, and ranging as southerly as Angola. The last confirmed record from Uganda was in the 1940s, but whether the species, which is easily overlooked, still survives there is unclear (it was always marginal in this country, only occurring in the far southwest).
Dwarf crocodiles live from lowlands to mid-altitude in streams, small rivers, swamps, pools and mangrove, but generally avoid main sections of large rivers. Most of their range is within forested regions, but it may extend into more open regions where the streams or river are well-shaded. They are also found in seasonally-flooded forest. Unlike most crocodiles, dwarf crocodiles only rarely bask in the sun. During the night they may move some distance from water on land. Reports exist of dwarf crocodiles in isolated pools in the savannah. Dwarf crocodiles living long-term in caves are known from western Gabon, which stand out as an isolated genetic group.
Biology and behaviour
The dwarf crocodile is a timid and mainly nocturnal reptile that spends the day hidden in pools or burrows, although it occasionally may be active during the day. Foraging is mainly done in or near the water, although it is considered to be one of the most terrestrial species of crocodilian and may expand the feeding pattern to land in extensive forays, especially after rains.
Dwarf crocodiles are generalist predators and have been recorded feeding on a wide range of small animals such as fish, crabs, frogs, gastropods, insects, lizards, water birds, bats and shrews.
In a study in the Democratic Republic of the Congo the primary food item was fish, and in a study in Nigeria the primary food items were gastropods and crabs. In the Congo there is a level of seasonality in its diet, changing from fish in the wet season to crustaceans in the dry season, when fish are less available. Plant material has also been found in the stomach of dwarf crocodiles, but it is suspected that this is ingested by accident. They can survive for relatively long periods without food. During the dry season, dwarf crocodiles often retreat to deep holes.True to its solitary, nocturnal nature, a dwarf crocodile digs out a burrow in which to hide and rest during the day, which can sometimes have a submerged entrance. An individual lacking the right conditions to do so usually lives between tree roots that hang over the ponds where it lives.
Reproduction
Interacting closely only in breeding season, female dwarf crocodiles build their nest mounds at the beginning of the wet season, which spans May and June. The nest, situated near the water, is a mound of wet, decaying vegetation that incubates the eggs due to the heat generated by the decomposition of the plant material. A small number of eggs is laid, usually about 10, though in extreme cases up to 20, and they incubate in 85 to 105 days. Hatchlings measure 28 cm when emerging from the eggs. The female guards the nest during the incubation period, and after the eggs hatch, she watches over the young for an unknown period of time, as young can be eaten by a great range of predators (birds, fish, mammals and reptiles, including other crocodiles).
Taxonomy and etymology
The second species has had a somewhat convoluted taxonomical history. It was first described as Osteoblepharon osborni by Schmidt in 1919, based on a few specimens from the Upper Congo River Basin in what is now the Democratic Republic of Congo. However, Inger in a 1948 paper found the specimens wanting of characteristics that would justify a generic separation from Osteolaemus and referred the specimens to Osteolaemus osborni. In 1961, it was reduced to subspecies rank.
A study of morphology published in 2007, and studies of DNA in 2009, 2013 and 2015 indicate that three distinctly different populations of Osteolaemus may merit full species recognition. These are O. tetraspis (Central Africa, except the Congo River Basin), O. osborni (Congo River Basin), and a third possibly unnamed species (West Africa). Uncertainty exists for the population in Nigeria (between O. tetraspis and the possibly unnamed West African species) as it has not been studied. A fourth clade was found in a study of captives in 2013, but where members of this clade live in the wild is unclear. In some regions the species may come into contact. For example, Cameroon is home to both O. tetraspis and O. osborni.
Etymology
The generic name, Osteolaemus, means "bony throat", and is derived from the Ancient Greek (bone) and (throat). The genus was named as such due to the osteoderms found among the scales in the neck and belly.
The specific epithet, tetraspis, means "four shields", and derives from the Ancient Greek (four) and (shield), as the back of the neck has four large, shield-like scales.
Phylogeny
A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodylidae. In 2021, Hekkala et al. were able to use paleogenomics, extracting DNA from the extinct Voay, to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae.
The below cladogram shows the results of the latest study:
Conservation
The dwarf crocodile is considered vulnerable by the IUCN, and it is listed on Appendix I of CITES. It is a little-known species, so unlike their more studied relatives, conservationists are often not as aware of how their populations are faring under the growing human pressure over the ecosystems where they abide. Survey data, when available, show some degree of decline, either by hunting for bushmeat or habitat loss due to deforestation. However, it is a widely spread, and presumably numerous overall. In some regions the populations remain healthy, but in others (such as Gambia and Liberia) it has seriously declined and may risk extirpation. Dwarf crocodiles occur in several protected reserves.
Though some skins are used in local manufacturing of leather products, they are of poor quality, so little interest is shown in captive breeding or a sustainable use program. In contrast, they are sometimes hunted for food and part of the bushmeat trade.
Dwarf crocodiles are widely kept and bred in zoos. Based on a study of individuals kept in AZA zoos, captives in North America are primarily O. tetrapis and the possibly unnamed West African species, but there are also some hybrids. Another study of individuals kept at EAZA zoos revealed a similar picture for Europe, but also that there were a few individuals of the fourth clade (native range in the wild unknown) and a single O. osborni.
Gallery
| Biology and health sciences | Crocodilia | Animals |
15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Soil steam sterilization | Soil steam sterilization (soil steaming) is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes vital cellular proteins to unfold. Biologically, the method is considered a partial disinfection. Important heat-resistant, spore-forming bacteria can survive and revitalize the soil after cooling down. Soil fatigue can be cured through the release of nutritive substances blocked within the soil. Steaming leads to a better starting position, quicker growth and strengthened resistance against plant disease and pests. Today, the application of hot steam is considered the best and most effective way to disinfect sick soil, potting soil and compost.
It is being used as an alternative to bromomethane, whose production and use was curtailed by the Montreal Protocol. "Steam effectively kills pathogens by heating the soil to levels that cause protein coagulation or enzyme inactivation."
Benefits of soil steaming
Soil sterilization provides secure and quick relief of soils from substances and organisms harmful to plants such as:
Bacteria
Viruses
Fungi
Nematodes
Other pests
Further positive effects are:
All weeds and weed seeds are killed
Significant increase of crop yields
Relief from soil fatigue through activation of chemical – biological reactions
Blocked nutritive substances in the soil are tapped and made available for plants
Alternative to methyl bromide and other critical chemicals in agriculture
Steaming with superheated steam
Through modern steaming methods with superheated steam at 180–200 °C, an optimal soil disinfection can be achieved. Soil only absorbs a small amount of humidity. Micro organisms become active once the soil has cooled down. This creates an optimal environment for instant tillage with seedlings and seeds.
Additionally the method of integrated steaming can promote a target-oriented resettlement of steamed soil with beneficial organisms. In the process, the soil is first freed from all organisms and then revitalized and microbiologically buffered through the injection of a soil activator based on compost which contains a natural mixture of favorable microorganisms (e.g. Bacillus subtilis, etc.).
Different types of such steam application are also available in practice, including substrate steaming, surface steaming, and deep soil steaming.
Surface steaming
Several methods for surface steaming are in use amongst which are: area sheet steaming, the steaming hood, the steaming harrow, the steaming plough and vacuum steaming with drainage pipes or mobile pipe systems.
In order to pick the most suitable steaming method, certain factors have to be considered such as soil structure, plant culture and area performance. At present, more advanced methods are being developed, such as sandwich steaming or partially integrated sandwich steaming in order to minimize energy consumption and associated costs as much as possible.
Deep soil steaming
Deep soil steaming is a concept adopted by the Norwegian company Soil Steam international AS. They have developed a technology that gets the steam down to 30 cm deep in the soil. This is done in a continuous process and their last prototype managed to treat 1 hectare in 20 hours. When steaming the soil this deep, they get deep enough to prevent fall plowing from bringing up new seeds, fungi or nematodes. This means that the soil stays free from weeds, seeds, fungi and nematodes for many years after one deep soil steam operation.
Sheet steaming
Surface steaming with special sheets (sheet steaming) is a method which has been established for decades in order to steam large areas reaching from 15 to 400 m2 in one step. If properly applied, sheet steaming is simple and highly economic. The usage of heat resistant, non-decomposing insulation fleece saves up to 50% energy, reduces the steaming time significantly and improves penetration. Single working step areas up to 400 m2 can be steamed in 4–5 hours down to 25–30 cm depth / 90 °C.
The usage of heat resistant and non-decomposing synthetic insulation fleece, 5 mm thick, 500 gr / m2, can reduce steaming time by about 30%. Through a steam injector or a perforated pipe, steam is injected underneath the sheet after it has been laid out and weighted with sand sacks.
The area performance in one working step depends on the capacity of the steam generator (e.g. steam boiler):
The steaming time depends on soil structure as well as outside temperature and amounts to 1–1.5 hours per 10 cm steaming depth. Hereby the soil reaches a temperature of about 85 °C. Milling for soil loosening is not recommended since soil structure may become too fine which reduces its penetrability for steam. The usage of spading machines is ideal for soil loosening. The best results can be achieved if the soil is cloddy at greater depth and granulated at lesser depth.
In practice, working with at least two sheets simultaneously has proven to be highly effective. While one sheet is used for steaming the other one is prepared for steam injection, therefore unnecessary steaming recesses are avoided.
Depth steaming with vacuum
Steaming with vacuum which is induced through a mobile or fixed installed pipe system in the depth of the area to be steamed, is the method that reaches the best penetration. Despite high capital cost, the fixed installation of drainage systems is reasonable for intensively used areas since steaming depths of up to 80 cm can be achieved.
In contrast to fixed installed drainage systems, pipes in mobile suction systems are on the surface. A central suction pipeline consisting of zinc-coated, fast-coupling pipes are connected in a regular spacing of 1.50 m and the ends of the hoses are pushed into the soil to the desired depth with a special tool.
The steaming area is covered with a special steaming sheet and weighted all around as with sheet steaming. The steam is injected underneath the sheet through an injector and protection tunnel. While with short areas up to 30 m length steam is frontally injected, with longer areas steam is induced in the middle of the sheet using a T-connection branching out to both sides.
As soon as the sheet is inflated to approximately 1 m by the steam pressure, the suction turbine is switched on. First, the air in the soil is removed via the suction hoses. A partial vacuum is formed and the steam is pulled downward.
During the final phase, when the required steaming depth has been reached, the ventilator runs non-stop and surplus steam is blown out. To ensure that this surplus steam is not lost, it is fed back under the sheet.
As with all other steaming systems, a post-steaming period of approximately 20–30 minutes is required. Steaming time is approximately 1 hour per 10 cm steaming depth. The steam requirement is approximately 7–8 kg/m2.
The most important requirement, as with all steaming systems, is that the soil is well loosened before steaming, to ensure optimal penetration.
Negative pressure technique
Negative pressure technique generates appropriate soil temperature at a 60 cm depth and complete control of nematodes, fungi and weeds is achieved. In this technique, the steam is introduced under the steaming sheath and forced to enter the soil profile by a negative pressure. The negative pressure is created by a fan that sucks the air out of the soil through buried perforated polypropylene pipes. This system requires a permanent installation of perforated pipes into the soil, at a depth of at least 60 cm to be protected from plough.
Steaming with hoods
A steaming hood is a mobile device consisting of corrosion-resistant materials such as aluminum, which is put down onto the area to be steamed. In contrast to sheet steaming, cost-intensive working steps such as laying out and weighting the sheets don't occur, however the area steamed per working step is smaller in accordance to the size of the hood.
Outdoors, a hood is positioned either manually or via tractor with a special pre-stressed 4 point suspension arm. Steaming time amounts to 30 min for a penetration down to 25 cm depth. Hereby a temperature of 90 °C can be reached. In large stable glasshouses, the hoods are attached to tracks. They are lifted and moved by pneumatic cylinders. Small and medium-sized hoods up to 12 m2 are lifted manually using a tipping lever or moved electrically with special winches.
Combined surface and depth injection of steam (Sandwich Steaming)
Sandwich steaming, which was developed in a project among DEIAFA, University of Turin (Italy, www.deiafa.unito.it) and Ferrari Costruzioni Meccaniche (see image), represents a combination of depth and surface steaming, offers an efficient method to induce hot steam into the soil. The steam is simultaneously pushed into the soil from the surface and from the depth. For this purpose, the area, which must be equipped with a deep steaming injection system, is covered with a steaming hood. The steam enters the soil from the top and the bottom at the same time. Sheets are not suitable, since a high pressure up to 30 mm water column arises underneath the cover.
Sandwich steaming offers several advantages. On the one hand, application of energy can be increased to up to 120 kg steam per m2/h. In comparison to other steaming methods up to 30% energy savings can be achieved and the usage of fuel (e.g. heating oil) accordingly decreases. The increased application of energy leads to a quick heating of the soil which reduces the loss of heat. On the other hand, only half of the regular steaming time is needed.
Comparison of sandwich steaming with other steam injection methods relating to steam output and energy demand(*):
(*) in soil max 30% moisture
Clearly, Sandwich steaming reaches the highest steam output at the lowest energy demand.
Partially integrated sandwich steaming
The partial integrated sandwich steaming is an advanced combined method for steaming merely the areas which shall be planted and purposely leaving out those areas which shall not be used. In order to avoid risk of re-infection of steamed areas with pest from unsteamed areas, beneficial organisms can directly be injected into the hygenized soil via a soil activator (e.g. special compost). The partial sandwich steaming unlocks further potential savings in the steaming process.
Container / Stack steaming
Stack steaming is used when thermically treating compost and substrates such as turf. Depending on the amount, the material to be steamed is piled up to 70 cm height in steaming boxes or in small dump trailers. Steam is evenly injected via manifolds. For huge amounts, steaming containers and soil boxes are used which are equipped with suction systems to improve steaming results. Midget amounts can be steamed in special small steaming devices.
The amount of soil steamed should be tuned in a way that steaming time amounts to at most 1.5 h in order to avoid large quantities of condensed water in the bottom layers of the soil.
In light substrates, such as turf, the performance per hour is significantly higher.
History
Modern soil steam sterilization was first discovered in 1888 (by Frank in Germany) and was first commercially used in the United States (by Rudd) in 1893 (Baker 1962). Since then, a wide variety of steam machines have been built to disinfest both commercial greenhouse and nursery field soils (Grossman and Liebman 1995). In the 1950s, for example, steam sterilization technologies expanded from disinfestation of potting soil and greenhouse mixes to commercial production of steam rakes and tractor-drawn steam blades for fumigating small acres of cut flowers and other high-value field crops (Langedijk 1959). Today, even more effective steam technologies are being developed.
Application of hot steam
In horticulture as well as nurseries for sterilization of substrates and top soil
In agriculture for sterilization and treatment of food waste for pig fattening and heating of molasses
In mushroom cultivation for pasteurization of growing rooms, sterilization of top soil and combined application as heating
In wineries as combination boiler for sterilization and cleaning of storage tanks, tempering of mash and for warm water generation.
| Technology | Pest and disease control | null |
9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Parthenogenesis | Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, and reptiles. This type of reproduction has been induced artificially in animal species that naturally reproduce through sex, including fish, amphibians, and mice.
Normal egg cells form in the process of meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles. In some types of parthenogenesis the offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation.
Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).
Life history types
Parthenogenesis is a form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. It occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, reptiles, and birds. This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice.
Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy or heterogony). The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like Daphnia). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This is because in asexual reproduction a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who will not give birth. Some species can produce both sexually and through parthenogenesis, and offspring in the same clutch of a species of tropical lizard can be a mix of sexually produced offspring and parthenogenically produced offspring. In California condors, facultative parthenogenesis can occur even when a male is present and available for a female to breed with. In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions.
Many taxa with heterogony have within them species that have lost the sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis.
The production of female offspring by parthenogenesis is referred to as thelytoky (e.g., aphids) while the production of males by parthenogenesis is referred to as arrhenotoky (e.g., bees). When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky.
Types and mechanisms
Parthenogenesis can occur without meiosis through mitotic oogenesis. This is called apomictic parthenogenesis. Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids.
Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid (e.g., male ants). In other cases, collectively called automictic parthenogenesis, the ploidy is restored to diploidy by various means. This is because haploid individuals are not viable in most species. In automictic parthenogenesis, the offspring differ from one another and from their mother. They are called half clones of their mother.
Automixis
Automixis includes several reproductive mechanisms, some of which are parthenogenetic.
Diploidy can be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed. This is an endomitotic cycle. Diploidy can also be restored by fusion of the first two blastomeres, or by fusion of the meiotic products. The chromosomes may not separate at one of the two anaphases (restitutional meiosis)l; or the nuclei produced may fuse; or one of the polar bodies may fuse with the egg cell at some stage during its maturation.
Some authors consider all forms of automixis sexual as they involve recombination. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined. The criterion for sexuality varies from all cases of restitutional meiosis, to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences.
The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosis or when central fusion occurs (restitutional meiosis of anaphase I or the fusion of its products), the offspring get all to more than half of the mother's genetic material and heterozygosity is mostly preserved (if the mother has two alleles for a locus, it is likely that the offspring will get both). This is because in anaphase I the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion. In the case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids.
If terminal fusion (restitutional meiosis of anaphase II or the fusion of its products) occurs, a little over half the mother's genetic material is present in the offspring and the offspring are mostly homozygous. This is because at anaphase II the sister chromatids are separated and whatever heterozygosity is present is due to crossing over. In the case of endomitosis after meiosis, the offspring is completely homozygous and has only half the mother's genetic material. This can result in parthenogenetic offspring being unique from each other and from their mother.
Sex of the offspring
In apomictic parthenogenesis, the offspring are clones of the mother and hence (except for aphids) are usually female. In the case of aphids, parthenogenetically produced males and females are clones of their mother except that the males lack one of the X chromosomes (XO).
When meiosis is involved, the sex of the offspring depends on the type of sex determination system and the type of apomixis. In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), ZZ (male), or WW (non-viable in most species, but a fertile, viable female in a few, e.g., boas). ZW offspring are produced by endoreplication before meiosis or by central fusion. ZZ and WW offspring occur either by terminal fusion or by endomitosis in the egg cell.
In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female.
In many hymenopteran insects such as honeybees, female eggs are produced sexually, using sperm from a drone father, while the production of further drones (males) depends on the queen (and occasionally workers) producing unfertilized eggs. This means that females (workers and queens) are always diploid, while males (drones) are always haploid, and produced parthenogenetically.
Facultative
Facultative parthenogenesis occurs when a female can produce offspring either sexually or via asexual reproduction. Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies; presumably, this is the default reproductive mode of all species in this insect order. Facultative parthenogenesis has generally been believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if a male is absent from the habitat or if it is unable to produce viable offspring. However, California condors and the tropical lizard Lepidophyma smithii both can produce parthenogenic offspring in the presence of males, indicating that facultative parthenogenesis may be more common than previously thought and is not simply a response to a lack of males.
In aphids, a generation sexually conceived by a male and a female produces only females. The reason for this is the non-random segregation of the sex chromosomes 'X' and 'O' during spermatogenesis.
Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals. For example, many cases of spontaneous parthenogenesis in sharks, some snakes, Komodo dragons, and a variety of domesticated birds were widely attributed to facultative parthenogenesis. These cases are examples of spontaneous parthenogenesis. The occurrence of such asexually produced eggs in sexual animals can be explained by a meiotic error, leading to eggs produced via automixis.
Obligate
Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means. Many species have transitioned to obligate parthenogenesis over evolutionary time. Well documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms. These transitions often occur as a result of inbreeding or mutation within large populations. Some documented species, specifically salamanders and geckos, that rely on obligate parthenogenesis as their major method of reproduction. As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species), amphibians and fishes in nature for which males are no longer a part of the reproductive process. A female produces an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring.
Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been introduced. Relying solely on parthenogenetic reproduction has several advantages for an invasive species: it obviates the need for individuals in a very sparse initial population to search for mates; and an exclusively female sex distribution allows a population to multiply and invade more rapidly (potentially twice as fast). Examples include several aphid species and the willow sawfly, Nematus oligospilus, which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.
Natural occurrence
Parthenogenesis does not apply to isogamous species. Parthenogenesis occurs naturally in aphids, Daphnia, rotifers, nematodes, and some other invertebrates, as well as in many plants. Among vertebrates, strict parthenogenesis is only known to occur in lizards, snakes, birds, and sharks. Fish, amphibians, and reptiles make use of various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis). The first all-female (unisexual) reproduction in vertebrates was described in the fish Poecilia formosa in 1932. Since then at least 50 species of unisexual vertebrate have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders.
Artificial induction
Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.
During oocyte development, high metaphase promoting factor (MPF) activity causes mammalian oocytes to arrest at the metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations, and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis.
To initiate unfertilised development of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide, a non-specific protein synthesis inhibitor, enhances the development of unfertilised eggs in swine presumably by continual inhibition of MPF/cyclin B. As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote The resulting embryos can be surgically transferred to a recipient oviduct for further development, but will succumb to developmental failure after ≈30 days of gestation. The swine placenta in these cases often appears hypo-vascular: see free image (Figure 1) in linked reference.
Induced parthenogenesis of this type in mice and monkeys results in abnormal development. This is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring for development to proceed normally. A mammal developing from parthenogenesis would have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities. It has been suggested that defects in placental folding or interdigitation are one cause of swine parthenote abortive development. As a consequence, research on the induced development of unfertilised eggs in humans is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy.
In 2022, researchers reported that they have produced viable offspring born from unfertilized eggs in mice, addressing the problems of genomic imprinting by "targeted DNA methylation rewriting of seven imprinting control regions".
In humans
In 1955, Helen Spurway, a geneticist specializing in the reproductive biology of the guppy (Lebistes reticulatus), claimed that parthenogenesis may occur (though very rarely) in humans, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike. Sometimes an embryo may begin to divide without fertilization, but it cannot fully develop on its own; so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes a type of benign tumor called an ovarian teratoma. Spontaneous ovarian activation is not rare and has been known about since the 19th century. Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs and other structures, but are non-viable.
In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as white blood cells) to be lacking in any genetic content from his father. Scientists believe that an unfertilized egg began to self-divide but then had some (but not all) of its cells fertilized by a sperm cell; this must have happened early in development, as self-activated eggs quickly lose their ability to be fertilized. The unfertilized cells eventually duplicated their DNA, boosting their chromosomes to 46. When the unfertilized cells hit a developmental block, the fertilized cells took over and developed that tissue. The boy had asymmetrical facial features and learning difficulties but was otherwise healthy. This would make him a parthenogenetic chimera (a child with two cell lineages in his body). While over a dozen similar cases have been reported since then (usually discovered after the patient demonstrated clinical abnormalities), there have been no scientifically confirmed reports of a non-chimeric, clinically healthy human parthenote (i.e. produced from a single, parthenogenetic-activated oocyte).
In 2007, the International Stem Cell Corporation of California announced that Elena Revazova had intentionally created human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way for creating stem cells genetically matched to a particular female to treat degenerative diseases. The same year, Revazova and ISCC published an article describing how to produce human stem cells that are homozygous in the HLA region of DNA. These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and would allow derivatives of these cells to be implanted without immune rejection. With selection of oocyte donors according to HLA haplotype, it would be possible to generate a bank of cell lines whose tissue derivatives, collectively, could be MHC-matched with a significant number of individuals within the human population.
After an independent investigation, it was revealed that the discredited South Korean scientist Hwang Woo-Suk unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result later found to be fabricated. Further examination of the chromosomes of these cells show indicators of parthenogenesis in those extracted stem cells, similar to those found in the mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he contributed a major breakthrough to stem cell research by creating human embryos using parthenogenesis.
Similar phenomena
Gynogenesis
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some salamanders of the genus Ambystoma are gynogenetic and appear to have been so for over a million years. The success of those salamanders may be due to rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million. In addition, the Amazon molly is known to reproduce by gynogenesis.
Hybridogenesis
Hybridogenesis is a mode of reproduction of hybrids. Hybridogenetic hybrids (for example AB genome), usually females, during gametogenesis exclude one of parental genomes (A) and produce gametes with unrecombined genome of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A) is restored by fertilization of these gametes with gametes from the first species (AA, sexual host, usually male). Hybridogenesis is not completely asexual, but hemiclonal: half the genome is passed to the next generation clonally, unrecombined, intact (B), other half sexually, recombined (A). This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from the father's side.
This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"):
P. kl. esculentus (edible frog): P. lessonae × P. ridibundus,
P. kl. grafi (Graf's hybrid frog): P. perezi × P. ridibundus
P. kl. hispanicus (Italian edible frog) – unknown origin: P. bergeri × P. ridibundus or P. kl. esculentus
Other examples where hybridogenesis is at least one of modes of reproduction include i.e.
Iberian minnow Tropidophoxinellus alburnoides (Squalius pyrenaicus × hypothetical ancestor related with Anaecypris hispanica)
spined loaches Cobitis hankugensis × C. longicorpus
Bacillus stick insects B. rossius × Bacillus grandii benazzii
In human culture
Parthenogenesis, in the form of reproduction from a single individual (typically a god), is common in mythology, religion, and folklore around the world, including in ancient Greek myth; for example, Athena was born from the head of Zeus. In Christianity and Islam, there is the virgin birth of Jesus; there are stories of miraculous births in other religions including Islam.
The theme is one of several aspects of reproductive biology explored in science fiction.
| Biology and health sciences | Biological reproduction | Biology |
5470669 | https://en.wikipedia.org/wiki/Fault%20block | Fault block | Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform lithology. The largest of these fault blocks are called crustal blocks. Large crustal blocks broken off from tectonic plates are called terranes. Those terranes which are the full thickness of the lithosphere are called microplates. Continent-sized blocks are called variously microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs.
Because most stresses relate to the tectonic activity of moving plates, most motion between blocks is horizontal, that is parallel to the Earth's crust by strike-slip faults. However vertical movement of blocks produces much more dramatic results. Landforms (mountains, hills, ridges, lakes, valleys, etc.) are sometimes formed when the faults have a large vertical displacement. Adjacent raised blocks (horsts) and down-dropped blocks (grabens) can form high escarpments. Often the movement of these blocks is accompanied by tilting, due to compaction or stretching of the crust at that point.
Fault-block mountains
Fault-block mountains often result from rifting, an indicator of extensional tectonics. These can be small or form extensive rift valley systems, such as the East African Rift zone. Death Valley in California is a smaller example. There are two main types of block mountains; uplifted blocks between two faults and tilted blocks mainly controlled by one fault.
Lifted type block mountains have two steep sides exposing both sides scarps, leading to the horst and graben terrain seen in various parts of Europe including the Upper Rhine valley, a graben between two horsts – the Vosges mountains (in France) and the Black Forest (in Germany), and also the Rila – Rhodope Massif in Bulgaria, Southeast Europe, including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain – a horst forming a massive anticline situated between the complex graben valleys of Struma and that of Mesta.
Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp, and are common in the Basin and Range region of the western United States.
An example of a graben is the basin of the Narmada River in India, between the Vindhya and Satpura horsts.
| Physical sciences | Montane landforms | Earth science |
5473867 | https://en.wikipedia.org/wiki/Near%20side%20of%20the%20Moon | Near side of the Moon | The near side of the Moon is the lunar hemisphere that always faces towards Earth, opposite to the far side. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as tidal locking.
The Moon is directly illuminated by the Sun, and the cyclically varying viewing conditions cause the lunar phases. Sometimes the dark portion of the Moon is faintly visible due to earthshine, which is indirect sunlight reflected from the surface of Earth and onto the Moon.
Since the Moon's orbit is both somewhat elliptical and inclined to its equatorial plane, libration allows up to 59% of the Moon's surface to be viewed from Earth (though only half at any moment from any point).
Orientation
The image of the Moon here is drawn as is normally shown on maps, that is with north on top and west to the left. Astronomers traditionally turn the map to have south on top to correspond with the northern-hemisphere view in astronomical telescopes, which typically show the image upside down.
West and east on the Moon are where they would be expected, when standing on the Moon. But when the Moon is seen from Earth, then the east–west direction is reversed. When specifying coordinates on the Moon it should therefore always be mentioned whether geographic (or rather selenographic) coordinates are used or astronomical coordinates.
The Moon's actual orientation in Earth's sky or on the horizon depends on the viewers geographic latitude on Earth. In the following description a few typical cases will be considered.
On the north pole, if the Moon is visible, it stands low above the horizon with its north pole up.
In mid northern latitudes (North America, Europe, Asia) the Moon rises in the east with its northeastern limb up (Mare Crisium), it reaches its highest point in the south with its north on top, and sets in the west with its northwestern limb (Mare Imbrium) on top.
On the equator, when the Moon rises in the east, its N — S axis appears horizontal and Mare Foecunditatis is on top. When it sets in the west, about 12.5 hours later, the axis is still horizontal, and Oceanus Procellarum is the last area to dip below the horizon. In between these events, the Moon reached its highest point in the zenith and then its selenographic directions are lined up with those on Earth.
In mid southern latitudes (South America, South Pacific, Australia, South Africa) the Moon rises in the east with its southeastern limb up (Mare Nectaris), it reaches its highest point in the north with its south on top, and sets in the west with its southwestern limb (Mare Humorum) on top.
On the south pole the Moon behaves as on the north pole, but there it appears with its south pole up.
Differences
The two hemispheres have distinctly different appearances, with the near side covered in multiple, large maria (Latin for 'seas'). These lowlands were believed to be seas of lunar water by the astronomers who first mapped them, in the 17th century (notably, Giovanni Battista Riccioli and Francesco Maria Grimaldi). Although no bodies of liquid exist on the Moon, the term "mare" (plural: maria) is still used. The far side has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria, compared to 31.2% on the near side. According to research analyzed by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, the reason for the difference is because the Moon's crust is thinner on the near side compared to the far side. The dark splotches that make up the large lunar maria are lava-filled impact basins that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters. These larger impact craters make up the Man in the Moon references from popular mythology.
| Physical sciences | Solar System | Astronomy |
573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Measurement in quantum mechanics | In quantum physics, a measurement is the testing or manipulation of a physical system to yield a numerical result. A fundamental feature of quantum theory is that the predictions it makes are probabilistic. The procedure for finding a probability involves combining a quantum state, which mathematically describes a quantum system, with a mathematical representation of the measurement to be performed on that system. The formula for this calculation is known as the Born rule. For example, a quantum particle like an electron can be described by a quantum state that associates to each point in space a complex number called a probability amplitude. Applying the Born rule to these amplitudes gives the probabilities that the electron will be found in one region or another when an experiment is performed to locate it. This is the best the theory can do; it cannot say for certain where the electron will be found. The same quantum state can also be used to make a prediction of how the electron will be moving, if an experiment is performed to measure its momentum instead of its position. The uncertainty principle implies that, whatever the quantum state, the range of predictions for the electron's position and the range of predictions for its momentum cannot both be narrow. Some quantum states imply a near-certain prediction of the result of a position measurement, but the result of a momentum measurement will be highly unpredictable, and vice versa. Furthermore, the fact that nature violates the statistical conditions known as Bell inequalities indicates that the unpredictability of quantum measurement results cannot be explained away as due to ignorance about "local hidden variables" within quantum systems.
Measuring a quantum system generally changes the quantum state that describes that system. This is a central feature of quantum mechanics, one that is both mathematically intricate and conceptually subtle. The mathematical tools for making predictions about what measurement outcomes may occur, and how quantum states can change, were developed during the 20th century and make use of linear algebra and functional analysis. Quantum physics has proven to be an empirical success and to have wide-ranging applicability. However, on a more philosophical level, debates continue about the meaning of the measurement concept.
Mathematical formalism
"Observables" as self-adjoint operators
In quantum mechanics, each physical system is associated with a Hilbert space, each element of which represents a possible state of the physical system. The approach codified by John von Neumann represents a measurement upon a physical system by a self-adjoint operator on that Hilbert space termed an "observable". These observables play the role of measurable quantities familiar from classical physics: position, momentum, energy, angular momentum and so on. The dimension of the Hilbert space may be infinite, as it is for the space of square-integrable functions on a line, which is used to define the quantum physics of a continuous degree of freedom. Alternatively, the Hilbert space may be finite-dimensional, as occurs for spin degrees of freedom. Many treatments of the theory focus on the finite-dimensional case, as the mathematics involved is somewhat less demanding. Indeed, introductory physics texts on quantum mechanics often gloss over mathematical technicalities that arise for continuous-valued observables and infinite-dimensional Hilbert spaces, such as the distinction between bounded and unbounded operators; questions of convergence (whether the limit of a sequence of Hilbert-space elements also belongs to the Hilbert space), exotic possibilities for sets of eigenvalues, like Cantor sets; and so forth. These issues can be satisfactorily resolved using spectral theory; the present article will avoid them whenever possible.
Projective measurement
The eigenvectors of a von Neumann observable form an orthonormal basis for the Hilbert space, and each possible outcome of that measurement corresponds to one of the vectors comprising the basis. A density operator is a positive-semidefinite operator on the Hilbert space whose trace is equal to 1. For each measurement that can be defined, the probability distribution over the outcomes of that measurement can be computed from the density operator. The procedure for doing so is the Born rule, which states that
where is the density operator, and is the projection operator onto the basis vector corresponding to the measurement outcome . The average of the eigenvalues of a von Neumann observable, weighted by the Born rule probabilities, is the expectation value of that observable. For an observable , the expectation value given a quantum state is
A density operator that is a rank-1 projection is known as a pure quantum state, and all quantum states that are not pure are designated mixed. Pure states are also known as wavefunctions. Assigning a pure state to a quantum system implies certainty about the outcome of some measurement on that system (i.e., for some outcome ). Any mixed state can be written as a convex combination of pure states, though not in a unique way. The state space of a quantum system is the set of all states, pure and mixed, that can be assigned to it.
The Born rule associates a probability with each unit vector in the Hilbert space, in such a way that these probabilities sum to 1 for any set of unit vectors comprising an orthonormal basis. Moreover, the probability associated with a unit vector is a function of the density operator and the unit vector, and not of additional information like a choice of basis for that vector to be embedded in. Gleason's theorem establishes the converse: all assignments of probabilities to unit vectors (or, equivalently, to the operators that project onto them) that satisfy these conditions take the form of applying the Born rule to some density operator.
Generalized measurement (POVM)
In functional analysis and quantum measurement theory, a positive-operator-valued measure (POVM) is a measure whose values are positive semi-definite operators on a Hilbert space. POVMs are a generalisation of projection-valued measures (PVMs) and, correspondingly, quantum measurements described by POVMs are a generalisation of quantum measurement described by PVMs. In rough analogy, a POVM is to a PVM what a mixed state is to a pure state. Mixed states are needed to specify the state of a subsystem of a larger system (see Schrödinger–HJW theorem); analogously, POVMs are necessary to describe the effect on a subsystem of a projective measurement performed on a larger system. POVMs are the most general kind of measurement in quantum mechanics, and can also be used in quantum field theory. They are extensively used in the field of quantum information.
In the simplest case, of a POVM with a finite number of elements acting on a finite-dimensional Hilbert space, a POVM is a set of positive semi-definite matrices on a Hilbert space that sum to the identity matrix,
In quantum mechanics, the POVM element is associated with the measurement outcome , such that the probability of obtaining it when making a measurement on the quantum state is given by
,
where is the trace operator. When the quantum state being measured is a pure state this formula reduces to
.
State change due to measurement
A measurement upon a quantum system will generally bring about a change of the quantum state of that system. Writing a POVM does not provide the complete information necessary to describe this state-change process. To remedy this, further information is specified by decomposing each POVM element into a product:
The Kraus operators , named for Karl Kraus, provide a specification of the state-change process. They are not necessarily self-adjoint, but the products are. If upon performing the measurement the outcome is obtained, then the initial state is updated to
An important special case is the Lüders rule, named for Gerhart Lüders. If the POVM is itself a PVM, then the Kraus operators can be taken to be the projectors onto the eigenspaces of the von Neumann observable:
If the initial state is pure, and the projectors have rank 1, they can be written as projectors onto the vectors and , respectively. The formula simplifies thus to
Lüders rule has historically been known as the "reduction of the wave packet" or the "collapse of the wavefunction". The pure state implies a probability-one prediction for any von Neumann observable that has as an eigenvector. Introductory texts on quantum theory often express this by saying that if a quantum measurement is repeated in quick succession, the same outcome will occur both times. This is an oversimplification, since the physical implementation of a quantum measurement may involve a process like the absorption of a photon; after the measurement, the photon does not exist to be measured again.
We can define a linear, trace-preserving, completely positive map, by summing over all the possible post-measurement states of a POVM without the normalisation:
It is an example of a quantum channel, and can be interpreted as expressing how a quantum state changes if a measurement is performed but the result of that measurement is lost.
Examples
The prototypical example of a finite-dimensional Hilbert space is a qubit, a quantum system whose Hilbert space is 2-dimensional. A pure state for a qubit can be written as a linear combination of two orthogonal basis states and with complex coefficients:
A measurement in the basis will yield outcome with probability and outcome with probability , so by normalization,
An arbitrary state for a qubit can be written as a linear combination of the Pauli matrices, which provide a basis for self-adjoint matrices:
where the real numbers are the coordinates of a point within the unit ball and
POVM elements can be represented likewise, though the trace of a POVM element is not fixed to equal 1. The Pauli matrices are traceless and orthogonal to one another with respect to the Hilbert–Schmidt inner product, and so the coordinates of the state are the expectation values of the three von Neumann measurements defined by the Pauli matrices. If such a measurement is applied to a qubit, then by the Lüders rule, the state will update to the eigenvector of that Pauli matrix corresponding to the measurement outcome. The eigenvectors of are the basis states and , and a measurement of is often called a measurement in the "computational basis." After a measurement in the computational basis, the outcome of a or measurement is maximally uncertain.
A pair of qubits together form a system whose Hilbert space is 4-dimensional. One significant von Neumann measurement on this system is that defined by the Bell basis, a set of four maximally entangled states:
A common and useful example of quantum mechanics applied to a continuous degree of freedom is the quantum harmonic oscillator. This system is defined by the Hamiltonian
where , the momentum operator and the position operator are self-adjoint operators on the Hilbert space of square-integrable functions on the real line. The energy eigenstates solve the time-independent Schrödinger equation:
These eigenvalues can be shown to be given by
and these values give the possible numerical outcomes of an energy measurement upon the oscillator. The set of possible outcomes of a position measurement on a harmonic oscillator is continuous, and so predictions are stated in terms of a probability density function that gives the probability of the measurement outcome lying in the infinitesimal interval from to .
History of the measurement concept
The "old quantum theory"
The old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics. The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as a semi-classical approximation to modern quantum mechanics. Notable results from this period include Planck's calculation of the blackbody radiation spectrum, Einstein's explanation of the photoelectric effect, Einstein and Debye's work on the specific heat of solids, Bohr and van Leeuwen's proof that classical physics cannot account for diamagnetism, Bohr's model of the hydrogen atom and Arnold Sommerfeld's extension of the Bohr model to include relativistic effects.
The Stern–Gerlach experiment, proposed in 1921 and implemented in 1922, became a prototypical example of a quantum measurement having a discrete set of possible outcomes. In the original experiment, silver atoms were sent through a spatially varying magnetic field, which deflected them before they struck a detector screen, such as a glass slide. Particles with non-zero magnetic moment are deflected, due to the magnetic field gradient, from a straight path. The screen reveals discrete points of accumulation, rather than a continuous distribution, owing to the particles' quantized spin.
Transition to the “new” quantum theory
A 1925 paper by Heisenberg, known in English as "Quantum theoretical re-interpretation of kinematic and mechanical relations", marked a pivotal moment in the maturation of quantum physics. Heisenberg sought to develop a theory of atomic phenomena that relied only on "observable" quantities. At the time, and in contrast with the later standard presentation of quantum mechanics, Heisenberg did not regard the position of an electron bound within an atom as "observable". Instead, his principal quantities of interest were the frequencies of light emitted or absorbed by atoms.
The uncertainty principle dates to this period. It is frequently attributed to Heisenberg, who introduced the concept in analyzing a thought experiment where one attempts to measure an electron's position and momentum simultaneously. However, Heisenberg did not give precise mathematical definitions of what the "uncertainty" in these measurements meant. The precise mathematical statement of the position-momentum uncertainty principle is due to Kennard, Pauli, and Weyl, and its generalization to arbitrary pairs of noncommuting observables is due to Robertson and Schrödinger.
Writing and for the self-adjoint operators representing position and momentum respectively, a standard deviation of position can be defined as
and likewise for the momentum:
The Kennard–Pauli–Weyl uncertainty relation is
This inequality means that no preparation of a quantum particle can imply simultaneously precise predictions for a measurement of position and for a measurement of momentum. The Robertson inequality generalizes this to the case of an arbitrary pair of self-adjoint operators and . The commutator of these two operators is
and this provides the lower bound on the product of standard deviations:
Substituting in the canonical commutation relation , an expression first postulated by Max Born in 1925, recovers the Kennard–Pauli–Weyl statement of the uncertainty principle.
From uncertainty to no-hidden-variables
The existence of the uncertainty principle naturally raises the question of whether quantum mechanics can be understood as an approximation to a more exact theory. Do there exist "hidden variables", more fundamental than the quantities addressed in quantum theory itself, knowledge of which would allow more exact predictions than quantum theory can provide? A collection of results, most significantly Bell's theorem, have demonstrated that broad classes of such hidden-variable theories are in fact incompatible with quantum physics.
Bell published the theorem now known by his name in 1964, investigating more deeply a thought experiment originally proposed in 1935 by Einstein, Podolsky and Rosen. According to Bell's theorem, if nature actually operates in accord with any theory of local hidden variables, then the results of a Bell test will be constrained in a particular, quantifiable way. If a Bell test is performed in a laboratory and the results are not thus constrained, then they are inconsistent with the hypothesis that local hidden variables exist. Such results would support the position that there is no way to explain the phenomena of quantum mechanics in terms of a more fundamental description of nature that is more in line with the rules of classical physics. Many types of Bell test have been performed in physics laboratories, often with the goal of ameliorating problems of experimental design or set-up that could in principle affect the validity of the findings of earlier Bell tests. This is known as "closing loopholes in Bell tests". To date, Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave.
Quantum systems as measuring devices
The Robertson–Schrödinger uncertainty principle establishes that when two observables do not commute, there is a tradeoff in predictability between them. The Wigner–Araki–Yanase theorem demonstrates another consequence of non-commutativity: the presence of a conservation law limits the accuracy with which observables that fail to commute with the conserved quantity can be measured. Further investigation in this line led to the formulation of the Wigner–Yanase skew information.
Historically, experiments in quantum physics have often been described in semiclassical terms. For example, the spin of an atom in a Stern–Gerlach experiment might be treated as a quantum degree of freedom, while the atom is regarded as moving through a magnetic field described by the classical theory of Maxwell's equations. But the devices used to build the experimental apparatus are themselves physical systems, and so quantum mechanics should be applicable to them as well. Beginning in the 1950s, Rosenfeld, von Weizsäcker and others tried to develop consistency conditions that expressed when a quantum-mechanical system could be treated as a measuring apparatus. One proposal for a criterion regarding when a system used as part of a measuring device can be modeled semiclassically relies on the Wigner function, a quasiprobability distribution that can be treated as a probability distribution on phase space in those cases where it is everywhere non-negative.
Decoherence
A quantum state for an imperfectly isolated system will generally evolve to be entangled with the quantum state for the environment. Consequently, even if the system's initial state is pure, the state at a later time, found by taking the partial trace of the joint system-environment state, will be mixed. This phenomenon of entanglement produced by system-environment interactions tends to obscure the more exotic features of quantum mechanics that the system could in principle manifest. Quantum decoherence, as this effect is known, was first studied in detail during the 1970s. (Earlier investigations into how classical physics might be obtained as a limit of quantum mechanics had explored the subject of imperfectly isolated systems, but the role of entanglement was not fully appreciated.) A significant portion of the effort involved in quantum computing is to avoid the deleterious effects of decoherence.
To illustrate, let denote the initial state of the system, the initial state of the environment and the Hamiltonian specifying the system-environment interaction. The density operator can be diagonalized and written as a linear combination of the projectors onto its eigenvectors:
Expressing time evolution for a duration by the unitary operator , the state for the system after this evolution is
which evaluates to
The quantities surrounding can be identified as Kraus operators, and so this defines a quantum channel.
Specifying a form of interaction between system and environment can establish a set of "pointer states," states for the system that are (approximately) stable, apart from overall phase factors, with respect to environmental fluctuations. A set of pointer states defines a preferred orthonormal basis for the system's Hilbert space.
Quantum information and computation
Quantum information science studies how information science and its application as technology depend on quantum-mechanical phenomena. Understanding measurement in quantum physics is important for this field in many ways, some of which are briefly surveyed here.
Measurement, entropy, and distinguishability
The von Neumann entropy is a measure of the statistical uncertainty represented by a quantum state. For a density matrix , the von Neumann entropy is
writing in terms of its basis of eigenvectors,
the von Neumann entropy is
This is the Shannon entropy of the set of eigenvalues interpreted as a probability distribution, and so the von Neumann entropy is the Shannon entropy of the random variable defined by measuring in the eigenbasis of . Consequently, the von Neumann entropy vanishes when is pure. The von Neumann entropy of can equivalently be characterized as the minimum Shannon entropy for a measurement given the quantum state , with the minimization over all POVMs with rank-1 elements.
Many other quantities used in quantum information theory also find motivation and justification in terms of measurements. For example, the trace distance between quantum states is equal to the largest difference in probability that those two quantum states can imply for a measurement outcome:
Similarly, the fidelity of two quantum states, defined by
expresses the probability that one state will pass a test for identifying a successful preparation of the other. The trace distance provides bounds on the fidelity via the Fuchs–van de Graaf inequalities:
Quantum circuits
Quantum circuits are a model for quantum computation in which a computation is a sequence of quantum gates followed by measurements. The gates are reversible transformations on a quantum mechanical analog of an n-bit register. This analogous structure is referred to as an n-qubit register. Measurements, drawn on a circuit diagram as stylized pointer dials, indicate where and how a result is obtained from the quantum computer after the steps of the computation are executed. Without loss of generality, one can work with the standard circuit model, in which the set of gates are single-qubit unitary transformations and controlled NOT gates on pairs of qubits, and all measurements are in the computational basis.
Measurement-based quantum computation
Measurement-based quantum computation (MBQC) is a model of quantum computing in which the answer to a question is, informally speaking, created in the act of measuring the physical system that serves as the computer.
Quantum tomography
Quantum state tomography is a process by which, given a set of data representing the results of quantum measurements, a quantum state consistent with those measurement results is computed. It is named by analogy with tomography, the reconstruction of three-dimensional images from slices taken through them, as in a CT scan. Tomography of quantum states can be extended to tomography of quantum channels and even of measurements.
Quantum metrology
Quantum metrology is the use of quantum physics to aid the measurement of quantities that, generally, had meaning in classical physics, such as exploiting quantum effects to increase the precision with which a length can be measured. A celebrated example is the introduction of squeezed light into the LIGO experiment, which increased its sensitivity to gravitational waves.
Laboratory implementations
The range of physical procedures to which the mathematics of quantum measurement can be applied is very broad. In the early years of the subject, laboratory procedures involved the recording of spectral lines, the darkening of photographic film, the observation of scintillations, finding tracks in cloud chambers, and hearing clicks from Geiger counters. Language from this era persists, such as the description of measurement outcomes in the abstract as "detector clicks".
The double-slit experiment is a prototypical illustration of quantum interference, typically described using electrons or photons. The first interference experiment to be carried out in a regime where both wave-like and particle-like aspects of photon behavior are significant was G. I. Taylor's test in 1909. Taylor used screens of smoked glass to attenuate the light passing through his apparatus, to the extent that, in modern language, only one photon would be illuminating the interferometer slits at a time. He recorded the interference patterns on photographic plates; for the dimmest light, the exposure time required was roughly three months. In 1974, the Italian physicists Pier Giorgio Merli, Gian Franco Missiroli, and Giulio Pozzi implemented the double-slit experiment using single electrons and a television tube. A quarter-century later, a team at the University of Vienna performed an interference experiment with buckyballs, in which the buckyballs that passed through the interferometer were ionized by a laser, and the ions then induced the emission of electrons, emissions which were in turn amplified and detected by an electron multiplier.
Modern quantum optics experiments can employ single-photon detectors. For example, in the "BIG Bell test" of 2018, several of the laboratory setups used single-photon avalanche diodes. Another laboratory setup used superconducting qubits. The standard method for performing measurements upon superconducting qubits is to couple a qubit with a resonator in such a way that the characteristic frequency of the resonator shifts according to the state for the qubit, and detecting this shift by observing how the resonator reacts to a probe signal.
Interpretations of quantum mechanics
Despite the consensus among scientists that quantum physics is in practice a successful theory, disagreements persist on a more philosophical level. Many debates in the area known as quantum foundations concern the role of measurement in quantum mechanics. Recurring questions include which interpretation of probability theory is best suited for the probabilities calculated from the Born rule; and whether the apparent randomness of quantum measurement outcomes is fundamental, or a consequence of a deeper deterministic process. Worldviews that present answers to questions like these are known as "interpretations" of quantum mechanics; as the physicist N. David Mermin once quipped, "New interpretations appear every year. None ever disappear."
A central concern within quantum foundations is the "quantum measurement problem," though how this problem is delimited, and whether it should be counted as one question or multiple separate issues, are contested topics. Of primary interest is the seeming disparity between apparently distinct types of time evolution. Von Neumann declared that quantum mechanics contains "two fundamentally different types" of quantum-state change. First, there are those changes involving a measurement process, and second, there is unitary time evolution in the absence of measurement. The former is stochastic and discontinuous, writes von Neumann, and the latter deterministic and continuous. This dichotomy has set the tone for much later debate. Some interpretations of quantum mechanics find the reliance upon two different types of time evolution distasteful and regard the ambiguity of when to invoke one or the other as a deficiency of the way quantum theory was historically presented. To bolster these interpretations, their proponents have worked to derive ways of regarding "measurement" as a secondary concept and deducing the seemingly stochastic effect of measurement processes as approximations to more fundamental deterministic dynamics. However, consensus has not been achieved among proponents of the correct way to implement this program, and in particular how to justify the use of the Born rule to calculate probabilities. Other interpretations regard quantum states as statistical information about quantum systems, thus asserting that abrupt and discontinuous changes of quantum states are not problematic, simply reflecting updates of the available information. Of this line of thought, Bell asked, "Whose information? Information about what?" Answers to these questions vary among proponents of the informationally-oriented interpretations.
| Physical sciences | Quantum mechanics | Physics |
574544 | https://en.wikipedia.org/wiki/Circular%20motion | Circular motion | In physics, circular motion is movement of an object along the circumference of a circle or rotation along a circular arc. It can be uniform, with a constant rate of rotation and constant tangential speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves the circular motion of its parts. The equations of motion describe the movement of the center of mass of a body, which remains at a constant distance from the axis of rotation. In circular motion, the distance between the body and a fixed point on its surface remains the same, i.e., the body is assumed rigid.
Examples of circular motion include: special satellite orbits around the Earth (circular orbits), a ceiling fan's blades rotating around a hub, a stone that is tied to a rope and is being swung in circles, a car turning through a curve in a race track, an electron moving perpendicular to a uniform magnetic field, and a gear turning inside a mechanism.
Since the object's velocity vector is constantly changing direction, the moving object is undergoing acceleration by a centripetal force in the direction of the center of rotation. Without this acceleration, the object would move in a straight line, according to Newton's laws of motion.
Uniform circular motion
In physics, uniform circular motion describes the motion of a body traversing a circular path at a constant speed. Since the body describes circular motion, its distance from the axis of rotation remains constant at all times. Though the body's speed is constant, its velocity is not constant: velocity, a vector quantity, depends on both the body's speed and its direction of travel. This changing velocity indicates the presence of an acceleration; this centripetal acceleration is of constant magnitude and directed at all times toward the axis of rotation. This acceleration is, in turn, produced by a centripetal force which is also constant in magnitude and directed toward the axis of rotation.
In the case of rotation around a fixed axis of a rigid body that is not negligibly small compared to the radius of the path, each particle of the body describes a uniform circular motion with the same angular velocity, but with velocity and acceleration varying with the position with respect to the axis.
Formula
For motion in a circle of radius , the circumference of the circle is . If the period for one rotation is , the angular rate of rotation, also known as angular velocity, is:
and the units are radians/second.
The speed of the object traveling the circle is:
The angle swept out in a time is:
The angular acceleration, , of the particle is:
In the case of uniform circular motion, will be zero.
The acceleration due to change in the direction is:
The centripetal and centrifugal force can also be found using acceleration:
The vector relationships are shown in Figure 1. The axis of rotation is shown as a vector perpendicular to the plane of the orbit and with a magnitude . The direction of is chosen using the right-hand rule. With this convention for depicting rotation, the velocity is given by a vector cross product as
which is a vector perpendicular to both and , tangential to the orbit, and of magnitude . Likewise, the acceleration is given by
which is a vector perpendicular to both and of magnitude and directed exactly opposite to .
In the simplest case the speed, mass, and radius are constant.
Consider a body of one kilogram, moving in a circle of radius one metre, with an angular velocity of one radian per second.
The speed is 1 metre per second.
The inward acceleration is 1 metre per square second, .
It is subject to a centripetal force of 1 kilogram metre per square second, which is 1 newton.
The momentum of the body is 1 kg·m·s−1.
The moment of inertia is 1 kg·m2.
The angular momentum is 1 kg·m2·s−1.
The kinetic energy is 0.5 joule.
The circumference of the orbit is 2 (~6.283) metres.
The period of the motion is 2 seconds.
The frequency is (2)−1 hertz.
In polar coordinates
During circular motion, the body moves on a curve that can be described in the polar coordinate system as a fixed distance from the center of the orbit taken as the origin, oriented at an angle from some reference direction. See Figure 4. The displacement vector is the radial vector from the origin to the particle location:
where is the unit vector parallel to the radius vector at time and pointing away from the origin. It is convenient to introduce the unit vector orthogonal to as well, namely . It is customary to orient to point in the direction of travel along the orbit.
The velocity is the time derivative of the displacement:
Because the radius of the circle is constant, the radial component of the velocity is zero. The unit vector has a time-invariant magnitude of unity, so as time varies its tip always lies on a circle of unit radius, with an angle the same as the angle of . If the particle displacement rotates through an angle in time , so does , describing an arc on the unit circle of magnitude . See the unit circle at the left of Figure 4. Hence:
where the direction of the change must be perpendicular to (or, in other words, along ) because any change in the direction of would change the size of . The sign is positive because an increase in implies the object and have moved in the direction of .
Hence the velocity becomes:
The acceleration of the body can also be broken into radial and tangential components. The acceleration is the time derivative of the velocity:
The time derivative of is found the same way as for . Again, is a unit vector and its tip traces a unit circle with an angle that is . Hence, an increase in angle by implies traces an arc of magnitude , and as is orthogonal to , we have:
where a negative sign is necessary to keep orthogonal to . (Otherwise, the angle between and would decrease with an increase in .) See the unit circle at the left of Figure 4. Consequently, the acceleration is:
The centripetal acceleration is the radial component, which is directed radially inward:
while the tangential component changes the magnitude of the velocity:
Using complex numbers
Circular motion can be described using complex numbers. Let the axis be the real axis and the axis be the imaginary axis. The position of the body can then be given as , a complex "vector":
where is the imaginary unit, and is the argument of the complex number as a function of time, .
Since the radius is constant:
where a dot indicates differentiation in respect of time.
With this notation, the velocity becomes:
and the acceleration becomes:
The first term is opposite in direction to the displacement vector and the second is perpendicular to it, just like the earlier results shown before.
Velocity
Figure 1 illustrates velocity and acceleration vectors for uniform motion at four different points in the orbit. Because the velocity is tangent to the circular path, no two velocities point in the same direction. Although the object has a constant speed, its direction is always changing. This change in velocity is caused by an acceleration , whose magnitude is (like that of the velocity) held constant, but whose direction also is always changing. The acceleration points radially inwards (centripetally) and is perpendicular to the velocity. This acceleration is known as centripetal acceleration.
For a path of radius , when an angle is swept out, the distance traveled on the periphery of the orbit is . Therefore, the speed of travel around the orbit is
where the angular rate of rotation is . (By rearrangement, .) Thus, is a constant, and the velocity vector also rotates with constant magnitude , at the same angular rate .
Relativistic circular motion
In this case, the three-acceleration vector is perpendicular to the three-velocity vector,
and the square of proper acceleration, expressed as a scalar invariant, the same in all reference frames,
becomes the expression for circular motion,
or, taking the positive square root and using the three-acceleration, we arrive at the proper acceleration for circular motion:
Acceleration
The left-hand circle in Figure 2 is the orbit showing the velocity vectors at two adjacent times. On the right, these two velocities are moved so their tails coincide. Because speed is constant, the velocity vectors on the right sweep out a circle as time advances. For a swept angle the change in is a vector at right angles to and of magnitude , which in turn means that the magnitude of the acceleration is given by
Non-uniform circular motion
In non-uniform circular motion, an object moves in a circular path with varying speed. Since the speed is changing, there is tangential acceleration in addition to normal acceleration.
The net acceleration is directed towards the interior of the circle (but does not pass through its center).
The net acceleration may be resolved into two components: tangential acceleration and centripetal acceleration. Unlike tangential acceleration, centripetal acceleration is present in both uniform and non-uniform circular motion.
In non-uniform circular motion, the normal force does not always point to the opposite direction of weight.
The normal force is actually the sum of the radial and tangential forces. The component of weight force is responsible for the tangential force (when we neglect friction). The centripetal force is due to the change in the direction of velocity.
The normal force and weight may also point in the same direction. Both forces can point downwards, yet the object will remain in a circular path without falling down.
The normal force can point downwards. Considering that the object is a person sitting inside a plane moving in a circle, the two forces (weight and normal force) will point down only when the plane reaches the top of the circle. The reason for this is that the normal force is the sum of the tangential force and centripetal force. The tangential force is zero at the top (as no work is performed when the motion is perpendicular to the direction of force). Since weight is perpendicular to the direction of motion of the object at the top of the circle and the centripetal force points downwards, the normal force will point down as well.
From a logical standpoint, a person travelling in that plane will be upside down at the top of the circle. At that moment, the person's seat is actually pushing down on the person, which is the normal force.
The reason why an object does not fall down when subjected to only downward forces is a simple one. Once an object is thrown into the air, there is only the downward gravitational force that acts on the object. That does not mean that once an object is thrown into the air, it will fall instantly. The velocity of the object keeps it up in the air. The first of Newton's laws of motion states that an object's inertia keeps it in motion; since the object in the air has a velocity, it will tend to keep moving in that direction.
A varying angular speed for an object moving in a circular path can also be achieved if the rotating body does not have a homogeneous mass distribution.
One can deduce the formulae of speed, acceleration and jerk, assuming that all the variables to depend on :
Further transformations may involve and their corresponding derivatives:
Applications
Solving applications dealing with non-uniform circular motion involves force analysis. With a uniform circular motion, the only force acting upon an object traveling in a circle is the centripetal force. In a non-uniform circular motion, there are additional forces acting on the object due to a non-zero tangential acceleration. Although there are additional forces acting upon the object, the sum of all the forces acting on the object will have to be equal to the centripetal force.
Radial acceleration is used when calculating the total force. Tangential acceleration is not used in calculating total force because it is not responsible for keeping the object in a circular path. The only acceleration responsible for keeping an object moving in a circle is the radial acceleration. Since the sum of all forces is the centripetal force, drawing centripetal force into a free body diagram is not necessary and usually not recommended.
Using , we can draw free body diagrams to list all the forces acting on an object and then set it equal to . Afterward, we can solve for whatever is unknown (this can be mass, velocity, radius of curvature, coefficient of friction, normal force, etc.). For example, the visual above showing an object at the top of a semicircle would be expressed as .
In a uniform circular motion, the total acceleration of an object in a circular path is equal to the radial acceleration. Due to the presence of tangential acceleration in a non uniform circular motion, that does not hold true any more. To find the total acceleration of an object in a non uniform circular, find the vector sum of the tangential acceleration and the radial acceleration.
Radial acceleration is still equal to . Tangential acceleration is simply the derivative of the speed at any given point: . This root sum of squares of separate radial and tangential accelerations is only correct for circular motion; for general motion within a plane with polar coordinates , the Coriolis term should be added to , whereas radial acceleration then becomes .
| Physical sciences | Classical mechanics | Physics |
574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Callinectes sapidus | Callinectes sapidus (from the Ancient Greek ,"beautiful" + , "swimmer", and Latin , "savory"), the blue crab, Atlantic blue crab, or, regionally, the Maryland blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.
C. sapidus is of considerable culinary and economic importance in the United States, particularly in Louisiana, the Carolinas, the Chesapeake Bay, Delaware, and New Jersey. It is the Maryland state crustacean and the state's largest commercial fishery. Due to overfishing and environmental pressures some of the fisheries have seen declining yields, especially in the Chesapeake Bay fishery.
Unlike the other fisheries affected by climate change, blue crab is expected to do well; warming causes better breeding conditions, more survivable winters, and a greater range of habitable areas on the Atlantic coast. Whether this will have negative effects on the surrounding ecosystems from an increased crab population is still unclear.
Description
C. sapidus is a decapod crab of the swimming crab family Portunidae. The genus Callinectes is distinguished from other portunid crabs by the lack of an internal cartilaginous spine on the carpus (the middle segment of the claw), as well as by the T-shape of the male abdomen. Blue crabs may grow to a carapace width of . C. sapidus individuals exhibit sexual dimorphism. Males and females are easily distinguished by the shape of the abdomen (known as the "apron") and by color differences in the chelipeds, or claws. The abdomen is long and slender in males, but wide and rounded in mature females. A popular mnemonic is that the male's apron is shaped like the Washington Monument, while the mature female's resembles the dome of the United States Capitol. Claw color differences are more subtle than apron shape. The immovable, fixed finger of the claws in males is blue with red tips, while females have orange coloration with purple tips. A female's abdomen changes as it matures: an immature female has a triangular-shaped abdomen, whereas a mature female's is rounded.
Other species of Callinectes may be easily confused with C. sapidus because of overlapping ranges and similar morphology. One species is the lesser blue crab (C. similis). It is found further offshore than the common blue crab, and has a smoother granulated carapace. Males of the lesser blue crab also have mottled white coloration on the swimming legs, and females have areas of violet coloration on the internal surfaces of the claws. C. sapidus can be distinguished from another related species found within its range, C. ornatus, by number of frontal teeth on the carapace. C. sapidus has four, while C. ornatus has six.
The crab's blue hue stems from a number of pigments in the shell, including alpha-crustacyanin, which interacts with a red pigment, astaxanthin, to form a greenish-blue coloration. When the crab is cooked, the alpha-crustacyanin breaks down, leaving only the astaxanthin, which turns the crab to a bright orange-red color.
Organochlorides are found by Sheridan et al 1975 to be transferred to the C. sapidus hepatopancreas. They find that among organochlorides, DDT specifically is converted both to DDE and DDD in this crab.
Distribution
C. sapidus is native to the western edge of the Atlantic Ocean from Cape Cod to Argentina and around the entire coast of the Gulf of Mexico. It has recently been reported north of Cape Cod in the Gulf of Maine, potentially representing a range expansion due to climate change. It has been introduced (via ballast water) to Japanese and European waters, and has been observed in the Baltic, North, Mediterranean, and Black Seas. The first record from European waters was made in 1901 at Rochefort, France. In some parts of its introduced range, C. sapidus has become the subject of crab fishery, including in Greece, where the local population may be decreasing as a result of overfishing. In Italy, public awareness of the detrimental impact of this species on local molluscs is rapidly growing and, especially in the Po delta area and on the Adriatic Sea coast, eradication efforts are undergoing, both by local authorities and by local fishermen.
Ecology
The natural predators of C. sapidus include eels, drum, striped bass, spot, trout, some sharks, humans, cownose rays, and whiptail stingrays. C. sapidus is an omnivore, eating both plants and animals. It typically consumes thin-shelled bivalves (such as clams, mussels, and oysters), crustaceans, annelids, small fish, plants (such as eelgrass), and nearly any other item it can find, including carrion, other C. sapidus individuals, and animal waste. In salt marshes, C. sapidus will eat marsh periwinkles, Littoraria irrorata during high tides. Although an aquatic predator, C. sapidus will remain in shallow pits in salt marshes at low tide and ambush intertidal prey such as fiddler crabs (e.g., Minuca pugnax) and purple marsh crabs (Sesarma reticulatum) C. sapidus may be able to control populations of the invasive green crab, Carcinus maenas; numbers of the two species are negatively correlated, and C. maenas is not found in the Chesapeake Bay, where C. sapidus is most abundant.
C. sapidus is subject to a number of diseases and parasites. These include a number of viruses, bacteria, microsporidians, ciliates, and others. The nemertean worm Carcinonemertes carcinophila commonly parasitizes C. sapidus, especially females and older crabs, although it has little adverse effect on the crab. A trematode that parasitizes C. sapidus is itself targeted by the hyperparasite Urosporidium crescens. The most harmful parasites may be the microsporidian Ameson michaelis, the amoeba Paramoeba perniciosa and the dinoflagellate Hematodinium perezi, which causes "bitter crab disease".
In 2021, scientists from the University of Maryland completed DNA sequencing on C. sapidus's genome in Baltimore after six years of research to help better understand the species. This genetic map is expected to help scientists understand how the blue crabs will be affected by climate change and warmer water temperatures, along with which mutations cause disease, traits that influence meat production, and which females have the best reproductive ability.
Lifecycle
Growth
Eggs of C. sapidus hatch in high-salinity waters of inlets, coastal waters, and mouths of rivers, and are carried to the ocean by ebb tides. During seven planktonic (zoeal) stages, blue crab larvae float near the surface and feed on microorganisms they encounter. After the eighth zoeal stage, larvae molt into megalopae. This larval form has small claws called chelipeds for grasping prey items. Megalopae selectively migrate upward in the water column as tides travel landward toward estuaries. Eventually, blue crabs arrive in brackish water, where they spend the majority of their lives. Chemical cues in estuarine water prompt metamorphosis to the juvenile phase, after which blue crabs appear similar to the adult form.
A blue crab grows by shedding its exoskeleton, or molting, to expose a new, larger exoskeleton. After it hardens, the new shell fills with body tissue. Shell hardening occurs most quickly in low-salinity water where high osmotic pressure allows the shell to become rigid soon after molting. Molting reflects only incremental growth, making age estimation difficult. For blue crabs, the number of molts in a lifetime is fixed at about 25. Females typically exhibit 18 molts after the larval stages, while postlarval males molt about 20 times.
Male blue crabs tend to grow broader and have more accentuated lateral spines than females. Growth and molting are profoundly influenced by temperature and food availability. Higher temperatures and greater food resources decrease the period of time between molts, as well as the change in size during molts (molt increment). Salinity and disease also have subtle impacts on molting and growth rate. Molting occurs more rapidly in low-salinity environments. The high osmotic pressure gradient causes water to quickly diffuse into a soft, recently molted blue crab's shell, allowing it to harden more quickly. The effects of diseases and parasites on growth and molting are less well understood, but in many cases have been observed to reduce growth between molts. For example, mature female blue crabs infected with the parasitic rhizocephalan barnacle Loxothylacus texanus appear extremely stunted in growth when compared to uninfected mature females. Blue crabs may reach maturity within one year of hatching in the Gulf of Mexico, while Chesapeake Bay crabs may take up to 18 months to mature. As a result of different growth rates, commercial and recreational crabbing occur year-round in the Gulf of Mexico, while crabbing seasons are closed for colder parts of the year in northern states.
Reproduction
Mating and spawning are distinct events in blue crab reproduction. Males may mate several times and undergo no major changes in morphology during the process. Female blue crabs mate only once in their lifetimes during their pubertal, or terminal, molt. During this transition, the abdomen changes from a triangular to a semicircular shape. Mating in blue crab is a complex process that requires precise timing of mating at the time of the female's terminal molt. It generally occurs during the warmest months of the year. Prepubertal females migrate to the upper reaches of estuaries, where males typically reside as adults. To ensure that a male can mate, he actively seeks a receptive female and guards her for up to seven days until she molts, when insemination occurs. Crabs compete with other individuals before, during, and after insemination, so mate guarding is very important for reproductive success. After mating, a male must continue to guard the female until her shell has hardened. Inseminated females retain spermatophores for up to one year, which they use for multiple spawnings in high salinity water. During spawning, a female extrudes fertilized eggs onto her swimmerets and carries them in a large egg mass, or sponge, while they develop. Females migrate to the mouth of the estuary to release the larvae, the timing of which is believed to be influenced by light, tide, and lunar cycles. Blue crabs have high fecundity; females may produce up to 2 million eggs per brood.
Migration and reproduction patterns differ between crab populations along the East Coast and the Gulf of Mexico. A distinct and large-scale migration occurs in Chesapeake Bay, where C. sapidus undergoes a seasonal migration of up to several hundred miles. In the middle and upper parts of the bay, mating peaks in mid- to late summer, while in the lower bay, peaks in mating activity occur during spring and late summer through early fall. Changes in salinity and temperature may impact time of mating because both factors are important during the molting process. After mating, the female crab travels to the southern portion of the Chesapeake, using ebb tides to migrate from areas of low salinity to areas of high salinity, fertilizing her eggs with sperm stored during her single mating months or almost a year before.
Spawning events in the Gulf of Mexico are less pronounced than in estuaries along the East Coast, like the Chesapeake. In northern waters of the Gulf of Mexico, spawning occurs in the spring, summer, and fall, and females generally spawn twice. During spawning, females migrate to high -salinity waters to develop a sponge, and return inland after hatching their larvae. They develop their second sponge inland, and again migrate to the high-salinity waters to hatch the second sponge. After this, they typically do not re-enter the estuary. Blue crabs along the southernmost coast of Texas may spawn year-round.
Commercial importance
Range of fisheries
Commercial fisheries for C. sapidus exist along much of the Atlantic coast of the United States, and in the Gulf of Mexico. Although the fishery has been historically centered on the Chesapeake Bay, contributions from other localities are increasing in importance. In the past two decades, most commercial crabs have been landed in four states: Maryland, Virginia, North Carolina, and Louisiana. Weight and value of harvests since 2000 are listed below.
History of the crab fishery
As early as the 1600s, the blue crab was an important food item for Native Americans and English settlers in the Chesapeake Bay area. Soft and hard blue crabs were not as valuable as fish, but gained regional popularity by the 1700s. Throughout their range, crabs were also an effective bait type for hook-and-line fisheries. Rapid perishing limited the distribution and hindered the growth of the fishery. Advances in refrigeration techniques in the late 1800s and early 1900s increased demand for blue crab nationwide.
Atlantic Coast
The early blue crab fishery along the Atlantic Coast was casual and productive because blue crabs were extremely abundant. In the lower Chesapeake Bay, crabs were even considered a nuisance species because they frequently clogged the nets of seine fishermen. Early on, the blue crab fishery of the Atlantic states was well documented. Atlantic states were the first to regulate the fishery, particularly the Chesapeake states. For example, after observing a slight decline in harvest, the fishing commissions of Virginia and Maryland put size limits into place by 1912 and 1917, respectively. Catch-per-unit-effort at the time was determined by packing houses, or crab processing plants.
Gulf of Mexico
The early history of the recreational blue crab fishery in the Gulf of Mexico is not well known. Commercial crabbing was first reported in the Gulf of Mexico in the 1880s. Early crab fishermen used long-handled dip nets and drop nets among other simple fishing gear types to trap crabs at night. Blue crab spoiled quickly, which limited distribution and hindered the growth of the fishery for several decades. The first commercial processing plant in Louisiana opened in Morgan City in 1924. Other plants opened soon after, although commercial processing of hard blue crabs was not widespread until World War II.
Louisiana fishery
Louisiana now has the world's largest blue-crab fishery. Commercial harvests in the state account for over half of all landings in the Gulf of Mexico. The industry was not commercialized for interstate commerce until the 1990s, when supply markedly decreased in Maryland due to problems (see above) in Chesapeake Bay. Since then, Louisiana has steadily increased its harvest. In 2002, Louisiana harvested 22% of the nation's blue crab. That number rose to 26% by 2009 and 28% by 2012. The vast majority of Louisiana crabs are shipped to Maryland, where they are sold as "Chesapeake" or "Maryland" crab. Louisiana's harvest remained high in 2013, with 17,597 metric tons of blue crab valued at $51 million. In addition to commercial harvesting, recreational crabbing is very popular along Louisiana's coast.
Chesapeake Bay fishery
The Chesapeake Bay has had the largest blue crab harvest for more than a century. Maryland and Virginia are usually the top two Atlantic coast states in annual landings, followed by North Carolina. In 2013, crab landings were valued at $18.7 million from Maryland waters and $16.1 million from Virginia waters. Although crab populations are currently declining, blue crab fishing in Maryland and Virginia remains a livelihood for thousands of coastal residents. As of 2001, Maryland and Virginia collectively had 4,816 commercial crab license holders. Three separate licenses are required for each of the three major jurisdictional areas: Maryland, the Potomac River, and Virginia waters. While the Bay's commercial sector lands the majority of hard crab landings and nearly all peeler or soft crab landings, the recreational fishery is also significant. In 2013, an estimated of blue crab were harvested recreationally.
Recent decline
Blue crab populations naturally fluctuate with annual changes in environmental conditions. They have been described as having a long-term dynamic equilibrium, which was first noted after irregular landings data in the Chesapeake in 1950. This tendency may have made it difficult for managers to predict the severe decline of the Chesapeake's blue crab populations. Once considered an overwhelmingly abundant annoyance, the declining blue crab population is now the subject of anxiety among fishermen and managers. Over the decade between the mid-1990s to 2004, the population fell from 900 million to around 300 million, and harvest weight fell from . Revenue fell further, from $72 million to $61 million. Long-term estimates say that the overall Chesapeake population decreased around 70% in the last few decades. Even more alarming, the number of females capable of reproducing, known as spawning age females, has plummeted 84% in just a few decades. Survival and addition of juveniles to the harvestable crab population is also low. Many factors are to blame for low blue crab numbers, including high fishing pressure, environmental degradation, and disease prevalence. The 2018 reduction in H-2B visas available for seasonal workers is affecting Maryland's 20 crab processors, which typically employ about 500 foreign workers, but the effect this will have on the crab fishery is not yet clear.
Crabbing gear
Many types of gear have been used to catch blue crabs along the Atlantic and Gulf Coasts. Initially, people used very simple techniques and gear, which included hand lines, dip nets, and push nets among a variety of other gear types. The trotline, a long baited twine set in waters 5–15 feet deep, was the first major gear type used commercially to target hard crabs. Use of commercial trotlines is now mostly limited to the tributaries of the Chesapeake Bay. In the Gulf of Mexico, trotline use drastically declined after invention of the crab pot in 1938. Crab pots are rigid, box-like traps made of hexagonal or square wire mesh. They possess between two and four funnels that extend into the trap, with the smaller end of the funnel inside of the trap. A central compartment made of smaller wire mesh holds bait. Crabs attracted by odorant plumes from the bait, often an oily fish, enter the trap through the funnels and cannot escape.
Bycatch
Species other than blue crab are often caught incidentally in crab pots, including fish, turtles, conch, and other crab species. In Georgia, hermit crabs (Pagurus spp.), channeled whelk (Busycon canaliculatum), spider crabs (Libinia spp.), and stone crabs (Menippe mercenaria) were the most common species observed as bycatch in commercial crab pots. Of important concern is the diamondback terrapin, Malaclemys terrapin. The blue crab and diamondback terrapin have overlapping ranges along the East and Gulf Coasts of the United States. Because the funnels in a crab pot are flexible, small terrapins may easily enter and become entrapped. Traps are checked every 24 hours or less, frequently resulting in drowning and death of terrapins. Crab pot bycatch may reduce local terrapin populations to less than half. To reduce terrapin entrapment, bycatch reduction devices (BRDs) may be installed on each of the funnels in a crab pot. BRDs effectively reduce bycatch (and subsequently mortality) of small terrapins without affecting blue crab catch.
Efforts to manage fisheries
Because of its commercial and environmental value, C. sapidus is the subject of management plans over much of its range. In 2012, the C. sapidus population in Louisiana was recognized as a certified sustainable fishery by the Marine Stewardship Council. It was the first and remains the only certified sustainable blue crab fishery worldwide. For the state to maintain its certification, it must undergo annual monitoring and conduct a full re-evaluation five years after the certification date.
Sports
The blue crab is the namesake of the Jersey Shore BlueClaws team in minor-league baseball playing in the South Atlantic League. They are located in Lakewood, New Jersey, and are a high-A affiliate of the Philadelphia Phillies.
Blue crabs are also the namesake of the Southern Maryland Blue Crabs, a professional baseball team located in Waldorf, Maryland.
| Biology and health sciences | Crabs and hermit crabs | Animals |
574874 | https://en.wikipedia.org/wiki/Mangrove%20crab | Mangrove crab | Mangrove crabs are crabs that live in and around mangroves. They belong to many different species and families and have been shown to be ecologically significant by burying and consuming leaf litter. Mangrove crabs have a variety of phylogenies because mangrove crab is an umbrella term that encompasses many species of crabs. Two of the most common families are sesarmid and fiddler crabs. They are omnivorous and are predated on by a variety of mammals and fish. They are distributed widely throughout the globe on coasts where mangroves are located. Mangrove crabs have wide variety of ecological and biogeochemical impacts due to the biofilms that live in symbiosis with them as well as their burrowing habits. Like many other crustaceans, they are also a human food source and have been impacted by humans as well as climate change.
Species and distribution
Current estimates place the number of mangrove crab species at 481 in 6 different families, with new species being discovered frequently. Mangrove crabs primarily live in the Indo-West Pacific region in mudflats along tropical coasts. The largest habitats for mangrove crabs are in Southeast Asia, South America, and Northern Australia. As their name suggests, they are primarily found among mangrove tree forests and form symbiotic relationships with the trees, restricting their habitat to where the trees can grow.
Phylogeny
A variety of different species are what makeup the umbrella term of mangrove crabs. The two main crabs that typically dominate mangrove ecosystems are the sesarmid (Grapsidae) and fiddler crabs (Ocypodidae). The main difference between the two crab groups is their foraging habits. Litter ingested by sesarmid crabs forms fragmented organic material that helps stimulate microbial respiration, in contrast fiddler crabs remove reactive organic carbon. Mangrove crabs are a part of the Animalia kingdom and are put into the Arthropoda phylum, Malacostraca class, and Decapoda order. Mangrove crabs can be classified into six different families: Camptandriidae, Dotillidae, Macrophthalmidae, Ocypodidae, Sesarmidae, and Oziidae.
Types of mangrove crabs
Sesarmid crabs
Fiddler crabs
Aratus pisonii, Americas
Haberma, genus of small mangrove crabs, Indo-Pacific, including:
Haberma tingkok, Hong Kong
Metopograpsus messor, Indo-Pacific
Metopograpsus thukuhar, Indo-Pacific
Neosarmatium meinerti, Indo-Pacific
Neosarmatium smithi, Indo-Pacific
Parasesarma leptosoma, western Indian Ocean
Perisesarma, genus with 23 species, primarily Indo-Pacific, with two West African species, including:
Perisesarma bidens, Indo-Pacific
Perisesarma guttatum, western Indian Ocean
Scylla serrata, Indo-Pacific
Scylla tranquebarica, Indo-Pacific
Sesarma, genus with close to 20 species, many of which live in mangroves, Americas, Indo-Pacific
Ucides cordatus, western Atlantic Ocean
Ecology and biogeochemistry
Diet and predators
When young, mangrove crabs get most of their nutrients from polychaete worms and a multitude of microorganisms found living in the sediments and leaves of their environment. As they grow older mangrove crabs are generally detritivores with their diet consisting of already dead organic material. Mangrove crabs consume a large amount of plant material but are primarily omnivorous. In the mangrove swamp this includes dead leaves and corpses of other crustaceans, even that of their own species. In some cases, mangrove crabs may also eat fresh mangrove leaves. Mangrove crabs are predated on by wading birds, fish, sharks, monkeys, hawks, and raccoons. The larvae of mangrove crabs is a major source of food for juvenile fish in waterways near the crabs. Adult mangrove crabs are food for the crab plover among other protected species. To protect themselves the crabs can climb trees. The only other crustaceans that climb trees are hermit crabs.
Habitat and ecosystem engineering
Mangrove crabs often construct and inhabit burrows in mangrove sediment. These burrows aid them in enduring the extremes that can be found in mangroves at high and low tide, allowing them to maintain more constant and ideal temperatures and oxygen levels. These constants can additionally aid other small benthic fauna, like polychaetes and juvenile crabs. Mangrove crabs may plug their burrows at intervals determined by their circadian rhythms, or they may leave them open. The variety in structures and maintenance of these burrows may lead to a variety of different impacts on mangrove sediments, such as increasing or decreasing erodibility. Fiddler crabs generally have very simple 10–40 cm “J-shaped” burrows, while sesarmid crabs that burrow often create complex, branching burrows that can reach over 100 cm in depth. Both types of crab significantly increase the surface area of the sediment and water/air interface to similar extents when scaled for relative abundance. These burrows also result in significant burial and downward travel of mangrove leaves. The burrowing dynamics of mangrove crabs dramatically impacts ecosystems, these dynamics were impacted by both abiotic factors like soil composition, and biotic factors like root depth and tree density.
Mangrove crabs modify particle size, nutrient availability, particle distribution, redox reactions, and organic matter. Aeration allows for additional microbial decomposition, oxidation of iron, and reduction of sulfur by anaerobic microbes. This leads to extremely high pyrite concentrations in mangrove soils, and removal of sulfides that negatively impact plant growth. Surface soils are similarly impacted when mixed by mangrove crab legs.
Depending on its nitrogen content, burial of detritus in crab burrows can stimulate microbial growth and activity and lead to variation in mangrove soils’ carbon dioxide efflux, ammonium content, and nitrate content.
The feces of mangrove crabs may help form a coprophagous food chain which contributes to mangrove secondary production.
Biofilms
Biofilm endosymbiosis occurs on the gills of some mangrove crabs, namely Aratus pisonii and Minuca rapax. Each species of these mangrove crabs likely have distinct bacterial compositions. These microbial biofilms are locations of nitrogen transformation, particularly nitrogen fixation. Bacteria like Cyanobacteria, Alphaproteobacteria, Actinobacteria, and Bacteroidota have been found on mangrove crab carapaces. The biofilms served as a net nitrogen sink and a source of ammonium and dissolved nitrogen to the environment. The importance of the biofilm may be dependent on if the crabs live primarily in burrows or outside burrows. Crabs that live outside burrows may consume their nitrogen from microphytobenthos, while crabs that live inside their burrows may rely more on their associated microbes.
Human impacts
Climate change
Ideal mangrove crab habitats rely heavily on coastal depth and surface temperature. Climate change due to anthropogenic activities is likely to create fluctuations in these two factors, driving the mangrove crab habitats to higher latitudes. As a result, it is predicted that mangrove habitats will continually shrink for the majority of crab species. This shrinking of habitat space isolates crab communities and shrinks genetic diversity, making many species more vulnerable to extinction.
Crabbing
Like many other crustaceans, mangrove crabs have historically been caught, prepared and eaten by people all over the world. Crab meat can be prepared simply by boiling the crab either dead or alive until the shell turns from black to red. This practice may be threatened by human activities, however, as microplastics have been found to be abundantly common in the gills of mangrove crabs due to human pollution. This not only negatively affects the health of the crabs, but could affect the health of humans who consume them.
Land use change
Around 6,000 km2 of mangrove was deforested between 1996 and 2016, usually redeveloped for fish and shrimp aquaculture, rice cultivation, palm oil plantations, and sometimes urbanization. Diversity of mangrove crabs does not seem to be negatively affected in abandoned aquaculture plots, though logging has significant negative effects on mangrove crab diversity.
| Biology and health sciences | Crabs and hermit crabs | Animals |
574964 | https://en.wikipedia.org/wiki/Motorboat | Motorboat | A motorboat or powerboat is a boat that is exclusively powered by an engine; faster examples may be called "speedboats".
Some motorboats are fitted with inboard engines, others have an outboard motor installed on the rear, containing the internal combustion engine, the gearbox and the propeller in one portable unit. An inboard-outboard contains a hybrid of an inboard and an outboard, where the internal combustion engine is installed inside the boat, and the gearbox and propeller are outside.
There are two configurations of an inboard, V-drive and direct drive. A direct drive has the powerplant mounted near the middle of the boat with the propeller shaft straight out the back, where a V-drive has the powerplant mounted in the back of the boat facing backwards having the shaft go towards the front of the boat then making a V towards the rear.
Overview
A motorboat is a small craft with one or more engines for propulsion. Motorboats are commonly used for work, recreation, sport, or racing.
Boat engines vary in shape, size, and type. These include inboard, outboard (integrating, the engine, gearbox, and propeller in one portable unit mounted in the rear), and inboard-outboard (or “sterndrive”, which mounts the engine inboard and the rest outboard).
Fuel types include gasoline, diesel, gas turbine, rotary combustion or steam.
High performance speedboats can reach speeds of over 50 knots. Their high speed and performance can be attributed to their hull technology and engine. With a more powerful and heavier engine, an appropriate hull shape is needed. High performance boats include yachts, HSIC (high speed interceptor craft) and racing powerboats.
A V-type hull helps a boat cut through the water. A deep V-hull helps keep the boat's bow down at low speeds, improving visibility. V-hulls also improve a boat's speed and maneuvering capabilities. They stabilize a boat in rough conditions.
History
Invention
Although the screw propeller had been added to an engine (steam engine) as early as the 18th century in Birmingham, England, by James Watt, boats powered by a petrol engine only came about in the later part of the 19th century with the invention of the internal combustion engine.
The earliest boat to be powered by a petrol engine was tested on the Neckar River by Gottlieb Daimler and Wilhelm Maybach in 1886, when they tested their new "longcase clock" engine. It had been constructed in the former greenhouse (converted into a workshop) in Daimler's back yard. The first public display took place on the Waldsee in Cannstatt, today a suburb of Stuttgart, at the end of that year. The engine of this boat had a single cylinder of 1 horse power. Daimler's second launch in 1887 had a second cylinder positioned at an angle of 15 degrees to the first one, and was known as the "V-type".
The first successful motor boat was designed by the Priestman Brothers in Hull, England, under the direction of William Dent Priestman. The company began trials of their first motorboat in 1888. The engine was powered with kerosene and used an innovative high-tension (high voltage) ignition system. The company was the first to begin large scale production of the motor boat, and by 1890, Priestman's boats were successfully being used for towing goods along canals.
Another early pioneer was Mr. J. D. Roots, who in 1891 fitted a launch with an internal combustion engine and operated a ferry service between Richmond and Wandsworth along the River Thames during the seasons of 1891 and 1892.
The eminent inventor Frederick William Lanchester recognized the potential of the motorboat and over the following 15 years, in collaboration with his brother George, perfected the modern motorboat, or powerboat. Working in the garden of their home in Olton, Warwickshire, they designed and built a river flat-bottomed launch with an advanced high-revving engine that drove via a stern paddle wheel in 1893. In 1897, he produced a second engine similar in design to his previous one but running on benzene at 800 r.p.m. The engine drove a reversible propeller. An important part of his new engine was the revolutionary carburettor, for mixing the fuel and air correctly. His invention was known as a "wick carburetor", because fuel was drawn into a series of wicks, from where it was vaporized. He patented this invention in 1905.
The Daimler Company began production of motor boats in 1897 from its manufacturing base in Coventry. The engines had two cylinders and the explosive charge of petroleum and air was ignited by compression into a heated platinum tube. The engine gave about six horse-power. The petrol was fed by air pressure to a large surface carburettor and also an auxiliary tank which supplied the burners for heating the ignition tubes. Reversal of the propeller was effected by means of two bevel friction wheels which engaged with two larger bevel friction wheels, the intermediate shaft being temporarily disconnected for this purpose. It was not until 1901 that a safer apparatus for igniting the fuel with an electric spark was used in motor boats.
Expansion
Interest in fast motorboats grew rapidly in the early years of the 20th century. The Marine Motor Association was formed in 1903 as an offshoot of the Royal Automobile Club. Motor Boat & Yachting was the first magazine to address technical developments in the field and was brought out by Temple Press, London from 1904. Large manufacturing companies, including Napier & Son and Thornycroft began producing motorboats.
Early racing
The first motorboating competition was established by Alfred Charles William Harmsworth in 1903. The Harmsworth Cup was envisioned as a contest between nations, rather than between boats or individuals. The boats were originally to be designed and built entirely by residents of the country represented, using materials and units built wholly within that country.
The first competition, held in July 1903, at Cork Harbour in Ireland, and officiated by the Automobile Club of Great Britain and Ireland and the Royal Victoria Yacht Club, was a very primitive affair, with many boats failing even to start. The competition was won by Dorothy Levitt in a Napier launch designed to the specifications of Selwyn Edge. This motorboat was the first proper motorboat designed for high speed. She set the world's first water speed record when she achieved in a steel-hulled, 75-horsepower Napier speedboat fitted with a three-blade propeller. As both the owner and entrant of the boat, "S. F. Edge" was engraved on the trophy as the winner.
An article in the Cork Constitution on 13 July reported "A large number of spectators viewed the first mile from the promenade of the Yacht Club, and at Cork several thousand people collected at both sides of the river to see the finishes." Levitt was then commanded to the Royal yacht of King Edward VII where he congratulated her on her pluck and skill, and they discussed the performance of the motorboat and its potential for British government despatch work.
France won the race in 1904, and the boat Napier II set a new world water speed record for a mile at almost 30 knots (56 km/h), winning the race in 1905.
The acknowledged genius of motor boat design in America was the naval architect John L. Hacker. His pioneering work, including the invention of the V-hull and the use of dedicated petrol engines revolutionized boat design from as early as 1908, when he founded the Hacker Boat Co. In 1911, Hacker designed the Kitty Hawk, the first successful step hydroplane which exceeded the then-unthinkable speed of and was at that time the fastest boat in the world. The Harmsworth Cup was first won by Americans in 1907. The US and England traded it back and forth until 1920. From 1920 to 1933, Americans had an unbroken winning streak. Gar Wood won this race eight times as a driver and nine times as an owner between 1920 and 1933.
Hull type
From a design point of view, a boat’s hull type reflects its use and the waters it will be used it. These include displacement hulls, vee-bottom hulls, modified vee-bottom hulls, deep-vee hulls and trim tabs for vee-bottom hulls. The three main hull materials are wood, reinforced fiberglass and metal. Wood hulls may be made of planks or plywood. Fiberglass hulls are reinforced with balsa wood. Metal hulls are either aluminum or steel.
Some gross configurations of motorboats include skiff, day cruiser, bow rider, pilothouse and cabin cruiser. These vary by such considerations as size, whether they have a deck, cabin, head, is sail, helm position, and additional seating.
Gallery
| Technology | Naval transport | null |
575135 | https://en.wikipedia.org/wiki/Submersible | Submersible | A submersible is an underwater vehicle which needs to be transported and supported by a larger watercraft or platform. This distinguishes submersibles from submarines, which are self-supporting and capable of prolonged independent operation at sea.
There are many types of submersibles, including both human-occupied vehicles (HOVs) and uncrewed craft, variously known as remotely operated vehicles (ROVs) or unmanned underwater vehicles (UUVs). Submersibles have many uses including oceanography, underwater archaeology, ocean exploration, tourism, equipment maintenance and recovery and underwater videography.
History
The first recorded self-propelled underwater vessel was a small oar-powered submarine conceived by William Bourne (c. 1535 – 1582) and designed and built by Dutch inventor Cornelis Drebbel in 1620, with two more improved versions built in the following four years. Contemporary accounts state that the final model was demonstrated to King James I in person, who may even have been taken aboard for a test dive. There do not appear to have been any further recorded submersibles until Bushnell's Turtle.
The first submersible to be used in war was designed and built by American inventor David Bushnell in 1775 as a means to attach explosive charges to enemy ships during the American Revolutionary War. The device, dubbed Bushnell's Turtle, was an oval-shaped vessel of wood and brass. It had tanks that were filled with water to make it dive and then emptied with the help of a hand pump to make it return to the surface. The operator used two hand-cranked propellers to move vertically or laterally under the water. The vehicle had small glass windows on top and naturally luminescent wood affixed to its instruments so that they could be read in the dark.
Bushnell's Turtle was first set into action on September 7, 1776, at New York Harbor to attack the British flagship . Sergeant Ezra Lee operated the vehicle at that time. Lee successfully brought Turtle against the underside of Eagles hull but failed to attach the charge because of the strong water currents.
Manned submersibles are primarily used by special forces, which can use this type of vessel for a range of specialised missions.
Operation
Apart from size, the main technical difference between a "submersible" and a "submarine" is that submersibles are not fully autonomous and may rely on a support facility or vessel for replenishment of power and breathing gases. Submersibles typically have shorter range, and operate primarily underwater, as most have little function at the surface. Some submersibles operate on a "tether" or "umbilical", remaining connected to a tender (a submarine, surface vessel or platform). Submersibles have been able to dive to full ocean depth, over below the surface.
Submersibles may be relatively small, hold only a small crew, and have no living facilities.
A submersible often has very dexterous mobility, provided by marine thrusters or pump-jets.
Technologies
Technologies used in the design and construction of submersibles:
Buoyancy control
Marine thrusters
Pressure vessel with external pressure load
Life support systems
Through-water communications
Manipulator arm
Submarine navigation
Absolute pressure: At sea level the atmosphere exerts a pressure of approximately 1 bar, or 103,000 N/m2. Underwater, the pressure increases by approximately 0.1 bar for every metre of depth. The total pressure at any given depth is the sum of the pressure of the water at that depth (hydrostatic pressure)and atmospheric pressure. This combined pressure is known as absolute pressure, and the relationship is:
Absolute pressure (bar abs) = gauge pressure(bar) + atmospheric pressure (about 1 bar)
To calculate absolute pressure, add the atmospheric pressure to the gauge pressure using the same unit. Working with depth rather than pressure may be convenient in diving calculations. In this context, atmospheric pressure is considered equivalent to a depth of 10 meters.
Absolute depth (m) = gauge depth (m) + 10 m.
Depth measurement: Pressure monitoring devices
The pressure the is more important for structural and physiological reasons than linear depth. Pressure at a given depth may vary due to variations in water density.
To express the linear depth in water accurately, the measurement should be in meters (m). The unit “meters of sea water” (msw) is a by definition a unit for measurement of pressure.
Note: A change in depth of 10 meters for a change in pressure of 1 bar equates to a water density of 1012.72 kg/m3
Single-atmosphere submersibles have a pressure hull with internal pressure maintained at surface atmospheric pressure. This requires the hull to be capable of withstanding the ambient hydrostatic pressure from the water outside, which can be many times greater than the internal pressure.
Ambient pressure submersibles maintain the same pressure both inside and outside the vessel. The interior is air-filled, at a pressure to balance the external pressure, so the hull does not have to withstand a pressure difference.
A third technology is the "wet sub", which refers to a vehicle that may or may not be enclosed, but in either case, water floods the interior, so underwater breathing equipment is used by the crew. This may be scuba carried by the divers, or a breathing gas supply carried by the vessel.
Buoyancy
When an object is immersed in a liquid, it displaces the liquid, pushing it out of the way.
Once the object is partially immersed, pressure forces exerted on the immersed parts are equal to the weight of water displaced, Consequently, objects submerged in liquids appear to weigh less due to this buoyant force. The relationship between the amount of liquid displaced and the resulting up-thrust is known as Archimedes' principle, which states:
"when an object is wholly or partially immersed in a liquid, the up-thrust it receives is equal to the weight of the liquid displaced."
Buoyancy and weight determine whether an object floats or sinks in a liquid. The relative magnitudes of weight and buoyancy determine the outcome, leading to three possible scenarios.
Negative Buoyancy: when the weight of an object is greater than the up-thrust it experiences due to the weight of the liquid displaced, the object sinks.
Neutral Buoyancy: if the weight of an object equals the up-thrust, the object remains stable in its current position, neither sinking or floating.
Positive Buoyancy: when the weight of an object is less than the up-thrust, the object rises and floats. As it reaches the liquid's surface, It partly emerges from the liquid, reducing the weight of the displaced liquid and, consequently, the up-thrust. Eventually, the reduced up-thrust balances the weight of the object, allowing it to float in a state of equilibrium.
Buoyancy control
During underwater operation a submersible will generally be neutrally buoyant, but may use positive or negative buoyancy to facilitate vertical motion. Negative buoyancy may also be useful at times to settle the vessel on the bottom, and positive buoyancy is necessary to float the vessel at the surface. Fine buoyancy adjustments may be made using one or more variable buoyancy pressure vessels as trim tanks, and gross changes of buoyancy at or near the surface may use ambient pressure ballast tanks, which are fully flooded during underwater operations. Some submersibles use high density external ballast which may be released at depth in an emergency to make the vessel sufficiently buoyant to float back to the surface even if all power is lost, or to travel faster vertically.
Deep-diving crewed submersibles
Some submersibles have been able to dive to great depths. The bathyscaphe Trieste was the first to reach the deepest part of the ocean, nearly below the surface, at the bottom of the Mariana Trench in 1960.
China, with its Jiaolong project in 2002, was the fifth country to send a person 3,500 meters below sea level, following the US, France, Russia and Japan. On June 22, 2012, the Jiaolong submersible set a deep-diving record for state-owned vessels when the three-person sub descended into the Pacific Ocean.
Among the most well-known and longest-in-operation submersibles is the deep-submergence research vessel , which takes 3 people to depths of up to . Alvin is owned by the United States Navy and operated by WHOI, and as of 2011 had made over 4,400 dives.
James Cameron made a record-setting, crewed submersible dive to the bottom of Challenger Deep, the deepest known point of the Mariana Trench on March 26, 2012. Cameron's submersible was named Deepsea Challenger and reached a depth of .
DSV Limiting Factor, known as Bakunawa since its sale in 2022, is a crewed deep-submergence vehicle (DSV) manufactured by Triton Submarines and owned and operated since 2022 by Gabe Newell's Inkfish ocean-exploration research organization. It holds the records for the deepest crewed dives in all five oceans.
Limiting Factor was commissioned by Victor Vescovo for $37 million and operated by his marine research organization, Caladan Oceanic, between 2018-2022. It is commercially certified by DNV for dives to full ocean depth, and is operated by a pilot, with facilities for an observer.
The vessel was used in the Five Deeps Expedition, becoming the first crewed submersible to reach the deepest point in all five oceans. Over 21 people have visited Challenger Deep, the deepest area on Earth, in the DSV. Limiting Factor was used to identify the wrecks of the destroyers at a depth of , and at , in the Philippine Trench, the deepest dives on wrecks. It has also been used for dives to the French submarine Minerve (S647) at about in the Mediterranean sea, and at about in the Atlantic.
Commercial submersibles
Private firms such as Triton Submarines, LLC. SEAmagine Hydrospace, Sub Aviator Systems (or 'SAS'), and Netherlands-based U-boat Worx have developed small submersibles for tourism, exploration and adventure travel. A Canadian company in British Columbia called Sportsub has been building personal recreational submersibles since 1986 with open-floor designs (partially flooded cockpits).
A privately owned U.S. company, OceanGate, also participated in building submersibles, though the company fell under scrutiny when their newest submersible imploded underwater with no survivors.
Marine remotely operated vehicles
Small uncrewed submersibles called "marine remotely operated vehicles," (MROVs), or 'remotely operated underwater vehicles' (ROUVs) are widely used to work in water too deep or too dangerous for divers, or when it is economically advantageous.
Remotely operated vehicles (ROVs) repair offshore oil platforms and attach cables to sunken ships to hoist them. Such remotely operated vehicles are attached by an umbilical cable (a thick cable providing power and communications) to a control center on a ship. Operators on the ship see video and/or sonar images sent back from the ROV and remotely control its thrusters and manipulator arm. The wreck of the Titanic was explored by such a vehicle, as well as by a crewed vessel.
Autonomous underwater vehicles
An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring continuous input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications an AUV is more often referred to as an unmanned undersea vehicle (UUV). Underwater gliders are a subclass of AUVs.
Diver lock-out submersible
Class of submersible which has an airlock and an integral diving chamber from which underwater divers can be deployed, such as:
| Technology | Naval transport | null |
575176 | https://en.wikipedia.org/wiki/Antifungal | Antifungal | An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as cryptococcal meningitis, and others. Such drugs are usually obtained by a doctor's prescription, but a few are available over the counter (OTC). The evolution of antifungal resistance is a growing threat to health globally.
Routes of administration
Ocular
Indicated when the fungal infection is located in the eye. There is currently only one ocular antifungal available. This is Natamycin. However, various other antifungal agents could be compounded in this formulation.
Intrathecal
Used occasionally when there's an infection of the central nervous system and other systemic options cannot reach the concentration required in that region for therapeutic benefit. Example(s): amphotericin B.
Vaginal
This may be used to treat some fungal infections of the vaginal region. An example of a condition they are sometimes used for is candida vulvovaginitis which is treated with intravaginal Clotrimazole
Topical
This is sometimes indicated when there's a fungal infection on the skin. An example is tinea pedis; this is sometimes treated with topical terbinafine.
Oral
If the antifungal has good bioavailability, this is a common route to handle a fungal infection. An example is the use of ketoconazole to treat coccidioidomycosis.
Intravenous
Like the oral route, this will reach the bloodstream and distribute throughout the body. However, it is faster and a good option if the drug has poor bioavailability. An example of this is IV amphotericin B for the treatment of coccidioidomycosis.
Classes
The available classes of antifungal drugs are still limited but as of 2021 novel classes of antifungals are being developed and are undergoing various stages of clinical trials to assess performance.
Polyenes
A polyene is a molecule with multiple conjugated double bonds. A polyene antifungal is a macrocyclic polyene with a heavily hydroxylated region on the ring opposite the conjugated system. This makes polyene antifungals amphiphilic. The polyene antimycotics bind with sterols in the fungal cell membrane, principally ergosterol. This changes the transition temperature (Tg) of the cell membrane, thereby placing the membrane in a less fluid, more crystalline state. (In ordinary circumstances membrane sterols increase the packing of the phospholipid bilayer making the plasma membrane more dense.) As a result, the cell's contents including monovalent ions (K+, Na+, H+, and Cl−) and small organic molecules leak, which is regarded as one of the primary ways a cell dies. Animal cells contain cholesterol instead of ergosterol and so they are much less susceptible. However, at therapeutic doses, some amphotericin B may bind to animal membrane cholesterol, increasing the risk of human toxicity. Amphotericin B is nephrotoxic when given intravenously. As a polyene's hydrophobic chain is shortened, its sterol binding activity is increased. Therefore, further reduction of the hydrophobic chain may result in it binding to cholesterol, making it toxic to animals.
Amphotericin B
Candicidin
Filipin – 35 carbons, binds to cholesterol (toxic)
Hamycin
Natamycin – 33 carbons, binds well to ergosterol
Nystatin
Rimocidin
Azoles
Azole antifungals inhibit the conversion of lanosterol to ergosterol by inhibiting lanosterol 14α-demethylase. These compounds have a five-membered ring containing two or three nitrogen atoms. The imidazole antifungals contain a 1,3-diazole (imidazole) ring (two nitrogen atoms), whereas the triazole antifungals have a ring with three nitrogen atoms.
Imidazoles
Bifonazole
Butoconazole
Clotrimazole
Econazole
Fenticonazole
Isoconazole
Ketoconazole
Luliconazole
Miconazole
Omoconazole
Oxiconazole
Sertaconazole
Sulconazole
Tioconazole
Triazoles
Albaconazole
Cyproconazole
Efinaconazole
Epoxiconazole
Fluconazole
Isavuconazole
Itraconazole
Posaconazole
Propiconazole
Ravuconazole
Terconazole
Voriconazole
Thiazoles
Abafungin
Allylamines
Allylamines inhibit squalene epoxidase, another enzyme required for ergosterol synthesis. Examples include butenafine, naftifine, and terbinafine.
Echinocandins
Echinocandins inhibit the creation of glucan in the fungal cell wall by inhibiting 1,3-Beta-glucan synthase:
Anidulafungin
Caspofungin
Micafungin
Echinocandins are administered intravenously, particularly for the treatment of resistant Candida species.
Triterpenoids
Ibrexafungerp
Others
Acrisorcin
Amorolfine – a morpholine derivative used topically in dermatophytosis
Aurones – possess antifungal properties
Benzoic acid – has antifungal properties, such as in Whitfield's ointment, Friar's Balsam, and Balsam of Peru
Carbol fuchsin (Castellani's paint)
Ciclopirox (ciclopirox olamine) – a hydroxypyridone antifungal that interferes with active membrane transport, cell membrane integrity, and fungal respiratory processes. It is most useful against tinea versicolour.
Clioquinol
Coal tar
Copper(II) sulfate
Crystal violet – a triarylmethane dye. It has antibacterial, antifungal, and anthelmintic properties and was formerly important as a topical antiseptic.
Chlorhexidine is a topical antibacterial and antifungal. It is commonly used in hospitals as an antiseptic. It is much more strongly antibacterial than antifungal, requiring at least a 10 times higher concentration to kill yeast compared to gram negative bacteria
Chlorophetanol
Diiodohydroxyquinoline (Iodoquinol)
Flucytosine (5-fluorocytosine) – an antimetabolite pyrimidine analog
Fumagillin
Griseofulvin – binds to microtubules and inhibits mitosis
Haloprogin – discontinued due to the emergence of antifungals with fewer side effects
Miltefosine works by damaging fungal cell membranes
Nikkomycin – blocks formation of chitin present in the cell wall of fungus.
Orotomide (F901318) – pyrimidine synthesis inhibitor
Piroctone olamine
Pentanenitrile
Potassium iodide – preferred treatment for lymphocutaneous sporotrichosis and subcutaneous zygomycosis (basidiobolomycosis). The mode of action is obscure.
Potassium permanganate - for use only on thicker, more insensitive skin such as the soles of the feet.
Selenium disulfide
Sodium thiosulfate
Sulfur
Tolnaftate – a thiocarbamate antifungal, which inhibits fungal squalene epoxidase (similar mechanism to allylamines like terbinafine)
Triacetin – hydrolysed to acetic acid by fungal esterases
Undecylenic acid – an unsaturated fatty acid derived from natural castor oil; fungistatic, antibacterial, antiviral, and inhibits Candida morphogenesis
Zinc pyrithione
Side effects
Incidents of liver injury or failure among modern antifungal medicines are very low to non-existent. However, some can cause allergic reactions in people.
There are also many drug interactions. Patients must read in detail the enclosed data sheet(s) of any medicine. For example, the azole antifungals such as ketoconazole or itraconazole can be both substrates and inhibitors of the P-glycoprotein, which (among other functions) excretes toxins and drugs into the intestines. Azole antifungals are also both substrates and inhibitors of the cytochrome P450 family CYP3A4, causing increased concentration when administering, for example, calcium channel blockers, immunosuppressants, chemotherapeutic drugs, benzodiazepines, tricyclic antidepressants, macrolides and SSRIs.
Before oral antifungal therapies are used to treat nail disease, a confirmation of the fungal infection should be made. Approximately half of suspected cases of fungal infection in nails have a non-fungal cause. The side effects of oral treatment are significant and people without an infection should not take these drugs.
Azoles are the group of antifungals which act on the cell membrane of fungi. They inhibit the enzyme 14-alpha-sterol demethylase, a microsomal CYP, which is required for the biosynthesis of ergosterol for the cytoplasmic membrane. This leads to the accumulation of 14-alpha-methylsterols resulting in impairment of function of certain membrane-bound enzymes and disruption of close packing of acyl chains of phospholipids, thus inhibiting growth of the fungi. Some azoles directly increase permeability of the fungal cell membrane.
Resistance
Antifungal resistance is a subset of antimicrobial resistance, that specifically applies to fungi that have become resistant to antifungals. Resistance to antifungals can arise naturally, for example by genetic mutation or through aneuploidy. Extended use of antifungals leads to the development of antifungal resistance through various mechanisms.
Some fungi (e.g. Candida krusei and fluconazole) exhibit intrinsic resistance to certain antifungal drugs or classes, whereas some species develop antifungal resistance to external pressures. Antifungal resistance is a One Health concern, driven by multiple extrinsic factors, including extensive fungicidal use, overuse of clinical antifungals, environmental change and host factors.
Like resistance to antibacterials, antifungal resistance can be driven by antifungal use in agriculture. Currently there is no regulation on the use of similar antifungal classes in agriculture and the clinic.
The emergence of Candida auris as a potential human pathogen that sometimes exhibits multi-class antifungal drug resistance is concerning and has been associated with several outbreaks globally. The WHO has released a priority fungal pathogen list, including pathogens with antifungal resistance.
| Biology and health sciences | Antifungals | Health |
575495 | https://en.wikipedia.org/wiki/Hide%20%28skin%29 | Hide (skin) | A hide or skin is an animal skin treated for human use.
The word "hide" is related to the German word , which means skin. The industry defines hides as "skins" of large animals e.g. cow, buffalo; while skins refer to "skins" of smaller animals: goat, sheep, deer, pig, fish, alligator, snake, etc.
Common commercial hides include leather from cattle and other livestock animals, buckskin, alligator skin and snake skin. All are used for shoes, clothes, leather bags, belts, or other fashion accessories. Leather is also used in cars, upholstery, interior decorating, horse tack and harnesses. Skins are sometimes still gathered from hunting and processed at a domestic or artisanal level but most leather making is now industrialized and large-scale. Various tannins are used for this purpose. Hides are also used as processed chews for dogs or other pets.
The term "skin" is sometimes expanded to include furs, which are harvested from various species, including cats, mustelids, and bears.
History
Archaeologists believe that animal hides provided an important source of clothing and shelter for all prehistoric humans and their use continued among non-agricultural societies into modern times. The Inuit, for example, used animal hides for summer tents, waterproof clothes, and kayaks. In early medieval ages hides were used to protect wooden castles and defense buildings from setting alight during a siege. Various American Indian tribes used hides in the construction of tepees and wigwams, moccasins, and buckskins. They were sometimes used as window coverings. Until the invention of plastic drum heads in the 1950s, animal hides or metal was used.
Parchment and vellum—a kind of paper made from processed skins—was introduced to the Eastern Mediterranean during the Iron Age, supposedly at Pergamon.
The Assize of Weights and Measures—one of the statutes of uncertain date from —mentions rawhide, gloves, parchment, and vellum among the principal items of England's commerce. A standardized shipload of leather (a last) consisted of 20 dicker of 10 cowhides. Rabbit and squirrel skins were traded and taxed in timbers of 40 hides each. Skins were also traded in binds of 32 or 33 skins each, while gloves were sold in dickers of 10 pair and dozens of 12 pair. The parchment and vellum was traded based on dozens of the original sheepskins from which they were prepared.
Rare furs have been a notable status symbol throughout history. Ermine fur was particularly associated with European nobility, with the black-tipped tails arranged around the edges of the robes to produce a pattern of black diamonds on a white field. Demand for beaver hats in the 17th and 18th century drove some of the initial exploration of North America, particularly in Canada, and even prompted wars among native tribes competing for the most productive areas. Natural leather continues to be used for many expensive products from limousine upholstery to designer cellular phone cases. There are, however, many forms of artificial leather and fur now available, which are usually cheaper alternatives.
Production
Animal hides and skins are usually processed fresh or salted and tanned. Skins sometimes are stretched, dried, and tanned. Most hides are processed from domesticated animals; the most common wild animals used for fur—mink and rabbit—are similarly raised in captivity and farmed. Some others—including lynx and wolves—are still trapped in the wild for their fur.
Use
Currently, hides are mainly used for footwear, upholstery, leather goods; skins are used for clothing, particularly as coats, gloves, leather goods and footwear. It is also used for bookbinding.
Many traditional drums, especially hand drums like the pandeiro, continue to be made using natural skins. The alligator drum was formerly important in Chinese music. The Chinese sanxian and Okinawan sanshin are usually prepared from snakeskin, while their Japanese equivalent, the shamisen, is made from dogskin in the case of students and catskin in the case of professional players. The African-American banjo was originally made from skins but is now often synthetic. "Hides" is used as a slang term to refer to a drumset.
Kangaroo leather is the most common material for the construction of bullwhips. Stingray rawhide is a common material for the grips of Chinese, Japanese, and Scottish swords.
Pig skins are processed as pork rinds.
Rabbit fur is popular for hats, coats, and glove linings.
Controversy
Animal rights activists generally protest the use of animal hides for human clothing. Forms of protest range from PETA's "I would rather go naked than wear fur" campaign, although more shocking and direct action, like damaging furs with red paint in imitation of blood, has been toned down, like the "Ink, not Mink" campaign.
Roadblocking and break-ins against meat/fur/leather industry is also used and extends to personal campaigns against such companies and also hunters which have included arson and assault in some cases.
| Technology | Materials | null |
575531 | https://en.wikipedia.org/wiki/Deltoid%20muscle | Deltoid muscle | The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle is made up of three distinct sets of muscle fibers, namely the
anterior or clavicular part (pars clavicularis)
posterior or scapular part (pars scapularis)
intermediate or acromial part (pars acromialis)
The deltoid's fibres are Pennate muscle.
However, electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.
It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). Deltoid is also further shortened in slang as "delt".
A study of 30 shoulders revealed an average mass of in humans, ranging from to .
Structure
Origin
The anterior or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle. The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.
Intermediate or acromial fibers arise from the superior surface of the acromion process of the scapula.
Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula.
Insertion
From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the intermediate fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.
Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally gives off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the medial and lateral intermuscular septa.
Blood supply
The deltoid is supplied by the thoracoacromial artery (acromial and deltoid branches), the circumflex humeral arteries, and the profunda brachii artery (deltoid branch).
Nerve supply
The deltoid is innervated by the axillary nerve. The axillary nerve originates from the anterior rami of the cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.
Studies have shown that there are seven neuromuscular segments to the deltoid muscle. Three of these lie in the anatomical anterior head of the deltoid, one in the anatomical middle head, and three in the anatomical posterior head of the deltoid. These neuromuscular segments are supplied by smaller branches of the axillary nerve, and work in coordination with other muscles of the shoulder girdle include pectoralis major and supraspinatus.
The axillary nerve is sometimes damaged during surgical procedures of the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus.
Structures under deltoid
Humerus
Pectoralis minor
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Pectoralis major
Teres major
Latissimus dorsi coracobrachialis
Biceps brachii
Triceps brachii
Anterior circumflex humeral vessels
Posterior circumflex humeral vessels
Axillary nerve
Shoulder joint
Rotator cuff
Coracoacromial ligament
Function
When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect. This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction. The anterior fibers assist the pectoralis major to flex the shoulder. The anterior deltoid also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus. The intermediate fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers. The posterior fibers assist the latissimus dorsi to extend the shoulder. Other transverse extensors, the infraspinatus and teres minor, also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats.
An important function of the deltoid in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation. The intermediate fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers.
The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.
Clinical significance
The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy may result from various causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoidal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation.
The Deltoid Muscle is tested by asking the patient to abduct the arm against resistance applied with one hand, and feeling for the contracting muscle with the other hand.
Site of the intramuscular injection in deltoid: The intramuscular injections are commonly given in the lower half of the deltoid to avoid injury to the axillary nerve, which winds around the surgical neck of the humerus.
Other animals
The deltoid is also found in members of the great ape family other than humans. The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan, which engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders. In other apes, like the common chimpanzee, the deltoid is much larger than in humans, weighing an average of 383.3 gram compared to 191.9 gram in humans. This reflects the need to strengthen the shoulders, particularly the rotatory cuff, in knuckle walking apes for the purpose of supporting the entire body weight.
The deltoid muscle is a main component of both the bat and pterosaur wing musculature, but in crown-group birds it is strongly reduced, as they favour sternum attached muscles. Some Mesozoic flying theropods, however, had more developed deltoideus.
| Biology and health sciences | Human anatomy | Health |
575590 | https://en.wikipedia.org/wiki/Navy%20blue | Navy blue | Navy blue is a dark shade of the color blue.
Navy blue got its name from the dark blue (contrasted with naval white) worn by officers in the Royal Navy since 1748 and subsequently adopted by other navies around the world. When this color name, taken from the usual color of the uniforms of sailors, originally came into use in the early 19th century, it was initially called marine blue, but the name of the color soon changed to navy blue.
An early use of navy blue as a color name in English was in 1840 though the Oxford English Dictionary has a citation from 1813.
Variations
Indigo dye
Indigo dye is the color that is called Añil (the Spanish word for "indigo dye") in the Guía de coloraciones (Guide to colorations) by Rosa Gallego and Juan Carlos Sanz, a color dictionary published in 2005 that is widely popular in the Hispanophone realm.
Indigo dye is the basis for all the historical navy blue colors, since in the 18th, 19th, and early 20th century, almost all navy uniforms were made by dyeing them with various shades of indigo dye.
Navy blue (Crayola)
The Crayola color named "navy blue" is not as dark a shade as the blues actually used by navies.
This tone of navy blue was formulated as a Crayola color in 1958.
Peacoat
The source of this color is the Pantone textile cotton extended color list, color #19-3920 TCX—peacoat.
Persian indigo
The color Persian indigo is displayed at right. Another name for this color is regimental because in the 19th century it was commonly used by many nations for navy uniforms, though it is seldom used in modern times.
Persian indigo is named for an association with a product from Persia: Persian cloth dyed with indigo.
The first recorded use of regimental (the original name for the color now called Persian indigo) as a color name in English was in 1912.
Space cadet
Space cadet is one of the colors on the Resene Color List, a color list widely popular in Australia and New Zealand. The color was formulated in 2007.
This color is apparently a formulation of an impression of the color that cadets in space navy training would wear.
In culture
Computers
The color navy was one of the original 16 HTML/CSS colors initially formulated for standardized computer display in the late 1980s.
Military
In many world navies, including the United States Navy and the Royal Canadian Navy, uniforms which are called "navy blue" are, in actuality, colored black, as the uniforms became progressively darker over time to counter fading of the dye, though for modern dyes are fade resistant. The Canadian Forces dress instructions specify that navy blue' is a tone of black". (See also uniforms of the United States Navy and uniforms of the Canadian Forces.)
Music
Navy Blue is an album by Diane Renay (all the songs are about sailors).
Sports
Navy blue is used by numerous professional and collegiate sports teams:
Association football
Scottish national team
United States men's and women's national teams
Falkirk F.C.
Manchester City F.C.
Tottenham Hotspur F.C.
West Bromwich Albion F.C.
York City F.C.
Genoa C.F.C.
Melbourne Victory
FC Girondins de Bordeaux
Fenerbahçe S.K.
Paris Saint-Germain F.C.
Chicago Fire Soccer Club
Los Angeles Galaxy
New England Revolution
New York City F.C.
Philadelphia Union
Sporting Kansas City
Vancouver Whitecaps
Viking Stavanger
Australian Football League
Adelaide Crows
Carlton Blues
Geelong Cats
Melbourne Demons
Major League Baseball
Atlanta Braves
Boston Red Sox
Cleveland Guardians
Detroit Tigers
Houston Astros
Los Angeles Angels
Milwaukee Brewers
Minnesota Twins
New York Yankees
St. Louis Cardinals
Seattle Mariners
Tampa Bay Rays
Toronto Blue Jays
Washington Nationals
National Basketball Association
Dallas Mavericks
Denver Nuggets
Indiana Pacers
Memphis Grizzlies
Minnesota Timberwolves
New Orleans Pelicans
Oklahoma City Thunder
Washington Wizards
National Football League
Chicago Bears
Dallas Cowboys
Denver Broncos
Houston Texans
New England Patriots
Los Angeles Chargers
Seattle Seahawks
Tennessee Titans
National Hockey League
Colorado Avalanche
Columbus Blue Jackets
Florida Panthers
Nashville Predators
New York Rangers
St. Louis Blues
Seattle Kraken
Washington Capitals
Winnipeg Jets
National Rugby League
Melbourne Storm
North Queensland Cowboys
Sydney Roosters
American Collegiate Teams
University of Arizona
University of California, Berkeley
University of Pittsburgh
Auburn University
Adamson University
Florida Atlantic University
Florida International University
Georgetown University
Georgia Institute of Technology
Gonzaga University
University of Illinois
University of Notre Dame
University of Maine
University of Michigan
University of Mississippi
University of Nevada, Reno
University of Virginia
Palm Beach Atlantic University
Pennsylvania State University
University of Rhode Island
Saint Mary's College of California
Shippensburg University of Pennsylvania
Syracuse University
West Virginia University
United States Naval Academy
Xavier University
Colegio de San Juan de Letran
Catawba College
University of Connecticut
| Physical sciences | Colors | Physics |
575613 | https://en.wikipedia.org/wiki/Moons%20of%20Jupiter | Moons of Jupiter | There are 95 moons of Jupiter with confirmed orbits . This number does not include a number of meter-sized moonlets thought to be shed from the inner moons, nor hundreds of possible kilometer-sized outer irregular moons that were only briefly captured by telescopes. All together, Jupiter's moons form a satellite system called the Jovian system. The most massive of the moons are the four Galilean moons: Io, Europa, Ganymede, and Callisto, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun. Much more recently, beginning in 1892, dozens of far smaller Jovian moons have been detected and have received the names of lovers (or other sexual partners) or daughters of the Roman god Jupiter or his Greek equivalent Zeus. The Galilean moons are by far the largest and most massive objects to orbit Jupiter, with the remaining 91 known moons and the rings together comprising just 0.003% of the total orbiting mass.
Of Jupiter's moons, eight are regular satellites with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane. The Galilean satellites are nearly spherical in shape due to their planetary mass, and are just massive enough that they would be considered major planets if they were in direct orbit around the Sun. The other four regular satellites, known as the inner moons, are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings. The remainder of Jupiter's moons are outer irregular satellites whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. The largest of these moons were likely asteroids that were captured from solar orbits by Jupiter before impacts with other small bodies shattered them into many kilometer-sized fragments, forming collisional families of moons sharing similar orbits. Jupiter is expected to have about 100 irregular moons larger than in diameter, plus around 500 more smaller retrograde moons down to diameters of . Of the 87 known irregular moons of Jupiter, 38 of them have not yet been officially given names.
Characteristics
The physical and orbital characteristics of the moons vary widely. The four Galileans are all over in diameter; the largest Galilean, Ganymede, is the ninth largest object in the Solar System, after the Sun and seven of the planets, Ganymede being larger than Mercury. All other Jovian moons are less than in diameter, with most barely exceeding . Their orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's rotation (retrograde motion).
Origin and evolution
Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk. They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history.
Simulations suggest that, while the disk had a relatively high mass at any given moment, over time a substantial fraction (several tens of a percent) of the mass of Jupiter captured from the solar nebula was passed through it. However, only 2% of the proto-disk mass of Jupiter is required to explain the existing satellites. Thus, several generations of Galilean-mass satellites may have been in Jupiter's early history. Each generation of moons might have spiraled into Jupiter, because of drag from the disk, with new moons then forming from the new debris captured from the solar nebula. By the time the present (possibly fifth) generation formed, the disk had thinned so that it no longer greatly interfered with the moons' orbits. The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance with each other, which still exists for Io, Europa, and Ganymede: they are in a 1:2:4 resonance. Ganymede's larger mass means that it would have migrated inward at a faster rate than Europa or Io. Tidal dissipation in the Jovian system is still ongoing and Callisto will likely be captured into the resonance in about 1.5 billion years, creating a 1:2:4:8 chain.
The outer, irregular moons are thought to have originated from captured asteroids, whereas the protolunar disk was still massive enough to absorb much of their momentum and thus capture them into orbit. Many are believed to have been broken up by mechanical stresses during capture, or afterward by collisions with other small bodies, producing the moons we see today.
History and discovery
Visual observations
Chinese historian Xi Zezong claimed that the earliest record of a Jovian moon (Ganymede or Callisto) was a note by Chinese astronomer Gan De of an observation around 364 BC regarding a "reddish star". However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. By January 1610, he had sighted the four massive Galilean moons with his 20× magnification telescope, and he published his results in March 1610.
Simon Marius had independently discovered the moons one day after Galileo, although he did not publish his book on the subject until 1614. Even so, the names Marius assigned are used today: Ganymede, Callisto, Io, and Europa. No additional satellites were discovered until E. E. Barnard observed Amalthea in 1892.
Photographic and spacecraft observations
With the aid of telescopic photography with photographic plates, further discoveries followed quickly over the course of the 20th century. Himalia was discovered in 1904, Elara in 1905, Pasiphae in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974.
By the time that the Voyager space probes reached Jupiter, around 1979, thirteen moons had been discovered, not including Themisto, which had been observed in 1975, but was lost until 2000 due to insufficient initial observation data. The Voyager spacecraft discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe.
Digital telescopic observations
No additional moons were discovered until two decades later, with the fortuitous discovery of Callirrhoe by the Spacewatch survey in October 1999. During the 1990s, photographic plates phased out as digital charge-coupled device (CCD) cameras began emerging in telescopes on Earth, allowing for wide-field surveys of the sky at unprecedented sensitivities and ushering in a wave of new moon discoveries. Scott Sheppard, then a graduate student of David Jewitt, demonstrated this extended capability of CCD cameras in a survey conducted with the Mauna Kea Observatory's UH88 telescope in November 2000, discovering eleven new irregular moons of Jupiter including the previously lost Themisto with the aid of automated computer algorithms.
From 2001 onward, Sheppard and Jewitt alongside other collaborators continued surveying for Jovian irregular moons with the Canada-France-Hawaii Telescope (CFHT), discovering an additional eleven in December 2001, one in October 2002, and nineteen in February 2003. At the same time, another independent team led by Brett J. Gladman also used the CFHT in 2003 to search for Jovian irregular moons, discovering four and co-discovering two with Sheppard. From the start to end of these CCD-based surveys in 2000–2004, Jupiter's known moon count had grown from 17 to 63. All of these moons discovered after 2000 are faint and tiny, with apparent magnitudes between 22–23 and diameters less than . As a result, many could not be reliably tracked and ended up becoming lost.
Beginning in 2009, a team of astronomers, namely Mike Alexandersen, Marina Brozović, Brett Gladman, Robert Jacobson, and Christian Veillet, began a campaign to recover Jupiter's lost irregular moons using the CFHT and Palomar Observatory's Hale Telescope. They discovered two previously unknown Jovian irregular moons during recovery efforts in September 2010, prompting further follow-up observations to confirm these by 2011. One of these moons, S/2010 J 2 (now Jupiter LII), has an apparent magnitude of 24 and a diameter of only , making it one of the faintest and smallest confirmed moons of Jupiter even . Meanwhile, in September 2011, Scott Sheppard, now a faculty member of the Carnegie Institution for Science, discovered two more irregular moons using the institution's Magellan Telescopes at Las Campanas Observatory, raising Jupiter's known moon count to 67. Although Sheppard's two moons were followed up and confirmed by 2012, both became lost due to insufficient observational coverage.
In 2016, while surveying for distant trans-Neptunian objects with the Magellan Telescopes, Sheppard serendipitously observed a region of the sky located near Jupiter, enticing him to search for Jovian irregular moons as a detour. In collaboration with Chadwick Trujillo and David Tholen, Sheppard continued surveying around Jupiter from 2016 to 2018 using the Cerro Tololo Observatory's Víctor M. Blanco Telescope and Mauna Kea Observatory's Subaru Telescope. In the process, Sheppard's team recovered several lost moons of Jupiter from 2003 to 2011 and reported two new Jovian irregular moons in June 2017. Then in July 2018, Sheppard's team announced ten more irregular moons confirmed from 2016 to 2018 observations, bringing Jupiter's known moon count to 79. Among these was Valetudo, which has an unusually distant prograde orbit that crosses paths with the retrograde irregular moons. Several more unidentified Jovian irregular satellites were detected in Sheppard's 2016–2018 search, but were too faint for follow-up confirmation.
From November 2021 to January 2023, Sheppard discovered twelve more irregular moons of Jupiter and confirmed them in archival survey imagery from 2003 to 2018, bringing the total count to 92. Among these was S/2018 J 4, a highly inclined prograde moon that is now known to be in same orbital grouping as the moon Carpo, which was previously thought to be solitary. On 22 February 2023, Sheppard announced three more moons discovered in a 2022 survey, now bringing Jupiter's total known moon count to 95. In a February 2023 interview with NPR, Sheppard noted that he and his team are currently tracking even more moons of Jupiter, which should place Jupiter's moon count over 100 once confirmed over the next two years.
Many more irregular moons of Jupiter will inevitably be discovered in the future, especially after the beginning of deep sky surveys by the upcoming Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope in the mid-2020s. The Rubin Observatory's aperture telescope and 3.5 square-degree field of view will probe Jupiter's irregular moons down to diameters of at apparent magnitudes of 24.5, with the potential of increasing the known population by up to tenfold. Likewise, the Roman Space Telescope's aperture and 0.28 square-degree field of view will probe Jupiter's irregular moons down to diameters of at magnitude 27.7, with the potential of discovering approximately 1,000 Jovian moons above this size. Discovering these many irregular satellites will help reveal their population's size distribution and collisional histories, which will place further constraints to how the Solar System formed.
Naming
The Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto) were named by Simon Marius soon after their discovery in 1610. However, these names fell out of favor until the 20th century. The astronomical literature instead simply referred to "Jupiter I", "Jupiter II", etc., or "the first satellite of Jupiter", "Jupiter's second satellite", and so on. The names Io, Europa, Ganymede, and Callisto became popular in the mid-20th century, whereas the rest of the moons remained unnamed and were usually numbered in Roman numerals V (5) to XII (12). Jupiter V was discovered in 1892 and given the name Amalthea by a popular though unofficial convention, a name first used by French astronomer Camille Flammarion.
The other moons were simply labeled by their Roman numeral (e.g. Jupiter IX) in the majority of astronomical literature until the 1970s. Several different suggestions were made for names of Jupiter's outer satellites, but none were universally accepted until 1975 when the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII, and provided for a formal naming process for future satellites still to be discovered. The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus) and, since 2004, also after their descendants. All of Jupiter's satellites from XXXIV (Euporie) onward are named after descendants of Jupiter or Zeus, except LIII (Dia), named after a lover of Jupiter. Names ending with "a" or "o" are used for prograde irregular satellites (the latter for highly inclined satellites), and names ending with "e" are used for retrograde irregulars. With the discovery of smaller, kilometre-sized moons around Jupiter, the IAU has established an additional convention to limit the naming of small moons with absolute magnitudes greater than 18 or diameters smaller than . Some of the most recently confirmed moons have not received names.
Some asteroids share the same names as moons of Jupiter: 9 Metis, 38 Leda, 52 Europa, 85 Io, 113 Amalthea, 239 Adrastea. Two more asteroids previously shared the names of Jovian moons until spelling differences were made permanent by the IAU: Ganymede and asteroid 1036 Ganymed; and Callisto and asteroid 204 Kallisto.
Groups
Regular satellites
These have prograde and nearly circular orbits of low inclination and are split into two groups:
Inner satellites or Amalthea group: Metis, Adrastea, Amalthea, and Thebe. These orbit very close to Jupiter; the innermost two orbit in less than a Jovian day. The latter two are respectively the fifth and seventh largest moons in the Jovian system. Observations suggest that at least the largest member, Amalthea, did not form on its present orbit, but farther from the planet, or that it is a captured Solar System body. These moons, along with a number of seen and as-yet-unseen inner moonlets (see Amalthea moonlets), replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, whereas Amalthea and Thebe each maintain their own faint outer rings.
Main group or Galilean moons: Io, Europa, Ganymede and Callisto. They are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of mass, larger than any known dwarf planet. Ganymede exceeds (and Callisto nearly equals) even the planet Mercury in diameter, though they are less massive. They are respectively the fourth-, sixth-, first-, and third-largest natural satellites in the Solar System, containing approximately 99.997% of the total mass in orbit around Jupiter, while Jupiter is almost 5,000 times more massive than the Galilean moons. The inner moons are in a 1:2:4 orbital resonance. Models suggest that they formed by slow accretion in the low-density Jovian subnebula—a disc of the gas and dust that existed around Jupiter after its formation—which lasted up to 10 million years in the case of Callisto. Europa, Ganymede, and Callisto are suspected of having subsurface water oceans, and Io may have a subsurface magma ocean.
Irregular satellites
The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis, inclination, eccentricity) and composition; it is believed that these are at least partially collisional families that were created when larger (but still small) parent bodies were shattered by impacts from asteroids captured by Jupiter's gravitational field. These families bear the names of their largest members. The identification of satellite families is tentative, but the following are typically listed:
Prograde satellites:
Themisto is the innermost irregular moon and is not part of a known family.
The Himalia group is confined within semi-major axes between , inclinations between 27 and 29°, and eccentricities between 0.12 and 0.21. It has been suggested that the group could be a remnant of the break-up of an asteroid from the asteroid belt. The largest two members, Himalia and Elara, are respectively the sixth- and eighth-largest Jovian moons.
The Carpo group includes two known moons on very high orbital inclinations of 50° and semi-major axes between . Due to their exceptionally high inclinations, the moons of the Carpo group are subject to gravitational perturbations that induce the Lidov–Kozai resonance in their orbits, which cause their eccentricities and inclinations to periodically oscillate in correspondence with each other. The Lidov–Kozai resonance can significantly alter the orbits of these moons: for example, the eccentricity and inclination of the group's namesake Carpo can fluctuate between 0.19–0.69 and 44–59°, respectively.
Valetudo is the outermost prograde moon and is not part of a known family. Its prograde orbit crosses paths with several moons that have retrograde orbits and may in the future collide with them.
Retrograde satellites:
The Carme group is tightly confined within semi-major axes between , inclinations between 164 and 166°, and eccentricities between 0.25 and 0.28. It is very homogeneous in color (light red) and is believed to have originated as collisional fragments from a D-type asteroid progenitor, possibly a Jupiter trojan.
The Ananke group has a relatively wider spread than the previous groups, with semi-major axes between , inclinations between 144 and 156°, and eccentricities between 0.09 and 0.25. Most of the members appear gray, and are believed to have formed from the breakup of a captured asteroid.
The Pasiphae group is quite dispersed, with semi-major axes spread over , inclinations between 141° and 157°, and higher eccentricities between 0.23 and 0.44. The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included in the Pasiphae group, is red and, given the difference in inclination, it could have been captured independently; Pasiphae and Sinope are also trapped in secular resonances with Jupiter.
Based on their survey discoveries in 2000–2003, Sheppard and Jewitt predicted that Jupiter should have approximately 100 irregular satellites larger than in diameter, or brighter than magnitude 24. Survey observations by Alexandersen et al. in 2010–2011 agreed with this prediction, estimating that approximately 40 Jovian irregular satellites of this size remained undiscovered in 2012.
In September 2020, researchers from the University of British Columbia identified 45 candidate irregular moons from an analysis of archival images taken in 2010 by the CFHT. These candidates were mainly small and faint, down to magnitude of 25.7 or above in diameter. From the number of candidate moons detected within a sky area of one square degree, the team extrapolated that the population of retrograde Jovian moons brighter than magnitude 25.7 is around within a factor of 2. Although the team considers their characterized candidates to be likely moons of Jupiter, they all remain unconfirmed due to insufficient observation data for determining reliable orbits. The true population of Jovian irregular moons is likely complete down to magnitude 23.2 at diameters over .
List
The moons of Jupiter are listed below by orbital period. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in bold. These are the four Galilean moons, which are comparable in size to the Moon. The other moons are much smaller. The Galilean moon with the smallest amount of mass is greater than 7,000 times more massive than the most massive of the other moons. The irregular captured moons are shaded light gray and orange when prograde and yellow, red, and dark gray when retrograde.
The orbits and mean distances of the irregular moons are highly variable over short timescales due to frequent planetary and solar perturbations, so proper orbital elements which are averaged over a period of time are preferably used. The proper orbital elements of the irregular moons listed here are averaged over a 400-year numerical integration by the Jet Propulsion Laboratory: for the above reasons, they may strongly differ from osculating orbital elements provided by other sources. Otherwise, recently discovered irregular moons without published proper elements are temporarily listed here with inaccurate osculating orbital elements that are italicized to distinguish them from other irregular moons with proper orbital elements. Some of the irregular moons' proper orbital periods in this list may not scale accordingly with their proper semi-major axes due to the aforementioned perturbations. The irregular moons' proper orbital elements are all based on the reference epoch of 1 January 2000.
Some irregular moons have only been observed briefly for a year or two, but their orbits are known accurately enough that they will not be lost to positional uncertainties.
Exploration
Nine spacecraft have visited Jupiter. The first were Pioneer 10 in 1973, and Pioneer 11 a year later, taking low-resolution images of the four Galilean moons and returning data on their atmospheres and radiation belts. The Voyager 1 and Voyager 2 probes visited Jupiter in 1979, discovering the volcanic activity on Io and the presence of water ice on the surface of Europa. Ulysses further studied Jupiter's magnetosphere in 1992 and then again in 2000.
The Galileo spacecraft was the first to enter orbit around Jupiter, arriving in 1995 and studying it until 2003. During this period, Galileo gathered a large amount of information about the Jovian system, making close approaches to all of the Galilean moons and finding evidence for thin atmospheres on three of them, as well as the possibility of liquid water beneath the surfaces of Europa, Ganymede, and Callisto. It also discovered a magnetic field around Ganymede.
Then the Cassini probe to Saturn flew by Jupiter in 2000 and collected data on interactions of the Galilean moons with Jupiter's extended atmosphere. The New Horizons spacecraft flew by Jupiter in 2007 and made improved measurements of its satellites' orbital parameters.
In 2016, the Juno spacecraft imaged the Galilean moons from above their orbital plane as it approached Jupiter orbit insertion, creating a time-lapse movie of their motion. With a mission extension, Juno has since begun close flybys of the Galileans, flying by Ganymede in 2021 followed by Europa and Io in 2022. It flew by Io again in late 2023 and once more in early 2024.
| Physical sciences | Solar System | Astronomy |
575697 | https://en.wikipedia.org/wiki/Cheminformatics | Cheminformatics | Cheminformatics (also known as chemoinformatics) refers to the use of physical chemistry theory with computer and information science techniques—so called "in silico" techniques—in application to a range of descriptive and prescriptive problems in the field of chemistry, including in its applications to biology and related molecular fields. Such in silico techniques are used, for example, by pharmaceutical companies and in academic settings to aid and inform the process of drug discovery, for instance in the design of well-defined combinatorial libraries of synthetic compounds, or to assist in structure-based drug design. The methods can also be used in chemical and allied industries, and such fields as environmental science and pharmacology, where chemical processes are involved or studied.
History
Cheminformatics has been an active field in various guises since the 1970s and earlier, with activity in academic departments and commercial pharmaceutical research and development departments. The term chemoinformatics was defined in its application to drug discovery by F.K. Brown in 1998:Chemoinformatics is the mixing of those information resources to transform data into information and information into knowledge for the intended purpose of making better decisions faster in the area of drug lead identification and optimization. Since then, both terms, cheminformatics and chemoinformatics, have been used, although, lexicographically, cheminformatics appears to be more frequently used, despite academics in Europe declaring for the variant chemoinformatics in 2006. In 2009, a prominent Springer journal in the field was founded by transatlantic executive editors named the Journal of Cheminformatics.
Background
Cheminformatics combines the scientific working fields of chemistry, computer science, and information science—for example in the areas of topology, chemical graph theory, information retrieval and data mining in the chemical space. Cheminformatics can also be applied to data analysis for various industries like paper and pulp, dyes and such allied industries.
Applications
Storage and retrieval
A primary application of cheminformatics is the storage, indexing, and search of information relating to chemical compounds. The efficient search of such stored information includes topics that are dealt with in computer science, such as data mining, information retrieval, information extraction, and machine learning. Related research topics include:
Digital libraries
Unstructured data
Structured data mining and mining of structured data
Database mining
Graph mining
Molecule mining
Sequence mining
Tree mining
File formats
The in silico representation of chemical structures uses specialized formats such as the Simplified molecular input line entry specifications (SMILES) or the XML-based Chemical Markup Language. These representations are often used for storage in large chemical databases. While some formats are suited for visual representations in two- or three-dimensions, others are more suited for studying physical interactions, modeling and docking studies.
Virtual libraries
Chemical data can pertain to real or virtual molecules. Virtual libraries of compounds may be generated in various ways to explore chemical space and hypothesize novel compounds with desired properties. Virtual libraries of classes of compounds (drugs, natural products, diversity-oriented synthetic products) were recently generated using the FOG (fragment optimized growth) algorithm. This was done by using cheminformatic tools to train transition probabilities of a Markov chain on authentic classes of compounds, and then using the Markov chain to generate novel compounds that were similar to the training database.
Virtual screening
In contrast to high-throughput screening, virtual screening involves computationally
screening in silico libraries of compounds, by means of various methods such as
docking, to identify members likely to possess desired properties
such as biological activity against a given target. In some cases, combinatorial chemistry is used in the development of the library to increase the efficiency in mining the chemical space. More commonly, a diverse library of small molecules or natural products is screened.
Quantitative structure-activity relationship (QSAR)
This is the calculation of quantitative structure–activity relationship and quantitative structure property relationship values, used to predict the activity of compounds from their structures. In this context there is also a strong relationship to chemometrics. Chemical expert systems are also relevant, since they represent parts of chemical knowledge as an in silico representation. There is a relatively new concept of matched molecular pair analysis or prediction-driven MMPA which is coupled with QSAR model in order to identify activity cliff.
| Physical sciences | Basics_2 | Chemistry |
575749 | https://en.wikipedia.org/wiki/Moons%20of%20Saturn | Moons of Saturn | The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to the enormous Titan, which is larger than the planet Mercury. There are 146 moons with confirmed orbits, the most of any planet in the Solar System. This number does not include the many thousands of moonlets embedded within Saturn's dense rings, nor hundreds of possible kilometer-sized distant moons that have been observed on single occasions. Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possibly Rhea, are currently in hydrostatic equilibrium. Three moons are particularly notable. Titan is the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring river networks and hydrocarbon lakes. Enceladus emits jets of ice from its south-polar region and is covered in a deep layer of snow. Iapetus has contrasting black and white hemispheres as well as an extensive ridge of equatorial mountains among the tallest in the solar system.
Twenty-four of the known moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane, with the exception of Iapetus which has a prograde but highly inclined orbit, an unusual characteristic for a regular moon. They include the seven major satellites, four small moons that exist in a trojan orbit with larger moons, and five that act as shepherd moons, of which two are mutually co-orbital. Two tiny moons orbit inside of Saturn's B and G rings. The relatively large Hyperion is locked in an orbital resonance with Titan. The remaining regular moons orbit near the outer edges of the dense A Ring and the narrow F Ring, and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.
The remaining 122, with mean diameters ranging from , orbit much farther from Saturn. They are irregular satellites, having high orbital inclinations and eccentricities mixed between prograde and retrograde. These moons are probably captured minor planets, or fragments from the collisional breakup of such bodies after they were captured, creating collisional families. Saturn is expected to have around 150 irregular satellites larger than in diameter, plus many hundreds more that are even smaller. The irregular satellites are classified by their orbital characteristics into the prograde Inuit and Gallic groups and the large retrograde Norse group, and their names are chosen from the corresponding mythologies (with the Gallic group corresponding to Celtic mythology). The sole exception is Phoebe, the largest irregular Saturnian moon, discovered at the end of the 19th century; it is part of the Norse group but named for a Greek Titaness.
The rings of Saturn are made up of objects ranging in size from microscopic to moonlets hundreds of meters across, each in its own orbit around Saturn. Thus an absolute number of Saturnian moons cannot be given, because there is no consensus on a boundary between the countless small unnamed objects that form Saturn's ring system and the larger objects that have been named as moons. Over 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.
, there are 83 designated moons that are still unnamed; all but one (the designated B-ring moonlet S/2009 S 1) are irregular. (There are many other undesignated ring moonlets.) If named, most of the irregulars will receive names from Gallic, Norse and Inuit mythology based on the orbital group of which they are a member.
Discovery
Early observations
Before the advent of telescopic photography, eight moons of Saturn were discovered by direct observation using optical telescopes. Saturn's largest moon, Titan, was discovered in 1655 by Christiaan Huygens using a objective lens on a refracting telescope of his own design. Tethys, Dione, Rhea and Iapetus (the "Sidera Lodoicea") were discovered between 1671 and 1684 by Giovanni Domenico Cassini. Mimas and Enceladus were discovered in 1789 by William Herschel. Hyperion was discovered in 1848 by W. C. Bond, G. P. Bond and William Lassell.
The use of long-exposure photographic plates made possible the discovery of additional moons. The first to be discovered in this manner, Phoebe, was found in 1899 by W. H. Pickering. In 1966 the tenth satellite of Saturn was discovered by Audouin Dollfus, when the rings were observed edge-on near an equinox. It was later named Janus. A few years later it was realized that all observations of 1966 could only be explained if another satellite had been present and that it had an orbit similar to that of Janus. This object is now known as Epimetheus, the eleventh moon of Saturn. It shares the same orbit with Janus—the only known example of co-orbitals in the Solar System. In 1980, three additional Saturnian moons were discovered from the ground and later confirmed by the Voyager probes. They are trojan moons of Dione (Helene) and Tethys (Telesto and Calypso).
Observations by spacecraft
The study of the outer planets has since been revolutionized by the use of uncrewed space probes. The arrival of the Voyager spacecraft at Saturn in 1980–1981 resulted in the discovery of three additional moons—Atlas, Prometheus and Pandora—bringing the total to 17. In addition, Epimetheus was confirmed as distinct from Janus. In 1990, Pan was discovered in archival Voyager images.
The Cassini mission, which arrived at Saturn in July 2004, initially discovered three small inner moons: Methone and Pallene between Mimas and Enceladus, and the second trojan moon of Dione, Polydeuces. It also observed three suspected but unconfirmed moons in the F Ring. In Cassini scientists announced that the structure of Saturn's rings indicates the presence of several more moons orbiting within the rings, although only one, Daphnis, had been visually confirmed at the time. In 2007 Anthe was announced. In 2008 it was reported that Cassini observations of a depletion of energetic electrons in Saturn's magnetosphere near Rhea might be the signature of a tenuous ring system around Saturn's second largest moon. In , Aegaeon, a moonlet within the G Ring, was announced. In July of the same year, S/2009 S 1, the first moonlet within the B Ring, was observed. In April 2014, the possible beginning of a new moon, within the A Ring, was reported. (related image)
Outer moons
Study of Saturn's moons has also been aided by advances in telescope instrumentation, primarily the introduction of digital charge-coupled devices which replaced photographic plates. For the 20th century, Phoebe stood alone among Saturn's known moons with its highly irregular orbit. Then in 2000, three dozen additional irregular moons were discovered using ground-based telescopes. A survey starting in late 2000 and conducted using three medium-size telescopes found thirteen new moons orbiting Saturn at a great distance, in eccentric orbits, which are highly inclined to both the equator of Saturn and the ecliptic. They are probably fragments of larger bodies captured by Saturn's gravitational pull. In 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons, in 2006, astronomers using the Subaru 8.2 m telescope reported the discovery of nine more irregular moons, in , Tarqeq (S/2007 S 1) was announced and in May of the same year S/2007 S 2 and S/2007 S 3 were reported. In 2019, twenty new irregular satellites of Saturn were reported, resulting in Saturn overtaking Jupiter as the planet with the most known moons for the first time since 2000.
In 2019, researchers Edward Ashton, Brett Gladman, and Matthew Beaudoin conducted a survey of Saturn's Hill sphere using the 3.6-meter Canada–France–Hawaii Telescope and discovered about 80 new Saturnian irregular moons. Follow-up observations of these new moons took place over 2019–2021, eventually leading to S/2019 S 1 being announced in November 2021 and an additional 62 moons being announced from 3–16 May 2023. These discoveries brought Saturn's total number of confirmed moons up to 145, making it the first planet known to have over 100 moons. Yet another moon, S/2006 S 20, was announced on 23 May 2023, bringing Saturn's total count moons to 146. All of these new moons are small and faint, with diameters over and apparent magnitudes of 25–27. The researchers found that the Saturnian irregular moon population is more abundant at smaller sizes, suggesting that they are likely fragments from a collision that occurred a few hundred million years ago. The researchers extrapolated that the true population of Saturnian irregular moons larger than in diameter amounts to , which is approximately three times as many Jovian irregular moons down to the same size. If this size distribution applies to even smaller diameters, Saturn would therefore intrinsically have more irregular moons than Jupiter.
Naming
The modern names for Saturnian moons were suggested by John Herschel in 1847. He proposed to name them after mythological figures associated with the Roman god of agriculture and harvest, Saturn (equated to the Greek Cronus). In particular, the then known seven satellites were named after Titans, Titanesses and Giants – brothers and sisters of Cronus. The idea was similar to Simon Marius' mythological naming scheme for the moons of Jupiter.
As Saturn devoured his children, his family could not be assembled around him, so that the choice lay among his brothers and sister, the Titans and Titanesses. The name Iapetus seemed indicated by the obscurity and remoteness of the exterior satellite, Titan by the superior size of the Huyghenian, while the three female appellations [Rhea, Dione, and Tethys] class together the three intermediate Cassinian satellites. The minute interior ones seemed appropriately characterized by a return to male appellations [Enceladus and Mimas] chosen from a younger and inferior (though still superhuman) brood. [Results of the Astronomical Observations made ... at the Cape of Good Hope, p. 415]
In 1848, Lassell proposed that the eighth satellite of Saturn be named Hyperion after another Titan. When in the 20th century the names of Titans were exhausted, the moons were named after different characters of the Greco-Roman mythology or giants from other mythologies. All the irregular moons (except Phoebe, discovered about a century before the others) are named after Inuit, and Gallic gods, and after Norse ice giants.
Some asteroids share the same names as moons of Saturn: 55 Pandora, 106 Dione, 577 Rhea, 1809 Prometheus, 1810 Epimetheus, and 4450 Pan. In addition, three more asteroids would share the names of Saturnian moons but for spelling differences made permanent by the International Astronomical Union (IAU): Calypso and asteroid 53 Kalypso; Helene and asteroid 101 Helena; and Gunnlod and asteroid 657 Gunlöd.
Physical characteristics
Saturn's satellite system is very lopsided: one moon, Titan, comprises more than 96% of the mass in orbit around the planet. The six other planemo (ellipsoidal) moons constitute roughly 4% of the mass, and the remaining small moons, together with the rings, comprise only 0.04%.
Orbital groups
Although the boundaries may be somewhat vague, Saturn's moons can be divided into ten groups according to their orbital characteristics. Many of them, such as Pan and Daphnis, orbit within Saturn's ring system and have orbital periods only slightly longer than the planet's rotation period. The innermost moons and most regular satellites all have mean orbital inclinations ranging from less than a degree to about 1.5 degrees (except Iapetus, which has an inclination of 7.57 degrees) and small orbital eccentricities. On the other hand, irregular satellites in the outermost regions of Saturn's moon system, in particular the Norse group, have orbital radii of millions of kilometers and orbital periods lasting several years. The moons of the Norse group also orbit in the opposite direction to Saturn's rotation.
Inner moons
Ring moonlets
During late July 2009, a moonlet, S/2009 S 1, was discovered in the B Ring, 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets (see below), it does not induce a 'propeller' feature, probably due to the density of the B Ring.
In 2006, four tiny moonlets were found in Cassini images of the A Ring. Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring. In contrast, a moonlet is only massive enough to clear two small—about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplane propeller. The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly.
In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings. This region is relatively free from the disturbances caused by resonances with larger satellites, although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite. It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km. In April 2014, NASA scientists reported the possible consolidation of a new moon within the A Ring, implying that Saturn's present moons may have formed in a similar process in the past when Saturn's ring system was much more massive.
Similar moonlets may reside in the F Ring. There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, of these moonlets with the core of the F Ring. One of the largest F Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.
One recently discovered moon, Aegaeon, resides within the bright arc of G Ring and is trapped in the 7:6 mean-motion resonance with Mimas. This means that it makes exactly seven revolutions around Saturn while Mimas makes exactly six. The moon is the largest among the population of bodies that are sources of dust in this ring.
Ring shepherds
Shepherd satellites are small moons that orbit within, or just beyond, a planet's ring system. They have the effect of sculpting the rings: giving them sharp edges, and creating gaps between them. Saturn's shepherd moons are Pan (Encke gap), Daphnis (Keeler gap), Prometheus (F Ring), Janus (A Ring), and Epimetheus (A Ring). These moons probably formed as a result of accretion of the friable ring material on preexisting denser cores. The cores with sizes from one-third to one-half the present-day moons may be themselves collisional shards formed when a parental satellite of the rings disintegrated.
Janus and Epimetheus are co-orbital moons. They are of similar size, with Janus being somewhat larger than Epimetheus. They have orbits with less than a 100-kilometer difference in semi-major axis, close enough that they would collide if they attempted to pass each other. Instead of colliding, their gravitational interaction causes them to swap orbits every four years.
Other inner moons
Other inner moons that are neither ring shepherds nor ring moonlets include Atlas and Pandora.
Inner large
The innermost large moons of Saturn orbit within its tenuous E Ring, along with three smaller moons of the Alkyonides group.
Mimas is the smallest and least massive of the inner round moons, although its mass is sufficient to alter the orbit of Methone. It is noticeably ovoid-shaped, having been made shorter at the poles and longer at the equator (by about 20 km) by the effects of Saturn's gravity. Mimas has a large impact crater one-third its diameter, Herschel, situated on its leading hemisphere Mimas has no known past or present geologic activity and its surface is dominated by impact craters, though it does have a water ocean 20–30 km beneath the surface. The only tectonic features known are a few arcuate and linear troughs, which probably formed when Mimas was shattered by the Herschel impact.
Enceladus is one of the smallest of Saturn's moons that is spherical in shape—only Mimas is smaller—yet is the only small Saturnian moon that is currently endogenously active, and the smallest known body in the Solar System that is geologically active today. Its surface is morphologically diverse; it includes ancient heavily cratered terrain as well as younger smooth areas with few impact craters. Many plains on Enceladus are fractured and intersected by systems of lineaments. The area around its south pole was found by Cassini to be unusually warm and cut by a system of fractures about 130 km long called "tiger stripes", some of which emit jets of water vapor and dust. These jets form a large plume off its south pole, which replenishes Saturn's E ring and serves as the main source of ions in the magnetosphere of Saturn. The gas and dust are released with a rate of more than 100 kg/s. Enceladus may have liquid water underneath the south-polar surface. The source of the energy for this cryovolcanism is thought to be a 2:1 mean-motion resonance with Dione. The pure ice on the surface makes Enceladus one of the brightest known objects in the Solar System—its geometrical albedo is more than 140%.
Tethys is the third largest of Saturn's inner moons. Its most prominent features are a large (400 km diameter) impact crater named Odysseus on its leading hemisphere and a vast canyon system named Ithaca Chasma extending at least 270° around Tethys. The Ithaca Chasma is concentric with Odysseus, and these two features may be related. Tethys appears to have no current geological activity. A heavily cratered hilly terrain occupies the majority of its surface, while a smaller and smoother plains region lies on the hemisphere opposite to that of Odysseus. The plains contain fewer craters and are apparently younger. A sharp boundary separates them from the cratered terrain. There is also a system of extensional troughs radiating away from Odysseus. The density of Tethys (0.985 g/cm3) is less than that of water, indicating that it is made mainly of water ice with only a small fraction of rock.
Dione is the second-largest inner moon of Saturn. It has a higher density than the geologically dead Rhea, the largest inner moon, but lower than that of active Enceladus. While the majority of Dione's surface is heavily cratered old terrain, this moon is also covered with an extensive network of troughs and lineaments, indicating that in the past it had global tectonic activity. The troughs and lineaments are especially prominent on the trailing hemisphere, where several intersecting sets of fractures form what is called "wispy terrain". The cratered plains have a few large impact craters reaching 250 km in diameter. Smooth plains with low impact-crater counts are also present on a small fraction of its surface. They were probably tectonically resurfaced relatively later in the geological history of Dione. At two locations within smooth plains strange landforms (depressions) resembling oblong impact craters have been identified, both of which lie at the centers of radiating networks of cracks and troughs; these features may be cryovolcanic in origin. Dione may be geologically active even now, although on a scale much smaller than the cryovolcanism of Enceladus. This follows from Cassini magnetic measurements that show Dione is a net source of plasma in the magnetosphere of Saturn, much like Enceladus.
Alkyonides
Three small moons orbit between Mimas and Enceladus: Methone, Anthe, and Pallene. Named after the Alkyonides of Greek mythology, they are some of the smallest moons in the Saturn system. Anthe and Methone have very faint ring arcs along their orbits, whereas Pallene has a faint complete ring. Of these three moons, only Methone has been photographed at close range, showing it to be egg-shaped with very few or no craters.
Trojan
Trojan moons are a unique feature only known from the Saturnian system. A trojan body orbits at either the leading L4 or trailing L5 Lagrange point of a much larger object, such as a large moon or planet. Tethys has two trojan moons, Telesto (leading) and Calypso (trailing), and Dione also has two, Helene (leading) and Polydeuces (trailing). Helene is by far the largest trojan moon, while Polydeuces is the smallest and has the most chaotic orbit. These moons are coated with dusty material that has smoothed out their surfaces.
Outer large
These moons all orbit beyond the E Ring. They are:
Rhea is the second-largest of Saturn's moons. It is even slightly larger than Oberon, the second-largest moon of Uranus. In 2005, Cassini detected a depletion of electrons in the plasma wake of Rhea, which forms when the co-rotating plasma of Saturn's magnetosphere is absorbed by the moon. The depletion was hypothesized to be caused by the presence of dust-sized particles concentrated in a few faint equatorial rings. Such a ring system would make Rhea the only moon in the Solar System known to have rings. Subsequent targeted observations of the putative ring plane from several angles by Cassini'''s narrow-angle camera turned up no evidence of the expected ring material, leaving the origin of the plasma observations unresolved. Otherwise Rhea has rather a typical heavily cratered surface, with the exceptions of a few large Dione-type fractures (wispy terrain) on the trailing hemisphere and a very faint "line" of material at the equator that may have been deposited by material deorbiting from present or former rings. Rhea also has two very large impact basins on its anti-Saturnian hemisphere, which are about 400 and 500 km across. The first, Tirawa, is roughly comparable to the Odysseus basin on Tethys. There is also a 48 km-diameter impact crater called Inktomi at 112°W that is prominent because of an extended system of bright rays, which may be one of the youngest craters on the inner moons of Saturn. No evidence of any endogenic activity has been discovered on the surface of Rhea.
Titan, at 5,149 km diameter, is the second largest moon in the Solar System and Saturn's largest. Out of all the large moons, Titan is the only one with a dense (surface pressure of 1.5 atm), cold atmosphere, primarily made of nitrogen with a small fraction of methane. The dense atmosphere frequently produces bright white convective clouds, especially over the south pole region. On 6 June 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan. On 23 June 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times. The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters and is probably very young. It contains a pattern of light and dark regions, flow channels and possibly cryovolcanos. Some dark regions are covered by longitudinal dune fields shaped by tidal winds, where sand is made of frozen water or hydrocarbons. Titan is the only body in the Solar System beside Earth with bodies of liquid on its surface, in the form of methane–ethane lakes in Titan's north and south polar regions. The largest lake, Kraken Mare, is larger than the Caspian Sea. Like Europa and Ganymede, it is believed that Titan has a subsurface ocean made of water mixed with ammonia, which can erupt to the surface of the moon and lead to cryovolcanism. On 2 July 2014, NASA reported the ocean inside Titan may be "as salty as the Earth's Dead Sea".
Hyperion is Titan's nearest neighbor in the Saturn system. The two moons are locked in a 4:3 mean-motion resonance with each other, meaning that while Titan makes four revolutions around Saturn, Hyperion makes exactly three. With an average diameter of about 270 km, Hyperion is smaller and lighter than Mimas. It has an extremely irregular shape, and a very odd, tan-colored icy surface resembling a sponge, though its interior may be partially porous as well. The average density of about 0.55 g/cm3 indicates that the porosity exceeds 40% even assuming it has a purely icy composition. The surface of Hyperion is covered with numerous impact craters—those with diameters 2–10 km are especially abundant. It is the only moon besides the small moons of Pluto known to have a chaotic rotation, which means Hyperion has no well-defined poles or equator. While on short timescales the satellite approximately rotates around its long axis at a rate of 72–75° per day, on longer timescales its axis of rotation (spin vector) wanders chaotically across the sky. This makes the rotational behavior of Hyperion essentially unpredictable.
Iapetus is the third-largest of Saturn's moons. Orbiting the planet at km, it is by far the most distant of Saturn's large moons, and also has the largest orbital inclination, at 15.47°. Iapetus has long been known for its unusual two-toned surface; its leading hemisphere is pitch-black and its trailing hemisphere is almost as bright as fresh snow. Cassini images showed that the dark material is confined to a large near-equatorial area on the leading hemisphere called Cassini Regio, which extends approximately from 40°N to 40°S. The pole regions of Iapetus are as bright as its trailing hemisphere. Cassini also discovered a 20 km tall equatorial ridge, which spans nearly the moon's entire equator. Otherwise both dark and bright surfaces of Iapetus are old and heavily cratered. The images revealed at least four large impact basins with diameters from 380 to 550 km and numerous smaller impact craters. No evidence of any endogenic activity has been discovered. A clue to the origin of the dark material covering part of Iapetus's starkly dichromatic surface may have been found in 2009, when NASA's Spitzer Space Telescope discovered a vast, nearly invisible disk around Saturn, just inside the orbit of the moon Phoebe – the Phoebe ring. Scientists believe that the disk originates from dust and ice particles kicked up by impacts on Phoebe. Because the disk particles, like Phoebe itself, orbit in the opposite direction to Iapetus, Iapetus collides with them as they drift in the direction of Saturn, darkening its leading hemisphere slightly. Once a difference in albedo, and hence in average temperature, was established between different regions of Iapetus, a thermal runaway process of water ice sublimation from warmer regions and deposition of water vapor onto colder regions ensued. Iapetus's present two-toned appearance results from the contrast between the bright, primarily ice-coated areas and regions of dark lag, the residue left behind after the loss of surface ice.
Irregular
Irregular moons are small satellites with large-radii, inclined, and frequently retrograde orbits, believed to have been acquired by the parent planet through a capture process. They often occur as collisional families or groups. The precise size as well as albedo of the irregular moons are not known for sure because the moons are very small to be resolved by a telescope, although the latter is usually assumed to be quite low—around 6% (albedo of Phoebe) or less. The irregulars generally have featureless visible and near infrared spectra dominated by water absorption bands. They are neutral or moderately red in color—similar to C-type, P-type, or D-type asteroids, though they are much less red than Kuiper belt objects.
Inuit
The Inuit group includes thirteen prograde outer moons that are similar enough in their distances from the planet (190–300 radii of Saturn), their orbital inclinations (45–50°) and their colors that they can be considered a group. The Inuit group is further split into three distinct subgroups at different semi-major axes, and are named after their respective largest members. Ordered by increasing semi-major axis, these subgroups are the Kiviuq group, the Paaliaq group, and the Siarnaq group. The Kiviuq group includes five members: Kiviuq, Ijiraq, S/2005 S 4, S/2019 S 1, and S/2020 S 1. The Siarnaq group includes seven members: Siarnaq, Tarqeq, S/2004 S 31, S/2019 S 14, S/2020 S 3, S/2019 S 6, and S/2020 S 5. In contrast to the Kiviuq and Siarnaq subgroups, the Paaliaq subgroup does not contain any other known members besides Paaliaq itself. Of the entire Inuit group, Siarnaq is the largest member with an estimated size of about 39 km.
Gallic
The Gallic group includes seven prograde outer moons that are similar enough in their distance from the planet (200–300 radii of Saturn), their orbital inclination (35–40°) and their color that they can be considered a group. They are Albiorix, Bebhionn, Erriapus, Tarvos, Saturn LX, S/2007 S 8, and S/2020 S 4. The largest of these moons is Albiorix with an estimated diameter of about 29 km.
Norse
All 100 retrograde outer moons of Saturn are broadly classified into the Norse group. They are Aegir, Angrboda, Alvaldi, Beli, Bergelmir, Bestla, Eggther, Farbauti, Fenrir, Fornjot, Geirrod, Gerd, Greip, Gridr, Gunnlod, Hati, Hyrrokkin, Jarnsaxa, Kari, Loge, Mundilfari, Narvi, Phoebe, Skathi, Skoll, Skrymir, Surtur, Suttungr, Thiazzi, Thrymr, Ymir, and 69 unnamed satellites. After Phoebe, Ymir is the largest of the known retrograde irregular moons, with an estimated diameter of only 22 km.
Phoebe, at in diameter, is by far the largest of Saturn's irregular satellites. It has a retrograde orbit and rotates on its axis every 9.3 hours. Phoebe was the first moon of Saturn to be studied in detail by Cassini, in ; during this encounter Cassini was able to map nearly 90% of the moon's surface. Phoebe has a nearly spherical shape and a relatively high density of about 1.6 g/cm3. Cassini images revealed a dark surface scarred by numerous impacts—there are about 130 craters with diameters exceeding 10 km. Such impacts may have ejected fragments of Phoebe into orbit around Saturn—two of these may be S/2006 S 20 and S/2006 S 9, whose orbits are similar to Phoebe. Spectroscopic measurement showed that the surface is made of water ice, carbon dioxide, phyllosilicates, organics and possibly iron-bearing minerals. Phoebe is believed to be a captured centaur that originated in the Kuiper belt. It also serves as a source of material for the largest known ring of Saturn, which darkens the leading hemisphere of Iapetus (see above).
Outlier prograde satellites
Two prograde moons of Saturn do not definitively belong to either the Inuit or Gallic groups. S/2004 S 24 and S/2006 S 12 have similar orbital inclinations as the Gallic group, but have much more distant orbits with semi-major axes of ~400 Saturn radii and ~340 Saturn radii, respectively.
List
Confirmed
The Saturnian moons are listed here by orbital period (or semi-major axis), from shortest to longest. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in bold and marked with a blue background, while the irregular moons are listed in red, orange, green, and gray background. The orbits and mean distances of the irregular moons are strongly variable over short timescales due to frequent planetary and solar perturbations, so the orbital elements of irregular moons listed here are averaged over a 5,000-year numerical integration by the Jet Propulsion Laboratory. These may sometimes strongly differ from the osculating orbital elements provided by other sources. Their orbital elements are all based on a reference epoch of 1 January 2000.
Unconfirmed
These F Ring moonlets listed in the following table (observed by Cassini) have not been confirmed as solid bodies. It is not yet clear if these are real satellites or merely persistent clumps within the F Ring.
Spurious
Two moons were claimed to be discovered by different astronomers but never seen again. Both moons were said to orbit between Titan and Hyperion.
Chiron which was supposedly sighted by Hermann Goldschmidt in 1861, but never observed by anyone else.
Themis was allegedly discovered in 1905 by astronomer William Pickering, but never seen again. Nevertheless, it was included in numerous almanacs and astronomy books until the 1960s.
Hypothetical
In 2022, scientists of the Massachusetts Institute of Technology proposed the hypothetical former moon Chrysalis, using data from the Cassini–Huygens mission. Chrysalis would have orbited between Titan and Iapetus, but its orbit would have gradually become more eccentric until it was torn apart by Saturn. 99% of its mass would have been absorbed by Saturn, while the remaining 1% would have formed Saturn's rings.
Temporary
Much like Jupiter, asteroids and comets will infrequently make close approaches to Saturn, even more infrequently becoming captured into orbit of the planet. The comet P/2020 F1 (Leonard) is calculated to have made a close approach of km ( mi) to Saturn on 8 May 1936, closer than the orbit of Titan to the planet, with an orbital eccentricity of only . The comet may have been orbiting Saturn prior to this as a temporary satellite, but difficulty modelling the non-gravitational forces makes whether or not it was indeed a temporary satellite uncertain.
Other comets and asteroids may have temporarily orbited Saturn at some point, but none are presently known to have.
Formation
It is thought that the Saturnian system of Titan, mid-sized moons, and rings developed from a set-up closer to the Galilean moons of Jupiter, though the details are unclear. It has been proposed either that a second Titan-sized moon broke up, producing the rings and inner mid-sized moons, or that two large moons fused to form Titan, with the collision scattering icy debris that formed the mid-sized moons. On 23 June 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times. Studies based on Enceladus's tidal-based geologic activity and the lack of evidence of extensive past resonances in Tethys, Dione, and Rhea's orbits suggest that the moons up to and including Rhea may be only 100 million years old.
| Physical sciences | Solar System | Astronomy |
575890 | https://en.wikipedia.org/wiki/House%20mouse | House mouse | The house mouse (Mus musculus) is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus Mus. Although a wild animal, the house mouse has benefited significantly from associating with human habitation to the point that truly wild populations are significantly less common than the semi-tame populations near human activity.
The house mouse has been domesticated as the pet or fancy mouse, and as the laboratory mouse, which is one of the most important model organisms in biology and medicine. The complete mouse reference genome was sequenced in 2002.
Characteristics
House mice have an adult body length (nose to base of tail) of and a tail length of . The weight is typically . In the wild they vary in color from grey and light brown to black (individual hairs are actually agouti coloured), but domesticated fancy mice and laboratory mice are produced in many colors ranging from white to champagne to black. They have short hair and some, but not all, sub-species have a light belly. The ears and tail have little hair. The hind feet are short compared to Apodemus mice, only long; the normal gait is a run with a stride of about , though they can jump vertically up to . The voice is a high-pitched squeak. House mice thrive under a variety of conditions; they are found in and around homes and commercial structures, as well as in open fields and agricultural lands.
Newborn males and females can be distinguished on close examination as the anogenital distance in males is about double that of the female. From the age of about 10 days, females have five pairs of mammary glands and nipples; males have no nipples. When sexually mature, the most striking and obvious difference is the presence of testicles on the males. These are large compared to the rest of the body and can be retracted into the body.
The tail, which is used for balance, has only a thin covering of hair as it is the main peripheral organ of heat loss in thermoregulation along with—to a lesser extent—the hairless parts of the paws and ears. Blood flow to the tail can be precisely controlled in response to changes in ambient temperature using a system of arteriovenous anastomoses to increase the temperature of the skin on the tail by as much as to lose body heat. Tail length varies according to the environmental temperature of the mouse during postnatal development, so mice living in colder regions tend to have shorter tails. The tail is also used for balance when the mouse is climbing or running, or as a base when the animal stands on its hind legs (a behaviour known as tripoding), and to convey information about the dominance status of an individual in encounters with other mice.
In addition to the regular pea-sized thymus organ in the chest, house mice have a second functional pinhead-sized thymus organ in the neck next to the trachea.
Taxonomy and subspecies
Mice are mammals of the Glires clade, which means they are amongst the closest relatives of humans other than lagomorphs, treeshrews, flying lemurs and other primates.
The three widely accepted subspecies are increasingly treated as distinct species by some:
Southeastern Asian house mouse (Mus musculus castaneus) (southern and southeastern Asia)
Western European house mouse (Mus musculus domesticus); includes the fancy mouse and the laboratory mouse (Western Europe, North America, South America, Africa and Oceania)
Eastern European house mouse (Mus musculus musculus) (Eastern Europe and northern Asia)
Two additional subspecies have been recognized more recently:
Southwestern Asian house mouse (Mus musculus bactrianus) (southwestern and Central Asia). However, due to significant genetic similarity observed between (Mus musculus bactrianus) and Mus musculus castaneus, the subspecies designation for Mus musculus bactrianus has now been questioned.
pygmy house mouse (Mus musculus gentilulus) (the Arabian Peninsula and Madagascar)
Many more subspecies' names have been given to house mice, but these are now regarded as synonyms of the five subspecies. Some populations are hybrids of different subspecies, including the Japanese house mouse (M. m. molossinus). A notable region of hybridization is a region in general Europe where M. m. domesticus and M. m. musculus are often found to hybridize. However, male hybrid mice typically experience hybrid sterility, which maintains reproductive separation between the two subspecies.
Chromosomal races
The standard species karyotype is composed of 40 chromosomes. Within Western Europe there are numerous populations – chromosomal races – with a reduced chromosome count arising from Robertsonian fusion.
Evolution
Suzuki et al., 2013 confirms the theory that M. musculus originates in Southwestern Asia and identifies 5 subspecies and their origins: musculus in northern Eurasia, castaneus in India and Southeast Asia, a previously unknown subspecies from Nepal, domesticus in western Europe, and gentilulus in Yemen.
A recent study using 89 whole-genome sequences revealed that the modern day Mus musculus castaneus emerged from an ancestral Mus musculus population in Indian subcontinent some time around 700 kya. From there, this ancestral population migrated to Iran around 360 kya to form Mus musculus domesticus and then to Afghanistan around 260 kya to form Mus musculus musculus.
Behavior
House mice usually run, walk, or stand on all fours, but when eating, fighting, or orienting themselves, they rear up on their hind legs with additional support from the tail – a behavior known as "tripoding". Mice are good jumpers, climbers, and swimmers, and are generally considered to be thigmotactic, i.e. usually attempt to maintain contact with vertical surfaces.
Mice are mostly crepuscular or nocturnal; they are averse to bright lights. The average sleep time of a captive house mouse is reported to be 12.5 hours per day. They live in a wide variety of hidden places near food sources, and construct nests from various soft materials. Mice are territorial, and one dominant male usually lives together with several females and young mice. Dominant males respect each other's territories and normally enter another's territory only if it is vacant. If two or more males are housed together in a cage, they often become aggressive unless they have been raised together from birth.
House mice primarily feed on plant matter, but are omnivorous. They eat their own faeces to acquire nutrients produced by bacteria in their intestines. House mice, like most other rodents, do not vomit.
Mice are generally afraid of rats which often kill and eat them, a behavior known as muricide. Despite this, free-living populations of rats and mice do exist together in forest areas in New Zealand, North America, and elsewhere. House mice are generally poor competitors and in most areas cannot survive away from human settlements in areas where other small mammals, such as wood mice, are present. However, in some areas (such as Australia), mice are able to coexist with other small rodent species.
Social behavior
The social behavior of the house mouse is not rigidly fixed into species-specific patterns but is instead adaptable to the environmental conditions, such as the availability of food and space. This adaptability allows house mice to inhabit diverse areas ranging from sandy dunes to apartment buildings.
House mice have two forms of social behaviour, the expression of which depends on the environmental context. House mice in buildings and other urbanized areas with close proximity to humans are known as commensal. Commensal mice populations often have an excessive food source resulting in high population densities and small home ranges. This causes a switch from territorial behaviour to a hierarchy of individuals. When populations have an excess of food, there is less female-female aggression, which usually occurs to gain access to food or to prevent infanticide. Male-male aggression occurs in commensal populations, mainly to defend female mates and protect a small territory. The high level of male-male aggression, with a low female-female aggression level is common in polygamous populations. The social unit of commensal house mouse populations generally consists of one male and two or more females, usually related. These groups breed cooperatively, with the females communally nursing. This cooperative breeding and rearing by related females helps increase reproductive success. When no related females are present, breeding groups can form from non-related females.
In open areas such as shrubs and fields, the house mouse population is known as noncommensal. These populations are often limited by water or food supply and have large territories. Female-female aggression in the noncommensal house mouse populations is much higher, reaching a level generally attributed to free-ranging species. Male aggression is also higher in noncommensal populations. In commensal populations, males come into contact with other males quite frequently due to high population densities and aggression must be mediated or the risk of injury becomes too great.
Both commensal and noncommensal house mouse males aggressively defend their territory and act to exclude all intruders. Males mark their territory by scent marking with urine. In marked territories, intruders showed significantly lower aggression than the territory residents. House mice show a male-biased dispersal; males generally leave their birth sites and migrate to form new territories whereas females generally stay and are opportunistic breeders rather than seasonal.
Senses and communication
Vision
The visual apparatus of mice is basically similar to that of humans but differs in that they are dichromats and have only two types of cone cells whereas humans are trichromats and have three. This means that mice do not perceive some of the colors in the human visual spectrum. However, the ventral area of the mouse retina has a much greater density of ultraviolet-sensitive cones than other areas of the retina, although the biological significance of this structure is unknown. In 2007, mice genetically engineered to produce the third type of cone were shown to be able to distinguish a range of colors similar to that perceived by tetrachromats.
Olfaction
House mice also rely on pheromones for social communication, some of which are produced by the preputial glands of both sexes. The tear fluid and urine of male mice also contains pheromones, such as major urinary proteins. Mice detect pheromones mainly with the vomeronasal organ (Jacobson's organ), located at the bottom of the nose.
The urine of house mice, especially that of males, has a characteristic strong odor. At least 10 different compounds, such as alkanes, alcohols, etc., are detectable in the urine. Among them, five compounds are specific to males, namely 3-cyclohexene-1-methanol, aminotriazole (3-amino-s-triazole), 4-ethyl phenol, 3-ethyl-2,7-dimethyl octane and 1-iodoundecane.
Odours from adult males or from pregnant or lactating females can speed up or retard sexual maturation in juvenile females and synchronise reproductive cycles in mature females (i.e. the Whitten effect). Odours of unfamiliar male mice may terminate pregnancies, i.e. the Bruce effect.
Tactile
Mice can sense surfaces and air movements with their whiskers which are also used during thigmotaxis. If mice are blind from birth, super-normal growth of the vibrissae occurs presumably as a compensatory response. Conversely, if the vibrissae are absent, the use of vision is intensified.
Life cycle and reproduction
Female house mice have an estrous cycle about four to six days long, with estrus itself lasting less than a day. If several females are held together under crowded conditions, they will often not have an estrus at all. If they are then exposed to male urine, they will come into estrus after 72 hours.
Male house mice court females by emitting characteristic ultrasonic calls in the 30 kHz–110 kHz range. The calls are most frequent during courtship when the male is sniffing and following the female; however, the calls continue after mating has begun, at which time the calls are coincident with mounting behaviour. Males can be induced to emit these calls by female pheromones. The vocalizations appear to differ between individuals and have been compared to bird songs because of their complexity. While females have the capability to produce ultrasonic calls, they typically do not do so during mating behaviour.
Following copulation, female mice will normally develop a mating plug which prevents further copulation. The plug is not necessary for pregnancy initiation, as this will also occur without the plug. The presence or absence of the plug will not affect litter size either. This plug stays in place for some 24 hours. The gestation period is about 19–21 days, and they give birth to a litter of 3–14 young (average six to eight). One female can have 5 to 10 litters per year, so the mouse population can increase very quickly. Breeding occurs throughout the year. (However, animals living in the wild do not reproduce in the colder months, even though they do not hibernate.)
The pups are born blind and without fur or ears. The ears are fully developed by the fourth day, fur begins to appear at about six days and the eyes open around 13 days after birth; the pups are weaned at around 21 days. Females reach sexual maturity at about six weeks of age and males at about eight weeks, but both can copulate as early as five weeks.
Polygamy
Although house mice can be either monogamous or polygamous, they are most commonly polygamous. They generally show characteristics of mate-defense polygyny in that males are highly territorial and protective of their mates, while females are less agonistic. The communal nursing groups that result from these behaviors lead to lower numbers of infanticide since more females are able to protect greater numbers of offspring.
Evolutionary and behavioural consequences
Both evolutionary and behavioral consequences result from the polygamous nature of the house mouse. One consequence is the paternal investment, which is lower in polygamous mice than in mice that are monogamous. This occurs due to the fact that males spend more time involved in sexual competition than do females, leaving less time for paternal care. Polygamous male house mice spend less time alone with pups. They are also less likely and slower to retrieve lost pups than males of monogamous mice. In contrast, the maternal investment is similar between female mice that have mated once versus multiply.
The polygamous behavior of female house mice promotes sperm competition, which affects both male and female evolutionary fitness. Females who mate with multiple males tend to produce both pups in greater numbers, and with higher survival rates, increasing female fitness. Sperm competition that arises from polygamy favors males with faster, more motile sperm in higher numbers, increasing male fitness. The competitive aspect of insemination increases the frequency of polyandrous events and fertilizations. Polyandry has evolved to increase reproductive success. Male mating behavior is also affected in response to the practice of polygamous behavior. Compared to monogamous house mice, polygamous house mice mate for longer periods of time. This behaviour allows for an increase in both the transfer of sperm and paternity success, which in turn increases male fitness.
Polyandry
As opposed to polygyny, polyandrous behavior in females is the act of breeding with several males in the same season. Variation in number of males that females mate with occurs among a population. Polyandrous behavior is a common mating pattern in the subspecies Mus musculus musculus as well as its relative Mus musculus domesticus.
Polyandry occurs in 30% of all wild populations of house mice. Litters from multiple sires tend to be more genetically diverse than litters of single sires. Multiple paternity is also more common in larger populations than smaller populations, because there is a larger number of mates and more diverse mates to choose from. Within a population, males and females show different levels of multiple mating. Females show bias toward unrelated males rather than related males during sexual selection, resulting in more genetically diverse offspring and a reduction of inbreeding depression. Inbreeding depression increases genetic incompatibilities, levels of homozygosity, and the chance of expression of deleterious recessive alleles. Polyandry has been shown to increase offspring survival compared to monandry.
Evolutionary consequences
The fitness of females increases in polyandrous lines due to more genetic diversity and greater litter size.
Due to polyandry, males can be confused by the identity of new offspring. Multiple mating by females and paternity confusion can decrease rates of infanticide. If the males are uncertain if the offspring are theirs, they are less likely to kill the offspring.
Intrauterine insemination causes an evolutionary consequence resulting from polyandrous behavior. When multiple males mate with one female, there are multiple sets of sperm gametes in a female mouse. Offspring fertilized by multiple males can compete more strongly for mother's resources and can lead to a decrease in body size and variation in body size.
Inbreeding avoidance
Since inbreeding is detrimental, it tends to be avoided. In the house mouse, the major urinary protein (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie kin recognition and inbreeding avoidance. Thus there are fewer matings between mice sharing MUP haplotypes than would be expected if there were random mating. Another mechanism for avoiding inbreeding is evident when a female house mouse mates with multiple males. In such a case, there appears to be egg-driven sperm selection against sperm from related males.
Genetics
A region of mouse chromosome 16 is associated with thyroid function in mice. However, mice with a knockout of 16 genes - 550kb - in this region produced a normal phenotype, excluding these genes in particular from the dysfunction being pursued in that study.
Life expectancy
House mice usually live less than one year in the wild, due to a high level of predation and exposure to harsh environments. In protected environments, however, they often live two to three years. The Methuselah Mouse Prize is a competition to breed or engineer extremely long-lived laboratory mice. , the record holder was a genetically engineered mouse that lived for 1,819 days (7 days short of 5 years). Another record holder that was kept in an enriched environment but did not receive any genetic, pharmacological, or dietary treatment lived for 1,551 days ().
Aging
In several different mouse strains, a significant increase was observed with age in 8-Oxo-2'-deoxyguanosine (8-oxo-dG) levels in nuclear DNA from liver, heart, brain, kidney, skeletal muscle and spleen. This increase in DNA damage was attributed to an age related increase in the sensitivity of these tissues to oxidative stress. Dietary restriction is known to increase the lifespan of rodents and to retard aging. Dietary restriction was found to significantly reduce the age-related accumulation of 8-oxo-dG levels in nuclear DNA of all tissues studied in mice. Thus it was suggested that oxidative DNA damages that arise from normal cellular metabolism could be highly relevant to aging and the diseases of aging. In another study, two types of DNA damage (8-hydroxy-2’-deoxyguanosine and DNA-protein crosslinks) were found to increase with age in mouse brain and liver.
Mice and humans
History
House mice usually live in proximity to humans, in or around houses or fields. They are native to India, and later they spread to the eastern Mediterranean about 13,000 BC, only spreading into the rest of Europe around 1000 BC. This time lag is thought to be because the mice require agrarian human settlements above a certain size. The house mouse first arrived in the Americas in the early sixteenth century. It was carried aboard on the ships of Spanish explorers and Conquistadors. About one hundred years later, it arrived in North America with French fur traders and English colonists. They have since been spread to all parts of the globe by humans.
Many studies have been done on mouse phylogenies to reconstruct early human movements. For example, one study suggests the possibility of a previously unsuspected early link between Northern Europe and Madeira on the basis of the origin of Madeiran mice. House mice were thought to be the primary reason for the domestication of cats.
As pets
The first written reference to mice kept as pets occurs in the Erya, the oldest extant Chinese dictionary, from a mention in an 1100 BC version. Human domestication led to numerous strains of "fancy" or hobby mice with a variety of colours and a docile temperament. Domestic varieties of the house mouse are bred as a food source for some carnivorous pet reptiles, birds, arthropods, and fish. The effects of domestication can be rapid, with captive-reared mice differing in boldness and activity patterns compared to wild-caught mice after 4–5 generations in recent research.
Mice as pests
Mice are widespread pest organisms, and one of the most common rodents to infest human buildings. They commonly forage outdoors during the spring and summer, but retreat into buildings through the autumn and winter to seek warmth and food. They typically feed on unattended food, leftovers and garden produce. Their foraging risks the contamination and degradation of food supplies, and can also spread other pests such as fleas, ticks, lice and mites.
When infesting homes, house mice may pose a risk of damaging and compromising the structure of furniture and the building itself. They gnaw various materials to file down their growing teeth and keep the length under control. Common damage includes gnawed electrical wires, marks on wooden furniture and construction supporting elements, and textile damage.
Mice and diseases
House mice can sometimes transmit diseases, contaminate food, and damage food packaging. Although the Centers for Disease Control and Prevention provides a list with diseases transmitted by rodents, only a few of the diseases are transmitted through the house mouse.
Lymphocytic choriomeningitis (LCMV) can be transmitted by mice, but is not a commonly reported infection in humans, though most infections are mild and are often never diagnosed. Some concern exists that women should not be infected with LCMV during pregnancy.
House mice are not usually a vector of human plague (bubonic plague) because they have fewer infestations with fleas than do rats, and because the fleas which house mice normally carry exhibit little tendency to bite humans rather than their natural host.
Rickettsialpox, caused by the bacterium Rickettsia akari and similar to chickenpox, is spread by mice in general, but is very rare and generally mild and resolves within two or three weeks if untreated. No known deaths have resulted from the disease. Murine typhus (also called endemic typhus), caused by the bacterium Rickettsia typhi, is transmitted by the fleas that infest rats. While rat fleas are the most common vectors, cat fleas and mouse fleas are less common modes of transmission. Endemic typhus is highly treatable with antibiotics. The U.S. CDC currently does not mention rickettsialpox or murine typhus on its website about diseases directly transmitted by rodents (in general).
Leptospirosis is carried by a variety of wild and domestic animals including dogs, rats, swine, cattle, mice in general, and can be transmitted by the urine of an infected animal and is contagious as long as the urine is still moist.
In Central Europe, the Dobriva sequence of hantavirus has been found in house mice. This is the most serious type of hanta that can infect humans.
Invasive species
Mice have become an invasive species on islands to where they have spread during the period of European exploration and colonisation.
New Zealand had no land mammals other than two species of bat prior to human occupation, and the house mouse is one of many species that have been introduced. Mice are responsible for a reduction in native bird species since they eat some of the same foods as birds. They are also known to kill lizards and have a large effect on native insects.
Gough Island in the South Atlantic is used by 20 species of seabirds for breeding, including almost all of the world's Tristan albatross (Diomedea dabbenena) and Atlantic petrel (Pterodroma incerta). Until house mice arrived on the island in the 19th century with sailors, the birds did not have any mammalian predators. The mice have since grown unusually large and have learned to attack albatross chicks, which can be 90 cm tall, but are largely immobile, by working in groups and gnawing on them until they bleed to death.
In the grain belt of southeastern Australia, the introduced subspecies Mus musculus domesticus breed so successfully, every three years or so they reach plague proportions, achieving densities of 1000 per hectare and causing massive disruption to communities, and losses to agriculture of A$36 million annually.
As a model organism
Mice are the most commonly used mammalian laboratory animal, due to their relatively close relationship, and associated high homology, with humans, their ease in maintenance and handling, and their high rate of reproduction. Laboratory mice typically belong to standardized inbred strains selected for the stability or clarity of specific harmful mutations. This allows research with laboratory mice to easily restrict genetic and biological variables, making them very useful model organisms in genetic and medicinal research. Mice have been used in scientific research since the 1650s.
In folk culture
Importance of mice as a house and agricultural pest resulted in a development of a variety of mouse-related rituals and stories in world's cultures. The Ancient Egyptians had a story about "The mouse as vizier".
Many South Slavs had a traditional annual "Mouse Day" celebration. In the eastern Balkans (most of Bulgaria, North Macedonia, the Torlak districts of Serbia), the "Mouse Day" () was celebrated on October 9 of the Julian calendar (corresponds to October 27 of the Gregorian calendar in the 20th and 21st centuries), the next day after the feast of Saint Demetrius. In the western Balkans (Bosnia, Croatia), the Mouse Day would usually be celebrated in the spring, during the Maslenitsa week or early in the Lent.
| Biology and health sciences | Rodents | Animals |
576108 | https://en.wikipedia.org/wiki/Parametric%20equation | Parametric equation | In mathematics, a parametric equation expresses several quantities, such as the coordinates of a point, as functions of one or several variables called parameters.
In the case of a single parameter, parametric equations are commonly used to express the trajectory of a moving point, in which case, the parameter is often, but not necessarily, time, and the point describes a curve, called a parametric curve. In the case of two parameters, the point describes a surface, called a parametric surface. In all cases, the equations are collectively called a parametric representation, or parametric system, or parameterization (alternatively spelled as parametrisation) of the object.
For example, the equations
form a parametric representation of the unit circle, where is the parameter: A point is on the unit circle if and only if there is a value of such that these two equations generate that point. Sometimes the parametric equations for the individual scalar output variables are combined into a single parametric equation in vectors:
Parametric representations are generally nonunique (see the "Examples in two dimensions" section below), so the same quantities may be expressed by a number of different parameterizations.
In addition to curves and surfaces, parametric equations can describe manifolds and algebraic varieties of higher dimension, with the number of parameters being equal to the dimension of the manifold or variety, and the number of equations being equal to the dimension of the space in which the manifold or variety is considered (for curves the dimension is one and one parameter is used, for surfaces dimension two and two parameters, etc.).
Parametric equations are commonly used in kinematics, where the trajectory of an object is represented by equations depending on time as the parameter. Because of this application, a single parameter is often labeled ; however, parameters can represent other physical quantities (such as geometric variables) or can be selected arbitrarily for convenience. Parameterizations are non-unique; more than one set of parametric equations can specify the same curve.
Implicitization
Converting a set of parametric equations to a single implicit equation involves eliminating the variable from the simultaneous equations This process is called . If one of these equations can be solved for , the expression obtained can be substituted into the other equation to obtain an equation involving and only: Solving to obtain and using this in gives the explicit equation while more complicated cases will give an implicit equation of the form
If the parametrization is given by rational functions
where , , and are set-wise coprime polynomials, a resultant computation allows one to implicitize. More precisely, the implicit equation is the resultant with respect to of and .
In higher dimensions (either more than two coordinates or more than one parameter), the implicitization of rational parametric equations may by done with Gröbner basis computation; see .
To take the example of the circle of radius , the parametric equations
can be implicitized in terms of and by way of the Pythagorean trigonometric identity. With
and
we get
and thus
which is the standard equation of a circle centered at the origin.
Parametric plane curves
Parabola
The simplest equation for a parabola,
can be (trivially) parameterized by using a free parameter , and setting
Explicit equations
More generally, any curve given by an explicit equation
can be (trivially) parameterized by using a free parameter , and setting
Circle
A more sophisticated example is the following. Consider the unit circle which is described by the ordinary (Cartesian) equation
This equation can be parameterized as follows:
With the Cartesian equation it is easier to check whether a point lies on the circle or not. With the parametric version it is easier to obtain points on a plot.
In some contexts, parametric equations involving only rational functions (that is fractions of two polynomials) are preferred, if they exist. In the case of the circle, such a is
With this pair of parametric equations, the point is not represented by a real value of , but by the limit of and when tends to infinity.
Ellipse
An ellipse in canonical position (center at origin, major axis along the -axis) with semi-axes and can be represented parametrically as
An ellipse in general position can be expressed as
as the parameter varies from to . Here is the center of the ellipse, and is the angle between the -axis and the major axis of the ellipse.
Both parameterizations may be made rational by using the tangent half-angle formula and setting
Lissajous curve
A Lissajous curve is similar to an ellipse, but the and sinusoids are not in phase. In canonical position, a Lissajous curve is given by
where and are constants describing the number of lobes of the figure.
Hyperbola
An east-west opening hyperbola can be represented parametrically by
or, rationally
A north-south opening hyperbola can be represented parametrically as
or, rationally
In all these formulae are the center coordinates of the hyperbola, is the length of the semi-major axis, and is the length of the semi-minor axis. Note that in the rational forms of these formulae, the points and , respectively, are not represented by a real value of , but are the limit of and as tends to infinity.
Hypotrochoid
A hypotrochoid is a curve traced by a point attached to a circle of radius rolling around the inside of a fixed circle of radius , where the point is at a distance from the center of the interior circle.
The parametric equations for the hypotrochoids are:
Some examples:
Parametric space curves
Helix
Parametric equations are convenient for describing curves in higher-dimensional spaces. For example:
describes a three-dimensional curve, the helix, with a radius of and rising by units per turn. The equations are identical in the plane to those for a circle.
Such expressions as the one above are commonly written as
where is a three-dimensional vector.
Parametric surfaces
A torus with major radius and minor radius may be defined parametrically as
where the two parameters and both vary between and .
As varies from to the point on the surface moves about a short circle passing through the hole in the torus. As varies from to the point on the surface moves about a long circle around the hole in the torus.
Straight line
The parametric equation of the line through the point and parallel to the vector is
Applications
Kinematics
In kinematics, objects' paths through space are commonly described as parametric curves, with each spatial coordinate depending explicitly on an independent parameter (usually time). Used in this way, the set of parametric equations for the object's coordinates collectively constitute a vector-valued function for position. Such parametric curves can then be integrated and differentiated termwise. Thus, if a particle's position is described parametrically as
then its velocity can be found as
and its acceleration as
Computer-aided design
Another important use of parametric equations is in the field of computer-aided design (CAD). For example, consider the following three representations, all of which are commonly used to describe planar curves.
Each representation has advantages and drawbacks for CAD applications.
The explicit representation may be very complicated, or even may not exist. Moreover, it does not behave well under geometric transformations, and in particular under rotations. On the other hand, as a parametric equation and an implicit equation may easily be deduced from an explicit representation, when a simple explicit representation exists, it has the advantages of both other representations.
Implicit representations may make it difficult to generate points on the curve, and even to decide whether there are real points. On the other hand, they are well suited for deciding whether a given point is on a curve, or whether it is inside or outside of a closed curve.
Such decisions may be difficult with a parametric representation, but parametric representations are best suited for generating points on a curve, and for plotting it.
Integer geometry
Numerous problems in integer geometry can be solved using parametric equations. A classical such solution is Euclid's parametrization of right triangles such that the lengths of their sides and their hypotenuse are coprime integers. As and are not both even (otherwise and would not be coprime), one may exchange them to have even, and the parameterization is then
where the parameters and are positive coprime integers that are not both odd.
By multiplying and by an arbitrary positive integer, one gets a parametrization of all right triangles whose three sides have integer lengths.
Underdetermined linear systems
A system of linear equations in unknowns is underdetermined if it has more than one solution. This occurs when the matrix of the system and its augmented matrix have the same rank and . In this case, one can select unknowns as parameters and represent all solutions as a parametric equation where all unknowns are expressed as linear combinations of the selected ones. That is, if the unknowns are one can reorder them for expressing the solutions as
Such a parametric equation is called a of the solution of the system.
The standard method for computing a parametric form of the solution is to use Gaussian elimination for computing a reduced row echelon form of the augmented matrix. Then the unknowns that can be used as parameters are the ones that correspond to columns not containing any leading entry (that is the left most non zero entry in a row or the matrix), and the parametric form can be straightforwardly deduced.
| Mathematics | Basics | null |
576193 | https://en.wikipedia.org/wiki/Squat%20toilet | Squat toilet | A squat toilet (or squatting toilet) is a toilet used by squatting, rather than sitting. This means that the posture for defecation and for female urination is to place one foot on each side of the toilet drain or hole and to squat over it. There are several types of squat toilets, but they all consist essentially of a toilet pan or bowl at floor level. Such a toilet pan is also called a "squatting pan". A squat toilet may use a water seal and therefore be a flush toilet, or it can be without a water seal and therefore be a dry toilet. The term "squat" refers only to the expected defecation posture and not any other aspects of toilet technology, such as whether it is water flushed or not.
Squat toilets are used all over the world, but are particularly common in some Asian and African nations, as well as in some Muslim countries. In many of those countries, anal cleansing with water is also the cultural norm and easier to perform than with toilets used in a sitting position. They are also occasionally found in some European and South American countries.
Squat toilets are regarded as traditional by many. In 1976, squatting toilets were said to be used by the majority of the world's population. However, there is a general trend in many countries to move from squatting toilets to sitting toilets (particularly in urban areas) as the latter are often regarded as more modern.
Design
Squat toilets are arranged at floor level, which requires the individual to squat with bent knees. In contrast to a pedestal or a sitting toilet, the opening of the drain pipe is located at the ground level.
Squatting slabs can be made of porcelain (ceramic), stainless steel, fibreglass, or in the case of low-cost versions in developing countries, with concrete, ferrocement, plastic, or wood covered with linoleum. Slabs can also be made of wood (timber), but need to be treated with preservatives, such as paint or linoleum, to prevent rotting and to enable thorough cleaning of the squatting slab.
There are two design variations: one where the toilet is level with the ground, and the other where it is raised on a platform approximately 30 cm (1 ft). The latter is easier to use for people who urinate while standing, but both types can be used for this purpose. There is also no difference for defecation or squatting urination.
Use
The user stands over the squat toilet facing the hood and pulls down (up in the case of skirts or dress) their trousers and underwear to the knees. The user then squats over the hole, as close to the front as possible, as excrement tends to fall onto the rear edge of the in-floor receptacle if the user squats too far back.
Health, hygiene and maintenance
The standing surface of the squatting pan should be kept clean and dry in order to prevent disease transmission and to limit odors.
Squat toilets are usually easier to clean than sitting toilets (pedestals), except that one has to bend down further if the squatting pan needs manual scrubbing. Squat toilets are properly cleaned using a mop in combination with a detergent solution.
Health effects
The squatting defecation posture is more physiological, ideal and relaxed. This is because it allows for better relaxation of the puborectalis muscle and hence straightening of the anorectal angle, and for faster, easier and more complete evacuation of stool. The squatting position therefore prevents excessive straining, and hence protects against stretching of the nerves, such as the pudendal nerve. Damage of these nerves can lead to permanent problems with urinary, defecation and sexual function. The squatting position also increases intra-abdominal pressure. The squatting position is often recommended as part of a range of measures to manage constipation and its sub-types, including obstructed defecation syndrome and dyssynergic defecation. Chronic, excessive straining during defecation, which is more likely to be needed in the sitting position, may be associated with the development of inflamed hemorrhoids or any of the spectrum of pelvic organ prolapse disorders, such as rectocele, rectal prolapse, etc.
However, according to some sources, excessive straining in the squatting position while defecating may increase the risk of severe hemorrhoids, or increase the tendency of prolapse of hemorrhoids, because of increased perineal descent and intra-abdominal pressure. Prolonged and repeated straining on a sitting toilet has the same effect.
Society and culture
Perceptions and trends
There are two different attitudes towards squat toilets, largely dependent on what users are used to, or whether the toilet is at a public or private place:
Some people regard squat toilets as more hygienic compared to sitting toilets. They might be easier to clean and there is no skin contact with the surface of the toilet seat. For that reason, some people perceive them as more hygienic, particularly for public toilets.
Some people regard sitting toilets as "more modern" than squat toilets. Sitting toilets have a lower risk of soiling clothing or shoes, as urine is less likely to splash on bottom parts of trousers or shoes. Furthermore, sitting toilets are more convenient for people with disabilities and the elderly.
A trend towards more sitting toilets in countries that were traditionally using squat toilets can be observed in some urban and more affluent areas, in areas with new buildings (as well as hotels and airports) or in tourist regions.
Public toilets
Squat toilets are used in public toilets, rather than household toilets, because they are perceived by some as easier to clean and more hygienic, therefore potentially more appropriate for general public use. For instance, this is the case in parts of France, Italy, Greece, or the Balkans, where such toilets are somewhat common in public toilets (restrooms).
Preferences by country or region
The following general statements can be made:
Squat toilets are common in many Asian countries, including China and India. They are also widespread in Turkey (), Nepal, Indonesia, Bangladesh, Pakistan, Sri Lanka, Malaysia, Myanmar, The Philippines, Iran and Iraq. They can be found in nations like Japan, South Korea, Thailand, and Singapore.
People in sub-Saharan African countries, especially in rural areas, widely use squat toilets, for example in Kenya, Rwanda, Somalia, Tanzania, and Uganda. Squat toilets are not common in South Africa.
Much of the world's population use squat toilets, especially in rural areas of developing countries.
Countries in the Middle East and North Africa often have both types of toilets, i.e. sitting and squatting.
In Hindu or Muslim cultures, the prevalence of squat toilets is generally quite high, as is the practice of anal cleansing with water.
In Latin and South America, flush toilets are always of the sitting type, whereas dry toilets may be either of the sitting or a squatting type. The occurrence of squat toilets in urban areas of Latin America appears to be rather low.
Squat toilets are rare in Australia, New Zealand, United States, Canada, and countries in Northern and Western Europe (except public toilets in France). Where they do exist, they have usually been installed to accommodate visitors, tourists, students, or recent migrants from places that use squatting toilets traditionally.
Europe
In Southern and Eastern Europe including parts of France, in Turkey, Greece, Italy, Albania, Balkans, and Russia they are common, especially in public toilets. Squat pit latrine toilets are still present in many areas of Russia.
Squat toilets are generally non-existent in Northern and Western Europe. France and Italy are an exception and have some squat toilets remaining in old buildings and public toilets because they used to be the norm there in the early 20th century. In BMW Welt in Munich, the public restrooms have some stalls with squat toilets. There are also a few squat toilets at Stuttgart Airport.
China
Many areas in China have traditional squat toilets instead of sitting toilets, especially in public toilets. Nevertheless, sitting toilets have increasingly become the norm in major urban areas and cities. Sitting toilets are on the one hand associated with development and modernization, and on the other hand with reduced hygiene and possible transmission of diseases.
Japan
Although in Japan it is believed that the squat toilet is traditional, the trend in Japan is to move away from squat toilets: According to Toto, one of Japan's major toilet manufacturers, the production of Western-style toilets increased rapidly since 1976. In 2015, only 1% of all toilets produced by this company were squat toilets.
Since the 1960s, the trend has been to replace squat toilets at schools and public places with sitting toilets. This trend was thought to accelerate in the run-up to the 2020 Summer Olympics in Tokyo.
Since the 1980s, high-tech sitting toilets are emerging that replace traditional squat toilets, especially in urban areas. However, many rural people have no experience with such high-tech toilets and need detailed instructions. High-tech sitting toilets have also become commonplace in South Korea.
Gallery
| Technology | Hydraulics and pneumatics | null |
576200 | https://en.wikipedia.org/wiki/Philodendron | Philodendron | Philodendron is a large genus of flowering plants in the family Araceae. , the Plants of the World Online accepted 621 species; other sources accept different numbers. Regardless of number of species, the genus is the second-largest member of the family Araceae, after genus Anthurium. Taxonomically, the genus Philodendron is still poorly known, with many undescribed species. Many are grown as ornamental and indoor plants. The name derives from the Greek words philo- 'love, affection' and dendron 'tree'. The generic name, Philodendron, is often used as the English name.
Description
Growth habit
Compared to other genera of the family Araceae, philodendrons have an extremely diverse array of growth methods. The habits of growth can be epiphytic, hemiepiphytic, or rarely terrestrial. Others can show a combination of these growth habits depending on the environment. Hemiepiphytic philodendrons can be classified into two types: primary and secondary hemiepiphytes. A primary hemiepiphytic philodendron starts life high up in the canopy where the seed initially sprouts. The plant then grows as an epiphyte. Once it has reached a sufficient size and age, it will begin producing aerial roots that grow toward the forest floor. Once they reach the forest floor, nutrients can be obtained directly from the soil. In this manner, the plant's strategy is to obtain light early in its life at the expense of nutrients. Some primary epiphytic species have a symbiotic relationship with ants. In these species, the ants' nest is grown amongst the plant's roots, which help keep the nest together. Philodendrons have extrafloral nectaries, glands that secrete nectar to attract the ants. The philodendron, in turn, obtains nutrients from the surrounding ant nest, and the aggressive nature of the ants serves to protect the plant from other insects which would eat it.
Secondary hemiepiphytes start life on the ground or on part of a tree trunk very close to the ground, where the seeds sprout. These philodendrons have their roots in the ground early in their lives. They then begin climbing up a tree and eventually may become completely epiphytic, doing away with their subterranean roots. Secondary hemiepiphytes do not always start their lives close to a tree. For these philodendrons, the plant will grow with long internodes along the ground until a tree is found. They find a suitable tree by growing towards darker areas, such as the dark shadow of a tree. This trait is called scototropism. After a tree has been found, the scototropic behavior stops and the philodendron switches to a phototropic growth habit and the internodes shorten and thicken. Usually, however, philodendrons germinate on trees.
A few species show three peaks in temperature during flowering, which stimulates beetles within the spathe and increasing the likelihood they will be sufficiently coated with pollen. A sticky resin is also produced in drops attached to the spadix which help to keep the pollen attached to the beetles. This resin producing quality is unique to Philodendron and Monstera, as other genera of Araceae do not produce it on their spadices. The resin is also found on the stems, leaves, and roots of philodendrons. Its color can be red, orange, yellow, or colorless when it is first produced. Yet, over time, it will turn brown as it is exposed to air. Also, some evidence suggests the thermogenesis triggers the beetles to mate. It also appears to distribute the pheromones into the air. The reason for the spadix being held at 45° relative to the spathe may be to maximize the heat's ability to waft the pheromones into the air. Oxidizing stored carbohydrates and lipids has been found to be the energy source for thermogenesis. The part of the spadix that heats up is the sterile zone. As it heats up, carbohydrates are used, but once the spadix has reached its maximum temperature, lipids are oxidized. The lipids are not first converted to carbohydrates, but rather are directly oxidized. The thermogenic reaction is triggered when concentrations of acetosalicytic acid form in the sterile zone. The acid sets off the mitochondria in the cells that make up the sterile zone to switch to an electron transport chain called the cyanide-resistant pathway, which results in the production of heat. Philodendrons consume oxygen during thermogenesis. The rate at which oxygen is used is remarkably high, close to that of hummingbirds and sphinx moths. The spadix has been shown to generate infrared radiation.
Leaves
The leaves are usually large and imposing, often lobed or deeply cut, and may be more or less pinnate. They can also be oval (Philodendron 'White Princess'), spear-shaped, divided (Philodendron tripartitum) or in many other possible shape variations. The leaves are borne alternately on the stem. A quality of philodendrons is that they do not have a single type of leaf on the same plant. Instead, they have juvenile leaves and adult leaves, which can be drastically different from one another. The leaves of seedling philodendrons are usually heart-shaped early in the life of the plant. But after it has matured past the seedling stage, the leaves will acquire the typical juvenile leaf's shape and size. Later in the philodendron's life, it starts producing adult leaves, a process called metamorphosis. Most philodendrons go through metamorphosis gradually; there is no immediately distinct difference between juvenile and adult leaves. Aside from being typically much bigger than the juvenile leaves, the shape of adult leaves can be significantly different. In fact, considerable taxonomic difficulty has occurred in the past due to these differences, causing juvenile and adult plants to mistakenly be classified as different species.
The trigger for the transformation to adult leaves can vary considerably. One possible trigger is the height of the plant. Secondary hemiepiphytes start off on the dark forest floor and climb their way up a tree, displaying their juvenile type leaves along the way. Once they reach a sufficient height, they begin developing adult type leaves. The smaller juvenile leaves are used for the darker forest floor where light is in scarce supply, but once they reach a sufficient height in the canopy the light is bright enough that the bigger adult leaves can serve a useful purpose. Another possible trigger occurs in primary hemiepiphytes. These philodendrons typically send their aerial roots downward. Once their roots have reached the ground below, the plant will begin taking up nutrients from the soil, of which it had been previously deprived. As a result, the plant will quickly morph into its adult leaves and gain in size dramatically. Another quality of philodendrons leaves is they are often quite different in shape and size even between two plants of the same species. As a result of all these different possible leaf shapes, it is often difficult to differentiate natural variations from morphogenesis.
Cataphylls
Philodendrons also produce cataphylls, which are modified leaves that surround and protect the newly forming leaves. Cataphylls are usually green, leaf-like, and rigid while they are protecting the leaf. In some species, they can even be rather succulent. Once the leaf has been fully formed, the cataphyll usually remains attached where the stem and base of the leaf meet. In philodendrons, cataphylls typically fall into two categories: deciduous and persistent types. A deciduous cataphyll curls away from the leaf once it has formed, eventually turning brown and drying out, and finally falling off the plant, leaving a scar on the stem where it was attached. Deciduous cataphylls are typically found on vining philodendrons, whereas persistent cataphylls are typical of epiphytic philodendrons or appressed climbers. In the latter, the cataphylls are prevented from falling off in a timely manner due to the short internodes of the plant. The cataphylls will remain attached, drying out and becoming nothing more than fibers attached at the nodes. In some philodendrons, the cataphylls build up over time and eventually form a wet mass at the nodes. This may keep emerging roots moist and provide some form of lubrication to new leaves.
Roots
Philodendrons have both aerial and subterranean roots. The aerial roots occur in many shapes and sizes and originate from most of the plant's nodes or occasionally from an internode. The size and number of aerial roots per node depends on the presence of a suitable substrate for the roots to attach themselves. Aerial roots serve two primary purposes. They allow the philodendron to attach itself to a tree or other plant, and they allow it to collect water and nutrients. As such, the roots are divided morphologically into these two categories. Aerial roots used for attaching to trees tend to be shorter, more numerous, and sometimes have a layer of root hairs attached; those used for collecting water and nutrients tend to be thicker and longer. These feeder roots tend to attach flush with the substrate to which the philodendron is attached, and make their way directly downwards in search of soil. In general, feeder roots tend to show both positive hydrotropic and negative heliotropic behaviors. Characteristic of roots in philodendrons is the presence of a sclerotic hypodermis, which are cylindrical tubes inside the epidermis that can be one to five cells long. The cells that line the sclerotic hypodermis are elongated and tend to be hardened. Underneath the epidermis is a unique layer of cells in a pattern of long cells followed by short cells.
Extrafloral nectaries
Some philodendrons have extrafloral nectaries (nectar-producing glands found outside of the flowers). The nectar attracts ants, with which the plant enjoys a protective symbiotic relationship. Nectaries can be found in a variety of locations on the plant, including the stalks, sheaths, lower surfaces of the leaves, and spathes. The nectaries produce a sweet, sticky substance the ants like to eat and which provides an incentive for them to build their nests amongst the roots of the given philodendron. In some cases, the amount of nectar produced can be quite extensive, resulting in the surface becoming entirely covered with it.
Reproduction
Sexual
When philodendrons are ready to reproduce, they will produce an inflorescence which consists of a leaf-like hood called a spathe within which is enclosed a tube-like structure called a spadix. Depending on the species, a single inflorescence can be produced or a cluster of up to 11 inflorescences can be produced at a single time on short peduncles. The spathe tends to be waxy and is usually bicolored. In some philodendrons, the color of the base of the spathe contrasts in color with the upper part, and in others, the inner and outer surfaces of the spathe differ in coloration. The paler color tends to be either white or green, and the darker usually red or crimson. Pelargonidin is the predominant pigment causing the red coloration in the spathes. The upper portion of the spathe is called the limb or blade, while the lower portion is called the convolute tube or chamber due to its tubular structure at the base. The spadix is more often than not white and shorter than the spathe. On the spadix are found fertile female, fertile male, and sterile male flowers. The fertile male and female flowers are separated on the spadix by a sterile zone or staminodal region composed of sterile male flowers. This barrier of sterile male flowers ensures fertile male flowers do not fertilize the female flowers. The arrangement tends to be vertical, with fertile male flowers at the top of the spadix followed by sterile male flowers, and fertile female flowers very close to the bottom in the region known as the spathe tube or chamber. In some philodendrons, an additional region of sterile male flowers is found at the very top of the spadix. The fertile female flowers are often not receptive to fertilization when the fertile males are producing pollen, which again prevents self-pollination. The pollen itself is thread-like and appears to project out from the region where the fertile male flowers are located.
Sexual reproduction is achieved by means of beetles, with many philodendron species requiring the presence of a specific beetle species to achieve pollination. The reverse is not always the case, as many beetle species will pollinate more than one philodendron species. These same beetles could also pollinate other genera outside of philodendron, as well as outside of the family Araceae. The pollinating beetles are males and members of the subfamily Rutelinae and Dynastinae, and to date the only beetles seen to pollinate the inflorescence are in the genera Cyclocephala or Erioscelis. Other smaller types of beetles in the genus Neelia visit the inflorescences, as well, but they are not believed to be involved in pollinating philodendrons. To attract the beetles, the sterile male flowers give off pheromones to attract the male beetles, usually at dusk. This process, female anthesis, is followed by male anthesis, in which the pollen is produced. Female anthesis typically lasts up to two days and includes the gradual opening of the spathe to allow the beetles to enter. Some evidence suggests the timing of opening of the spathe is dependent on light levels, where cloudy, darker days result in the spathe opening up earlier than on clear days. During female anthesis, the spadix will project forward at roughly 45° relative to the spathe.
Once female anthesis is nearing its end and the female flowers have been pollinated, the spathe will be fully open and male anthesis begins. In the beginning of male anthesis, the fertile male flowers complete the process of producing the pollen and the female flowers become unreceptive to further pollination. Additionally, the spadix moves from its 45° position and presses up flush to the spathe. Towards the end of male anthesis, the spathe begins to close from the bottom, working its way up and forcing the beetles to move up and across the upper region of the spathe, where the fertile male flowers are located. In doing so, the philodendron controls when the beetles come and when they leave and forces them to rub against the top of the spadix where the pollen is located as they exit, thus ensuring they are well-coated with pollen. One would expect the beetles to stay indefinitely if they could due to the very favorable conditions the inflorescence provides. After male anthesis, the males will go off and find another philodendron undergoing female anthesis, so will pollinate the female flowers with the pollen it had collected from its previous night of mating.
Fruit
Botanically, the fruit produced is a berry. The berries develop later in the season; berry development time varies from species to species from a few weeks to a year, although most philodendrons take a few months. The spathe will enlarge to hold the maturing berries. Once the fruit are mature, the spathe will begin to open again, but this time it will break off at the base and fall to the forest floor. Additionally, the berries are edible, although they contain calcium oxalate crystals, and have a taste akin to bananas. Many botanical sources will indicate that the berries are poisonous, probably due to the oxalate crystals. Many tropical plants contain oxalates in varying amounts. Sometimes proper preparation can render these harmless, and in many cases eating minor amounts causes most people no distress or minor gastric irritation. However, care should be taken to verify the toxicity of any particular species before ingesting these berries, particularly regularly or in large amounts.
The color of the berries can vary depending on the species, but most produce a white berry with slight tones of green. Some produce orange berries and others yellow berries, though. Still others will produce berries that start off white, but then change to another color with time. Philodendrons that produce orange berries tend to be members of the section Calostigma. Contained within the berries are the seeds which are extremely small compared to other members of the family Araceae. The berries often give off odors to attract animals to eat and disperse them. For example, Philodendron alliodorum berries are known to emit an odor similar to that of garlic. The animals that distribute the seeds depends on the species, but some possible dispersers include bats and monkeys. Insects also may be responsible for dispersing seeds, as beetles and wasps have been seen feeding on philodendron berries.
Eurytomid wasps also seek out philodendrons and are known to lay their eggs in the ovaries of many Philodendron species, resulting in galled inflorescences.
Hybridization
Philodendrons exhibit extremely few physical reproductive barriers to prevent hybridization, but very few natural hybrids are found in nature. This may be because philodendrons have many geographic and time barriers to prevent any such cross pollination. For example, it is rare for more than one philodendron species to be flowering at the same time or to be pollinated by the same species of beetles. The beetles have also been observed to be selective to the height of the plant they pollinate, which would serve as an additional preventive measure to make hybrids less likely. Because of these outside barriers, philodendrons may not have had to evolve physical mechanisms to prevent cross-pollination. Hybrids in nature are only rarely reported. When found, these hybrids often can show remarkable genetic relationships. Crosses between two philodendrons in different sections can occur successfully.
Taxonomy
History
Philodendrons are known to have been collected from the wild as early as 1644 by Georg Marcgraf, but the first partly successful scientific attempt to collect and classify the genus was done by Charles Plumier. Plumier collected approximately six species from the islands of Martinique, Hispaniola, and St. Thomas. Since then, many exploration attempts have been made to collect new species by others. These include those by N.J. Jacquin who collected new species in the West Indies, Colombia, and Venezuela. At this time in history, the names of the philodendrons they were discovering were being published with the genus name Arum, since most aroids were considered to belong to this same genus. The genus Philodendron had not yet been created. Throughout the late 17th, 18th century, and early 19th centuries, many plants were removed from the genus Arum and placed into newly created genera in an attempt to improve the classification. Heinrich Wilhelm Schott addressed the problem of providing improved taxonomy and created the genus Philodendron and described it in 1829. The genus was first spelled as 'Philodendrum', but in 1832, Schott published a system for classifying plants in the family Araceae titled Meletemata Botanica in which he provided a method of classifying philodendrons based on flowering characteristics. In 1856, Schott published a revision of his previous work titled Synopsis aroidearum, and then published his final work Prodromus Systematis Aroidearum in 1860, in which he provided even more details about the classification of Philodendron and described 135 species.
Modern classification
Philodendron are usually extremely distinctive and not usually confused with other genera, although a few exceptions in the genera Anthurium and Homalomena resemble Philodendron.
The genus Philodendron has been subdivided into three subgenera: Meconostigma, Pteromischum, and Philodendron. In 2018, it was proposed that Philodendron subg. Meconostigma be recognized as a separate genus, Thaumatophyllum.
The genus Philodendron can also be subdivided into several sections and subsections. Section Baursia, section Philopsammos, section Philodendron (subsections Achyropodium, Canniphyllium, Macrolonchium, Philodendron, Platypodium, Psoropodium and Solenosterigma), section Calostigma (subsections Bulaoana, Eucardium, Glossophyllum, Macrobelium and Oligocarpidium), section Tritomophyllum, section Schizophyllum, section Polytomium, section Macrogynium and section Camptogynium.
Typically, the inflorescence is of great importance in determining the species of a given philodendron, since it tends to be less variable than the leaves. The genus Philodendron could be classified further by means of differentiating them based on the pattern of thermogenesis observed, although this is not currently used.
Selected species
Philodendron acutatum Schott
Philodendron alliodorum Croat & Grayum
Philodendron appendiculatum Nadruz & Mayo
Philodendron auriculatum Standl. & L. O. Williams
Philodendron balaoanum Engl.
Philodendron bipennifolium Schott
Philodendron carinatum E.G.Gonç.
Philodendron chimboanum Engl.
Philodendron consanguineum Schott - rascagarganta
Philodendron cordatum (Vell.) Kunth
Philodendron crassinervium Lindl.
Philodendron cruentospathum Madison
Philodendron davidsonii Croat
Philodendron devansayeanum L. Linden
Philodendron domesticum G. S. Bunting
Philodendron duckei Croat & Grayum
Philodendron ensifolium Croat & Grayum
Philodendron erubescens K. Koch & Augustin
Philodendron eximium Schott
Philodendron fragrantissimum (Hook.) G. Don in Sweet
Philodendron ferrugineum Croat
Philodendron giganteum Schott - giant philodendron
Philodendron gigas Croat
Philodendron gloriosum André
Philodendron gualeanum Engl.
Philodendron hastatum K. Koch & Sello - silver philodendron, also known incorrectly as Philodendron glaucophyllum
Philodendron hederaceum (Jacq.) Schott - vilevine, heartleaf philodendron, velvet-leaved philodendron
Philodendron herbaceum Croat & Grayum
Philodendron hooveri Croat & Grayum
Philodendron imbe Schott ex Endl. - philodendron
Philodendron jacquinii Schott
Philodendron lacerum (Jacq.) Schott
Philodendron lingulatum (L.) K. Koch - treelover
Philodendron mamei André
Philodendron marginatum Urban - Puerto Rico philodendron
Philodendron martianum Engl.- also known incorrectly as Philodendron cannifolium
Philodendron mayoii Symon Mayo
Philodendron maximum K. Krause
Philodendron melanochrysum Linden & André
Philodendron microstictum Standl. & L. O. Williams
Philodendron musifolium Engl.
Philodendron nanegalense Engl.
Philodendron opacum Croat & Grayum
Philodendron ornatum Schott
Philodendron pachycaule K. Krause
Philodendron panduriforme (Kunth) Kunth
Philodendron pedatum (Hook.) Kunth
Philodendron pinnatifidum (Jacq.) Schott
Philodendron pogonocaule Madison
Philodendron pterotum K.Koch & Augustin
Philodendron quitense Engl.
Philodendron radiatum Schott
Philodendron recurvifolium Schott
Philodendron renauxii Reitz
Philodendron riparium Engl.
Philodendron robustum Schott
Philodendron rugosum Bogner & G.S.Bunting
Philodendron sagittifolium Liebm.
Philodendron santa leopoldina Liebm.
Philodendron sphalerum Schott
Philodendron squamiferum Poepp.
Philodendron standleyi Grayum
Philodendron tatei Krause
Philodendron tripartitum (Jacq.) Schott
Philodendron validinervium Engl.
Philodendron ventricosum Madison
Philodendron verrucosum L. Mathieu ex Schott
Philodendron victoriae G.S. Bunting
Philodendron warszewiczii K. Koch & C. D. Bouché
Philodendron wendlandii Schott
Evolution
Philodendron diverged from Adelonema and diversified during the late Oligocene, 25 million years ago, in the New World.
Distribution and habitat
Philodendron species can be found in many diverse habitats in the tropical Americas and the West Indies. Most occur in humid tropical forests, but can also be found in swamps and on river banks, roadsides and rock outcrops. They are also found throughout the diverse range of elevations from sea level to over 2000 m above sea level. Species of this genus are often found clambering over other plants, or climbing the trunks of trees with the aid of aerial roots. Philodendrons usually distinguish themselves in their environment by their large numbers compared to other plants, making them a highly noticeable component of the ecosystems in which they are found. They are found in great numbers in road clearings.
Philodendrons can also be found in Australia, some Pacific islands, Africa and Asia, although they are not indigenous and were introduced or accidentally escaped.
Ecology
The leaves of philodendrons are also known to be eaten by Venezuelan red howler monkeys, making up 3.1% of all the leaves they eat.
The resins produced during the flowering of Monstera and Philodendron are known to be used by Trigona bees in the construction of their nests.
The spathe provides a safe breeding area for beetles. As such, male beetles are often followed there by female beetles. The philodendrons benefit from this symbiotic relationship because the males will eventually leave the spathe covered in pollen and repeat the process at another philodendron, pollinating it in the process. Females that see a male beetle headed for a philodendron flower know he does so with intention of mating, and females which are sexually receptive and need to mate know that they can find males if they follow the pheromones produced by the philodendron flowers. As a result, the male beetles benefit from this relationship with the philodendrons because they do not have to produce pheromones to attract females. Additionally, male beetles benefit because they are ensured of mating with only sexually receptive females. Pheromones produced by the philodendrons may be similar to those produced by female beetles when they wish to attract males to mate. Also, the pheromones have a sweet, fruity smell in many species and no noticeable smell for others. Additionally, the beetles consume pollen from the fertile male flowers throughout the night, in addition to the sterile male flowers which are rich in lipids.
Typically, five to 12 beetles will be within the spathe throughout the night. Rarely, cases of 200 beetles at a time have been observed and almost always the beetles are of the same species. Another feature of this symbiotic relationship, less well understood, is the series of events in which the spadix begins to heat up prior to the spathe opening up for the beetles. This process is known as thermogenesis. By the time the spathe is open and the beetles have arrived, the spadix is usually quite hot; up to around 46 °C in some species, but usually around 35 °C. The thermogenesis coincides with the arrival of the beetles and appears to increase their presence. The maximum temperature reached by the spadix remains about 20 °C higher than the outside ambient temperature. The time dependence of the temperature can vary from species to species. In some species, the temperature of the spadix will peak on the arrival of the beetles, then decrease, and finally increase reaching a maximum once again when the philodendron is ready for the beetles to leave. Other species, though, only show a maximum temperature on the arrival of the beetles, which remains roughly constant for about a day, and then steadily decreases.
As the beetles home in on the inflorescence, they first move in a zig-zag pattern until they get reasonably close, when they switch to a straight-line path. The beetles may use scent to find the inflorescence when they are far away, but once within range, they find it by means of the infrared radiation, accounting for the two types of paths the beetles follow.
Cultivation
Growing
Philodendrons can be grown outdoors in mild climates in shady spots. They thrive in moist soils with high organic matter. In milder climates, they can be grown in pots of soil or in the case of Philodendron oxycardium in containers of water. Indoor plants thrive at temperatures between 15 and 18 °C and can survive at lower light levels than other house plants. Although philodendrons can survive in dark places, they much prefer bright lights. Wiping the leaves off with water will remove any dust and insects. Plants in pots with good root systems will benefit from a weak fertilizer solution every other week.
Propagation
New plants can be grown by taking stem cuttings with at least two joints. Cuttings then can be rooted in pots of sand and peat moss mixtures. These pots are placed in greenhouses with bottom heat of 21–24 °C. During the rooting, cuttings should be kept out of direct sunlight. Once rooted, the plants can be transplanted to larger pots or directly outside in milder climates. Stem cuttings, particularly from trailing varieties, can be rooted in water. In four to five weeks, the plant should develop roots and can be transferred to pots. Philodendrons can also propagate through air layering which is a more advanced method of propagation that involves creating a new plant on the stem of an existing plant.
Hybridizing philodendrons is quite easy if flowering plants are available, because they have very few barriers to prevent hybridization. However, some aspects of making crosses can make philodendron hybridization more difficult. Philodendrons often flower at different times and the time when the spathe opens up varies from plant to plant. The pollen and the inflorescence both have short lives, which means a large collection of philodendrons is necessary if crossbreeding is to be done successfully. The pollen life can be extended to a few weeks by storing it in film canisters in a refrigerator. Artificial pollination is usually achieved by first mixing the pollen with water. A window is then cut into the spathe and the water-pollen mixture is rubbed on the fertile female flowers. The entire spathe is then covered in a plastic bag so the water–pollen mixture does not dry out; the bag is removed a few days later. If the inflorescence has not been fertilized, it will fall off, usually within a few weeks.
Toxicity
Philodendrons can contain as much as 0.7% of oxalates in the form of calcium oxalate crystals as raphides. The risk of death, if even possible, is extremely low if ingested by an average adult, although its consumption is generally considered unhealthy. In general, the calcium oxalate crystals have a very mild effect on humans, and large quantities have to be consumed for symptoms to even appear. Possible symptoms include increased salivation, a sensation of burning of the mouth, swelling of the tongue, stomatitis, dysphagia, an inability to speak, and edema. Cases of mild dermatitis due to contact with the leaves have also been reported, with symptoms including vesiculation and erythema. The chemical derivatives of alkenyl resorcinol are believed to be responsible for the dermatitis in some people. Contact with philodendron oils or fluids with the eyes have also been known to result in conjunctivitis. Fatal poisonings are extremely rare; one case of an infant eating small quantities of a philodendron resulting in hospitalization and death has been reported. This one case study, however, was found to be inconsistent with the findings from a second study. In this study, 127 cases of children ingesting philodendrons were studied, and they found only one child showed symptoms; a 10-month-old had minor upper lip swelling when he chewed on a philodendron leaf. The study also found the symptoms could subside without treatment and that previously reported cases of severe complications were exaggerated.
In a 1961 study, 72 cases of cat poisonings were examined, of which 37 resulted in the death of the cat. The symptoms of the poisoned cats included excitability, spasms, seizures, kidney failure, and encephalitis. In a 1978 study, three cats (two adults and one kitten) were tube-fed a puréed leaf and water mixture of P. cordatum, then euthanized. A necropsy showed no signs or symptoms of acute poisoning or toxicity. Dosages of 2.8, 5.6, and 9.1 g/kg were used, the highest dose being much more than a house cat could consume. Earlier epidemiological studies (which did not necessarily invoke a purée-and-water feeding method) were suggested to be wrong based on the premise that many of the sick cats in those studies may have had conditions and merely consumed philodendrons in an attempt to alleviate their illnesses.
Some philodendrons are known to be toxic to mice and rats. In one study, 100 mg of P. cordatum leaves suspended in distilled water were fed to six mice. Three of the mice died. The same experiment was done with 100 mg of P. cordatum stems on three mice and none of them died. Leaves and flowers of P. sagittifolium were also orally administered in 100-mg doses to the mice. Three mice were used for each of the leaves and flowers; none of the mice died. A similar experiment was done on rats with the leaves and stems of P. cordatum, but instead of oral administration of the dose, it was injected intraperitoneally using 3 g of plant extract from either the leaves or stems. Six rats were injected with the leaf extract and five of them died. Eight rats were injected with the stem extract and two of them died.
Uses
Indigenous people from South America use the resin from bees' nests (made from the species) to make their blowguns air- and watertight.
Though they contain calcium oxalate crystals, the berries of some species are eaten by the locals. For example, the sweet white berries of Thaumatophyllum bipinnatifidum are known to be used. Additionally, the aerial roots are also used for rope in this particular species.
Also, in the making of a particular recipe for curare by the Amazonian Taiwanos, the leaves and stems of an unknown philodendron species are used. The leaves and stems are mixed with the bark of Vochysia ferruginea and with some parts of a species in the genus Strychnos.
Yet another use of philodendrons is for catching fish. A tribe in the Colombian Amazon is known to use P. craspedodromum to add poison to the water, temporarily stunning the fish, which rise up to the surface, where they can be easily scooped up. To add the poison to the water, the leaves are cut into pieces and tied together to form bundles, which are allowed to ferment for a few days. The bundles are crushed and added to the water into which the poison will dissipate. Although the toxicity of P. craspedodromum is not fully known, active ingredients in the poisoning of the fish possibly are coumarins formed during the fermentation process.
Some philodendrons are also used for ceremonial purposes. Among the Kubeo tribe, native to Colombia, P. insigne is used by witch doctors to assuage ill patients. They use the juice of the spathe to stain their hands red, since many such tribes view the color red as a sign of power.
| Biology and health sciences | Monocots | null |
576517 | https://en.wikipedia.org/wiki/Clydesdale%20horse | Clydesdale horse | The Clydesdale is a Scottish breed of draught horse. It takes its name from Clydesdale, a region of Scotland centred on the River Clyde.
The origins of the breed lie in the seventeenth century, when Flemish stallions were imported to Scotland and mated with local mares; in the nineteenth century, Shire blood was introduced. The first recorded use of the name "Clydesdale" for the breed was in 1826; the horses spread through much of Scotland and into northern England. After the breed society was formed in 1877, thousands of Clydesdales were exported to many countries of the world, particularly to Australia and New Zealand. In the early twentieth century numbers began to fall, both because many were taken for use in the First World War, and because of the increasing mechanisation of agriculture. By the 1970s, the Rare Breeds Survival Trust considered the breed vulnerable to extinction. Numbers have since increased slightly.
It is a large and powerful horse, although now not as heavy as in the past. It was traditionally used for draught power, both in farming and in road haulage. It is now principally a carriage horse. It may be ridden or driven in parades or processions. In the United States the Anheuser-Busch brewery uses a matched team of eight for publicity.
History
The Clydesdale horse takes its name from Clydesdale, the valley of the River Clyde. In the late seventeenth century, stallions of Friesian and Flemish stock from the Low Countries were imported to Scotland and bred to local mares. These included a black unnamed stallion imported from England by a John Paterson of Lochlyloch and an unnamed dark-brown stallion owned by the Duke of Hamilton.
Another prominent stallion was a coach horse stallion of unknown lineage named Blaze. Written pedigrees were kept of these foals beginning in the early nineteenth century, and in 1806, a filly, later known as "Lampits mare" after the farm name of her owner, was born that traced her lineage to the black stallion. This mare is listed in the ancestry of almost every Clydesdale living today. One of her foals was Thompson's Black Horse (known as Glancer), which was to have a significant influence on the Clydesdale breed.
The first recorded use of the name "Clydesdale" in reference to the breed was in 1826 at an exhibition in Glasgow. Another theory of their origin, that of them descending from Flemish horses brought to Scotland as early as the 15th century, was also promulgated in the late 18th century. However, even the author of that theory admitted that the common story of their ancestry is more likely.
A system of hiring stallions between districts existed in Scotland, with written records dating back to 1837. This programme consisted of local agriculture improvement societies holding breed shows to choose the best stallion, whose owner was then awarded a monetary prize. The owner was then required, in return for additional monies, to take the stallion throughout a designated area, breeding to the local mares. Through this system and by purchase, Clydesdale stallions were sent throughout Scotland and into northern England.
Through extensive crossbreeding with local mares, these stallions spread the Clydesdale type throughout the areas where they were placed, and by 1840, Scottish draught horses and the Clydesdale were one and the same. In 1877, the Clydesdale Horse Society of Scotland was formed, followed in 1879 by the American Clydesdale Association (later renamed the Clydesdale Breeders of the USA), which served both U.S. and Canadian breed enthusiasts. The first American stud book was published in 1882. In 1883, the short-lived Select Clydesdale Horse Society was founded to compete with the Clydesdale Horse Society. It was started by two breeders dedicated to improving the breed, who also were responsible in large part for the introduction of Shire blood into the Clydesdale.
Large numbers of Clydesdales were exported from Scotland in the late nineteenth and early twentieth centuries, with 1617 stallions leaving the country in 1911 alone. Between 1884 and 1945, export certificates were issued for 20,183 horses. These horses were exported to other countries in the British Empire, as well as North and South America, continental Europe, and Russia.
The First World War had the conscription of thousands of horses for the war effort, and after the war, breed numbers declined as farms became increasingly mechanised. This decline continued between the wars. Following the Second World War, the number of Clydesdale breeding stallions in England dropped from more than 200 in 1946 to 80 in 1949. By 1975, the Rare Breeds Survival Trust considered them vulnerable to extinction, meaning fewer than 900 breeding females remained in the UK.
Many of the horses exported from Scotland in the nineteenth and twentieth centuries went to Australia and New Zealand. In 1918, the Commonwealth Clydesdale Horse Society was formed as the association for the breed in Australia. Between 1906 and 1936, Clydesdales were bred so extensively in Australia that other draught breeds were almost unknown. By the late 1960s, it was noted that "Excellent Clydesdale horses are bred in Victoria and New Zealand; but, at least in the former place, it is considered advisable to keep up the type by frequent importations from England." Over 25,000 Clydesdales were registered in Australia between 1924 and 2008. The popularity of the Clydesdale led to it being called "the breed that built Australia".
Conservation status
In the 1990s, numbers began to rise. By 2005, the Rare Breeds Survival Trust had moved the breed to "at risk" status, meaning that there were fewer than 1,500 breeding females in the UK. By 2010 it had been moved back to "vulnerable".
In 2010, the worldwide Clydesdale horse population was estimated to be 5,000, with around 4,000 in the United States and Canada, 800 in the UK, and the rest in other countries, including Russia, Japan, Germany, and South Africa.. The same year, the Clydesdale was listed as "watch" by The Livestock Conservancy, meaning that fewer than 2500 horses were registered annually in the USA, and there were fewer than 10,000 worldwide. By 2024, the Clydesdale was listed as "threatened" (<1,000 annual US registrations and <5,000 global population). According to The Livestock Conservancy, "The North American population of Clydesdale horses had increased steadily for several decades, but a sharp decline began around 2010, prompted by the economic downturn that affected the entire equine market. Globally, the breed is well-known, but not common, with an estimated global population of fewer than 5,000 horses."
Inbreeding has also become an issue for the breed, and a 2013 study found that the Clydesdale had one of the highest inbreeding coefficients among all horse breeds.
Characteristics
The conformation of the Clydesdale has changed greatly throughout its history. In the 1920s and 1930s, it was a compact horse smaller than the Shire, Percheron, and Belgian Draught. Beginning in the 1940s, breeding animals were selected to produce taller horses that looked more impressive in parades and shows. Today, the Clydesdale stands high and weighs . Some mature males are larger, standing taller than 183 cm and weighing up to . The breed has a straight facial profile or a slight Roman nose, broad forehead, and wide muzzle.
It is well-muscled and strong, with an arched neck, high withers, and a sloped shoulder. Breed associations pay close attention to the quality of the hooves and legs, as well as the general movement. Their gaits are active, with clearly lifted hooves and a general impression of power and quality. Clydesdales are energetic, with a manner described by the Clydesdale Horse Society as a "gaiety of carriage and outlook".
Clydesdales are usually bay or brown in colour. Roans are common, and black, grey and chestnut also occur. Most have white markings, including white on the face, feet, and legs, and occasional white patches on the body (generally on the lower belly). They have extensive feathering on their lower legs. Cow hocks, where the hocks turn inward are a breed characteristic and not a fault.
Many buyers pay a premium for bay and black horses, especially those with four white legs and white facial markings. Specific colours are often preferred over other physical traits, and some buyers even choose horses with soundness problems if they have the desired colour and markings. Buyers do not favour Sabino-like horses, despite one draught-breed writer theorising that they are needed to keep the desired coat colours and texture. Breed associations, however, state that no colour is bad, and that horses with roaning and body spots are increasingly accepted.
Clydesdales have been identified to be at risk for chronic progressive lymphedema, a disease with clinical signs that include progressive swelling, hyperkeratosis, and fibrosis of distal limbs that is similar to chronic lymphedema in humans. Another health concern is a skin condition on the lower leg where feathering is heavy. Colloquially called "Clyde's itch", it is thought to be caused by a type of mange. Clydesdales are also known to develop sunburn on any pink (unpigmented) skin around their faces.
Uses
The Clydesdale was originally used for agriculture, hauling coal in Lanarkshire, and heavy hauling in Glasgow. Today, Clydesdales are still used for draught purposes, including agriculture, logging, and driving. They are also shown and ridden, as well as kept for pleasure. Clydesdales are known to be the popular breed choice with carriage services and parade horses because of their white, feathered legs.
Along with carriage horses, Clydesdales are also used as show horses. They are shown in lead line and harness classes at county and state fairs, as well as national exhibitions.
Some of the most famous members of the breed are the teams that make up the hitches of the Budweiser Clydesdales. The Budweiser Brewery first formed these teams at the end of Prohibition, and they have since become an international symbol of both the breed and the brand. The Budweiser breeding programme, with its strict standards of colour and conformation, have influenced the look of the breed in the United States to the point that many people believe that Clydesdales are always bay with white markings.
Influence on other breeds
In the second half of the 1800s, Clydesdale and Shire blood was added to the Irish Draught breed in an attempt to reinvigorate that declining breed. However, those efforts were not seen as successful, as Irish Draught breeders thought the Clydesdale blood made their horses coarser and prone to lower leg faults, such as tied-in below the knee.
The Australian Draught horse was created using European draft breeds, including the Clydesdale, imported in the late 1800s.
In the early 1900s it was considered profitable to breed Clydesdale stallions to Dales Pony mares to create a mid-sized draught horses for pulling commercial wagons and military artillery. Unfortunately, after just a few years, the Dales breed was two-thirds Clydesdale. They started a breed registry in 1916 to preserve the Dales, and by 1923 the Army was buying only Dales with no signs of carthorse blood. The modern Dales shows no signs of Clydesdale characteristics.
The Clydesdale contributed to the development of the Gypsy horse in Great Britain along with Friesian, Shire and Dale, although no written records were kept.
| Biology and health sciences | Horses | Animals |
576681 | https://en.wikipedia.org/wiki/Speedometer | Speedometer | A speedometer or speed meter is a gauge that measures and displays the instantaneous speed of a vehicle. Now universally fitted to motor vehicles, they started to be available as options in the early 20th century, and as standard equipment from about 1910 onwards. Other vehicles may use devices analogous to the speedometer with different means of sensing speed, eg. boats use a pit log, while aircraft use an airspeed indicator.
Charles Babbage is credited with creating an early type of a speedometer, which was usually fitted to locomotives.
The electric speedometer was invented by the Croat Josip Belušić in 1888 and was originally called a velocimeter.
History
The speedometer was originally patented by Josip Belušić (Giuseppe Bellussich) in 1888. He presented his invention at the 1889 Exposition Universelle in Paris. His invention had a pointer and a magnet, using electricity to work.
German inventor Otto Schultze patented his version (which, like Belušić's, ran on eddy currents) on 7 October 1902.
Operation
Mechanical
Many speedometers use a rotating flexible cable driven by gearing linked to the vehicle's transmission. The early Volkswagen Beetle and many motorcycles, however, use a cable driven from a front wheel.
Some early mechanical speedometers operated on the governor principle where a rotating weight acting against a spring moved further out as the speed increased, similar to the governor used on steam engines. This movement was transferred to the pointer to indicate speed.
This was followed by the Chronometric speedometer where the distance traveled was measured over a precise interval of time (Some Smiths speedometers used 3/4 of a second) measured by an escapement. This was transferred to the speedometer pointer. The chronometric speedometer is tolerant of vibration and was used in motorcycles up to the 1970s.
When the vehicle is in motion, a speedometer gear assembly turns a speedometer cable, which then turns the speedometer mechanism itself. A small permanent magnet affixed to the speedometer cable interacts with a small aluminium cup (called a speedcup) attached to the shaft of the pointer on the analogue speedometer instrument. As the magnet rotates near the cup, the changing magnetic field produces eddy current in the cup, which itself produces another magnetic field. The effect is that the magnet exerts a torque on the cup, "dragging" it, and thus the speedometer pointer, in the direction of its rotation with no mechanical connection between them.
The pointer shaft is held toward zero by a fine torsion spring. The torque on the cup increases with the speed of rotation of the magnet. Thus an increase in the speed of the car will twist the cup and speedometer pointer against the spring. The cup and pointer will turn until the torque of the eddy currents on the cup are balanced by the opposing torque of the spring, and then stop. Given the torque on the cup is proportional to the car's speed, and the spring's deflection is proportional to the torque, the angle of the pointer is also proportional to the speed, so that equally spaced markers on the dial can be used for gaps in speed. At a given speed, the pointer will remain motionless and point to the appropriate number on the speedometer's dial.
The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tail shaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires.
One of the key disadvantages of the eddy current speedometer is that it cannot show the vehicle speed when running in reverse gear since the cup would turn in the opposite direction – in this scenario, the needle would be driven against its mechanical stop pin on the zero position.
Electronic
Many modern speedometers are electronic. In designs derived from earlier eddy-current models, a rotation sensor mounted in the transmission delivers a series of electronic pulses whose frequency corresponds to the (average) rotational speed of the driveshaft, and therefore the vehicle's speed, assuming the wheels have full traction. The sensor is typically a set of one or more magnets mounted on the output shaft or (in transaxles) differential crown wheel, or a toothed metal disk positioned between a magnet and a magnetic field sensor. As the part in question turns, the magnets or teeth pass beneath the sensor, each time producing a pulse in the sensor as they affect the strength of the magnetic field it is measuring. Alternatively, particularly in vehicles with multiplex wiring, some manufacturers use the pulses coming from the ABS wheel sensors which communicate to the instrument panel via the CAN Bus. Most modern electronic speedometers have the additional ability over the eddy current type to show the vehicle's speed when moving in reverse gear.
A computer converts the pulses to a speed and displays this speed on an electronically controlled, analogue-style needle or a digital display. Pulse information is also used for a variety of other purposes by the ECU or full-vehicle control system, e.g. triggering ABS or traction control, calculating average trip speed, or increment the odometer in place of it being turned directly by the speedometer cable.
Another early form of electronic speedometer relies upon the interaction between a precision watch mechanism and a mechanical pulsator driven by the car's wheel or transmission. The watch mechanism endeavours to push the speedometer pointer toward zero, while the vehicle-driven pulsator tries to push it toward infinity. The position of the speedometer pointer reflects the relative magnitudes of the outputs of the two mechanisms.
Virtual Speedometer
A virtual speedometer is a computer-generated tool that displays the current speed of a vehicle or object. The virtual speedometer typically calculates the object's speed based on the distance it travels over time. Such speedometers are programmed using programming languages such as HTML, CSS, and Javascript. The program uses the mobile device's GPS module.
Consistent use of the GPS module on mobile devices can result in faster battery drain. Furthermore, virtual speedometers calculate speed by measuring the distance and time between two points using GPS signals. However, various environmental factors such as weather conditions, terrain, and obstructions can interfere with the accuracy of these signals and result in inaccurate speed readings.
Bicycle speedometers
Typical bicycle speedometers measure the time between each wheel revolution and give a readout on a small, handlebar-mounted digital display. The sensor is mounted on the bike at a fixed location, pulsing when the spoke-mounted magnet passes by. In this way, it is analogous to an electronic car speedometer using pulses from an ABS sensor, but with a much cruder time/distance resolution – typically one pulse/display update per revolution, or as seldom as once every 2–3 seconds at low speed with a wheel. However, this is rarely a critical problem, and the system provides frequent updates at higher road speeds where the information is of more importance. The low pulse frequency also has little impact on measurement accuracy, as these digital devices can be programmed by wheel size, or additionally by wheel or tire circumference to make distance measurements more accurate and precise than a typical motor vehicle gauge. However, these devices carry some minor disadvantages in requiring power from batteries that must be replaced every so often in the receiver (and sensor, for wireless models), and, in wired models, the signal is carried by a thin cable that is much less robust than that used for brakes, gears, or cabled speedometers.
Other, usually older bicycle speedometers are cable driven from one or other wheel, as in the motorcycle speedometers described above. These do not require battery power, but can be relatively bulky and heavy, and may be less accurate. The turning force at the wheel may be provided either from a gearing system at the hub (making use of the presence of e.g. a hub brake, cylinder gear, or dynamo) as per a typical motorcycle, or with a friction wheel device that pushes against the outer edge of the rim (same position as rim brakes, but on the opposite edge of the fork) or the sidewall of the tire itself. The former type is quite reliable and low maintenance but needs a gauge and hub gearing properly matched to the rim and tire size, whereas the latter requires little or no calibration for a moderately accurate readout (with standard tires, the "distance" covered in each wheel rotation by a friction wheel set against the rim should scale fairly linearly with wheel size, almost as if it were rolling along the ground itself) but are unsuitable for off-road use, and must be kept properly tensioned and clean of road dirt to avoid slipping or jamming.
Error
Most speedometers have tolerances of some ±10%, mainly due to variations in tire diameter. Sources of error due to tire diameter variations are wear, temperature, pressure, vehicle load, and nominal tire size. Vehicle manufacturers usually calibrate speedometers to read high by an amount equal to the average error, to ensure that their speedometers never indicate a lower speed than the actual speed of the vehicle, to ensure they are not liable for drivers violating speed limits.
Excessive speedometer errors after manufacture can come from several causes, but most commonly is due to nonstandard tire diameter, in which case the error is:
Nearly all tires now have their size is shown as "T/A_W" on the side of the tire (See: Tire code), and the tires.
For example, a standard tire is "185/70R14" with diameter = 2*185*(70/100)+(14*25.4) = 614.6 mm (185x70/1270 + 14 = 24.20 in). Another is "195/50R15" with 2*195*(50/100)+(15*25.4) = 576.0 mm (195x50/1270 + 15 = 22.68 in). Replacing the first tire (and wheels) with the second (on 15" = 381 mm wheels), a speedometer reads 100 * ((614.6/576) - 1) = 100 * (24.20/22.68 - 1) = 6.7% higher than the actual speed. At an actual speed of 100 km/h (60 mph), the speedometer will indicate 100 x 1.067 = 106.7 km/h (60 * 1.067 = 64.02 mph), approximately.
In the case of wear, a new "185/70R14" tire of 620 mm (24.4 inch) diameter will have ≈8 mm tread depth, at legal limit this reduces to 1.6 mm, the difference being 12.8 mm in diameter or 0.5 inches which is 2% in 620 mm (24.4 inches).
International agreements
In many countries the legislated error in speedometer readings is ultimately governed by the United Nations Economic Commission for Europe (UNECE) Regulation 39, which covers those aspects of vehicle type approval that relate to speedometers. The main purpose of the UNECE regulations is to facilitate trade in motor vehicles by agreeing on uniform type approval standards rather than requiring a vehicle model to undergo different approval processes in each country where it is sold.
European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers are similar to the UNECE regulation in that they specify that:
The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
The indicated speed must not be more than 110 percent of the true speed plus at specified test speeds. For example, at , the indicated speed must be no more than .
The standards specify both the limits on accuracy and many of the details of how it should be measured during the approvals process. For example, the test measurements should be made (for most vehicles) at , and at a particular ambient temperature and road surface. There are slight differences between the different standards, for example in the minimum accuracy of the equipment measuring the true speed of the vehicle.
The UNECE regulation relaxes the requirements for vehicles mass-produced following type approval. At Conformity of Production Audits the upper limit on indicated speed is increased to 110 percent plus for cars, buses, trucks, and similar vehicles, and 110 percent plus for two- or three-wheeled vehicles that have a maximum speed above (or a cylinder capacity, if powered by a heat engine, of more than ). European Union Directive 2000/7/EC, which relates to two- and three-wheeled vehicles, provides similar slightly relaxed limits in production.
Australia
There were no Australian Design Rules in place for speedometers in Australia before July 1988. They had to be introduced when speed cameras were first used. This means there are no legally accurate speedometers for these older vehicles. All vehicles manufactured on or after 1 July 2007, and all models of vehicle introduced on or after 1 July 2006, must conform to UNECE Regulation 39.
The speedometers in vehicles manufactured before these dates but after 1 July 1995 (or 1 January 1995 for forward control passenger vehicles and off-road passenger vehicles) must conform to the previous Australian design rule. This specifies that they need only display the speed to an accuracy of ±10% at speeds above 40 km/h, and there is no specified accuracy at all for speeds below 40 km/h.
All vehicles manufactured in Australia or imported for supply to the Australian market must comply with the Australian Design Rules. The state and territory governments may set policies for the tolerance of speed over the posted speed limits that may be lower than the 10% in the earlier versions of the Australian Design Rules permitted, such as in Victoria. This has caused some controversy since it would be possible for a driver to be unaware that they are speeding should their vehicle be fitted with an under-reading speedometer.
United Kingdom
The amended Road Vehicles (Construction and Use) Regulations 1986 permits the use of speedometers that meet either the requirements of EC Council Directive 75/443 (as amended by Directive 97/39) or UNECE Regulation 39.
The Motor Vehicles (Approval) Regulations 2001 permits single vehicles to be approved. As with the UNECE regulation and the EC Directives, the speedometer must never show an indicated speed less than the actual speed. However, it differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower than this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph.
For example, if the vehicle is actually traveling at 50 mph, the speedometer must not show more than 61.25 mph or less than 50 mph.
United States
Federal standards in the United States allow a maximum 5 mph error at a speed of 50 mph on speedometer readings for commercial vehicles. Aftermarket modifications, such as different tire and wheel sizes or different differential gearing, can cause speedometer inaccuracy.
Regulation in the US
Starting with U.S. automobiles manufactured on or after 1 September 1979, the NHTSA required speedometers to have a special emphasis on 55 mph (90 km/h) and display no more than a maximum speed of 85 mph (136 km/h). On 25 March 1982, the NHTSA revoked the rule because no "significant safety benefits" could come from maintaining the standard.
GPS
GPS devices can measure speeds in two ways:
The first and simpler method is based on how far the receiver has moved since the last measurement. Such speed calculations are not subject to the same sources of error as the vehicle's speedometer (wheel size, transmission/drive ratios). Instead, the GPS's positional accuracy, and therefore the accuracy of its calculated speed, is dependent on the satellite signal quality at the time. Speed calculations will be more accurate at higher speeds when the ratio of positional error to positional change is lower. The GPS software may also use a moving average calculation to reduce error. Some GPS devices do not take into account the vertical position of the car so will under-report the speed by the road's gradient.
Alternatively, the GPS may take advantage of the Doppler effect to estimate its velocity. In ideal conditions, the accuracy for commercial devices is within 0.2–0.5 km/h, but it may worsen if the signal quality degrades.
As mentioned in the satnav article, GPS data has been used to overturn a speeding ticket; the GPS logs showed the defendant traveling below the speed limit when they were ticketed. That the data came from a GPS device was likely less important than the fact that it was logged; logs from the vehicle's speedometer could likely have been used instead, had they existed.
| Technology | Measuring instruments | null |
577188 | https://en.wikipedia.org/wiki/Compsognathus | Compsognathus | Compsognathus (; Greek kompsos/κομψός; "elegant", "refined" or "dainty", and gnathos/γνάθος; "jaw") is a genus of small, bipedal, carnivorous theropod dinosaur. Members of its single species Compsognathus longipes could grow to around the size of a chicken. They lived about 150 million years ago, during the Tithonian age of the late Jurassic period, in what is now Europe. Paleontologists have found two well-preserved fossils, one in Germany in the 1850s and the second in France more than a century later. Today, C. longipes is the only recognized species, although the larger specimen discovered in France in the 1970s was once thought to belong to a separate species and named C. corallestris.
Many presentations still describe Compsognathus as "chicken-sized" dinosaurs because of the size of the German specimen, which is now believed to be a juvenile. Compsognathus longipes is one of the few dinosaur species whose diet is known with certainty: the remains of small, agile lizards are preserved in the bellies of both specimens. Teeth discovered in Portugal may be further fossil remains of the genus.
Although not recognized as such at the time of its discovery, Compsognathus is the first theropod dinosaur known from a reasonably complete fossil skeleton. Until the 1990s, it was the smallest-known non-avialan dinosaur, with the preceding centuries incorrectly labelling them as the closest relative of Archaeopteryx.
Discovery and species
Compsognathus is known from two almost complete skeletons. The German specimen (specimen number BSP AS I 563) stems from limestone deposits in Bavaria and was part of the collection of the physician and fossil collector Joseph Oberndorfer. Oberndorfer lent the specimen to paleontologist Johann A. Wagner, who published a brief discussion in 1859, where he coined the name Compsognathus longipes. Wagner did not recognise Compsognathus as a dinosaur, but instead described it as one of the "most curious forms among the lizards". He published a more detailed description in 1861. In 1866, Oberndorfer's collection, including the Compsognathus specimen, was acquired by the paleontological state collection in Munich.
Both the year of discovery and the exact locality of the German specimen are unknown, possibly because Oberndorfer did not reveal details of the discovery to prevent other collectors from exploiting the locality; later authors have suggested that the German specimen was probably discovered during the 1850s. Weathering of the slab on which the fossil is preserved indicates that it was collected from a pile of waste rock left behind by quarrying. The specimen either stems from Jachenhausen or the region Riedenburg–Kehlheim. All possible localities are part of lagoonal deposits of the Painten Formation, and date to the latest part of the late Kimmeridgian or the earlier part of the early Tithonian. In the Jurassic, the region was part of the Solnhofen archipelago. The limestone of the area, the Solnhofen limestone, had been quarried for centuries, and yielded such well-preserved fossils as Archaeopteryx with feather impressions and pterosaurs with imprints of their wing membranes.
In two publications in 1868 and 1870, Thomas Huxley, a major proponent of Charles Darwin's theory of evolution, compared Compsognathus with Archaeopteryx, which was considered the earliest known bird. Following earlier suggestions by Carl Gegenbaur and Edward Drinker Cope, Huxley found that Archaeopteryx was closely similar to Compsognathus, and referred to the latter as a "bird-like reptile". He concluded that birds must have evolved from dinosaurs, an assessment that established Compsognathus as one of the most widely known dinosaurs. The specimen has since been studied by many prominent paleontologists, including Othniel Charles Marsh, who visited Munich in 1881. The German paleontologist J.G. Baur, who worked as an assistant of Marsh, removed the right ankle from the slab for illustration and study; this removed part got lost since. Although Baur published a detailed study of the ankle in 1882, which is now the only available source of information of this part of the skeleton, his reconstruction was later found to be inconsistent with corresponding impressions on the slab. John Ostrom thoroughly described the German specimen as well as the newly discovered French specimen in 1978, making Compsognathus one of the best-known small theropods at that time. He also concluded that the German specimen likely belongs to an immature individual.
The larger French specimen (Y85R M4M) was discovered in around 1971 in the Portlandian lithographic limestone of Canjuers near Nice. It dates to the lower Tithonian, as indicated by ammonite index fossils. As Solnhofen, Canjures was famous for its limestone plates, which were quarried and sold under the name "dalles de Provence". The specimen was originally part of a large private fossil collection of Louis Ghirardi, the owner of the Canjures quarries. The collection, including the Compsognathus specimen, was sold to the National Museum of Natural History in Paris in 1983. Alain Bidar and Gérard Thomel, in a brief 1972 description, announced the new find under a separate species, Compsognathus corallestris. A more comprehensive description followed in the same year. According to these authors, the new species differed from the German species in its larger size and modified, flipper-like hand. Ostrom, Jean-Guy Michard and others have since relabeled it as another example of Compsognathus longipes. In 1984, George Callison and Helen Quimby identified the smaller German specimen as a juvenile of the same species.
Collector Heinrich Fischer had originally labeled a partial foot consisting of three metatarsals and a phalanx, from the Solnhofen area, as belonging to Compsognathus longipes. This identification was rejected by Wilhelm Dames, when he described the specimen for the first time in 1884. Friedrich von Huene, in 1925 and 1932, also found that the foot did probably not belong to Compsognathus itself but to a closely related genus. Ostrom, in his 1978 monography, questioned the attribution of this fossil to Compsognathus once more. Jens Zinke, in 1998, assigned forty-nine isolated teeth from the Guimarota coal mine of Portugal to the genus. Zinke found that these teeth are not identical to those of Compsognathus longipes, having serrations on the front edge, and thus labeled the teeth as Compsognathus sp. (of unknown species).
Description
For decades, Compsognathus was known as the smallest known non-avian dinosaur, although some dinosaurs discovered later, such as Mahakala and Microraptor, were even smaller. The German specimen was estimated to be and in length by separate authors, while the larger French specimen was estimated at and in length. The height at the hip has been estimated at for the German specimen and at for the French specimen. The German specimen was estimated to have weighed and , and the French specimen and . Compared to other compsognathids, the larger French specimen would have been similar in size to larger Sinosauropteryx specimens, but smaller than Huaxiagnathus and Mirischia.
Compsognathus were small, bipedal animals with long hind legs and longer tails, which they used for balance during locomotion. The forelimbs were smaller than the hindlimbs. The hand bore two large, clawed digits and a third, smaller digit that may have been non-functional. Their delicate skulls were narrow and long, with tapered snouts. The skull had five pairs of fenestrae (skull openings), the largest of which was for the orbit (eye socket), with the eyes being larger in proportion to the rest of the skull. The lower jaw was slender and had no mandibular fenestra, a hole in the side of the lower jawbone commonly seen in archosaurs.
The teeth were small and pointed, suited for its diet of small vertebrates and possibly other small animals, such as insects. The German specimen had three teeth in each premaxilla (front bone of the lower jaw), 15 or 16 teeth in each maxilla, and 18 teeth in the lower jaw. The French specimen had more teeth, including four in each premaxilla, 17 or 18 in the maxilla, and at least 21 teeth in the dentary. Compsognathids were unique among theropods in having tooth crowns that curved backwards at two thirds of their height, while their mid-parts were straight; also, the crowns had expanded bases. In Compsognathus, the frontmost teeth of the upper and lower jaws were unserrated, while those further back had fine serrations on their rear edges. In the German specimen, the crowns were around two times higher than wide in the front of the jaws but diminished in height further back, with the last tooth about as high as wide. The German specimen also shows a diastema (tooth gap) behind the first three teeth of the premaxilla. As such a gap was not present in the French specimen, Peyer suggested that additional teeth were possibly present in this region the German specimen.
The number of digits on the hand of Compsognathus has been a source of debate. For much of its history, Compsognathus was typically depicted with three digits, as is typical for theropods. However, the type specimen only preserved phalanges from the first two digits, leading to the suggestion that Compsognathus bore only two functional digits, with the third metacarpal being extremely slender and reduced. Study of the French specimen indicated that the third digit bore at least one or two small phalanges. However, there remains no evidence for an ungual phalanx on the third digit, so the digit may have been reduced and non-functional.
Integument
Some relatives of Compsognathus, namely Sinosauropteryx and Sinocalliopteryx, have been preserved with the remains of simple feathers covering the body like fur, prompting some scientists to suggest that Compsognathus might have been feathered in a similar way. Consequently, many depictions of Compsognathus show them with coverings of downy proto-feathers. However, no feathers or feather-like covering have been preserved with Compsognathus fossils, in contrast to Archaeopteryx, which are found in the same sediments. Karin Peyer, in 2006, reported skin impressions preserved on the side of the tail starting at the 13th tail vertebra. The impressions showed small bumpy tubercles, similar to the scales found on the tail and hind legs of Juravenator. Additional scales had in 1901 been reported by Von Huene, in the abdominal region of the German Compsognathus, but Ostrom subsequently disproved this interpretation; in 2012 they were by Achim Reisdorf seen as plaques of adipocere, corpse wax.
Like Compsognathus, and unlike Sinosauropteryx, a patch of fossilized skin from the tail and hindlimb of the possible relative Juravenator starki shows mainly scales, though there is some indication that simple feathers were also present in the preserved areas. This may mean that a feather covering was not ubiquitous in this group of dinosaurs, or maybe that some species had fewer feathers than others.
Classification
Originally classified as a lizard, the dinosaurian affinities of Compsognathus were first noted by Gegenbaur, Cope, and Huxley between 1863 and 1868. Cope, in 1870, classified Compsognathus within a new clade of dinosaurs, the Symphypoda, which also contained Ornithotarsus (today classified as Hadrosaurus). Later, both genera were found to belong to other groups of Cope's classification of dinosaurs: Compsognathus to the Gonipoda (equivalent to Theropoda, in which it is now classified), and Ornithotarsus to the Orthopoda (equivalent to Ornithischia). Huxley, in 1870, rejected Cope's dinosaur classification scheme, and instead proposed the new clade Ornithoscelida, in which he included the Dinosauria (comprising several forms now considered as ornithischians) and another new clade, the Compsognatha, which contained Compsognathus as the only member. Later, these groups fell into disuse, although a resurrection of the Ornithoscelida was proposed in 2017. The group Compsognatha was used for the last time by Marsh in a 1896 publication, where it was treated as a suborder of Theropoda. In the same publication, Marsh erected the new family Compsognathidae. Friedrich von Huene, in 1914, erected the new infraorder Coelurosauria, which includes the Compsognathidae amongst other families of small theropods; this classification remained in use since.
The Compsognathidae are a group of mostly small dinosaurs from the late Jurassic and early Cretaceous periods of China, Europe and South America. For many years, Compsognathus was the only member known, but in recent decades paleontologists have discovered several related genera. The clade includes Aristosuchus, Huaxiagnathus, Mirischia, Sinosauropteryx, and perhaps Juravenator and Scipionyx. At one time, Mononykus was proposed as a member of the family, but this was rejected by Chen and coauthors in a 1998 paper; they considered the similarities between Mononykus and the compsognathids to be an example of convergent evolution. The position of Compsognathus and its relatives within the coelurosaur group is uncertain. Some, such as theropod expert Thomas Holtz Jr. and co-authors Ralph Molnar and Phil Currie in the landmark 2004 text Dinosauria, hold the family as the most basal of the coelurosaurs, while others as part of the Maniraptora.
For almost a century, Compsognathus longipes was the only well-known small theropod species. This led to comparisons with Archaeopteryx and to suggestions of an especially close relationship with birds. In fact, Compsognathus, rather than Archaeopteryx, piqued Huxley's interest in the origin of birds. The two animals share similarities in shape and proportions, so many in fact that two specimens of Archaeopteryx, the "Eichstätt" and the "Solnhofen", were for a time misidentified as those of Compsognathus. Many other types of theropod dinosaurs, such as maniraptorans, are now known to have been more closely related to birds.
Below is a simplified cladogram placing Compsognathus in Compsognathidae by Senter et al. in 2012.
Here is an alternative phylogeny, published by Cau in 2024, with both specimens in bold.
Paleobiology
In a 2001 study conducted by Bruce Rothschild and other paleontologists, nine foot bones referred to Compsognathus were examined for signs of stress fracture, but none were found.
Habitat
Bidar and colleagues, in their 1972 description of the French specimen, argued that this specimen had webbed hands which would look like flippers in life. This interpretation was based on a supposed impression of the flipper that consists of several undulating wrinkles running parallel to the forelimb on the surface of the slab. In a 1975 popular book, L. Beverly Halstead depicts the animal as an amphibious dinosaur capable of feeding on aquatic prey and swimming out of reach of larger predators. Ostrom debunked this hypothesis, noting that the forelimb of the French specimen is poorly preserved, and that the wrinkles extend well beyond the skeleton and thus are likely sedimentary structures unrelated to the fossil.
Diet
The remains of a lizard in the German specimen's thoracic cavity show that Compsognathus preyed on small vertebrates. Marsh, who examined the specimen in 1881, thought that this small skeleton in the Compsognathus belly was an embryo, but in 1903, Franz Nopcsa concluded that it was a lizard. Ostrom identified the remains as belonging to a lizard of the genus Bavarisaurus, which he concluded was a fast and agile runner owing to its long tail and limb proportions. This in turn led to the conclusion that its predators, Compsognathus, must have had sharp vision and the ability to rapidly accelerate and outrun the lizard. Conrad made the lizard found in the thoracic cavity of the German specimen of Compsognathus the holotype of a new species Schoenesmahl dyspepsia. The lizard is in several pieces, indicating that the Compsognathus must have dismembered it while restraining it with its hands and teeth, and then swallowed the remains whole; a similar strategy is used by modern predatory birds. The French specimen's gastric contents consist of unidentified lizards or sphenodontids.
Possible eggs
The plate of the German Compsognathus shows several circular irregularities in diameter near the skeletal remains. Peter Griffiths interpreted them as immature eggs in 1993. However, later researchers have doubted their connection to the genus because they were found outside the body cavity of the animal. A well-preserved fossil of a Sinosauropteryx, a genus related to Compsognathus, shows two oviducts bearing two unlaid eggs. These proportionally larger and less numerous eggs of Sinosauropteryx cast further doubt on the original identification of the purported Compsognathus eggs. In 1964 German geologist Karl Werner Barthel had explained the discs as gas bubbles formed in the sediment because of the putrefaction of the carcass.
Speed
In 2007, William Sellers and Phillip Manning estimated a maximum speed of based on a computer model of the skeleton and muscles. This estimate has been criticized by other scholars.
Paleoenvironment
During the late Jurassic, Europe was a dry, tropical archipelago at the edge of the Tethys Sea. The fine limestone in which the skeletons of Compsognathus have been found originated in calcite from the shells of marine organisms. Both the German and French areas where Compsognathus specimens have been preserved were lagoons situated between the beaches and coral reefs of the Jurassic European islands in the Tethys Sea. Contemporaries of Compsognathus longipes include the early avialan Archaeopteryx lithographica and the pterosaurs Rhamphorhynchus muensteri and Pterodactylus antiquus. The same sediments in which Compsognathus have been preserved also contain fossils of a number of marine animals such as fish, crustaceans, echinoderms and marine mollusks, confirming the coastal habitat of this theropod. No other dinosaur has been found in association with Compsognathus, indicating that these little dinosaurs might in fact have been the top land predator in these islands.
Taphonomy
Much discussion revolved around the taphonomy of the German specimen, i.e. how the individual died and became fossilized. Reisdorf and Wuttke, in 2012, speculated about the events that lead to the death and transportation of the specimen to its place of burial. First, the individual must have been brought into the lagoon from its habitat, which probably was on the surrounding islands. It is possible that a flash flood swept the animal into the sea, in which case it likely died by drowning. It is also possible that the animal swam or drifted onto the sea, or that it rafted on plants, and was then transported by surface currents to its place of burial. In any case, the specimen would have arrived on the sea floor within a few hours after its death, as otherwise gases forming in its body cavity would have prevented it from sinking in one piece. Water depth at the burial site would have been large enough to prevent refloating of the carcass after such gases were produced. Rounded structures on the slab might have been formed by the release of these gases.
Taphonomic reconstructions are complicated as the exact locality and the position and orientation of the fossil within the sediments is no longer known. As a compression fossil, the specimen would originally have been preserved on both the upper surface of a layer and the lower surface of the subsequent layer (i.e., on a slab and its counter-slab); the counter-slab is now lost. Reisdorf and Wuttke, in 2012, argued that the front and hind limbs of the left side of the body were better (still connected together) than those of the right side. This suggests that the specimen is located on the bottom side of the upper slab, and was lying on its left side. The German specimen was preserved with a high degree of articulation – only the skull, hands, cervical ribs and gastralia show disarticulation. The braincase was displaced behind the skull, the first tail vertebra was rotated by 90°, and the tail shows a break between the seventh and eighth tail vertebra.
In both Compsognathus specimens, the neck is strongly curved, with the head coming to rest above the pelvis; the spine of the tail was likewise curved. This posture, known as the death pose, is found in many vertebrate fossils, and the German Compsognathus specimen was central in several studies that sought to explain this phenomenon. The physician Moodie, in 1918, suggested that the death pose in Compsognathus and similar fossils was the result of an opisthotonus – death throes causing spastic stiffening of the back musculature – while the animal was dying. This hypothesis was soon challenged by paleontologist Friedrich von Huene, who argued that the death pose was the result of desiccation and therefore occurred only after the death. Peter Wellnhofer, in 1991, argued that death poses resulted from the elastic pull of the ligaments, which are released after death. The veterinarian Cynthia Faux and the paleontologist Kevin Padian, in a 2007 study that gained much attention, supported the original opisthotonus hypothesis of Moodie. These authors furthermore argued that upon death, muscles are relaxed and body parts can be easily moved relative to each other. Since opisthotonic postures are already established during death, they may only be preserved if the animal dies in place and becomes buried rapidly. This contradicts previous interpretations on the environment and taphonomy of Compsognathus and other fossils from the Solnhofen limestones, which assumed very slow burial at the bottom of lagoons into which the carcasses were transported from nearby islands. Reisdorf and Wuttke concluded that the death posture indeed resulted from the release of ligaments, more specifically the , which spans the spine from the neck to tail in modern birds. The release of this ligament would have occurred gradually while the surrounding muscle tissue decayed, and only after the carcass was transported to its final site of deposition.
The bottom water of the lagoon was likely anaerobic (devoid in oxygen), resulting in a sea floor devoid of life except for microbial mats, and therefore preventing scavenging of the carcass. In the trunk region of the German specimen, the surface of the slab is markedly different in texture to the surrounding areas of the slab, showing irregular, nodular surfaces within depressions. Ostrom, in 1978, interpreted these structures as traces of weathering that took place just before the fossil was collected. Nopcsa, in 1903, instead suggested that these structures resulted from decomposing tissue of the carcass. Reisdorf and Wuttke, in their 2012 study, suggested that the structures are the remains of adipocere (corpse wax formed by bacteria) that formed around the carcass before burial. Such adipocere would have helped in conserving the state of articulation of the fossil for years when burial was very slow. The presence of adipocere would possibly rule out hypersalinity (very high salt contents) of the bottom water, because such conditions appear to be unfavorable for the adipocere producing bacteria.
In popular culture
Compsognathus is one of the more popular dinosaurs. For a long time it was considered unique in its small size, which is commonly compared to that of a chicken. These animals have appeared in the Jurassic Park franchise: in the films The Lost World: Jurassic Park, Jurassic Park III, Jurassic World: Fallen Kingdom and Jurassic World Dominion and in the series Camp Cretaceous, where they were often nicknamed Compies. In The Lost World: Jurassic Park, one of the characters incorrectly identifies the species as "Compsognathus triassicus", combining the genus name of Compsognathus longipes with the specific name of Procompsognathus triassicus, a distantly related small carnivore featured in the Jurassic Park novels.
| Biology and health sciences | Theropods | Animals |
577301 | https://en.wikipedia.org/wiki/Magnitude%20%28mathematics%29 | Magnitude (mathematics) | In mathematics, the magnitude or size of a mathematical object is a property which determines whether the object is larger or smaller than other objects of the same kind. More formally, an object's magnitude is the displayed result of an ordering (or ranking) of the class of objects to which it belongs. Magnitude as a concept dates to Ancient Greece and has been applied as a measure of distance from one object to another. For numbers, the absolute value of a number is commonly applied as the measure of units between a number and zero.
In vector spaces, the Euclidean norm is a measure of magnitude used to define a distance between two points in space. In physics, magnitude can be defined as quantity or distance. An order of magnitude is typically defined as a unit of distance between one number and another's numerical places on the decimal scale.
History
Ancient Greeks distinguished between several types of magnitude, including:
Positive fractions
Line segments (ordered by length)
Plane figures (ordered by area)
Solids (ordered by volume)
Angles (ordered by angular magnitude)
They proved that the first two could not be the same, or even isomorphic systems of magnitude. They did not consider negative magnitudes to be meaningful, and magnitude is still primarily used in contexts in which zero is either the smallest size or less than all possible sizes.
Numbers
The magnitude of any number is usually called its absolute value or modulus, denoted by .
Real numbers
The absolute value of a real number r is defined by:
Absolute value may also be thought of as the number's distance from zero on the real number line. For example, the absolute value of both 70 and −70 is 70.
Complex numbers
A complex number z may be viewed as the position of a point P in a 2-dimensional space, called the complex plane. The absolute value (or modulus) of z may be thought of as the distance of P from the origin of that space. The formula for the absolute value of is similar to that for the Euclidean norm of a vector in a 2-dimensional Euclidean space:
where the real numbers a and b are the real part and the imaginary part of z, respectively. For instance, the modulus of is . Alternatively, the magnitude of a complex number z may be defined as the square root of the product of itself and its complex conjugate, , where for any complex number , its complex conjugate is .
(where ).
Vector spaces
Euclidean vector space
A Euclidean vector represents the position of a point P in a Euclidean space. Geometrically, it can be described as an arrow from the origin of the space (vector tail) to that point (vector tip). Mathematically, a vector x in an n-dimensional Euclidean space can be defined as an ordered list of n real numbers (the Cartesian coordinates of P): x = [x1, x2, ..., xn]. Its magnitude or length, denoted by , is most commonly defined as its Euclidean norm (or Euclidean length):
For instance, in a 3-dimensional space, the magnitude of [3, 4, 12] is 13 because
This is equivalent to the square root of the dot product of the vector with itself:
The Euclidean norm of a vector is just a special case of Euclidean distance: the distance between its tail and its tip. Two similar notations are used for the Euclidean norm of a vector x:
A disadvantage of the second notation is that it can also be used to denote the absolute value of scalars and the determinants of matrices, which introduces an element of ambiguity.
Normed vector spaces
By definition, all Euclidean vectors have a magnitude (see above). However, a vector in an abstract vector space does not possess a magnitude.
A vector space endowed with a norm, such as the Euclidean space, is called a normed vector space. The norm of a vector v in a normed vector space can be considered to be the magnitude of v.
Pseudo-Euclidean space
In a pseudo-Euclidean space, the magnitude of a vector is the value of the quadratic form for that vector.
Logarithmic magnitudes
When comparing magnitudes, a logarithmic scale is often used. Examples include the loudness of a sound (measured in decibels), the brightness of a star, and the Richter scale of earthquake intensity. Logarithmic magnitudes can be negative. In the natural sciences, a logarithmic magnitude is typically referred to as a level.
Order of magnitude
Orders of magnitude denote differences in numeric quantities, usually measurements, by a factor of 10—that is, a difference of one digit in the location of the decimal point.
Other mathematical measures
| Mathematics | Linear algebra | null |
577307 | https://en.wikipedia.org/wiki/Tunnel%20boring%20machine | Tunnel boring machine | A tunnel boring machine (TBM), also known as a "mole" or a "worm", is a machine used to excavate tunnels. Tunnels are excavated through hard rock, wet or dry soil, or sand, each of which requires specialized technology.
Tunnel boring machines are an alternative to drilling and blasting (D&B) methods and "hand mining".
TBMs limit the disturbance to the surrounding ground and produce a smooth tunnel wall. This reduces the cost of lining the tunnel, and is suitable for use in urban areas. TBMs are expensive to construct, and larger ones are challenging to transport. These fixed costs become less significant for longer tunnels.
TBM-bored tunnel cross-sections range from to date. Narrower tunnels are typically bored using trenchless construction methods or horizontal directional drilling rather than TBMs. TBM tunnels are typically circular in cross-section although they may be u-shaped, horseshoes, square or rectangular.
Tunneling speeds increase over time. The first TBM peaked at 4 meters per week. This increased to 16 meters per week four decades later. By the end of the 19th century, speeds had reached over 30 meters per week. 21st century rock TBMs can excavate over 700 meters per week, while soil tunneling machines can exceed 200 meters per week. Speed generally declines as tunnel size increases.
History
1800s
The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods.
The first boring machine reported to have been built was Henri Maus's Mountain Slicer. Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through the Alps, Maus had it built in 1846 in an arms factory near Turin. It consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. The Revolutions of 1848 affected the funding, and the tunnel was not completed until 10 years later, by using less innovative and less expensive methods such as pneumatic drills.
In the United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel in northwest Massachusetts. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine, after inventor Charles Wilson. It drilled into the rock before breaking down (the tunnel was eventually completed more than 20 years later, and as with the Fréjus Rail Tunnel, by using less ambitious methods). Wilson's machine anticipated modern TBMs in the sense that it employed cutting discs, like those of a disc harrow, which were attached to the rotating head of the machine. In contrast to traditional chiseling or drilling and blasting, this innovative method of removing rock relied on simple metal wheels to apply a transient high pressure that fractured the rock.
In 1853, the American Ebenezer Talbot also patented a TBM that employed Wilson's cutting discs, although they were mounted on rotating arms, which in turn were mounted on a rotating plate. In the 1870s, John D. Brunton of England built a machine employing cutting discs that were mounted eccentrically on rotating plates, which in turn were mounted eccentrically on a rotating plate, so that the cutting discs would travel over almost all of the rock face that was to be removed.
The first TBM that tunneled a substantial distance was invented in 1863 and improved in 1875 by British Army officer Major Frederick Edward Blackett Beaumont (1833–1895); Beaumont's machine was further improved in 1880 by British Army officer Major Thomas English (1843–1935). In 1875, the French National Assembly approved the construction of a tunnel under the English Channel and the British Parliament supported a trial run using English's TBM. Its cutting head consisted of a conical drill bit behind which were a pair of opposing arms on which were mounted cutting discs. From June 1882 to March 1883, the machine tunneled, through chalk, a total of 1,840 m (6,036 ft). A French engineer, Alexandre Lavalley, who was also a Suez Canal contractor, used a similar machine to drill 1,669 m (5,476 ft) from Sangatte on the French side. However, despite this success, the cross-Channel tunnel project was abandoned in 1883 after the British military raised fears that the tunnel might be used as an invasion route. Nevertheless, in 1883, this TBM was used to bore a railway ventilation tunnel — in diameter and long — between Birkenhead and Liverpool, England, through sandstone under the Mersey River.
The Hudson River Tunnel was constructed from 1889 to 1904 using a Greathead shield TBM. The project used air compressed to to reduce cave-ins. However, many workers died via cave-in or decompression sickness.
1900s
During the late 19th and early 20th century, inventors continued to design, build, and test TBMs for tunnels for railroads, subways, sewers, water supplies, etc. TBMs employing rotating arrays of drills or hammers were patented. TBMs that resembled giant hole saws were proposed. Other TBMs consisted of a rotating drum with metal tines on its outer surface, or a rotating circular plate covered with teeth, or revolving belts covered with metal teeth. However, these TBMs proved expensive, cumbersome, and unable to excavate hard rock; interest in TBMs therefore declined. Nevertheless, TBM development continued in potash and coal mines, where the rock was softer.
A TBM with a bore diameter of was manufactured by The Robbins Company for Canada's Niagara Tunnel Project. The machine was used to bore a hydroelectric tunnel beneath Niagara Falls. The machine was named "Big Becky" in reference to the Sir Adam Beck hydroelectric dams to which it tunnelled to provide an additional hydroelectric tunnel.
2000s
An earth pressure balance TBM known as Bertha with a bore diameter of was produced by Hitachi Zosen Corporation in 2013. It was delivered to Seattle, Washington, for its Highway 99 tunnel project. The machine began operating in July 2013, but stalled in December 2013 and required substantial repairs that halted the machine until January 2016. Bertha completed boring the tunnel on April 4, 2017.
Two TBMs supplied by CREG excavated two tunnels for Kuala Lumpur's Rapid Transit with a boring diameter of . The medium was water saturated sandy mudstone, schistose mudstone, highly weathered mudstone as well as alluvium. It achieved a maximum advance rate of more than per month.The world's largest hard rock TBM, known as Martina, was built by Herrenknecht AG. Its excavation diameter was , total length ; excavation area of , thrust value 39,485 t, total weight 4,500 tons, total installed capacity 18 MW. Its yearly energy consumption was about 62 GWh. It is owned and operated by the Italian construction company Toto S.p.A. Costruzioni Generali (Toto Group) for the Sparvo gallery of the Italian Motorway Pass A1 ("Variante di Valico A1"), near Florence. The same company built the world's largest-diameter slurry TBM, excavation diameter of , owned and operated by the French construction company Dragages Hong Kong (Bouygues' subsidiary) for the Tuen Mun Chek Lap Kok link in Hong Kong.
Types
TBMs typically consist of a rotating cutting wheel in front, called a cutter head, followed by a main bearing, a thrust system, a system to remove excavated material (muck), and support mechanisms. Machines vary with site geology, amount of ground water present, and other factors.
Rock boring machines differ from earth boring machines in the way they cut the tunnel, the way they provide traction to support the boring activity, and in the way they support the newly formed tunnels walls.
Tunnel wall types
Concrete lining
Shielded TBMs are typically used to excavate tunnels in soil. They erect concrete segments behind the TBM to support the tunnel walls.
The machine stabilizes itself in the tunnel with hydraulic cylinders that press against the shield, allowing the TBM to apply pressure at the tunnel face.
Main Beam
Main Beam machines do not install concrete segments behind the cutter head. Instead, the rock is held up using ground support methods such as ring beams, rock bolts, shotcrete, steel straps, ring steel and wire mesh.
Shield types
Depending on the stability of the local geology, the newly formed walls of the tunnel often need to be supported immediately after being dug to avoid collapse, before any permanent support or lining has been constructed. Many TBMs are equipped with one or more cylindrical shields following behind the cutter head to support the walls until permanent tunnel support is constructed further along the machine. The stability of the walls also influences the method by which the TBM anchors itself in place so that it can apply force to the cutting head. This in turn determines whether the machine can bore and advance simultaneously, or whether these are done in alternating modes.
Open/Gripper
Gripper TBMs are used in rock tunnels. They forgo the use of a shield and instead push directly against the unreinforced sides of the tunnel.
Machines such as a Wirth machine can be moved only while ungripped. Other machines can move continuously. At the end of a Wirth boring cycle, legs drop to the ground, the grippers are retracted, and the machine advances. The grippers then reengage and the rear legs lift for the next cycle.
Single shield
A single-shield TBM has a single cylindrical shield after the cutting head. A permanent concrete lining is constructed immediately after the shield, and the TBM pushes off the lining to apply force to the cutter head. Because this pushing cannot be done while a next ring of lining is being constructed, the single-shield TBM operates in alternating cutting and lining modes.
Double shield
Double Shield (or telescopic shield) TBMs have a leading shield that advances with the cutting head and a trailing shield that acts as a gripper. The two shields can move axially relative to each other (i.e., telescopically) over a limited distance. The gripper shield anchors the TBM so that pressure can be applied to the cutter head while simultaneously the concrete lining is being constructed.
Tunnel-face support methods
In hard rock with minimal ground water, the area around the cutter head of a TBM can be unpressurized, as the exposed rock face can support itself. In weaker soil, or when there is significant ground water, pressure must be applied to the face of the tunnel to prevent collapse and/or the infiltration of ground water into the machine.
Earth Pressure Balance
Earth pressure balance (EPB) machines are used in soft ground with less than of pressure. It uses muck to maintain pressure at the tunnel face. The muck (or spoil) is admitted into the TBM via a screw conveyor. By adjusting the rate of extraction of muck and the advance rate of the TBM, the pressure at the face of the TBM can be controlled without the use of slurry. Additives such as bentonite, polymers and foam can be injected ahead of the face to stabilize the ground. Such additives can separately be injected in the cutter head and extraction screw to ensure that the muck is sufficiently cohesive to maintain pressure and restrict water flow.
Like some other TBM types, EPB's use thrust cylinders to advance by pushing against concrete segments. The cutter head uses a combination of tungsten carbide cutting bits, carbide disc cutters, drag picks and/or hard rock disc cutters.
EPB has allowed soft, wet, or unstable ground to be tunneled with a speed and safety not previously possible. The Channel Tunnel, the Thames Water Ring Main, sections of the London Underground, and most new metro tunnels completed in the last 20 years worldwide were excavated using this method. EPB has historically competed with the slurry shield method (see below), where the slurry is used to stabilize the tunnel face and transport spoil to the surface. EPB TBMs are mostly used in finer ground (such as clay) while slurry TBMs are mostly used for coarser ground (such as gravel).
Slurry shield
Slurry shield machines can be used in soft ground with high water pressure or where granular ground conditions (sands and gravels) do not allow a plug to form in the screw. The cutter head is filled with pressurised slurry, typically made of bentonite clay that applies hydrostatic pressure to the face. The slurry mixes with the muck before it is pumped to a slurry separation plant, usually outside the tunnel.
Slurry separation plants use multi-stage filtration systems that separate spoil from slurry to allow reuse. The degree to which slurry can be 'cleaned' depends on the relative particle sizes of the muck. Slurry TBMs are not suitable for silts and clays as the particle sizes of the spoil are less than that of the bentonite. In this case, water is removed from the slurry leaving a clay cake, which may be polluted.
A caisson system is sometimes placed at the cutting head to allow workers to operate the machine, although air pressure may reach elevated levels in the caisson, requiring workers to be medically cleared as "fit to dive" and able to operate pressure locks.
Open face soft ground
Open face soft ground TBMs rely on the excavated ground to briefly stand without support. They are suitable for use in ground with a strength of up to about with low water inflows. They can bore tunnels with cross-section in excess of . A backactor arm or cutter head bore to within of the edge of the shield. After a boring cycle, the shield is jacked forward to begin a new cycle. Ground support is provided by precast concrete, or occasionally spheroidal graphite iron (SGI) segments that are bolted or supported until a support ring has been added. The final segment, called the key, is wedge-shaped, and expands the ring until it is tight against the ground.
Tunnel size
TBMs range diameter from . Micro tunnel shield TBMs are used to construct small tunnels, and is a smaller equivalent to a general tunnelling shield and generally bore tunnels of , too small for operators to walk in.
Backup systems
Behind all types of tunnel boring machines, in the finished part of the tunnel, are trailing support decks known as the backup system, whose mechanisms can include conveyors or other systems for muck removal; slurry pipelines (if applicable); control rooms; electrical, dust-removal and ventilation systems; and mechanisms for transport of pre-cast segments.
Urban tunnelling and near-surface tunnelling
Urban tunnelling has the special requirement that the surface remain undisturbed, and that ground subsidence be avoided. The normal method of doing this in soft ground is to maintain soil pressures during and after construction.
TBMs with positive face control, such as earth pressure balance (EPB) and slurry shield (SS), are used in such situations. Both types (EPB and SS) are capable of reducing the risk of surface subsidence and voids if ground conditions are well documented. When tunnelling in urban environments, other tunnels, existing utility lines and deep foundations must be considered, and the project must accommodate measures to mitigate any detrimental effects to other infrastructure.
| Technology | Transport infrastructure | null |
8644994 | https://en.wikipedia.org/wiki/Extraterrestrial%20vortex | Extraterrestrial vortex | An extraterrestrial vortex is a vortex that occurs on planets and natural satellites other than Earth that have sufficient atmospheres. Most observed extraterrestrial vortices have been seen in large cyclones, or anticyclones. However, occasional dust storms have been known to produce vortices on Mars and Titan. Various spacecraft missions have recorded evidence of past and present extraterrestrial vortices. The largest extraterrestrial vortices are found on the gas giants, Jupiter and Saturn; and the ice giants, Uranus and Neptune.
Mercury
Due to Mercury's thin atmosphere, it does not experience weather-like storms or other atmospheric weather phenomena such as clouds, winds, or rain. Rather unusually, Mercury has magnetic 'tornadoes' that were observed by NASA's Mercury MESSENGER during a flyby in 2008. The tornadoes are twisted bundles of magnetic fields that connect Mercury's magnetic field to space.
Venus
Venus Express observed two large shape-shifting vortices on Venus' poles (polar vortices) in 2006 on one of its close-up flybys of the planet. The south pole was seen to have a large, constantly changing, double-eye vortex through high-resolution infrared measurements obtained by the VIRTIS instrument on Venus Express. The cause of the double-eyed vortex is unknown but the polar vortices are caused by the Hadley Cell atmospheric circulation of the lower atmosphere. Unusually, neither of the double vortices at the south pole ever line up and are located at slightly different altitudes. The southern pole's cyclone-like storm is roughly the size of Europe. In addition, the southern polar vortex is constantly changing shape but the cause is still unknown.
In 1979, NASA's Pioneer Venus observed a double vortex cyclone at the north pole. There have not been many more close-up observations of the north pole since Pioneer Venus.
Since most of the planet's water has escaped to space, Venus does not experience rain like Earth does. However, there has been evidence of lightning on Venus as confirmed by data from Venus Express. The lightning on Venus is different than the lightning on all other planets as it is associated with sulfuric acid clouds instead of water clouds. The magnetometer instrument on Venus Express detected electrical discharges when the spacecraft was orbiting close to the upper atmosphere of Venus. Most storms form high up in the atmosphere about 25 miles from the surface and all precipitation evaporates about 20 miles above the surface.
Mars
Most of the observed atmospheric events on Mars are dust storms which can sometimes disrupt enough dust to be seen from Earth. Many large dust storms occur every year on Mars but even more rare are the global dust storms that Mars experiences on average every 6 Earth years. NASA has observed global dust storms in 1971, 1977, 1982, 1994, 2001, 2007, and 2018. While these massive dust storms do cause problems for rovers and spacecraft operating on solar power, the winds on Mars top out at , less than half as strong as hurricane-force winds on Earth, which is not enough to rip apart mechanical equipment.
While Mars is most known for its recurring dust storms, it still experiences cyclone-like storms and polar vortices similar to Earth.
On April 27, 1999, a rare cyclone in diameter was detected by the Hubble Space Telescope in the northern polar region of Mars. It consisted of three cloud bands wrapped around a massive diameter eye, and contained features similar to storms that have been detected in the poles of Earth (see: polar low). It was only observed briefly, as it seemed to be dissipating when it was imaged six hours later, and was not seen on later imaging passes. Several other cyclones were imaged in about the same area: the March 2, 2001 cyclone, January 19, 2003 cyclone, and the November 27, 2004 cyclone.
In addition, NASA's 2001 Mars Odyssey Spacecraft observed a cold, low density, polar vortex in the planet's atmosphere above latitudes 70 degrees north and higher. NASA determined that every winter a polar vortex forms over the north pole above the atmosphere. The vortex and atmosphere are separated by a transition zone where strong winds encircle the pole and terrestrial jet stream-like characteristics. The stability of these annular polar vortices are still being researched as scientists believe Martian dust may play a role in their formation.
Jupiter
Jupiter's atmosphere is lined with hundreds of vortices most likely to be cyclones, or anticyclones, similar to those on Earth. Voyager and Cassini discovered that, unlike the terrestrial atmosphere, 90% of Jovian vortices are anticyclones, meaning they rotate in the opposite direction of the planet's rotation. Many cyclones have showed up and disappeared over the years with some even merging to form larger cyclones.
When NASA's Juno Spacecraft arrived at Jupiter in 2016, it observed giant cyclones encircling the north and south poles of the planet. Nine large cyclones were spotted around the north pole and 6 around the south pole. Upon further flybys, Juno spotted another cyclone at the south pole and noticed that 6 of the 7 cyclones formed a hexagonal arrangement around the cyclone at the center of the south pole. Data from Juno has shown that this storm system is stable and there have been no signs of vortices attempting to merge.
The Great Red Spot on Jupiter is, by far, the largest extraterrestrial anticyclone (or cyclone) known. The Great Red Spot is located in the southern hemisphere and has wind speeds greater than any storm ever measured on Earth. New data from Juno found that the storm penetrates into Jupiter's atmosphere about . The giant storm has been monitored since 1830 but has possibly survived for over 350 years. Over 100 years ago, the Great Red Spot was well over two Earths wide but has been shrinking ever since. When Voyagers 1 and 2 flew by in 1979, they measured the massive cyclone to be twice Earth's diameter. Measurements today from telescopes have measured a diameter of 1.3 Earths wide.
Oval BA (or Red Spot Jr.) is the second-largest storm on Jupiter and formed from the merging of 3 smaller cyclones in 2000. It is located just to the south of the Great Red Spot and has been increasing in size in recent years, slowly turning a more uniform white.
The Great Dark Spot is a feature observed near Jupiter's north pole in 2000 by the Cassini–Huygens spacecraft that was a short-lived dark cloud that grew to the size of the Great Red Spot before disappearing after 11 weeks. The phenomenon is speculated by scientists to be a side-effect of strong auroras on Jupiter.
Saturn
Every Saturn year, about 28 Earth years, Saturn has massive planet-circling storms, called Great White Spots. The Great White Spots are short-lived but can impact the atmosphere and temperature of the planet for up to 3 Earth years after their collapse. The spots can be several thousand kilometers wide and can even run into their own tails and fade out once they circle the planet.
Most storms on Saturn occur in a zone in the southern hemisphere dubbed 'storm alley' by scientists for its high abundance of storm activity. Storm alley lies 35 degrees south of the equator and it is still unknown why there is such a large quantity of storms that form here. There is also a long-lived storm known as the Dragon Storm, which flares occasionally on Saturn's southern latitudes. Cassini detected bursts of radio emissions from the storm on multiple occasions, similar to the short bursts of static that are produced from lightning on earth.
On October 11, 2006, the Cassini-Huygens spacecraft took images of a storm with a well-defined distinct eyewall over the south pole of Saturn. It was across, with storms in the eyewall reaching high. The storm had wind speeds of and appeared to be stationary over Saturn's south pole.
Saturn currently holds the record for the longest continuous thunderstorm in the Solar System with a storm that Cassini observed back in 2009 that lasted for over 8 months. Instruments on Cassini detected powerful radio waves coming from lightning discharges in Saturn's atmosphere. These radio waves are about 10,000 times stronger than the ones emitted by terrestrial lightning.
A hexagonal cyclone in Saturn's north pole has been spotted since the passage of Voyager 1 and 2, and was first imaged by Cassini on January 3, 2009. It is just under in diameter, with a depth of about , and encircles the north pole of the ringed planet at roughly 78° N latitude.
Titan
Titan is very similar to Earth and is the only known planetary body with a substantial atmosphere and stable bodies of surface liquid that still exist. Titan experiences storms similar to Earth, but instead of water there is methane and ethane liquids on Titan.
Data from Cassini found that Titan experiences dust storms similar to those on Earth and Mars. When Titan is in equinox, strong down-burst winds raise micron-sized particles up from sand dunes and create dust storms. The dust storms are relatively short but create intense infrared bright spots in the atmosphere, which is how Cassini detected them.
Cassini captured an image of a south polar vortex on Titan in June 2012. Titan was also found to have a northern polar vortex with similar characteristics as the southern polar vortex. Scientists later found that these vortices formed during the winter, meaning they were seasonal, similar to Earth's polar vortices.
The south polar vortex was imaged again in 2013 and it was determined that the vortex forms higher up in the atmosphere than previously thought. The hazy atmosphere that Titan has leaves the moon unilluminated in the Sun's rays but the image of the vortex showed a bright spot on the south pole. Scientists derived that the vortex is high up in the atmosphere, possibly above the haze, because it can still be illuminated by the Sun.
Uranus
Uranus was long thought to be atmospherically static due to the lack of storms observed, but in recent years astronomers have started to see more storm activity on the planet. However, there is still limited data on Uranus as it is so far away from Earth and hard to observe regularly.
In 2018, Hubble Space Telescope (HST) captured an image of Uranus that showed a large, bright, polar cap over the north pole. The storm is thought to be long-lived and scientists hypothesize it formed by seasonal changes in atmospheric flow.
In 2006, Hubble Space Telescope imaged the Uranus Dark Spot. Scientists saw similarities between the Uranus Dark Spot (UDS) and the Great Dark Spots (GDS) on Neptune, although UDS was much smaller. GDS were thought to be anticyclonic vortices in Neptune's atmosphere and UDS is assumed to be similar in nature.
In 1998, HST captured infrared images of multiple storms raging on Uranus due to seasonal changes.
Neptune
The Great Dark Spot was an Earth-sized vortex observed in the southern hemisphere of Neptune by Voyager 2 in 1989. The storm had some of the highest recorded wind speeds in the Solar System at approximately and rotated around the planet once every 18.3 hours. When the Hubble Space Telescope turned its gaze to Neptune in 1994, the spot had vanished; but the storm causing the spot might have continued lower in the atmosphere.
The Small Dark Spot (sometimes called Great Dark Spot 2 or Wizard's Eye) was another vortex observed by Voyager 2 in its 1989 pass of Neptune. This spot is located approximately 30° further south on the planet and transits the planet once every 16.1 hours. The Small Dark Spot's distinct appearance comes from white methane-ice clouds which upwell through the center of the storm and give it an eye-like appearance. This storm had also apparently vanished by the time the Hubble Space Telescope inspected the planet in 1994.
A total of 4 additional dark spots have been observed on Neptune since the discovery of the first two. A small storm which formed in the southern hemisphere in 2015 was tracked by Amy Simon and her team at NASA Goddard (she is now part of the Outer Planet Atmospheres Legacy project) from its birth to its death. While focused on tracking this small storm the team was able to discover the emergence of a giant spot the size of the Great Dark Spot at 23° North of the equator in 2018. The observations taken by this team were able to point to the importance of "companion clouds" in identifying the storms that cause these spots even while a dark spot was not present. This team also concluded that the storms have a likely lifespan of 2 years with a life of up to 6 years being possible, and will look to study the shape and speed of dark spots in the future.
| Physical sciences | Planetary science | Astronomy |
11779912 | https://en.wikipedia.org/wiki/Marine%20sediment | Marine sediment | Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either have their origins in soil and rocks and have been transported from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea, or they are biogenic deposits from marine organisms or from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris.
Except within a few kilometres of a mid-ocean ridge, where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediment. This material comes from several different sources and is highly variable in composition. Seafloor sediment can range in thickness from a few millimetres to several tens of kilometres. Near the surface seafloor sediment remains unconsolidated, but at depths of hundreds to thousands of metres the sediment becomes lithified (turned to rock).
Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Sediment transported from the land accumulates the fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher. Biogenous oozes accumulate at a rate of about one centimetre per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years.
Sediments from the land are deposited on the continental margins by surface runoff, river discharge, and other processes. Turbidity currents can transport this sediment down the continental slope to the deep ocean floor. The deep ocean floor undergoes its own process of spreading out from the mid-ocean ridge, and then slowly subducts accumulated sediment on the deep floor into the molten interior of the earth. In turn, molten material from the interior returns to the surface of the earth in the form of lava flows and emissions from deep sea hydrothermal vents, ensuring the process continues indefinitely. The sediments provide habitat for a multitude of marine life, particularly of marine microorganisms. Their fossilized remains contain information about past climates, plate tectonics, ocean circulation patterns, and the timing of major extinctions.
Overview
Except within a few kilometres of a mid-ocean ridge, where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediments. This material comes from several different sources and is highly variable in composition, depending on proximity to a continent, water depth, ocean currents, biological activity, and climate. Seafloor sediments (and sedimentary rocks) can range in thickness from a few millimetres to several tens of kilometres. Near the surface, the sea-floor sediments remain unconsolidated, but at depths of hundreds to thousands of metres (depending on the type of sediment and other factors) the sediment becomes lithified.
The various sources of seafloor sediment can be summarized as follows:
Terrigenous sediment is derived from continental sources transported by rivers, wind, ocean currents, and glaciers. It is dominated by quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter.
Pelagic carbonate sediment is derived from organisms (e.g., foraminifera) living in the ocean water (at various depths, but mostly near surface) that make their shells (a.k.a. tests) out of carbonate minerals such as calcite.
Pelagic silica sediment is derived from marine organisms (e.g., diatoms and radiolaria) that make their tests out of silica (microcrystalline quartz).
Volcanic ash and other volcanic materials are derived from both terrestrial and submarine eruptions.
Iron and manganese nodules form as direct precipitates from ocean-bottom water.
The distributions of some of these materials around the seas are shown in the diagram at the start of this article ↑. Terrigenous sediments predominate near the continents and within inland seas and large lakes. These sediments tend to be relatively coarse, typically containing sand and silt, but in some cases even pebbles and cobbles. Clay settles slowly in nearshore environments, but much of the clay is dispersed far from its source areas by ocean currents. Clay minerals are predominant over wide areas in the deepest parts of the ocean, and most of this clay is terrestrial in origin. Siliceous oozes (derived from radiolaria and diatoms) are common in the south polar region, along the equator in the Pacific, south of the Aleutian Islands, and within large parts of the Indian Ocean. Carbonate oozes are widely distributed in all of the oceans within equatorial and mid-latitude regions. In fact, clay settles everywhere in the oceans, but in areas where silica- and carbonate-producing organisms are prolific, they produce enough silica or carbonate sediment to dominate over clay.
Carbonate sediments are derived from a wide range of near-surface pelagic organisms that make their shells out of carbonate. These tiny shells, and the even tinier fragments that form when they break into pieces, settle slowly through the water column, but they don't necessarily make it to the bottom. While calcite is insoluble in surface water, its solubility increases with depth (and pressure) and at around 4,000 m, the carbonate fragments dissolve. This depth, which varies with latitude and water temperature, is known as the carbonate compensation depth. As a result, carbonate oozes are absent from the deepest parts of the ocean (deeper than 4,000 m), but they are common in shallower areas such as the mid-Atlantic ridge, the East Pacific Rise (west of South America), along the trend of the Hawaiian/Emperor Seamounts (in the northern Pacific), and on the tops of many isolated seamounts.
Texture
Sediment texture can be examined in several ways. The first way is grain size. Sediments can be classified by particle size according to the Wentworth scale. Clay sediments are the finest with a grain diameter of less than .004 mm and boulders are the largest with grain diameters of 256 mm or larger. Among other things, grain size represents the conditions under which the sediment was deposited. High energy conditions, such as strong currents or waves, usually results in the deposition of only the larger particles as the finer ones will be carried away. Lower energy conditions will allow the smaller particles to settle out and form finer sediments.
Sorting is another way to categorize sediment texture. Sorting refers to how uniform the particles are in terms of size. If all of the particles are of a similar size, such as in beach sand, the sediment is well-sorted. If the particles are of very different sizes, the sediment is poorly sorted, such as in glacial deposits.
A third way to describe marine sediment texture is its maturity, or how long its particles have been transported by water. One way which can indicate maturity is how round the particles are. The more mature a sediment the rounder the particles will be, as a result of being abraded over time. A high degree of sorting can also indicate maturity, because over time the smaller particles will be washed away, and a given amount of energy will move particles of a similar size over the same distance. Lastly, the older and more mature a sediment the higher the quartz content, at least in sediments derived from rock particles. Quartz is a common mineral in terrestrial rocks, and it is very hard and resistant to abrasion. Over time, particles made from other materials are worn away, leaving only quartz behind. Beach sand is a very mature sediment; it is composed primarily of quartz, and the particles are rounded and of similar size (well-sorted).
Origins
Marine sediments can also classified by their source of origin. There are four types:
Lithogenous sediments, also called terrigenous sediments, are derived from preexisting rock and come from land via rivers, ice, wind and other processes. They are referred to as terrigenous sediments since most comes from the land.
Biogenous sediments are composed of the remains of marine organisms, and come from organisms like plankton when their exoskeletons break down
Hydrogenous sediments come from chemical reactions in the water, and are formed when materials that are dissolved in water precipitate out and form solid particles.
Cosmogenous sediments are derived from extraterrestrial sources, coming from space, filtering in through the atmosphere or carried to Earth on meteorites.
Lithogenous
Lithogenous or terrigenous sediment is primarily composed of small fragments of preexisting rocks that have made their way into the ocean. These sediments can contain the entire range of particle sizes, from microscopic clays to large boulders, and they are found almost everywhere on the ocean floor. Lithogenous sediments are created on land through the process of weathering, where rocks and minerals are broken down into smaller particles through the action of wind, rain, water flow, temperature- or ice-induced cracking, and other erosive processes. These small eroded particles are then transported to the oceans through a variety of mechanisms:
Streams and rivers: Various forms of runoff deposit large amounts of sediment into the oceans, mostly in the form of finer-grained particles. About 90% of the lithogenous sediment in the oceans is thought to have come from river discharge, particularly from Asia. Most of this sediment, especially the larger particles, will be deposited and remain fairly close to the coastline, however, smaller clay particles may remain suspended in the water column for long periods of time and may be transported great distances from the source.
Wind: Windborne (aeolian) transport can take small particles of sand and dust and move them thousands of kilometres from the source. These small particles can fall into the ocean when the wind dies down, or can serve as the nuclei around which raindrops or snowflakes form. Aeolian transport is particularly important near desert areas.
Glaciers and ice rafting: As glaciers grind their way over land, they pick up lots of soil and rock particles, including very large boulders, that get carried by the ice. When the glacier meets the ocean and begins to break apart or melt, these particles get deposited. Most of the deposition will happen close to where the glacier meets the water, but a small amount of material is also transported longer distances by rafting, where larger pieces of ice drift far from the glacier before releasing their sediment.
Gravity: Landslides, mudslides, avalanches, and other gravity-driven events can deposit large amounts of material into the ocean when they happen close to shore.
Waves: Wave action along a coastline will erode rocks and will pull loose particles from beaches and shorelines into the water.
Volcanoes: Volcanic eruptions emit vast amounts of ash and other debris into the atmosphere, where it can then be transported by wind to eventually get deposited in the oceans.
Gastroliths: Another, relatively minor, means of transporting lithogenous sediment to the ocean are gastroliths. Gastrolith means "stomach stone". Many animals, including seabirds, pinnipeds, and some crocodiles deliberately swallow stones and regurgitate them latter. Stones swallowed on land can be regurgitated at sea. The stones can help grind food in the stomach or act as ballast regulating buoyancy. Mostly these processes deposit lithogenous sediment close to shore. Sediment particles can then be transported farther by waves and currents, and may eventually escape the continental shelf and reach the deep ocean floor.
Composition
Lithogenous sediments usually reflect the composition of whatever materials they were derived from, so they are dominated by the major minerals that make up most terrestrial rock. This includes quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter. Quartz (silicon dioxide, the main component of glass) is one of the most common minerals found in nearly all rocks, and it is very resistant to abrasion, so it is a dominant component of lithogenous sediments, including sand.
Biogenous
Biogenous sediments come from the remains of living organisms that settle out as sediment when the organisms die. It is the "hard parts" of the organisms that contribute to the sediments; things like shells, teeth or skeletal elements, as these parts are usually mineralized and are more resistant to decomposition than the fleshy "soft parts" that rapidly deteriorate after death.
Macroscopic sediments contain large remains, such as skeletons, teeth, or shells of larger organisms. This type of sediment is fairly rare over most of the ocean, as large organisms do not die in enough of a concentrated abundance to allow these remains to accumulate. One exception is around coral reefs; here there is a great abundance of organisms that leave behind their remains, in particular the fragments of the stony skeletons of corals that make up a large percentage of tropical sand.
Microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or tests. Although very small, these organisms are highly abundant and as they die by the billions every day their tests sink to the bottom to create biogenous sediments. Sediments composed of microscopic tests are far more abundant than sediments from macroscopic particles, and because of their small size they create fine-grained, mushy sediment layers. If the sediment layer consists of at least 30% microscopic biogenous material, it is classified as a biogenous ooze. The remainder of the sediment is often made up of clay.
The primary sources of microscopic biogenous sediments are unicellular algaes and protozoans (single-celled amoeba-like creatures) that secrete tests of either calcium carbonate (CaCO3) or silica (SiO2). Silica tests come from two main groups, the diatoms (algae) and the radiolarians (protozoans).
Diatoms are particularly important members of the phytoplankton, functioning as small, drifting algal photosynthesizers. A diatom consists of a single algal cell surrounded by an elaborate silica shell that it secretes for itself. Diatoms come in a range of shapes, from elongated, pennate forms, to round, or centric shapes that often have two halves, like a Petri dish. In areas where diatoms are abundant, the underlying sediment is rich in silica diatom tests, and is called diatomaceous earth.
Radiolarians are planktonic protozoans (making them part of the zooplankton), that like diatoms, secrete a silica test. The test surrounds the cell and can include an array of small openings through which the radiolarian can extend an amoeba-like "arm" or pseudopod. Radiolarian tests often display a number of rays protruding from their shells which aid in buoyancy. Oozes that are dominated by diatom or radiolarian tests are called siliceous oozes.
Like the siliceous sediments, the calcium carbonate, or calcareous sediments are also produced from the tests of microscopic algae and protozoans; in this case the coccolithophores and foraminiferans. Coccolithophores are single-celled planktonic algae about 100 times smaller than diatoms. Their tests are composed of a number of interlocking CaCO3 plates (coccoliths) that form a sphere surrounding the cell. When coccolithophores die the individual plates sink out and form an ooze. Over time, the coccolithophore ooze lithifies to becomes chalk. The White Cliffs of Dover in England are composed of coccolithophore-rich ooze that turned into chalk deposits.
Foraminiferans (also referred to as forams) are protozoans whose tests are often chambered, similar to the shells of snails. As the organism grows, is secretes new, larger chambers in which to reside. Most foraminiferans are benthic, living on or in the sediment, but there are some planktonic species living higher in the water column. When coccolithophores and foraminiferans die, they form calcareous oozes.
Older calcareous sediment layers contain the remains of another type of organism, the discoasters; single-celled algae related to the coccolithophores that also produced calcium carbonate tests. Discoaster tests were star-shaped, and reached sizes of 5-40 μm across. Discoasters went extinct approximately 2 million years ago, but their tests remain in deep, tropical sediments that predate their extinction.
Because of their small size, these tests sink very slowly; a single microscopic test may take about 10–50 years to sink to the bottom! Given that slow descent, a current of only 1 cm/sec could carry the test as much as 15,000 km away from its point of origin before it reaches the bottom. Despite this, the sediments in a particular location are well-matched to the types of organisms and degree of productivity that occurs in the water overhead. This means the sediment particles must be sinking to the bottom at a much faster rate, so they accumulate below their point of origin before the currents can disperse them. Most of the tests do not sink as individual particles; about 99% of them are first consumed by some other organism, and are then aggregated and expelled as large fecal pellets, which sink much more quickly and reach the ocean floor in only 10–15 days. This does not give the particles as much time to disperse, and the sediment below will reflect the production occurring near the surface. The increased rate of sinking through this mechanism has been called the "fecal express".
Hydrogenous
Seawater contains many different dissolved substances. Occasionally chemical reactions occur that cause these substances to precipitate out as solid particles, which then accumulate as hydrogenous sediment. These reactions are usually triggered by a change in conditions, such as a change in temperature, pressure, or pH, which reduces the amount of a substance that can remain in a dissolved state. There is not a lot of hydrogenous sediment in the ocean compared to lithogenous or biogenous sediments, but there are some interesting forms.
In hydrothermal vents seawater percolates into the seafloor where it becomes superheated by magma before being expelled by the vent. This superheated water contains many dissolved substances, and when it encounters the cold seawater after leaving the vent, these particles precipitate out, mostly as metal sulfides. These particles make up the "smoke" that flows from a vent, and may eventually settle on the bottom as hydrogenous sediment. Hydrothermal vents are distributed along the Earth's plate boundaries, although they may also be found at intra-plate locations such as hotspot volcanoes. Currently there are about 500 known active submarine hydrothermal vent fields, about half visually observed at the seafloor and the other half suspected from water column indicators and/or seafloor deposits.
Manganese nodules are rounded lumps of manganese and other metals that form on the seafloor, generally ranging between 3–10 cm in diameter, although they may sometimes reach up to 30 cm. The nodules form in a manner similar to pearls; there is a central object around which concentric layers are slowly deposited, causing the nodule to grow over time. The composition of the nodules can vary somewhat depending on their location and the conditions of their formation, but they are usually dominated by manganese- and iron oxides. They may also contain smaller amounts of other metals such as copper, nickel and cobalt. The precipitation of manganese nodules is one of the slowest geological processes known; they grow on the order of a few millimetres per million years. For that reason, they only form in areas where there are low rates of lithogenous or biogenous sediment accumulation, because any other sediment deposition would quickly cover the nodules and prevent further nodule growth. Therefore, manganese nodules are usually limited to areas in the central ocean, far from significant lithogenous or biogenous inputs, where they can sometimes accumulate in large numbers on the seafloor (Figure 12.4.2 right). Because the nodules contain a number of commercially valuable metals, there has been significant interest in mining the nodules over the last several decades, although most of the efforts have thus far remained at the exploratory stage. A number of factors have prevented large-scale extraction of nodules, including the high costs of deep sea mining operations, political issues over mining rights, and environmental concerns surrounding the extraction of these non-renewable resources.
Evaporites are hydrogenous sediments that form when seawater evaporates, leaving the dissolved materials to precipitate into solids, particularly halite (salt, NaCl). In fact, the evaporation of seawater is the oldest form of salt production for human use, and is still carried out today. Large deposits of halite evaporites exist in a number of places, including under the Mediterranean Sea. Beginning around 6 million years ago, tectonic processes closed off the Mediterranean Sea from the Atlantic, and the warm climate evaporated so much water that the Mediterranean was almost completely dried out, leaving large deposits of salt in its place (an event known as the Messinian Salinity Crisis). Eventually the Mediterranean re-flooded about 5.3 million years ago, and the halite deposits were covered by other sediments, but they still remain beneath the seafloor.
Oolites are small, rounded grains formed from concentric layers of precipitation of material around a suspended particle. They are usually composed of calcium carbonate, but they may also from phosphates and other materials. Accumulation of oolites results in oolitic sand, which is found in its greatest abundance in the Bahamas.
Methane hydrates are another type of hydrogenous deposit with a potential industrial application. All terrestrial erosion products include a small proportion of organic matter derived mostly from terrestrial plants. Tiny fragments of this material plus other organic matter from marine plants and animals accumulate in terrigenous sediments, especially within a few hundred kilometres of shore. As the sediments pile up, the deeper parts start to warm up (from geothermal heat), and bacteria get to work breaking down the contained organic matter. Because this is happening in the absence of oxygen (a.k.a. anaerobic conditions), the by-product of this metabolism is the gas methane (CH4). Methane released by the bacteria slowly bubbles upward through the sediment toward the seafloor. At water depths of 500 m to 1,000 m, and at the low temperatures typical of the seafloor (close to 4 °C), water and methane combine to create a substance known as methane hydrate. Within a few metres to hundreds of metres of the seafloor, the temperature is low enough for methane hydrate to be stable and hydrates accumulate within the sediment. Methane hydrate is flammable because when it is heated, the methane is released as a gas. The methane within seafloor sediments represents an enormous reservoir of fossil fuel energy. Although energy corporations and governments are anxious to develop ways to produce and sell this methane, anyone that understands the climate-change implications of its extraction and use can see that this would be folly.
Cosmogenous
Cosmogenous sediment is derived from extraterrestrial sources, and comes in two primary forms; microscopic spherules and larger meteor debris. Spherules are composed mostly of silica or iron and nickel, and are thought to be ejected as meteors burn up after entering the atmosphere. Meteor debris comes from collisions of meteorites with Earth. These high impact collisions eject particles into the atmosphere that eventually settle back down to Earth and contribute to the sediments. Like spherules, meteor debris is mostly silica or iron and nickel. One form of debris from these collisions are tektites, which are small droplets of glass. They are likely composed of terrestrial silica that was ejected and melted during a meteorite impact, which then solidified as it cooled upon returning to the surface.
Cosmogenous sediment is fairly rare in the ocean and it does not usually accumulate in large deposits. However, it is constantly being added to through space dust that continuously rains down on Earth. About 90% of incoming cosmogenous debris is vaporized as it enters the atmosphere, but it is estimated that 5 to 300 tons of space dust land on the Earth's surface each day.
Composition
Siliceous ooze
Siliceous ooze is a type of biogenic pelagic sediment located on the deep ocean floor. Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians. Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica Si(O2), as opposed to calcareous oozes, which are made from skeletons of calcium carbonate organisms (i.e. coccolithophores). Silica (Si) is a bioessential element and is efficiently recycled in the marine environment through the silica cycle. Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes.
Calcareous ooze
The term calcareous can be applied to a fossil, sediment, or sedimentary rock which is formed from, or contains a high proportion of, calcium carbonate in the form of calcite or aragonite. Calcareous sediments (limestone) are usually deposited in shallow water near land, since the carbonate is precipitated by marine organisms that need land-derived nutrients. Generally speaking, the farther from land sediments fall, the less calcareous they are. Some areas can have interbedded calcareous sediments due to storms, or changes in ocean currents. Calcareous ooze is a form of calcium carbonate derived from planktonic organisms that accumulates on the sea floor. This can only occur if the ocean is shallower than the carbonate compensation depth. Below this depth, calcium carbonate begins to dissolve in the ocean, and only non-calcareous sediments are stable, such as siliceous ooze or pelagic red clay.
Lithified sediments
Distribution
Where and how sediments accumulate will depend on the amount of material coming from a source, the distance from the source, the amount of time that sediment has had to accumulate, how well the sediments are preserved, and the amounts of other types of sediments that are also being added to the system.
Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Lithogenous sediment accumulates the fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher.
Biogenous oozes accumulate at a rate of about 1 cm per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years. As described above, manganese nodules have an incredibly slow rate of accumulation, gaining 0.001 millimetres per thousand years.
Marine sediments are thickest near the continental margins where they can be over 10 km thick. This is because the crust near passive continental margins is often very old, allowing for a long period of accumulation, and because there is a large amount of terrigenous sediment input coming from the continents. Near mid-ocean ridge systems where new oceanic crust is being formed, sediments are thinner, as they have had less time to accumulate on the younger crust.
As distance increases from a ridge spreading center the sediments get progressively thicker, increasing by approximately 100–200 m of sediment for every 1000 km distance from the ridge axis. With a seafloor spreading rate of about 20–40 km/million years, this represents a sediment accumulation rate of approximately 100–200 m every 25–50 million years.
The diagram at the start of this article ↑ shows the distribution of the major types of sediment on the ocean floor. Cosmogenous sediments could potentially end up in any part of the ocean, but they accumulate in such small abundances that they are overwhelmed by other sediment types and thus are not dominant in any location. Similarly, hydrogenous sediments can have high concentrations in specific locations, but these regions are very small on a global scale. So cosmogenous and hydrogenous sediments can mostly be ignored in the discussion of global sediment patterns.
Coarse lithogenous/terrigenous sediments are dominant near the continental margins as land runoff, river discharge, and other processes deposit vast amounts of these materials on the continental shelf. Much of this sediment remains on or near the shelf, while turbidity currents can transport material down the continental slope to the deep ocean floor (abyssal plain). Lithogenous sediment is also common at the poles where thick ice cover can limit primary production, and glacial breakup deposits sediments along the ice edge.
Coarse lithogenous sediments are less common in the central ocean, as these areas are too far from the sources for these sediments to accumulate. Very small clay particles are the exception, and as described below, they can accumulate in areas that other lithogenous sediment will not reach.
The distribution of biogenous sediments depends on their rates of production, dissolution, and dilution by other sediments. Coastal areas display very high primary production, so abundant biogenous deposits might be expected in these regions. However, sediment must be >30% biogenous to be considered a biogenous ooze, and even in productive coastal areas there is so much lithogenous input that it swamps the biogenous materials, and that 30% threshold is not reached. So coastal areas remain dominated by lithogenous sediment, and biogenous sediments will be more abundant in pelagic environments where there is little lithogenous input.
In order for biogenous sediments to accumulate their rate of production must be greater than the rate at which the tests dissolve. Silica is undersaturated throughout the ocean and will dissolve in seawater, but it dissolves more readily in warmer water and lower pressures; that is, it dissolves faster near the surface than in deep water. Silica sediments will therefore only accumulate in cooler regions of high productivity where they accumulate faster than they dissolve. This includes upwelling regions near the equator and at high latitudes where there are abundant nutrients and cooler water.
Oozes formed near the equatorial regions are usually dominated by radiolarians, while diatoms are more common in the polar oozes. Once the silica tests have settled on the bottom and are covered by subsequent layers, they are no longer subject to dissolution and the sediment will accumulate. Approximately 15% of the seafloor is covered by siliceous oozes.
Biogenous calcium carbonate sediments also require production to exceed dissolution for sediments to accumulate, but the processes involved are a little different than for silica. Calcium carbonate dissolves more readily in more acidic water. Cold seawater contains more dissolved CO2 and is slightly more acidic than warmer water. So calcium carbonate tests are more likely to dissolve in colder, deeper, polar water than in warmer, tropical, surface water. At the poles the water is uniformly cold, so calcium carbonate readily dissolves at all depths, and carbonate sediments do not accumulate. In temperate and tropical regions calcium carbonate dissolves more readily as it sinks into deeper water.
The depth at which calcium carbonate dissolves as fast as it accumulates is called the calcium carbonate compensation depth or calcite compensation depth, or simply the CCD. The lysocline represents the depths where the rate of calcium carbonate dissolution increases dramatically (similar to the thermocline and halocline). At depths shallower than the CCD carbonate accumulation will exceed the rate of dissolution, and carbonate sediments will be deposited. In areas deeper than the CCD, the rate of dissolution will exceed production, and no carbonate sediments can accumulate (see diagram at right). The CCD is usually found at depths of 4 – 4.5 km, although it is much shallower at the poles where the surface water is cold. Thus calcareous oozes will mostly be found in tropical or temperate waters less than about 4 km deep, such as along the mid-ocean ridge systems and atop seamounts and plateaus.
The CCD is deeper in the Atlantic than in the Pacific since the Pacific contains more CO2, making the water more acidic and calcium carbonate more soluble. This, along with the fact that the Pacific is deeper, means that the Atlantic contains more calcareous sediment than the Pacific. All told, about 48% of the seafloor is dominated by calcareous oozes.
Much of the rest of the deep ocean floor (about 38%) is dominated by abyssal clays. This is not so much a result of an abundance of clay formation, but rather the lack of any other types of sediment input. The clay particles are mostly of terrestrial origin, but because they are so small they are easily dispersed by wind and currents, and can reach areas inaccessible to other sediment types. Clays dominate in the central North Pacific, for example. This area is too far from land for coarse lithogenous sediment to reach, it is not productive enough for biogenous tests to accumulate, and it is too deep for calcareous materials to reach the bottom before dissolving.
Because clay particles accumulate so slowly, the clay-dominated deep ocean floor is often home to hydrogenous sediments like manganese nodules. If any other type of sediment was produced here it would accumulate much more quickly and would bury the nodules before they had a chance to grow.
Coastal sediments
Shallow water marine environments are found in areas between the shore and deeper water, such as a reef wall or a shelf break. The water in this environment is shallow and clear, allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
The sediment itself is often composed of limestone, which forms readily in shallow, warm calm waters. The shallow marine environments are not exclusively composed of siliciclastic or carbonaceous sediments. While they cannot always coexist, it is possible to have a shallow marine environment composed solely of carbonaceous sediment or one that is composed completely of siliciclastic sediment. Shallow water marine sediment is made up of larger grain sizes because smaller grains have been washed out to deeper water. Within sedimentary rocks composed of carbonaceous sediment, there may also be evaporite minerals. The most common evaporite minerals found within modern and ancient deposits are gypsum, anhydrite, and halite; they can occur as crystalline layers, isolated crystals or clusters of crystals.
In terms of geologic time, it is said that most Phanerozoic sedimentary rock was deposited in shallow marine environments as about 75% of the sedimentary carapace is made up of shallow marine sediments; it is then assumed that Precambrian sedimentary rocks were too, deposited in shallow marine waters, unless it is specifically identified otherwise. This trend is seen in the North American and Caribbean region. Also, as a result of supercontinent breakup and other shifting tectonic plate processes, shallow marine sediment displays large variations in terms of quantity in the geologic time.
Bioturbation
Bioturbation is the reworking of sediment by animals or plants. These include burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.
Bioturbators are ecosystem engineers because they alter resource availability to other species through the physical changes they make to their environments. This type of ecosystem change affects the evolution of cohabitating species and the environment, which is evident in trace fossils left in marine and terrestrial sediments. Other bioturbation effects include altering the texture of sediments (diagenesis), bioirrigation, and displacement of microorganisms and non-living particles. Bioturbation is sometimes confused with the process of bioirrigation, however these processes differ in what they are mixing; bioirrigation refers to the mixing of water and solutes in sediments and is an effect of bioturbation
Walruses and salmon are examples of large bioturbators. Although the activities of these large macrofaunal bioturbators are more conspicuous, the dominant bioturbators are small invertebrates, such as polychaetes, ghost shrimp and mud shrimp. The activities of these small invertebrates, which include burrowing and ingestion and defecation of sediment grains, contribute to mixing and the alteration of sediment structure.
Bioirrigation
Bioirrigation is the process of benthic organisms flushing their burrows with overlying water. The exchange of dissolved substances between the porewater and overlying seawater that results is an important process in the context of the biogeochemistry of the oceans. Coastal aquatic environments often have organisms that destabilize sediment. They change the physical state of the sediment. Thus improving the conditions for other organisms and themselves. These organisms often also cause Bioturbation, which is commonly used interchangeably or in reference with bioirrigation.
Bioirrigation works as two different processes. These processes are known as particle reworking and ventilation, which is the work of benthic macro-invertebrates (usually ones that burrow). This particle reworking and ventilation is caused by the organisms when they feed (faunal feeding), defecate, burrow, and respire. Bioirrigation is responsible for a large amount of oxidative transport and has a large impact on biogeochemical cycles.
Pelagic sediments
Pelagic sediments, or pelagite, are fine-grained sediments that accumulate as the result of the settling of particles to the floor of the open ocean, far from land. These particles consist primarily of either the microscopic, calcareous or siliceous shells of phytoplankton or zooplankton; clay-size siliciclastic sediment; or some mixture of these. Trace amounts of meteoric dust and variable amounts of volcanic ash also occur within pelagic sediments.
Based upon the composition of the ooze, there are three main types of pelagic sediments: siliceous oozes, calcareous oozes, and red clays.
An extensive body of work on deep-water processes and sediments has been built over the past 150 years since the voyage of HMS Challenger (1872–1876), during which the first systematic study of seafloor sediments was made. For many decades since that pioneering expedition, and through the first half of the twentieth century, the deep sea was considered entirely pelagic in nature.
The composition of pelagic sediments is controlled by three main factors. The first factor is the distance from major landmasses, which affects their dilution by terrigenous, or land-derived, sediment. The second factor is water depth, which affects the preservation of both siliceous and calcareous biogenic particles as they settle to the ocean bottom. The final factor is ocean fertility, which controls the amount of biogenic particles produced in surface waters.
Turbidites
Turbidites are the geologic deposits of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Turbidites are deposited in the deep ocean troughs below the continental shelf, or similar structures in deep lakes, by underwater avalanches which slide down the steep slopes of the continental shelf edge. When the material comes to rest in the ocean trough, it is the sand and other coarse material which settles first followed by mud and eventually the very fine particulate matter. This sequence of deposition creates the Bouma sequences that characterize these rocks.
Turbidites were first recognised in the 1950s and the first facies model was developed by Bouma in 1962. Since that time, turbidites have been one of the better known and most intensively studied deep-water sediment facies. They are now very well known from sediment cores recovered from modern deep-water systems, subsurface (hydrocarbon) boreholes and ancient outcrops now exposed on land. Each new study of a particular turbidite system reveals specific deposit characteristics and facies for that system. The most commonly observed facies have been variously synthesised into a range of facies schemes.
Contourites
A contourite is a sedimentary deposit commonly formed on continental rise to lower slope settings, although they may occur anywhere that is below storm wave base. Countourites are produced by thermohaline-induced deepwater bottom currents and may be influenced by wind or tidal forces. The geomorphology of contourite deposits is mainly influenced by the deepwater bottom-current velocity, sediment supply, and seafloor topography.
Contourites were first identified in the early 1960s by Bruce Heezen and co-workers at Woods Hole Oceanographic Institute. Their now seminal paper demonstrated the very significant effects of contour-following bottom currents in shaping sedimentation on the deep continental rise off eastern North America. The deposits of these semi-permanent alongslope currents soon became known as contourites, and the demarcation of slope-parallel, elongate and mounded sediment bodies made up largely of contourites became known as contourite drifts.
Hemipelagic
Hemipelagic sediments, or hemipelagite, are a type of marine sediments that consists of clay and silt-sized grains that are terrigenous and some biogenic material derived from the landmass nearest the deposits or from organisms living in the water. Hemipelagic sediments are deposited on continental shelves and continental rises, and differ from pelagic sediment compositionally. Pelagic sediment is composed of primarily biogenic material from organisms living in the water column or on the seafloor and contains little to no terrigenous material. Terrigenous material includes minerals from the lithosphere like feldspar or quartz. Volcanism on land, wind blown sediments as well as particulates discharged from rivers can contribute to Hemipelagic deposits. These deposits can be used to qualify climatic changes and identify changes in sediment provenances.
Ecology
Benthos () is the community of organisms that live on, in, or near the seafloor, also known as the benthic zone.
Hyperbenthos (or hyperbenthic organisms), prefix , live just above the sediment.
Epibenthos (or epibenthic organisms), prefix , live on top of the sediments.
Endobenthos (or endobenthic organisms), prefix , live buried, or burrowing in the sediment, often in the oxygenated top layer.
Microbenthos
Marine microbenthos are microorganisms that live in the benthic zone of the ocean – that live near or on the seafloor, or within or on surface seafloor sediments. The word benthos comes from Greek, meaning "depth of the sea". Microbenthos are found everywhere on or about the seafloor of continental shelves, as well as in deeper waters, with greater diversity in or on seafloor sediments. In shallow waters, seagrass meadows, coral reefs and kelp forests provide particularly rich habitats. In photic zones benthic diatoms dominate as photosynthetic organisms. In intertidal zones changing tides strongly control opportunities for microbenthos.
Diatoms form a (disputed) phylum containing about 100,000 recognised species of mainly unicellular algae. Diatoms generate about 20 per cent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, and contribute nearly half of the organic material found in the oceans.
Coccolithophores are minute unicellular photosynthetic protists with two flagella for locomotion. Most of them are protected by a shell covered with ornate circular plates or scales called coccoliths. The coccoliths are made from calcium carbonate. The term coccolithophore derives from the Greek for a seed carrying stone, referring to their small size and the coccolith stones they carry. Under the right conditions they bloom, like other phytoplankton, and can turn the ocean milky white.
Radiolarians are unicellular predatory protists encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the ocean sediment. These remains, as microfossils, provide valuable information about past oceanic conditions.
Like radiolarians, foraminiferans (forams for short) are single-celled predatory protists, also protected with shells that have holes in them. Their name comes from the Latin for "hole bearers". Their shells, often called tests, are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of agglutinated sediment particles or chiton, and (rarely) of silica. Most forams are benthic, but about 40 species are planktic. They are widely researched with well established fossil records which allow scientists to infer a lot about past environments and climates.
Both foraminifera and diatoms have planktonic and benthic forms, that is, they can drift in the water column or live on sediment at the bottom of the ocean. Either way, their shells end up on the seafloor after they die. These shells are widely used as climate proxies. The chemical composition of the shells are a consequence of the chemical composition of the ocean at the time the shells were formed. Past water temperatures can be also be inferred from the ratios of stable oxygen isotopes in the shells, since lighter isotopes evaporate more readily in warmer water leaving the heavier isotopes in the shells. Information about past climates can be inferred further from the abundance of forams and diatoms, since they tend to be more abundant in warm water.
The sudden extinction event which killed the dinosaurs 66 million years ago also rendered extinct three-quarters of all other animal and plant species. However, deep-sea benthic forams flourished in the aftermath. In 2020 it was reported that researchers have examined the chemical composition of thousands of samples of these benthic forams and used their findings to build the most detailed climate record of Earth ever.
Some endoliths have extremely long lives. In 2013 researchers reported evidence of endoliths in the ocean floor, perhaps millions of years old, with a generation time of 10,000 years. These are slowly metabolizing and not in a dormant state. Some Actinomycetota found in Siberia are estimated to be half a million years old.
Sediment cores
The diagram on the right shows an example of a sediment core. The sample was retrieved from the Upernavik Fjord circa 2018. Grain-size measurements were made, and the top 50 cm was dated with the 210Pb method.
Carbon processing
Thinking about ocean carbon and carbon sequestration has shifted in recent years from a structurally-based chemical reactivity viewpoint toward a view that includes the role of the ecosystem in organic carbon degradation rates. This shift in view towards organic carbon and ecosystem involvement includes aspects of the "molecular revolution" in biology, discoveries on the limits of life, advances in quantitative modelling, paleo studies of ocean carbon cycling, novel analytical techniques, and interdisciplinary efforts. In 2020, LaRowe et al. outlined a broad view of this issue that is spread across multiple scientific disciplines related to marine sediments and global carbon cycling.
Evolutionary history
To begin with, the Earth was molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust and water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans.
By the start of the Archean, about four billion years ago, rocks were often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. High-grade rocks were derived from volcanic island arcs, while low-grade metamorphic rocks represented deep-sea sediments eroded from the neighboring island rocks and deposited in a forearc basin. The earliest-known supercontinent Rodinia assembled about one billion years ago, and began to break apart after about 250 million years during the latter part of the Proterozoic.
The Paleozoic, (Ma), started shortly after the breakup of Pannotia and at the end of a global ice age. Throughout the early Paleozoic, the Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era the continents gathered together into a supercontinent called Pangaea, which included most of the Earth's land area. During the Silurian, which started 444 Ma, Gondwana continued a slow southward drift to high southern latitudes. The melting of ice caps and glaciers contributed to a rise in sea levels, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. Other cratons and continent fragments drifted together near the equator, starting the formation of a second supercontinent known as Euramerica.
During the Triassic deep-ocean sediments were laid down and subsequently disappeared through the subduction of oceanic plates, so very little is known of the Triassic open ocean. The supercontinent Pangaea rifted during the Triassic – especially late in the period – but had not yet separated. The first non-marine sediments in the rift that marks the initial break-up of Pangea are of Late Triassic age. Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare; despite their prominence in Western Europe where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west. Thus Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans and terrestrial vertebrates.
Patterns or traces of bioturbation are preserved in lithified rock. The study of such patterns is called ichnology, or the study of "trace fossils", which, in the case of bioturbators, are fossils left behind by digging or burrowing animals. This can be compared to the footprint left behind by these animals. In some cases bioturbation is so pervasive that it completely obliterates sedimentary structures, such as laminated layers or cross-bedding. Thus, it affects the disciplines of sedimentology and stratigraphy within geology. The study of bioturbator ichnofabrics uses the depth of the fossils, the cross-cutting of fossils, and the sharpness (or how well defined) of the fossil to assess the activity that occurred in old sediments. Typically the deeper the fossil, the better preserved and well defined the specimen.
Important trace fossils from bioturbation have been found in marine sediments from tidal, coastal and deep sea sediments. In addition sand dune, or Eolian, sediments are important for preserving a wide variety of fossils. Evidence of bioturbation has been found in deep-sea sediment cores including into long records, although the act extracting the core can disturb the signs of bioturbation, especially at shallower depths. Arthropods, in particular are important to the geologic record of bioturbation of Eolian sediments. Dune records show traces of burrowing animals as far back as the lower Mesozoic, 250 Ma, although bioturbation in other sediments has been seen as far back as 550 Ma.
Research history
The first major study of deep-ocean sediments occurred between 1872 and 1876 with the HMS Challenger expedition, which travelled nearly 70,000 nautical miles sampling seawater and marine sediments. The scientific goals of the expedition were to take physical measurements of the seawater at various depths, as well as taking samples so the chemical composition could be determined, along with any particulate matter or marine organisms that were present. This included taking samples and analysing sediments from the deep ocean floor. Before the Challenger voyage, oceanography had been mainly speculative. As the first true oceanographic cruise, the Challenger expedition laid the groundwork for an entire academic and research discipline.
Earlier theories of continental drift proposed that continents in motion "plowed" through the fixed and immovable seafloor. Later in the 1960s the idea that the seafloor itself moves and also carries the continents with it as it spreads from a central rift axis was proposed by Harold Hess and Robert Dietz. The phenomenon is known today as plate tectonics. In locations where two plates move apart, at mid-ocean ridges, new seafloor is continually formed during seafloor spreading. In 1968, the oceanographic research vessel Glomar Challenger was launched and embarked on a 15-year-long program, the Deep Sea Drilling Program. This program provided crucial data that supported the seafloor spreading hypothesis by collecting rock samples that confirmed that the farther from the mid-ocean ridge, the older the rock was.
| Physical sciences | Oceanography | Earth science |
320320 | https://en.wikipedia.org/wiki/Speculum%20%28medicine%29 | Speculum (medicine) | A speculum (Latin for 'mirror'; : specula or speculums) is a medical tool for investigating body orifices, with a form dependent on the orifice for which it is designed. In old texts, the speculum may also be referred to as a diopter or dioptra. Like an endoscope, a speculum allows a view inside the body; endoscopes, however, tend to have optics while a speculum is intended for direct vision.
History
Vaginal and anal specula were used by the ancient Greeks and Romans, and speculum artifacts have been found in Pompeii. The modern vaginal speculum, developed by J. Marion Sims, consists of a hollow cylinder with a rounded end that is divided into two hinged parts, somewhat like the beak of a duck. This speculum is inserted into the vagina to dilate it for examination of the vagina and cervix.
The modern vaginal speculum was developed by J. Marion Sims, a plantation doctor in Lancaster County, United States. Between 1845 and 1849, Sims performed dozens of surgeries, without anesthesia, on at least 12 enslaved women. In these experiments, Sims developed a technique to repair fistula and in the process invented the duckbill speculum. These experiments, and the development of the modern specula, led some to regard Sims as the "father of modern gynaecology."
By the 1860s, specula were integrated into criminal justice practices in the UK. In Great Britain, examinations of the cervix were made mandatory for all women convicted of prostitution by the country's Contagious Disease Act.
In the 19th century, the vaginal speculum became a cultural symbol of the tenuous relationship between women and their physicians. Use of the speculum was generally avoided in medical practices, and most vaginal conditions were diagnosed through symptoms or palpating the abdomen. Many practitioners had moral concerns about the use of the speculum, and preferred to diagnose through palpating the abdomen. As late as 1910, physicians believed the vaginal speculum to be inferior to the "educated touch."
These concerns continued into the early 20th century as the speculum became commonplace in gynecology practices. Often, nurses played a major role in ensuring the proper use of the speculum during medical exams. The 1946 and 1956 editions of a multi-volume gynecology text for nurses required that nurses remain present during examination to protect both the patient and physician from "blackmail by designing persons."
, 85% of gynecologists are women. As a result of this demographic shift, the procedures around speculum use have also changed.
Construction
Specula have been made of glass or metal. They were generally made of stainless steel and sterilized between uses, but particularly in the 21st century, many — especially those used in emergency departments and doctor's offices — are made of plastic, and are disposable, single-use items. Those used in surgical suites are still commonly made of stainless steel.
Types
Specula come in a variety of shapes based on their purpose, and a variety of sizes; in any case the cylinder or bill(s) of the instrument allow the operator a direct vision of the area of interest and the possibility to introduce instruments for further interventions such as a biopsy.
Vaginal
The most common specula used in gynecologic practice are varying sizes of bivalved vaginal speculum; the two bills are hinged and are "closed" when the speculum is inserted to facilitate its entry and "opened" in its final position where they can be arrested by a screw mechanism, so that the operator is freed from keeping the bills apart.
A cylindrical-shaped speculum, introduced in 2001, the dilating vaginal speculum (also known as the Veda-scope) invented by Clemens van der Weegen, inflates the vagina with filtered air. (see diagram) The device has two main functions: a) to take a normal Pap smear with a cervical brush or a cytology brush; and b) as an internal colposcope so that the operator can pivot the Veda-scope to view any part of the vagina barrel and cervix facilitated by an internal light source that can illuminate the vaginal wall and cervix with multi-coloured light filters, which can detect pre-cancerous cells with the aid of acetic acid solution and iodine solution. It also has a facility to attach a digital camera for viewing and recording.
A specialized form of vaginal speculum is the weighted speculum, which consists of a broad half tube which is bent at about a 90-degree angle, with the channel of the tube on the exterior side of the angle. One end of the tube has a roughly spherical metal weight surrounding the channel of the speculum. A weighted speculum is placed in the vagina during vaginal surgery with the patient in the lithotomy position. The weight holds the speculum in place and frees the surgeon's hands for other tasks.
A vaginal speculum is also used in fertility treatments, particularly artificial insemination, and allows the vaginal cavity to be opened and observed thereby facilitating the deposit of semen into the vagina.
Cylindrical shape
One bill
Two bills (bivalved)
Three bills
Rectal
Vaginal specula are also used for anal surgery, although several other forms of anal specula exist. One form, the anoscope, resembles a tube that has a removable bullet-shaped insert. When the anoscope is inserted into the anus, the insert dilates the anus to the diameter of the tube. The insert is then removed, leaving the tube to allow examination of the lower rectum and anus.
This style of anal speculum is one of the oldest designs for surgical instruments still in use, with examples dating back many centuries. The sigmoidoscope can be further advanced into the lower intestinal tract and requires an endoscopic set-up.
Tubal shape
One bill
Two bills
Three bills
Nasal
Nasal specula have two relatively flat bills with handle. The instrument is hinged so that when the handles are squeezed together the bills spread laterally, allowing examination.
Additionally, the Thudichum nasal speculum is commonly used in the outpatient examination of the nose.
Aural
Ear or aural specula resemble a funnel, and come in a variety of sizes.
Eyelid
For ophthalmic surgery such as cataract surgery, a speculum designed to retract the eyelids is used.
Oral
In veterinary medicine, a McPherson Speculum can be used for oral examination. The speculum helps keep the mouth open during the exam and helps avoid biting injuries.
Non-medical use
Specula are used for sexual pleasure, both vaginally and anally.
| Biology and health sciences | Diagnostics | Health |
320336 | https://en.wikipedia.org/wiki/Hand%20axe | Hand axe | A hand axe (or handaxe or Acheulean hand axe) is a prehistoric stone tool with two faces that is the longest-used tool in human history. It is made from stone, usually flint or chert that has been "reduced" and shaped from a larger piece by knapping, or hitting against another stone. They are characteristic of the lower Acheulean and middle Palaeolithic (Mousterian) periods, roughly 1.6 million years ago to about 100,000 years ago, and used by Homo erectus and other early humans, but rarely by Homo sapiens.
Their technical name (biface) comes from the fact that the archetypical model is a generally bifacial (with two wide sides or faces) and almond-shaped (amygdaloidal) lithic flake. Hand axes tend to be symmetrical along their longitudinal axis and formed by pressure or percussion. The most common hand axes have a pointed end and rounded base, which gives them their characteristic almond shape, and both faces have been knapped to remove the natural cortex, at least partially. Hand axes are a type of the somewhat wider biface group of two-faced tools or weapons.
Hand axes were the first prehistoric tools to be recognized as such: the first published representation of a hand axe was drawn by John Frere and appeared in a British publication in 1800. Until that time, their origins were thought to be natural or supernatural. They were called thunderstones, because popular tradition held that they had fallen from the sky during storms or were formed inside the earth by a lightning strike and then appeared at the surface. They are used in some rural areas as an amulet to protect against storms.
Handaxes are generally thought to have been primarily used as cutting tools, with the wide base serving as an ergonomic area for the hand to grip the tool, though other uses, such as throwing weapons and use as social and sexual signaling have been proposed.
Terminology
The four classes of hand axe are:
Large, thick hand axes reduced from cores or thick flakes, referred to as blanks
Thinned blanks. While form remains rough and uncertain, an effort has been made to reduce the thickness of the flake or core
Either a preform or crude formalized tool, such as an adze
Finer formalized tool types such as projectile points and fine bifaces
While Class 4 hand axes are referred to as "formalized tools", bifaces from any stage of a lithic reduction sequence may be used as tools. (Other biface typologies make five divisions rather than four.)
French antiquarian André Vayson de Pradenne introduced the word in 1920. This term co-exists with the more popular hand axe (), that was coined by Gabriel de Mortillet much earlier. The continued use of the word biface by François Bordes and Lionel Balout supported its use in France and Spain, where it replaced the term hand axe. Use of the expression hand axe has continued in English as the equivalent of the French ( in Spanish), while biface applies more generally for any piece that has been carved on both sides by the removal of shallow or deep flakes. The expression is used in German; it can be literally translated as hand axe, although in a stricter sense it means "fist wedge". It is the same in Dutch where the expression used is which literally means "fist axe". The same locution occurs in other languages.
However, the general impression of these tools was based on ideal (or classic) pieces that were of such perfect shape that they caught the attention of non-experts. Their typology broadened the term's meaning. Biface hand axes and bifacial lithic items are distinguished. A hand axe need not be a bifacial item and many bifacial items are not hand axes. Nor were hand axes and bifacial items exclusive to the Lower Palaeolithic period in the Old World. They appear throughout the world and in many different pre-historical epochs, without necessarily implying an ancient origin. Lithic typology is not a reliable chronological reference and was abandoned as a dating system. Examples of this include the "quasi-bifaces" that sometimes appear in strata from the Gravettian, Solutrean and Magdalenian periods in France and Spain, the crude bifacial pieces of the Lupemban culture (9000 B.C.) or the pyriform tools found near Sagua La Grande in Cuba. The word biface refers to something different in English than in French or in Spanish, which could lead to many misunderstandings. Bifacially carved cutting tools, similar to hand axes, were used to clear scrub vegetation throughout the Neolithic and Chalcolithic periods. These tools are similar to more modern adzes and were a cheaper alternative to polished axes. The modern day villages along the Sepik river in New Guinea continue to use tools that are virtually identical to hand axes to clear forest. "The term biface should be reserved for items from before the Würm II-III interstadial", although certain later objects could exceptionally be called bifaces.
Hand axe does not relate to axe, which was overused in lithic typology to describe a wide variety of stone tools. At the time the use of such items was not understood. In the particular case of Palaeolithic hand axes the term axe is an inadequate description. Lionel Balout stated, "the term should be rejected as an erroneous interpretation of these objects that are not 'axes. Subsequent studies supported this idea, particularly those examining the signs of use.
Materials
Hand axes are mainly made of flint, but rhyolites, phonolites, quartzites and other coarse rocks were used as well. Obsidian, natural volcanic glass, shatters easily and was rarely used.
Uses
Most researchers think that handaxes were primarily used as cutting tools. The pioneers of Palaeolithic tool studies first suggested that bifaces were used as axes despite the fact that they have a sharp border all around. Other uses seem to show that hand axes were a multi-functional tool, leading some to describe them as the "Acheulean Swiss Army knife". Other academics have suggested that the hand axe was simply a byproduct of being used as a core to make other tools, a weapon, or was perhaps used ritually.
Wells proposed in 1899 that hand axes were used as missile weapons to hunt prey – an interpretation supported by Calvin, who suggested that some of the rounder specimens of Acheulean hand axes were used as hunting projectiles or as "killer frisbees" meant to be thrown at a herd of animals at a water hole so as to stun one of them. This assertion was inspired by findings from the Olorgesailie archaeological site in Kenya. Few specimens indicate hand axe hafting, and some are too large for that use. However, few hand axes show signs of heavy damage indicative of throwing, modern experiments have shown the technique to often result in flat-faced landings, and many modern scholars consider the "hurling" theory to be poorly conceived but so attractive that it has taken a life of its own.
As hand axes can be recycled, resharpened and remade, they could have been used for varied tasks. For this reason it may be misleading to think of them as axes, they could have been used for tasks such as digging, cutting, scraping, chopping, piercing and hammering. However, other tools, such as small knives, are better suited for some of these tasks, and many hand axes have been found with no traces of use.
Baker suggested that since so many hand axes have been found that have no retouching, perhaps the hand axe was not itself a tool, but a large lithic core from which flakes had been removed and used as tools (flake core theory). On the other hand, there are many hand axes found with retouching such as sharpening or shaping, which casts doubt on this idea.
Other theories suggest the shape is part tradition and part by-product of its manufacture. Many early hand axes appear to be made from simple rounded pebbles (from river or beach deposits). It is necessary to detach a 'starting flake', often much larger than the rest of the flakes (due to the oblique angle of a rounded pebble requiring greater force to detach it), thus creating an asymmetry. Correcting the asymmetry by removing material from the other faces, encouraged a more pointed (oval) form factor. (Knapping a completely circular hand axe requires considerable correction of the shape.) Studies in the 1990s at Boxgrove, in which a butcher attempted to cut up a carcass with a hand axe, revealed that the hand axe was able to expose bone marrow.
Kohn and Mithen independently arrived at the explanation that symmetric hand axes were favoured by sexual selection as fitness indicators. Kohn in his book As We Know It wrote that the hand axe is "a highly visible indicator of fitness, and so becomes a criterion of mate choice." Miller followed their example and said that hand axes have characteristics that make them subject to sexual selection, such as that they were made for over a million years throughout Africa, Europe and Asia, they were made in large numbers, and most were impractical for utilitarian use. He claimed that a single design persisting across time and space cannot be explained by cultural imitation and draws a parallel between bowerbirds' bowers (built to attract potential mates and used only during courtship) and Pleistocene hominids' hand axes. He called hand axe building a "genetically inherited propensity to construct a certain type of object." He discards the idea that they were used as missile weapons because more efficient weapons were available, such as javelins. Although he accepted that some hand axes may have been used for practical purposes, he agreed with Kohn and Mithen who showed that many hand axes show considerable skill, design and symmetry beyond that needed for utility. Some were too big, such as the Maritime Academy handaxe or the "Great Hand Axe" found in Furze Platt, England that is 30.6 cm long (other scholars measure it as 39.5 cm long). Some were too small - less than two inches. Some were "overdetermined", featuring symmetry beyond practical requirements and showing evidence of unnecessary attention to form and finish. Some were actually made out bone instead of stone and thus were not very practical, suggesting a cultural or ritual use. Miller thinks that the most important clue is that under electron microscopy hand axes show no signs of use or evidence of edge wear. Others argue that little evidence for use-wear simply relates to the particular sedimentological conditions, rather than being evidence of discarding without use. It has been noted that hand axes can be good handicaps in Zahavi's handicap principle theory: learning costs are high, risks of injury, they require physical strength, hand-eye coordination, planning, patience, pain tolerance and resistance to infection from cuts and bruises when making or using such a hand axe.
Evidence from wear analysis
The use-wear analysis of Palaeolithic hand axes is carried out on findings from emblematic sites across nearly all of Western Europe. Keeley and Semenov were the pioneers of this specialized investigation. Keeley stated, "The morphology of typical hand axes suggests a greater range of potential activities than those of flakes".
Many problems need to be overcome in carrying out this type of analysis. One is the difficulty in observing larger pieces with a microscope. Of the millions of known pieces and despite their long role in human history, few have been thoroughly studied. Another arises from the clear evidence that the same tasks were performed more effectively using utensils made from flakes:
Keeley based his observations on archaeological sites in England. He proposed that in base settlements where it was possible to predict future actions and where greater control on routine activities was common, the preferred tools were made from specialized flakes, such as racloirs, backed knives, scrapers and punches. However, hand axes were more suitable on expeditions and in seasonal camps, where unforeseen tasks were more common. Their main advantage in these situations was the lack of specialization and adaptability to multiple eventualities. A hand axe has a long blade with different curves and angles, some sharper and others more resistant, including points and notches. All of this is combined in one tool. Given the right circumstances, it is possible to make use of loose flakes. In the same book, Keeley states that a number of the hand axes studied were used as knives to cut meat (such as hand axes from Hoxne and Caddington). He identified that the point of another hand axe had been used as a clockwise drill. This hand axe came from Clacton-on-Sea (all of these sites are located in the east of England). Toth reached similar conclusions for pieces from the Spanish site in Ambrona (Soria). Analysis carried out by Domínguez-Rodrigo and co-workers on the primitive Acheulean site in Peninj (Tanzania) on a series of tools dated 1.5 mya shows clear microwear produced by plant phytoliths, suggesting that the hand axes were used to work wood. Among other uses, use-wear evidence for fire making has been identified on dozens of later Middle Palaeolithic hand axes from France, suggesting Neanderthals struck these tools with the mineral pyrite to produce sparks at least 50,000 years ago.
Macroscopic traces
Some hand axes were used with force that left clearly visible marks. Other visible marks can be left as the scars from retouching, on occasion it is possible to distinguish them from marks left by the initial manufacture. One of the most common cases is when a point breaks. This was seen at sites in Europe, Africa and Asia. One example comes from the El Basalito site in Salamanca, where excavation uncovered fragments of a hand axe with marks at the tip that appeared to be the result of the action of a wedge, which would have subjected the object to high levels of torsion that broke the tip. A break or extreme wear can affect a tool's point or any other part. Such wear was reworked by means of a secondary working as discussed above. In some cases this reconstruction is easily identifiable and was carried out using techniques such as the (French, meaning "tranchet blow"), or simply with scale or scalariform retouches that alter an edge's symmetry and line.
Forms
The most characteristic and common shape is a pointed area at one end, cutting edges along its side and a rounded base (this includes hand axes with a lanceolate and amygdaloidal shape as well as others from the family). The axes are almost always symmetrical despite studies showing that hand axe symmetry does not help in tasks such as skinning animals. While there is a "typical" shape to most hand axes, there are some displaying a variety of shapes, including circular, triangular and elliptical—calling in to question the contention that they had a constant and only symbolic significance. They are typically between long, although they can be bigger or smaller.
They were typically made from a rounded stone, a block or lithic flake, using a hammer to remove flakes from both sides of the item. This hammer can be made of hard stone, or of wood or antler. The latter two, softer hammers can produce more delicate results. However, a hand axe's technological aspect can reflect more differences. For example, uniface tools have only been worked on one side and partial bifaces retain a high proportion of the natural cortex of the tool stone, often making them easy to confuse with chopping tools. Further, simple bifaces may have been created from a suitable tool stone, but they rarely show evidence of retouching. Later hand axes were improved by the use of the Levallois technique to make the more sophisticated and lighter Levallois core.
In summary, hand axes are recognized by many typological schools under different archaeological paradigms and are quite recognisable (at least the most typical examples). However, they have not been definitively categorized. Stated more formally, the idealised model combines a series of well-defined properties, but no set of these properties are necessary or sufficient to identify a hand axe.
History and distribution
In 1969 in the 2nd edition of World Prehistory, Grahame Clark proposed an evolutionary progression of flint-knapping industries (also known as complexes or technocomplexes) in which the "dominant lithic technologies" occurred in a fixed sequence where simple Oldowan one-edged tools were replaced by these more complex Acheulean hand axes, which were then eventually replaced by the even more complex Mousterian tools made with the Levallois technique.
The oldest known Oldowan tools were found in Gona, Ethiopia. These are dated to about 2.6 mya.
Early examples of hand axes date back to 1.6 mya in the later Oldowan (Mode I), called the "developed Oldowan" by Mary Leakey. These hand axes became more abundant in mode II Acheulean industries that appeared in Southern Ethiopia around 1.4 mya. Some of the best specimens come from 1.2 mya deposits in Olduvai Gorge.
By 1.8 mya early man was present in Europe. Remains of their activities were excavated in Spain at sites in the Guadix-Baza basin and near Atapuerca. Most early European sites yield "mode 1" or Oldowan assemblages. The earliest Acheulean sites in Europe appear around 0.5 mya. In addition, the Acheulean tradition did not spread to Eastern Asia. In Europe and particularly in France and England, the oldest hand axes appear after the Beestonian Glaciation–Mindel Glaciation, approximately 750,000 years ago, during the so-called Cromerian complex. They became more widely produced during the Abbevillian tradition.
The apogee of hand axe manufacture took place in a wide area of the Old World, especially during the Riss glaciation, in a cultural complex that can be described as cosmopolitan and which is known as the Acheulean. The use of hand axes survived the Middle Palaeolithic in a much smaller area and were especially important during the Mousterian, up to the middle of the Last glacial period.
Hand axes dating from the lower Palaeolithic were found on the Asian continent, on the Indian subcontinent and in the Middle East (to the south of parallel 40° N), but they were absent from the area to the east of the 90° E meridian. Movius designated a border (the so-called Movius Line) between the cultures that used hand axes to the west and those that made chopping tools and small retouched lithic flakes, such as were made by Peking Man and the Ordos culture in China, or their equivalents in Indochina such as the Hoabinhian. However, Movius' hypothesis was proved incorrect when many hand axes made in Palaeolithic era were found in 1978 at Hantan River, Jeongok, Yeoncheon County, South Korea for the first time in East Asia. Some of them are exhibited at the Jeongok Prehistory Museum, South Korea.
The Padjitanian culture from Java was traditionally thought to be the only oriental culture to manufacture hand axes. However, a site in Baise, Guangxi, China shows that hand axes were made in eastern Asia.
Hand axe technology is almost unknown in Australian prehistory, although a few have been found.
Construction
Experiments in knapping have demonstrated the relative ease with which a hand axe can be made, which could help explain their success. In addition, they demand relatively little maintenance and allow a choice of raw materials–any rock will suffice that supports a conchoidal fracture. With early hand axes, it is easy to improvise their manufacture, correct mistakes without requiring detailed planning, and no long or demanding apprenticeship is necessary to learn the necessary techniques. These factors combine to allow these objects to remain in use throughout pre-history. Their adaptability makes them effective in a variety of tasks, from heavy duty such as digging in soil, felling trees or breaking bones to delicate such as cutting ligaments, slicing meat or perforating a variety of materials.
Later examples of hand axes are more sophisticated with their use of two layers of knapping (one made with stone knapping and one made with bone knapping).
Lastly, a hand axe represents a prototype that can be refined giving rise to more developed, specialised and sophisticated tools such as the tips of various projectiles, knives, adzes and hatchets.
Analysis
Given the typological difficulties in defining the essence of a hand axe, it is important when analysing them to take account of their archaeological context (geographical location, stratigraphy, the presence of other elements associated with the same level, chronology etc.). It is necessary to study their physical state to establish any natural alterations that may have occurred: patina, shine, wear and tear, mechanical, thermal and / or physical-chemical changes such as cracking, in order to distinguish these factors from the scars left during the tool's manufacture or use.
The raw material is an important factor, because of the result that can be obtained by working it and in order to reveal the economy and movement of prehistoric humans. In the Olduvai Gorge the raw materials were most readily available some ten kilometres from the nearest settlements. However, flint or silicate is readily available on the fluvial terraces of Western Europe. This means that different strategies were required for the procurement and use of available resources. The supply of materials was the most important factor in the manufacturing process as Palaeolithic artisans were able to adapt their methods to available materials, obtaining adequate results from even the most difficult raw materials. Despite this it is important to study the rock's grain, texture, the presence of joints, veins, impurities or shatter cones etc.
In order to study the use of individual items it is necessary to look for traces of wear such as pseudo-retouches, breakage or wear, including areas that are polished. If the item is in a good condition it is possible to submit it to use-wear analysis, which is discussed in more detail below. Apart from these generalities, which are common to all carved archaeological pieces, hand axes need a technical analysis of their manufacture and a morphological analysis.
Technical analysis
The technical analysis of a hand axe tries to discover each of the phases in its chaîne opératoire (operational sequence). The chain is highly flexible, as a toolmaker may focus narrowly on just one of the sequence's links or equally on each link. The links examined in this type of study start with the extraction methods of the raw material, then include the actual manufacture of the item, its use, maintenance throughout its working life, and finally its disposal.
A toolmaker may put a lot of effort into finding the highest quality raw material or the most suitable tool stone. In this way more effort is invested in obtaining a good foundation, but time is saved on shaping the stone: that is, the effort is focused on the start of the operational chain. Equally the artisan may concentrate the most effort in the manufacture so that the quality or suitability of the raw material is less important. This will minimize the initial effort, but will result in a greater effort at the end of the operational chain.
Tool stone and cortex
Hand axes are most commonly made from rounded pebbles or nodules, but many are also made from a large flake. Hand axes made from flakes first appeared at the start of the Acheulean period and became more common with time. Manufacturing a hand axe from a flake is actually easier than from a pebble. It is also quicker, as flakes are more likely to be closer to the desired shape. This allows easier manipulation and fewer knaps are required to finish the tool; it is also easier to obtain straight edges. When analysing a hand axe made from a flake, it should be remembered that its shape was predetermined (by use of the Levallois technique or Kombewa technique or similar). Notwithstanding this, it is necessary to note a tool's characteristics: type of flake, heel, knap direction.
The natural external cortex or rind of the tool stone, which is due to erosion and the physical-chemical alterations of weathering, is different from the stone's interior. In the case of chert, quartz or quartzite, this alteration is basically mechanical, and apart from the colour and the wear it has the same characteristics as the interior in terms of hardness, toughness etc. However, flint is surrounded by a limestone cortex that is soft and unsuitable for stone tools. As hand axes are made from a tool stone's core, it is normal to indicate the thickness and position of the cortex in order to better understand the techniques that are required in their manufacture. The variation in cortex between utensils should not be taken as an indication of their age.
Many partially-worked hand axes do not require further work in order to be effective tools. They can be considered to be simple hand axes. Less suitable tool stone requires more thorough working. In some specimens the cortex is unrecognisable due to the complete working that it has undergone, which has eliminated any vestige of the original cortex.
Types
It is possible to distinguish multiple types of hand axe:
Uniface—flaked on one face with cortex completely covering the other side. This characteristic does not disqualify such tools as hand axes and gives no indication of their age.
Partial biface—The cortex is present on the tool's base and central part. The overall area that is not knapped may extend to up to two thirds of its length.
Bifaces with basal cortex coverage—Only the artefact's base is covered with cortex, which does not cover more than a third of total length. In some cases the cortex is present on both the base and one side, thereby affecting one edge: such tools are called "natural backed". De Mortillet emphasised the importance of the presence or absence of the cortex around the edge in the 19th century: "Even on some of the best worked pieces it is common to see, sometimes on the base but more often on the side, a small area that has not been worked, that is uncut. It could be thought that this is a mistake or an error. But often the most probable reason for this is that it was intentional. There are a large number of hand axes with an uncut base, unworked or partially cleaned ... an area has intentionally been left on these pieces as a grip, it is called the heel. This heel acts as a handle as it is easy to grip". (This hypothesis remains unproven and is not commonly used.)
Hand axes with residual cortex on an edge—The whole of their edges are knapped except for a small area where the cortex remains (leaving a small area without a sharp edge). This area can be at the base, side or oblique. In all cases it is small, leaving cutting edges on both sides.
Hand axes with a cutting edge around the whole circumference—The circumference is knapped to a cutting edge, although some residual areas of cortex may persist on either face, without affecting the cutting edge's effectiveness.
Production
Older hand axes were produced by direct percussion with a stone hammer and can be distinguished by their thickness and a sinuous border. Mousterian hand axes were produced with a soft billet of antler or wood and are much thinner, more symmetrical and have a straight border. An experienced flintknapper needs less than 15 minutes to produce a good quality hand axe. A simple hand axe can be made from a beach pebble in less than 3 minutes.
The manufacturing process employs lithic reduction. This phase is commonly thought of as the most important in hand axe fabrication, although it is not always used, such as for hand axes made from flakes or a suitable tool stone. An important concern is the implement that has been used to form the biface. If multiple implements were used, it is essential to discover in what order they were used and the result obtained by each one. The most common implements are:
Hard hammer faces
Hand axes can be made without subsequent reworking of the edges. A hammerstone was the most common percussive tool used during the Acheulean. The resulting artefact is usually easily recognizable given its size and irregular edges, as the removed flakes leave pronounced percussion bulbs and compression rings. A hammerstone produces a small number of flakes that are wide and deep leaving long edges on the tool as their highly concave form yields curving edges. The cross-section is irregular, often sub-rhombic, while the intersection between the faces forms an acute angle of between 60° and 90° degrees. The shape is similar to that of the core as the irregularities formed during knapping are not removed. The notches obtained were exploited in the production sequence. It is common that this type of manufacture yields "partial bifaces" (an incomplete working that leaves many areas covered with cortex), "unifaces" (tools that have only been worked on one face), "bifaces in the Abbevillian style" and "nucleiform bifaces". This type of manufacturing style is generally an indication of the age when a tool was made and with other archaeological data can provide a context that allows its age to be estimated.
Hard hammer faces and edges
These hand axes have a more balanced appearance as the modification consists of a second (or third) series of blows to make the piece more uniform and provide a better finish. The modification is often called retouching and is sometimes carried out using invasive retouching or using softer, marginal, shallow blows that are only applied to the most marked irregularities leaving scale-like marks. The modification of edges with a hard hammer was carried out from the beginning of the Acheulean and persisted into the Mousterian. It is therefore not useful as an indicator of chronology (in order for it to be considered as a marker it has to be accompanied by other complementary and independent archaeological data). The hand axes arising from this methodology have a more classical profile with either a more symmetrical almond or oval shape and with a lower proportion of the cortex of the original core. It is not always the case that the retouching had the objective of reducing an edge's irregularities or deformities. In fact, it has been shown that in some cases the retouching was carried out to sharpen an edge that had been blunted by use or a point that had deteriorated.
Soft hammer finish
Some hand axes were formed with a hard hammer and finished with a soft hammer. Blows that result in deep conchoidal fractures (the first phase of manufacture) can be distinguished from features resulting from sharpening with a soft hammer. The latter leaves shallower, more distended, broader scars, sometimes with small, multiple shock waves. However, marks left by a small, hard hammer can leave similar marks to a soft hammer.
Soft hammer finished pieces are usually balanced and symmetrical, and can be relatively smooth. Soft hammer works first appeared in the Acheulean period, allowing tools with these markings to be used as a estimation, but with no greater precision. The main advantage of a soft hammer is that a flintknapper is able to remove broader, thinner flakes with barely developed heels, which allows a cutting edge to be maintained or even improved with minimal raw material wastage. However, a high-quality raw material is required to make their use effective. No studies compare the two methods in terms of yield per unit weight of raw material, or the difference in energy use. The use of a soft hammer requires greater use of force by the flintknapper and a steeper learning curve, although it offers more flakes for less raw material.
Soft hammer only
Hand axes made using only a soft hammer are much less common. In most cases at least initial work was done with a hard hammer, before subsequent flaking with a soft hammer erased all vestiges of that work. A soft hammer is not suitable for all types of percussion platform and it cannot be used on certain types of raw material. It is, therefore, necessary to start with a hard hammer or with a flake as a core as its edge will be fragile (flat, smooth pebbles are also useful). This means that although it was possible to manufacture a hand axe using a soft hammer, it is reasonable to suppose that a hard hammer was used to prepare a blank followed by one or more phases of retouching to finish the piece. However, the degree of separation between the phases is not certain, as the work could have been carried out in one operation.
Working with a soft hammer allows a knapper greater control of the knapping and reduces waste of the raw material, allowing the production of longer, sharper, more uniform edges that will increase the tool's working life. Hand axes made with a soft hammer are usually more symmetrical and smooth, with rectilinear edges and shallow indentations that are broad and smooth so that it is difficult to distinguish where one flake starts and another ends. They generally have a regular biconvex cross-section and the intersection of the two faces forms an edge with an acute angle, usually of around 30°. They were worked with great skill and therefore they are more aesthetically attractive. They are usually associated with periods of highly developed tool making such as the Micoquien or the Mousterian. Soft hammer manufacturing is not reliable as the sole dating method.
Hand axes were created to be tools and as such they wore out, deteriorated and/or broke during use. Relics have suffered dramatic changes throughout their useful lives. It is common to find edges that have been sharpened, points that have been reconstructed and profiles that have been deformed by reworking in order to extend the piece's useful lifetime. Some tools were recycled later, leading Bordes to note that hand axes "are sometimes found in the Upper Palaeolithic. Their presence, which is quite normal in the Perigordian I, is often due, in other levels, to the collection of Mousterian or Acheulean tools."
Morphology
Hand axes have traditionally been oriented with their narrowest part upwards (presupposing that this would have been the most active part, which is not unreasonable given the many hand axes that have unworked bases). The following typological conventions are used to facilitate communication. The axis of symmetry that divides a biface in two is called the morphological axis. The main face is usually the most regular and better worked face. The base (not the heel) is the bottom of the hand axe.
Terminal zone—the narrowest end, opposite the base. Its most common shape is pointed, more or less acute or oval. Some hand axes have terminal ends that are rounded or polygonal (i.e. not pointed) while others have terminal ends that are transversal to the axis, called cleaver or spatulate.
Proximal end (base)—opposite the terminal end (usually broader and thicker), it can be described as either reserved (partially or totally worked, but not cut); or cut, with a rounded (polygonal), flat or pointed end.
Edges—convex, rectilinear or concave, and more or less even. Edges on some specimens are denticulate—scalloped—or notched. Some specimens have unsharpened edges. The profile of a hand axe's worked edges can be regular without pronounced rectilinear deviations (the edge is gently curved in the form of an S) or an edge may be more sinuous and wave-formed with pronounced curves or deviations in the edge's profile. On some specimens only selected areas have been formed into a working edge.
Cross section—the horizontal cross-section taken at some distance from the base. It is possible to discern retouching or rebuilding in deteriorated parts of the edges. The following types of cross section are commonly seen: triangular (sub-triangular and backed triangular), rhombic (rhomboidal and backed rhomboidal), trapezium (trapezoid and backed trapezoidal), pentagon (pentagonal and backed pentagonal), polygonal, biconvex or lenticular (sub lenticular).
Profile—By definition, hand axes have a roughly balanced outline, with a morphological axis that also serves as an axis of bilateral symmetry and a plane that serves as an axis of bifacial symmetry. Not all hand axes are perfectly symmetrical. Symmetry was achieved only after millennia of development. Symmetry may not make tools more useful. Hand axes were used in a variety of heavy physical tasks. They deteriorated, wore out and broke and were often repaired with retouching of their edges, recovery of their points or complete reworking. The majority of discovered pieces are remains, pieces that have been discarded after a long life as tools, during which they often were damaged and/or adapted for specialized tasks. Such pieces may have lost whatever symmetry they initially had. Hand axe profiles can be classified into the following categories:
Dimensions and ratios
Hand axe measurements use the morphological axis as a reference and for orientation. In addition to length, width, depth, specialists have proposed a wide range of other physical quantities. The most common were proposed by Bordes and Balout:
Maximum length (L)
Maximum width (m)
Maximum depth (e)
Distance from the base to the zone with the maximum width (a)
Width 3/4 of the way along the piece (o)
A and o can be used to delineate the contour's cross section and to measure the angles of the edges (provided this is not an area covered in the stone's original cortex). These angular measurements for the edges are made using a goniometer.
Edge length, weight and the length of the chord described by the edges (if the piece has a transverse terminal bezel) can be measured. These measurements allow morphological and technical ratios to be established (for example, the relationship between the weight and the length of the cutting edges, or the relationship between the hammer used to form the piece and the angle obtained etc.).
The most commonly used coefficients were established by Bordes for the morphological-mathematical classification of what he called "classic bifaces" (Balout proposed other, similar indices):
Bordes hand axe typology
The following guide is strongly influenced by the possibly outdated and basically morphological "Bordes method" classification system. This classification is particularly applicable to classic hand axes, those that can be defined and catalogued by measuring dimensions and mathematical ratios, while disregarding nearly all subjective criteria. "Distinguishing between different types of hand axes is not always easy. There is often no room for doubts, however, there are a number of cases where the difficulty is real." In the majority of cases, this system agrees with previously established categories (although slightly redefining them). Balout made a similar attempt at categorization.
Non-classic specimens
Many specimens defeat objective classification. Bordes created a group he called "non-classic bifaces" to which mathematical indexes do not apply.
Tools sometimes categorized as bifaces
Hand axes constitute an important group artefacts from the Acheulean. They are particularly important in open air archaeological sites (Keelley suggested that they are less common in cave sites). Hand axes, chopping tools and trihedral picks are considered core utensils, which were commonly manufactured out of stones, blocks or rock nodules. However this grouping is problematic as these tools were often also fabricated from (large) flakes. Another common suggestion is to refer to flake tools as micro industry, as opposed to the more general size referred to as macro industry, which includes hand axes and cleavers. However, some scrapers are as big as hand axes.
The most elaborated chopping tools and partial hand axes are linked and it is often difficult to distinguish between them. The concept of chopping tools is based on their lack of formal standardization (which is typical of hand axes) and includes the possibility that the pieces are shallow cores, which is unthinkable for the bifaces (except the nucleiforms).
While hand axes and cleavers occasionally served for similar tasks, their design is fundamentally different.
Trihedral picks are no longer considered a specialized type of hand axe.
Another group of tools commonly associated with hand axes is the biface leafpoint tools from the Lower and Middle Palaeolithic in the Old World. The difference between the two types is based on the latter's fine, light finishing with a soft hammer and in a morphology that suggests a specific function, possibly as the point of a projectile or a knife. Representatives of these tools include well known examples from the specialized literature:
The biface leafpoint tools of central Europe are called (). They are projectile points belonging to the Middle Palaeolithic with a leaf-shaped form. They are often dual pointed and flat, making them similar to Solutrean laurel leaf blades. It is possible to distinguish the two only from their archaeological context. survived in some Upper Palaeolithic cultures. The pieces from the eastern European Szeletien culture (both and Micoquian bifaces) could be the link that connects the tradition of Lower and Middle Palaeolithic bifacial objects with those from the Upper Palaeolithic and beyond.
Hand axes found in Africa come from both the Aterian culture of North Africa and the Stillbay culture from East Africa. Both these cases relate to Mousterian cultures, although they are relatively late and have their own style, at the end of the so-called African Middle Stone Age. In both cases a variety of objects are found, triangular, oval and other leaf-point. Hand axes and unifaces also came from other cultures.
Importance
The hand axe helped establish that early humans were capable of constructing relatively sophisticated tools that also reflected a sense of aesthetics. The 19th century publications of Frere, and more importantly of Boucher de Perthes, in France, described pieces that were balanced, symmetrical and crafted with a formal purity. Vilanova i Piera published similar works in Spain. This work was continued by Pérez de Barradas and del Prado at the start of the 20th century.
As Leroi-Gourhan explained, it is important to ask what was understood of art at the time, considering the psychologies of non-modern humans. Archaeological records documenting rapid progress towards symmetry and balance surprised Leroi-Gourha. He felt that he could recognize beauty in early prehistoric tools made during the Acheulean:
Many authors who comment on the Westfield aspect of hand axes refer only to exceptional pieces. The majority of hand axes tended to symmetry, but lack artistic appeal. Generally, only the most striking pieces are considered, mainly 19th or early 20th century collections. At that time a lack of knowledge regarding prehistoric technology prevented a recognition of human actions in these objects. Other collections were made by aficionados, whose interests were not scientific, so that they collected only objects they considered to be outstanding, abandoning humbler elements that were sometimes necessary to interpret an archaeological site. Exceptions include sites methodically studied by experts where magnificently carved, abundant hand axes caused archaeologists to express admiration for the artists:
The discovery in 1998 of an oval hand axe of excellent workmanship in the Sima de los Huesos in the Atapuerca Mountains mixed in with the fossil remains of Homo heidelbergensis reignited this controversy. Given that this is the only lithic remnant from this section of the site (possibly a burial ground), combined with the piece's qualities led it to receive special treatment, it was even baptized Excalibur and it became a star item. Interest in the symbolic meaning of this example in particular, and hand axes in general, has multiplied in recent years, feeding both scientific and more general debate and literature.
Basch offered this counterargument:
Paradoxically, within the wide range of Acheulean objects, hand axes are one of the simplest tools. They do not require as much planning as other types of object, generally made from flakes, that are less striking but more sophisticated.
Archaeologists have evidence of hand axes that are 1.2 million years old in Melka Kunturé (Ethiopia), but the oldest, from Konso-Gardula, could be 1.9 million years old: Although it is now known that they are the heritage of a number of human species, with Homo ergaster the earliest, up until 1954 no solid evidence indicated who had fabricated hand axes: in that year, in Ternifine, Algeria, Arambourg discovered remains that he called Atlanthropus, along with some hand axes. All the species associated with hand axes (from H. ergaster to H. neanderthalensis) show an advanced intelligence that in some cases is accompanied by modern features such as a relatively sophisticated technology, systems to protect against inclement weather (huts, control of fire, clothing), and certain signs of spiritual awareness (early indications of art such as adorning the body, carving of bones, ritual treatment of bodies, articulated language).
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| Technology | Hand tools | null |
320351 | https://en.wikipedia.org/wiki/Hypodermic%20needle | Hypodermic needle | A hypodermic needle (from Greek ὑπο- (hypo- = under), and δέρμα (derma = skin)) is a very thin, hollow tube with one sharp tip. It is one of a category of medical tools which enter the skin, called sharps. It is commonly used with a syringe, a hand-operated device with a plunger, to inject substances into the body (e.g., saline solution, solutions containing various drugs or liquid medicines) or extract fluids from the body (e.g., blood). Large-bore hypodermic intervention is especially useful in catastrophic blood loss or treating shock.
A hypodermic needle is used for rapid delivery of liquids, or when the injected substance cannot be ingested, either because it would not be absorbed (as with insulin), or because it would harm the liver. It is also useful to deliver certain medications that cannot be delivered orally due to vomiting. There are many possible routes for an injection, with intramuscular (into a muscle) and intravenous (into a vein) being the most common. A hypodermic syringe has the ability to retain liquid and blood in it up to years after the last use and a great deal of caution should be taken to use a new syringe every time.
The hypodermic needle also serves an important role in research environments where sterile conditions are required. The hypodermic needle significantly reduces contamination during inoculation of a sterile substrate. The hypodermic needle reduces contamination for two reasons: First, its surface is extremely smooth, which prevents airborne pathogens from becoming trapped between irregularities on the needle's surface, which would subsequently be transferred into the media (e.g. agar) as contaminants; second, the needle's surface is extremely sharp, which significantly reduces the diameter of the hole remaining after puncturing the membrane and consequently prevents microbes larger than this hole from contaminating the substrate.
History
Early use and experimentation
The ancient Greeks and Romans knew injection as a method of medicinal delivery from observations of snakebites and poisoned weapons. There are also references to "anointing" and "inunction" in the Old Testament as well as the works of Homer, but injection as a legitimate medical tool was not truly explored until the 17th century.
Christopher Wren performed the earliest confirmed experiments with crude hypodermic needles, performing intravenous injection into dogs in 1656. These experiments consisted of using animal bladders (as the syringe) and goose quills (as the needle) to administer drugs such as opium intravenously to dogs. Wren and others' main interest was to learn if medicines traditionally administered orally would be effective intravenously. In the 1660s, Johann Daniel Major of Kiel and Johann Sigismund Elsholtz of Berlin were the first to experiment with injections in humans.
19th-century development
The 19th century saw the development of medicines that were effective in small doses, such as opiates and strychnine. This spurred a renewed interest in direct, controlled application of medicine. "Some controversy surrounds the question of priority in hypodermic medication." Irish physician Francis Rynd is generally credited with the first successful injection in 1844, in the Meath Hospital in Dublin, Ireland.
Alexander Wood's main contribution was the all-glass syringe in 1851, which allowed the user to estimate dosage based on the levels of liquid observed through the glass. Wood used hypodermic needles and syringes primarily for the application of localized, subcutaneous injection (localized anesthesia) and therefore was not as interested in precise dosages.
Simultaneous to Wood's work in Edinburgh, Charles Pravaz of Lyon also experimented with sub-dermal injections in sheep using a syringe of his own design. Pravaz designed a hypodermic needle measuring 3 cm (1.18 in) long and 5 mm (0.2 in) in diameter; it was made entirely of silver.
Charles Hunter, a London surgeon, is credited with the coining of the term "hypodermic" to describe subcutaneous injection in 1858. The name originates from two Greek words: hypo, "under", and derma, "skin". Furthermore, Hunter is credited with acknowledging the systemic effects of injection after noticing that a patient's pain was alleviated regardless of the injection's proximity to the pained area. Hunter and Wood were involved in a lengthy dispute over not only the origin of the modern hypodermic needle, but also because of their disagreement as to the medicine's effect once administered.
Modern improvements
Dr. Francis Rynd used the first "Hollow Needle" as a hypodermic syringe on Ms. Margaret Cox in Ireland on June 3rd, 1844. Dr. Wood can be largely credited with the popularization and acceptance of injection as a medical technique, as well as the widespread use and acceptance of the hypodermic needle. The basic technology of the hypodermic needle has stayed largely unchanged since the 19th century, but as the years progressed and medical and chemical knowledge improved, small refinements have been made to increase safety and efficacy, with needles being designed and tailored for very particular uses. Hypodermic needles remain essential to large volume administration or exchange in settings of trauma or dialysis. The trend of needle specification for use began in the 1920s, particularly for the administration of insulin to diabetics.
The onset of World War II spurred the early development of partially disposable syringes for the administration of morphine and penicillin on the battlefield. Development of the fully disposable hypodermic needle was spurred on in the 1950s for several reasons. The Korean War created blood shortages and in response disposable, sterile syringes were developed for collecting blood. The widespread immunization against polio during the period required the development of a fully disposable syringe system.
The 1950s also saw the rise and recognition of cross-contamination from used needles. This led to the development of the first fully disposable plastic syringe by New Zealand pharmacist Colin Murdoch in 1956. This period also marked a shift in interest from needle specifications to general sterility and safety.
The 1980s saw the rise of the HIV epidemic and with it renewed concern over the safety of cross-contamination from used needles. New safety controls were designed on disposable needles to ensure the safety of medical workers in particular. These controls were implemented on the needles themselves, such as retractable needles, but also in the handling of used needles, particularly in the use of hard-surface disposal receptacles found in every medical office today.
By 2008, all-plastic needles were in production and in limited use. One version was made of Vectra (plastic) aromatic liquid crystal polymer tapered from 1.2 mm at the hub to 0.72 mm at the tip (equivalent to 22 gauge metal needle), with an ID/OD ratio of 70%.
Manufacture
Hypodermic needles are normally made from a stainless-steel or Niobium tube through a process known as tube drawing where the tube is drawn through progressively smaller dies to make the needle. The end of the needle is bevelled to create a sharp pointed tip, letting the needle easily penetrate the skin.
Gauge
The main system for measuring the diameter of a hypodermic needle is the Birmingham gauge (also known as the Stubs Iron Wire Gauge); the French gauge is used mainly for catheters. Various needle lengths are available for any given gauge. Needles in common medical use range from 7 gauge (the largest) to 34 (the smallest). 21-gauge needles are most commonly used for drawing blood for testing purposes, and 16- or 17-gauge needles are most commonly used for blood donation, as the larger luminal cross-sectional area results in lower fluid shear, reducing harm to red blood cells while also allowing more blood to be collected in a shorter time.
Although reusable needles remain useful for some scientific applications, disposable needles are far more common in medicine. Disposable needles are embedded in a plastic or aluminium hub that attaches to the syringe barrel by means of a press-fit or twist-on fitting. These are sometimes referred to as "Luer Lock" connections, referring to the trademark Luer-Lok. The male and female luer lock and hub—produced by pharmaceutical equipment manufacturers—are two of the most critical parts of disposable hypodermic needles.
Use by non-specialists
Hypodermic needles are usually used by medical professionals (dentists, phlebotomists, physicians, pharmacists, nurses, paramedics), but they are sometimes used by patients themselves. This is most common with type one diabetics, who may require several insulin injections a day. It also occurs with patients who have asthma or other severe allergies. Such patients may need to take desensitization injections or they may need to carry injectable medicines to use for first aid in case of a severe allergic reaction. In the latter case, such patients often carry a syringe loaded with epinephrine (e.g. EpiPen), diphenhydramine (e.g. Benadryl), or dexamethasone. Rapid injection of one of these drugs may stop a severe allergic reaction.
Multiple sclerosis patients may also treat themselves by injection; several MS therapies, including various interferon preparations, are designed to be self-administered by subcutaneous or intramuscular injection.
Transgender people may also inject their own hormone replacement therapy, using either intramuscular injection or subcutaneous injection methods.
Hypodermic needles are also used for erotic piercing.
Phobia
It is estimated that anywhere from nearly 3.5 to 10% of the world's population may have a phobia of needles (trypanophobia), and it is much more common in children, ages 5–17. Topical anesthetics can be used to desensitize the area where the injection will take place to reduce pain and discomfort. For children, various techniques may be effective at reducing distress or pain related to needles. Techniques include: distraction, hypnosis, combined cognitive behavioral therapy, and breathing techniques.
| Technology | Equipment | null |
320509 | https://en.wikipedia.org/wiki/Pine%20nut | Pine nut | Pine nuts, also called piñón (), pinoli (), or pignoli, are the edible seeds of pines (family Pinaceae, genus Pinus). According to the Food and Agriculture Organization, only 29 species provide edible nuts, while 20 are traded locally or internationally owing to their seed size being large enough to be worth harvesting; in other pines, the seeds are also edible but are too small to be of notable value as human food. The biggest producers of pine nuts are China, Russia, North Korea, Pakistan and Afghanistan.
As pines are gymnosperms, not angiosperms (flowering plants), pine nuts are not "true nuts"; they are not botanical fruits, the seed not being enclosed in an ovary which develops into the fruit, but simply bare seeds—"gymnosperm" meaning literally "naked seed" (from and ). The similarity of pine nuts to some angiosperm fruits is an example of convergent evolution.
Species and geographic spread
In Asia, two species, in particular, are widely harvested: Korean pine (Pinus koraiensis) in northeast Asia (the most important species in international trade) and chilgoza pine (P. gerardiana) in the western Himalaya. Four other species, Siberian pine (P. sibirica), Siberian dwarf pine (P. pumila), Chinese white pine (P. armandii) and lacebark pine (P. bungeana), are also used to a lesser extent. Russia is the largest producer of P. sibirica nuts in the world, followed by either Mongolia or Afghanistan. They each produce over annually, most of it exported to China.
Pine nuts produced in Europe mostly come from the stone pine (P. pinea), which has been cultivated for its nuts for over 5,000 years. Pine nuts have been harvested from wild trees for far longer. The Swiss pine (P. cembra) is also used, to a very small extent.
In North America, the main species are three of the pinyon pines: Colorado pinyon (P. edulis), single-leaf pinyon (P. monophylla), and Mexican pinyon (P. cembroides). The other eight pinyon species are used to a small extent, as is gray pine (P. sabineana), Coulter pine (P. coulteri), Torrey pine (P. torreyana), sugar pine (P. lambertiana) and Parry pinyon (P. quadrifolia). Here, the nuts themselves are known by the Spanish name for the pinyon pine, piñón (plural: piñones).
In the United States, pine nuts are mainly harvested by Native American and Hispano communities, particularly in the Western United States and Southwestern United States, by the Shoshone, Paiute, Navajo, Pueblo, Hopi, Washoe, and Hispanos of New Mexico. Certain treaties negotiated by tribes and laws in Nevada guarantee Native Americans' right to harvest pine nuts, and the state of New Mexico protects the use of the word piñon for use with pine nuts from certain species of indigenous New Mexican pines.
Species list
Commonly used species include:
Old World
Pinus armandii – Chinese white pine
Pinus bungeana – lacebark pine
Pinus cembra – Swiss pine
Pinus gerardiana – Chilgoza pine
Pinus koraiensis – Korean pine
Pinus pinea – Mediterranean stone pine
Pinus pumila – Siberian dwarf pine
Pinus sibirica – Siberian pine
New World
pinyon pine group – in southwestern North America
Pinus albicaulis – Whitebark pine
Pinus cembroides – Mexican pinyon
Pinus coulteri – Coulter pine
Pinus culminicola – Potosi pinyon
Pinus edulis – Two-needle piñon or Colorado pinyon (when grown in Colorado)
Pinus johannis – Johann's pinyon (includes P. discolor – Border pinyon)
Pinus monophylla – Single-leaf pinyon
Pinus orizabensis – Orizaba pinyon
Pinus quadrifolia – Four-leaved pinyon or Parry pinyon
Pinus remota – Papershell pinyon or Texas pinyon
Pinus sabiniana – California foothill pine
Pollination and seed development
Pine nuts will not reach full maturity unless the environmental conditions are favorable for the tree and the cone. The time to maturity varies depending on the species.
For some American species, development begins in early spring with pollination. A tiny cone, about the size of a small marble, will form from mid-spring through the end of summer; this immature cone will temporarily cease growing and remain dormant until the following spring, then grow again until it reaches maturity near the end of its second summer. The mature piñon pine cone is ready to harvest ten days before the green cone begins to open. A cone is harvested by placing it in a burlap bag and exposing it to a heat source such as the sun to begin drying. It takes about 20 days until the cone fully opens. Once it is fully open and dry, the seed can be easily extracted in various ways. The most common and practical extraction method used is the repeated striking of the burlap bag containing the cone(s) against a rough surface to cause the cone(s) to shatter, leaving just the job of separating by hand the seed from the residue within the bag.
Another option for harvesting is to wait until the cone opens on the tree (as it naturally will) and harvest the cone from the piñon pine, followed by the extracting process mentioned above. Fallen seeds can also be gathered beneath the trees.
Ecology and status
Because pine nuts are an important food source for many animals, overharvesting of pine nuts threatens local ecosystems, an effect occurring during the early 21st century with increased culinary uses for pine nuts. In the United States, millions of hectares of productive pinyon pine woods have been destroyed due to conversion of lands, and in China and Russia, destructive harvesting techniques (such as breaking off whole branches to harvest the cones) and removal of trees for timber have led to losses in production capacity.
Elevation and pinecone production
Some growers claim that the elevation of the pinyon pine is an important determinant of the quantity of pine cone production and, therefore, will largely determine the number of pine nuts the tree will yield. The US Department of Agriculture notes that variation in cone production between trees growing on identical sites is often observed.
American pinyon pine cone production is most commonly found at an elevation between , and ideally at . This is due to higher temperatures at elevations lower than during the spring, which dry up humidity and moisture content (particularly snow packs) that provide for the tree throughout the spring and summer, causing little nourishment for pine cone maturity.
Although several other environmental factors determine the conditions of the ecosystem (such as clouds and rain), the trees tend to abort cones without sufficient water. High humidity encourages cone development. There are certain topographical areas found in lower elevations, such as shaded canyons, where the humidity remains constant throughout the spring and summer, allowing pine cones to fully mature and produce seed.
At elevations above , the temperature substantially drops, drastically affecting the state of the dormant cone. During the winter, frequent dramatic changes in temperature, drying, and gusty winds make the cones susceptible to freeze-drying that permanently damages them; in this case, growth is stunted, and the seeds deteriorate.
Physical characteristics
When first extracted from the pine cone, they are covered with a hard shell (seed coat), thin in some species and thick in others. The nutrition is stored in the embryo (sporophyte) in the center. Although a nut in the culinary sense, in the botanical sense, pine nuts are seeds; being a gymnosperm, they lack a carpel (fruit) outside.
The shell must be removed before the pine nut can be eaten. Unshelled pine nuts have a long shelf life if kept dry and refrigerated (); shelled nuts (and unshelled nuts in warm conditions) deteriorate rapidly, becoming rancid within a few weeks or even days in warm, humid conditions. Pine nuts are commercially available in the shelled form, but due to poor storage, they can have poor flavor and may already be rancid at the time of purchase. Consequently, pine nuts are often frozen to preserve their flavor.
European pine nuts may be distinguished from Asian ones by their greater length than girth; Asian pine nuts are stubbier, shaped somewhat like long kernels of corn. The American piñon nuts are known for their large size and ease of shelling. In the United States, Pinus edulis, the hard shell of New Mexico and Colorado, became a sought-after species due to the trading post system and the Navajo people who used the nuts as a means of commerce. The Italian pine nut (P. pinea) was brought to the United States by immigrants and became a favored treat along the East Coast in the early 1930s, when bumper crops of American pine nuts were readily available at low prices.
Nutrition
When dried for eating, pine nuts are 2% water, 13% carbohydrates, 14% protein, and 68% fat (table). In a reference serving, dried pine nuts supply of food energy and are a rich source (20% or more of the Daily Value, DV) of numerous micronutrients, particularly manganese (419% DV), phosphorus (82% DV), magnesium (71% DV), zinc (67% DV), copper (65% DV), vitamin E (62% DV), vitamin K (51% DV), and the B vitamins, thiamin and niacin (29–35% DV), among others (table).
Culinary uses
Pine nuts have been eaten in Europe and Asia since the Paleolithic period. They are frequently added to meat, fish, salads, and vegetable dishes or baked into bread.
In Italian, they are called pinoli (in the US, they are often called pignoli, but in Italy, pignolo is actually a word far more commonly used to describe a fussy, overly fastidious or extremely meticulous person) and are an essential component of Italian pesto sauce; the upsurge in the popularity of this sauce since the 1990s has increased the visibility of the nut in America, primarily on the West Coast. Torta della nonna (literally "granny's cake") is a generic Italian dish name that in most families indicates an old family recipe for any cake but often is used for a tart or a pie filled with custard, topped with pine nuts and optionally dusted with icing sugar. Pignoli cookies, an Italian American specialty confection (in Italy, these would be called biscotti ai pinoli), are made of almond flour formed into a dough similar to that of a macaroon and then topped with pine nuts.
In Catalonia, a sweet is made of small marzipan balls covered with pine nuts, painted with egg, and lightly cooked, and those are called "panellets". Pine nuts are also featured in the salade landaise of southwestern France. Nevada, or Great Basin, pine nut has a sweet fruity flavor and is promoted for its large size, sweet flavor, and ease of peeling.
Pine nuts are also widely used in Levantine cuisine, reflected in a diverse range of dishes such as kibbeh, sambusak, fatayer, and Maqluba, desserts such as baklava, meghli, and many others.
Throughout Europe, the Levant, and West Asia, the pine nuts used are traditionally from Pinus pinea (stone pine). They are easily distinguished from the Asian pine nuts by their more slender shape and more homogeneous flesh. Because of the lower price, Asian pine nuts are also often used, especially in cheaper preparations.
Pine nut oil is added to foods for flavor.
Taste disturbances
Some raw pine nuts can cause pine mouth syndrome, a taste disturbance lasting from a few days to a few weeks after consumption. A bitter, metallic, unpleasant taste is reported. There are no known lasting effects, with the United States Food and Drug Administration reporting that there are "no apparent adverse clinical side effects". Raw nuts from Pinus armandii, mainly in China, may be the cause of the problem. Metallic taste disturbance is typically reported 1–3 days after ingestion, being worse on day two and typically lasting up to two weeks. Cases are self-limited and resolve without treatment.
Food fraud
In the United States, from 2008 to 2012, some people reported a bitter metallic taste ("pine mouth") that sometimes lasted for weeks after they ate pine nuts. After an international investigation, the FDA found that some manufacturers substituted a non-food species of pine nuts in place of more expensive edible pine nut species as a form of food fraud.
Other uses
Some Native American tribes use the hard outer shell of the pine nut as a bead for decorative purposes in traditional regalia and jewelry. In the Great Basin area of the US, collecting pine nuts is a protected right through state law and treaty.
In northern California, pine nuts are collected from the grey pine or bull pine. Tribes burn designs into the hard shell, reflecting the same design they use in baskets; however, they are often left blank or burned to blacken. These are more often used in women's regalia and jewelry.
| Biology and health sciences | Nuts | Plants |
320568 | https://en.wikipedia.org/wiki/Air-to-air%20missile | Air-to-air missile | An air-to-air missile (AAM) is a missile fired from an aircraft for the purpose of destroying another aircraft (including unmanned aircraft such as cruise missiles). AAMs are typically powered by one or more rocket motors, usually solid fueled but sometimes liquid fueled. Ramjet engines, as used on the Meteor, are emerging as propulsion that will enable future medium- to long-range missiles to maintain higher average speed across their engagement envelope.
Air-to-air missiles are broadly put in two groups. Those designed to engage opposing aircraft at ranges of around 30 km to 40 km maximum are known as short-range or "within visual range" missiles (SRAAMs or WVRAAMs) and are sometimes called "dogfight" missiles because they are designed to optimize their agility rather than range. Most use infrared guidance and are called heat-seeking missiles. In contrast, medium- or long-range missiles (MRAAMs or LRAAMs), which both fall under the category of beyond-visual-range missiles (BVRAAMs), tend to rely upon radar guidance, of which there are many forms. Some modern ones use inertial guidance and/or "mid-course updates" to get the missile close enough to use an active homing sensor. The concepts of air-to-air missiles and surface-to-air missiles are closely related, and in some cases versions of the same weapon may be used for both roles, such as the ASRAAM and Sea Ceptor.
History
The air-to-air missile grew out of the unguided air-to-air rockets used during the First World War. Le Prieur rockets were sometimes attached to the struts of biplanes and fired electrically, usually against observation balloons, by such early pilots as Albert Ball and A. M. Walters. Facing the Allied air superiority, Germany in World War II invested limited effort into missile research, initially adapting the projectile of the unguided 21 cm Nebelwerfer 42 infantry barrage rocket system into the air-launched BR 21 anti-aircraft rocket in 1943; leading to the deployment of the R4M unguided rocket and the development of various guided missile prototypes such as the Ruhrstahl X-4.
The US Navy and US Air Force began equipping guided missiles in 1956, deploying the USAF's AIM-4 Falcon and the USN's AIM-7 Sparrow and AIM-9 Sidewinder. Post-war research led the Royal Air Force to introduce Fairey Fireflash into service in 1957 but their results were unsuccessful. The Soviet Air Force introduced its K-5 into service in 1957. As missile systems have continued to advance, modern air warfare consists almost entirely of missile firing. The use of beyond-visual-range combat became so pervasive in the US that early F-4 variants were armed only with missiles in the 1960s. High casualty rates during the Vietnam War caused the US to reintroduce autocannon and traditional dogfighting tactics but the missile remains the primary weapon in air combat.
In the Falklands War British Harriers, using AIM-9L missiles were able to defeat faster Argentinian opponents. Since the late 20th century all-aspect heat-seeking designs can lock-on to a target from various angles, not just from behind, where the heat signature from the engines is strongest. Other types rely on radar guidance (either on-board or "painted" by the launching aircraft).
Use of air-to-air missiles as surface-to-air missiles
In 1999 R-73 missile were adapted by Serb forces for surface to air missiles. The Houthi movement Missile Research and Development Centre and the Missile Force have tried to fire R-27/R-60/R-73/R-77 against Saudi aircraft. Using stockpiles of missiles from Yemeni Air Force stocks. The issue for the R-27 and R-77 is the lack of a radar to support their guidance to the target. However the R-73 and R-60 are infra-red heat seeking missiles. They only require power, liquid nitrogen "to cool the seeker head", and a pylon to launch the missile. These missiles have been paired with a "US made FLIR Systems ULTRA 8500 turrets". Only one near miss has been verified and that was a R-27T fired at Royal Saudi Air Force F-15SA. However the drawback is that these missiles are intended to be fired from one jet fighter against another. So the motors and fuel load are smaller than a purpose built surface to air missile.
On the Western side, the Norwegian-American made NASAMS air defense system has been developed for using AIM-9 Sidewinder, IRIS-T and AMRAAM air-to-air missiles to intercept targets. None of these missiles require modifications and hence it is possible for the system to take missiles straight from an aircraft. After a live-fire test occurred in September 2020 off the coasts of Florida, during which it successfully engaged a simulated cruise missile, in 2022 NASAMS was deployed to Ukraine, where for the first time this missile system was used in real combat conditions, and, according to Ukrainian government, was able to shoot down more than 100 aerial targets.
Warhead
A conventional explosive blast warhead, fragmentation warhead, or continuous rod warhead (or a combination of any of those three warhead types) is typically used in the attempt to disable or destroy the target aircraft. Warheads are typically detonated by a proximity fuze or by an impact fuze if it scores a direct hit. Less commonly, nuclear warheads have been mounted on a small number of air-to-air missile types (such as the AIM-26 Falcon) although these have never been used in combat.
Guidance
Guided missiles operate by detecting their target (usually by either radar or infrared methods, although rarely others such as laser guidance or optical tracking), and then "homing" in on the target on a collision course.
Although the missile may use radar or infra-red guidance to home on the target, the launching aircraft may detect and track the target before launch by other means. Infra-red guided missiles can be "slaved" to an attack radar in order to find the target and radar-guided missiles can be launched at targets detected visually or via an infra-red search and track (IRST) system, although they may require the attack radar to illuminate the target during part or all of the missile interception itself.
Radar guidance
Radar guidance is normally used for medium- or long-range missiles, where the infra-red signature of the target would be too faint for an infra-red detector to track. There are three major types of radar-guided missile – active, semi-active, and passive.
Radar-guided missiles can be countered by rapid maneuvering (which may result in them "breaking lock", or may cause them to overshoot), deploying chaff or using electronic counter-measures.
Active radar homing
Active radar (AR)-guided missiles carry their own radar system to detect and track their target. However, the size of the radar antenna is limited by the small diameter of missiles, limiting its range which typically means such missiles are launched at a predicted future location of the target, often relying on separate guidance systems such as Global Positioning System, inertial guidance, or a mid-course update from either the launching aircraft or other system that can communicate with the missile to get the missile close to the target. At a predetermined point (frequently based on time since launch or arrival near the predicted target location) the missile's radar system is activated (the missile is said to "go active"), and the missile then homes in on the target.
If the range from the attacking aircraft to the target is within the range of the missile's radar system, the missile can "go active" immediately upon launch.
The great advantage of an active radar homing system is that it enables a "fire-and-forget" mode of attack, where the attacking aircraft is free to pursue other targets or escape the area after launching the missile.
Semi-active radar homing
Semi-active radar homing (SARH) guided missiles are simpler and more common. They function by detecting radar energy reflected from the target. The radar energy is emitted from the launching aircraft's own radar system.
However, this means that the launch aircraft has to maintain a "lock" on the target (keep illuminating the target aircraft with its own radar) until the missile makes the interception. This limits the attacking aircraft's ability to maneuver, which may be necessary should threats to the attacking aircraft appear.
An advantage of SARH-guided missiles is that they are homing on the reflected radar signal, so accuracy actually increases as the missile gets closer because the reflection comes from a "point source": the target. Against this, if there are multiple targets, each will be reflecting the same radar signal and the missile may become confused as to which target is its intended victim. The missile may well be unable to pick a specific target and fly through a formation without passing within lethal range of any specific aircraft. Newer missiles have logic circuits in their guidance systems to help prevent this problem.
At the same time, jamming the missile lock-on is easier because the launching aircraft is further from the target than the missile, so the radar signal has to travel further and is greatly attenuated over the distance. This means that the missile may be jammed or "spoofed" by countermeasures whose signals grow stronger as the missile gets closer. One counter to this is a "home on jam" capability in the missile that allows it to home in on the jamming signal.
Beam riding
An early form of radar guidance was "beam-riding" (BR). In this method, the attacking aircraft directs a narrow beam of radar energy at the target. The air-to-air missile was launched into the beam, where sensors on the aft of the missile controlled the missile, keeping it within the beam. So long as the beam was kept on the target aircraft, the missile would ride the beam until making the interception.
While conceptually simple, the move is hard because of the challenge of simultaneously keeping the beam solidly on the target (which could not be relied upon to cooperate by flying straight and level), continuing to fly one's own aircraft, and monitoring enemy countermeasures.
An added complication was that the beam will spread out into a cone shape as the distance from the attacking aircraft increases. This will result in less accuracy for the missile because the beam may actually be larger than the target aircraft when the missile arrives. The missile could be securely within the beam but still not be close enough to destroy the target.
Infrared guidance
Infrared guided (IR) missiles home on the heat produced by an aircraft. Early infra-red detectors had poor sensitivity, so could only track the hot exhaust pipes of an aircraft. This meant an attacking aircraft had to maneuver to a position behind its target before it could fire an infra-red guided missile. This also limited the range of the missile as the infra-red signature soon become too small to detect with increasing distance and after launch the missile was playing "catch-up" with its target. Early infrared seekers were unusable in clouds or rain (which is still a limitation to some degree) and could be distracted by the sun, a reflection of the sun off of a cloud or ground object, or any other "hot" object within its view.
More modern infra-red guided missiles can detect the heat of an aircraft's skin, warmed by the friction of airflow, in addition to the fainter heat signature of the engine when the aircraft is seen from the side or head-on. This, combined with greater maneuverability, gives them an "all-aspect" capability, and an attacking aircraft no longer had to be behind its target to fire. Although launching from behind the target increases the probability of a hit, the launching aircraft usually has to be closer to the target in such a tail-chase engagement.
An aircraft can defend against infra-red missiles by dropping flares that are hotter than the aircraft, so the missile homes in on the brighter, hotter target. In turn, IR missiles may employ filters to enable it to ignore targets whose temperature is not within a specified range.
Towed decoys which closely mimic engine heat and infra-red jammers can also be used. Some large aircraft and many combat helicopters make use of so-called "hot brick" infra-red jammers, typically mounted near the engines. Current research is developing laser devices which can spoof or destroy the guidance systems of infra-red guided missiles. See Infrared countermeasure.
Start of the 21st century missiles such as the ASRAAM use an "imaging infrared" seeker which "sees" the target (much like a digital video camera), and can distinguish between an aircraft and a point heat source such as a flare. They also feature a very wide detection angle, so the attacking aircraft does not have to be pointing straight at the target for the missile to lock on. The pilot can use a helmet mounted sight (HMS) and target another aircraft by looking at it, and then firing. This is called "off-boresight" launch. For example, the Russian Su-27 is equipped with an infra-red search and track (IRST) system with laser rangefinder for its HMS-aimed missiles.
Electro-optical
A recent advancement in missile guidance is electro-optical imaging. The Israeli Python-5 has an electro-optical seeker that scans designated area for targets via optical imaging. Once a target is acquired, the missile will lock-on to it for the kill. Electro-optical seekers can be programmed to target vital area of an aircraft, such as the cockpit. Since it does not depend on the target aircraft's heat signature, it can be used against low-heat targets such as UAVs and cruise missiles. However, clouds can get in the way of electro-optical sensors.
Passive anti-radiation
Evolving missile guidance designs are converting the anti-radiation missile (ARM) design, pioneered during Vietnam and used to home in against emitting surface-to-air missile (SAM) sites, to an air intercept weapon. Current air-to-air passive anti-radiation missile development is thought to be a countermeasure to airborne early warning and control (AEW&C – also known as AEW or AWACS) aircraft which typically mount powerful search radars.
Due to their dependence on target aircraft radar emissions, when used against fighter aircraft passive anti-radiation missiles are primarily limited to forward-aspect intercept geometry. For examples, see Vympel R-27 and Brazo.
Another aspect of passive anti-radiation homing is the "home on jam" mode which, when installed, allows a radar-guided missile to home in on the jammer of the target aircraft if the primary seeker is jammed by the electronic countermeasures of the target aircraft.
Design
Air-to-air missiles are typically long, thin cylinders in order to reduce their cross section and thus minimize drag at the high speeds at which they travel. Missiles are divided into five primary systems (moving forward to aft): seeker, guidance, warhead, motor, and control actuation.
At the front is the seeker, either a radar system, radar homer, or infra-red detector. Behind that lies the avionics which control the missile. Typically after that, in the centre of the missile, is the warhead, usually several kilograms of high explosive surrounded by metal that fragments on detonation (or in some cases, pre-fragmented metal).
The rear part of the missile contains the propulsion system, usually a rocket of some type and the control actuation system or CAS. Dual-thrust solid-fuel rockets are common, but some longer-range missiles use liquid-fuel motors that can "throttle" to extend their range and preserve fuel for energy-intensive final maneuvering. Some solid-fuelled missiles mimic this technique with a second rocket motor which burns during the terminal homing phase. There are missiles, such as the MBDA Meteor, that "breathe" air (using a ramjet, similar to a jet engine) in order to extend their range.
Modern missiles use "low-smoke" motors – early missiles produced thick smoke trails, which were easily seen by the crew of the target aircraft alerting them to the attack and helping them determine how to evade it.
The CAS is typically an electro-mechanical, servo control actuation system, which takes input from the guidance system and manipulates the airfoils or fins at the rear of the missile that guide or steers the weapon to target.
Nowadays, countries start developing hypersonic air-to-air missile using scramjet engines (such as R-37, or AIM-260 JATM), which not only increases efficiency for BVR battles, but it also makes survival chances of target aircraft drop to nearly zero.
Performance
A number of terms frequently crop up in discussions of air-to-air missile performance.
Launch success zone The Launch Success Zone is the range within which there is a high (defined) kill probability against a target that remains unaware of its engagement until the final moment. When alerted visually or by a warning system the target attempts a last-ditch-manoeuvre sequence.
F-pole A closely related term is the F-Pole. This is the slant range between the launch aircraft and target, at the time of interception. The greater the F-Pole, the greater the confidence that the launch aircraft will achieve air superiority with that missile.
A-pole This is the slant range between the launch aircraft and target at the time that the missile begins active guidance or acquires the target with the missile's active seeker. The greater the A-Pole means less time and possibly greater distance that the launch aircraft needs to support the missile guidance until missile seeker acquisition.
No-escape zone The no-escape zone is the zone within which there is a high (defined) kill probability against a target even if it has been alerted. This zone is defined as a conical shape with the tip at the missile launch. The cone's length and width are determined by the missile and seeker performance. A missile's speed, range and seeker sensitivity will mostly determine the length of this imaginary cone, while its agility (turn rate) and seeker complexity (speed of detection and ability to detect off axis targets) will determine the width of the cone.
Missile minimum range
A missile is subject to a minimum range, before which it cannot maneuver effectively. In order to maneuver sufficiently from a poor launch angle at short ranges to hit its target, some missiles use thrust vectoring, which allow the missile to start turning "off the rail", before its motor has accelerated it up to high enough speeds for its small aerodynamic surfaces to be useful.
Short-range air-to-air missile
Short-range air-to-air missiles (SRAAMs), typically used in "dogfighting" or close range air combat compare to the beyond-visual-range missiles. Most of the short-range air-to-air missiles are infrared guided.
SRAAM missile evolution
Those missiles usually classified into five "generations" according to the historical technological advances. Most of these advances were in infrared seeker technology (later combined with digital signal processing).
First generation
Early short-range missiles such as the early Sidewinders and K-13 (missile) (AA-2 Atoll) had infrared seekers with a narrow (30-degree) field of view and required the attacker to position himself behind the target (rear aspect engagement). This meant that the target aircraft only had to perform a slight turn to move outside the missile seeker's field of view and cause the missile to lose track of the target ("break lock").
Second generation
The second-generation of short-range missiles utilized more effective seekers that were better cooled than its predecessors while being typically "uncaged"; resulting in improved sensitivity to heat signatures, an increase in field of view as well as allowing the possibility of leading a missile within its FOV for an increased probability of kill against a maneuvering target. In some cases, the improved sensitivity to heat signatures allows for a very limited side and even all-aspect tracking, as is the case with the Red Top missile. In conjunction with improved control surfaces and propulsion motors over the first generation of dogfight missiles, the technological advances of the second-generation short-range missiles allowed them to be used not just on non-maneuvering bombers, but also actively maneuvering fighters. Examples include advanced derivatives of the K-13 (missile) and AIM-9 such as K-13M (R-13M, Object 380) or AIM-9D / G / H.
Third generation
This generation introduced much more sensitive seekers that are capable of locking onto the warm heat irradiated by the skins of aircraft from the front or side aspects, as opposed to just the hotter engine nozzle(s) from rear-aspect, allowing for a true all-aspect capability. This significantly expanded potential attacking envelopes, allowing the attacker to fire at a target which was side-on or front-on to itself as opposed to just the rear. While the field-of-view was still restricted to a fairly narrow cone, the attack at least did not have to be behind the target.
Also typical of the third generation of short-range missiles are further improved agility over the previous generation as well as their ability to radar-slave; which is acquiring tracking data from the launching aircraft's radar or IRST systems, allowing attackers to launch missiles without ever pointing the nose of the aircraft at an enemy prior to leading the missile. Examples of this generation of dogfight missiles include the R-60M or the Python-3.
Fourth generation
The R-73 (missile) (AA-11 Archer) entered service in 1985 and marked a new generation of dogfight missile. It had a wider field of view and could be cued onto a target using a helmet mounted sight. This allowed it to be launched at targets that would otherwise not be seen by older generation missiles that generally stared forward while waiting to be launched. This capability, combined with a more powerful motor that allows the missile to maneuver against crossing targets and launch at greater ranges, gives the launching aircraft improved tactical freedom.
Other members of the 4th generation use focal plane arrays to offer greatly improved scanning and countermeasures resistance (especially against flares). These missiles are also much more agile, some by employing thrust vectoring (typically gimballed thrust).
Fifth generation
The latest generation of short-range missiles again defined by advances in seeker technologies, this time electro-optical imaging infrared (IIR) seekers that allow the missiles to "see" images rather than single "points" of infrared radiation (heat). The sensors combined with more powerful digital signal processing provide the following benefits:
greater infrared counter countermeasures (IRCCM) ability, by being able to distinguish aircraft from infrared countermeasures (IRCM) such as flares.
greater sensitivity means greater range and ability to identify smaller low flying targets such as UAVs.
more detailed target image allows targeting of more vulnerable parts of aircraft instead of just homing in on the brightest infrared source (exhaust).
Examples of fifth generation short-range missiles include:
R-74M2 ("AA-11 Archer") – Russia (1983–)
R-77T ("AA-12 Adder") – Russia (1994–)
ASRAAM – UK (1998–)
AIM-9X Sidewinder – US (2003–)
Python 5 – Israel (2003–)
AAM-5 – Japan (2004–)
IRIS-T – Germany (2005–)
PL-10 – China (2015–)
A-Darter – South Africa and Brazil (2019–)
Merlin – Turkey (2024–)
List of missiles by country
For each missile, short notes are given, including an indication of its range and guidance mechanism.
Brazil
MAA-1A Piranha – Short-range IR
MAA-1B Piranha – IR-guided missile.
A-Darter – Short-range IR (With South Africa)
Canada
Velvet Glove - short range, semi-active radar-guided
France
Nord AA.20, AA.25 – radio-guided, beam-riding
Matra R.510 – IR-guided
Matra R.511 – radar-guided
Matra R.550 Magic – short-range, IR-guided
Matra Magic II – IR-guided
Matra R.530 – medium-range, IR- or radar-guided
Matra Super 530F/Super 530D – medium-range, radar-guided
Matra Mistral – IR-guided
MBDA MICA – medium-range, IR- or active radar-guided
MBDA Meteor – long-range active radar-guided missile, integrated on Rafale.
TRIGAT LR
Germany
Henschel Hs 298 – World War II design, MCLOS, never saw service
IRIS-T
MBDA Meteor long-range, active radar-guided, pending contract for integration on Eurofighter.
Ruhrstahl X-4 – World War II design, first practical anti-aircraft missile, MCLOS, never saw service
RZ 65 missile project developed by Rheinmetall-Borsig in 1941. After about 3000 tests it revealed itself unsatisfactory owing to an accuracy of only 15%. The project was terminated by the end of the war.
Dornier Viper
India
Astra Mk 1 – Long-range radar-guided
Astra Mk 2 – Long-range radar-guided
Astra Mk 3 – Long-range radar-guided
Astra IR – Short-range infrared homing
K-100 (missile) – Inertial navigation and active radar homing (with Russia)
Iran
Fatter – copy of U.S. AIM-9 Sidewinder
Sedjil – copy of U.S. MIM-23 Hawk converted to be carried by aircraft
Fakour-90 – copy of U.S. AIM-54 Phoenix
Iraq
Al Humurrabi – Long-range, semi active radar
Israel
Python:
Rafael Shafrir – first Israeli domestic AAM
Rafael Shafrir 2 – improved Shafrir missile
Rafael Python 3 – medium-range IR-homing missile with all aspect capability
Rafael Python 4 – medium-range IR-homing missile with HMS-guidance capability
Python-5 – improved Python 4 with electro-optical imaging seeker, and 360 degrees lock on. (and launch)
Rafael Derby – Also known as the Alto, this is a medium-range, BVR active radar-homing missile
I-Derby ER – long range BVR active radar-homing missile
Sky Spear – 6th generation long-range, air-to-air missile
Italy
Alenia Aspide – Copy of the U.S.AIM-7 Sparrow, based on the AIM-7E.
Japan
AAM-1 – (Type 69 air-to-air missile) short-range, IR-seeking air-to-air missile; copy of U.S. AIM-9B Sidewinder.
AAM-2 – short-range, IR-seeking air-to-air missile; similar to AIM-4D, prototype-only.
AAM-3 – (Type 90 air-to-air missile) short-range, all-aspect IR-seeking air-to-air missile.
AAM-4 – (Type 99 air-to-air missile) medium-range, active radar-guided air-to-air missile.
AAM-5 – (Type 04 air-to-air missile) short-range, all-aspect IR-seeking air-to-air missile.
People's Republic of China
PL-1 – PRC version of the Soviet K-5 (missile) (AA-1 Alkali), retired.
PL-2 – PRC version of the Soviet Vympel K-13 (AA-2 Atoll), which was based on AIM-9B Sidewinder. Retired & replaced by PL-5 in PLAAF service.
PL-3 – updated version of the PL-2, did not enter service.
PL-4 – experimental BVR missile based on AIM-7D, did not enter service.
PL-6 – updated version of PL-3, also did not enter service.
PL-5 – updated version of the PL-2, known versions include:
PL-5A – semi-active radar-homing AAM intended to replace the PL-2, did not enter service. Resembles AIM-9G in appearance.
PL-5B – IR version, entered service in the 1990s to replace the PL-2 SRAAM. Limited off-boresight
PL-5C – Improved version comparable to AIM-9H or AIM-9L in performance
PL-5E – All-aspect attack version, resembles AIM-9P in appearance.
PL-7 – PRC version of the IR-homing French R550 Magic AAM, did not enter service.
PL-8 – PRC version of the Israeli Rafael Python 3
PL-9 – short-range IR-guided missile, marketed for export. One known improved version (PL-9C).
PL-10(old);– semi-active radar-homing medium-range missile based on the HQ-61 SAM, often confused with PL-11. Did not enter service.
PL-10(new)/PL-ASR – short-range off-boresight all-aspect IR-guided missile.
PL-11 – medium-range air-to-air missile (MRAAM), based on the HQ-61C & Italian Aspide (AIM-7) technology. Limited service with J-8-B/D/H fighters. Known versions include:
PL-11 – MRAAM with semi-active radar homing, based on the HQ-61C SAM and Aspide seeker technology, exported as FD-60
PL-11A – Improved PL-11 with increased range, warhead, and more effective seeker. The new seeker only requires fire-control radar guidance during the terminal stage, providing a basic LOAL (lock-on after launch) capability.
PL-11B – Also known as PL-11 AMR, improved PL-11 with AMR-1 active radar-homing seeker.
LY-60 – PL-11 adopted for navy ships for air-defense, sold to Pakistan but does not appear to be in service with the Chinese Navy.
PL-12 (SD-10) – medium-range active radar missile
PL-12A – with upgraded motor
PL-12B – with upgraded guidance
PL-12C – with foldable tailfins
PL-12D – with belly inlet and ramjet motors
F80 – medium-range active radar missile
PL-15 – long-range active radar missile
PL-17 – extreme long-range active radar missile
PL-21 - long-range active radar missile (In Development)
TY-90 – light IR-homing air-to-air missile designed for helicopters
Soviet Union/Russian Federation
K-5 (missile) (NATO reporting name AA-1 'Alkali') – beam-riding
Vympel K-13 (NATO reporting name AA-2 'Atoll') – short-range IR or SARH
Kaliningrad K-8 (NATO reporting name AA-3 'Anab') – IR or SARH
Raduga K-9 (NATO reporting name AA-4 'Awl') – IR or SARH
Bisnovat R-4 (NATO reporting name AA-5 'Ash') – IR or SARH
Bisnovat R-40 (NATO reporting name AA-6 'Acrid') – long-range IR or SARH
Vympel R-23/R-24 (NATO reporting name AA-7 'Apex') – medium-range SARH or IR
Molniya R-60 (NATO reporting name AA-8 'Aphid') – short-range IR
Vympel R-33 (NATO reporting name AA-9 'Amos') – long-range active radar
Vympel R-27 (NATO reporting name AA-10 'Alamo') – medium-range SARH or IR
Vympel R-73 (NATO reporting name AA-11 'Archer') – short-range IR
Vympel R-77 (NATO reporting name AA-12 'Adder') – medium-range active radar
Vympel R-37 (NATO reporting name AA-13 'Axehead') – long-range SARH or active radar homing
Novator KS-172 AAM-L – extreme long-range, inertial navigation with terminal active radar homing
South Africa
A-Darter – Short-range IR (With Brazil)
V3 Kukri – Short-range IR
R-Darter – Beyond-visual-range (BVR) radar-guided missile
Taiwan
Sky Sword I (TC-1) – air-to-air
Sky Sword II (TC-2) – air-to-air
Turkey
Bozdoğan (Merlin) – WVRAAM (within-visual-range air-to-air missile)
Gökdoğan (Peregrine) – BVRAAM (beyond-visual-range air-to-air missile)
Akdoğan (Gyrfalcon) – Akdoğan is a 'mini' air-to-air missile intended to be cost-effective and to be used in UAVs such as Bayraktar Akıncı and TAI Aksungur.
Gökhan – it was officially confirmed that this variant would have a Ramjet.
United Kingdom
Fireflash – short-range beam-riding
Firestreak – short-range IR
Red Top – short-range IR
Taildog/SRAAM – short-range IR
Skyflash – medium-range radar-guided missile based on the AIM-7E2, said to have quick warm-up times of 1 to 2 seconds.
AIM-132 ASRAAM – short-range IR
MBDA Meteor – long-range active radar-guided missile with a solid fuel ducted ramjet
United States
Retired
AIM-4 Falcon – radar-guided (later IR-seeking)
AIM-26 Falcon
AIM-54 Phoenix – long-range, semi-active-guided and active radar-guided; retired in 2004
AIM-47 Falcon
Operational
AIM-7 Sparrow – medium-range, semi-active radar-guided
AIM-9 Sidewinder – short-range, IR-seeking
AIM-92 Stinger – short-range, IR-seeking; launched from helicopters
AIM-120 AMRAAM – medium-range, active radar-guided; replaces AIM-7 Sparrow
AIM-174 - extreme long-range, active radar-guided
In development
AIM-260 JATM – Under development by Lockheed Martin
AIM-160 CUDA/SACM – Under development
Boeing LRAAM
LREW (Long-Range Engagement Weapon programme)
MAM (Modular Advanced Missile)
Raytheon Peregrine – Compact medium-range active radar missile
Typical air-to-air missiles
| Technology | Missiles | null |
320760 | https://en.wikipedia.org/wiki/Body%20fluid | Body fluid | Body fluids, bodily fluids, or biofluids, sometimes body liquids, are liquids within the body of an organism. In lean healthy adult men, the total body water is about 60% (60–67%) of the total body weight; it is usually slightly lower in women (52–55%). The exact percentage of fluid relative to body weight is inversely proportional to the percentage of body fat. A lean man, for example, has about 42 (42–47) liters of water in his body.
The total body of water is divided into fluid compartments, between the intracellular fluid compartment (also called space, or volume) and the extracellular fluid (ECF) compartment (space, volume) in a two-to-one ratio: 28 (28–32) liters are inside cells and 14 (14–15) liters are outside cells.
The ECF compartment is divided into the interstitial fluid volume – the fluid outside both the cells and the blood vessels – and the intravascular volume (also called the vascular volume and blood plasma volume) – the fluid inside the blood vessels – in a three-to-one ratio: the interstitial fluid volume is about 12 liters; the vascular volume is about 4 liters.
The interstitial fluid compartment is divided into the lymphatic fluid compartment – about 2/3, or 8 (6–10) liters, and the transcellular fluid compartment (the remaining 1/3, or about 4 liters).
The vascular volume is divided into the venous volume and the arterial volume; and the arterial volume has a conceptually useful but unmeasurable subcompartment called the effective arterial blood volume.
Compartments by location
intracellular fluid (ICF), which consist of cytosol and fluids in the cell nucleus
Extracellular fluid
Intravascular fluid (blood plasma)
Interstitial fluid
Lymphatic fluid (sometimes included in interstitial fluid)
Transcellular fluid
Health
Clinical samples
Clinical samples are generally defined as non-infectious human or animal materials including blood, saliva, excreta, body tissue and tissue fluids, and also FDA-approved pharmaceuticals that are blood products. In medical contexts, it is a specimen taken for diagnostic examination or evaluation, and for identification of disease or condition.
| Biology and health sciences | Animal anatomy and morphology | Biology |
320861 | https://en.wikipedia.org/wiki/Constant%20function | Constant function | In mathematics, a constant function is a function whose (output) value is the same for every input value.
Basic properties
As a real-valued function of a real-valued argument, a constant function has the general form or just For example, the function is the specific constant function where the output value is . The domain of this function is the set of all real numbers. The image of this function is the singleton set . The independent variable does not appear on the right side of the function expression and so its value is "vacuously substituted"; namely , , , and so on. No matter what value of is input, the output is .
The graph of the constant function is a horizontal line in the plane that passes through the point . In the context of a polynomial in one variable , the constant function is called non-zero constant function because it is a polynomial of degree 0, and its general form is , where is nonzero. This function has no intersection point with the axis, meaning it has no root (zero). On the other hand, the polynomial is the identically zero function. It is the (trivial) constant function and every is a root. Its graph is the axis in the plane. Its graph is symmetric with respect to the axis, and therefore a constant function is an even function.
In the context where it is defined, the derivative of a function is a measure of the rate of change of function values with respect to change in input values. Because a constant function does not change, its derivative is 0. This is often written: . The converse is also true. Namely, if for all real numbers , then is a constant function. For example, given the constant function The derivative of is the identically zero function
Other properties
For functions between preordered sets, constant functions are both order-preserving and order-reversing; conversely, if is both order-preserving and order-reversing, and if the domain of is a lattice, then must be constant.
Every constant function whose domain and codomain are the same set is a left zero of the full transformation monoid on , which implies that it is also idempotent.
It has zero slope or gradient.
Every constant function between topological spaces is continuous.
A constant function factors through the one-point set, the terminal object in the category of sets. This observation is instrumental for F. William Lawvere's axiomatization of set theory, the Elementary Theory of the Category of Sets (ETCS).
For any non-empty , every set is isomorphic to the set of constant functions in . For any and each element in , there is a unique function such that for all . Conversely, if a function satisfies for all , is by definition a constant function.
As a corollary, the one-point set is a generator in the category of sets.
Every set is canonically isomorphic to the function set , or hom set in the category of sets, where 1 is the one-point set. Because of this, and the adjunction between Cartesian products and hom in the category of sets (so there is a canonical isomorphism between functions of two variables and functions of one variable valued in functions of another (single) variable, ) the category of sets is a closed monoidal category with the Cartesian product of sets as tensor product and the one-point set as tensor unit. In the isomorphisms natural in , the left and right unitors are the projections and the ordered pairs and respectively to the element , where is the unique point in the one-point set.
A function on a connected set is locally constant if and only if it is constant.
| Mathematics | Specific functions | null |
321263 | https://en.wikipedia.org/wiki/Birth%20defect | Birth defect | A birth defect is an abnormal condition that is present at birth, regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth defects are divided into two main types: structural disorders in which problems are seen with the shape of a body part and functional disorders in which problems exist with how a body part works. Functional disorders include metabolic and degenerative disorders. Some birth defects include both structural and functional disorders.
Birth defects may result from genetic or chromosomal disorders, exposure to certain medications or chemicals, or certain infections during pregnancy. Risk factors include folate deficiency, drinking alcohol or smoking during pregnancy, poorly controlled diabetes, and a mother over the age of 35 years old. Many birth defects are believed to involve multiple factors. Birth defects may be visible at birth or diagnosed by screening tests. A number of defects can be detected before birth by different prenatal tests.
Treatment varies depending on the defect in question. This may include therapy, medication, surgery, or assistive technology. Birth defects affected about 96 million people . In the United States, they occur in about 3% of newborns. They resulted in about 628,000 deaths in 2015, down from 751,000 in 1990. The types with the greatest numbers of deaths are congenital heart disease (303,000), followed by neural tube defects (65,000).
Classification
Much of the language used for describing congenital conditions antedates genome mapping, and structural conditions are often considered separately from other congenital conditions. Many metabolic conditions are now known to have subtle structural expression, and structural conditions often have genetic links. Still, congenital conditions are often classified on a structural basis, organized when possible by primary organ system affected.
Primarily structural
Several terms are used to describe congenital abnormalities. (Some of these are also used to describe noncongenital conditions, and more than one term may apply in an individual condition.)
Terminology
A congenital physical anomaly is an abnormality of the structure of a body part. It may or may not be perceived as a problem condition. Many, if not most, people have one or more minor physical anomalies if examined carefully. Examples of minor anomalies can include curvature of the fifth finger (clinodactyly), a third nipple, tiny indentations of the skin near the ears (preauricular pits), shortness of the fourth metacarpal or metatarsal bones, or dimples over the lower spine (sacral dimples). Some minor anomalies may be clues to more significant internal abnormalities.
Birth defect is a widely used term for a congenital malformation, i.e. a congenital, physical anomaly that is recognizable at birth, and which is significant enough to be considered a problem. According to the Centers for Disease Control and Prevention (CDC), most birth defects are believed to be caused by a complex mix of factors including genetics, environment, and behaviors, though many birth defects have no known cause. An example of a birth defect is cleft palate, which occurs during the fourth through seventh weeks of gestation. Body tissue and special cells from each side of the head grow toward the center of the face. They join to make the face. A cleft means a split or separation; the "roof" of the mouth is called the palate.
A congenital malformation is a physical anomaly that is deleterious, i.e. a structural defect perceived as a problem. A typical combination of malformations affecting more than one body part is referred to as a malformation syndrome.
Some conditions are due to abnormal tissue development:
A malformation is associated with a disorder of tissue development. Malformations often occur in the first trimester.
A dysplasia is a disorder at the organ level that is due to problems with tissue development.
Conditions also can arise after tissue is formed:
A deformation is a condition arising from mechanical stress to normal tissue. Deformations often occur in the second or third trimester, and can be due to oligohydramnios.
A disruption involves breakdown of normal tissues.
When multiple effects occur in a specified order, they are known as a sequence. When the order is not known, it is a syndrome.
Examples of primarily structural congenital disorders
A limb anomaly is called a dysmelia. These include all forms of limbs anomalies, such as amelia, ectrodactyly, phocomelia, polymelia, polydactyly, syndactyly, polysyndactyly, oligodactyly, brachydactyly, achondroplasia, congenital aplasia or hypoplasia, amniotic band syndrome, and cleidocranial dysostosis.
Congenital heart defects include patent ductus arteriosus, atrial septal defect, ventricular septal defect, and tetralogy of Fallot.
Congenital anomalies of the nervous system include neural tube defects such as spina bifida, encephalocele, and anencephaly. Other congenital anomalies of the nervous system include the Arnold–Chiari malformation, the Dandy–Walker malformation, hydrocephalus, microencephaly, megalencephaly, lissencephaly, polymicrogyria, holoprosencephaly, and agenesis of the corpus callosum.
Congenital anomalies of the gastrointestinal system include numerous forms of stenosis and atresia, and perforation, such as gastroschisis.
Congenital anomalies of the kidney and urinary tract include renal parenchyma, kidneys, and urinary collecting system.
Defects can be bilateral or unilateral, and different defects often coexist in an individual child.
Primarily metabolic
A congenital metabolic disease is also referred to as an inborn error of metabolism. Most of these are single-gene defects, usually heritable. Many affect the structure of body parts, but some simply affect the function.
Other
Other well-defined genetic conditions may affect the production of hormones, receptors, structural proteins, and ion channels.
Causes
Alcohol exposure
The mother's consumption of alcohol during pregnancy can cause a continuum of various permanent birth defects: craniofacial abnormalities, brain damage, intellectual disability, heart disease, kidney abnormality, skeletal anomalies, ocular abnormalities.
The prevalence of children affected is estimated at least 1% in U.S. as well in Canada.
Very few studies have investigated the links between paternal alcohol use and offspring health.
However, recent animal research has shown a correlation between paternal alcohol exposure and decreased offspring birth weight. Behavioral and cognitive disorders, including difficulties with learning and memory, hyperactivity, and lowered stress tolerance have been linked to paternal alcohol ingestion. The compromised stress management skills of animals whose male parent was exposed to alcohol are similar to the exaggerated responses to stress that children with fetal alcohol syndrome display because of maternal alcohol use. These birth defects and behavioral disorders were found in cases of both long- and short-term paternal alcohol ingestion. In the same animal study, paternal alcohol exposure was correlated with a significant difference in organ size and the increased risk of the offspring displaying ventricular septal defects at birth.
Toxic substances
Substances whose toxicity can cause congenital disorders are called teratogens, and include certain pharmaceutical and recreational drugs in pregnancy, as well as many environmental toxins in pregnancy.
A review published in 2010 identified six main teratogenic mechanisms associated with medication use: folate antagonism, neural crest cell disruption, endocrine disruption, oxidative stress, vascular disruption, and specific receptor- or enzyme-mediated teratogenesis.
An estimated 10% of all birth defects are caused by prenatal exposure to a teratogenic agent. These exposures include medication or drug exposures, maternal infections and diseases, and environmental and occupational exposures. Paternal smoking has also been linked to an increased risk of birth defects and childhood cancer for the offspring, where the paternal germline undergoes oxidative damage due to cigarette use. Teratogen-caused birth defects are potentially preventable. Nearly 50% of pregnant women have been exposed to at least one medication during gestation. During pregnancy, a woman can also be exposed to teratogens from contaminated clothing or toxins within the seminal fluid of a partner. An additional study found that of 200 individuals referred for genetic counseling for a teratogenic exposure, 52% were exposed to more than one potential teratogen.
The United States Environmental Protection Agency studied 1,065 chemical and drug substances in their ToxCast program (part of the CompTox Chemicals Dashboard) using in silico modeling and a human pluripotent stem cell-based assay to predict in vivo developmental intoxicants based on changes in cellular metabolism following chemical exposure. Findings of the study published in 2020 were that 19% of the 1065 chemicals yielded a prediction of developmental toxicity.
Medications and supplements
Probably, the most well-known teratogenic drug is thalidomide. It was developed near the end of the 1950s by Chemie Grünenthal as a sleep-inducing aid and antiemetic. Because of its ability to prevent nausea, it was prescribed for pregnant women in almost 50 countries worldwide between 1956 and 1962. Until William McBride published the study leading to its withdrawal from the market in 1961, about 8,000 to 10,000 severely malformed children were born. The most typical disorders induced by thalidomide were reductional deformities of the long bones of the extremities. Phocomelia, otherwise a rare deformity, therefore helped to recognise the teratogenic effect of the new drug. Among other malformations caused by thalidomide were those of ears, eyes, brain, kidney, heart, and digestive and respiratory tracts; 40% of the prenatally affected children died soon after birth. As thalidomide is used today as a treatment for multiple myeloma and leprosy, several births of affected children were described in spite of the strictly required use of contraception among female patients treated by it.
Vitamin A is the sole vitamin that is embryotoxic even in a therapeutic dose, for example in multivitamins, because its metabolite, retinoic acid, plays an important role as a signal molecule in the development of several tissues and organs. Its natural precursor, β-carotene, is considered safe, whereas the consumption of animal liver can lead to malformation, as the liver stores lipophilic vitamins, including retinol. Isotretinoin (13-cis-retinoic-acid; brand name Roaccutane), vitamin A analog, which is often used to treat severe acne, is such a strong teratogen that just a single dose taken by a pregnant woman (even transdermally) may result in serious birth defects. Because of this effect, most countries have systems in place to ensure that it is not given to pregnant women and that the patient is aware of how important it is to prevent pregnancy during and at least one month after treatment. Medical guidelines also suggest that pregnant women should limit vitamin A intake to about 700 μg/day, as it has teratogenic potential when consumed in excess. Vitamin A and similar substances can induce spontaneous abortions, premature births, defects of eyes (microphthalmia), ears, thymus, face deformities, and neurological (hydrocephalus, microcephalia) and cardiovascular defects, as well as intellectual disability.
Tetracycline, an antibiotic, should never be prescribed to women of reproductive age or to children, because of its negative impact on bone mineralization and teeth mineralization. The "tetracycline teeth" have brown or grey colour as a result of a defective development of both the dentine and the enamel of teeth.
Several anticonvulsants are known to be highly teratogenic. Phenytoin, also known as diphenylhydantoin, along with carbamazepine, is responsible for the fetal hydantoin syndrome, which may typically include broad nose base, cleft lip and/or palate, microcephalia, nails and fingers hypoplasia, intrauterine growth restriction, and intellectual disability. Trimethadione taken during pregnancy is responsible for the fetal trimethadione syndrome, characterized by craniofacial, cardiovascular, renal, and spine malformations, along with a delay in mental and physical development. Valproate has antifolate effects, leading to neural tube closure-related defects such as spina bifida. Lower IQ and autism have recently also been reported as a result of intrauterine valproate exposure.
Hormonal contraception is considered harmless for the embryo. Peterka and Novotná do, however, state that synthetic progestins used to prevent miscarriage in the past frequently caused masculinization of the outer reproductive organs of female newborns due to their androgenic activity. Diethylstilbestrol is a synthetic estrogen used from the 1940s to 1971, when the prenatal exposition has been linked to the clear-cell adenocarcinoma of the vagina. Following studies showed elevated risks for other tumors and congenital malformations of the sex organs for both sexes.
All cytostatics are strong teratogens; abortion is usually recommended when pregnancy is discovered during or before chemotherapy. Aminopterin, a cytostatic drug with antifolate effect, was used during the 1950s and 1960s to induce therapeutic abortions. In some cases, the abortion did not happen, but the newborns had a fetal aminopterin syndrome consisting of growth retardation, craniosynostosis, hydrocephalus, facial dismorphities, intellectual disability, or leg deformities
Toxic substances
Drinking water is often a medium through which harmful toxins travel. Heavy metals, elements, nitrates, nitrites, and fluoride can be carried through water and cause congenital disorders.
Nitrate, which is found mostly in drinking water from ground sources, is a powerful teratogen. A case-control study in rural Australia that was conducted following frequent reports of prenatal mortality and congenital malformations found that those who drank the nitrate-containing groundwater, as opposed to rain water, ran the risk of giving birth to children with central nervous system disorders, muscoskeletal defects, and cardiac defects.
Chlorinated and aromatic solvents such as benzene and trichloroethylene sometimes enter the water supply due to oversights in waste disposal. A case-control study on the area found that by 1986, leukemia was occurring in the children of Woburn, Massachusetts, at a rate that was four times the expected rate of incidence. Further investigation revealed a connection between the high occurrence of leukemia and an error in water distribution that delivered water to the town with significant contamination with manufacturing waste containing trichloroethylene.
As an endocrine disruptor, DDT was shown to induce miscarriages, interfere with the development of the female reproductive system, cause the congenital hypothyroidism, and suspectably childhood obesity.
Fluoride, when transmitted through water at high levels, can also act as a teratogen. Two reports on fluoride exposure from China, which were controlled to account for the education level of parents, found that children born to parents who were exposed to 4.12 ppm fluoride grew to have IQs that were, on average, seven points lower than their counterparts whose parents consumed water that contained 0.91 ppm fluoride. In studies conducted on rats, higher fluoride in drinking water led to increased acetylcholinesterase levels, which can alter prenatal brain development. The most significant effects were noted at a level of 5 ppm.
The fetus is even more susceptible to damage from carbon monoxide intake, which can be harmful when inhaled during pregnancy, usually through first- or second-hand tobacco smoke. The concentration of carbon monoxide in the infant born to a nonsmoking mother is around 2%, and this concentration drastically increases to a range of 6%–9% if the mother smoked tobacco. Other possible sources of prenatal carbon monoxide intoxication are exhaust gas from combustion motors, use of dichloromethane (paint thinner, varnish removers) in enclosed areas, defective gas water heaters, indoor barbeques, open flames in poorly ventilated areas, and atmospheric exposure in highly polluted areas. Exposure to carbon monoxide at toxic levels during the first two trimesters of pregnancy can lead to intrauterine growth restriction, leading to a baby who has stunted growth and is born smaller than 90% of other babies at the same gestational age. The effect of chronic exposure to carbon monoxide can depend on the stage of pregnancy in which the mother is exposed. Exposure during the embryonic stage can have neurological consequences, such as telencephalic dysgenesis, behavioral difficulties during infancy, and reduction of cerebellum volume. Also, possible skeletal defects could result from exposure to carbon monoxide during the embryonic stage, such as hand and foot malformations, hip dysplasia, hip subluxation, agenesis of a limb, and inferior maxillary atresia with glossoptosis. Also, carbon monoxide exposure between days 35 and 40 of embryonic development can lead to an increased risk of the child developing a cleft palate. Exposure to carbon monoxide or polluted ozone exposure can also lead to cardiac defects of the ventrical septal, pulmonary artery, and heart valves. The effects of carbon monoxide exposure are decreased later in fetal development during the fetal stage, but they may still lead to anoxic encephalopathy.
Industrial pollution can also lead to congenital defects. Over a period of 37 years, the Chisso Corporation, a petrochemical and plastics company, contaminated the waters of Minamata Bay with an estimated 27 tons of methylmercury, contaminating the local water supply. This led many people in the area to develop what became known as the "Minamata disease". Because methylmercury is a teratogen, the mercury poisoning of those residing by the bay resulted in neurological defects in the offspring. Infants exposed to mercury poisoning in utero showed predispositions to cerebral palsy, ataxia, inhibited psychomotor development, and intellectual disability.
Landfill sites have been shown to have adverse effects on fetal development. Extensive research has shown that landfills have several negative effects on babies born to mothers living near landfill sites: low birth weight, birth defects, spontaneous abortion, and fetal and infant mortality. Studies done around the Love Canal site near Niagara Falls and the Lipari Landfill in New Jersey have shown a higher proportion of low birth-weight babies than communities farther away from landfills. A study done in California showed a positive correlation between time and quantity of dumping and low birth weights and neonatal deaths. A study in the United Kingdom showed a correlation between pregnant women living near landfill sites and an increased risk of congenital disorders, such as neural tube defects, hypospadias, epispadia, and abdominal wall defects, such as gastroschisis and exomphalos. A study conducted on a Welsh community also showed an increased incidence of gastroschisis. Another study on 21 European hazardous-waste sites showed that those living within 3 km had an increased risk of giving birth to infants with birth defects and that as distance from the land increased, the risk decreased. These birth defects included neural tube defects, malformations of the cardiac septa, anomalies of arteries and veins, and chromosomal anomalies. Looking at communities that live near landfill sites brings up environmental justice. A vast majority of sites are located near poor, mostly black, communities. For example, between the early 1920s and 1978, about 25% of Houston's population was black. However, over 80% of landfills and incinerators during this time were located in these black communities.
Another issue regarding environmental justice is lead poisoning. A fetus exposed to lead during the pregnancy can result in learning difficulties and slowed growth. Some paints (before 1978) and pipes contain lead. Therefore, pregnant women who live in homes with lead paint inhale the dust containing lead, leading to lead exposure in the fetus. When lead pipes are used for drinking water and cooking water, this water is ingested, along with the lead, exposing the fetus to this toxin. This issue is more prevalent in poorer communities because more well-off families are able to afford to have their homes repainted and pipes renovated.
Endometriosis
Endometriosis can impact a woman's fetus, causing a 30% higher risk for congenital malformations and a 50% higher risk of neonates being under-sized for their gestational age.
Smoking
Paternal smoking prior to conception has been linked with the increased risk of congenital abnormalities in offspring.
Smoking causes DNA mutations in the germline of the father, which can be inherited by the offspring. Cigarette smoke acts as a chemical mutagen on germ cell DNA. The germ cells suffer oxidative damage, and the effects can be seen in altered mRNA production, infertility issues, and side effects in the embryonic and fetal stages of development. This oxidative damage may result in epigenetic or genetic modifications of the father's germline. Fetal lymphocytes have been damaged as a result of a father's smoking habits prior to conception.
Correlations between paternal smoking and the increased risk of offspring developing childhood cancers (including acute leukemia, brain tumors, and lymphoma) before age five have been established. Little is currently known about how paternal smoking damages the fetus, and what window of time in which the father smokes is most harmful to offspring.
Infections
A vertically transmitted infection is an infection caused by bacteria, viruses, or in rare cases, parasites transmitted directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth.
Congenital disorders were initially believed to be the result of only hereditary factors. However, in the early 1940s, Australian pediatric ophthalmologist Norman Gregg began recognizing a pattern in which the infants arriving at his surgery were developing congenital cataracts at a higher rate than those who developed it from hereditary factors. On October 15, 1941, Gregg delivered a paper that explained his findings-68 out of the 78 children with congenital cataracts had been exposed in utero to rubella due to an outbreak in Australian army camps. These findings confirmed, to Gregg, that, in fact, environmental causes for congenital disorders could exist.
Rubella is known to cause abnormalities of the eye, internal ear, heart, and sometimes the teeth. More specifically, fetal exposure to rubella during weeks five to ten of development (the sixth week particularly) can cause cataracts and microphthalmia in the eyes. If the mother is infected with rubella during the ninth week, a crucial week for internal ear development, destruction of the organ of Corti can occur, causing deafness. In the heart, the ductus arteriosus can remain after birth, leading to hypertension. Rubella can also lead to atrial and ventricular septal defects in the heart. If exposed to rubella in the second trimester, the fetus can develop central nervous system malformations. However, because infections of rubella may remain undetected, misdiagnosed, or unrecognized in the mother, and/or some abnormalities are not evident until later in the child's life, precise incidence of birth defects due to rubella are not entirely known. The timing of the mother's infection during fetal development determines the risk and type of birth defect. As the embryo develops, the risk of abnormalities decreases. If exposed to the rubella virus during the first four weeks, the risk of malformations is 47%. Exposure during weeks five through eight creates a 22% chance, while weeks 9–12, a 7% chance exists, followed by 6% if the exposure is during the 13th-16th weeks. Exposure during the first eight weeks of development can also lead to premature birth and fetal death. These numbers are calculated from immediate inspection of the infant after birth. Therefore, mental defects are not accounted for in the percentages because they are not evident until later in the child's life. If they were to be included, these numbers would be much higher.
Other infectious agents include cytomegalovirus, the herpes simplex virus, hyperthermia, toxoplasmosis, and syphilis. Maternal exposure to cytomegalovirus can cause microcephaly, cerebral calcifications, blindness, chorioretinitis (which can cause blindness), hepatosplenomegaly, and meningoencephalitis in fetuses. Microcephaly is a disorder in which the fetus has an atypically small head, cerebral calcifications means certain areas of the brain have atypical calcium deposits, and meningoencephalitis is the enlargement of the brain. All three disorders cause abnormal brain function or intellectual disability. Hepatosplenomegaly is the enlargement of the liver and spleen which causes digestive problems. It can also cause some kernicterus and petechiae. Kernicterus causes yellow pigmentation of the skin, brain damage, and deafness. Petechaie is when the capillaries bleed resulting in red/purple spots on the skin. However, cytomegalovirus is often fatal in the embryo. The Zika virus can also be transmitted from the pregnant mother to her baby and cause microcephaly.
The herpes simplex virus can cause microcephaly, microphthalmus (abnormally small eyeballs), retinal dysplasia, hepatosplenomegaly, and intellectual disability. Both microphthalmus and retinal dysplasia can cause blindness. However, the most common symptom in infants is an inflammatory response that develops during the first three weeks of life. Hyperthermia causes anencephaly, which is when part of the brain and skull are absent in the infant. Mother exposure to toxoplasmosis can cause cerebral calcification, hydrocephalus (causes mental disabilities), and intellectual disability in infants. Other birth abnormalities have been reported as well, such as chorioretinitis, microphthalmus, and ocular defects. Syphilis causes congenital deafness, intellectual disability, and diffuse fibrosis in organs, such as the liver and lungs, if the embryo is exposed.
Malnutrition
For example, a lack of folic acid, a B vitamin, in the diet of a mother can cause cellular neural tube deformities that result in spina bifida. Congenital disorders such as a neural tube deformity can be prevented by 72% if the mother consumes 4 mg of folic acid before the conception and after twelve weeks of pregnancy. Folic acid, or vitamin B9, aids the development of the foetal nervous system.
Studies with mice have found that food deprivation of the male mouse prior to conception leads to the offspring displaying significantly lower blood glucose levels.
Physical restraint
External physical shocks or constraints due to growth in a restricted space may result in unintended deformation or separation of cellular structures resulting in an abnormal final shape or damaged structures unable to function as expected. An example is Potter syndrome due to oligohydramnios. This finding is important for future understanding of how genetics may predispose individuals for diseases such as obesity, diabetes, and cancer.
For multicellular organisms that develop in a womb, the physical interference or presence of other similarly developing organisms such as twins can result in the two cellular masses being integrated into a larger whole, with the combined cells attempting to continue to develop in a manner that satisfies the intended growth patterns of both cell masses. The two cellular masses can compete with each other, and may either duplicate or merge various structures. This results in conditions such as conjoined twins, and the resulting merged organism may die at birth when it must leave the life-sustaining environment of the womb and must attempt to sustain its biological processes independently.
Genetics
Genetic causes of birth defects include inheritance of abnormal genes from the mother or the father, as well as new mutations in one of the germ cells that gave rise to the fetus. Male germ cells mutate at a much faster rate than female germ cells, and as the father ages, the DNA of the germ cells mutates quickly. If an egg is fertilized with sperm that has damaged DNA, a possibility exists that the fetus could develop abnormally.
Genetic disorders are all congenital (present at birth), though they may not be expressed or recognized until later in life. Genetic disorders may be grouped into single-gene defects, multiple-gene disorders, or chromosomal defects. Single-gene defects may arise from abnormalities of both copies of an autosomal gene (a recessive disorder) or of only one of the two copies (a dominant disorder). Some conditions result from deletions or abnormalities of a few genes located contiguously on a chromosome. Chromosomal disorders involve the loss or duplication of larger portions of a chromosome (or an entire chromosome) containing hundreds of genes. Large chromosomal abnormalities always produce effects on many different body parts and organ systems.
Defective sperm
Non-genetic defects in sperm cells, such as deformed centrioles and other components in the tail and neck of the sperm which are important for the embryonic development, may result in defects.
Socioeconomics
A low socioeconomic status in a deprived neighborhood may include exposure to "environmental stressors and risk factors". Socioeconomic inequalities are commonly measured by the Cartairs-Morris score, Index of Multiple Deprivation, Townsend deprivation index, and the Jarman score. The Jarman score, for example, considers "unemployment, overcrowding, single parents, under-fives, elderly living alone, ethnicity, low social class and residential mobility". In Vos' meta-analysis these indices are used to view the effect of low SES neighborhoods on maternal health. In the meta-analysis, data from individual studies were collected from 1985 up until 2008. Vos concludes that a correlation exists between prenatal adversities and deprived neighborhoods. Other studies have shown that low SES is closely associated with the development of the fetus in utero and growth retardation. Studies also suggest that children born in low SES families are "likely to be born prematurely, at low birth weight, or with asphyxia, a birth defect, a disability, fetal alcohol syndrome, or AIDS". Bradley and Corwyn also suggest that congenital disorders arise from the mother's lack of nutrition, a poor lifestyle, maternal substance abuse and "living in a neighborhood that contains hazards affecting fetal development (toxic waste dumps)". In a meta-analysis that viewed how inequalities influenced maternal health, it was suggested that deprived neighborhoods often promoted behaviors such as smoking, drug and alcohol use. After controlling for socioeconomic factors and ethnicity, several individual studies demonstrated an association with outcomes such as perinatal mortality and preterm birth.
Radiation
For the survivors of the atomic bombing of Hiroshima and Nagasaki, who are known as the Hibakusha, no statistically demonstrable increase of birth defects/congenital malformations was found among their later conceived children, or found in the later conceived children of cancer survivors who had previously received radiotherapy.
The surviving women of Hiroshima and Nagasaki who were able to conceive, though exposed to substantial amounts of radiation, later had children with no higher incidence of abnormalities/birth defects than in the Japanese population as a whole.
Relatively few studies have researched the effects of paternal radiation exposure on offspring. Following the Chernobyl disaster, it was assumed in the 1990s that the germ line of irradiated fathers suffered minisatellite mutations in the DNA, which was inherited by descendants. More recently, however, the World Health Organization states, "children conceived before or after their father's exposure showed no statistically significant differences in mutation frequencies". This statistically insignificant increase was also seen by independent researchers analyzing the children of the liquidators. Animal studies have shown that incomparably massive doses of X-ray irradiation of male mice resulted in birth defects of the offspring.
In the 1980s, a relatively high prevalence of pediatric leukemia cases in children living near a nuclear processing plant in West Cumbria, UK, led researchers to investigate whether the cancer was a result of paternal radiation exposure. A significant association between paternal irradiation and offspring cancer was found, but further research areas close to other nuclear processing plants did not produce the same results. Later this was determined to be the Seascale cluster in which the leading hypothesis is the influx of foreign workers, who have a different rate of leukemia within their race than the British average, resulted in the observed cluster of 6 children more than expected around Cumbria.
Parent's age
Certain birth complications can occur more often in advanced maternal age (greater than 35 years). Complications include fetal growth restriction, preeclampsia, placental abruption, pre-mature births, and stillbirth. These complications not only may put the child at risk, but also the mother.
The effects of the father's age on offspring are not yet well understood and are studied far less extensively than the effects of the mother's age. Fathers contribute proportionally more DNA mutations to their offspring via their germ cells than the mother, with the paternal age governing how many mutations are passed on. This is because, as humans age, male germ cells acquire mutations at a much faster rate than female germ cells.
Around a 5% increase in the incidence of ventricular septal defects, atrial septal defects, and patent ductus arteriosus in offspring has been found to be correlated with advanced paternal age. Advanced paternal age has also been linked to increased risk of achondroplasia and Apert syndrome. Offspring born to fathers under the age of 20 show increased risk of being affected by patent ductus arteriosus, ventricular septal defects, and the tetralogy of Fallot. It is hypothesized that this may be due to environmental exposures or lifestyle choices.
Research has found that there is a correlation between advanced paternal age and risk of birth defects such as limb anomalies, syndromes involving multiple systems, and Down syndrome. Recent studies have concluded that 5-9% of Down syndrome cases are due to paternal effects, but these findings are controversial.
There is concrete evidence that advanced paternal age is associated with the increased likelihood that a mother will have a miscarriage or that fetal death will occur.
Unknown
Although significant progress has been made in identifying the etiology of some birth defects, approximately 65% have no known or identifiable cause. These are referred to as sporadic, a term that implies an unknown cause, random occurrence regardless of maternal living conditions, and a low recurrence risk for future children. For 20-25% of anomalies there seems to be a "multifactorial" cause, meaning a complex interaction of multiple minor genetic anomalies with environmental risk factors. Another 10–13% of anomalies have a purely environmental cause (e.g. infections, illness, or drug abuse in the mother). Only 12–25% of anomalies have a purely genetic cause. Of these, the majority are chromosomal anomalies.
Congenital disorders are not limited to humans and can be found in a variety of other species, including cattle. One such condition is called schistosomus reflexus and is defined by spinal inversion, exposure of abdominal viscera, and limb abnormalities.
Prevention
Folate supplements decrease the risk of neural tube defects. Tentative evidence supports the role of L-arginine in decreasing the risk of intrauterine growth restriction.
Screening
Newborn screening tests were introduced in the early 1960s and initially dealt with just two disorders. Since then tandem mass spectrometry, gas chromatography–mass spectrometry, and DNA analysis has made it possible for a much larger range of disorders to be screened. Newborn screening mostly measures metabolite and enzyme activity using a dried blood spot sample. Screening tests are carried out in order to detect serious disorders that may be treatable to some extent. Early diagnosis makes possible the readiness of therapeutic dietary information, enzyme replacement therapy and organ transplants. Different countries support the screening for a number of metabolic disorders (inborn errors of metabolism (IEM)), and genetic disorders including cystic fibrosis and Duchenne muscular dystrophy.
Tandem mass spectroscopy can also be used for IEM, and investigation of sudden infant death, and shaken baby syndrome.
Screening can also be carried out prenatally and can include obstetric ultrasonography to give scans such as the nuchal scan. 3D ultrasound scans can give detailed information of structural anomalies.
Epidemiology
Congenital anomalies resulted in about 632,000 deaths per year in 2013 down from 751,000 in 1990. The types with the greatest death are congenital heart defects (323,000), followed by neural tube defects (69,000).
Many studies have found that the frequency of occurrence of certain congenital malformations depends on the sex of the child (table). For example, pyloric stenosis occurs more often in males while congenital hip dislocation is four to five times more likely to occur in females. Among children with one kidney, there are approximately twice as many males, whereas among children with three kidneys there are approximately 2.5 times more females. The same pattern is observed among infants with excessive number of ribs, vertebrae, teeth and other organs which in a process of evolution have undergone reduction—among them there are more females. Contrarily, among the infants with their scarcity, there are more males. Anencephaly is shown to occur approximately twice as frequently in females. The number of boys born with 6 fingers is two times higher than the number of girls. Now various techniques are available to detect congenital anomalies in fetus before birth.
About 3% of newborns have a "major physical anomaly", meaning a physical anomaly that has cosmetic or functional significance.
Physical congenital abnormalities are the leading cause of infant mortality in the United States, accounting for more than 20% of all infant deaths. Seven to ten percent of all children will require extensive medical care to diagnose or treat a birth defect.
{| class="wikitable"
|+ The sex ratio of patients with congenital malformations
! Congenital anomaly !! Sex ratio, ♂♂:♀♀
|-
| Defects with female predominance ||
|-
| Congenital hip dislocation || 1 : 5.2; 1 : 5; 1 : 8; 1 : 3.7
|-
| Cleft palate || 1 : 3
|-
| Anencephaly || 1 : 1.9; 1 : 2
|-
| Craniocele || 1 : 1.8
|-
| Aplasia of lung || 1 : 1.51
|-
| Spinal herniation || 1 : 1.4
|-
| Diverticulum of the esophagus || 1 : 1.4
|-
| Stomach || 1 : 1.4
|-
| Neutral defects ||
|-
| Hypoplasia of the tibia and femur || 1 : 1.2
|-
| Spina bifida || 1 : 1.2
|-
| Atresia of small intestine || 1 : 1
|-
| Microcephaly || 1.2 : 1
|-
| Esophageal atresia || 1.3 : 1; 1.5 : 1
|-
| Hydrocephalus || 1.3 : 1
|-
| Defects with male predominance ||
|-
| Diverticula of the colon || 1.5 : 1
|-
| Atresia of the rectum || 1.5 : 1; 2 : 1
|-
| Unilateral renal agenesis || 2 : 1; 2.1 : 1
|-
| Schistocystis || 2 : 1
|-
| Cleft lip and palate || 2 : 1; 1.47 : 1
|-
| Bilateral renal agenesis || 2.6 : 1
|-
| Congenital anomalies of the genitourinary system || 2.7 : 1
|-
| Pyloric stenosis, congenital || 5 : 1; 5.4 : 1
|-
| Meckel's diverticulum || More common in boys
|-
| Congenital megacolon || More common in boys
|-
| All defects || 1.22 : 1; 1.29 : 1
|}
Data obtained on opposite-sex twins. ** — Data were obtained in the period 1983–1994.
P. M. Rajewski and A. L. Sherman (1976) have analyzed the frequency of congenital anomalies in relation to the system of the organism. Prevalence of men was recorded for the anomalies of phylogenetically younger organs and systems.
In respect of an etiology, sexual distinctions can be divided on appearing before and after differentiation of male's gonads during embryonic development, which begins from the eighteenth week. The testosterone level in male embryos thus raises considerably. The subsequent hormonal and physiological distinctions of male and female embryos can explain some sexual differences in frequency of congenital defects. It is difficult to explain the observed differences in the frequency of birth defects between the sexes by the details of the reproductive functions or the influence of environmental and social factors.
United States
The CDC and National Birth Defect Project studied the incidence of birth defects in the US. Key findings include:
Down syndrome was the most common condition with an estimated prevalence of 14.47 per 10,000 live births, implying about 6,000 diagnoses each year.
About 7,000 babies are born with a cleft palate, cleft lip or both.
| Biology and health sciences | Disabilities | Health |
321365 | https://en.wikipedia.org/wiki/Railway%20track | Railway track | A railway track ( and UIC terminology) or railroad track (), also known as permanent way () or "P Way" ( and Indian English), is the structure on a railway or railroad consisting of the rails, fasteners, sleepers (railroad ties in American English) and ballast (or slab track), plus the underlying subgrade. It enables trains to move by providing a dependable, low-friction surface on which their wheels can roll. Early tracks were constructed with wooden or cast-iron rails, and wooden or stone sleepers. Since the 1870s, rails have almost universally been made from steel.
Historical development
The first railway in Britain was the Wollaton wagonway, built in 1603 between Wollaton and Strelley in Nottinghamshire. It used wooden rails and was the first of about 50 wooden-railed tramways built over the subsequent 164 years. These early wooden tramways typically used rails of oak or beech, attached to wooden sleepers with iron or wooden nails. Gravel or small stones were packed around the sleepers to hold them in place and provide a walkway for the people or horses that moved wagons along the track. The rails were usually about long and were not joined - instead, adjacent rails were laid on a common sleeper. The straight rails could be angled at these joints to form primitive curved track.
The first iron rails laid in Britain were at the Darby Ironworks in Coalbrookdale in 1767.
When steam locomotives were introduced, starting in 1804, the track then in use proved too weak to carry the additional weight. Richard Trevithick's pioneering locomotive at Pen-y-darren broke the plateway track and had to be withdrawn. As locomotives became more widespread in the 1810s and 1820s, engineers built rigid track formations, with iron rails mounted on stone sleepers, and cast-iron chairs holding them in place. This proved to be a mistake, and was soon replaced with flexible track structures that allowed a degree of elastic movement as trains passed over them.
Structure
Traditional track structure
Traditionally, tracks are constructed using flat-bottomed steel rails laid on and spiked or screwed into timber or pre-stressed concrete sleepers (known as ties in North America), with crushed stone ballast placed beneath and around the sleepers.
Most modern railroads with heavy traffic use continuously welded rails that are attached to the sleepers with base plates that spread the load. When concrete sleepers are used, a plastic or rubber pad is usually placed between the rail and the tie plate. Rail is usually attached to the sleeper with resilient fastenings, although cut spikes are widely used in North America. For much of the 20th century, rail track used softwood timber sleepers and jointed rails, and a considerable amount of this track remains on secondary and tertiary routes.
In North America and Australia, flat-bottomed rails were typically fastened to the sleepers with dog spikes through a flat tie plate. In Britain and Ireland, bullhead rails were carried in cast-iron chairs which were spiked to the sleepers. In 1936, the London, Midland and Scottish Railway pioneered the conversion to flat-bottomed rail in Britain, though earlier lines had made some use of it.
Jointed rails were used at first because contemporary technology did not offer any alternative. However, the intrinsic weakness in resisting vertical loading results in the ballast becoming depressed and a heavy maintenance workload is imposed to prevent unacceptable geometrical defects at the joints. The joints also needed to be lubricated, and wear at the fishplate (joint bar) mating surfaces needed to be rectified by shimming. For this reason jointed track is not financially appropriate for heavily operated railroads.
Timber sleepers are of many available timbers, and are often treated with creosote, chromated copper arsenate, or other wood preservatives. Pre-stressed concrete sleepers are often used where timber is scarce and where tonnage or speeds are high. Steel is used in some applications.
Track ballast is usually stone crushed to particular specifications. Its purpose is to support the sleepers and allow some adjustment of their position while allowing free drainage.
Ballastless track
A disadvantage of traditional track structures is the heavy demand for maintenance, particularly surfacing (tamping) and lining to restore the desired track geometry and smoothness of vehicle running. Weakness of the subgrade and drainage deficiencies also lead to heavy maintenance costs. This can be overcome by using ballastless track. In its simplest form this consists of a continuous slab of concrete (like a highway structure) with the rails supported directly on its upper surface (using a resilient pad).
There are a number of proprietary systems; variations include a continuous reinforced concrete slab and the use of pre-cast pre-stressed concrete units laid on a base layer. Many permutations of design have been put forward.
However, ballastless track has a high initial cost, and in the case of existing railroads the upgrade to such requires closure of the route for a long period. Its whole-life cost can be lower because of the reduction in maintenance. Ballastless track is usually considered for new very high speed or very high loading routes, in short extensions that require additional strength (e.g. railway stations), or for localised replacement where there are exceptional maintenance difficulties, for example in tunnels. Most rapid transit lines and rubber-tyred metro systems use ballastless track.
Continuous longitudinally supported track
Early railways (c. 1840s) experimented with continuous bearing railtrack, in which the rail was supported along its length, with examples including Brunel's baulk road on the Great Western Railway, as well as use on the Newcastle and North Shields Railway, on the Lancashire and Yorkshire Railway to a design by John Hawkshaw, and elsewhere. Continuous-bearing designs were also promoted by other engineers. The system was tested on the Baltimore and Ohio railway in the 1840s, but was found to be more expensive to maintain than rail with cross sleepers.
This type of track still exists on some bridges on Network Rail where the timber baulks are called waybeams or longitudinal timbers. Generally the speed over such structures is low.
Later applications of continuously supported track include Balfour Beatty's 'embedded slab track', which uses a rounded rectangular rail profile (BB14072) embedded in a slipformed (or pre-cast) concrete base (development 2000s). The 'embedded rail structure', used in the Netherlands since 1976, initially used a conventional UIC 54 rail embedded in concrete, and later developed (late 1990s) to use a 'mushroom' shaped SA42 rail profile; a version for light rail using a rail supported in an asphalt concrete–filled steel trough has also been developed (2002).
Modern ladder track can be considered a development of baulk road. Ladder track utilizes sleepers aligned along the same direction as the rails with rung-like gauge restraining cross members. Both ballasted and ballastless types exist.
Rail
Modern track typically uses hot-rolled steel with a profile of an asymmetrical rounded I-beam. Unlike some other uses of iron and steel, railway rails are subject to very high stresses and have to be made of very high-quality steel alloy. It took many decades to improve the quality of the materials, including the change from iron to steel. The stronger the rails and the rest of the trackwork, the heavier and faster the trains the track can carry.
Other profiles of rail include: bullhead rail; grooved rail; flat-bottomed rail (Vignoles rail or flanged T-rail); bridge rail (inverted U–shaped used in baulk road); and Barlow rail (inverted V).
North American railroads until the mid- to late-20th century used rails long so they could be carried in gondola cars (open wagons), often long; as gondola sizes increased, so did rail lengths.
According to the Railway Gazette International the planned-but-cancelled 150-kilometre rail line for the Baffinland Iron Mine, on Baffin Island, would have used older carbon steel alloys for its rails, instead of more modern, higher performance alloys, because modern alloy rails can become brittle at very low temperatures.
Iron-topped wooden rails
Early North American railroads used iron on top of wooden rails as an economy measure but gave up this method of construction after the iron came loose, began to curl, and intruded into the floors of the coaches, leading early railroaders to refer to them as "snake heads".
The Deeside Tramway in North Wales used this form of rail. It opened around 1870 and closed in 1947, with long sections still using these rails. It was one of the last uses of iron-topped wooden rails.
Rail classification (weight)
Rail is graded by its linear density, that is, its mass over a standard length. Heavier rail can support greater axle loads and higher train speeds without sustaining damage than lighter rail, but at a greater cost. In North America and the United Kingdom, rail is graded in pounds per yard (usually shown as pound or lb), so 130-pound rail would weigh . The usual range is . In Europe, rail is graded in kilograms per metre and the usual range is . The heaviest mass-produced rail was , rolled for the Pennsylvania Railroad.
Rail lengths
The rails used in rail transport are produced in sections of fixed length. Rail lengths are made as long as possible, as the joints between rails are a source of weakness. Throughout the history of rail production, lengths have increased as manufacturing processes have improved.
Timeline
The following are lengths of single sections produced by steel mills, without any thermite welding. Shorter rails may be welded with flashbutt welding, but the following rail lengths are unwelded.
(1767) Richard Reynolds laid the first iron rails at Coalbrookdale.
(1825) Stockton and Darlington Railway
(1830) Liverpool and Manchester Railway. Fish-belly rails at , laid mostly on stone blocks
(1831) long and weighing , reached Philadelphia the first use of the flanged T-rail in the United States
(1880) United States to suit gondola waggons
(1928) London, Midland and Scottish Railway
(1950) British Rail
(1900) – steel works weighing machine for rails (steelyard balance)
(1940s) – double 39 ft
(1953) Australia
Welding of rails into longer lengths was first introduced around 1893, making train rides quieter and safer. With the introduction of thermite welding after 1899, the process became less labour-intensive, and ubiquitous.
(1895) Hans Goldschmidt developed exothermic welding
(1899) the Essen Tramway became the first railway to use thermite welding; also suited track circuits
(1904) George Pellissier welded the Holyoke Street Railway, first to use the process in the Americas
(1935) Charles Cadwell developed non-ferrous exothermic welding
(1950) welded – (4 x )
Modern production techniques allowed the production of longer unwelded segments.
(2007) Corus (now British Steel (2016–present))
(2011) Tata Steel Europe
(2011) Voestalpine,
(2011) Jindal
Multiples
Newer longer rails tend to be made as simple multiples of older shorter rails, so that old rails can be replaced without cutting. Some cutting would be needed as slightly longer rails are needed on the outside of sharp curves compared to the rails on the inside.
Boltholes
Rails can be supplied pre-drilled with boltholes for fishplates or without where they will be welded into place. There are usually two or three boltholes at each end.
Joining rails
Rails are produced in fixed lengths and need to be joined end-to-end to make a continuous surface on which trains may run. The traditional method of joining the rails is to bolt them together using metal fishplates (jointbars in the US), producing jointed track. For more modern usage, particularly where higher speeds are required, the lengths of rail may be welded together to form continuous welded rail (CWR).
Jointed track
Jointed track is made using lengths of rail, usually about long (in the UK) and long (in North America), bolted together using perforated steel plates known as fishplates (UK) or joint bars (North America).
Fishplates are usually long, used in pairs either side of the rail ends and bolted together (usually four, but sometimes six bolts per joint). The bolts have alternating orientations so that in the event of a derailment and a wheel flange striking the joint, only some of the bolts will be sheared, reducing the likelihood of the rails misaligning with each other and worsening the derailment. This technique is not applied universally; European practice is to have all the bolt heads on the same side of the rail.
Small gaps which function as expansion joints are deliberately left between the rail ends to allow for expansion of the rails in hot weather. European practice was to have the rail joints on both rails adjacent to each other; North American practice is to stagger them. Because of these small gaps, when trains pass over jointed tracks they make a "clickety-clack" sound, and in time the rail ends are deflected downwards. Unless it is well-maintained, jointed track does not have the ride quality of welded rail and is not suitable for high speed trains. However, jointed track is still used in many countries on lower-speed lines and sidings, and is used extensively in poorer countries due to the lower construction cost and the simpler equipment required for its installation and maintenance.
A major problem of jointed track is cracking around the bolt holes, which can lead to breaking of the rail head (the running surface). This was the cause of the Hither Green rail crash which caused British Railways to begin converting much of its track to continuous welded rail.
Insulated joints
Where track circuits exist for signalling purposes, insulated block joints are required. These compound the weaknesses of ordinary joints. Specially-made glued joints, where all the gaps are filled with epoxy resin, increase the strength again.
As an alternative to the insulated joint, audio frequency track circuits can be employed using a tuned loop formed in approximately of the rail as part of the blocking circuit. Some insulated joints are unavoidable within turnouts.
Another alternative is an axle counter, which can reduce the number of track circuits and thus the number of insulated rail joints required.
Continuous welded rail
Most modern railways use continuous welded rail, sometimes referred to as ribbon rails or seamless rails. In this form of track, the rails are welded together by utilising flash butt welding to form one continuous rail that may be several kilometres long. Because there are few joints, this form of track is very strong, gives a smooth ride, and needs less maintenance; trains can travel on it at higher speeds and with less friction. Welded rails are more expensive to lay than jointed tracks, but have much lower maintenance costs. The first welded track was used in Germany in 1924. and has become common on main lines since the 1950s.
The preferred process of flash butt welding involves an automated track-laying machine running a strong electric current through the touching ends of two unjoined rails. The ends become white hot due to electrical resistance and are then pressed together forming a strong weld. Thermite welding is used to repair or splice together existing continuous welded rail segments. This manual process requires a reaction crucible and form to contain the molten iron.
North American practice is to weld segments of rail at a rail facility and load it on a special train to carry it to the job site. This train is designed to carry many segments of rail which are placed so they can slide off their racks to the rear of the train and be attached to the ties (sleepers) in a continuous operation.
If not restrained, rails would lengthen in hot weather and shrink in cold weather. To provide this restraint, the rail is prevented from moving in relation to the sleeper by use of clips or anchors. Attention needs to be paid to compacting the ballast effectively, including under, between, and at the ends of the sleepers, to prevent the sleepers from moving. Anchors are more common for wooden sleepers, whereas most concrete or steel sleepers are fastened to the rail by special clips that resist longitudinal movement of the rail. There is no theoretical limit to how long a welded rail can be. However, if longitudinal and lateral restraint are insufficient, the track could become distorted in hot weather and cause a derailment. Distortion due to heat expansion is known in North America as sun kink, and elsewhere as buckling. In extreme hot weather special inspections are required to monitor sections of track known to be problematic. In North American practice, extreme temperature conditions will trigger slow orders to allow for crews to react to buckling or "sun kinks" if encountered. The German railway company Deutsche Bahn is starting to paint rails white to lower the peak temperatures reached in summer days.
After new segments of rail are laid, or defective rails replaced (welded-in), the rails can be artificially stressed if the temperature of the rail during laying is cooler than what is desired. The stressing process involves either heating the rails, causing them to expand, or stretching the rails with hydraulic equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched elastic firmly fastened down. In extremely cold weather, rails are heated to prevent "pull aparts".
Continuous welded rails, complete with fastenings, are laid at a temperature known as "rail neutral temperature" that is approximately midway between the extremes experienced at that location. This installation procedure is intended to prevent tracks from buckling in summer heat or pulling apart in the winter cold. In North America, because broken rails are typically detected by interruption of the current in the signaling system, they are seen as less of a potential hazard than undetected heat kinks.
Joints are used in the continuous welded rail when necessary, usually for signal circuit gaps. Instead of a joint that passes straight across the rail, the two rail ends are sometimes cut at an angle to give a smoother transition. In extreme cases, such as at the end of long bridges, a breather switch (referred to in North America and Britain as an expansion joint) gives a smooth path for the wheels while allowing the end of one rail to expand relative to the next rail.
Sleepers
A sleeper (tie or crosstie) is a rectangular object on which the rails are supported and fixed. The sleeper has two main roles: to transfer the loads from the rails to the track ballast and the ground underneath, and to hold the rails to the correct width apart (to maintain the rail gauge). They are generally laid transversely to the rails.
Fixing rails to sleepers
Various methods exist for fixing the rail to the sleeper. Historically, rails were spiked directly on to ties, the practice giving way baseplates being fitted between the rails and sleepers; subsequently, spikes were replaced by sprung steel clips, such as Pandrol clips, to fix the rail to the baseplates.
Portable track
Sometimes rail tracks are designed to be portable and moved from one place to another as required. During construction of the Panama Canal, tracks were moved around excavation works. These track gauge were and the rolling stock full size. Portable tracks have often been used in open pit mines. In 1880 in New York City, sections of heavy portable track (along with much other improvised technology) helped in the move of the ancient obelisk in Central Park to its final location from the dock where it was unloaded from the cargo ship SS Dessoug.
Cane railways often had permanent tracks for the main lines, with portable tracks serving the canefields themselves. These tracks were narrow gauge (for example, ) and the portable track came in straights, curves, and turnouts, rather like on a model railway.
Decauville was a source of many portable light rail tracks, also used for military purposes.
The permanent way is so called because temporary way tracks were often used in the construction of that permanent way.
Layout
The geometry of the tracks is three-dimensional by nature, but the standards that express the speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface are usually expressed in two separate layouts for horizontal and vertical.
Horizontal layout is the track layout on the horizontal plane. This involves the layout of three main track types: tangent track (straight line), curved track, and track transition curve (also called transition spiral or spiral) which connects between a tangent and a curved track.
Vertical layout is the track layout on the vertical plane including the concepts such as crosslevel, cant and gradient.
A sidetrack is a railroad track other than siding that is auxiliary to the main track. The word is also used as a verb (without object) to refer to the movement of trains and railcars from the main track to a siding, and in common parlance to refer to giving in to distractions apart from a main subject. Sidetracks are used by railroads to order and organise the flow of rail traffic.
Gauge
During the early days of rail, there was considerable variation in the gauge used by different systems, and in the UK during the railway building boom of the 1840s Brunel's broad gauge of was in competition with what was referred to at the time as the 'narrow' gauge of . Eventually the gauge won the battle, and became the standard gauge, with the term 'narrow gauge' henceforth used for gauges narrower than the new standard. , about 60% of the world's railways use a gauge of , known as standard or international gauge Gauges wider than standard gauge are called broad gauge; narrower, narrow gauge. Some stretches of track are dual gauge, with three (or sometimes four) parallel rails in place of the usual two, to allow trains of two different gauges to use the same track.
Gauge can safely vary over a range. For example, U.S. federal safety standards allow standard gauge to vary from to for operation up to .
Maintenance
Track needs regular maintenance to remain in good order, especially when high-speed trains are involved. Inadequate maintenance may lead to a "slow order" (North American terminology, or temporary speed restriction in the United Kingdom) being imposed to avoid accidents (see Slow zone). Track maintenance was at one time hard manual labour, requiring teams of labourers, or trackmen (US: gandy dancers; UK: platelayers; Australia: fettlers or packers) under the supervision of a skilled ganger, who used lining bars to correct irregularities in horizontal alignment (line) of the track, and tamping and jacks to correct vertical irregularities (surface). Currently, maintenance is facilitated by a variety of specialised machines.
The surface of the head of each of the two rails can be maintained by using a railgrinder.
Common maintenance jobs include changing sleepers, lubricating and adjusting switches, tightening loose track components, and surfacing and lining track to keep straight sections straight and curves within maintenance limits. The process of sleeper and rail replacement can be automated by using a track renewal train.
Spraying ballast with herbicide to prevent weeds growing through and redistributing the ballast is typically done with a special weed killing train.
Over time, ballast is crushed or moved by the weight of trains passing over it, periodically requiring relevelling ("tamping") and eventually to be cleaned or replaced. If this is not done, the tracks may become uneven, causing swaying, rough riding and possibly derailments. An alternative to tamping is to lift the rails and sleepers and reinsert the ballast beneath. For this, specialist "stoneblower" trains are used.
Rail inspections utilize nondestructive testing methods to detect internal flaws in the rails. This is done by using specially equipped HiRail trucks, inspection cars, or in some cases, handheld inspection devices.
Rails must be replaced before the railhead profile wears to a degree that may trigger a derailment. Worn mainline rails usually have sufficient life remaining to be used on a branch line, siding or stub afterwards and are "cascaded" to those applications.
The environmental conditions along railroad track create a unique railway ecosystem. This is particularly so in the United Kingdom, where steam locomotives are only used on special services and vegetation has not been trimmed back so thoroughly. This creates a fire risk in prolonged dry weather.
In the UK, the cess is used by track repair crews to walk to a work site, and as a safe place to stand when a train is passing. This helps when doing minor work, while needing to keep trains running, by not needing a Hi-railer or transport vehicle blocking the line to transport crew to get to the site.
Bed and foundation
Railway tracks are generally laid on a bed of stone track ballast or track bed, which in turn is supported by prepared earthworks known as the track formation. The formation comprises the subgrade and a layer of sand or stone dust (often sandwiched in impervious plastic), known as the blanket, which restricts the upward migration of wet clay or silt. There may also be layers of waterproof fabric to prevent water penetrating to the subgrade. The track and ballast form the permanent way. The foundation may refer to the ballast and formation, i.e. all man-made structures below the tracks.
Some railroads are using asphalt pavement below the ballast in order to keep dirt and moisture from moving into the ballast and spoiling it. The fresh asphalt also serves to stabilize the ballast so it does not move around so easily.
Additional measures are required where the track is laid over permafrost, such as on the Qingzang Railway in Tibet. For example, transverse pipes through the subgrade allow cold air to penetrate the formation and prevent that subgrade from melting.
Geosynthetic reinforcement
Geosynthetics are used to reduce or replace traditional layers in trackbed construction and rehabilitation worldwide to improve track support and reduce track maintenance costs. Reinforcement geosynthetics, such as geocells (which rely on 3D soil confinement mechanisms) have demonstrated efficacy in stabilizing soft subgrade soils and reinforcing substructural layers to limit progressive track degradation. Reinforcement geosynthetics increase soil bearing capacity, limit ballast movement and degradation and reduce differential settlement that affects track geometry. They also reduce construction time and cost, while reducing environmental impact and carbon footprint. The increased use of geosynthetic reinforcement solutions is supported by new high-performance geocell materials (e.g., NPA - Novel Polymeric Alloy), published research, case studies projects and international standards (ISO, ASTM, CROW/SBRCURnet)
The hybrid use of high-performance geogrids at the subgrade and high-performance geocell in the upper subbase/subballast layer has been shown to increase the reinforcement factor greater than their separate sums, and is particularly effective in attenuating heaving of expansive subgrade clay soils. A field test project on Amtrak's NE Corridor suffering clay mud-pumping demonstrated how the hybrid solution improved track quality index (TQI) significantly reduced track geometry degradation and lowered track surface maintenance by factor of 6.7x utilizing high-performance NPA geocell. Geosynthetic reinforcement is also used to stabilize railway embankments, which must be robust enough to withstand repeated cyclical loading. Geocells can utilize recycled marginal or poorly graded granular material to create stable embankments, make railway construction more economical and sustainable.
Buses
Some buses can use tracks. This concept came out of Germany and was called . The first such track, the O-Bahn Busway, was built in Adelaide, Australia.
| Technology | Trains | null |
321382 | https://en.wikipedia.org/wiki/Energy%20flow%20%28ecology%29 | Energy flow (ecology) | Energy flow is the flow of energy through living things within an ecosystem. All living organisms can be organized into producers and consumers, and those producers and consumers can further be organized into a food chain. Each of the levels within the food chain is a trophic level. In order to more efficiently show the quantity of organisms at each trophic level, these food chains are then organized into trophic pyramids. The arrows in the food chain show that the energy flow is unidirectional, with the head of an arrow indicating the direction of energy flow; energy is lost as heat at each step along the way.
The unidirectional flow of energy and the successive loss of energy as it travels up the food web are patterns in energy flow that are governed by thermodynamics, which is the theory of energy exchange between systems. Trophic dynamics relates to thermodynamics because it deals with the transfer and transformation of energy (originating externally from the sun via solar radiation) to and among organisms.
Energetics and the carbon cycle
The first step in energetics is photosynthesis, where in water and carbon dioxide from the air are taken in with energy from the sun, and are converted into oxygen and glucose. Cellular respiration is the reverse reaction, wherein oxygen and sugar are taken in and release energy as they are converted back into carbon dioxide and water. The carbon dioxide and water produced by respiration can be recycled back into plants.
Energy loss can be measured either by efficiency (how much energy makes it to the next level), or by biomass (how much living material exists at those levels at one point in time, measured by standing crop). Of all the net primary productivity at the producer trophic level, in general only 10% goes to the next level, the primary consumers, then only 10% of that 10% goes on to the next trophic level, and so on up the food pyramid. Ecological efficiency may be anywhere from 5% to 20% depending on how efficient or inefficient that ecosystem is. This decrease in efficiency occurs because organisms need to perform cellular respiration to survive, and energy is lost as heat when cellular respiration is performed. That is also why there are fewer tertiary consumers than there are producers.
Primary production
A producer is any organism that performs photosynthesis. Producers are important because they convert energy from the sun into a storable and usable chemical form of energy, glucose, as well as oxygen. The producers themselves can use the energy stored in glucose to perform cellular respiration. Or, if the producer is consumed by herbivores in the next trophic level, some of the energy is passed on up the pyramid. The glucose stored within producers serves as food for consumers, and so it is only through producers that consumers are able to access the sun’s energy. Some examples of primary producers are algae, mosses, and other plants such as grasses, trees, and shrubs.
Chemosynthetic bacteria perform a process similar to photosynthesis, but instead of energy from the sun they use energy stored in chemicals like hydrogen sulfide. This process, referred to as chemosynthesis, usually occurs deep in the ocean at hydrothermal vents that produce heat and chemicals such as hydrogen, hydrogen sulfide and methane. Chemosynthetic bacteria can use the energy in the bonds of the hydrogen sulfide and oxygen to convert carbon dioxide to glucose, releasing water and sulfur in the process. Organisms that consume the chemosynthetic bacteria can take in the glucose and use oxygen to perform cellular respiration, similar to herbivores consuming producers.
One of the factors that controls primary production is the amount of energy that enters the producer(s), which can be measured using productivity. Only one percent of solar energy enters the producer, the rest bounces off or moves through. Gross primary productivity is the amount of energy the producer actually gets. Generally, 60% of the energy that enters the producer goes to the producer’s own respiration. The net primary productivity is the amount that the plant retains after the amount that it used for cellular respiration is subtracted. Another factor controlling primary production is organic/inorganic nutrient levels in the water or soil that the producer is living in.
Secondary production
Secondary production is the use of energy stored in plants converted by consumers to their own biomass. Different ecosystems have different levels of consumers, all end with one top consumer. Most energy is stored in organic matter of plants, and as the consumers eat these plants they take up this energy. This energy in the herbivores and omnivores is then consumed by carnivores. There is also a large amount of energy that is in primary production and ends up being waste or litter, referred to as detritus. The detrital food chain includes a large amount of microbes, macroinvertebrates, meiofauna, fungi, and bacteria. These organisms are consumed by omnivores and carnivores and account for a large amount of secondary production. Secondary consumers can vary widely in how efficient they are in consuming. The efficiency of energy being passed on to consumers is estimated to be around 10%. Energy flow through consumers differs in aquatic and terrestrial environments.
In aquatic environments
Heterotrophs contribute to secondary production and it is dependent on primary productivity and the net primary products. Secondary production is the energy that herbivores and decomposers use and thus depends on primary productivity. Primarily herbivores and decomposers consume all the carbon from two main organic sources in aquatic ecosystems, autochthonous and allochthonous. Autochthonous carbon comes from within the ecosystem and includes aquatic plants, algae and phytoplankton. Allochthonous carbon from outside the ecosystem is mostly dead organic matter from the terrestrial ecosystem entering the water. In stream ecosystems, approximately 66% of annual energy input can be washed downstream. The remaining amount is consumed and lost as heat.
In terrestrial environments
Secondary production is often described in terms of trophic levels, and while this can be useful in explaining relationships it overemphasizes the rarer interactions. Consumers often feed at multiple trophic levels. Energy transferred above the third trophic level is relatively unimportant. The assimilation efficiency can be expressed by the amount of food the consumer has eaten, how much the consumer assimilates and what is expelled as feces or urine. While a portion of the energy is used for respiration, another portion of the energy goes towards biomass in the consumer. There are two major food chains: The primary food chain is the energy coming from autotrophs and passed on to the consumers; and the second major food chain is when carnivores eat the herbivores or decomposers that consume the autotrophic energy. Consumers are broken down into primary consumers, secondary consumers and tertiary consumers. Carnivores have a much higher assimilation of energy, about 80% and herbivores have a much lower efficiency of approximately 20 to 50%. Energy in a system can be affected by animal emigration/immigration. The movements of organisms are significant in terrestrial ecosystems. Energetic consumption by herbivores in terrestrial ecosystems has a low range of ~3-7%. The flow of energy is similar in many terrestrial environments. The fluctuation in the amount of net primary product consumed by herbivores is generally low. This is in large contrast to aquatic environments of lakes and ponds where grazers have a much higher consumption of around ~33%. Ectotherms and endotherms have very different assimilation efficiencies.
Detritivores
Detritivores consume organic material that is decomposing and are in turn consumed by carnivores. Predator productivity is correlated with prey productivity. This confirms that the primary productivity in ecosystems affects all productivity following.
Detritus is a large portion of organic material in ecosystems. Organic material in temperate forests is mostly made up of dead plants, approximately 62%.
In an aquatic ecosystem, leaf matter that falls into streams gets wet and begins to leech organic material. This happens rather quickly and will attract microbes and invertebrates. The leaves can be broken down into large pieces called coarse particulate organic matter (CPOM). The CPOM is rapidly colonized by microbes. Meiofauna is extremely important to secondary production in stream ecosystems. Microbes breaking down and colonizing this leaf matter are very important to the detritovores. The detritovores make the leaf matter more edible by releasing compounds from the tissues; it ultimately helps soften them. As leaves decay nitrogen will decrease since cellulose and lignin in the leaves is difficult to break down. Thus the colonizing microbes bring in nitrogen in order to aid in the decomposition. Leaf breakdown can depend on initial nitrogen content, season, and species of trees. The species of trees can have variation when their leaves fall. Thus the breakdown of leaves is happening at different times, which is called a mosaic of microbial populations.
Species effect and diversity in an ecosystem can be analyzed through their performance and efficiency. In addition, secondary production in streams can be influenced heavily by detritus that falls into the streams; production of benthic fauna biomass and abundance decreased an additional 47–50% during a study of litter removal and exclusion.
Energy flow across ecosystems
Research has demonstrated that primary producers fix carbon at similar rates across ecosystems. Once carbon has been introduced into a system as a viable source of energy, the mechanisms that govern the flow of energy to higher trophic levels vary across ecosystems. Among aquatic and terrestrial ecosystems, patterns have been identified that can account for this variation and have been divided into two main pathways of control: top-down and bottom-up. The acting mechanisms within each pathway ultimately regulate community and trophic level structure within an ecosystem to varying degrees. Bottom-up controls involve mechanisms that are based on resource quality and availability, which control primary productivity and the subsequent flow of energy and biomass to higher trophic levels. Top-down controls involve mechanisms that are based on consumption by consumers. These mechanisms control the rate of energy transfer from one trophic level to another as herbivores or predators feed on lower trophic levels.
Aquatic vs terrestrial ecosystems
Much variation in the flow of energy is found within each type of ecosystem, creating a challenge in identifying variation between ecosystem types. In a general sense, the flow of energy is a function of primary productivity with temperature, water availability, and light availability. For example, among aquatic ecosystems, higher rates of production are usually found in large rivers and shallow lakes than in deep lakes and clear headwater streams. Among terrestrial ecosystems, marshes, swamps, and tropical rainforests have the highest primary production rates, whereas tundra and alpine ecosystems have the lowest. The relationships between primary production and environmental conditions have helped account for variation within ecosystem types, allowing ecologists to demonstrate that energy flows more efficiently through aquatic ecosystems than terrestrial ecosystems due to the various bottom-up and top-down controls in play.
Bottom-up
The strength of bottom-up controls on energy flow are determined by the nutritional quality, size, and growth rates of primary producers in an ecosystem. Photosynthetic material is typically rich in nitrogen (N) and phosphorus (P) and supplements the high herbivore demand for N and P across all ecosystems. Aquatic primary production is dominated by small, single-celled phytoplankton that are mostly composed of photosynthetic material, providing an efficient source of these nutrients for herbivores. In contrast, multi-cellular terrestrial plants contain many large supporting cellulose structures of high carbon but low nutrient value. Because of this structural difference, aquatic primary producers have less biomass per photosynthetic tissue stored within the aquatic ecosystem than in the forests and grasslands of terrestrial ecosystems. This low biomass relative to photosynthetic material in aquatic ecosystems allows for a more efficient turnover rate compared to terrestrial ecosystems. As phytoplankton are consumed by herbivores, their enhanced growth and reproduction rates sufficiently replace lost biomass and, in conjunction with their nutrient dense quality, support greater secondary production.
Additional factors impacting primary production includes inputs of N and P, which occurs at a greater magnitude in aquatic ecosystems. These nutrients are important in stimulating plant growth and, when passed to higher trophic levels, stimulate consumer biomass and growth rate. If either of these nutrients are in short supply, they can limit overall primary production. Within lakes, P tends to be the greater limiting nutrient while both N and P limit primary production in rivers. Due to these limiting effects, nutrient inputs can potentially alleviate the limitations on net primary production of an aquatic ecosystem. Allochthonous material washed into an aquatic ecosystem introduces N and P as well as energy in the form of carbon molecules that are readily taken up by primary producers. Greater inputs and increased nutrient concentrations support greater net primary production rates, which in turn supports greater secondary production.
Top-down
Top-down mechanisms exert greater control on aquatic primary producers due to the roll of consumers within an aquatic food web. Among consumers, herbivores can mediate the impacts of trophic cascades by bridging the flow of energy from primary producers to predators in higher trophic levels. Across ecosystems, there is a consistent association between herbivore growth and producer nutritional quality. However, in aquatic ecosystems, primary producers are consumed by herbivores at a rate four times greater than in terrestrial ecosystems. Although this topic is highly debated, researchers have attributed the distinction in herbivore control to several theories, including producer to consumer size ratios and herbivore selectivity.
Modeling of top-down controls on primary producers suggests that the greatest control on the flow of energy occurs when the size ratio of consumer to primary producer is the highest. The size distribution of organisms found within a single trophic level in aquatic systems is much narrower than that of terrestrial systems. On land, the consumer size ranges from smaller than the plant it consumes, such as an insect, to significantly larger, such as an ungulate, while in aquatic systems, consumer body size within a trophic level varies much less and is strongly correlated with trophic position. As a result, the size difference between producers and consumers is consistently larger in aquatic environments than on land, resulting in stronger herbivore control over aquatic primary producers.
Herbivores can potentially control the fate of organic matter as it is cycled through the food web. Herbivores tend to select nutritious plants while avoiding plants with structural defense mechanisms. Like support structures, defense structures are composed of nutrient poor, high carbon cellulose. Access to nutritious food sources enhances herbivore metabolism and energy demands, leading to greater removal of primary producers. In aquatic ecosystems, phytoplankton are highly nutritious and generally lack defense mechanisms. This results in greater top-down control because consumed plant matter is quickly released back into the system as labile organic waste. In terrestrial ecosystems, primary producers are less nutritionally dense and are more likely to contain defense structures. Because herbivores prefer nutritionally dense plants and avoid plants or plant parts with defense structures, a greater amount of plant matter is left unconsumed within the ecosystem. Herbivore avoidance of low-quality plant matter may be why terrestrial systems exhibit weaker top-down control on the flow of energy.
| Biology and health sciences | Ecology | Biology |
321438 | https://en.wikipedia.org/wiki/Perfect%20information | Perfect information | In economics, perfect information (sometimes referred to as "no hidden information") is a feature of perfect competition. With perfect information in a market, all consumers and producers have complete and instantaneous knowledge of all market prices, their own utility, and own cost functions.
In game theory, a sequential game has perfect information if each player, when making any decision, is perfectly informed of all the events that have previously occurred, including the "initialization event" of the game (e.g. the starting hands of each player in a card game).
Perfect information is importantly different from complete information, which implies common knowledge of each player's utility functions, payoffs, strategies and "types". A game with perfect information may or may not have complete information.
Games where some aspect of play is hidden from opponents – such as the cards in poker and bridge – are examples of games with imperfect information.
Examples
Chess is an example of a game with perfect information, as each player can see all the pieces on the board at all times. Other games with perfect information include tic-tac-toe, Reversi, checkers, and Go.
Academic literature has not produced consensus on a standard definition of perfect information which defines whether games with chance, but no secret information, and games with simultaneous moves are games of perfect information.
Games which are sequential (players alternate in moving) and which have chance events (with known probabilities to all players) but no secret information, are sometimes considered games of perfect information. This includes games such as backgammon and Monopoly. But there are some academic papers which do not regard such games as games of perfect information because the results of chance themselves are unknown prior to them occurring.
Games with simultaneous moves are generally not considered games of perfect information. This is because each player holds information which is secret, and must play a move without knowing the opponent's secret information. Nevertheless, some such games are symmetrical, and fair. An example of a game in this category includes rock paper scissors.
| Mathematics | Game theory | null |
321567 | https://en.wikipedia.org/wiki/Thoracic%20diaphragm | Thoracic diaphragm | The thoracic diaphragm, or simply the diaphragm (; ), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the most important muscle of respiration, and separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs. Its high oxygen consumption is noted by the many mitochondria and capillaries present; more than in any other skeletal muscle.
The term diaphragm in anatomy, created by Gerard of Cremona, can refer to other flat structures such as the urogenital diaphragm or pelvic diaphragm, but "the diaphragm" generally refers to the thoracic diaphragm. In humans, the diaphragm is slightly asymmetric—its right half is higher up (superior) to the left half, since the large liver rests beneath the right half of the diaphragm. There is also speculation that the diaphragm is lower on the other side due to heart's presence.
Other mammals have diaphragms, and other vertebrates such as amphibians and reptiles have diaphragm-like structures, but important details of the anatomy may vary, such as the position of the lungs in the thoracic cavity.
Structure
The diaphragm is an upward curved, c-shaped structure of muscle and fibrous tissue that separates the thoracic cavity from the abdomen. The superior surface of the dome forms the floor of the thoracic cavity, and the inferior surface the roof of the abdominal cavity.
As a dome, the diaphragm has peripheral attachments to structures that make up the abdominal and chest walls. The muscle fibres from these attachments converge in a central tendon, which forms the crest of the dome. Its peripheral part consists of muscular fibers that take origin from the circumference of the inferior thoracic aperture and converge to be inserted into a central tendon.
The muscle fibres of the diaphragm radiate outward from the central tendon. While the diaphragm is one muscle, it is composed of two distinct muscle regions: the costal, which serves as the driver in the work of breathing, and crural diaphragm, which serves as an "anchor;" attaching the muscle to the lower ribs and lumbar vertebrae. The costal diaphragm is further divided into ventral, medial, and dorsal costal portions.
The vertebral part of the diaphragm arises from the crura and arcuate ligaments. Right crus arises from L1-L3 vertebral bodies and their intervertebral discs. Smaller left crus arises from L1, L2 vertebral bodies and their intervertebral discs. Medial arcuate ligament arises from the fascia thickening from body of L2 vertebrae to transverse process of L1 vertebrae, crossing over the body of the psoas major muscle. The lateral arcuate ligament arises from the transverse process of L1 vertebrae and is attached laterally to the 12th rib. The lateral arcuate ligament also arises from fascia thickening that covers the quadratus lumborum muscle. The median arcuate ligament arises from the fibrous parts of right and left crura where descending thoracic aorta passes behind it. No diaphragmatic muscle arises from the median arcuate ligament. Both adrenal glands lie near the diaphragmatic crus and arcuate ligament.
The costal part of diaphragm arises from the lower four ribs (7 to 10) costal cartilages.
The central tendon of the diaphragm is a thin but strong aponeurosis near the center of the vault formed by the muscle, closer to the front than to the back of the thorax. The central part of the tendon is attached above to pericardium. The both sides of the posterior fibres are attached to paracolic gutters (the curving of ribs before attaching to both sides of the vertebral bodies).
Openings
There are a number of openings in the diaphragm through which structures pass between the thorax and abdomen. There are three large openings — one for the aorta (aortic hiatus), one for the esophagus (esophageal hiatus), and one for the inferior vena cava (the caval opening), as well as a series of smaller openings.
The inferior vena cava passes through the caval opening, a quadrilateral opening at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. Surrounded by tendons, the opening is stretched open every time inspiration occurs. However, there has been argument that the caval opening actually constricts during inspiration. Since thoracic pressure decreases upon inspiration and draws the caval blood upwards toward the right atrium, increasing the size of the opening allows more blood to return to the heart, maximizing the efficacy of lowered thoracic pressure returning blood to the heart. The aorta does not pierce the diaphragm but rather passes behind it in between the left and right crus.
There are several structures that pierce through the diaphragm, including: left phrenic nerve pierces through the central tendon, greater, lesser, and least thoracic splanchnic nerves pierces through bilateral crura, and lymphatic vessels that pierce throughout the diaphragm, especially behind the diaphragm.
Nerve supply
The diaphragm is primarily innervated by the phrenic nerve which is formed from the cervical nerves C3, C4 and C5. While the central portion of the diaphragm sends sensory afferents via the phrenic nerve, the peripheral portions of the diaphragm send sensory afferents via the intercostal (T5–T11) and subcostal nerves (T12).
Blood supply
Arteries and veins above and below the diaphragm supply and drain blood.
From above, the diaphragm receives blood from branches of the internal thoracic arteries, namely the pericardiacophrenic artery and musculophrenic artery; from the superior phrenic arteries, which arise directly from the thoracic aorta; and from the lower internal intercostal arteries. From below, the inferior phrenic arteries supply the diaphragm.
The diaphragm drains blood into the brachiocephalic veins, azygos veins, and veins that drain into the inferior vena cava and left suprarenal vein.
Variation
The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers.
Development
The thoracic diaphragm develops during embryogenesis, beginning in the third week after fertilization with two processes known as transverse folding and longitudinal folding. The septum transversum, the primitive central tendon of the diaphragm, originates at the rostral pole of the embryo and is relocated during longitudinal folding to the ventral thoracic region. Transverse folding brings the body wall anteriorly to enclose the gut and body cavities. The pleuroperitoneal membrane and body wall myoblasts, from somatic lateral plate mesoderm, meet the septum transversum to close off the pericardio-peritoneal canals on either side of the presumptive esophagus, forming a barrier that separates the peritoneal and pleuropericardial cavities. Furthermore, dorsal mesenchyme surrounding the presumptive esophagus form the muscular crura of the diaphragm.
Because the earliest element of the embryological diaphragm, the septum transversum, forms in the cervical region, the phrenic nerve that innervates the diaphragm originates from the cervical spinal cord (C3,4, and 5). As the septum transversum descends inferiorly, the phrenic nerve follows, accounting for its circuitous route from the upper cervical vertebrae, around the pericardium, finally to innervate the diaphragm.
Function
The diaphragm is the main muscle of respiration and functions in breathing. During inhalation, the diaphragm contracts and moves in the inferior direction, enlarging the volume of the thoracic cavity and reducing intra-thoracic pressure (the external intercostal muscles also participate in this enlargement), forcing the lungs to expand. In other words, the diaphragm's movement downwards creates a partial vacuum in the thoracic cavity, which forces the lungs to expand to fill the void, drawing air in the process.
Cavity expansion happens in two extremes, along with intermediary forms. When the lower ribs are stabilized and the central tendon of the diaphragm is mobile, a contraction brings the insertion (central tendon) towards the origins and pushes the lower cavity towards the pelvis, allowing the thoracic cavity to expand downward. This is often called belly breathing. When the central tendon is stabilized and the lower ribs are mobile, a contraction lifts the origins (ribs) up towards the insertion (central tendon) which works in conjunction with other muscles to allow the ribs to slide and the thoracic cavity to expand laterally and upwards.
When the diaphragm relaxes (moves in the superior direction), air is exhaled by elastic recoil process of the lung and the tissues lining the thoracic cavity. Assisting this function with muscular effort (called forced exhalation) involves the internal intercostal muscles used in conjunction with the abdominal muscles, which act as an antagonist paired with the diaphragm's contraction. Diaphragm dysfunction is a well-known factor associated with various complications in patients, such as prolonged respiratory failure, difficulties in weaning from mechanical ventilation, extended hospitalization, increased morbidity, and mortality. Studies have reported that a thin diaphragm leads to greater lung compliance, which can contribute to respiratory failure. Furthermore, reduction in diaphragm thickness during the early stages of disease can serve as a prognostic marker in sepsis patients, and COVID-19 patients.
The diaphragm is also involved in non-respiratory functions. It helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure, aids in childbirth, and prevents acid reflux by exerting pressure on the esophagus as it passes through the esophageal hiatus.
In some non-human animals, the diaphragm is not crucial for breathing; a cow, for instance, can survive fairly asymptomatically with diaphragmatic paralysis as long as no massive aerobic metabolic demands are made of it.
Clinical significance
Paralysis
If either the phrenic nerve, cervical spine or brainstem is damaged, this will sever the nervous supply to the diaphragm. The most common damage to the phrenic nerve is by bronchial cancer, which usually only affects one side of the diaphragm. Other causes include Guillain–Barré syndrome and systemic lupus erythematosus.
Herniation
A hiatus hernia is a hernia in which parts of the lower esophagus or stomach that are normally in the abdomen pass abnormally through the diaphragm and are present in the thorax. Hernias are described as rolling, in which the hernia is beside the oesophagus, or sliding, in which the hernia directly involves the esophagus. These hernias are implicated in the development of reflux, as the different pressures between the thorax and abdomen normally act to keep pressure on the esophageal hiatus. With herniation, this pressure is no longer present, and the angle between the cardia of the stomach and the oesophagus disappears. Not all hiatus hernias cause symptoms, although almost all people with Barrett's oesophagus or oesophagitis have a hiatus hernia.
Hernias may also occur as a result of congenital malformation, a congenital diaphragmatic hernia. When the pleuroperitoneal membranes fail to fuse, the diaphragm does not act as an effective barrier between the abdomen and thorax. Herniation is usually of the left, and commonly through the posterior lumbocostal triangle, although rarely through the anterior foramen of Morgagni. The contents of the abdomen, including the intestines, may be present in the thorax, which may impact development of the growing lungs and lead to hypoplasia. This condition is present in 0.8 - 5/10,000 births. A large herniation has high mortality rate, and requires immediate surgical repair.
Imaging
Due to its position separating the thorax and abdomen, fluid abnormally present in the thorax, or air abnormally present in the abdomen, may collect on one side of the diaphragm. An X-ray may reveal this. Pleural effusion, in which there is fluid abnormally present between the two pleurae of the lungs, is detected by an X-ray of the chest, showing fluid collecting in the angle between the ribs and diaphragm. An X-ray may also be used to reveal a pneumoperitoneum, in which there is gas in the abdomen.
An X-ray may also be used to check for herniation.
Significance in strength training
The adoption of a deeper breathing pattern typically occurs during physical exercise in order to facilitate greater oxygen absorption. During this process the diaphragm more consistently adopts a lower position within the body's core. In addition to its primary role in breathing, the diaphragm also plays a secondary role in strengthening the posture of the core. This is especially evident during deep breathing where its generally lower position increases intra-abdominal pressure, which serves to strengthen the lumbar spine.
The key to real core stabilization is to maintain the increased IAP while going through normal breathing cycles. [...] The diaphragm then performs its breathing function at a lower position to facilitate a higher IAP.
Therefore, if a person's diaphragm position is lower in general, through deep breathing, then this assists the strengthening of their core during that period. This can be an aid in strength training and other forms of athletic endeavour. For this reason, taking a deep breath or adopting a deeper breathing pattern is typically recommended when lifting heavy weights.
Other animals
The existence of a membrane separating the pharynx from the stomach can be traced widely among the chordates. Thus the model organism, the marine chordate lancelet, possesses an atriopore by which water exits the pharynx, which has been claimed (and disputed) to be homologous to structures in ascidians and hagfishes. The tunicate epicardium separates digestive organs from the pharynx and heart, but the anus returns to the upper compartment to discharge wastes through an outgoing siphon.
Thus the diaphragm emerges in the context of a body plan that separated an upper feeding compartment from a lower digestive tract, but the point at which it originates is a matter of definition. Structures in fish, amphibians, reptiles, and birds have been called diaphragms, but it has been argued that these structures are not homologous. For instance, the alligator diaphragmaticus muscle does not insert on the esophagus and does not affect pressure of the lower esophageal sphincter. The lungs are located in the abdominal compartment of amphibians and reptiles, so that contraction of the diaphragm expels air from the lungs rather than drawing it into them. In birds and mammals, lungs are located above the diaphragm. The presence of an exceptionally well-preserved fossil of Sinosauropteryx, with lungs located beneath the diaphragm as in crocodiles, has been used to argue that dinosaurs could not have sustained an active warm-blooded physiology, or that birds could not have evolved from dinosaurs. An explanation for this (put forward in 1905), is that lungs originated beneath the diaphragm, but as the demands for respiration increased in warm-blooded birds and mammals, natural selection came to favor the parallel evolution of the herniation of the lungs from the abdominal cavity in both lineages.
However, birds lack diaphragms. They do not breathe in the same way as mammals and do not rely on creating a negative pressure in the thoracic cavity, at least not to the same extent. They rely on a rocking motion of the keel of the sternum to create local areas of reduced pressure to supply thin, membranous airsacs cranially and caudally to the fixed-volume, non-expansive lungs. A complicated system of valves and air sacs cycles air constantly over the absorption surfaces of the lungs so allowing maximal efficiency of gaseous exchange. Thus, birds do not have the reciprocal tidal breathing flow of mammals. On careful dissection, around eight air sacs can be clearly seen. They extend quite far caudally into the abdomen.
| Biology and health sciences | Respiratory system | Biology |
321671 | https://en.wikipedia.org/wiki/Tessellation | Tessellation | A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called tiles, with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of geometries.
A periodic tiling has a repeating pattern. Some special kinds include regular tilings with regular polygonal tiles all of the same shape, and semiregular tilings with regular tiles of more than one shape and with every corner identically arranged. The patterns formed by periodic tilings can be categorized into 17 wallpaper groups. A tiling that lacks a repeating pattern is called "non-periodic". An aperiodic tiling uses a small set of tile shapes that cannot form a repeating pattern (an aperiodic set of prototiles). A tessellation of space, also known as a space filling or honeycomb, can be defined in the geometry of higher dimensions.
A real physical tessellation is a tiling made of materials such as cemented ceramic squares or hexagons. Such tilings may be decorative patterns, or may have functions such as providing durable and water-resistant pavement, floor, or wall coverings. Historically, tessellations were used in Ancient Rome and in Islamic art such as in the Moroccan architecture and decorative geometric tiling of the Alhambra palace. In the twentieth century, the work of M. C. Escher often made use of tessellations, both in ordinary Euclidean geometry and in hyperbolic geometry, for artistic effect. Tessellations are sometimes employed for decorative effect in quilting. Tessellations form a class of patterns in nature, for example in the arrays of hexagonal cells found in honeycombs.
History
Tessellations were used by the Sumerians (about 4000 BC) in building wall decorations formed by patterns of clay tiles.
Decorative mosaic tilings made of small squared blocks called tesserae were widely employed in classical antiquity, sometimes displaying geometric patterns.
In 1619, Johannes Kepler made an early documented study of tessellations. He wrote about regular and semiregular tessellations in his ; he was possibly the first to explore and to explain the hexagonal structures of honeycomb and snowflakes.
Some two hundred years later in 1891, the Russian crystallographer Yevgraf Fyodorov proved that every periodic tiling of the plane features one of seventeen different groups of isometries. Fyodorov's work marked the unofficial beginning of the mathematical study of tessellations. Other prominent contributors include Alexei Vasilievich Shubnikov and Nikolai Belov in their book Colored Symmetry (1964), and Heinrich Heesch and Otto Kienzle (1963).
Etymology
In Latin, tessella is a small cubical piece of clay, stone, or glass used to make mosaics. The word "tessella" means "small square" (from tessera, square, which in turn is from the Greek word τέσσερα for four). It corresponds to the everyday term tiling, which refers to applications of tessellations, often made of glazed clay.
Overview
Tessellation in two dimensions, also called planar tiling, is a topic in geometry that studies how shapes, known as tiles, can be arranged to fill a plane without any gaps, according to a given set of rules. These rules can be varied. Common ones are that there must be no gaps between tiles, and that no corner of one tile can lie along the edge of another. The tessellations created by bonded brickwork do not obey this rule. Among those that do, a regular tessellation has both identical regular tiles and identical regular corners or vertices, having the same angle between adjacent edges for every tile. There are only three shapes that can form such regular tessellations: the equilateral triangle, square and the regular hexagon. Any one of these three shapes can be duplicated infinitely to fill a plane with no gaps.
Many other types of tessellation are possible under different constraints. For example, there are eight types of semi-regular tessellation, made with more than one kind of regular polygon but still having the same arrangement of polygons at every corner. Irregular tessellations can also be made from other shapes such as pentagons, polyominoes and in fact almost any kind of geometric shape. The artist M. C. Escher is famous for making tessellations with irregular interlocking tiles, shaped like animals and other natural objects. If suitable contrasting colours are chosen for the tiles of differing shape, striking patterns are formed, and these can be used to decorate physical surfaces such as church floors.
More formally, a tessellation or tiling is a cover of the Euclidean plane by a countable number of closed sets, called tiles, such that the tiles intersect only on their boundaries. These tiles may be polygons or any other shapes. Many tessellations are formed from a finite number of prototiles in which all tiles in the tessellation are congruent to the given prototiles. If a geometric shape can be used as a prototile to create a tessellation, the shape is said to tessellate or to tile the plane. The Conway criterion is a sufficient, but not necessary, set of rules for deciding whether a given shape tiles the plane periodically without reflections: some tiles fail the criterion, but still tile the plane. No general rule has been found for determining whether a given shape can tile the plane or not, which means there are many unsolved problems concerning tessellations.
Mathematically, tessellations can be extended to spaces other than the Euclidean plane. The Swiss geometer Ludwig Schläfli pioneered this by defining polyschemes, which mathematicians nowadays call polytopes. These are the analogues to polygons and polyhedra in spaces with more dimensions. He further defined the Schläfli symbol notation to make it easy to describe polytopes. For example, the Schläfli symbol for an equilateral triangle is {3}, while that for a square is {4}. The Schläfli notation makes it possible to describe tilings compactly. For example, a tiling of regular hexagons has three six-sided polygons at each vertex, so its Schläfli symbol is {6,3}.
Other methods also exist for describing polygonal tilings. When the tessellation is made of regular polygons, the most common notation is the vertex configuration, which is simply a list of the number of sides of the polygons around a vertex. The square tiling has a vertex configuration of 4.4.4.4, or 44. The tiling of regular hexagons is noted 6.6.6, or 63.
In mathematics
Introduction to tessellations
Mathematicians use some technical terms when discussing tilings. An edge is the intersection between two bordering tiles; it is often a straight line. A vertex is the point of intersection of three or more bordering tiles. Using these terms, an isogonal or vertex-transitive tiling is a tiling where every vertex point is identical; that is, the arrangement of polygons about each vertex is the same. The fundamental region is a shape such as a rectangle that is repeated to form the tessellation. For example, a regular tessellation of the plane with squares has a meeting of four squares at every vertex.
The sides of the polygons are not necessarily identical to the edges of the tiles. An edge-to-edge tiling is any polygonal tessellation where adjacent tiles only share one full side, i.e., no tile shares a partial side or more than one side with any other tile. In an edge-to-edge tiling, the sides of the polygons and the edges of the tiles are the same. The familiar "brick wall" tiling is not edge-to-edge because the long side of each rectangular brick is shared with two bordering bricks.
A normal tiling is a tessellation for which every tile is topologically equivalent to a disk, the intersection of any two tiles is a connected set or the empty set, and all tiles are uniformly bounded. This means that a single circumscribing radius and a single inscribing radius can be used for all the tiles in the whole tiling; the condition disallows tiles that are pathologically long or thin.
A is a tessellation in which all tiles are congruent; it has only one prototile. A particularly interesting type of monohedral tessellation is the spiral monohedral tiling. The first spiral monohedral tiling was discovered by Heinz Voderberg in 1936; the Voderberg tiling has a unit tile that is a nonconvex enneagon. The Hirschhorn tiling, published by Michael D. Hirschhorn and D. C. Hunt in 1985, is a pentagon tiling using irregular pentagons: regular pentagons cannot tile the Euclidean plane as the internal angle of a regular pentagon, , is not a divisor of 2.
An isohedral tiling is a special variation of a monohedral tiling in which all tiles belong to the same transitivity class, that is, all tiles are transforms of the same prototile under the symmetry group of the tiling. If a prototile admits a tiling, but no such tiling is isohedral, then the prototile is called anisohedral and forms anisohedral tilings.
A regular tessellation is a highly symmetric, edge-to-edge tiling made up of regular polygons, all of the same shape. There are only three regular tessellations: those made up of equilateral triangles, squares, or regular hexagons. All three of these tilings are isogonal and monohedral.
A semi-regular (or Archimedean) tessellation uses more than one type of regular polygon in an isogonal arrangement. There are eight semi-regular tilings (or nine if the mirror-image pair of tilings counts as two). These can be described by their vertex configuration; for example, a semi-regular tiling using squares and regular octagons has the vertex configuration 4.82 (each vertex has one square and two octagons). Many non-edge-to-edge tilings of the Euclidean plane are possible, including the family of Pythagorean tilings, tessellations that use two (parameterised) sizes of square, each square touching four squares of the other size. An edge tessellation is one in which each tile can be reflected over an edge to take up the position of a neighbouring tile, such as in an array of equilateral or isosceles triangles.
Wallpaper groups
Tilings with translational symmetry in two independent directions can be categorized by wallpaper groups, of which 17 exist. It has been claimed that all seventeen of these groups are represented in the Alhambra palace in Granada, Spain. Although this is disputed, the variety and sophistication of the Alhambra tilings have interested modern researchers. Of the three regular tilings two are in the p6m wallpaper group and one is in p4m. Tilings in 2-D with translational symmetry in just one direction may be categorized by the seven frieze groups describing the possible frieze patterns. Orbifold notation can be used to describe wallpaper groups of the Euclidean plane.
Aperiodic tilings
Penrose tilings, which use two different quadrilateral prototiles, are the best known example of tiles that forcibly create non-periodic patterns. They belong to a general class of aperiodic tilings, which use tiles that cannot tessellate periodically. The recursive process of substitution tiling is a method of generating aperiodic tilings. One class that can be generated in this way is the rep-tiles; these tilings have unexpected self-replicating properties. Pinwheel tilings are non-periodic, using a rep-tile construction; the tiles appear in infinitely many orientations. It might be thought that a non-periodic pattern would be entirely without symmetry, but this is not so. Aperiodic tilings, while lacking in translational symmetry, do have symmetries of other types, by infinite repetition of any bounded patch of the tiling and in certain finite groups of rotations or reflections of those patches. A substitution rule, such as can be used to generate Penrose patterns using assemblies of tiles called rhombs, illustrates scaling symmetry. A Fibonacci word can be used to build an aperiodic tiling, and to study quasicrystals, which are structures with aperiodic order.
Wang tiles are squares coloured on each edge, and placed so that abutting edges of adjacent tiles have the same colour; hence they are sometimes called Wang dominoes. A suitable set of Wang dominoes can tile the plane, but only aperiodically. This is known because any Turing machine can be represented as a set of Wang dominoes that tile the plane if, and only if, the Turing machine does not halt. Since the halting problem is undecidable, the problem of deciding whether a Wang domino set can tile the plane is also undecidable.
Truchet tiles are square tiles decorated with patterns so they do not have rotational symmetry; in 1704, Sébastien Truchet used a square tile split into two triangles of contrasting colours. These can tile the plane either periodically or randomly.
An einstein tile is a single shape that forces aperiodic tiling. The first such tile, dubbed a "hat", was discovered in 2023 by David Smith, a hobbyist mathematician. The discovery is under professional review and, upon confirmation, will be credited as solving a longstanding mathematical problem.
Tessellations and colour
Sometimes the colour of a tile is understood as part of the tiling; at other times arbitrary colours may be applied later. When discussing a tiling that is displayed in colours, to avoid ambiguity, one needs to specify whether the colours are part of the tiling or just part of its illustration. This affects whether tiles with the same shape, but different colours, are considered identical, which in turn affects questions of symmetry. The four colour theorem states that for every tessellation of a normal Euclidean plane, with a set of four available colours, each tile can be coloured in one colour such that no tiles of equal colour meet at a curve of positive length. The colouring guaranteed by the four colour theorem does not generally respect the symmetries of the tessellation. To produce a colouring that does, it is necessary to treat the colours as part of the tessellation. Here, as many as seven colours may be needed, as demonstrated in the image at left.
Tessellations with polygons
Next to the various tilings by regular polygons, tilings by other polygons have also been studied.
Any triangle or quadrilateral (even non-convex) can be used as a prototile to form a monohedral tessellation, often in more than one way. Copies of an arbitrary quadrilateral can form a tessellation with translational symmetry and 2-fold rotational symmetry with centres at the midpoints of all sides. For an asymmetric quadrilateral this tiling belongs to wallpaper group p2. As fundamental domain we have the quadrilateral. Equivalently, we can construct a parallelogram subtended by a minimal set of translation vectors, starting from a rotational centre. We can divide this by one diagonal, and take one half (a triangle) as fundamental domain. Such a triangle has the same area as the quadrilateral and can be constructed from it by cutting and pasting.
If only one shape of tile is allowed, tilings exist with convex N-gons for N equal to 3, 4, 5, and 6. For , see Pentagonal tiling, for , see Hexagonal tiling, for , see Heptagonal tiling and for , see octagonal tiling.
With non-convex polygons, there are far fewer limitations in the number of sides, even if only one shape is allowed.
Polyominoes are examples of tiles that are either convex of non-convex, for which various combinations, rotations, and reflections can be used to tile a plane. For results on tiling the plane with polyominoes, see Polyomino § Uses of polyominoes.
Voronoi tilings
Voronoi or Dirichlet tilings are tessellations where each tile is defined as the set of points closest to one of the points in a discrete set of defining points. (Think of geographical regions where each region is defined as all the points closest to a given city or post office.) The Voronoi cell for each defining point is a convex polygon. The Delaunay triangulation is a tessellation that is the dual graph of a Voronoi tessellation. Delaunay triangulations are useful in numerical simulation, in part because among all possible triangulations of the defining points, Delaunay triangulations maximize the minimum of the angles formed by the edges. Voronoi tilings with randomly placed points can be used to construct random tilings of the plane.
Tessellations in higher dimensions
Tessellation can be extended to three dimensions. Certain polyhedra can be stacked in a regular crystal pattern to fill (or tile) three-dimensional space, including the cube (the only Platonic polyhedron to do so), the rhombic dodecahedron, the truncated octahedron, and triangular, quadrilateral, and hexagonal prisms, among others. Any polyhedron that fits this criterion is known as a plesiohedron, and may possess between 4 and 38 faces. Naturally occurring rhombic dodecahedra are found as crystals of andradite (a kind of garnet) and fluorite.
Tessellations in three or more dimensions are called honeycombs. In three dimensions there is just one regular honeycomb, which has eight cubes at each polyhedron vertex. Similarly, in three dimensions there is just one quasiregular honeycomb, which has eight tetrahedra and six octahedra at each polyhedron vertex. However, there are many possible semiregular honeycombs in three dimensions. Uniform honeycombs can be constructed using the Wythoff construction.
The Schmitt-Conway biprism is a convex polyhedron with the property of tiling space only aperiodically.
A Schwarz triangle is a spherical triangle that can be used to tile a sphere.
Tessellations in non-Euclidean geometries
It is possible to tessellate in non-Euclidean geometries such as hyperbolic geometry. A uniform tiling in the hyperbolic plane (that may be regular, quasiregular, or semiregular) is an edge-to-edge filling of the hyperbolic plane, with regular polygons as faces; these are vertex-transitive (transitive on its vertices), and isogonal (there is an isometry mapping any vertex onto any other).
A uniform honeycomb in hyperbolic space is a uniform tessellation of uniform polyhedral cells. In three-dimensional (3-D) hyperbolic space there are nine Coxeter group families of compact convex uniform honeycombs, generated as Wythoff constructions, and represented by permutations of rings of the Coxeter diagrams for each family.
In art
In architecture, tessellations have been used to create decorative motifs since ancient times. Mosaic tilings often had geometric patterns. Later civilisations also used larger tiles, either plain or individually decorated. Some of the most decorative were the Moorish wall tilings of Islamic architecture, using Girih and Zellige tiles in buildings such as the Alhambra and La Mezquita.
Tessellations frequently appeared in the graphic art of M. C. Escher; he was inspired by the Moorish use of symmetry in places such as the Alhambra when he visited Spain in 1936. Escher made four "Circle Limit" drawings of tilings that use hyperbolic geometry. For his woodcut "Circle Limit IV" (1960), Escher prepared a pencil and ink study showing the required geometry. Escher explained that "No single component of all the series, which from infinitely far away rise like rockets perpendicularly from the limit and are at last lost in it, ever reaches the boundary line."
Tessellated designs often appear on textiles, whether woven, stitched in, or printed. Tessellation patterns have been used to design interlocking motifs of patch shapes in quilts.
Tessellations are also a main genre in origami (paper folding), where pleats are used to connect molecules, such as twist folds, together in a repeating fashion.
In manufacturing
Tessellation is used in manufacturing industry to reduce the wastage of material (yield losses) such as sheet metal when cutting out shapes for objects such as car doors or drink cans.
Tessellation is apparent in the mudcrack-like cracking of thin films – with a degree of self-organisation being observed using micro and nanotechnologies.
In nature
The honeycomb is a well-known example of tessellation in nature with its hexagonal cells.
In botany, the term "tessellate" describes a checkered pattern, for example on a flower petal, tree bark, or fruit. Flowers including the fritillary, and some species of Colchicum, are characteristically tessellate.
Many patterns in nature are formed by cracks in sheets of materials. These patterns can be described by Gilbert tessellations, also known as random crack networks. The Gilbert tessellation is a mathematical model for the formation of mudcracks, needle-like crystals, and similar structures. The model, named after Edgar Gilbert, allows cracks to form starting from being randomly scattered over the plane; each crack propagates in two opposite directions along a line through the initiation point, its slope chosen at random, creating a tessellation of irregular convex polygons. Basaltic lava flows often display columnar jointing as a result of contraction forces causing cracks as the lava cools. The extensive crack networks that develop often produce hexagonal columns of lava. One example of such an array of columns is the Giant's Causeway in Northern Ireland. Tessellated pavement, a characteristic example of which is found at Eaglehawk Neck on the Tasman Peninsula of Tasmania, is a rare sedimentary rock formation where the rock has fractured into rectangular blocks.
Other natural patterns occur in foams; these are packed according to Plateau's laws, which require minimal surfaces. Such foams present a problem in how to pack cells as tightly as possible: in 1887, Lord Kelvin proposed a packing using only one solid, the bitruncated cubic honeycomb with very slightly curved faces. In 1993, Denis Weaire and Robert Phelan proposed the Weaire–Phelan structure, which uses less surface area to separate cells of equal volume than Kelvin's foam.
In puzzles and recreational mathematics
Tessellations have given rise to many types of tiling puzzle, from traditional jigsaw puzzles (with irregular pieces of wood or cardboard) and the tangram, to more modern puzzles that often have a mathematical basis. For example, polyiamonds and polyominoes are figures of regular triangles and squares, often used in tiling puzzles. Authors such as Henry Dudeney and Martin Gardner have made many uses of tessellation in recreational mathematics. For example, Dudeney invented the hinged dissection, while Gardner wrote about the "rep-tile", a shape that can be dissected into smaller copies of the same shape. Inspired by Gardner's articles in Scientific American, the amateur mathematician Marjorie Rice found four new tessellations with pentagons. Squaring the square is the problem of tiling an integral square (one whose sides have integer length) using only other integral squares. An extension is squaring the plane, tiling it by squares whose sizes are all natural numbers without repetitions; James and Frederick Henle proved that this was possible.
Examples
| Mathematics | Geometry | null |
321796 | https://en.wikipedia.org/wiki/Microsoft%20Paint | Microsoft Paint | Microsoft Paint (commonly known as MS Paint or Paint for short) is a simple raster graphics editor that has been included with all versions of Microsoft Windows. The program opens, modifies and saves image files in Windows bitmap (BMP), JPEG, GIF, PNG, and single-page TIFF formats. The program can be in color mode or two-color black-and-white, but there is no grayscale mode. For its simplicity and wide availability, it rapidly became one of the most used Windows applications, introducing many to painting on a computer for the first time.
In July 2017, Microsoft added Paint to the list of deprecated features of Windows 10 and announced that it had become a free standalone application in Microsoft Store, with Paint 3D as its replacement. However, as a result of public demand from users, Paint has continued to be included with Windows 10 and even Windows 11, with Microsoft instead deprecating Paint 3D. Windows 11 also includes an updated version of Paint in later versions that added, among others updates, a revamped UI and dark mode support.
History
Paint was initially programmed, licensed and adapted from PC Paintbrush made by ZSoft, by Dan McCabe at Microsoft for Windows 1.0, released in late 1985. PC Paintbrush had been previously licensed and published with the Microsoft Mouse DOS drivers from version 4 (circa 1985), to compete with Mouse Systems publishing PCPaint with its own mice in 1984. PC Paintbrush’s inclusion in version 4 of the DOS drivers replaced the previously included Microsoft bitmap color editing application “Doodle,” released in 1983 with the first version of the Microsoft Mouse drivers. With improved functionality over Doodle, it competed successfully against PCPaint and Mouse Systems. Paint included with the first version of Windows, Windows 1.0 in November 1985, had 24 tools and could read and write files in the proprietary "MSP" format drawn in monochrome graphics. Aside from "pencil" and "shape" tools and a brush that draws in 24 "brush shapes and patterns", the toolset also contained two features unique for the time: one the ability to draw Bézier curves and the other that forces lines to be drawn on three angles to create an isometric three-quarter perspective. Paintbrush can only read MSP files; Microsoft has since deprecated the MSP format, repurposing the MSP extension for the Windows Installer Package format.
Paint was later superseded by Paintbrush in Windows 3.0, with a redesigned user interface, true color support, and support for the BMP and PCX file formats. This version was also based on a newer licensed version of PC Paintbrush by ZSoft.
Windows 9x
Microsoft shipped an updated version of Paint with Windows 95 and Windows NT 4.0. At this point Microsoft began updating the source code entirely from scratch, and did not license any further code or versions of PC Paintbrush. This version allows saving and loading a custom set of color wells as color palette (.pal) files. This functionality only works correctly if the color depth of images is 16-bits per pixel (bpp) or higher. Later versions of Paint do not support this feature.
In Windows 95–98, Windows 2000 and Windows Me, Paint can open JPEG, GIF and 48-bit (16-bpp) TIF images and save images in JPEG and GIF formats when appropriate graphics filters are installed. Such plug-ins are included with Microsoft Office and Microsoft PhotoDraw. This also allows Paint to use transparent backgrounds. Support for PCX files was dropped. Starting with Windows Me, the canvas size expands automatically when larger images are opened or pasted instead of asking like in previous versions of Windows.
Windows XP and Vista
In Windows XP and later, Paint uses GDI+ and therefore can natively save images as BMP, JPEG, GIF, TIFF and PNG without requiring additional graphics filters. Support for saving and loading custom color palettes was dropped.
In Windows Vista, the toolbar icons were updated and the default color palette was changed. Paint in Windows Vista can undo a change up to 10 times, compared to 3 in previous versions; it also includes a slider for image magnification and a crop function. This version saves in JPEG format by default.
Windows 7 and 8.x
The version of Paint in Windows 7 and later features a ribbon in its user interface. It also features "artistic" brushes composed of varying shades of gray and some degree of transparency that give a more realistic result. To add to the realism, the oil and watercolor brushes can only paint for a small distance before the user must re-click (this gives the illusion that the paintbrush has run out of paint). In addition, Paint can now undo up to 50 subsequent changes. It also has anti-aliased shapes, which can be resized freely until they are rasterized when another tool is selected. This version supports viewing (but not saving) transparent PNG and ICO file formats and saves files in the .png file format by default.
Text can now be pasted into text boxes that don't have enough room to display the text. A text box can then be enlarged or reshaped appropriately to fit the text if desired. Previous versions of Paint would display an error message if a user tried to paste more text than there was room for.
The Windows 8 version of Paint mostly corrects a long-standing defect from previous versions involving the inability to scroll the window when editing in Zoom view over 100%. However, when the user inserts text in Zoom view, they cannot move the text beyond the zoomed viewport while the text window is in edit mode with either the mouse or keyboard.
Windows 10
In the April 2017 "Creators Update" for Windows 10, Microsoft released Paint 3D alongside Paint. In addition to the traditional two-dimensional drawing tools, Paint 3D can import and manipulate three-dimensional models. Three months later, on July 23, 2017, Microsoft added Paint to the list of deprecated Windows features. The next day, in the wake of "an incredible outpouring of support and nostalgia", Microsoft clarified that Paint would become a free app on Microsoft Store, even though Paint 3D offers the same functionality.
Despite the deprecation, Paint continues to be a part of all versions of Windows 10 up to version 22H2. The closest that Microsoft ever got to enacting said decision was adding a removal notice to Paint's user interface in Windows 10 versions 1803 and 1809.
In March 2021, with the release of Windows 10 Insider build 21332 to the Dev Channel, Microsoft removed Paint 3D from clean installations of the build, in addition to the 3D Objects app. In April 2021, Microsoft released Windows 10 Insider build 21354, which made Paint (along with Snipping Tool) updatable from the Microsoft Store. It had also been moved from the Windows Accessories folder of the Start menu to its own section.
Windows 11
In August 2021, Microsoft teased an updated version of Paint for Windows 11, featuring a refreshed user interface (UI), improved font picker, and a dark theme. This newly updated version of Paint was released with Windows 11 Insider build 22468 in September 2021, and was officially released as part of the Windows 11 2022 Update in September 2022. In September 2023, Microsoft released an update that added layers, support for transparent PNG files, AI art generator and other AI tools and a background removal tool.
Despite new features being added into Paint in Windows 11, some older features have disappeared. Paint in Windows 11 also automatically anti-aliases all fonts that are inputted using the "Text" feature, even those that are aliased by design, such as Courier New. Smaller images are also harder to manipulate and work with in newer versions of Paint, as it automatically blurs images when they are resized or re-copied. This is especially noticeable when working with video game sprites and pixel art. These issues are due to interpolation algorithms that Paint is using, according to Microsoft.
Features
Paint has a few functions not mentioned in the help file: a stamp mode, trail mode, regular shapes, and moving pictures. For the stamp mode, the user can select a part of the image, hold the key, and move it to another part of the canvas. This, instead of cutting the piece out, creates a copy of it. The process can be repeated as many times as desired, as long as the key is held down. The trail mode works exactly the same, but it uses the instead of the key.
It is also possible to thicken or thin a line either before or simultaneously while it is being drawn via (NumPad only) or (NumPad only).
To crop whitespace or eliminate parts of a graphic, the blue handle in the lower right corner can be dragged to increase canvas size or crop a graphic. Users can also draw perfect shapes (which have a width equal to the height) using any shape tool by holding down the while dragging.
Older versions of Paint, such as the one bundled with Windows 3.1, featured a color-replace brush, which replaced a single color underneath the brush with another without affecting the rest of the image. In later versions of Paint, the color erase brush was removed as an option, however it can still be simulated by selecting the color to be replaced as the primary color, and the one it is replaced with as the secondary color, and then right-click dragging the erase tool.
Support for indexed palettes
By default, almost all versions of Paint are generally unable to properly downgrade created images to indexed palettes using fewer than 24 bits per pixel. When saving an image in a format that uses indexed palettes with fewer than 24 bits per pixel, a warning message appears about the loss of quality. Paint does not utilize binary, color or grayscale dithering or palette optimization, and the image will be saved with usually irreversibly scrambled colors.
Paint is nonetheless able to correctly load and save indexed palettes in any of the supported formats if an image is opened as an 8-bit or otherwise indexed palette image. In that case, the image's palette is preserved when saving. However, there is no way to see the actual palette; color choices for brushes, text, and erasers as well as user-defined colors will be limited to the closest available color in the indexed palette.
| Technology | Multimedia_2 | null |
321814 | https://en.wikipedia.org/wiki/Fibula | Fibula | The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the knee joint and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia and forms the lateral part of the ankle joint.
Structure
The bone has the following components:
Lateral malleolus
Interosseous membrane connecting the fibula to the tibia, forming a syndesmosis joint
The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula.
The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia.
Blood supply
The blood supply is important for planning free tissue transfer because the fibula is commonly used to reconstruct the mandible. The shaft is supplied in its middle third by a large nutrient vessel from the fibular artery. It is also perfused from its periosteum which receives many small branches from the fibular artery. The proximal head and the epiphysis are supplied by a branch of the anterior tibial artery. In harvesting the bone the middle third is always taken and the ends preserved (4 cm proximally and 6 cm distally)
Development
The fibula is ossified from three centers, one for the shaft, and one for either end. Ossification begins in the body about the eighth week of fetal life, and extends toward the extremities. At birth the ends are cartilaginous.
Ossification commences in the lower end in the second year, and in the upper about the fourth year. The lower epiphysis, the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins about the twenty-fifth year.
Head
The upper extremity or head of the fibula is of an irregular quadrate form, presenting above a flattened articular surface, directed upward, forward, and medialward, for articulation with a corresponding surface on the lateral condyle of the tibia.
On the lateral side is a thick and rough prominence continued behind into a pointed eminence, the apex (styloid process), which projects upward from the posterior part of the head.
The prominence, at its upper and lateral part, gives attachment to the tendon of the biceps femoris and to the fibular collateral ligament of the knee-joint, the ligament dividing the tendon into two parts.
The remaining part of the circumference of the head is rough, for the attachment of muscles and ligaments.
It presents in front a tubercle for the origin of the upper and anterior fibers of the peroneus longus, and a surface for the attachment of the anterior ligament of the head; and behind, another tubercle, for the attachment of the posterior ligament of the head and the origin of the upper fibers of the soleus.
Body
The body of the fibula presents four borders - the antero-lateral, the antero-medial, the postero-lateral, and the postero-medial; and four surfaces - anterior, posterior, medial, and lateral.
Borders
The antero-lateral border begins above in front of the head, runs vertically downward to a little below the middle of the bone, and then curving somewhat lateralward, bifurcates so as to embrace a triangular subcutaneous surface immediately above the lateral malleolus. This border gives attachment to an intermuscular septum, which separates the extensor muscles on the anterior surface of the leg from the peronaei longus and brevis on the lateral surface.
The antero-medial border, or interosseous crest, is situated close to the medial side of the preceding, and runs nearly parallel with it in the upper third of its extent, but diverges from it in the lower two-thirds. It begins above just beneath the head of the bone (sometimes it is quite indistinct for about 2.5 cm. below the head), and ends at the apex of a rough triangular surface immediately above the articular facet of the lateral malleolus. It serves for the attachment of the interosseous membrane, which separates the extensor muscles in front from the flexor muscles behind.
The postero-lateral border is prominent; it begins above at the apex, and ends below in the posterior border of the lateral malleolus. It is directed lateralward above, backward in the middle of its course, backward, and a little medialward below, and gives attachment to an aponeurosis which separates the peronaei on the lateral surface from the flexor muscles on the posterior surface.
The postero-medial border, sometimes called the oblique line, begins above at the medial side of the head, and ends by becoming continuous with the interosseous crest at the lower fourth of the bone. It is well-marked and prominent at the upper and middle parts of the bone. It gives attachment to an aponeurosis which separates the tibialis posterior from the soleus and flexor hallucis longus.
Surfaces
The anterior surface is the interval between the antero-lateral and antero-medial borders. It is extremely narrow and flat in the upper third of its extent; broader and grooved longitudinally in its lower third; it serves for the origin of three muscles: the extensor digitorum longus, extensor hallucis longus, and peroneus tertius.
The posterior surface is the space included between the postero-lateral and the postero-medial borders; it is continuous below with the triangular area above the articular surface of the lateral malleolus; it is directed backward above, backward and medialward at its middle, directly medialward below. Its upper third is rough, for the origin of the soleus; its lower part presents a triangular surface, connected to the tibia by a strong interosseous ligament; the intervening part of the surface is covered by the fibers of origin of the flexor hallucis longus. Near the middle of this surface is the nutrient foramen, which is directed downward.
The medial surface is the interval included between the antero-medial and the postero-medial borders. It is grooved for the origin of the tibialis posterior.
The lateral surface is the space between the antero-lateral and postero-lateral borders. It is broad, and often deeply grooved; it is directed lateralward in the upper two-thirds of its course, backward in the lower third, where it is continuous with the posterior border of the lateral malleolus. This surface gives origin to the peronaei longus and brevis.
Function
The fibula does not carry any significant load (weight) of the body. It extends past the lower end of the tibia and forms the outer part of the ankle providing stability to this joint. It has grooves(a depression) for certain ligaments which gives them leverage and multiplies the muscle force. It provides attachment points for the following muscles:
Clinical significance
As much of the fibula can be removed without it impacting an individual's ability to walk, the fibula is utilised as a source of bone material in fibular free flap surgeries.
Fractures
The most common type of fibula fracture is located at the distal end of the bone, and is classified as ankle fracture. In the Danis–Weber classification it has three categories:
Type A: Fracture of the lateral malleolus, distal to the syndesmosis (the connection between the distal ends of the tibia and fibula).
Type B: Fracture of the fibula at the level of the syndesmosis
Type C: Fracture of the fibula proximal to the syndesmosis.
A Maisonneuve fracture is a spiral fracture of the proximal third of the fibula associated with a tear of the distal tibiofibular syndesmosis and the interosseous membrane. There is an associated fracture of the medial malleolus or rupture of the deep deltoid ligament.
An avulsion fracture of the head of the fibula refers to the fracture of the fibular head because of a sudden contraction of the biceps femoris muscle that pulls its site of attachment on the bone. The attachment of the biceps femoris tendon on the fibular head is closely related to the lateral collateral ligament of the knee. Therefore, this ligament is prone to injury in this type of avulsion fracture.
History
Etymology
The word fibula can be dated back to c. 1670. It derives from Latin fībula, which describes a clasp or brooch – see fibula (brooch) – and was first used in English for the smaller bone in the lower leg c. 1706. The bone was so called because it resembles a clasp like a modern safety pin.
The adjective peroneal referring to the fibula bone or its surrounding structures derives from : perónē, the Ancient Greek word for a clasp.
Other animals
Because the fibula bears relatively little weight in comparison with the tibia, it is typically narrower in all but the most primitive tetrapods. In many animals, it still articulates with the posterior part of the lower extremity of the femur, but this feature is frequently lost (as it is in humans). In some animals, the reduction of the fibula has proceeded even further than it has in humans, with the loss of the tarsal articulation, and, in extreme cases (such as the horse), partial fusion with the tibia.
| Biology and health sciences | Skeletal system | Biology |
321869 | https://en.wikipedia.org/wiki/Coding%20theory | Coding theory | Coding theory is the study of the properties of codes and their respective fitness for specific applications. Codes are used for data compression, cryptography, error detection and correction, data transmission and data storage. Codes are studied by various scientific disciplines—such as information theory, electrical engineering, mathematics, linguistics, 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.
There are four types of coding:
Data compression (or source coding)
Error control (or channel coding)
Cryptographic coding
Line coding
Data compression attempts to remove unwanted redundancy from the data from a source in order to transmit it more efficiently. For example, DEFLATE data compression makes files smaller, for purposes such as to reduce Internet traffic. Data compression and error correction may be studied in combination.
Error correction adds useful redundancy to the data from a source to make the transmission more robust to disturbances present on the transmission channel. The ordinary user may not be aware of many applications using error correction. A typical music compact disc (CD) uses the Reed–Solomon code to correct for scratches and dust. In this application the transmission channel is the CD itself. Cell phones also use coding techniques to correct for the fading and noise of high frequency radio transmission. Data modems, telephone transmissions, and the NASA Deep Space Network all employ channel coding techniques to get the bits through, for example the turbo code and LDPC codes.
History of coding theory
In 1948, Claude Shannon published "A Mathematical Theory of Communication", an article in two parts in the July and October issues of the Bell System Technical Journal. This work focuses on the problem of how best to encode the information a sender wants to transmit. In this fundamental work he used tools in probability theory, developed by Norbert Wiener, which were in their nascent stages of being applied to communication theory at that time. Shannon developed information entropy as a measure for the uncertainty in a message while essentially inventing the field of information theory.
The binary Golay code was developed in 1949. It is an error-correcting code capable of correcting up to three errors in each 24-bit word, and detecting a fourth.
Richard Hamming won the Turing Award in 1968 for his work at Bell Labs in numerical methods, automatic coding systems, and error-detecting and error-correcting codes. He invented the concepts known as Hamming codes, Hamming windows, Hamming numbers, and Hamming distance.
In 1972, Nasir Ahmed proposed the discrete cosine transform (DCT), which he developed with T. Natarajan and K. R. Rao in 1973. The DCT is the most widely used lossy compression algorithm, the basis for multimedia formats such as JPEG, MPEG and MP3.
Source coding
The aim of source coding is to take the source data and make it smaller.
Definition
Data can be seen as a random variable , where appears with probability .
Data are encoded by strings (words) over an alphabet .
A code is a function
(or if the empty string is not part of the alphabet).
is the code word associated with .
Length of the code word is written as
Expected length of a code is
The concatenation of code words .
The code word of the empty string is the empty string itself:
Properties
is non-singular if injective.
is uniquely decodable if injective.
is instantaneous if is not a proper prefix of (and vice versa).
Principle
Entropy of a source is the measure of information. Basically, source codes try to reduce the redundancy present in the source, and represent the source with fewer bits that carry more information.
Data compression which explicitly tries to minimize the average length of messages according to a particular assumed probability model is called entropy encoding.
Various techniques used by source coding schemes try to achieve the limit of entropy of the source. C(x) ≥ H(x), where H(x) is entropy of source (bitrate), and C(x) is the bitrate after compression. In particular, no source coding scheme can be better than the entropy of the source.
Example
Facsimile transmission uses a simple run length code. Source coding removes all data superfluous to the need of the transmitter, decreasing the bandwidth required for transmission.
Channel coding
The purpose of channel coding theory is to find codes which transmit quickly, contain many valid code words and can correct or at least detect many errors. While not mutually exclusive, performance in these areas is a trade-off. So, different codes are optimal for different applications. The needed properties of this code mainly depend on the probability of errors happening during transmission. In a typical CD, the impairment is mainly dust or scratches.
CDs use cross-interleaved Reed–Solomon coding to spread the data out over the disk.
Although not a very good code, a simple repeat code can serve as an understandable example. Suppose we take a block of data bits (representing sound) and send it three times. At the receiver we will examine the three repetitions bit by bit and take a majority vote. The twist on this is that we do not merely send the bits in order. We interleave them. The block of data bits is first divided into 4 smaller blocks. Then we cycle through the block and send one bit from the first, then the second, etc. This is done three times to spread the data out over the surface of the disk. In the context of the simple repeat code, this may not appear effective. However, there are more powerful codes known which are very effective at correcting the "burst" error of a scratch or a dust spot when this interleaving technique is used.
Other codes are more appropriate for different applications. Deep space communications are limited by the thermal noise of the receiver which is more of a continuous nature than a bursty nature. Likewise, narrowband modems are limited by the noise, present in the telephone network and also modeled better as a continuous disturbance. Cell phones are subject to rapid fading. The high frequencies used can cause rapid fading of the signal even if the receiver is moved a few inches. Again there are a class of channel codes that are designed to combat fading.
Linear codes
The term algebraic coding theory denotes the sub-field of coding theory where the properties of codes are expressed in algebraic terms and then further researched.
Algebraic coding theory is basically divided into two major types of codes:
Linear block codes
Convolutional codes
It analyzes the following three properties of a code – mainly:
Code word length
Total number of valid code words
The minimum distance between two valid code words, using mainly the Hamming distance, sometimes also other distances like the Lee distance
Linear block codes
Linear block codes have the property of linearity, i.e. the sum of any two codewords is also a code word, and they are applied to the source bits in blocks, hence the name linear block codes. There are block codes that are not linear, but it is difficult to prove that a code is a good one without this property.
Linear block codes are summarized by their symbol alphabets (e.g., binary or ternary) and parameters (n,m,dmin) where
n is the length of the codeword, in symbols,
m is the number of source symbols that will be used for encoding at once,
dmin is the minimum hamming distance for the code.
There are many types of linear block codes, such as
Cyclic codes (e.g., Hamming codes)
Repetition codes
Parity codes
Polynomial codes (e.g., BCH codes)
Reed–Solomon codes
Algebraic geometric codes
Reed–Muller codes
Perfect codes
Locally recoverable code
Block codes are tied to the sphere packing problem, which has received some attention over the years. In two dimensions, it is easy to visualize. Take a bunch of pennies flat on the table and push them together. The result is a hexagon pattern like a bee's nest. But block codes rely on more dimensions which cannot easily be visualized. The powerful (24,12) Golay code used in deep space communications uses 24 dimensions. If used as a binary code (which it usually is) the dimensions refer to the length of the codeword as defined above.
The theory of coding uses the N-dimensional sphere model. For example, how many pennies can be packed into a circle on a tabletop, or in 3 dimensions, how many marbles can be packed into a globe. Other considerations enter the choice of a code. For example, hexagon packing into the constraint of a rectangular box will leave empty space at the corners. As the dimensions get larger, the percentage of empty space grows smaller. But at certain dimensions, the packing uses all the space and these codes are the so-called "perfect" codes. The only nontrivial and useful perfect codes are the distance-3 Hamming codes with parameters satisfying (2r – 1, 2r – 1 – r, 3), and the [23,12,7] binary and [11,6,5] ternary Golay codes.
Another code property is the number of neighbors that a single codeword may have.
Again, consider pennies as an example. First we pack the pennies in a rectangular grid. Each penny will have 4 near neighbors (and 4 at the corners which are farther away). In a hexagon, each penny will have 6 near neighbors. When we increase the dimensions, the number of near neighbors increases very rapidly. The result is the number of ways for noise to make the receiver choose a neighbor (hence an error) grows as well. This is a fundamental limitation of block codes, and indeed all codes. It may be harder to cause an error to a single neighbor, but the number of neighbors can be large enough so the total error probability actually suffers.
Properties of linear block codes are used in many applications. For example, the syndrome-coset uniqueness property of linear block codes is used in trellis shaping, one of the best-known shaping codes.
Convolutional codes
The idea behind a convolutional code is to make every codeword symbol be the weighted sum of the various input message symbols. This is like convolution used in LTI systems to find the output of a system, when you know the input and impulse response.
So we generally find the output of the system convolutional encoder, which is the convolution of the input bit, against the states of the convolution encoder, registers.
Fundamentally, convolutional codes do not offer more protection against noise than an equivalent block code. In many cases, they generally offer greater simplicity of implementation over a block code of equal power. The encoder is usually a simple circuit which has state memory and some feedback logic, normally XOR gates. The decoder can be implemented in software or firmware.
The Viterbi algorithm is the optimum algorithm used to decode convolutional codes. There are simplifications to reduce the computational load. They rely on searching only the most likely paths. Although not optimum, they have generally been found to give good results in low noise environments.
Convolutional codes are used in voiceband modems (V.32, V.17, V.34) and in GSM mobile phones, as well as satellite and military communication devices.
Cryptographic coding
Cryptography or cryptographic coding 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 block adversaries; various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.
Cryptography prior to the modern age was effectively synonymous with encryption, the conversion of information from a readable state to apparent nonsense. The originator of an encrypted message shared the decoding technique needed to recover the original information only with intended recipients, thereby precluding unwanted persons from doing the same. Since World War I and the advent of the computer, the methods used to carry out cryptology have become increasingly complex and its application more widespread.
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.
Line coding
A line code (also called digital baseband modulation or digital baseband transmission method) is a code chosen for use within a communications system for baseband transmission purposes. Line coding is often used for digital data transport.
Line coding consists of representing the digital signal to be transported by an amplitude- and time-discrete signal that is optimally tuned for the specific properties of the physical channel (and of the receiving equipment). The waveform pattern of voltage or current used to represent the 1s and 0s of a digital data on a transmission link is called line encoding. The common types of line encoding are unipolar, polar, bipolar, and Manchester encoding.
Other applications of coding theory
Another concern of coding theory is designing codes that help synchronization. A code may be designed so that a phase shift can be easily detected and corrected and that multiple signals can be sent on the same channel.
Another application of codes, used in some mobile phone systems, is code-division multiple access (CDMA). Each phone is assigned a code sequence that is approximately uncorrelated with the codes of other phones. When transmitting, the code word is used to modulate the data bits representing the voice message. At the receiver, a demodulation process is performed to recover the data. The properties of this class of codes allow many users (with different codes) to use the same radio channel at the same time. To the receiver, the signals of other users will appear to the demodulator only as a low-level noise.
Another general class of codes are the automatic repeat-request (ARQ) codes. In these codes the sender adds redundancy to each message for error checking, usually by adding check bits. If the check bits are not consistent with the rest of the message when it arrives, the receiver will ask the sender to retransmit the message. All but the simplest wide area network protocols use ARQ. Common protocols include SDLC (IBM), TCP (Internet), X.25 (International) and many others. There is an extensive field of research on this topic because of the problem of matching a rejected packet against a new packet. Is it a new one or is it a retransmission? Typically numbering schemes are used, as in TCP.
Group testing
Group testing uses codes in a different way. Consider a large group of items in which a very few are different in a particular way (e.g., defective products or infected test subjects). The idea of group testing is to determine which items are "different" by using as few tests as possible. The origin of the problem has its roots in the Second World War when the United States Army Air Forces needed to test its soldiers for syphilis.
Analog coding
Information is encoded analogously in the neural networks of brains, in analog signal processing, and analog electronics. Aspects of analog coding include analog error correction,
analog data compression and analog encryption.
Neural coding
Neural coding is a neuroscience-related field concerned with how sensory and other information is represented in the brain by networks of neurons. The main goal of studying neural coding is to characterize the relationship between the stimulus and the individual or ensemble neuronal responses and the relationship among electrical activity of the neurons in the ensemble. It is thought that neurons can encode both digital and analog information, and that neurons follow the principles of information theory and compress information, and detect and correct
errors in the signals that are sent throughout the brain and wider nervous system.
| Mathematics | Discrete mathematics | null |
321940 | https://en.wikipedia.org/wiki/Honeypot%20ant | Honeypot ant | Honeypot ants, also called honey ants, are ants which have specialized workers (repletes, plerergates, or rotunds) that consume large amounts of food to the point that their abdomens swell enormously. Other ants then extract nourishment from them, through the process of trophallaxis. They function as living larders. Honeypot ants belong to any of several genera, including Myrmecocystus and Camponotus. They were first documented in 1881 by Henry C. McCook, and described further in 1908 by William Morton Wheeler.
Behavior
Many insects, notably honey bees and some wasps, collect and store liquid for use at a later date. However, these insects store their food within their nest or in combs. Honey ants are unique in using their own bodies as living storage, used later by their fellow ants when food is otherwise scarce. When the liquid stored inside a honeypot ant is needed, the worker ants stroke the antennae of the honeypot ant, causing the honeypot ant to regurgitate the stored liquid from its crop.
Anatomy
The abdomen of species like Camponotus inflatus consists of hard dorsal sclerites (stiff plates) connected by a softer, more flexible arthrodial membrane. When the abdomen is empty, the arthrodial membrane is folded and the sclerites overlap, but when the abdomen fills the arthrodial membrane becomes fully stretched, leaving the sclerites widely separated.
Ecology
Myrmecocystus nests are found in a variety of arid or semiarid environments. Some species live in extremely hot deserts, others reside in transitional habitats, and still other species can be found in woodlands which are somewhat cool but still very dry for a large part of the year. For instance, the well-studied Myrmecocystus mexicanus resides in the arid and semiarid habitats of the southwestern United States. Sterile workers in this species act as plerergates or repletes during times of food scarcity. When the plerergates are fully engorged, they become immobile and hang from the ceilings of the underground nests. Other workers drain them of their liquid food stores to feed the rest of the colony. Plerergates can live anywhere in the nest, but in the wild, they are found deep underground, unable to move, swollen to the size of grapes.
In Camponotus inflatus in Australia, repletes formed 49% (516 ants) of a colony of 1063 ants, and 46% (1835 ants) of a colony of 4019 ants. The smaller colony contained six wingless queens. The larger colony had 66 chambers containing repletes, with a maximum of 191 repletes in a chamber. The largest replete was 15 millimetres long and had a mass of 1.4 grams. The nest had a maximum depth of 1.7 metres, and tunnels stretched 2.4 metres from the nest entrance. The workers went out foraging during daylight to collect nectar from Mulga nectaries, and meat from the carcass of a Tiliqua blue-tongued lizard.
Genera
Honeypot food storage has been adopted in several seasonally active ant genera:
Camponotus of Australia
Cataglyphis of North Africa
Leptomyrmex of Melanesia
Melophorus of Australia
Myrmecocystus of North America.
Plagiolepis of South Africa
Prenolepis of North America
In human culture
Honeypot ants such as Melophorus bagoti and Camponotus spp. are edible insects and form an occasional part of the diet of various Indigenous Australians. These people scrape the surface to locate the ants' vertical tunnels, and then dig as much as two metres deep to find the honeypots. Papunya, in Australia's Northern Territory, is named after a honey ant creation story, or Dreaming, which belongs to the people there, such as the Warlpiri. The honey ants were celebrated in the Western Desert Art Movement's The Honey Ant Mural, painted in 1971.
Indigenous medicinal use
Indigenous Australians from the Tjupan language group use honeypot ant honey to treat sore throats, and as a topical ointment to treat skin infections. A Sydney University study has investigated the efficacy of honey from Camponotus inflatus, and found it effective against the bacterium Staphylococcus aureus, and the fungi Aspergillus and Cryptococcus. The antimicrobial mechanism is significantly different to that of Mānuka honey.
| Biology and health sciences | Hymenoptera | Animals |
321957 | https://en.wikipedia.org/wiki/M4%20carbine | M4 carbine | The M4 carbine (officially Carbine, Caliber 5.56 mm, M4) is a 5.56×45mm NATO assault rifle developed in the United States during the 1980s. It is a shortened version of the M16A2 assault rifle. The M4 is extensively used by the US military, with decisions to largely replace the M16 rifle in US Army (starting 2010) and US Marine Corps (starting 2016) combat units as the primary infantry weapon and service rifle. The M4 has been adopted by over 60 countries worldwide, and has been described as "one of the defining firearms of the 21st century".
Since its adoption in 1994, the M4 has undergone over 90 modifications to improve the weapon's adaptability, ergonomics and modularity, including: the M4A1, which strengthened the barrel and replaced the burst-fire option with a fully automatic option; the SOPMOD, an accessory kit containing optical attachments; and the underbarrel weapons such as M203 and M320 grenade launchers to the Masterkey and M26-MASS shotguns.
In April 2022, the U.S. Army selected the XM7 rifle, a variant of SIG MCX Spear, as the winner of the Next Generation Squad Weapon Program to replace the M16/M4.
History
Development of the M4
Following the military adoption of the Armalite AR-15 as the M16 rifle, carbine variants were also adopted for CQC operations, the first of which was the CAR-15 family of weapons, which was used in the Vietnam War. However, these rifles had design issues, as the barrel length was halved to , which upset the ballistics, reducing its range and accuracy and leading to considerable muzzle flash and blast, meaning that a large flash suppressor had to be fitted.
In 1982, the U.S. Government requested Colt to make a carbine version of the M16A2. At the time, the Colt M16A2 was the Colt 645, also known as the M16A1E1. Later that year, the U.S. Army Armament Munitions Chemical Command helped Colt develop a new variant of the XM177E2, and the U.S. Army redesignated the XM177E2 to the XM4 Carbine, giving the name as the successor to the M3 carbine. The carbine used the same upper and lower receiver as the M16A1, and fires the M855 cartridge along with the older M193 cartridges. In 1983, the 9th Infantry Division requested a Quick Reaction Program (QRP) for a 5.56mm carbine to replace the M1 carbine and M3 submachine gun in service. The XM4 was tested by the Army's Armament Research and Development Center (ARDC) in June 1983. Later, the gun was updated with improved furniture, and a barrel with rifling of 1 turn in . The ARDC recommended additional commonality with the M16A2 rifle, as well as lengthening the barrel to . In January 1984, the U.S. Army revised the QRP, and a month later, it formally approved development of the new carbine.
In June 1985, the Picatinny Arsenal was given a contract to produce 40 prototypes of the XM4. Initially a joint program between the Army and Marines, in 1986 the Army withdrew their funding. The XM4 was finished in 1987, and the Marines adopted 892 for that fiscal year, with the designation "carbine, 5.56mm, M4". Owing to experience from the 1991 Gulf War, the Army gave Colt its first production contracts for M4 carbines in May and July 1993, and M4A1 carbines for United States Special Operations Command (SOCOM) operators in February 1994.
Interest in the M4 carbine was accelerated after the Battle of Mogadishu (1993), in which Rangers complained that their M16 rifles were "unwieldy", whereas members of Delta Force in the same battle, equipped with the CAR-15, had no such complaints. The M4 carbine first saw action in the hands of U.S. troops deployed to Kosovo in 1999 in support of the NATO-led Kosovo Force. It would subsequently be used heavily by U.S. forces during the war on terror, including in Operation Enduring Freedom and the Iraq War. In the Army, the M4 had largely replaced M16A2s as the primary weapon of forward deployed personnel by 2005. The M4 carbine also replaced most submachine guns and selected handguns in U.S. military service, as it fires more effective rifle ammunition that offers superior stopping power and is better able to penetrate modern body armor.
In 2007, the USMC ordered its officers (up to the rank of lieutenant colonel) and staff non-commissioned officers to carry the M4 carbine instead of the M9 handgun. This is in keeping with the Marine Corps doctrine, "Every Marine a rifleman." The Marine Corps, however, chose the full-sized M16A4 over the M4 as its standard infantry rifle. United States Navy corpsmen E5 and below are also issued M4s instead of the M9. While ordinary riflemen in the Marine Corps were armed with M16A4s, M4s were fielded by troops in positions where a full-length rifle would be too bulky, including vehicle operators, fireteam and squad leaders. As of 2013, the U.S. Marine Corps had 80,000 M4 carbines in their inventory.
By July 2015, major Marine Corps commands were endorsing switching to the M4 over the M16A4 as the standard infantry rifle, just as the Army had done. This is because of the carbine's lighter weight, compact length, and ability to address modern combat situations that happen mostly within close quarters; if a squad needs to engage at longer ranges, the M27 Infantry Automatic Rifle can be used as a designated marksman rifle. Approval of the change would move the M16 to support personnel, while armories already had the 17,000 M4s in the inventory needed to outfit all infantrymen who needed one. In October 2015, Commandant Robert Neller formally approved of making the M4 carbine the primary weapon for all infantry battalions, security forces, and supporting schools in the USMC. The switch was to be completed by September 2016. In December 2017, the Marine Corps revealed a decision to equip every Marine in an infantry squad with the M27, while the M4 would be retained for leadership billets at the platoon level and above. MARSOC also retains the M4, as its shorter barrel is more suited to how they operate in confined spaces.
Improved M4
In 2009, the U.S. Army took complete ownership of the M4 design. This allowed companies other than Colt to compete with their own M4 designs. The Army planned on fielding the last of its M4 requirement in 2010. In October 2009, Army weapons officials proposed a series of changes to the M4 to Congress. Requested changes included an electronic round counter that records the number of shots fired, a heavier "SOCOM barrel", and possibly replacing the Stoner expanding gas system with a gas piston system. The heavier "SOCOM barrel" was first issued to special forces operators in the early 2000s to enable greater sustained automatic fire in certain immediate-action drills, although SOCOM itself would eventually return to the standard "government profile" barrel in its subsequent M4 improvement programs.
The benefits of these changes, however, have come under scrutiny from both the military and civilian firearms community. According to a PDF detailing the M4 Carbine improvement plans released by PEO Soldier, the direct impingement system would be replaced only after reviews were done comparing the direct impingement system to commercial gas piston operating system to find out and use the best available operating system in the U.S. Army's improved M4A1.
In September 2010, the Army announced it would buy 12,000 M4A1s from Colt Firearms by the end of 2010, and would order 25,000 more M4A1s by early 2011. Additionally, the service branch planned to buy 12,000 M4A1 conversion kits in early 2011 and bought 65,000 more later that year. Eventually, the Army would upgrade all of its M4s to M4A1s, although the Marine Corps would largely abstain from the effort. Conversion of M4s to the M4A1 in the Army began in 2011, as part of the Product Improvement Program, which included the conversion of 300,000 M4 carbines to the M4A1. The 101st Airborne Division began fielding newly built M4A1s in 2012, and the U.S. 1st Infantry Division became the first unit to convert their M4s to M4A1-standard in May 2014. Upgrades included the heavier SOCOM barrel to better dissipate heat from sustained automatic firing, the full-auto trigger group with a more consistent trigger pull than the burst group's to enable better semi-automatic accuracy, and the ambidextrous selector lever for easier use with left-handed shooters. The M4-M4A1 conversion increases weapon weight from to , counting a back-up iron sight, forward pistol grip, empty magazine, and sling. Each carbine upgrade costs $240 per rifle, for a total cost of $120 million for half a million conversions. Three hundred conversions can be done per day to equip a brigade combat team per week, with all M4A1 conversions to be completed by 2019.
In addition to upgrade kits, in April 2012, the U.S. Army announced it would begin purchasing over 120,000 M4A1 carbines to start reequipping front line units from the original M4 to the new M4A1 version. The first 24,000 were to be made by Remington Arms Company. Remington was to produce the M4A1s from mid-2013 to mid-2014. After completion of that contract, it was to be between Colt and Remington to produce over 100,000 more M4A1s for the U.S. Army. Because of efforts from Colt to sue the Army to force them not to use Remington to produce M4s, the Army reworked the original solicitation for new M4A1s to avoid legal issues from Colt. On 16 November 2012, Colt's protest of Remington receiving the M4A1 production contract was dismissed. Instead of the contract being re-awarded to Remington, the Army awarded the contract for 120,000 M4A1 carbines worth $77 million to FN Herstal on 22 February 2013. The order was expected to be completed by 2018.
Replacement efforts
Replacements for the M4 have mostly focused on two factors: improving its reliability, and its penetration. The first attempt to find a replacement for the M4 came in 1986, with the Advanced Combat Rifle program, in which the caseless Heckler & Koch G11 and various flechette rifles were tested, but this was quickly dropped as these designs were mostly prototypes, which demonstrated a lack of reliability. In the 1990s, the Objective Individual Combat Weapon competition was put forth to find a replacement for the M4. Two designs were produced, both by Heckler & Koch: the XM29 OICW, which incorporated a smart grenade launcher, but was canceled in 2004 as it was too heavy, and the XM8, which was canceled in 2005 as it did not offer significant enough improvements over the M4.
The Heckler & Koch HK416 was introduced in 2005, incorporating the same lower receiver as the M4A1, but replacing its direct impingement system with a gas-operated rotating bolt, more comparable to that of the G36. The HK416 was adopted by the Navy SEALs, Delta Force, and other special forces. In 2010, it was adopted by the Marines as the M27 Infantry Automatic Rifle. The same year, the Rangers and Navy SEALs adopted the FN SCAR, but later withdrew their purchase, as it was not a significant enough improvement over the M4A1.
Individual Carbine
The U.S. Army briefly had a tender in 2011 called the Individual Carbine, which solicited proposals for a potential M4 carbine replacement, but this was canceled in 2013 after determining that none of the entrants offered an adequate improvement over the M4.
For the Individual Carbine competition, Colt submitted their Enhanced M4 design, also known as the Colt Advanced Piston Carbine (APC). The weapon has a suppression-ready fluted barrel, which is lighter and cools better than previous M4 barrels. It is claimed to have "markedly better" accuracy. To improve reliability, Colt used an articulating link piston (ALP), which "reduces the inherent stress in the piston stroke by allowing for deflection and thermal expansion". In traditional short-stroke gas piston operating systems designed for the AR platform, the force of the piston striking the bolt carrier can push the bolt carrier downwards and into the wall of the buffer tube, leading to accelerated wear and even chipped metal. This is known as carrier tilt. The ALP allows the operating rod to wiggle to correct for the downward pressure on the bolt and transfers the force straight backwards in line with the bore and buffer assembly, eliminating the carrier tilt. This relieves stress on parts and helps to increase accuracy. The Individual Carbine competition was canceled before a winning weapon was chosen.
Next Generation Squad Weapon
After the failure of the Individual Carbine program, the Next Generation Squad Weapon (NGSW) was started in 2017. The program aimed to replace the M4 Carbine and the M249 SAW with weapons that would compensate for their perceived deficiencies when fighting at longer ranges, as well as addressing concerns about the effectiveness of traditional 5.56x45mm ammunition against troops wearing body armor in a future peer or near-peer conflict. In order to achieve these goals, all weapon submissions were to be chambered in a new 6.8x51 mm caliber. SIG Sauer, Textron Systems, FN Herstal, True Velocity (previously Lonestar Future Weapons and General Dynamics), and PCP Tactical took part in the program. Textron submitted a cased-telescoped (CT) ammunition-firing rifle for the program; FN Herstal submitted their HAMR IAR re-chambered in 6.8mm caliber; PCP Tactical submitted a modified Desert Tech MDRx; SIG Sauer submitted a redesigned MCX variant known as the MCX-SPEAR. In early 2022, the program concluded, with SIG Sauer being declared the winner. Their rifle entry was designated the XM5 (later changed to XM7 to avoid confusion with the Colt M5), and the XM250 Squad Automatic Weapon. Operational testing and fielding were scheduled for 2024.
Design
The M4, and its variants, is a lightweight 5.56×45mm NATO (and .223 Remington) caliber, gas-operated, magazine-fed, air-cooled selective fire AR-15-pattern firearm. Its gas operation consists of an internal piston (often incorrectly referred to as direct impingement), a rotating bolt, and bolt carrier that reciprocates into a receiver extension that is inline with the barrel. The gas system, bolt carrier, and bolt-locking design is ammunition specific, since it does not have an adjustable gas port or valve to adjust the weapon to various propellant and projectile or barrel length specific pressure behavior. The receiver is made of forged 7075-T6 aluminum, while the barrel, bolt, bolt carrier, and fire control group are made of steel; these components can be easily serviced and replaced by unit armories, enabling the addition of enhanced components and thus making the platform readily upgradable. The flattop upper receiver's Picatinny rail enables the replacement of the removable carrying handle with various optics. The furniture, including the buttstock, grip, and handguard are made of reinforced plastic, although the modular nature of the weapon means that these can be swapped by the end user. The receiver extension can accommodate either a multi-position telescoping stock or a fixed A2 or LE tactical stock. The M4 is a shorter and lighter variant of the M16A2 rifle, sharing much of the same operation mechanisms and has 80% parts commonality; the chief differences are a shorter barrel of 14.5 inches rather than 20 inches as well as a shortened receiver extension and buffer.
Two fire control groups exist for the M4 family, the three-round burst for the baseline model and the fully automatic for the M4A1. Some M4A1 may also have a heavier profile barrel initially developed for SOCOM for prolonged automatic fire; models with this heavier "SOCOM profile" barrel use the same M4A1 designation, and existing weapons can swap to the heavier profile barrel at the unit armory level. Despite being its namesake, SOCOM itself has reverted to the original lighter "government profile" barrel while adopting a longer "mid length" gas system with its newer Upper Receiver Group-Improved (URG-I) modifications. As the modifications only affect the upper receiver assembly, rifles with the URG-I still retain the M4A1 designation.
The M4's maneuverability makes it beneficial for non-infantry troops (vehicle crews, clerks and staff officers), as well as for close quarters battle. The M4, along with the M16A4, has mostly replaced the M16A2 in the Army and Marines. The U.S. Air Force, for example, has transitioned completely to the M4 for Security Forces squadrons, while other armed personnel retain the M16A2. The U.S. Navy uses M4A1s for Special Operations and vehicle crews. However, the M4's shorter barrel reduces its range, with its rear iron sights integrated in the (removable) carry handle only adjustable from up to , compared to the M16A2 rear iron sights integrated in the fixed carry handle, which can reach up to .
Accessories
Like all the variants of the M16, the M4 and the M4A1 can be fitted with many accessories, such as slings, night-vision devices, flash suppressors, suppressors, laser sights, telescopic sights, bipods, M9 bayonet, either M203 or M320 grenade launcher, M26-MASS shotgun, forward hand grips, a detachable rail-mounted carrying handle, or anything else compatible with a MIL-STD-1913 picatinny rail.
Other common accessories include the AN/PEQ-2, AN/PEQ-15 multi-mode laser, AN/PEQ-16 Mini Integrated Pointing Illumination Module (MIPIM), Trijicon TA01 and TA31 Advanced Combat Optical Gunsights (ACOG), EOTech 550 series holographic sights, and Aimpoint M68 Close Combat Optic. Visible and infrared lights of various manufacturers are commonly attached using various mounting methods. As with all versions of the M16, the M4 accepts a blank-firing attachment (BFA) for training purposes.
The M4 and the M4A1 feed from 30-round STANAG magazines. Other types of STANAG compatible magazines with different capacities may also be used. In January 2017, a USMC unit deployed with suppressors mounted to every infantry M4 service weapon. Exercises showed that having all weapons suppressed improved squad communication and surprise during engagements; disadvantages included additional heat and weight, increased maintenance, and the greater cost of equipping so many troops with the attachment. In July 2020, the Marine Corps announced it would be ordering suppressors for use by all M4 carbines used by close combat units. The Marines began to roll out suppressors for all M4/M4A1 carbines in infantry, reconnaissance and special operations units in December 2020.
Special Operations Peculiar Modification
In 1992, U.S. Special Operations Command (USSOCOM) developed the Special Operations Peculiar Modification (SOPMOD) Block I kit for the carbines used by US Special Operations Forces units operating under its command. The kit features an M4A1, a Rail Interface System (RIS) handguard developed by Knight's Armament Company (KAC), a shortened quick-detachable M203 grenade launcher and leaf sight, a KAC sound suppressor, a KAC back-up rear sight, an Insight Technologies AN/PEQ-2A visible laser/infrared designator, along with Trijicon's ACOG TA-01NSN model and Reflex sights, and a night vision sight, among many other accessories. This kit was designed to be configurable (modular) for various missions, and the kit is currently in service with special operations units.
In 2002, the Block II modification kit was adopted featuring two new upper receivers: the Special Purpose Receiver (SPR) with a barrel and Close Quarter Battle Receiver (CQBR) with a barrel. M4A1s fitted with the SPR were designated by the Navy as the Mk 12 Special Purpose Rifle, a type of designated marksman rifle. M4A1s with the CQBR were designated the Mk 18 Mod 0. The Block II program then focused on component improvements to the M4A1, with the adoption of the heavier "SOCOM profile" barrel in 2004 and free-float Rail Interface System II (RIS-II) handguard from Daniel Defense in 2008. Owing to the modularity of the AR-15/M4 platform, some operators have replaced issued optics, handguards, and buttstocks with aftermarket ones.
In 2018, the Upper Receiver Group-Improved (URG-I) modification kit (unofficially the Block III) was approved for the conversion of Block I and Block II carbine's upper receiver "to an improved barrel and rail assembly.." which includes a lighter free-float handguard from Geissele Automatics that incorporates the Magpul Industries M-LOK rail interface system. The URG-I also replaces the Block II's heavier barrel with a standard "government profile" cold hammer forged barrel with a longer gas system.
Variants
The initial order of M4 carbines had a fixed carrying handle and rear sight similar to the M16A2. The flattop upper receiver with the Picatinny rail was introduced with the M4A1 variant in 1994, and all subsequent orders for all M4 variants would have a flattop upper receiver. Variants of the carbine built by different manufacturers are also in service with many other foreign special forces units, such as the Australian Special Air Service Regiment (SASR). While the SASR uses weapons of essentially the same pattern built by Colt for export (Colt uses different models to separate weapons for the U.S. military and those for commercial/export purposes), the British Special Air Service uses a variant on the basic theme, the Colt Canada C8SFW.
M4 MWS (Modular Weapon System)
Colt Model 925 carbines were tested and fitted with the KAC M4 RAS under the designation M4E2, but this designation appears to have been scrapped in favor of mounting this system to existing carbines without changing the designation. The U.S. Army Field Manual specifies for the Army that adding the Rail Adapter System (RAS) turns the weapon into the M4 MWS or modular weapon system.
M4A1
The M4A1 carbine is a fully automatic variant of the basic M4 carbine. The M4A1 was developed in May 1991 and entered service in 1994; starting in 2014 the U.S. Army began upgrading all of its existing M4s to the M4A1 standard. The M4A1 was the first M4 model with the removable carry handle. The M4A1 has a "S-1-F" (safe/semi-automatic/fully automatic) trigger group, while the M4 has a "S-1-3" (safe/semi-automatic/3-round burst) trigger group. The M4A1 is used by almost all U.S. special operation units; and is the standard service rifle across the U.S. Army (including conventional forces). It has a maximum effective range of . The fully automatic trigger gives a more consistent trigger pull, which leads to better accuracy. According to Mark Westrom, owner of ArmaLite, Inc., automatic fire is better for clearing rooms than burst fire.
A subvariant of the M4A1 uses a heavier barrel than the standard M4, as the regular M4 barrel, which can fire 6,000 rounds before requiring inspection for possible replacement, was not sufficient for the higher consumption of ammunition by SOCOM operators. The redesigned barrel, colloquially referred to as the "SOCOM barrel", has an increased diameter in the area between the receiver and front sight. Despite the different barrel profile, this subvariant did not receive a new designation, and was still referred to as the M4A1. Ironically, SOCOM itself would dispense with its namesake heavier barrel and return to the original "government profile" with its Upper Receiver Group-Improved (URG-I) program's mid-length gassed, cold hammer forged barrels.
Mk 18 CQBR
The Close Quarters Battle Receiver (CQBR) was originally a Special Operations Peculiar Modification (SOPMOD) program item that would increase the close quarters maneuverability of the M4A1 by mating the lower receiver with a barreled upper receiver; with the CQBR installed, the weapon would then be classified as the Mk. 18 CQBR. The Mk. 18 CQBR may be issued as a standalone complete weapon system to SOCOM personnel, or as a separate upper receiver for their M4A1 to enable greater mission flexibility.
Mk 12 SPR
The SOPMOD program also introduced the Special Purpose Receiver (SPR), a barreled upper receiver that would be mated to an M4A1 lower receiver to allow the weapon to serve as a designated marksman rifle (DMR). Although originally intended as an upper receiver kit for the M4A1 like the CQBR, the SPR would eventually be issued as a standalone complete rifle designated the Mk. 12 Special Purpose Rifle, with some assembled from M4A1 lower receivers.
SOPMOD Block II
The SOPMOD Block II is a more radical modification kit for the baseline M4A1 that can be fitted at first-echelon unit maintenance level. Components of the Block II were phased in gradually, but the most distinctive feature is the free-floated Daniel Defense Rail Interface System II (RIS II), first issued in 2008. The RIS II is available in 9.5 inches for the Mk 18 Mod 1 or 12.5 inches for the M4A1. Other components of the Block II include the L3 Advanced Target Pointer Illuminator Aiming Laser (ATPIAL), or the AN/PEQ-15 as well as the LA5 high-power variants, and the ELCAN SpecterDR 1-4 optic.
Upper Receiver Group-Improved (URG-I)
The Upper Receiver Group-Improved (URG-I) is a U.S. Army Special Operations Command (USASOC) program to further improve the durability and reliability of the SOPMOD Block II by introducing additional component improvements. First fielded in 2018, the main improvements are the lighter Geissele Mark 16 free-float rail that incorporates M-LOK as the mounting method and a Daniel Defense cold hammer-forged barrel that returns to the lighter "government" profile contour as well as a mid-length gas system. Although initially an Army program, the URG-I has seen use by other components of SOCOM as well.
GAU-5/A
The GAU-5/A Aircrew Self Defense Weapon (ASDW) is an Air Force modified M4 with a detachable barrel and handguard assembly, folding pistol grip, and fold-down iron sights to enable compact packaging. This weapon is stowed in ejection seats of tactical aircraft and is intended to allow aircrew who egress in hostile environments to better defend themselves until rescue than existing handguns. The weapons entered service in 2018. Confusingly, this weapon shares the same designation as the Air Force CAR-15 variant in service since 1966.
Performance
The M4 carbine has been used for close quarters operations where the M16 would be too long and bulky to use effectively. It has been a compact, light, customizable, and accurate weapon. Like other firearms, failure to properly maintain the M4 can result in malfunctions. This became apparent as it saw continued use in the sandy environments of Iraq and Afghanistan. Despite this, in post-combat surveys, 94% of soldiers rated the M4 as an effective weapons system.
2006 CNA report
In December 2006, the Center for Naval Analyses (CNA) released a report on U.S. small arms in combat. The CNA conducted surveys on 2,608 troops returning from combat in Iraq and Afghanistan over the previous 12 months. Only troops who fired their weapons at enemy targets were allowed to participate. 917 troops were armed with M4 Carbines, making up 35% of the survey. 89% of M4 users reported they were satisfied with the weapon. 90% were satisfied with handling qualities such as handguards, size, and weight. M4 users had the highest levels of satisfaction with weapon performance, including 94% with accuracy, 92% with range, and 93% with rate of fire. Only 19% of M4 users reported a stoppage, and 82% of those that experienced a stoppage said it had little impact on their ability to clear the stoppage and re-engage their target. The lowest rated weapon was the M9, and the M249 had the highest rate of stoppages. 53% of the M4 users never experienced failures of their magazines to feed. 81% did not need their rifles repaired while in theater. 80% were confident in the M4's reliability, defined as confidence their weapon will fire without malfunction, and 83% were confident in its durability, defined as confidence their weapon will not break or need repair. Both factors were attributed to high levels of soldiers performing their own maintenance. 54% of M4 users offered recommendations for improvements. 20% of requests were for greater bullet lethality, and 10% were for better quality magazines, as well as other minor recommendations. Only 75% of M16 users were satisfied with it, and some expressed their desire to be issued the M4. Some issues from this report have been addressed with the issuing of the improved STANAG magazine in March 2009, and the M855A1 Enhanced Performance Round in June 2010.
2007 dust test
In summer and fall 2007, the Army tested the M4 against three other carbines in "sandstorm conditions" at Aberdeen Proving Ground, Maryland: the Heckler & Koch XM8, Fabrique Nationale de Herstal SOF Combat Assault Rifle (SCAR) and the Heckler & Koch HK416. Ten of each type of rifle were used to fire 6,000 rounds each, for a total of 60,000 rounds per rifle type. The M4 suffered far more stoppages than its competitors: 882 stoppages, 19 requiring an armorer to fix. The XM8 had the fewest stoppages, 116 minor stoppages and 11 major ones, followed by the FN SCAR with 226 stoppages and the HK416 with 233.
Despite 863 minor stoppages—termed "class one" stoppages, which require 10 seconds or less to clear, or "class two" stoppages, which require more than ten seconds to clear—the M4 functioned well, with over 98% of the 60,000 total rounds firing without a problem. The Army said it planned to improve the M4 with a new cold-hammer-forged barrel to give longer life and more reliable magazines to reduce the stoppages. Magazine failures caused 239 of the M4's failures. Army officials said the new magazines could be combat-ready by spring if testing went well. The Army began issuing an improved STANAG magazine in March 2009.
According to the Army, the M4 only suffered 296 stoppages and said that the high number reported could be attributed to discrepancies in the scoring process. The Army testing command stated that, if the number of stoppages caused by a broken part met some threshold, they would be eliminated from the final report pending redesign of the part. The methodology of the test has been debated, as many of the M4s in the test had already seen use, whereas the other rifles were brand new, and that the wide variance in results between summer and fall showed that the test was not accurate, as it was not repeatable with consistent results. Furthermore, the trial M4s had burst-mode fire groups, which are more complicated and prone to failure than the fully automatic fire groups the other manufacturers presented for testing.
There were three extreme dust tests performed in 2007. The second test results showed a large difference from the last test with the M4 having 148 class 1 stoppages caused by rifle malfunctions and 148 class 1 stoppages caused by magazine stoppages. The full-size M16 rifle had 61 stoppages during the same extreme dust test.
Reliability
In early 2010, two journalists from the New York Times spent three months with soldiers and Marines in Afghanistan. While there, they questioned around 100 infantrymen about the reliability of their M4 carbines, as well as the M16 rifle. Troops did not report reliability problems with their rifles. While only 100 troops were asked, they fought at least a dozen intense engagements in Helmand Province, where the ground is covered in fine powdered sand (called "moon dust" by troops) that can stick to firearms. Weapons were often dusty, wet, and covered in mud. Intense firefights lasted hours with several magazines being expended. Only one soldier reported a jam when his M16 was covered in mud after climbing out of a canal. The weapon was cleared and resumed firing with the next chambered round. Furthermore, a Marine chief warrant officer reported that there were no issues with his battalion's 700 M4s and 350 M16s.
The reliability of the M4 has increased as the design was upgraded. In 1990, the M4 was required to fire 600 mean rounds between stoppages using M855 ammunition. In 2013, the current M4A1 version can fire 1,691 mean rounds between stoppages using M855A1 ammunition. During the 2009 Marine Corps Infantry Automatic Rifle testing, the Colt IAR displayed a MRBS of CLASS I/II Stoppages of 952 rounds, with a MRBEFF (Mean Rounds Between Essential Function Failure) of Class III Stoppages of 60,000 rounds.
Gas piston
An array of firearms accessory makers have offered gas piston conversion kits for the M4. The claimed benefits include less needed lubrication for the bolt carrier group to run reliably and reduced fouling. The argument against it is increased weight and reduced accuracy. The Enhanced M4 uses an articulating link piston operating system. Complicating the Army search for higher reliability in the M4 is a number of observations of M4 gas piston alternatives that suffer unintended design problems. The first is that many of the gas piston modifications for the M4 isolate the piston so that piston jams or related malfunction require the entire weapon be disassembled, such disassembly cannot be performed by the end-user and requires a qualified armorer to perform out of field, whereas almost any malfunction with the direct-impingement system can be fixed by the end-user in field. The second is that gas piston alternatives use an off-axis operation of the piston that can introduce carrier tilt, whereby the bolt carrier fails to enter the buffer tube at a straight angle, resulting in part wearing. This can also tilt the bolt during extraction, leading to increased bolt lug failures. The third is that the use of a sound suppressor results in hot gases entering the chamber, regardless of a direct-gas impingement or gas piston design choice. The gas piston system may also cause the firearm to become proprietary to the manufacturer, making modifications and changes with parts from other manufacturers difficult.
Accuracy
In a study conducted by the Army Marksmanship Unit, they found that at a distance of , the M16 achieved a grouping, and the M4 achieved a grouping, which dropped to and respectively when using match grade ammunition. As the average male torso is wide, author Chris McNab concluded that this meant the M4 can be consistently accurate up to 300 yards, and noted that the frequent usage of optical attachments meant it could be accurate to higher ranges.
ArmWest, LLC modified M4
In 2014, American firearms designer Jim Sullivan provided a video interview regarding his contributions to the M16 and M4 family of rifles while working for Armalite. A noted critic of the M4, he illustrates the deficiencies found in the rifle in its current configuration. In the video, he demonstrates his "ArmWest, LLC modified M4", with enhancements he believes necessary to rectify the issues with the weapon. Proprietary issues aside, the weapon is said to borrow features in his prior development, the Ultimax. Sullivan has stated (without exact details as to how) the weapon can fire from the closed bolt in semi-automatic and switch to open bolt when firing in fully automatic, improving accuracy. The weight of the cyclic components of the gun has been doubled (while retaining the weapon's weight at less than 8 pounds). Compared to the standard M4, which in automatic fires 700–950 rounds a minute, the rate of fire of the ArmWest, LLC M4 is heavily reduced both to save ammunition and reduce barrel wear. The reduced rate also renders the weapon more controllable and accurate in automatic firing.
Manufacturers
Colt's Manufacturing Company, US
Remington Arms Company, US
FN Herstal, Belgium
SME Ordnance, Malaysia
Sarsılmaz, Turkey
United Defense Manufacturing Corporation, Philippines
Trademark issues
The M4 was developed and produced for the United States government by Colt Firearms, which had an exclusive contract to produce the M4 family of weapons through 2011. However, a number of other manufacturers offer M4-like firearms. Colt previously held a U.S. trademark on the term "M4". Many manufacturers offer production firearms that are essentially identical to a military M4, but with a barrel. The Bushmaster M4 Type Carbine is a popular example. Civilian models are sometimes colloquially referred to as "M4gery" ( , a portmanteau of "M4" and "forgery.") Colt had maintained that it retained sole rights to the M4 name and design, while other manufacturers had long maintained that Colt had been overstating its rights, and that "M4" had now become a generic term for a shortened AR-15.
In April 2004, Colt filed a lawsuit against Heckler & Koch and Bushmaster Firearms, claiming acts of trademark infringement, trade dress infringement, trademark dilution, false designation of origin, false advertising, patent infringement, unfair competition, and deceptive trade practices. Heckler & Koch later settled out of court, changing one product's name from "HK M4" to "HK416". However, on December 8, 2005, a district court judge in Maine granted a summary judgment in favor of Bushmaster Firearms, dismissing all of Colt's claims except for false advertising. On the latter claim, Colt could not recover monetary damages. The court also ruled that "M4" was now a generic name and that Colt's trademark should be revoked.
Users
Afghanistan: Former Afghan National Army commando stocks in use by the Taliban.
: Used by Albanian Land Force 2015.
: M4/M4A1s announced to be sold via FMS program in 2017.
: Used by Argentine Army, Argentine Navy and Argentine National Gendarmerie
: M4A1 (designated M4A5), used by Special Operations Command, Clearance Divers, and Police Tactical Groups.
: M4 Carbine used by the special military units and State Border Service (DSX).
: M4A1s sold as a 2008 Foreign Military Sales package. More M4/M4A1s announced to be sold via FMS program in 2017.
: M4s/M4A1s sold as part of a 2006 Foreign Military Sales package. More M4/M4A1s announced to be sold via FMS program in 2017.
: M4A1s used by the military and air guard units.
: M4s used by UMOPAR and GTIDE units of the Policia Nacional. M4A1 in use with rangers.
: Used by Civil Police, Military Police of Espirito Santo State, Military Police of Rio de Janeiro State, the Brazilian Federal Police and Special Forces of the Brazilian Army, Brazilian Navy.
: User since 2003, several hundred purchased for Croatian ISF contingent as well as Special Forces.
: Bushmaster M4A3 B.M.A.S., Daniel Defense M4A1 and MK18 is used by (601st Special forces group, Military police, 43rd Airborne mechanized battalion) of Czech Army.
: A variant is made by Norinco as the Norinco CQ. CQ-A carbine variant used by the Sichuan Police Department, Chongqing SWAT teams, and the Snow Leopard Commando Unit.
: M4A1s as part of a 2008 Foreign Military Sales. More M4/M4A1s announced to be sold via FMS program in 2017.
: M4s sold as a 2008 Foreign Military Sales package.
: M4s sold as part of a 2007 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package.
: Used by the 1er RPIMa
: Bushmaster M4s being replaced by Colt M4s for the military. More M4/M4A1s announced to be sold via FMS program in 2017. Joint Georgian-Israeli production M4 based "GI-4" launched in 2021
: M16A2s and M4s are used by the "Special Forces" branch as well as by the airborne battalions of the Hellenic Army.
: M4A1 SOPMOD by Hungarian MH 34th Bercsényi László special operation battalion More M4/M4A1s announced to be sold via FMS program in 2017.
: M4A1s as part of a 2008 Foreign Military Sales. M4A1 is used by the Mizoram Armed Police, PARA SF and Force One of the Mumbai Police.
: Used by Detachment 88 Counter-terrorism Police Squad operators. Also used by Komando Pasukan Katak (Kopaska) tactical diver group and Komando Pasukan Khusus (Kopassus) special forces group.
: Used by the Iraqi Army. Main weapon of the Iraqi National Counter-Terrorism Force. More M4/M4A1s announced to be sold via FMS program in 2017.
: Used by Peshmerga.
: Sold as part of a January 2001 Foreign Military Sales package to Israel. Standard issue in the Israel Defense Forces, but it has been gradually replaced with the IWI Tavor since 2001.
: Special Forces
: M4s sold as part of a 2007 Foreign Military Sales package.
: M4A1s as part of a 2008 Foreign Military Sales package. M4A1 SOPMOD rifles are in use by the Japanese Special Forces Group, but is supposedly denied by the JGSDF after Ishiba was arrested for violating American export laws.
: M4s sold as part of a 2007 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package. More M4/M4A1s announced to be sold via FMS program in 2017.
: Used by Kenyan troops Kenya Defence Forces in AMISOM ops.
: M4 components being sold to Lebanese special forces. M4/M4A1s sold as a 2008 Foreign Military Sales package. More M4/M4A1s announced to be sold via FMS program in 2017.
: Made under license by SME Ordnance Sdn Bhd. Used by military and police special forces.
: 1,070 M4s, sold as part of a 2005 Foreign Military Sales package.
: Used by NZSAS operators and standard issue to New Zealand Police including Special Tactics Group and Armed Offenders Squad units.
: Used by the Army of North Macedonia
: M4/M4A1s announced to be sold via FMS program in 2017.
: M4A1 variant used by the Special Forces of the Pakistani military besides the POF G3P4 standard rifle for the Pakistani military— also used by the Special Security Unit (SSU) of the Sindh Police. More M4/M4A1s announced to be sold via FMS program in 2017.
: Used by Palestinian security forces.
: M4A1s sold as a 2008 Foreign Military Sales package. More M4/M4A1s announced to be sold via FMS program in 2017.
: Airforce Special Group and anti-narcotics units
: Colt M4/M4A1s sold as a 2008 Foreign Military Sales package. 63,000 R4A3 rifles from Remington Arms for the Philippine Army and the Philippine Marine Corps. Several units also used by the Defense Intelligence and Security Group.
: Used by Wojska Specjalne military unit JW Grom.
: M4/M4A1s announced to be sold via FMS program in 2017.
: Used in limited quantities by FSB Alpha and spotted in hands of RuAF in a training exercise.
: M4/M4A1s announced to be sold via FMS program in 2017. 2,200 M4s sold through FMS program in 2019.
: Used by Gendarmery and Special Anti-Terrorist Unit.
: Used by the Commandos and the Police Coast Guard (only the Port Squadron and the Coastal Patrol Squadron) of the Singapore Police Force.
: M4/M4A1s announced to be procured via FMS program in 2017.
: 15000 M4A1s purchased directly from US Army stocks in 2024 to act as interim service weapons while awaiting full delivery of the new Automatkarbin 24
: Used by Republic of China Army and National Police Agency
: M4A1s sold as part of a 2006 Foreign Military Sales package.
: M4/M4A1s sold as a 2008 Foreign Military Sales package.
: Used by the Tunisian Army's Special Forces Group (GFS), 51st Infantry Navy Commandos Regiment, Presidential Guard and various National Guard and Police special forces units. Used by the Unité Spéciale – Garde Nationale.
: Produced under license by Sarsılmaz Firearms.
: Used by Ugandan troops in AMISOM ops.
: Purchased 2,500 M4 carbines in 1993.
: Colt M4 and Bushmaster M4 carbines for Special Operation Group (Metropolitan Police)
: M4s sold as part of a 2006 Foreign Military Sales package.
Former users
: Used by Afghan National Army commandos during the Taliban insurgency. M4s sold as part of a 2006 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package. Captured stocks currently in use with the Islamic Emirate of Afghanistan.
Conflicts
1990s
Colombian conflict (1964–present)
Civil conflict in the Philippines (1969–present)
Insurgency in Jammu and Kashmir (1989–present)
Kosovo War (1998–1999), first US military usage of the M4 carbine
2000s
War in Afghanistan (2001–2021)
Internal conflict in Peru
Iraq War (2003–2011)
South Thailand insurgency (2004–present)
2006 Lebanon War (2006)
Mexican drug war (2006–present)
Russo-Georgian War (2008)
Gaza War (2008–2009)
Insurgency in Paraguay
2010s
Syrian civil war (2011–present)
Lahad Datu standoff (2013)
War in Iraq (2013–2017)
Battle of Arsal (2014)
Yemeni civil war (2014–present)
Battle of Marawi (2017)
2020s
2021 Beirut clashes (2021)
Russian invasion of Ukraine (2022–present)
Israel–Hamas war (2023–present)
2024 Enga Clashes (2024)
| Technology | Specific firearms | null |
322091 | https://en.wikipedia.org/wiki/Beekeeping | Beekeeping | Beekeeping (or apiculture) is the maintenance of bee colonies, commonly in artificial beehives. Honey bees in the genus Apis are the most commonly kept species but other honey producing bees such as Melipona stingless bees are also kept. Beekeepers (or apiarists) keep bees to collect honey and other products of the hive: beeswax, propolis, bee pollen, and royal jelly. Other sources of beekeeping income include pollination of crops, raising queens, and production of package bees for sale. Bee hives are kept in an apiary or "bee yard".
The earliest evidence of humans collecting honey are from Spanish caves paintings dated 6,000 BCE, however it is not until 3,100 BCE that there is evidence from Egypt of beekeeping being practiced.
In the modern era, beekeeping is often used for crop pollination and the collection of its by products, such as wax and propolis. The largest beekeeping operations are agricultural businesses but many small beekeeping operations are run as a hobby. As beekeeping technology has advanced, beekeeping has become more accessible, and urban beekeeping was described as a growing trend as of 2016. Some studies have found city-kept bees are healthier than those in rural settings because there are fewer pesticides and greater biodiversity in cities.
History
Early history
At least 10,000 years ago, humans began to attempt to maintain colonies of wild bees in artificial hives made from hollow logs, wooden boxes, pottery vessels, and woven straw baskets known as skeps. Depictions of humans collecting honey from wild bees date to 10,000 years ago. Beekeeping in pottery vessels began about 9,000 years ago in North Africa. Traces of beeswax have been found in potsherds throughout the Middle East beginning about 7,000 BCE. Domestication of bees is shown in Egyptian art from around 4,500 years ago. Simple hives and smoke were used, and honey was stored in jars, some of which were found in the tombs of pharaohs such as Tutankhamun. In the 18th century, European understanding of the colonies and biology of bees allowed the construction of the movable comb hive so honey could be harvested without destroying the entire colony.
Honeybees were kept in Egypt from antiquity. On the walls of the sun temple of Nyuserre Ini from the Fifth Dynasty before 2,422 BCE, workers are depicted blowing smoke into hives as they remove honeycombs. Inscriptions detailing the production of honey are found on the tomb of Pabasa from the Twenty-sixth Dynasty , in which cylindrical hives are depicted along with people pouring honey into jars.
An inscription records the introduction of honey bees into the land of Suhum in Mesopotamia, where they were previously unknown:
The oldest archaeological finds directly relating to beekeeping have been discovered at Rehov, a Bronze and Iron Age archaeological site in the Jordan Valley, Israel. Thirty intact hives made of straw and unbaked clay were discovered in the ruins of the city, dating from about 900 BCE, by archaeologist Amihai Mazar. The hives were found in orderly rows, three high, in a manner that according to Mazar could have accommodated around 100 hives, held more than one million bees and had a potential annual yield of of honey and of beeswax, and are evidence an advanced honey industry in Tel Rehov, Israel 3,000 years ago.
In ancient Greece, in Crete and Mycenae, there existed a system of high-status apiculture that is evidenced by the finds of hives, smoking pots, honey extractors and other beekeeping paraphernalia in Knossos. Beekeeping was considered a highly valued industry controlled by beekeeping overseers—owners of gold rings depicting apiculture scenes rather than religious ones as they have been reinterpreted recently, contra Sir Arthur Evans.
Aspects of the lives of bees and beekeeping are discussed at length by Aristotle. Beekeeping was also documented by the Roman writers Virgil, Gaius Julius Hyginus, Varro, and Columella.
Beekeeping has been practiced in ancient China since antiquity. In a book written by Fan Li (or Tao Zhu Gong) during the Spring and Autumn period are sections describing beekeeping, stressing the importance of the quality of the wooden box used and its effects on the quality of the honey. The Chinese word for honey mi (), reconstructed Old Chinese pronunciation ) was borrowed from proto-Tocharian *ḿət(ə) (where *ḿ is palatalized; cf. Tocharian B mit), cognate with English .
The ancient Maya domesticated a species of stingless bee, which they used for several purposes, including making balché, a mead-like alcoholic drink. By 300 BCE they had achieved the highest levels of stingless beekeeping practices in the world. The use of stingless bees is referred to as meliponiculture, which is named after bees of the tribe Meliponini such as Melipona quadrifasciata in Brazil. This variation of beekeeping still occurs today. For instance, in Australia, the stingless bee Tetragonula carbonaria is kept for the production of honey.
Scientific study of honey bees
European natural philosophers began to scientifically study bee colonies in the 18th century. Eminent among these scientists were Swammerdam, René Antoine Ferchault de Réaumur, Charles Bonnet and François Huber. Swammerdam and Réaumur were among the first to use a microscope and dissection to understand the internal biology of honey bees. Réaumur was among the first to construct a glass-walled observation hive to better observe activities inside hives. He observed queens laying eggs in open cells but did not know how queens were fertilized; the mating of a queen and drone had not yet been observed and many theories held queens were "self-fertile" while others believed a vapor or "miasma" emanating from the drones fertilized queens without physical contact. Huber was the first to prove by observation and experiment that drones physically inseminate queens outside the confines of the hive, usually a great distance away.
Following Réaumur's design, Huber built improved glass-walled observation hives and sectional hives that could be opened like the leaves of a book. This allowed the inspection of individual wax combs and greatly improved direct observation of hive activity. Although he went blind before he was twenty, Huber employed a secretary named François Burnens to make daily observations, conduct experiment and keep accurate notes for more than twenty years. Huber confirmed a hive consists of one queen, who is the mother of every female worker and male drone in the colony. He was also the first to confirm mating with drones takes place outside hives and that queens are inseminated in successive matings with male drones, which occur high in the air at a great distance from the hive. Together, Huber and Burnens dissected bees under the microscope, and were among the first to describe the ovaries and spermatheca (sperm store) of queens, as well as the penis of male drones. Huber is regarded as "the father of modern bee-science" and his work Nouvelles Observations sur Les Abeilles (New Observations on Bees) revealed all of the basic scientific facts of the biology and ecology of honeybees.
Hive designs
Before the invention of the movable comb hive, the harvesting of honey frequently resulted in the destruction of the whole colony. The wild hive was broken into using smoke to quieten the bees. The honeycombs were pulled out and either immediately eaten whole or crushed, along with the eggs, larvae, and honey they held. A sieve or basket was used to separate the liquid honey from the demolished brood nest. In medieval times in northern Europe, although skeps and other containers were made to house bees, the honey and wax were still extracted after the bee colony was killed. This was usually accomplished by using burning sulfur to suffocate the colony without harming the honey within. It was impossible to replace old, dark-brown brood comb in which larval bees are constricted by layers of shed pupal skins.
The movable frames of modern hives are considered to have been developed from the traditional basket top bar (movable comb) hives of Greece, which allowed the beekeeper to avoid killing the bees. The oldest evidence of their use dates to 1669, although it is probable their use is more than 3,000 years old.
Intermediate stages in the transition from older methods of beekeeping were recorded in 1768 by Thomas Wildman, who described advances over the destructive, skep-based method so bees no longer had to be killed to harvest their honey. Wildman fixed an array of parallel wooden bars across the top of a straw hive in diameter "so that there are in all seven bars of deal to which the bees fix their combs", foreshadowing future uses of movable-comb hives. He also described using such hives in a multi-story configuration, foreshadowing the modern use of supers: he added successive straw hives below and later removed the ones above when free of brood and filled with honey so the bees could be separately preserved at the harvest the following season. Wildman also described the use of hives with "sliding frames" in which the bees would build their comb.
Wildman's book acknowledges the advances in knowledge of bees made by Swammerdam, Maraldi, and de Réaumur—he includes a lengthy translation of Réaumur's account of the natural history of bees. Wildman also describes the initiatives of others in designing hives for the preservation of bees when taking the harvest, citing reports from Brittany in the 1750s due to the Comte de la Bourdonnaye. Another hive design was invented by Rev. John Thorley in 1744; the hive was placed in a bell jar that was screwed onto a wicker basket. The bees were free to move from the basket to the jar, and honey was produced and stored in the jar. The hive was designed to keep the bees from swarming as much as they would have in other hive designs.
In the 19th century, changes in beekeeping practice were completed through the development of the movable comb hive by the American Lorenzo Lorraine Langstroth, who was the first person to make practical use of Huber's earlier discovery of a specific spatial distance between the wax combs, later called the bee space, which bees do not block with wax but keep as a free passage. Having determined this bee space, which is commonly given as between , though up to has been found in populations in Ethiopia. Langstroth then designed a series of wooden frames within a rectangular hive box, carefully maintaining the correct space between successive frames. He found the bees would build parallel honeycombs in the box without bonding them to each other or to the hive walls. This enables the beekeeper to slide any frame out of the hive for inspection without harming the bees or the comb; and protecting the eggs, larvae and pupae in the cells. It also meant combs containing honey could be gently removed and the honey extracted without destroying the comb. The emptied honeycombs could then be returned intact to the bees for refilling. Langstroth's book The Hive and Honey-bee (1853), describes his rediscovery of the bee space and the development of his patent movable comb hive. The invention and development of the movable comb hive enabled the growth of large-scale, commercial honey production in both Europe and the U.S.
20th and 21st century hive designs
Langstroth's design of movable comb hives was adopted by apiarists and inventors in both North America and Europe, and a wide range of moveable comb hives were developed in England, France, Germany and the United States. Classic designs evolved in each country; Dadant hives and Langstroth hives are still dominant in the U.S.; in France the De-Layens trough hive became popular, in the UK a British National hive became standard by the 1930s, although in Scotland the smaller Smith hive is still popular. In some Scandinavian countries and in Russia, the traditional trough hive persisted until late in the 20th century and is still kept in some areas. The Langstroth and Dadant designs, however, remain ubiquitous in the U.S. and in many parts of Europe, though Sweden, Denmark, Germany, France and Italy all have their own national hive designs. Regional variations of hive were developed according to climate, floral productivity and reproductive characteristics of the subspecies of native honey bees in each bio-region.
The differences in hive dimensions are insignificant in comparison to the common factors in these hives: they are all square or rectangular; they all use movable wooden frames; and they all consist of a floor, brood-box, honey super, crown-board and roof. Hives have traditionally been constructed from cedar, pine or cypress wood but in recent years, hives made from injection-molded, dense polystyrene have become increasingly common. Hives also use queen excluders between the brood-box and honey supers to keep the queen from laying eggs in cells next to those containing honey intended for consumption. With the 20th-century advent of mite pests, hive floors are often replaced, either temporarily or permanently, with a wire mesh and a removable tray.
In 2015, the Flow Hive system was invented in Australia by Cedar Anderson and his father Stuart Anderson, whose design allows honey to be extracted without cumbersome centrifuge equipment.
Pioneers of practical and commercial beekeeping
In the 19th century, improvements were made in the design and production of beehives, systems of management and husbandry, stock improvement by selective breeding, honey extraction and marketing. Notable innovators of modern beekeeping include:
Petro Prokopovych used frames with channels in the side of the woodwork; these were packed side-by-side in stacked boxes. Bees traveled between frames and boxes via these channels, which were similar to the cutouts in the sides of modern wooden sections.
Jan Dzierżon' beehive design has influenced modern beehives.
François Huber made significant discoveries about the bee life cycle and communication between bees. Despite being blind, Huber discovered a large amount of information about the queen bee's mating habits and her contact with the rest of the hive. His work was published as New Observations on the Natural History of Bees.
L. L. Langstroth has influenced modern beekeeping practice more than anyone else. His book The Hive and Honey-bee was published in 1853.
Moses Quinby, author of Mysteries of Bee-Keeping Explained, invented the bee smoker in 1873.
Amos Root, author of the A B C of Bee Culture, which has been continuously revised and remains in print, pioneered the manufacture of hives and the distribution of bee packages in the United States.
A. J. Cook author of The Bee-Keepers' Guide; or Manual of the Apiary, 1876.
Dr. C.C. Miller was one of the first entrepreneurs to make a living from apiculture. By 1878, he made beekeeping his sole business activity. His book, Fifty Years Among the Bees, remains a classic and his influence on bee management persists into the 21st century.
Franz Hruschka was an Austrian/Italian military officer who in 1865 invented a simple machine for extracting honey from the comb by means of centrifugal force. His original idea was to support combs in a metal framework and then spin them within a container to collect honey that was thrown out by centrifugal force. This meant honeycombs could be returned to a hive empty and undamaged, saving the bees a vast amount of work, time and materials. This invention significantly improved the efficiency of honey harvesting and catalyzed the modern honey industry.
Walter T. Kelley was an American pioneer of modern beekeeping in the early-and mid-20th century. He greatly improved upon beekeeping equipment and clothing, and went on to manufacture these items and other equipment. His company sold products worldwide and his book How to Keep Bees & Sell Honey, encouraged a boom in beekeeping following World War II.
Cary W. Hartman (1859–1947), lecturer, well known beekeeping enthusiast and honey promoter was elected President of the California State Beekeepers' Association in 1921.
In the UK, practical beekeeping was led in the early 20th century by a few men, pre-eminently Brother Adam and his Buckfast bee, and R.O.B. Manley, author of books including Honey Production in the British Isles and inventor of the Manley frame, which is still universally popular in the UK. Other notable British pioneers include William Herrod-Hempsall and Gale.
Ahmed Zaky Abushady (1892–1955) was an Egyptian poet, medical doctor, bacteriologist, and bee scientist, who was active in England and Egypt in the early twentieth century. In 1919, Abushady patented a removable, standardized aluminum honeycomb. In the same year, he founded The Apis Club in Benson, Oxfordshire, which later became the International Bee Research Association (IBRA). In Egypt in the 1930s, Abushady established The Bee Kingdom League and its organ The Bee Kingdom.
Hives and other equipment
Horizontal hives
A Horizontal top-bar hive is a single-story, frameless beehive in which the comb hangs from removable bars that form a continuous roof over the comb, whereas the frames in most current hives allow space for bees to move between boxes. Hives that have frames or that use honey chambers in summer and use management principles similar to those of regular top-bar hives are sometimes also referred to as top-bar hives. Top-bar hives are rectangular and are typically more than twice as wide as multi-story framed hives commonly found in English-speaking countries. Top-bar hives usually include one box and allow for beekeeping methods that interfere very little with the colony. While conventional advice often recommends inspecting each colony each week during the warmer months, some beekeepers fully inspect top-bar hives only once a year, and only one comb needs to be lifted at a time.
Vertical stackable hives
There are three types of vertical stackable hives: hanging or top-access frame, sliding or side-access frame, and top bar.
Hanging-frame hive designs include Langstroth, the British National, Dadant, Layens, and Rose, which differ in size and number of frames. The Langstroth was the first successful top-opened hive with movable frames. Many other hive designs are based on the principle of bee space that was first described by Langstroth, and is a descendant of Jan Dzierzon's Polish hive designs. Langstroth hives are the most-common size in the United States and much of the world; the British National is the most common size in the United Kingdom; Dadant and Modified Dadant hives are widely used in France and Italy, and Layens by some beekeepers, where their large size is an advantage. Square Dadant hives–often called 12-frame Dadant or Brother Adam hives–are used in large parts of Germany and other parts of Europe by commercial beekeepers.
Any hanging-frame hive design can be built as a sliding frame design. The AZ Hive, the original sliding frame design, integrates hives using Langstroth-sized frames into a honey house to streamline the workflow of honey harvest by localization of labor, similar to cellular manufacturing. The honey house can be a portable trailer, allowing the beekeeper to move hives to a site and provide pollination services.
Top-bar stackable hives use top bars instead of full frames. The most common type is the Warre hive, although any hive with hanging frames can be converted into a top-bar stackable hive by using only the top bar rather than the whole frame. This may work less well with larger frames, where crosscomb and attachment can occur more readily.
Protective clothing
Most beekeepers wear some protective clothing. Novice beekeepers usually wear gloves and a hooded suit or hat and veil. Experienced beekeepers sometimes choose not to use gloves because they inhibit delicate manipulations. The face and neck are the most important areas to protect, so most beekeepers wear at least a veil. Defensive bees are attracted to the breath; a sting on the face can lead to much more pain and swelling than a sting elsewhere, while a sting on a bare hand can usually be quickly removed by fingernail scrape to reduce the amount of venom injected.
Traditionally, beekeeping clothing is pale-colored because of the natural color of cotton and the cost of coloring is an expense not warranted for workwear, though some consider this to provide better differentiation from the colony's natural predators such as bears and skunks, which tend to be dark-colored. It is now known bees see in ultraviolet wavelengths and are also attracted to scent. The type of fabric conditioner used has more impact than the color of the fabric.
Stings that are retained in clothing fabric continue to pump out an alarm pheromone that attracts aggressive action and further stinging attacks. Attraction can be minimized with regular washing.
Smoker
Most beekeepers use a smoker, a device that generates smoke from the incomplete combustion of fuels. Although the exact mechanism is disputed, it is said smoke calms bees. Some claim it initiates a feeding response in anticipation of possible hive abandonment due to fire. It is also thought smoke masks alarm pheromones released by guard bees or bees that are squashed in an inspection. The ensuing confusion creates an opportunity for the beekeeper to open the hive and work without triggering a defensive reaction.
Many types of fuel can be used in a smoker as long as it is natural and not contaminated with harmful substances. Common fuels include hessian, twine, pine needles, corrugated cardboard, and rotten or punky wood. Indian beekeepers, especially in Kerala, often use coconut fibers, which are readily available, safe, and cheap. Some beekeeping supply sources also sell commercial fuels like pulped paper, compressed cotton and aerosol cans of smoke. Other beekeepers use sumac as fuel because it ejects much smoke and lacks an odor.
Some beekeepers use "liquid smoke" as a safer, more convenient alternative. It is a water-based solution that is sprayed onto the bees from a plastic spray bottle. A spray of clean water can also be used to encourage bees to move on. Torpor may also be induced by the introduction of chilled air into the hive, while chilled carbon dioxide may have harmful, long-term effects.
Few anecdotal stories of using the smoke from burning fungi in England or Europe for centuries have been published. Several more recent studies describe anaesthesia of honeybees use of smoke from burning fungi. The fungi reported to have been used to smoke bees are the puffballs Lycoperdon gigantium, L. wahlbergii and the conks, Fomes fomentarius and F. igiarius. When fungi are burned, the characteristic smell is due to the pyrolysis of the keratin cell wall of fungi. Besides being a major fungi constituent, keratin is found in animal tissues, such as hair or feathers. Anaesthesia experiments done using smoke from pyrolysis of L. wahlbergii, human hair and chicken feathers showed no difference in long-term mortality of anesthetized honeybees and non-treated bees in the same hive. Hydrogen sulphide was identified as the major combustion product that is responsible for putting the bees to sleep. Note – hydrogen sulphide is toxic to humans at high concentrations.
Hive tool
Most beekeepers use a hive tool when working on their hives. The two main types are the American hive tool; and the Australian hive tool often called a 'frame lifter'. They are used to scrape off burr-comb from around the hive, especially on top of the frames. They are also used to separate the frames before lifting out of the hive.
Safety and husbandry
Stings
Some beekeepers believe pain and irritation from stings decreases if a beekeeper receives more stings, and they consider it important for safety of the beekeeper to be stung a few times a season. Beekeepers have high levels of antibodies, mainly Immunoglobulin G, caused by a reaction to the major antigen of bee venom, phospholipase A2 (PLA). Antibodies correlate with the frequency of bee stings.
The entry of venom into the body from bee stings may be hindered and reduced by protective clothing that allows the wearer to remove stings and venom sacs with a simple tug on the clothing. Although the stinger is barbed, a worker bee's stinger is less likely to become lodged into clothing than human skin.
Symptoms of being stung include redness, swelling and itching around the site of the sting. In mild cases, pain and swelling subside in two hours. In moderate cases, the red welt at the sting site will become slightly larger for one or two days before beginning to heal. A severe reaction, which is rare among beekeepers, results in anaphylactic shock.
If a beekeeper is stung by a bee, the sting should be removed without squeezing the attached venom glands. A quick scrape with a fingernail is effective and intuitive, and ensures the venom injected does not spread so the side effects of the sting will go away sooner. Washing the affected area with soap and water can also stop the spread of venom. Ice or a cold compress can be applied to the sting area.
Internal temperature of a hive
Bees maintain the internal temperature of their hive at about . Their ability to do this is known as social homeostasis and was first described by Gates in 1914. During hot weather, bees cool the hive by circulating cool air from the entrance through the hive and out again; and if necessary by placing water, which they fetch, throughout the hive to create evaporative cooling. In cold weather, packing and insulation of the bee hive is believed to be beneficial. The extra insulation is believed to reduce the amount of honey the bees consume and makes it easier for them to maintain the hive's temperature. The desire for insulation encouraged the use of double-walled hives with an outer wall of timber or polystyrene; and hives constructed from a ceramic.
Location of hives
There has been considerable debate about the best location for hives. Virgil thought they should be located near clear springs, ponds or shallow brooks. Wildman thought they should face to the south or west. All writers agree hives should be sheltered from strong winds. In hot climates, hives are often placed under the shade of trees in summer. Researchers in the U.S. found domestic honey bees placed in national parks compete with native bee species for resources. A further review of the literature concluded large concentrations of beehives on continents where they are not native, such as North and South America, could compete against the native bees; this, however, was not as strongly observed in areas where domestic bees are native such as Europe and Africa, where the different bee species have adapted to have a narrower overlapping of forage preferences.
Natural beekeeping
The natural beekeeping movement believes bee hives are weakened by modern beekeeping and agricultural practices, such as crop spraying, hive movement, frequent hive inspections, artificial insemination of queens, routine medication, and sugar water feeding. Practitioners of "natural beekeeping" tend to use variations of the top-bar hive, which is a simple design that retains the concept of having a movable comb without the use of frames or a foundation. The horizontal top-bar hive, as promoted by many writers, can be seen as a modernization of hollow log hives, with the addition of wooden bars of specific width from which bees hang their combs. The widespread adoption of Natural Beekeeping methods in recent years can be attributed to the 2007 publications of Natural Beekeeping by Ross Conrad, and The Barefoot Beekeeper by Philip Chandler, which challenges many aspects of modern beekeeping and offers the horizontal top-bar hive as a viable alternative to the ubiquitous Langstroth-style movable-frame hive.
A vertical top-bar hive is the Warré hive, based on a design by the French priest Abbé Émile Warré (1867–1951) and popularized by David Heaf in his English translation of Warré's book L'Apiculture pour Tous as Beekeeping For All.
Urban and backyard beekeeping
Related to natural beekeeping, urban beekeeping is an attempt to revert to a less-industrialized way of obtaining honey by using small-scale colonies that pollinate urban gardens. Some have found city bees are healthier than rural bees because there are fewer pesticides and greater biodiversity in urban gardens. Urban bees may fail to find forage, however, and homeowners can use their land to help feed local bee populations by planting flowers that provide nectar and pollen. An environment of year-round, uninterrupted bloom creates an ideal environment for colony reproduction.
Using managed honeybee colonies to fill the ecological niche of pollinators in urban environments is also thought to be crucial to preventing the formation of feral colonies by more destructive species like the Africanized honeybee (AHB).
Indoor beekeeping
Modern beekeepers have experimented with raising bees indoors in a controlled environment or in indoor observation hives. This may be done for reasons of space and monitoring, or in the cooler months, when large commercial beekeepers may move colonies to "wintering" warehouses with fixed temperature, light, and humidity. This helps bees remain healthy but relatively dormant. These relatively dormant "wintered" bees survive on stored honey, and new bees are not born.
Experiments in raising bees indoors for longer durations have looked into more precise and varying environment controls. In 2015, MIT's "Synthetic Apiary" project simulated springtime inside a closed environment for several hives throughout the winter. They provided food sources and simulated long days, and saw activity and reproduction levels comparable to the levels seen outdoors in warm weather. They concluded such an indoor apiary could be sustained year-round if needed.
Behavior of honey bees
Colony reproduction
Honey bee colonies are dependent on their queen, who is the only egg-layer. Although queens have a three-to-four-year adult lifespan, diminished longevity of queens—less than a year—is commonly and increasingly observed. The queen can choose whether to fertilize an egg as she lays it; fertilized eggs develop into a female worker bees and unfertilized eggs become male drones. The queen's choice of egg type depends on the size of the open brood cell she encounters on the comb. In a small worker cell, she lays a fertilized egg; she lays unfertilized drone eggs in larger drone cells.
When the queen is fertile and laying eggs, she produces a variety of pheromones that control the behavior of the bees in the hive; these are commonly called queen substance. Each pheromone has a different function. As the queen ages, she begins to run out of stored sperm and her pheromones begin to fail.
As the queen's pheromones fail, the bees replace her by creating a new queen from one of her worker eggs. They may do this because she has been physically injured, because she has run out of sperm and cannot lay fertilized eggs, and has become a drone-laying queen, or because her pheromones have dwindled to the point at which they cannot control all of the bees in the hive. At this juncture, the bees produce one or more queen cells by modifying existing worker cells that contain a normal female egg. They then either supersede the queen without swarming or divide the hive into two colonies through swarm-cell production, which leads to swarming.
Supersedure is a valued behavioral trait because hive that supersedes its old queen does not lose any stock; rather it creates a new queen and the old one either naturally dies or is killed when the new queen emerges. In these hives, bees produce only one or two queen cells, most often in the center of the face of a broodcomb. Swarm-cell production involves the creation of twelve or more queen cells. These are large, peanut-shaped protrusions requiring space, for which reason they are often located around the edges—commonly at the sides and the bottom—of the broodcomb.
Once either process has begun, the old queen leaves the hive when the first queen cells hatch, and is accompanied by a large number of bees—predominantly young bees called wax-secretors—which form the basis of the new hive. Scouts are sent from the swarm to find suitable hollow trees or rock crevices; when one is found, the entire swarm moves in. Within hours, the new colony's bees build new wax brood combs using honey stores with which the young bees have filled themselves before leaving the old hive. Only young bees can secrete wax from special abdominal segments, which is why swarms tend to contain more young bees. Often a number of virgin queens accompany the first swarm, known as the "prime swarm", and the old queen is replaced as soon as a daughter queen mates and begins laying. Otherwise, she is quickly superseded in the new hive.
Different sub-species of Apis mellifera exhibit differing swarming characteristics. In North America, northern black races are thought to swarm less and supersede more whereas the southern yellow-and-gray varieties are said to swarm more frequently. Swarming behavior is complicated because of the prevalence of cross-breeding and hybridization of the sub-species. Italian bees are very prolific and inclined to swarm; Northern European black bees have a strong tendency to supersede their old queen without swarming. These differences are the result of differing evolutionary pressures in the regions in which each sub-species evolved.
Factors that trigger swarming
According to George S. Demuth, the main factors that increase the swarming tendency of bees are:
The genetics of bees; the strength of the swarming instinct
Congestion of the brood nest
Insufficient empty combs for ripening nectar and storing honey
Inadequate ventilation
Having an old queen
Warming weather conditions.
Demuth attributed some of his comments to Snelgrove.
Some beekeepers carefully monitor their colonies in spring for the appearance of queen cells, which are a dramatic signal the colony is determined to swarm. After leaving the old hive, the swarm looks for shelter. A beekeeper may capture it and introduce it into a new hive. Otherwise, the swarm reverts to a feral state and finds shelter in a hollow tree or other suitable habitat. A small after-swarm has less chance of survival and may threaten the original hive's survival if the number of remaining bees is unsustainable. When a hive swarms despite the beekeeper's preventative efforts, the beekeeper may give the reduced hive two frames of open brood with eggs. This helps replenish the hive more quickly and gives a second opportunity to raise a queen if there is a mating failure.
Artificial swarming
When a colony accidentally loses its queen, it is said to be queenless. The workers realize the queen is absent after around an hour as her pheromones in the hive fade. Instinctively, the workers select cells containing eggs aged less than three days and dramatically enlarge the cells to form "emergency queen cells". These appear similar to large, -long, peanut-like structures that hang from the center or side of the brood combs. The developing larva in a queen cell is fed differently than an ordinary worker bee; in addition to honey and pollen, she receives a great deal of royal jelly, a special food secreted from the hypopharyngeal gland of young nurse bees. Royal jelly dramatically alters the growth and development of the larva so after metamorphosis and pupation, it emerges from the cell as a queen bee. The queen is the only bee in a colony that has fully developed ovaries; she secretes a pheromone that suppresses the normal development of ovaries in all of her workers.
Beekeepers use the ability of the bees to produce new queens to increase their colonies in a procedure called splitting a colony. To do this, they remove several brood combs from a healthy hive, leaving the old queen behind. These combs must contain eggs or larvae less than three days old and be covered by young nurse bees, which care for the brood and keep it warm. These brood combs and nurse bees are then placed into a small "nucleus hive" with other combs containing honey and pollen. As soon as the nurse bees find themselves in this new hive, and realize they have no queen and begin constructing emergency queen cells using the eggs and larvae in the combs.
Pests and diseases
Diseases
The common agents of disease that affect adult honey bees include fungi, bacteria, protozoa, viruses, parasites and poisons. The gross symptoms displayed by affected adult bees are very similar, whatever the cause, making it difficult to ascertain the causes without microscopic identification of microorganisms or chemical analysis of poisons. Since 2006, colony losses from colony collapse disorder (CCD) have been increasing across the world, although the causes of the syndrome are unknown. In the U.S., commercial beekeepers have been increasing the number of hives to deal with higher rates of attrition.
Parasites
Nosema apis is a microsporidian that causes nosemosis, also called nosema, the most-common and widespread disease of the adult honey bee.
Galleria mellonella and Achroia grisella wax moth larvae hatch, tunnel through and destroy comb that contains bee larvae and their honey stores. The tunnels they create are lined with silk, which entangles and starves emerging bees. Destruction of honeycombs also results in leakage and wasting of honey. A healthy hive can manage wax moths but weak colonies, unoccupied hives and stored frames can be decimated.
Small hive beetle (Aethina tumida) is native to Africa but has now spread to most continents. It is a serious pest among honey bees unadapted to it.
Varroa destructor, the Varroa mite, is an established pest of two species of honey bee through many parts of the world and is blamed by many researchers as a leading cause of CCD.
Tropilaelaps mites, of which there are four species, are native to Apis dorsata, Apis laboriosa, and Apis breviligula, but spread to Apis mellifera after they were introduced to Asia.
Acarapis woodi, the tracheal mite, infests the trachea of honey bees.
Predators
Most predators prefer not to eat honeybees due to their unpleasant sting. Common honeybee predators include large animals such as skunks and bears, which seek the hive's honey and brood, as well as adult bees. Some birds will also eat bees, (for example, bee-eaters, as do some robber flies, such as Mallophora ruficauda, which is a pest of apiculture in South America due to its habit of eating workers while they are foraging in meadows.
Decreasing lifespan
A 2022 study by researchers at University of Maryland, College Park observed lifespan of caged worker bees is half as long as that observed 50 years ago, and hypothesized decreased worker-bee lifespans should correlate to decreased honey production.
Recent developments
World Beekeeping Awards 2024
The World Beekeeping Awards, held in December 2024, showcased the global importance of apiculture and honey production. The event, which took place in London, United Kingdom, featured entries from over 50 countries and highlighted the diverse range of honey varieties produced worldwide.
Honey fraud scandal
However, the 2024 World Beekeeping Awards were marred by a significant scandal involving honey fraud. Investigators uncovered a sophisticated operation where some contestants had submitted adulterated honey samples.
The fraudulent entries contained:
Honey diluted with sugar syrup
Mislabeled honey varieties
Honey from undisclosed geographical origins
This incident has raised concerns about the integrity of honey production and labeling practices in the global market. As a result, the World Beekeeping Association has announced plans to implement more rigorous testing procedures for future competitions.
Industry response
In response to the fraud scandal, several measures have been proposed to enhance honey authenticity and protect consumers:
Advanced testing methods: Implementation of more sophisticated laboratory techniques to detect adulteration.
Blockchain technology: Exploration of blockchain-based traceability systems to track honey from hive to shelf.
Stricter regulations: Calls for more stringent international standards and enforcement of honey labeling and production practices.
These developments highlight the ongoing challenges faced by the beekeeping industry in maintaining product integrity and consumer trust in an increasingly global market.
World apiculture
According to Food and Agriculture Organization data, the world's beehive stock rose from around 50 million in 1961 to around 83 million in 2014, which represents an annual average growth of 1.3%. Average annual growth has accelerated to 1.9% since 2009.
Gallery: Harvesting honey
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322105 | https://en.wikipedia.org/wiki/Mangosteen | Mangosteen | Mangosteen (Garcinia mangostana), also known as the purple mangosteen, is a tropical evergreen tree with edible fruit native to Island Southeast Asia, from the Malay Peninsula to Borneo. It has been cultivated extensively in tropical Asia since ancient times. It is grown mainly in Southeast Asia, southwest India and other tropical areas such as Colombia, Puerto Rico and Florida, where the tree has been introduced. The tree grows from tall.
The fruit of the mangosteen is sweet and tangy, juicy, somewhat fibrous, with fluid-filled vesicles (like the flesh of citrus fruits), with an inedible, deep reddish-purple colored rind (exocarp) when ripe. In each fruit, the fragrant edible flesh that surrounds each seed is botanically endocarp, i.e., the inner layer of the ovary. The seeds are of similar size and shape to almonds.
Genus Garcinia also contains several less-known fruit-bearing species, such as the button mangosteen (G. prainiana) and the charichuelo (G. madruno).
Description
Tree
A tropical tree, the mangosteen must be grown in consistently warm conditions, as exposure to temperatures below for prolonged periods will usually kill a mature plant. They are known to recover from brief cold spells rather well, often with damage only to young growth. Experienced horticulturists have grown this species outdoors, and brought them to fruit in extreme south Florida.
The tree grows from tall.
Fruit
The juvenile mangosteen fruit, which does not require fertilisation to form (see agamospermy), first appears as pale green or almost white in the shade of the canopy. As the fruit enlarges over the next two to three months, the exocarp colour deepens to darker green. During this period, the fruit increases in size until its exocarp is in outside diameter, remaining hard until a final, abrupt ripening stage.
The subsurface chemistry of the mangosteen exocarp comprises an array of polyphenols, including xanthones and tannins that assure astringency which discourages infestation by insects, fungi, plant viruses, bacteria, and animal predation while the fruit is immature. Colour changes and softening of the exocarp are natural processes of ripening that indicate the fruit can be eaten and the seeds have finished developing.
Once the developing mangosteen fruit has stopped expanding, chlorophyll synthesis slows as the next colour phase begins. Initially streaked with red, the exocarp pigmentation transitions from green to red to dark purple, indicating a final ripening stage. This entire process takes place over a period of ten days as the edible quality of the fruit peaks. Over the days following removal from the tree, the exocarp hardens to an extent depending upon post-harvest handling and ambient storage conditions, especially relative humidity levels. If the ambient humidity is high, exocarp hardening may take a week or longer when the flesh quality is peaking and excellent for consumption. However, after several additional days of storage, especially if unrefrigerated, the flesh inside the fruit might spoil without any obvious external indications. Using the hardness of the rind as an indicator of freshness for the first two weeks following harvest is therefore unreliable because the rind does not accurately reveal the interior condition of the flesh. If the exocarp is soft and yielding as it is when ripe and fresh from the tree, the fruit is usually good.
The edible endocarp of the mangosteen has the same shape and size as a tangerine in diameter, but is white. The number of fruit segments corresponds exactly with the number of stigma lobes on the exterior apex; accordingly, a higher number of fleshy segments also corresponds with the fewest seeds. The circle of wedge-shaped segments contains 4–8, rarely 9 segments, the larger ones harbouring the apomictic seeds that are unpalatable unless roasted. As a non-climacteric fruit, picked mangosteen does not ripen further, so it must be consumed shortly after harvest.
Often described as a subtle delicacy, the flesh bears an exceptionally mild aroma, quantitatively having about 1/400th of the chemical constituents of fragrant fruits, explaining its relative mildness. The main volatile components having caramel, grass and butter notes as part of the mangosteen fragrance are hexyl acetate, hexenol and α-copaene. Ethyl octanoate, ethyl hexanoate and 3-methyl-2-butene-1-thiol were detected as aroma components in mangosteen wine.
Origins and history
Cultivated mangosteen (Garcinia mangostana var. mangostana) is dioecious, but male trees are unknown. The trees produce viable seeds via apomixis, where all the embryos are essentially clones of the mother. Its extensive cultivation has made its original native range difficult to ascertain. Garcinia mangostana var. mangostana is likely to be the domesticated descendant of wild populations of Garcinia mangostana var. malaccensis (previously thought to be a separate species) and Garcinia mangostana var. borneensis, native to the Malay Peninsula and Borneo respectively. Both of these wild varieties still possess male trees, unlike the domesticated mangosteen. It may have also hybridized to a limited extent with closely-related species, including Garcinia penangiana and Garcinia venulosa.
Mangosteen is highly valued for its juicy, delicate texture and slightly sweet and sour flavor, the mangosteen has been cultivated in Malaysia, Borneo, Sumatra, Mainland Southeast Asia, and the Philippines since ancient times. The 15th-century Chinese record Yingya Shenglan described mangosteen as mang-chi-shih (derived from Malay manggis), a native plant of Southeast Asia of white flesh with a delectable sweet and sour taste.
A description of mangosteen was included in the Species Plantarum by Linnaeus in 1753. The mangosteen was introduced into English greenhouses in 1855. Subsequently, its culture was introduced into the Western Hemisphere, where it became established in West Indies islands, especially Jamaica. It was later established on the Americas mainland in Guatemala, Honduras, Panama, and Ecuador. The mangosteen tree generally does not grow well outside the tropics.
In Southeast Asia, mangosteen is commonly known as the "Queen of Fruits", and is frequently paired with durian, the "King of Fruits". In Chinese food therapy, mangosteen is considered "cooling", making it a good counterbalance to the "heaty" durian. There is also a legend about Queen Victoria offering a reward of one hundred pounds sterling to anyone who could deliver a fresh mangosteen to her. Although this legend can be traced to a 1930 publication by the fruit explorer David Fairchild, it is not substantiated by any known historical document.
The journalist and gourmet R. W. Apple Jr. once said of the fruit, "No other fruit, for me, is so thrillingly, intoxicatingly luscious...I'd rather eat one than a hot fudge sundae, which for a big Ohio boy is saying a lot." Since 2006, private small-volume orders for fruits grown in Puerto Rico were sold to American specialty food stores and gourmet restaurants who serve the flesh segments as a delicacy dessert.
Propagation, cultivation and harvest
Mangosteen is usually propagated by seedlings. Vegetative propagation is difficult and seedlings are more robust and reach fruiting earlier than vegetatively propagated plants.
Mangosteen produces a recalcitrant seed which is not a true seed strictly defined, but rather described as a nucellar asexual embryo. As seed formation involves no sexual fertilization, the seedling is genetically identical to the mother plant. If allowed to dry, a seed dies quickly, but if soaked, seed germination takes between 14 and 21 days when the plant can be kept in a nursery for about 2 years growing in a small pot.
When the trees are approximately , they are transplanted to the field at a spacing of . After planting, the field is mulched in order to control weeds. Transplanting takes place in the rainy season because young trees are likely to be damaged by drought. Because young trees need shade, intercropping with banana, plantain, rambutan, durian or coconut leaves is effective. Coconut palms are mainly used in areas with a long dry season, as palms also provide shade for mature mangosteen trees. Another advantage of intercropping in mangosteen cultivation is the suppression of weeds.
The growth of the trees is retarded if the temperature is below . The ideal temperature range for growing and producing fruits is with relative humidity over 80%. The maximal temperature is , with both leaves and fruit being susceptible to scorching and sunburn, while the minimum temperature is . Young seedlings prefer a high level of shade and mature trees are shade-tolerant.
Mangosteen trees have a weak root system and prefer deep, well-drained soils with high moisture content, often growing on riverbanks. The mangosteen is not adapted to limestone soils, sandy, alluvial soils, or sandy soils with low organic matter content. Mangosteen trees need a well-distributed rainfall over the year (<40 mm/month) and a 3–5 week dry season.
Mangosteen trees are sensitive to water availability and application of fertilizer input which is increased with the age of trees, regardless of region. Maturation of mangosteen fruits takes 5–6 months, with harvest occurring when the pericarps are purple.
Breeding
In the breeding of perennial mangosteen, the selection of rootstock and grafting are significant issues to overcome constraints to production, harvesting, or seasonality. Most of the genetic resources for breeding are in germplasm collections, whereas some wild species are cultivated in Malaysia and the Philippines. Conservation methods are chosen because storage of seeds under dried and low-temperature conditions has not been successful.
Because of the long duration until the trees yield fruits and the long resulting breeding cycles, mangosteen breeding has not proven attractive for transplanting or research. Breeding objectives that may enhance mangosteen production include:
Drought tolerance, especially sensitivity to drought in the first 5 years after germination
Tree architecture to produce a tree with a crown that is regular and pyramid-shaped
Fruit quality including i) overcoming bitter taste components caused by changes in pulp, pericarp or aril and ii) pericarp cracking resulting from excessive water uptake
Rootstock for improved adaptation to drought and robust development in early years of growth
Yield
Mangosteen trees may reach fruit-bearing in as little as 6 years but may require 12 or more years, depending on climate and cultivation methods. The yield of the mangosteen is variable, depending on the climate and age of the tree. If the young tree is bearing for the first time, 200–300 fruits may be produced, whereas at maturity, 500 fruits per season are average. At age 30 to 45 years in full maturity, each tree may yield as many as 3,000 fruits, with trees as old as 100 years still producing.
Regional production
Major mangosteen production occurs in Southeast Asia, mainly in Thailand as the country with the most acreage planted, estimated at 4,000 ha in 1965 and 11,000 ha in 2000, giving a total yield of 46,000 tons. Mangosteen is seasonally available in Thailand from May through September. Indonesia, Malaysia and the Philippines are other major Asian producers. Mangosteen production in Colombia and Puerto Rico has been successful.
Diseases and pests
Common diseases and pests
The pathogens that attack mangosteen are common in other tropical trees. The diseases can be divided into foliar, fruit, stem and soil-borne diseases.
Pestalotiopsis leaf blight (Pestalotiopsis flagisettula (only identified in Thailand)) is one of the diseases that infect especially young leaves. Furthermore, the pathogen causes the fruits to rot before and after the harvest. Additional stem canker and dieback are caused by the pathogen. Some of the symptoms of stem canker are branch splitting, gummosis and bark blistering. The main areas where the disease was observed are Thailand, Malaysia, and North Queensland.
Another common disease is the thread blight or white thread blight disease (Marasmiellus scandens) whereas the name comes from the mycelia which resembles thread. Leaves, twigs, and branches may also be damaged by the disease. The spores spread with the help of wind, raindrops, and insects, and thrive in shady, humid, and wet conditions.
An important post-harvest disease affecting mangosteen, especially in Thailand is called Diplodia fruit rot (Diplodia theobromae) which, as a secondary pathogen, enters the host plant through wounds.
Phellinus noxius living on the roots and trunk bases causes brown root disease, a name derived from the appearance of the mycelium-binding soil particles. The distribution of the fungus happens through contact with infected wood or thick rhizomorphs on tree stumps.
There are a few pests that feed on mangosteen leaves and fruits including leaf eater (Stictoptera sp.), leaf miner (Phyllocnictis citrella) and fruit borer (Curculio sp.). Especially in nurseries, the larval stage of the leaf eater can cause visible damage on young leaves, but can be managed by biological control agents. The larval stage of fruit borer (Curculio sp.) feeds on different parts of fruit before ripening.
Control measures for diseases and pests
Different management options can be applied to control mangosteen diseases.
Measures to inhibit sun scalding to minimize leaf blight and stem canker.
Reduction of wounds caused by insects and storm damage to minimize disease incidence.
Change of the microclimate by tree spacing and pruning.
Chemicals applied to root collars and tree stumps to control root diseases.
Fungicides to control fungal pathogens.
Biological pest control or insecticides to control insects.
Nutritional content
The endocarp the white part of the fruit having a mild flavor is edible, but its nutrition content is modest, as all nutrients analyzed are at a low percentage of the Daily Value (see table for canned fruit in syrup, USDA FoodData Central; note that nutrient values for fresh fruit are likely different, but have not been published by a reputable source).
Uses
Culinary
Without fumigation or irradiation (to kill the Asian fruit fly), fresh mangosteens were illegal to import into the United States until 2007. Following export from its natural growing regions in Southeast Asia (particularly Thailand), the fresh fruit is available seasonally in some local markets in North America such as those of Chinatowns. Mangosteens are available fresh, canned and frozen in Western countries. The fruit may be served as a dessert or made into jams. In Vietnam, the ripe fruit is also used as a salad ingredient.
Upon arrival in the US in 2007, fresh mangosteens sold at up to in specialty produce stores in New York City, but wider availability and somewhat lower prices have become common in the United States and Canada. Despite efforts described above to grow mangosteen in the Western Hemisphere, nearly the entire supply is imported from Thailand.
Before ripening, the mangosteen shell is fibrous and firm but becomes soft and easy to pry open when the fruit ripens. To open a mangosteen, the shell can be scored with a knife, pried gently along the score with the thumbs until it cracks, and then pulled apart to reveal the fruit. Alternatively, the mangosteen can be opened without a knife by squeezing the shell from the bottom until it breaks, allowing the shell to be removed and the fruit eaten while intact with the stem. In Southeast Asian countries, the mangosteen is usually served with the bottom part of the shell intact. Occasionally, during peeling of ripe fruits, the purple exocarp juice may stain skin or fabric.
Traditional medicine
Various parts of the plant have a history of use in traditional medicine, mostly in Southeast Asia; it may have been used to treat skin infections, wounds, dysentery, urinary tract infections, and gastrointestinal complaints, although there is no high-quality clinical evidence for any of these effects.
Dried fruits are shipped to Singapore to be processed for medical uses which may include dysentery, skin disorders, and various other minor diseases in several countries across Asia. There is no reliable evidence that mangosteen juice, puree, bark or extracts is effective as a treatment for human diseases.
Natural dye
The extract of mangosteen peels is traditionally used in Indonesia as natural dye for coloring of brown, dark brown, purple or red hues applied to tenun ikat and batik textiles.
Other uses
Mangosteen twigs have been used as chew sticks in Ghana, and the wood has been used to make spears and cabinetry in Thailand. The rind of the mangosteen fruit has also been used to tan leather in China.
Phytochemicals
Mangosteen peel contains xanthonoids, such as mangostin, and other phytochemicals.
Polysaccharide and xanthone compounds are found in the fruit, leaves, and heartwood of the mangosteen. Fully ripe fruit contain the xanthones gartanin, 8-disoxygartanin, and normangostin.
Marketing
Fresh mangosteen is marketed for only a short period of six to ten weeks due to its seasonal nature. It is mainly grown by smallholders and sold at fruit stalls by roadsides. Its irregular, short supply leads to wide price fluctuations throughout its season and over the years. Additionally, there is no standard product quality assessment or grading system, making international trade of the fruit difficult. The mangosteen still remains rare in Western markets, though its popularity is increasing, and it is often sold at a high price.
| Biology and health sciences | Other culinary fruits | Plants |
322177 | https://en.wikipedia.org/wiki/Penile%20cancer | Penile cancer | Penile cancer, or penile carcinoma, is a cancer that develops in the skin or tissues of the penis. Symptoms may include abnormal growth, an ulcer or sore on the skin of the penis, and bleeding or foul smelling discharge.
Risk factors include phimosis (inability to retract foreskin of the penis), chronic inflammation, smoking, HPV infection, condylomata acuminate, having multiple sexual partners, and early age of sexual intercourse.
Around 95% of penile cancers are squamous-cell carcinomas. Other types of penile cancer such as Merkel-cell carcinoma, small-cell carcinoma, and melanoma are generally rare. In 2020, it occurred in 36,000 men and caused 13,000 deaths.
Signs and symptoms
Penile cancer can present as redness and irritation on the penis with a skin thickening on the glans or inner foreskin or an ulcerative, outward growing (exophytic) or “finger-like” (papillary) growth. Penile cancer may accompany penile discharge with or without difficulty or burning or tingling while urinating (dysuria) and bleeding from the penis.
Risk factors
Infections
HIV infection—HIV-positive men have eight-fold increased risk of developing penile cancer than HIV-negative men.
Human papillomavirus—HPV is a risk factor in the development of penile cancer. According to the Centers for Disease Control and Prevention (CDC), HPV is responsible for about 800 (about 40%) of 1,570 cases of penile cancer diagnosed annually in the United States. There are more than 120 types of HPV.
Genital warts—Genital or perianal warts increase the risk of invasive penile cancer by about 3.7 times if they occurred more than two years before the reference date. About half of men with penile cancer also have genital warts, which are caused by HPV.
Hygiene and injury
Poor hygiene—Poor hygiene can increase a man's risk of penile cancer.
Smegma—Smegma, a whitish substance that can accumulate beneath the foreskin, is associated with greater risk of penile cancer. The American Cancer Society suggests that smegma may not be carcinogenic, but may increase the risk by causing irritation and inflammation of the penis.
Balanitis and penile injury—Inflammation of the foreskin and/or the glans penis (balanitis) is associated with about 3.1 times increased risk of penile cancer. It is usually caused by poor hygiene, allergic reactions to certain soaps, or an underlying health condition such as reactive arthritis, infection, or diabetes. Small tears and abrasions of the penis are associated with about 3.9 times increased risk of cancer.
Phimosis—Phimosis is a medical condition where the foreskin cannot be fully retracted over the glans. It is considered a significant risk factor in the development of penile cancer (odds ratio of 38–65). Phimosis may also be a symptom of penile cancer.
Paraphimosis—Paraphimosis is a medical condition where the foreskin becomes trapped behind the glans. It is considered a risk factor for the development of penile cancer.
Circumcision—Some studies show that circumcision during infancy or in childhood may provide partial protection against penile cancer, but this is not the case when performed in adulthood. It has been suggested that the reduction in risk may be due to reduced risk of phimosis; other possible mechanisms include reduction in risk of smegma and HPV infection.
Other
Age—Penile cancer is rarely seen in men under the age of 50. About 4 out of 5 men diagnosed with penile cancer are over the age of 55.
Lichen sclerosus—Lichen sclerosus is a disease causing white patches on the skin. Lichen sclerosus increases the risk of penile cancer. As the exact cause of lichen sclerosus is unknown, there is no known way to prevent it.
Tobacco—Chewing or smoking tobacco increases the risk of penile cancer by 1.5–6 times depending on the duration smoking and daily number of cigarettes.
Ultraviolet light—Men with psoriasis who have been treated using UV light and a drug known as psoralen have an increased risk of penile cancer.
Pathogenesis
Penile cancer arises from precursor lesions, which generally progress from low-grade to high-grade lesions. For HPV related penile cancers this sequence is as follows:
Squamous hyperplasia;
Low-grade penile intraepithelial neoplasia (PIN);
High-grade PIN (carcinoma in situ—Bowen's disease, Erythroplasia of Queyrat and bowenoid papulosis (BP));
Invasive carcinoma of the penis.
However, in some cases, non-dysplastic or mildly dysplastic lesions may progress directly into cancer. Examples include flat penile lesions (FPL) and condylomata acuminata.
In HPV negative cancers, the most common precursor lesion is lichen sclerosus (LS).
Diagnosis
The International Society of Urological Pathology (ISUP) recommends the use of p16INK4A immunostaining for the diagnosis and classification of HPV-related penile cancer.
Classification
Around 95% of penile cancers are squamous-cell carcinomas. They are classified into the following types:
basaloid (4%)
warty (6%)
mixed warty-basaloid (17%)
verrucous (8%)
papillary (7%)
other SCC mixed (7%)
sarcomatoid carcinomas (1%)
not otherwise specified (49%)
Other types of carcinomas are rare and may include small-cell, Merkel-cell, clear-cell, sebaceous-cell or basal-cell tumors. Non-epithelial malignancies such as melanomas and sarcomas are even more rare.
Staging
Like many malignancies, penile cancer can spread to other parts of the body. It is usually a primary malignancy, the initial place from which cancer spreads in the body. Much less often it is a secondary malignancy, one in which the cancer has spread to the penis from elsewhere. The staging of penile cancer is determined by the extent of tumor invasion, nodal metastasis, and distant metastasis.
The T portion of the AJCC TNM staging guidelines are for the primary tumor as follows:
TX: Primary tumor cannot be assessed.
T0: No evidence of primary tumor.
Tis: Carcinoma in situ.
Ta: Noninvasive verrucous carcinoma.
T1a: Tumor invades subepithelial connective tissue without lymph vascular invasion and is not poorly differentiated (i.e., grade 3–4).
T1b: Tumor invades subepithelial connective tissue with lymph vascular invasion or is poorly differentiated.
T2: Tumor invades the corpus spongiosum or cavernosum.
T3: Tumor invades the urethra or prostate.
T4: Tumor invades other adjacent structures.
Anatomic Stage or Prognostic Groups of penile cancer are as follows:
Stage 0—Carcinoma in situ.
Stage I—The cancer is moderately or well-differentiated and only affects the subepithelial connective tissue.
Stage II—The cancer is poorly differentiated, affects lymphatics, or invades the corpora or urethra.
Stage IIIa—There is deep invasion into the penis and metastasis in one lymph node.
Stage IIIb—There is deep invasion into the penis and metastasis into multiple inguinal lymph nodes.
Stage IV—The cancer has invaded into structures adjacent to the penis, metastasized to pelvic nodes, or distant metastasis is present.
HPV positive tumors
Human papillomavirus prevalence in penile cancers is high at about 40%. HPV16 is the predominant genotype accounting for approximately 63% of HPV-positive tumors. Among warty/basaloid cancers the HPV prevalence is 70–100% while in other types it is around 30%.
Prevention
HPV vaccines such as Gardasil or Cervarix may reduce the risk of HPV and, consequently, penile cancer.
The use of condoms is thought to be protective against HPV-associated penile cancer.
Good genital hygiene, which involves washing the penis, the scrotum, and the foreskin daily with water, may prevent balanitis and penile cancer. However, soaps with harsh ingredients should be avoided.
Cessation of smoking may reduce the risk of penile cancer.
Circumcision during infancy or in childhood may provide partial protection against penile cancer. Several authors have proposed circumcision as a possible strategy for penile cancer prevention; however, the American Cancer Society points to the rarity of the disease and notes that neither the American Academy of Pediatrics nor the Canadian Academy of Pediatrics recommend routine neonatal circumcision.
Phimosis can be prevented by practising proper hygiene and by retracting the foreskin on a regular basis.
Paraphimosis can be prevented by not leaving the foreskin retracted for prolonged periods of time.
Treatment
Treatment of penile cancer will vary depending on the clinical stage of the tumor at the time of diagnosis. There are several treatment options for penile cancer, depending on staging. They include surgery, radiation therapy, chemotherapy, and biological therapy. The most common treatment is one of five types of surgery:
Wide local excision—the tumor and some surrounding healthy tissue are removed
Microsurgery—surgery performed with a microscope is used to remove the tumor and as little healthy tissue as possible
Laser surgery—laser light is used to burn or cut away cancerous cells
Circumcision—cancerous foreskin is removed
Amputation (penectomy)—a partial or total removal of the penis, and possibly the associated lymph nodes.
The role of radiation therapy includes an organ-sparing approach for early-stage penile cancer at specialized centres. Furthermore, adjuvant therapy is used for patients with locally advanced disease or for symptom management.
Prognosis
Prognosis can range considerably for patients, depending where on the scale they have been staged. Generally speaking, the earlier the cancer is diagnosed, the better the prognosis. The overall 5-year survival rate for all stages of penile cancer is about 50%.
Epidemiology
Penile cancer is a rare cancer in developed nations, with annual incidence varying from 0.3 to 1 per 100,000 per year, accounting for around 0.4–0.6% of all malignancies. The annual incidence is approximately 1 in 100,000 men in the United States, 1 in 250,000 in Australia, and 0.82 per 100,000 in Denmark. In the United Kingdom, fewer than 500 men are diagnosed with penile cancer every year.
In the developing world, penile cancer is much more common. For instance, in Paraguay, Uruguay, Uganda and Brazil the incidence is 4.2, 4.4, 2.8 and 1.5–3.7 per 100,000, respectively. In some South American countries, Africa, and Asia, this cancer type constitutes up to 10% of malignant diseases in men.
the lifetime risk was estimated as 1 in 1,437 in the United States and 1 in 1,694 in Denmark.
| Biology and health sciences | Cancer | Health |
322197 | https://en.wikipedia.org/wiki/Tension%20headache | Tension headache | Tension headache, stress headache, or tension-type headache (TTH), is the most common type of primary headache. The pain usually radiates from the lower back of the head, the neck, the eyes, or other muscle groups in the body typically affecting both sides of the head. Tension-type headaches account for nearly 90% of all headaches.
Pain medications, such as paracetamol and ibuprofen, are effective for the treatment of tension headache. Tricyclic antidepressants appear to be useful for prevention. Evidence is poor for SSRIs, propranolol and muscle relaxants.
The 2016 Global Burden of Disease study revealed that TTHs affect about 1.89 billion people and are more common in women than men (30.8% to 21.4% respectively). TTH was most prevalent between ages 35 and 39. Despite its benign character, tension-type headache, especially in its chronic form, can impart significant disability on patients as well as burden on society at large. In 2016, the global burden of TTH was reported to be 7.2 million years of life lived with disability (YLDs). The YLD was calculated using TTH prevalence and average time spent with TTH multiplied by percentage health loss caused by TTH (3.7%).
Signs and symptoms
According to the third edition of the International Classification of Headache Disorders, the attacks must meet the following criteria:
A duration of between 30 minutes and 7 days.
At least two of the following four characteristics:
bilateral location
pressing or tightening (non-pulsating) quality
mild or moderate intensity
not aggravated by routine physical activity such as walking or climbing stairs
Both of the following:
no nausea or vomiting
no more than one of photophobia (sensitivity to bright light) or phonophobia (sensitivity to loud sounds)
Tension-type headaches may be accompanied by tenderness of the scalp on manual pressure during an attack.
Risk factors
Various precipitating factors may cause tension-type headaches in susceptible individuals:
Anxiety
Stress
Sleep problems
Young age
Poor health
Mechanism
Although the musculature of the head and neck and psychological factors such as stress may play a role in the overall pathophysiology of TTH, neither is currently believed to be the sole cause of the development of TTH. The pathologic basis of TTH is most likely derived from a combination of personal factors, environmental factors, and alteration of both peripheral and central pain pathways. Peripheral pain pathways receive pain signals from pericranial (around the head) myofascial tissue (protective tissue of muscles) and alteration of this pathway likely underlies episodic tension-type headache (ETTH). In addition, pericranial muscle tenderness, inflammation, and muscle ischemia have been postulated in headache literature to be causal factors in the peripheral pathophysiology of TTH. However, multiple studies have failed to illustrate evidence for a pathologic role of either ischemia or inflammation within the muscles. Pericranial tenderness is also not likely a peripheral causal factor for TTH, but may instead act to trigger a chronic pain cycle. This is when the peripheral pain response is transformed over time into a centralized pain response. These prolonged alterations in the peripheral pain pathways can lead to increased excitability of the central nervous system pain pathways, resulting in the transition of ETTH into chronic tension-type headache (CTTH). Specifically, the hyperexcitability occurs in central nociceptive neurons (the trigeminal spinal nucleus, thalamus, and cerebral cortex) resulting in central sensitization, which manifests clinically as allodynia and hyperalgesia of CTTH. Additionally, CTTH patients exhibit decreased thermal and pain thresholds which further bolsters support for central sensitization occurring in CTTH.
The alterations in physiology that leads to the overall process of central sensitization, involves changes at the level of neural tracts, neurotransmitters and their receptors, the neural synapse, and the post-synaptic membrane. Evidence also suggests that dysfunction in supraspinal descending inhibitory pain pathways may contribute to the pathogenesis of central sensitization in CTTH.
Neurotransmitters
Specific neuronal receptors and neurotransmitters thought to be most involved include NMDA and AMPA receptors, glutamate, serotonin (5-HT), β-endorphin, and nitric oxide (NO). Of the neurotransmitters, NO plays a major role in central pain pathways and likely contributes to the process of central sensitization. Briefly, the enzyme nitric oxide synthase (NOS) forms NO which ultimately results in vasodilatation and activation of central nervous system pain pathways. Serotonin may also be of significant importance and involved in malfunctioning pain filter located in the brain stem. The view is that the brain misinterprets information—for example from the temporal muscle or other muscles—and interprets this signal as pain. Evidence for this theory comes from the fact that chronic tension-type headaches may be successfully treated with certain antidepressants such as nortriptyline. However, the analgesic effect of nortriptyline, as well as amitriptyline in chronic tension-type headache, is not solely due to serotonin reuptake inhibition, and likely other mechanisms are involved.
Synapses
Regarding synaptic level changes, homosynaptic facilitation and heterosynaptic facilitation are both likely to be involved in central sensitization. Homosynaptic facilitation occurs when synapses normally involved in pain pathways undergo changes involving receptors on the post-synaptic membrane as well as the molecular pathways activated upon synaptic transmission. Lower pain thresholds of CTTH result from this homosynaptic facilitation. In contrast, heterosynaptic facilitation occurs when synapses not normally involved in pain pathways become involved. Once this occurs innocuous signals are interpreted as painful signals. Allodynia and hyperalgesia of CTTH represent this heterosynaptic facilitation clinically.
Stress
In the literature, stress is mentioned as a factor and may be implicated via the adrenal axis. This ultimately results in downstream activation of NMDA receptor activation, NFκB activation, and upregulation of iNOS with subsequent production of NO leading to pain as described above.
Diagnosis
With TTH, the physical exam is expected to be normal with perhaps the exception of either pericranial tenderness upon palpation of the cranial muscles, or presence of either photophobia or phonophobia.
Classification
The International Headache Society's most current classification system for headache disorders is the International Classification of Headache Disorders 3rd edition (ICHD-3) as of 2018. This classification system separates tension-type headache (TTH) into two main groups: episodic (ETTH) and chronic (CTTH). CTTH is defined as fifteen days or more per month with headache for greater than three months, or one-hundred eighty days or more, with headache per year. ETTH is less than fifteen days per month with headache or less than one-hundred eighty days with headache per year. However, ETTH is further sub-divided into frequent and infrequent TTH. Frequent TTH is defined as ten or more episodes of headache over the course of one to fourteen days per month for greater than three months, or at least twelve days per year, but less than one-hundred eighty days per year. Infrequent TTH is defined as ten or more episodes of headache for less than one day per month or less than twelve days per year. Furthermore, all sub-classes of TTH can be classified as having presence or absence of pericranial tenderness, which is tenderness of the muscles of the head. Probable TTH is utilized for patients with some characteristics, but not all characteristics of a given sub-type of TTH.
Differential diagnosis
Extensive testing is not needed as TTH is diagnosed by history and physical examination. However, if symptoms indicative of a more serious diagnosis are present, a contrast enhanced MRI may be utilized. Furthermore, giant cell arteritis should be considered in those 50 years of age and beyond. Screening for giant cell arteritis involves the blood tests of erythrocyte sedimentation rate (ESR) and c-reactive protein.
Migraine
Oromandibular dysfunction
Sinus disease
Eye disease
Cervical spine disease
Infection in immunocompromised
Intracranial mass
Idiopathic intracranial hypertension
Medication overuse headache
Secondary headache (headache due to other disorder)
Giant cell arteritis (≥50 years of age)
Dermatochalasis
Prevention
Lifestyle
Good posture might prevent headaches if there is neck pain.
Drinking alcohol can make headaches more likely or severe.
Drinking water and avoiding dehydration helps in preventing tension headache.
People who have jaw clenching might develop headaches, and getting treatment from a dentist might prevent those headaches.
Using stress management and relaxing often makes headaches less likely.
Biofeedback techniques may also help.
Medications
People who have 15 or more headaches in a month may be treated with certain types of daily antidepressants which act to prevent continued tension headaches from occurring. In those who are predisposed to tension type headaches the first-line preventative treatment is amitriptyline, whereas mirtazapine and venlafaxine are second-line treatment options. Tricyclic antidepressants appear to be useful for prevention. Tricyclic antidepressants have been found to be more effective than SSRIs but have greater side effects. Evidence is poor for the use of SSRIs, propranolol, and muscle relaxants for prevention of tension headaches.
Treatment
Treatment for a current tension headache is to drink water and confirm that there is no dehydration. If symptoms do not resolve within an hour for a person who has had water, then stress reduction might resolve the issue.
Exercise
Evidence supports simple neck and shoulder exercises in managing ETTH and CTTH for headaches associated with neck pain. Exercises include stretching, strengthening and range of motion exercises. CTTH can also benefit from combined therapy from stress therapy, exercises and postural correction.
Medications
Episodic
Over-the-counter drugs, like paracetamol, or NSAIDs (ibuprofen, aspirin, naproxen, ketoprofen), can be effective but tend to only be helpful as a treatment for a few times in a week at most. For those with gastrointestinal problems (ulcers and bleeding), and/or kidney problems, acetaminophen is the better choice over aspirin, though both provide roughly equivalent pain relief. It is important to note that large daily doses of paracetamol should be avoided as it may cause liver damage especially in those that consume 3 or more drinks/day and those with pre-existing liver disease. Ibuprofen, one of the NSAIDs listed above, is a common choice for pain relief but may also lead to gastrointestinal discomfort.
Analgesic/caffeine combinations are popular such as the aspirin-caffeine combination or the aspirin, paracetamol and caffeine combinations. Frequent use (daily or skipping just one day in between use for 7–10 days) of any of the above analgesics may, however, lead to medication overuse headache.
Analgesic/sedative combinations are widely used (e.g., analgesic/antihistamine combinations, analgesic/barbiturate combinations such as Fiorinal).
Muscle relaxants are typically used for and are helpful with acute post-traumatic TTH rather than ETTH. Opioid medications are not utilized to treat ETTH. Botulinum toxin does not appear to be helpful.
Chronic
Classes of medications involved in treatment of CTTH include tricyclic antidepressants (TCAs), SSRIs, benzodiazepine (Clonazepam in small evening dose), and muscle relaxants. The most commonly utilized TCA is amitriptyline due to the postulated role in decreasing central sensitization and analgesic relief. Another popular TCA used is Doxepine. SSRIs may also be utilized for management of CTTH. For patients with concurrent muscle spasm and CTTH, the muscle relaxant Tizanidine can be a helpful option.
These medications however, are not effective if concurrent overuse of over the counter medications or other analgesics is occurring. Stopping overuse must occur prior to proceeding with other forms of treatment.
Manual therapy
Current evidence for acupuncture is slight. A 2016 systematic review suggests better evidence among those with frequent tension headaches, but concludes that further trials comparing acupuncture with other treatment options are needed.
People with tension-type headache often use spinal manipulation, soft tissue therapy, and myofascial trigger point treatment. Studies of effectiveness are mixed. A 2006 systematic review found no rigorous evidence supporting manual therapies for tension headache. A 2005 structured review found only weak evidence for the effectiveness of chiropractic manipulation for tension headache, and that it was probably more effective for tension headache than for migraine. Two other systematic reviews published between 2000 and May 2005 did not find conclusive evidence in favor of spinal manipulation. A 2012 systematic review of manual therapy found that hands-on work may reduce both the frequency and the intensity of chronic tension-type headaches. More current literature also appears to be mixed however, CTTH patients may benefit from massage and physiotherapy as suggested by a systemic review examining these modalities via RCTs specifically for this patient population Despite being helpful, the review also makes a point to note that there is no difference in effectiveness long term (6 months) between those CTTH patients utilizing TCAs and physiotherapy. Another systemic review comparing manual therapy to pharmacologic therapy also supports little long term difference in outcome regarding TTH frequency, duration, and intensity.
Epidemiology
As of 2016 tension headaches affect about 1.89 billion people and are more common in women than men (23% to 18% respectively). Despite its benign character, tension-type headache, especially in its chronic form, can impart significant disability on patients as well as burden on society at large.
| Biology and health sciences | Specific diseases | Health |
322239 | https://en.wikipedia.org/wiki/European%20hare | European hare | The European hare (Lepus europaeus), also known as the brown hare, is a species of hare native to Europe and parts of Asia. It is among the largest hare species and is adapted to temperate, open country. Hares are herbivorous and feed mainly on grasses and herbs, supplementing these with twigs, buds, bark and field crops, particularly in winter. Their natural predators include large birds of prey, canids and felids. They rely on high-speed endurance running to escape predation, having long, powerful limbs and large nostrils.
Generally nocturnal and shy in nature, hares change their behaviour in the spring, when they can be seen in broad daylight chasing one another around in fields. During this spring frenzy, they sometimes strike one another with their paws ("boxing"). This is not just competition between males, but also a female hitting a male, either to show she is not yet ready to mate or to test his determination. The female nests in a depression on the surface of the ground rather than in a burrow and the young are active as soon as they are born. Litters may consist of three or four young and a female can bear three litters a year, with hares living for up to twelve years. The breeding season lasts from January to August.
The European hare is listed as being of least concern by the International Union for Conservation of Nature because it has a wide range and is moderately abundant. However, populations have been declining in mainland Europe since the 1960s, at least partly due to changes in farming practices. The hare has been hunted across Europe for centuries, with more than five million being shot each year; in Britain, it has traditionally been hunted by beagling and hare coursing, but these field sports are now illegal. The hare has been a traditional symbol of fertility and reproduction in some cultures and its courtship behaviour in the spring inspired the English idiom mad as a March hare.
Taxonomy and genetics
The European hare was first described in 1778 by German zoologist Peter Simon Pallas. It shares the genus Lepus (Latin for "hare") with 32 other hare and jackrabbit species, jackrabbits being the name given to some species of hare native to North America. They are distinguished from other leporids (hares and rabbits) by their longer legs and wider nostrils. The Corsican hare, broom hare and Granada hare were at one time considered to be subspecies of the European hare, but DNA sequencing and morphological analysis support their status as separate species.
There is some debate as to whether the European hare and the Cape hare are the same species. A 2005 nuclear gene pool study suggested that they are, but a 2006 study of the mitochondrial DNA of these same animals concluded that they had diverged sufficiently widely to be considered separate species. A 2008 study claims that in the case of Lepus species, with their rapid evolution, species designation cannot be based solely on mtDNA but should also include an examination of the nuclear gene pool. It is possible that the genetic differences between the European and Cape hare are due to geographic separation rather than actual divergence. It has been speculated that in the Near East, hare populations are intergrading and experiencing gene flow. Another 2008 study suggests that more research is needed before a conclusion is reached as to whether a species complex exists; the European hare remains classified as a single species until further data contradicts this assumption.
Cladogenetic analysis suggests that European hares survived the last glacial period during the Pleistocene via refugia in southern Europe (Italian peninsula and Balkans) and Asia Minor. Subsequent colonisations of Central Europe appear to have been initiated by human-caused environmental changes. Genetic diversity in current populations is high with no signs of inbreeding. Gene flow appears to be biased towards males, but overall populations are matrilineally structured. There appears to be a particularly large degree of genetic diversity in hares in the North Rhine-Westphalia region of Germany. It is however possible that restricted gene flow could reduce genetic diversity within populations that become isolated.
Historically, up to 30 subspecies of European hare have been described, although their status has been disputed. These subspecies have been distinguished by differences in pelage colouration, body size, external body measurements, skull morphology and tooth shape.
Sixteen subspecies are listed in the IUCN red book, following Hoffmann and Smith (2005):
Twenty-nine subspecies of "very variable status" are listed by Chapman and Flux in their book on lagomorphs, including the subspecies above (with the exceptions of L. e. connori, L. e. creticus, L. e. cyprius, L. e. judeae, L. e. rhodius, and L. e. syriacus) and additionally:
Description
The European hare, like other members of the family Leporidae, is a fast-running terrestrial mammal; it has eyes set high on the sides of its head, long ears and a flexible neck. Its teeth grow continuously, the first incisors being modified for gnawing while the second incisors are peg-like and non-functional. There is a gap (diastema) between the incisors and the cheek teeth, the latter being adapted for grinding coarse plant material. The dental formula is 2/1, 0/0, 3/2, 3/3. The dark limb musculature of hares is adapted for high-speed endurance running in open country. By contrast, cottontail rabbits are built for short bursts of speed in more vegetated habitats. Other adaptions for high speed running in hares include wider nostrils and larger hearts. In comparison to the European rabbit, the hare has a proportionally smaller stomach and caecum.
This hare is one of the largest of the lagomorphs. Its head and body length can range from with a tail length of . The body mass is typically between . The hare's elongated ears range from from the notch to tip. It also has long hind feet that have a length of between . The skull has nasal bones that are short, but broad and heavy. The supraorbital ridge has well-developed anterior and posterior lobes and the lacrimal bone projects prominently from the anterior wall of the orbit.
The fur colour is grizzled yellow-brown on the back; rufous on the shoulders, legs, neck and throat; white on the underside and black on the tail and ear tips. The fur on the back is typically longer and more curled than on the rest of the body. The European hare's fur does not turn completely white in the winter as is the case with some other members of the genus, although the sides of the head and base of the ears do develop white areas and the hip and rump region may gain some grey.
Distribution and habitat
The European hare is native to much of continental Europe and part of Asia. Its range extends from northern Spain to southern Scandinavia, eastern Europe, and northern parts of Western and Central Asia. It has been extending its range into Siberia. It may have been introduced to Great Britain by the Romans about 2000 years ago, based on a lack of archaeological evidence before that, although new radiocarbon dates suggest that it was introduced earlier, between 500-300BCE. It is not present in Ireland, where the mountain hare is the only native hare species. Undocumented introductions probably occurred in some Mediterranean Islands. It has also been introduced, mostly as game animal, to North America in Ontario and New York State, and unsuccessfully in Pennsylvania, Massachusetts, and Connecticut, the Southern Cone in Brazil, Argentina, Uruguay, Paraguay, Bolivia, Chile, Peru and the Falkland Islands, Australia, both islands of New Zealand and the south Pacific coast of Russia.
The European hare primarily lives in open fields with scattered brush for shelter. It is very adaptable and thrives in mixed farmland. According to a study in the Czech Republic, the mean hare densities were highest at elevations below , 40 to 60 days of annual snow cover, of annual precipitation, and a mean annual air temperature of around . With regards to climate, the European hare density was highest in "warm and dry districts with mild winters". In Poland, the European hare is most abundant in areas with few forest edges, perhaps because foxes can use these for cover. It requires cover, such as hedges, ditches and permanent cover areas, because these habitats supply the varied diet it requires, and are found at lower densities in large open fields. Intensive cultivation of the land results in greater mortality of young hares.
In Great Britain, the European hare is seen most frequently on arable farms, especially those with crop rotation and fallow land, wheat and sugar beet crops. In mainly grass farms, its numbers increased with are improved pastures, some arable crops and patches of woodland. It is seen less frequently where foxes are abundant or where there are many common buzzards. It also seems to be fewer in number in areas with high European rabbit populations, although there appears to be little interaction between the two species and no aggression. Although European hares are shot as game when plentiful, this is a self-limiting activity and is less likely to occur in localities where the species is scarce.
Behaviour and life history
The European hare is primarily nocturnal and spends a third of its time foraging. During daytime, it hides in a depression in the ground called a "form" where it is partially hidden. It can run at , and when confronted by predators it relies on outrunning them in the open. It is generally thought of as asocial but can be seen in both large and small groups. It does not appear to be territorial, living in shared home ranges of around . It communicates with each other by a variety of visual signals. To show interest it raises its ears, while lowering the ears warns others to keep away. When challenging a conspecific, a hare thumps its front feet; the hind feet are used to warn others of a predator. It squeals when hurt or scared, and a female makes "guttural" calls to attract her young. It can live for as long as twelve years.
Food and foraging
The European hare is primarily herbivorous and forages for wild grasses and weeds. With the intensification of agriculture, it has taken to feeding on crops when preferred foods are not available. During the spring and summer, it feeds on soy, clover and corn poppy as well as grasses and herbs. During autumn and winter, it primarily chooses winter wheat, and is also attracted to piles of sugar beet and carrots provided by hunters. It also eats twigs, buds and the bark of shrubs and young fruit trees during winter. It avoids cereal crops when other more attractive foods are available, and appears to prefer high energy foodstuffs over crude dietary fiber. When eating twigs, it strips off the bark to access the vascular tissues which store soluble carbohydrates. Compared to the European rabbit, food passes through the gut more rapidly in the European hare, although digestion rates are similar. It is sometimes coprophagial eating its own green, faecal pellets to recover undigested proteins and vitamins. Two to three adult hares can eat more food than a single sheep.
European hares forage in groups. Group feeding is beneficial as individuals can spend more time feeding knowing that other hares are being vigilant. Nevertheless, the distribution of food affects these benefits. When food is well-spaced, all hares are able to access it. When food is clumped together, only dominant hares can access it. In small gatherings, dominants are more successful in defending food, but as more individuals join in, they must spend more time driving off others. The larger the group, the less time dominant individuals have in which to eat. Meanwhile, the subordinates can access the food while the dominants are distracted. As such, when in groups, all individuals fare worse when food is clumped as opposed to when it is widely spaced.
Mating and reproduction
European hares have a prolonged breeding season which lasts from January to August. Females, or does, can be found pregnant in all breeding months and males, or bucks, are fertile all year round except during October and November. After this hiatus, the size and activity of the males' testes increase, signalling the start of a new reproductive cycle. This continues through December, January and February when the reproductive tract gains back its functionality. Matings start before ovulation occurs and the first pregnancies of the year often result in a single foetus, with pregnancy failures being common. Peak reproductive activity occurs in March and April, when all females may be pregnant, the majority with three or more foetuses.
The mating system of the hare has been described as both polygynous (single males mating with multiple females) and promiscuous. Females have six-weekly reproductive cycles and are receptive for only a few hours at a time, making competition among local bucks intense. At the height of the breeding season, this phenomenon is known as "March madness", when the normally nocturnal bucks are forced to be active in the daytime. In addition to dominant animals subduing subordinates, the female fights off her numerous suitors if she is not ready to mate. Fights can be vicious and can leave numerous scars on the ears. In these encounters, hares stand upright and attack each other with their paws, a practice known as "boxing", and this activity is often between a female and a male and not purely between competing males as was previously believed. When a doe is ready to mate, she runs across the countryside, starting a chase that tests the stamina of the following males. When only the fittest male remains, the female stops and allows him to copulate. Female fertility continues through May, June and July, but testosterone production decreases in males and sexual behaviour becomes less overt. Litter sizes decrease as the breeding season draws to a close with no pregnancies occurring after August. The testes of males begin to regress and sperm production ends in September.
Does give birth in hollow depressions in the ground. An individual female may have three litters in a year with a 41- to 42-day gestation period. The young have an average weight of around at birth. The leverets are fully furred and are precocial, being ready to leave the nest soon after they are born, an adaptation to the lack of physical protection relative to that afforded by a burrow. Leverets disperse during the day and come together in the evening close to where they were born. Their mother visits them for nursing soon after sunset; the young suckle for around five minutes, urinating while they do so, with the doe licking up the fluid. She then leaps away so as not to leave an olfactory trail, and the leverets disperse once more. Young can eat solid food after two weeks and are weaned when they are four weeks old. While young of either sex commonly explore their surroundings, natal dispersal tends to be greater in males. Sexual maturity occurs at seven or eight months for females and six months for males.
Health and mortality
European hares are large leporids and adults can only be tackled by large predators such as canids, felids and the largest birds of prey. In Poland it was found that the consumption of hares by foxes was at its highest during spring, when the availability of small animal prey was low; at this time of year, hares may constitute up to 50% of the biomass eaten by foxes, with 50% of the mortality of adult hares being caused by their predation. In Scandinavia, a natural epizootic of sarcoptic mange which reduced the population of red foxes dramatically, resulted in an increase in the number of European hares, which returned to previous levels when the numbers of foxes subsequently increased. The golden eagle preys on the European hare in the Alps, the Carpathians, the Apennines and northern Spain. In North America, foxes and coyotes are probably the most common predators, with bobcats and lynx also preying on them in more remote locations.
European hares have both external and internal parasites. One study found that 54% of animals in Slovakia were parasitised by nematodes and over 90% by coccidia. In Australia, European hares were reported as being infected by four species of nematode, six of coccidian, several liver flukes and two canine tapeworms. They were also found to host rabbit fleas (Spilopsyllus cuniculi), stickfast fleas (Echidnophaga myrmecobii), lice (Haemodipsus setoni and H. lyriocephalus), and mites (Leporacarus gibbus).
European brown hare syndrome (EBHS) is a disease caused by a calicivirus similar to that causing rabbit haemorrhagic disease (RHD) and can similarly be fatal, but cross infection between the two mammal species does not occur. Other threats to the hare are pasteurellosis, yersiniosis (pseudo-tuberculosis), coccidiosis and tularaemia, which are the principal sources of mortality.
In October 2018, it was reported that a mutated form of the rabbit haemorrhagic disease virus (RHDV2) may have jumped to hares in the UK. Normally rare in hares, a significant die-off from the virus has also occurred in Spain.
Relationship with humans
In folklore, literature, and art
In Europe, the hare has been a symbol of sex and fertility since at least Ancient Greece. The Greeks associated it with the gods Dionysus, Aphrodite and Artemis as well as with satyrs and cupids. The Christian Church connected the hare with lustfulness and homosexuality, but also associated it with the persecution of the church because of the way it was commonly hunted.
In Northern Europe, Easter imagery often involves hares or rabbits. Citing folk Easter customs in Leicestershire, England, where "the profits of the land called Harecrop Leys were applied to providing a meal which was thrown on the ground at the 'Hare-pie Bank'", the 19th-century scholar Charles Isaac Elton proposed a possible connection between these customs and the worship of Ēostre. In his 19th-century study of the hare in folk custom and mythology, Charles J. Billson cites folk customs involving the hare around Easter in Northern Europe, and argues that the hare was probably a sacred animal in prehistoric Britain's festival of springtime. Observation of the hare's springtime mating behaviour led to the popular English idiom "mad as a March hare", with similar phrases from the sixteenth century writings of John Skelton and Sir Thomas More onwards. The mad hare reappears in Alice's Adventures in Wonderland by Lewis Carroll, in which Alice participates in a crazy tea-party with the March Hare and the Hatter.
Any connection of the hare to Ēostre is doubtful. John Andrew Boyle cites an etymology dictionary by Alfred Ernout and Antoine Meillet, who wrote that the lights of Ēostre were carried by hares, that Ēostre represented spring fecundity, love and sexual pleasure. Boyle responds that almost nothing is known about Ēostre, and that the authors had seemingly accepted the identification of Ēostre with the Norse goddess Freyja, but that the hare is not associated with Freyja either. Boyle adds that "when the authors speak of the hare as the 'companion of Aphrodite and of satyrs and cupids' and 'in the Middle Ages [the hare] appears beside the figure of [mythological] Luxuria', they are on much surer ground."
The hare is a character in some fables, such as The Tortoise and the Hare of Aesop. The story was annexed to a philosophical problem by Zeno of Elea, who created a set of paradoxes to support Parmenides' attack on the idea of continuous motion, as each time the hare (or the hero Achilles) moves to where the tortoise was, the tortoise moves just a little further away. The German Renaissance artist Albrecht Dürer realistically depicted a hare in his 1502 watercolour painting Young Hare.
Food and hunting
Across Europe, over five million European hares are shot each year, making it probably the most important game mammal on the continent. This popularity has threatened regional varieties such as those of France and Denmark, through large-scale importing of hares from Eastern European countries such as Hungary. Hares have traditionally been hunted in Britain by beagling and hare coursing. In beagling, the hare is hunted with a pack of small hunting dogs, beagles, followed by the human hunters on foot. In Britain, the 2004 Hunting Act banned hunting of hares with dogs, so the 60 beagle packs now use artificial "trails", or may legally continue to hunt rabbits. Hare coursing with greyhounds was once an aristocratic pursuit, forbidden to lower social classes. More recently, informal hare coursing became a lower class activity and was conducted without the landowner's permission; it is also now illegal. In Scotland concerns have been raised over the increasing numbers of hares shot under license.
Hare is traditionally cooked by jugging: a whole hare is cut into pieces, marinated and cooked slowly with red wine and juniper berries in a tall jug that stands in a pan of water. It is traditionally served with (or briefly cooked with) the hare's blood and port wine. Hare can also be cooked in a casserole. The meat is darker and more strongly flavoured than that of rabbits. Young hares can be roasted; the meat of older hares becomes too tough for roasting, and may be slow-cooked.
Status
The European hare has a wide range across Europe and western Asia and has been introduced to a number of other countries around the globe, often as a game species. In general it is considered moderately abundant in its native range, but declines in populations have been noted in many areas since the 1960s. These have been associated with the intensification of agricultural practices. The hare is an adaptable species and can move into new habitats, but it thrives best when there is an availability of a wide variety of weeds and other herbs to supplement its main diet of grasses. The hare is considered a pest in some areas; it is more likely to damage crops and young trees in winter when there are not enough alternative foodstuffs available.
The International Union for Conservation of Nature has evaluated the European hare's conservation status as being of least concern. However, at low population densities, hares are vulnerable to local extinctions as the available gene pool declines, making inbreeding more likely. This is the case in northern Spain and in Greece, where the restocking by hares brought from outside the region has been identified as a threat to regional gene pools. To counteract this, a captive breeding program has been implemented in Spain, and the relocation of some individuals from one location to another has increased genetic variety. The Bern Convention lists the hare under Appendix III as a protected species. Several countries, including Norway, Germany, Austria and Switzerland, have placed the species on their Red Lists as "near threatened" or "threatened".
| Biology and health sciences | Lagomorphs | Animals |
322376 | https://en.wikipedia.org/wiki/Ecological%20succession | Ecological succession | Ecological succession is the process of change in the species that make up an ecological community over time.
The process of succession occurs either after the initial colonization of a newly created habitat, or after a disturbance substantially alters a pre-existing habitat. Succession that begins in new habitats, uninfluenced by pre-existing communities, is called primary succession, whereas succession that follows disruption of a pre-existing community is called secondary succession. Primary succession may happen after a lava flow or the emergence of a new island from the ocean. Surtsey, a volcanic island off the southern coast of Iceland, is an important example of a place where primary succession has been observed. On the other hand, secondary succession happens after disturbance of a community, such as from a fire, severe windthrow, or logging.
Succession was among the first theories advanced in ecology. Ecological succession was first documented in the Indiana Dunes of Northwest Indiana and remains an important ecological topic of study. Over time, the understanding of succession has changed from a linear progression to a stable climax state, to a more complex, cyclical model that de-emphasizes the idea of organisms having fixed roles or relationships.
History
Precursors of the idea of ecological succession go back to the beginning of the 19th century. As early as 1742 French naturalist Buffon noted that poplars precede oaks and beeches in the natural evolution of a forest. Buffon was later forced by the theological committee at the University of Paris to recant many of his ideas because they contradicted the biblical narrative of Creation.
Swiss geologist Jean-André Deluc and the later French naturalist Adolphe Dureau de la Malle were the first to make use of the word succession concerning the vegetation development after forest clear-cutting. In 1859 Henry David Thoreau wrote an address called "The Succession of Forest Trees" in which he described succession in an oak-pine forest. "It has long been known to observers that squirrels bury nuts in the ground, but I am not aware that any one has thus accounted for the regular succession of forests." The Austrian botanist Anton Kerner published a study about the succession of plants in the Danube river basin in 1863.
Ragnar Hult's 1885 study on the stages of forest development in Blekinge noted that grassland becomes heath before the heath develops into forest. Birch dominated the early stages of forest development, then pine (on dry soil) and spruce (on wet soil). If the birch is replaced by oak it eventually develops to beechwood. Swamps proceed from moss to sedges to moor vegetation followed by birch and finally spruce.
H. C. Cowles
Between 1899 and 1910, Henry Chandler Cowles, at the University of Chicago, developed a more formal concept of succession. Inspired by studies of Danish dunes by Eugen Warming, Cowles studied vegetation development on sand dunes on the shores of Lake Michigan (the Indiana Dunes). He recognized that vegetation on dunes of different ages might be interpreted as different stages of a general trend of vegetation development on dunes (an approach to the study of vegetation change later termed space-for-time substitution, or chronosequence studies). He first published this work as a paper in the Botanical Gazette in 1899 ("The ecological relations of the vegetation of the sand dunes of Lake Michigan"). In this classic publication and subsequent papers, he formulated the idea of primary succession and the notion of a sere—a repeatable sequence of community changes specific to particular environmental circumstances.
Gleason and Clements
From about 1900 to 1960, however, understanding of succession was dominated by the theories of Frederic Clements, a contemporary of Cowles, who held that seres were highly predictable and deterministic and converged on a climatically determined stable climax community regardless of starting conditions. Clements explicitly analogized the successional development of ecological communities with ontogenetic development of individual organisms, and his model is often referred to as the pseudo-organismic theory of community ecology. Clements and his followers developed a complex taxonomy of communities and successional pathways.
Henry Gleason offered a contrasting framework as early as the 1920s. The Gleasonian model was more complex and much less deterministic than the Clementsian. It differs most fundamentally from the Clementsian view in suggesting a much greater role of chance factors and in denying the existence of coherent, sharply bounded community types. Gleason argued that species distributions responded individualistically to environmental factors, and communities were best regarded as artifacts of the juxtaposition of species distributions. Gleason's ideas, first published in 1926, were largely ignored until the late 1950s.
Two quotes illustrate the contrasting views of Clements and Gleason. Clements wrote in 1916:
while Gleason, in his 1926 paper, said:
Gleason's ideas were, in fact, more consistent with Cowles' original thinking about succession. About Clements' distinction between primary succession and secondary succession, Cowles wrote (1911):
Eugene Odum
In 1969, Eugene Odum published The Strategy of Ecosystem Development, a paper that was highly influential to conservation and environmental restoration. Odum argued that ecological succession was an orderly progression toward a climax state where “maximum biomass and symbiotic function between organisms are maintained per unit energy flow." Odum highlighted how succession was not merely a change in the species composition of an ecosystem, but also created change in more complex attributes of the ecosystem, such as structure and nutrient cycling.
Modern era
A more rigorous, data-driven testing of successional models and community theory generally began with the work of Robert Whittaker and John Curtis in the 1950s and 1960s. Succession theory has since become less monolithic and more complex. J. Connell and R. Slatyer attempted a codification of successional processes by mechanism. Among British and North American ecologists, the notion of a stable climax vegetation has been largely abandoned, and successional processes have come to be seen as much less deterministic, with important roles for historical contingency and for alternate pathways in the actual development of communities. Debates continue as to the general predictability of successional dynamics and the relative importance of equilibrial vs. non-equilibrial processes. Former Harvard professor Fakhri A. Bazzaz introduced the notion of scale into the discussion, as he considered that at local or small area scale the processes are stochastic and patchy, but taking bigger regional areas into consideration, certain tendencies can not be denied.
More recent definitions of succession highlight change as the central characteristic. New research techniques are greatly enhancing contemporary scientists' ability to study succession, which is now seen as neither entirely random nor entirely predictable.
Factors
Both consistent patterns and variability are observed in ecological succession. Theories of ecological succession identify different factors that help explain why plant communities change the way they do.
Diversity of possible trajectories
Ecological succession was formerly seen as an orderly progression through distinct stages, where several plant communities would replace each other in a fixed order and eventually reach a stable end point known as the climax. The climax community was sometimes referred to as the 'potential vegetation' of a site, and thought to be primarily determined by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of ecosystems dynamics. Most natural ecosystems experience disturbance at a rate that makes a "climax" community unattainable. Climate change often occurs at a rate and frequency sufficient to prevent arrival at a climax state.
The trajectory of successional change can be influenced by initial site conditions, by the type of disturbance that triggers succession, by the interactions of the species present, and by more random factors such as availability of colonists or seeds or weather conditions at the time of disturbance. Some aspects of succession are broadly predictable; others may proceed more unpredictably than in the classical view of ecological succession. Coupled with the stochastic nature of disturbance events and other long-term (e.g., climatic) changes, such dynamics make it doubtful whether the 'climax' concept ever applies or is particularly useful in considering actual vegetation.
Stochastic events
Succession is influenced partially by random chance, but it is debated how much random chance directs the trajectory of succession, as opposed to more deterministic factors. The timing of a disturbance such as a weather event may be random and unpredictable. Dispersal of propagules to a new site may also be random. However, community assembly is also determined by processes that select species non-randomly from the local species pool.
Dispersal limitation vs. environmental filtering
Succession is impacted both by the ability of seeds to disperse to new sites, and the suitability of site conditions for those seeds to grow and survive. Dispersal limitation means that even though favorable sites for a plant to live might exist, the plant's seeds may be unable to reach those sites. Environmental filtering, also called establishment limitation, implies that although seeds may be distributed to a site, those seeds may be unable to survive due to various characteristics of the site. The predicted impact of these two factors varies under different models of ecological succession.
Feedback loops
Ecological succession is driven by feedbacks between plants and their environment. As plants grow following a disturbance, they change their environment, for example by creating shade, attracting seed dispersers, contributing organic matter to the soil, changing the availability of soil nutrients, creating microhabitats, and buffering temperature and moisture fluctuations. This creates opportunities for different plants to grow, which causes directional change in the ecosystem. The development of some ecosystem attributes, such as soil properties and nutrient cycles, are both influenced by community properties, and, in turn, influence further successional development. This feed-back process may occur over centuries or millennia. Plants may facilitate the establishment of other plants by creating suitable conditions for them to grow, for example by providing shade or allowing for soil formation. Plants may also competitively exclude or otherwise prevent the growth of other plants.
Patterns
Though the idea of a fixed, predictable process of succession with a single well-defined climax is an overly simplified model, several predictions made by the classical model are accurate. Species diversity, overall plant biomass, plant lifespans, the importance of decomposer organisms, and overall stability all increase as a community approaches a climax state, while the rate at which soil nutrients are consumed, rate of biogeochemical cycling, and rate of net primary productivity all decrease as a community approaches a climax state.
Communities in early succession will be dominated by fast-growing, well-dispersed species (opportunist, fugitive, or r-selected life-histories). These are also called pioneer species. As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species.
Some of these trends do not apply in all cases. For example, species diversity almost necessarily increases during early succession as new species arrive, but may decline in later succession as competition eliminates opportunistic species and leads to dominance by locally superior competitors. Net Primary Productivity, biomass, and trophic properties all show variable patterns over succession, depending on the particular system and site.
Disruptions
Two important perturbation factors today are human actions and climatic change. Additions to available species pools through range expansions and introductions can also continually reshape communities.
Types
Primary succession
Successional dynamics beginning with colonization of an area that has not been previously occupied by an ecological community are referred to as primary succession. This includes newly exposed rock or sand surfaces, lava flows, and newly exposed glacial tills. The stages of primary succession include pioneer microorganisms, plants (lichens and mosses), grassy stage, smaller shrubs, and trees. Animals begin to return when there is food there for them to eat. When it is a fully functioning ecosystem, it has reached the climax community stage.
Secondary succession
Secondary succession follows severe disturbance or removal of a preexisting community that has remnants of the previous ecosystem. Secondary succession is strongly influenced by pre-disturbance conditions such as soil development, seed banks, remaining organic matter, and residual living organisms. Because of residual fertility and preexisting organisms, community change in early stages of secondary succession can be relatively rapid.
Secondary succession is much more commonly observed and studied than primary succession. Particularly common types of secondary succession include responses to natural disturbances such as fire, flood, and severe winds, and to human-caused disturbances such as logging and agriculture. In secondary succession, the soils and organisms need to be left unharmed so there is a way for the new material to rebuild.
As an example, in a fragmented old field habitat created in eastern Kansas, woody plants "colonized more rapidly (per unit area) on large and nearby patches".
Secondary succession can quickly change a landscape. In the 1900s, Acadia National Park had a wildfire that destroyed much of the landscape. Originally evergreen trees grew in the landscape. After the fire, the area took at least a year to grow shrubs. Eventually, deciduous trees started to grow instead of evergreens.
Secondary succession has been occurring in Shenandoah National Park following the 1995 flood of the Moorman's and Rapidan rivers, which destroyed plant and animal life.
Seasonal and cyclic dynamics
Unlike secondary succession, these types of vegetation change are not dependent on disturbance but are periodic changes arising from fluctuating species interactions or recurring events. These models modify the climax concept towards one of dynamic states.
Causes of plant succession
Autogenic succession can be brought by changes in the soil caused by the organisms there. These changes include accumulation of organic matter in litter or humic layer, alteration of soil nutrients, or change in the pH of soil due to the plants growing there. The structure of the plants themselves can also alter the community. For example, when larger species like trees mature, they produce shade on to the developing forest floor that tends to exclude light-requiring species. Shade-tolerant species will invade the area.
Allogenic succession is caused by external environmental influences and not by the vegetation. For example, soil changes due to erosion, leaching or the deposition of silt and clays can alter the nutrient content and water relationships in the ecosystems. Animals also play an important role in allogenic changes as they are pollinators, seed dispersers and herbivores. They can also increase nutrient content of the soil in certain areas, or shift soil about (as termites, ants, and moles do) creating patches in the habitat. This may create regeneration sites that favor certain species.
Climatic factors may be very important, but on a much longer time-scale than any other. Changes in temperature and rainfall patterns will promote changes in communities. As the climate warmed at the end of each ice age, great successional changes took place. The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest. The greenhouse effect resulting in increase in temperature is likely to bring profound Allogenic changes in the next century. Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes.
Mechanisms
In 1916, Frederic Clements published a descriptive theory of succession and advanced it as a general ecological concept. His theory of succession had a powerful influence on ecological thought. Clements' concept is usually termed classical ecological theory.
According to Clements, succession is a process involving several phases:
Nudation: Succession begins with the development of a bare site, called Nudation (disturbance).
Migration: refers to arrival of propagules.
Ecesis: involves establishment and initial growth of vegetation.
Competition: as vegetation becomes well established, grows, and spreads, various species begin to compete for space, light and nutrients.
Reaction: during this phase autogenic changes such as the buildup of humus affect the habitat, and one plant community replaces another.
Stabilization: a supposedly stable climax community forms.
Seral communities
A seral community is an intermediate stage found in an ecosystem advancing towards its climax community. In many cases more than one seral stage evolves until climax conditions are attained. A prisere is a collection of seres making up the development of an area from non-vegetated surfaces to a climax community. Depending on the substratum and climate, different seres are found.
Changes in animal life
Succession theory was developed primarily by botanists. The study of succession applied to whole ecosystems initiated in the writings of Ramon Margalef, while Eugene Odum's publication of The Strategy of Ecosystem Development is considered its formal starting point.
Animal life also exhibits changes with changing communities. In the lichen stage, fauna is sparse. It comprises a few mites, ants, and spiders living in cracks and crevices. The fauna undergoes a qualitative increase during the herb grass stage. The animals found during this stage include nematodes, insect larvae, ants, spiders, mites, etc. The animal population increases and diversifies with the development of the forest climax community. The fauna consists of invertebrates like slugs, snails, worms, millipedes, centipedes, ants, bugs; and vertebrates such as squirrels, foxes, mice, moles, snakes, various birds, salamanders and frogs.
A review of succession research by Hodkinson et al. (2002) documented what was likely first noted by Darwin during his voyage on the H.M.S. Beagle:
These naturalists note that prior to the establishment of autotrophs, there is a foodweb formed by heterotrophs built on allochthonous inputs of dead organic matter (necromass). Work on volcanic systems such as Kasatochi Volcano in the Aleutians by Sikes and Slowik (2010) supports this idea.
Microsuccession
Succession of micro-organisms including fungi and bacteria occurring within a microhabitat is known as microsuccession or serule. In artificial bacterial meta-communities of motile strains on-chip it has been shown that ecological succession is based on a trade-off between colonization and competition abilities. To exploit locations or explore the landscape? Escherichia coli is a fugitive species, whereas Pseudomonas aeruginosa is a slower colonizer but superior competitor. Like in plants, microbial succession can occur in newly available habitats (primary succession) such as surfaces of plant leaves, recently exposed rock surfaces (i.e., glacial till) or animal infant guts, and also on disturbed communities (secondary succession) like those growing in recently dead trees, decaying fruits, or animal droppings. Microbial communities may also change due to products secreted by the bacteria present. Changes of pH in a habitat could provide ideal conditions for a new species to inhabit the area. In some cases the new species may outcompete the present ones for nutrients leading to the primary species demise. Changes can also occur by microbial succession with variations in water availability and temperature. Theories of macroecology have only recently been applied to microbiology and so much remains to be understood about this growing field. A recent study of microbial succession evaluated the balances between stochastic and deterministic processes in the bacterial colonization of a salt marsh chronosequence. The results of this study show that, much like in macro succession, early colonization (primary succession) is mostly influenced by stochasticity while secondary succession of these bacterial communities was more strongly influenced by deterministic factors.
Climax concept
According to classical ecological theory, succession stops when the sere has arrived at an equilibrium or steady state with the physical and biotic environment. Barring major disturbances, it will persist indefinitely. This end point of succession is called climax.
Climax community
The final or stable community in a sere is the climax community or climatic vegetation. It is self-perpetuating and in equilibrium with the physical habitat. There is no net annual accumulation of organic matter in a climax community. The annual production and use of energy is balanced in such a community.
Characteristics
The vegetation is tolerant of environmental conditions.
It has a wide diversity of species, a well-drained spatial structure, and complex food chains.
The climax ecosystem is balanced. There is equilibrium between gross primary production and total respiration, between energy used from sunlight and energy released by decomposition, between uptake of nutrients from the soil and the return of nutrient by litter fall to the soil.
Individuals in the climax stage are replaced by others of the same kind. Thus the species composition maintains equilibrium.
It is an index of the climate of the area. The life or growth forms indicate the climatic type.
Types of climax
Climatic Climax If there is only a single climax and the development of climax community is controlled by the climate of the region, it is termed as climatic climax. For example, development of Maple-beech climax community over moist soil. Climatic climax is theoretical and develops where physical conditions of the substrate are not so extreme as to modify the effects of the prevailing regional climate.
Edaphic Climax When there are more than one climax communities in the region, modified by local conditions of the substrate such as soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity, it is called edaphic climax. Succession ends in an edaphic climax where topography, soil, water, fire, or other disturbances are such that a climatic climax cannot develop.
Catastrophic Climax Climax vegetation vulnerable to a catastrophic event such as a wildfire. For example, in California, chaparral vegetation is the final vegetation. The wildfire removes the mature vegetation and decomposers. A rapid development of herbaceous vegetation follows until the shrub dominance is re-established. This is known as catastrophic climax.
Disclimax When a stable community, which is not the climatic or edaphic climax for the given site, is maintained by man or his domestic animals, it is designated as Disclimax (disturbance climax) or anthropogenic subclimax (man-generated). For example, overgrazing by stock may produce a desert community of bushes and cacti where the local climate actually would allow grassland to maintain itself.
Subclimax The prolonged stage in succession just preceding the climatic climax is subclimax.
Preclimax and Postclimax In certain areas different climax communities develop under similar climatic conditions. If the community has life forms lower than those in the expected climatic climax, it is called preclimax; a community that has life forms higher than those in the expected climatic climax is postclimax. Preclimax strips develop in less moist and hotter areas, whereas Postclimax strands develop in more moist and cooler areas than that of surrounding climate.
Theories
There are three schools of interpretations explaining the climax concept:
Monoclimax or Climatic Climax Theory was advanced by Clements (1916) and recognizes only one climax whose characteristics are determined solely by climate (climatic climax). The processes of succession and modification of environment overcome the effects of differences in topography, parent material of the soil, and other factors. The whole area would be covered with uniform plant community. Communities other than the climax are related to it, and are recognized as subclimax, postclimax and disclimax.
Polyclimax Theory was advanced by Tansley (1935). It proposes that the climax vegetation of a region consists of more than one vegetation climaxes controlled by soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity.
Climax Pattern Theory was proposed by Whittaker (1953). The climax pattern theory recognizes a variety of climaxes governed by responses of species populations to biotic and abiotic conditions. According to this theory the total environment of the ecosystem determines the composition, species structure, and balance of a climax community. The environment includes the species' responses to moisture, temperature, and nutrients, their biotic relationships, availability of flora and fauna to colonize the area, chance dispersal of seeds and animals, soils, climate, and disturbance such as fire and wind. The nature of climax vegetation will change as the environment changes. The climax community represents a pattern of populations that corresponds to and changes with the pattern of environment. The central and most widespread community is the climatic climax.
The theory of alternative stable states suggests there is not one end point but many which transition between each other over ecological time.
Succession by habitat type
Forest succession
Forests, being an ecological system, are subject to the species succession process. There are "opportunistic" or "pioneer" species that produce great quantities of seed that are disseminated by the wind, and therefore can colonize big empty extensions. They are capable of germinating and growing in direct sunlight. Once they have produced a closed canopy, the lack of direct sun radiation at the soil makes it difficult for their own seedlings to develop. It is then the opportunity for shade-tolerant species to become established under the protection of the pioneers. When the pioneers die, the shade-tolerant species replace them. These species are capable of growing beneath the canopy, and therefore, in the absence of disturbances, will stay. For this reason it is then said the stand has reached its climax. When a disturbance occurs, the opportunity for the pioneers opens up again, provided they are present or within a reasonable range.
An example of pioneer species, in forests of northeastern North America are Betula papyrifera (White birch) and Prunus serotina (Black cherry), that are particularly well-adapted to exploit large gaps in forest canopies, but are intolerant of shade and are eventually replaced by other shade-tolerant species in the absence of disturbances that create such gaps. In the tropics, well known pioneer forest species can be found among the genera Cecropia, Ochroma and Trema.
Things in nature are not black and white, and there are intermediate stages. It is therefore normal that between the two extremes of light and shade there is a gradient, and there are species that may act as pioneer or tolerant, depending on the circumstances. It is of paramount importance to know the tolerance of species in order to practice an effective silviculture.
Wetland succession
Since many types of wetland environments exist, succession may follow a wide array of trajectories and patterns in wetlands. Under the classical model, the process of secondary succession holds that a wetland progresses over time from an initial state of open water with few plants, to a forested climax state where decayed organic matter has built up over time, forming peat. However, many wetlands are maintained by regular disturbance or natural processes at an equilibrium state that does not resemble the predicted forested "climax." The idea that ponds and wetlands gradually fill in to become dry land has been criticized and called into question due to lack of evidence.
Wetland succession is a uniquely complex, non-linear process shaped by hydrology. Hydrological factors often work against linear processes that predict a succession to a "climax" state. The energy carried by moving water may create a continuous source of disturbance. For example, in coastal wetlands, the tides moving in and out continuously acts upon the ecological community. Fire may also maintain an equilibrium state in a wetland by burning off vegetation, thus interrupting the accumulation of peat.
Water entering and leaving the wetland follows patterns that are broadly cyclical but erratic. For example, seasonal flooding and drying may occur with yearly changes in precipitation, causing seasonal changes in the wetland community that maintain it at a stable state. However, unusually heavy rain or unusually severe drought may cause the wetland to enter a positive feedback loop where it begins to change in a linear direction. Since wetlands are sensitive to changes in the natural processes that maintain them, human activities, invasive species, and climate change could initiate long-term changes in wetland ecosystems.
Grassland succession
For a long time, grasslands were thought to be early stages of succession, dominated by weedy species and with little conservation value. However, comparing grasslands that form after recovery from long-term disruptions like agricultural tillage with ancient or "old-growth" grasslands has shown that grasslands are not inherently early-successional communities. Rather, grasslands undergo a centuries-long process of succession, and a grassland that is tilled up for agriculture or otherwise destroyed is estimated to take a minimum of 100 years, and potentially on average 1,400 years, to recover to its previous level of biodiversity. However, planting a high diversity of late-successional grassland species in a disturbed environment can accelerate the recovery of the soil's ability to sequester carbon, resulting in twice as much carbon storage as a naturally recovering grassland over the same period of time.
Many grassland ecosystems are maintained by disturbance, such as fire and grazing by large animals, or else the process of succession will change them to forest or shrubland. In fact, it is debated whether fire should be considered disturbance at all for the North American prairie ecosystems, since it maintains, rather than disrupts, an equilibrium state. Many late-successional grassland species have adaptations that allow them to store nutrients underground and re-sprout rapidly after "aboveground" disturbances like fire or grazing. Disturbance events that severely disrupt or destroy the soil, such as tilling, eliminate these late-successional species, reverting the grassland to an early successional stage dominated by pioneers, whereas fire and grazing benefit late-successional species. Both too much and too little disturbance can damage the biodiversity of disturbance-dependent ecosystems like grasslands.
In North American semi-arid grasslands, the introduction of livestock ranching and absence of fire was observed to cause a transition away from grasses to woody vegetation, particularly mesquite. However, the means by which ecological succession under frequent disturbance results in ecosystems of the sort seen in remnant prairies is poorly understood.
| Biology and health sciences | Ecology | Biology |
322553 | https://en.wikipedia.org/wiki/Aneurysm | Aneurysm | An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (starting point) for clot formation (thrombosis) and embolization. As an aneurysm increases in size, the risk of rupture, which leads to uncontrolled bleeding, increases. Although they may occur in any blood vessel, particularly lethal examples include aneurysms of the circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms. Aneurysms can arise in the heart itself following a heart attack, including both ventricular and atrial septal aneurysms. There are congenital atrial septal aneurysms, a rare heart defect.
Etymology
The word is from Greek: ἀνεύρυσμα, aneurysma, "dilation", from ἀνευρύνειν, aneurynein, "to dilate".
Classification
Aneurysms are classified by type, morphology, or location.
True and false aneurysms
A true aneurysm is one that involves all three layers of the wall of an artery (intima, media and adventitia). True aneurysms include atherosclerotic, syphilitic, and congenital aneurysms, as well as ventricular aneurysms that follow transmural myocardial infarctions (aneurysms that involve all layers of the attenuated wall of the heart are also considered true aneurysms).
A false aneurysm, or pseudoaneurysm, is a collection of blood leaking completely out of an artery or vein but confined next to the vessel by the surrounding tissue. This blood-filled cavity will eventually either thrombose (clot) enough to seal the leak or rupture out of the surrounding tissue.
Pseudoaneurysms can be caused by trauma that punctures the artery, such as knife and bullet wounds, as a result of percutaneous surgical procedures such as coronary angiography or arterial grafting, or use of an artery for injection.
Morphology
Aneurysms can also be classified by their macroscopic shapes and sizes and are described as either saccular or fusiform. The shape of an aneurysm is not specific for a specific disease. The size of the base or neck is useful in determining the chance of for example endovascular coiling.
Saccular aneurysms, or "berry" aneurysms, are spherical in shape and involve only a portion of the vessel wall; they usually range from in diameter, and are often filled, either partially or fully, by a thrombus.Saccular aneurysms have a "neck" that connects the aneurysm to its main ("parent") artery, a larger, rounded area, called the dome.
Fusiform aneurysms ("spindle-shaped" aneurysms) are variable in both their diameter and length; their diameters can extend up to . They often involve large portions of the ascending and transverse aortic arch, the abdominal aorta, or, less frequently, the iliac arteries.
Location
Aneurysms can also be classified by their location:
Arterial and venous, with arterial being more common.
The heart, including coronary artery aneurysms, ventricular aneurysms, aneurysm of sinus of Valsalva, and aneurysms following cardiac surgery.
The aorta, namely aortic aneurysms including thoracic aortic aneurysms and abdominal aortic aneurysms.
The brain, including cerebral aneurysms, berry aneurysms, and Charcot–Bouchard aneurysms.
The legs, including the popliteal arteries.
The kidney, including renal artery aneurysms and intraparenchymal aneurysms.
Capillary aneurysms are flesh-colored solitary lesions, resembling an intradermal nevus, which may suddenly grow larger and darker and become blue-black or black as a result of thrombosis.
The large vessels such as external and internal jugular veins
Cerebral aneurysms, also known as intracranial or brain aneurysms, occur most commonly in the anterior cerebral artery, which is part of the circle of Willis. This can cause severe strokes leading to death. The next most common sites of cerebral aneurysm occurrence are in the internal carotid artery.
Size
Abdominal aortic aneurysms are commonly divided according to their size and symptomatology. An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm), or more than 50% of normal diameter that of a healthy individual of the same sex and age. If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large.
The common iliac artery is classified as:
Signs and symptoms
Aneurysm presentation may range from life-threatening complications of hypovolemic shock to being found incidentally on X-ray. Symptoms will differ by the site of the aneurysm and can include:
Cerebral aneurysm
Symptoms can occur when the aneurysm pushes on a structure in the brain. Symptoms will depend on whether an aneurysm has ruptured or not. There may be no symptoms present at all until the aneurysm ruptures. For an aneurysm that has not ruptured the following symptoms can occur:
Fatigue
Loss of perception
Loss of balance
Speech problems
Double vision
For a ruptured aneurysm, symptoms of a subarachnoid hemorrhage may present:
Severe headaches
Loss of vision
Double vision
Neck pain or stiffness
Pain above or behind the eyes
Abdominal aneurysm
Abdominal aortic aneurysm involves a regional dilation of the aorta and is diagnosed using ultrasonography, computed tomography, or magnetic resonance imaging. A segment of the aorta that is found to be greater than 50% larger than that of a healthy individual of the same sex and age is considered aneurysmal. Abdominal aneurysms are usually asymptomatic but in rare cases can cause lower back pain or lower limb ischemia.
Renal (kidney) aneurysm
Flank pain and tenderness
Hypertension
Haematuria
Signs of hypovolemic shock
Risk factors
Risk factors for an aneurysm include diabetes, obesity, hypertension, tobacco use, alcoholism, high cholesterol, copper deficiency, increasing age, and tertiary syphilis infection. Connective tissue disorders such as Loeys-Dietz syndrome, Marfan syndrome, and certain forms of Ehlers-Danlos syndrome are also associated with aneurysms. Aneurysms, dissections, and ruptures in individuals under 40 years of age are a major diagnostic criteria of the vascular form of Ehlers-Danlos syndrome (vEDS).
Specific infective causes associated with aneurysm include:
Advanced syphilis infection resulting in syphilitic aortitis and an aortic aneurysm
Tuberculosis, causing Rasmussen's aneurysms
Brain infections, causing infectious intracranial aneurysms
A minority of aneurysms are associated with genetic factors. Examples include:
Berry aneurysms of the anterior communicating artery of the circle of Willis, associated with autosomal dominant polycystic kidney disease
Familial thoracic aortic aneurysms
Cirsoid aneurysms, secondary to congenital arteriovenous malformations
Pathophysiology
Aneurysms form for a variety of interacting reasons. Multiple factors, including factors affecting a blood vessel wall and the blood through the vessel, contribute.
The pressure of blood within the expanding aneurysm may also injure the blood vessels supplying the artery itself, further weakening the vessel wall. Without treatment, these aneurysms will ultimately progress and rupture.
Infection. A mycotic aneurysm is an aneurysm that results from an infectious process that involves the arterial wall. A person with a mycotic aneurysm has a bacterial infection in the wall of an artery, resulting in the formation of an aneurysm. One of the causes of mycotic aneurysms is infective endocarditis. The most common locations include arteries in the abdomen, thigh, neck, and arm. A mycotic aneurysm can result in sepsis, or life-threatening bleeding if the aneurysm ruptures. Less than 3% of abdominal aortic aneurysms are mycotic aneurysms.
Syphilis. The third stage of syphilis also manifests as aneurysm of the aorta, which is due to loss of the vasa vasorum in the tunica adventitia.
Copper deficiency. A minority of aneurysms are caused by copper deficiency, which results in a decreased activity of the lysyl oxidase enzyme, affecting elastin, a key component in vessel walls. Copper deficiency results in vessel wall thinning, and thus has been noted as a cause of death in copper-deficient humans, chickens, and turkeys.
Mechanics
Aneurysmal blood vessels are prone to rupture under normal blood pressure and flow due to the special mechanical properties that make them weaker. To better understand this phenomenon, we can first look at healthy arterial vessels which exhibit (for a biomaterial in vivo). Unlike crystalline materials whose linear elastic region follows Hooke's Law under uniaxial loading, many biomaterials exhibit a J-shaped stress-strain curve which is non-linear and concave up. The blood vessel can be under large strain, or the amount of stretch the blood vessel can undergo, for a range of low applied stress before fracture, as shown by the lower part of the curve. The area under the curve up to a given strain is much lower than that for the equivalent Hookean curve, which is correlated to toughness. Toughness is defined as the amount of energy per unit volume material can absorb before rupturing. Because the amount of energy released is proportional to the amount of crack propagation, the blood vessel wall can withstand pressure and is "tough". Thus, healthy blood vessels with the mechanical properties of the J-shaped stress-strain curve have greater stability against aneurysms than materials with linear elasticity.
Blood vessels with aneurysms, on the other hand, are under the influence of an S-shaped stress-strain curve. As a visual aid, aneurysms can be understood as a long, cylindrical balloon. Because it's a tight balloon under pressure, it can pop at any time stress beyond a certain force threshold is applied. In the same vein, an unhealthy blood vessel has elastic instabilities that lead to rupture. Initially, for a given radius and pressure, stiffness of the material increases linearly. At a certain point, the stiffness of the arterial wall starts to decrease with increasing load. At higher strain values, the area under the curve increases, thus increasing the impact on the material that would promote crack propagation. The differences in the mechanical properties of the aneurysmal blood vessels and the healthy blood vessels stem from the compositional differences of the vessels. Compared to normal aortas, aneurysmal aortas have a much higher volume fraction of collagen and ground substance (54.8% vs. 95.6%) and a much lower volume fraction of elastin (22.7% vs. 2.4%) and smooth muscles (22.6% vs. 2.2%), which contribute to higher initial stiffness. It was also found that the ultimate tensile strength, or the strength to withstand rupture, of aneurysmal vessel wall is 50% lower than that of normal aortas. The wall strength of ruptured aneurysmal aortic wall was also found to be 54.2 N/cm2, which is much lower than that of a repaired aorta wall, 82.3 N/cm2. Due to the change in composition of the arterial wall, aneurysms overall have much lower strength to resist rupture. Predicting the risk of rupture is difficult due to the regional anisotropy the hardened blood vessels exhibit, meaning that the stress and strength values vary depending on the region and the direction of the vessel they are measured along.
Diagnosis
Diagnosis of a ruptured cerebral aneurysm is commonly made by finding signs of subarachnoid hemorrhage on a computed tomography (CT) scan. If the CT scan is negative but a ruptured aneurysm is still suspected based on clinical findings, a lumbar puncture can be performed to detect blood in the cerebrospinal fluid. Computed tomography angiography (CTA) is an alternative to traditional angiography and can be performed without the need for arterial catheterization. This test combines a regular CT scan with a contrast dye injected into a vein. Once the dye is injected into a vein, it travels to the cerebral arteries, and images are created using a CT scan. These images show exactly how blood flows into the brain arteries.
Treatment
Historically, the treatment of arterial aneurysms has been limited to either surgical intervention or watchful waiting in combination with control of blood pressure. At least, in the case of abdominal aortic aneurysm (AAA), the decision does not come without significant risk and cost, hence, there is a great interest in identifying more advanced decision-making approaches that are not solely based on the AAA diameter, but involve other geometrical and mechanical nuances such as local thickness and wall stress. In recent years, endovascular or minimally invasive techniques have been developed for many types of aneurysms. Aneurysm clips are used for surgical procedure i.e. clipping of aneurysms.
Intracranial
There are currently two treatment options for brain aneurysms: surgical clipping or endovascular coiling. There is currently debate in the medical literature about which treatment is most appropriate given particular situations.
Surgical clipping was introduced by Walter Dandy of the Johns Hopkins Hospital in 1937. It consists of a craniotomy to expose the aneurysm and closing the base or neck of the aneurysm with a clip. The surgical technique has been modified and improved over the years.
Endovascular coiling was introduced by Italian neurosurgeon Guido Guglielmi at UCLA in 1989. It consists of passing a catheter into the femoral artery in the groin, through the aorta, into the brain arteries, and finally into the aneurysm itself. Platinum coils initiate a clotting reaction within the aneurysm that, if successful, fills the aneurysm dome and prevents its rupture. A flow diverter can be used, but risks complications.
Aortic and peripheral
For aneurysms in the aorta, arms, legs, or head, the weakened section of the vessel may be replaced by a bypass graft that is sutured at the vascular stumps. Instead of sewing, the graft tube ends, made rigid and expandable by nitinol wireframe, can be easily inserted in its reduced diameter into the vascular stumps and then expanded up to the most appropriate diameter and permanently fixed there by external ligature. New devices were recently developed to substitute the external ligature by expandable ring allowing use in acute ascending aorta dissection, providing airtight (i.e. not dependent on the coagulation integrity), easy and quick anastomosis extended to the arch concavity Less invasive endovascular techniques allow covered metallic stent grafts to be inserted through the arteries of the leg and deployed across the aneurysm.
Renal
Renal aneurysms are very rare consisting of only 0.1–0.09% while rupture is even more rare. Conservative treatment with control of concomitant hypertension being the primary option with aneurysms smaller than 3 cm. If symptoms occur, or enlargement of the aneurysm, then endovascular or open repair should be considered. Pregnant women (due to high rupture risk of up to 80%) should be treated surgically.
Epidemiology
Incidence rates of cranial aneurysms are estimated at between 0.4% and 3.6%. Those without risk factors have expected prevalence of 2–3%. In adults, females are more likely to have aneurysms. They are most prevalent in people ages 35 – 60 but can occur in children as well. Aneurysms are rare in children with a reported prevalence of .5% to 4.6%. The most common incidence is among 50-year-olds, and there are typically no warning signs. Most aneurysms develop after the age of 40.
Pediatric aneurysms
Pediatric aneurysms have different incidences and features than adult aneurysms. Intracranial aneurysms are rare in childhood, with over 95% of all aneurysms occurring in adults.
Risk factors
Incidence rates are two to three times higher in males, while there are more large and giant aneurysms and fewer multiple aneurysms. Intracranial hemorrhages are 1.6 times more likely to be due to aneurysms than cerebral arteriovenous malformations in whites, but four times less in certain Asian populations.
Most patients, particularly infants, present with subarachnoid hemorrhage and corresponding headaches or neurological deficits. The mortality rate for pediatric aneurysms is lower than in adults.
Modeling
Modeling of aneurysms consists of creating a 3D model that mimics a particular aneurysm. Using patient data for the blood velocity, and blood pressure, along with the geometry of the aneurysm, researchers can apply computational fluid dynamics (CFD) to predict whether an aneurysm is benign or if it is at risk of complication. One risk is rupture. Analyzing the velocity and pressure profiles of the blood flow leads to obtaining the resulting wall shear stress on the vessel and aneurysm wall. The neck of the aneurysm is the most at risk due to the combination of a small wall thickness and high wall shear stress. When the wall shear stress reaches its limit, the aneurysm ruptures, leading to intracranial hemorrhage. Conversely, another risk of aneurysms is the creation of clots. Aneurysms create a pocket which diverts blood flow. This diverted blood flow creates a vortex inside of the aneurysm. This vortex can lead to areas inside of the aneurysm where the blood flow is stagnant, which promotes formations of clots. Blood clots can dislodge from the aneurysm, which can then lead to an embolism when the clot gets stuck and disrupts blood flow. Model analysis allows these risky aneurysms to be identified and treated.
In the past, aneurysms were modeled as rigid spheres with linear inlets and outlets. As technology advances, the ability to detect and analyze aneurysms becomes easier. Researchers are able to CT scan a patient's body to create a 3D computer model that possesses the correct geometry. Aneurysms can now be modeled with their distinctive "balloon" shape. Nowadays researchers are optimizing the parameters required to accurately model a patient's aneurysm that will lead to a successful intervention. Current modeling is not able to take into account all variables though. For example, blood is considered to be a non-Newtonian fluid. Some researchers treat blood as a Newtonian fluid instead, as it sometimes has negligible effects to the analysis in large vessels. When analyzing small vessels though, such as those present in intracranial aneurysms. Similarly, sometimes it is difficult to model the varying wall thickness in small vessels, so researchers treat wall thickness as constant. Researchers make these assumptions to reduce computational time. Nonetheless, making erroneous assumptions could lead to a misdiagnosis that could put a patient's life at risk.
Notable cases
U.S. Senator Joe Biden, who later became President, had two brain aneurysms in 1988. He recovered after successful surgeries to correct them.
Lucille Ball died from an aortic rupture in the abdominal area days after having undergone apparently successful heart surgery for a dissecting aortic aneurysm.
Laura Branigan died of a cerebral aneurysm.
David Cone had an aneurysm and missed most of the 1996 baseball season.
Davie Cooper died in 1995 following a subarachnoid hemorrhage whilst filming a football television series.
John Olerud had an aneurysm in 1989 and has worn a batting helmet on the field all of his career since then.
Albert Einstein died from a repaired aortic aneurysm.
Thomas Mikal Ford died from a ruptured aneurysm in his abdomen at age 52.
Charles de Gaulle died from a ruptured aneurysm within his neck.
Richard Holbrooke died from a thoracic aortic aneurysm.
Édith Piaf died from an aneurysm due to liver failure.
Stuart Sutcliffe died from an aneurysm in his brain's right hemisphere.
Raymond F. Boyce died in 1974 as a result of an aneurysm.
John Ritter died in 2003 of a misdiagnosed thoracic aortic dissection (aortic aneurysm).
Isabel Granada died of a cerebral aneurysm.
Geoffrey Thompson died of a brain aneurysm at his daughter's wedding, hosted at his theme park, Blackpool Pleasure Beach.
Edwin Rosario died of an aneurysm in 1997.
Joni Mitchell had a brain aneurysm in 2015 and survived.
Grant Imahara died from a brain aneurysm in July 2020.
Dr. Dre had a brain aneurysm in January 2021.
Jovit Baldivino died from a brain aneurysm in December 2022.
Tom Sizemore died from a brain aneurysm in March 2023.
| Biology and health sciences | Injury | null |
322562 | https://en.wikipedia.org/wiki/Trionychidae | Trionychidae | Trionychidae is a family of turtles, commonly known as softshell turtles or simply softshells. The family was described by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to living in highly brackish waters. Members of this family occur in Africa, Asia, and North America, with extinct species known from Australia. Most species have traditionally been included in the genus Trionyx, but the vast majority have since been moved to other genera. Among these are the North American Apalone softshells that were placed in Trionyx until 1987.
Characteristics
Turtles of the family Trionychidae are called "softshell" because their carapaces lack horny scutes (scales), though the spiny softshell, Apalone spinifera, does have some scale-like projections, to which its common name refers. The carapace is leathery and pliable, particularly at the sides. The central part of the carapace has a layer of solid bone beneath it, as in other turtles, but this is absent at the outer edges. Some species also have dermal bones in the plastron, but these are not attached to the bones of the shell. The light and flexible shell of these turtles allows them to move more easily in open water or in muddy lake bottoms. Having a soft shell also allows them to move much faster on land than most turtles. Their feet are webbed and three-clawed, hence the family name "Trionychidae," which means "three-clawed". The carapace color of each type of softshell turtle tends to match the sand or mud color of its geographical region, assisting in their "lie in wait" feeding methodology.
These turtles have many characteristics pertaining to their aquatic lifestyle. Many must be submerged in order to swallow their food. They have elongated, soft, snorkel-like nostrils. Their necks are disproportionately long in comparison to their body sizes, enabling them to breathe surface air while their bodies remain submerged in the substrate (mud or sand) a foot or more below the surface.
Females can grow up to several feet in carapace diameter, while males stay much smaller; this is their main form of sexual dimorphism. Pelochelys cantorii, found in southeastern Asia, is the largest softshell turtle.
Most are strict carnivores, with diets consisting mainly of fish, aquatic crustaceans, snails, amphibians, and sometimes birds and small mammals.
Softshells are able to "breathe" underwater with rhythmic movements of their mouth cavity, which contains numerous processes copiously supplied with blood, acting similarly to gill filaments in fish. This enables them to stay underwater for prolonged periods. Moreover, the Chinese softshell turtle has been shown to excrete urea while "breathing" underwater; this is an efficient solution when the animal does not have access to fresh water, e.g., in brackish-water environments.
According to Ditmars (1910): "The mandibles of many species form the outer border of powerful crushing processes—the alveolar surfaces of the jaws", which aids the ingestion of tough prey such as molluscs. These jaws make large turtles dangerous, as they are capable of amputating a person's finger, or possibly their hand.
Unlike the temperature-dependent sex determination of most turtles, Trionychids have ZZ/ZW genetic sex determination; microchromosomes play a role in determining sex.
As food
In East Asia
Softshell turtles are eaten as a delicacy in most parts of their range, particularly in East Asia. A Chinese dish stews them with chicken. According to a 1930 report by Soame Jenyns, Guangdong restaurants had them imported from Guangxi in large numbers; "eaten stewed with almonds, roast with chili sauce or fried with bamboo shoots, they [were] considered a great delicacy."
Worldwide, the most commonly consumed softshell species is the Chinese softshell Pelodiscus sinensis. As a noted Japanese biologist pointed out in 1904, the Japanese variety of this turtle, which at time was classified as Trionyx japonicus, occupied a place in Japanese cuisine as esteemed as the diamondback terrapin in the United States or the green turtle in England. The farming of this "luscious reptile", known in Japan as suppon, was already developed on an industrial scale in that country by the late 19th century.
Due to rising demand and overhunting, the price of Pelodiscus sinensis in China skyrocketed by the mid-1990s; large-scale turtle farming in China and neighboring countries; raising this species by hundreds of millions was the response, with prices soon returning to a more affordable level. Another species, Palea steindachneri, is farmed in China, as well, but on a much smaller scale (with farm herds measured in hundreds of thousands, rather than hundreds of millions).
In the United States
In the United States, harvesting softshells (e.g. Apalone ferox) was, until recently, legal in Florida. Environmental groups have been advocating the authorities' banning or restricting the practice. The Florida Fish and Wildlife Conservation Commission responded by introducing the daily limit of 20 turtles for licensed harvesters—a level which the turtle advocates consider unsustainable, as there may be between 100 and 500 hunters statewide. While some catch was consumed locally, most was exported; the Commission estimated (2008) around 3,000 pounds of softshell turtles were exported to China each week via Tampa International Airport.
New rules, in effect as of July 20, 2009, restrict collecting any wild turtles to one turtle per person per day, completely prohibit collection of softshells (Apalone) in May through July, and prohibit trade in turtles caught from the wild. An exemption is provided for licensed turtle farms that need to catch turtles in the wild to serve as their breeding stock.
Some other US states, too, have already adopted strict limitations on wild turtle trade. In 2009, South Carolina passed a law (Bill H.3121) restricting interstate and international export of wild-caught turtles (both soft-shell and some other species) to 10 turtles per person at one time, and 20 turtles per person per year.
Taxonomy
Family Trionychidae
Palaeotrionyx (fossil) Paleotrionyx jimenezfuentesi
Subfamily Plastomeninae (fossil)
Genus Gilmoremys
Genus Hutchemys
Genus Plastomenus
Subfamily Cyclanorbinae
Genus Cyclanorbis
Genus Cycloderma
Genus Lissemys
Subfamily Trionychinae
Genus Amyda, Amyda menneri
Genus Apalone
Genus Chitra, Chitra minor
Genus Dogania
Genus Nilssonia
Genus Palea
Genus Pelochelys
Genus Pelodiscus
Genus Rafetus
Genus Trionyx
Past classification
Genus Aspideretes
Phylogeny
The following cladogram shows the relationships among the species:
Gallery
| Biology and health sciences | Turtles | Animals |
322578 | https://en.wikipedia.org/wiki/Leatherback%20sea%20turtle | Leatherback sea turtle | The leatherback sea turtle (Dermochelys coriacea), sometimes called the lute turtle, leathery turtle or simply the luth, is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to and weights of . It is the only living species in the genus Dermochelys and family Dermochelyidae. It can easily be differentiated from other modern sea turtles by its lack of a bony shell; instead, its carapace is covered by oily flesh and flexible, leather-like skin, for which it is named. Leatherback turtles have a global range, although there are multiple distinct subpopulations. The species as a whole is considered vulnerable, and some of its subpopulations are critically endangered.
Taxonomy and evolution
Taxonomy
Dermochelys coriacea is the only species in genus Dermochelys. The genus, in turn, contains the only extant member of the family Dermochelyidae.
Domenico Agostino Vandelli named the species first in 1761 as Testudo coriacea after an animal captured at Ostia and donated to the University of Padua by Pope Clement XIII. In 1816, French zoologist Henri Blainville coined the term Dermochelys. The leatherback was then reclassified as Dermochelys coriacea. In 1843, the zoologist Leopold Fitzinger put the genus in its own family, Dermochelyidae. In 1884, the American naturalist Samuel Garman described the species as Sphargis coriacea schlegelii. The two were then united in D. coriacea, with each given subspecies status as D. c. coriacea and D. c. schlegelii. The subspecies were later labeled invalid synonyms of D. coriacea.
Both the turtle's common and scientific names come from the leathery texture and appearance of its carapace (Dermochelys coriacea literally translates to "Leathery Skin-turtle"). Older names include "leathery turtle" and "trunk turtle". The common names incorporating "lute" and "luth" compare the seven ridges that run the length of the animal's back to the seven strings on the musical instrument of the same name. But probably more accurately derived from the lute's ribbed back which is in the form of a shell.
Evolution
Relatives of modern leatherback turtles have existed in relatively the same form since the first true sea turtles evolved over 110 million years ago during the Cretaceous period. The dermochelyids are relatives of the family Cheloniidae, which contains the other six extant sea turtle species. However, their sister taxon is the extinct family Protostegidae that included other species that did not have a hard carapace.
Anatomy and physiology
Leatherback turtles have the most hydrodynamic body of any sea turtle, with a large, teardrop-shaped body. A large pair of front flippers powers the turtles through the water. Like other sea turtles, the leatherback has flattened forelimbs adapted for swimming in the open ocean. Claws are absent from both pairs of flippers. The leatherback's flippers are the largest in proportion to its body among extant sea turtles. Leatherback's front flippers can grow up to in large specimens, the largest flippers (even in comparison to its body) of any sea turtle.
The leatherback has several characteristics that distinguish it from other sea turtles. Its most notable feature is the lack of a bony carapace. Instead of scutes, it has thick, leathery skin with embedded minuscule osteoderms. Seven distinct ridges rise from the carapace, crossing from the cranial to caudal margin of the turtle's back. Leatherbacks are unique among reptiles in that their scales lack β-keratin. The entire turtle's dorsal surface is colored dark grey to black, with a scattering of white blotches and spots. Demonstrating countershading, the turtle's underside is lightly colored. Instead of teeth, the leatherback turtle has points on the tomium of its upper lip, with backwards spines in its throat (esophagus) to help it swallow food and to stop its prey from escaping once caught.
D. coriacea adults average in curved carapace length (CCL), in total length, and in weight. In the Caribbean, the mean size of adults was reported at in weight and in CCL. Similarly, those nesting in French Guiana, weighed an average of and measured in CCL. The largest verified specimen ever found was discovered on the Pakistani beach of Sandspit and measured in CCL and in weight. A previous contender, the "Harlech turtle", was purportedly in CCL and in weight, however recent inspection of its remains housed at the National Museum Cardiff have found that its true CCL is closer to , casting doubt on the accuracy of the claimed weight, as well. On the other hand, one scientific paper has claimed that the species can weigh up to without providing more verifiable detail. The leatherback turtle is scarcely larger than any other sea turtle upon hatching, as they average in carapace length and weigh around when freshly hatched.
D. coriacea exhibits several anatomical characteristics believed to be associated with a life in cold waters, including an extensive covering of brown adipose tissue, temperature-independent swimming muscles, countercurrent heat exchangers between the large front flippers and the core body, and an extensive network of countercurrent heat exchangers surrounding the trachea.
Mechanical properties
The carapace of the leatherback sea turtle has a unique design which enables the sea turtles to withstand high hydrostatic pressures as they dive to depths of 1200 m. Unlike other sea turtles, the leatherback sea turtle has a soft, leathery skin which covers the osteoderms rather than a hard keratinous shell. The osteoderms are made up of bone-like hydroxyapatite/collagen tissue and have jagged edges, referred to as teeth. These osteoderms are connected by a configuration of interpenetrating extremities called sutures that provide flexibility to the carapace, enabling in plane and out of plane movement between osteoderms. This is important since the lungs, and thus the carapace, expand when taking in air and contract when deep diving.
The sutures connect rigid elements and flexible joints in a zig-zag configuration, so there is no region where teeth can easily penetrate the carapace. There are two main failure mechanisms for the tires in tension: tooth failure corresponding to mineral-brittle failure; and interfacial failure between teeth corresponding to collagen-ductile failure. The triangular tooth geometry is able to evenly distribute load and absorb energy. This leads to a high strength in tension since this geometry takes advantage of the tensile strength of bone and the interface. Additionally, the carapace is tough because sutures prevent crack propagation. Under load, cracks interact with the sutures which can resist crack growth via crack bridging. This phenomenon was observed in sequential compression of osteoderm samples.
Physiology
Leatherbacks have been viewed as unique among extant non-avian reptiles for their ability to maintain high body temperatures using metabolically generated heat, or endothermy. Initial studies on their metabolic rates found leatherbacks had resting metabolisms around three times higher than expected for reptiles of their size. However, recent studies using reptile representatives encompassing all the size ranges leatherbacks pass through during ontogeny discovered the resting metabolic rate of a large D. coriacea is not significantly different from predicted results based on allometry.
Rather than using a high resting metabolism, leatherbacks appear to take advantage of a high activity rate. Studies on wild D. coriacea discovered individuals may spend as little as 0.1% of the day resting. This constant swimming creates muscle-derived heat. Coupled with their countercurrent heat exchangers, insulating fat covering, and large size, leatherbacks are able to maintain high temperature differentials compared to the surrounding water. Adult leatherbacks have been found with core body temperatures that were above the water in which they were swimming.
Leatherback turtles are one of the deepest-diving marine animals. Individuals have been recorded diving to depths as great as .
Typical dive durations are between 3 and 8 minutes, with dives of 30–70 minutes occurring infrequently.
They are also the fastest-moving non-avian reptiles. The 1992 edition of the Guinness Book of World Records lists the leatherback turtle moving at in the water. More typically, they swim at .
Distribution
The leatherback turtle is a species with a cosmopolitan global range. Of all the extant sea turtle species, D. coriacea has the widest distribution, reaching as far north as Alaska and Norway and as far south as Cape Agulhas in Africa and the southernmost tip of New Zealand. The leatherback is found in all tropical and subtropical oceans, and its range extends well into the Arctic Circle.
The three major, genetically distinct populations occur in the Atlantic, eastern Pacific, and western Pacific Oceans. While nesting beaches have been identified in the region, leatherback populations in the Indian Ocean remain generally unassessed and unevaluated.
Recent estimates of global nesting populations are that 26,000 to 43,000 females nest annually, which is a dramatic decline from the 115,000 estimated in 1980.
Atlantic subpopulation
The leatherback turtle population in the Atlantic Ocean ranges across the entire region. They range as far north as the North Sea and to the Cape of Good Hope in the south. Unlike other sea turtles, leatherback feeding areas are in colder waters, where an abundance of their jellyfish prey is found, which broadens their range. However, only a few beaches on both sides of the Atlantic provide nesting sites.
Off the Atlantic coast of Canada, leatherback turtles feed in the Gulf of Saint Lawrence near Quebec and as far north as Newfoundland and Labrador. The most significant Atlantic nesting sites are in Suriname, Guyana, French Guiana in South America, Antigua and Barbuda, and Trinidad and Tobago in the Caribbean, and Gabon in Central Africa. The beaches of Mayumba National Park in Mayumba, Gabon, host the largest nesting population on the African continent and possibly worldwide, with nearly 30,000 turtles visiting its beaches each year between October and April. Off the northeastern coast of the South American continent, a few select beaches between French Guiana and Suriname are primary nesting sites of several species of sea turtles, the majority being leatherbacks. A few hundred nest annually on the eastern coast of Florida. In Costa Rica, the beaches of Gandoca and Parismina provide nesting grounds.
Pacific subpopulation
Pacific leatherbacks divide into two populations. One population nests on beaches in Papua, Indonesia, and the Solomon Islands, and forages across the Pacific in the Northern Hemisphere, along the coasts of California, Oregon, and Washington in North America. The eastern Pacific population forages in the Southern Hemisphere, in waters along the western coast of South America, nesting in Mexico, Panama, El Salvador, Nicaragua, and Costa Rica, as well as eastern Australia.
The continental United States offers two major Pacific leatherback feeding areas. One well-studied area is just off the northwestern coast near the mouth of the Columbia River. The other American area is located in California. Further north, off the Pacific coast of Canada, leatherbacks visit the beaches of British Columbia.
Estimates by the WWF suggest only 2,300 adult females of the Pacific leatherback remain, making it the most endangered marine turtle subpopulation.
South China Sea subpopulation
A third possible Pacific subpopulation has been proposed, those that nest in Malaysia. This subpopulation, however, has effectively been eradicated. The beach of Rantau Abang in Terengganu, Malaysia, once had the largest nesting population in the world, hosting 10,000 nests per year. The major cause of the decline was egg consumption by humans. Conservation efforts initiated in the 1960s were ineffective because they involved excavating and incubating eggs at artificial sites which inadvertently exposed the eggs to high temperatures. It only became known in the 1980s that sea turtles undergo temperature-dependent sex determination; it is suspected that nearly all the artificially incubated hatchlings were female. In 2008, two turtles nested at Rantau Abang, and unfortunately, the eggs were infertile. Additionally, there are small nesting sites in southern Thailand where 18 turtles nested in 2021.
Indian Ocean subpopulation
While little research has been done on Dermochelys populations in the Indian Ocean, nesting populations are known from Sri Lanka and the Nicobar Islands. These turtles are proposed to form a separate, genetically distinct Indian Ocean subpopulation.
Ecology and life history
Habitat
Leatherback sea turtles can be found primarily in the open ocean. Scientists tracked a leatherback turtle that swam from Jen Womom beach of Tambrauw Regency in West Papua of Indonesia to the US in a foraging journey over a period of 647 days. Leatherbacks follow their jellyfish prey throughout the day, resulting in turtles "preferring" deeper water in the daytime, and shallower water at night (when the jellyfish rise up the water column). This hunting strategy often places turtles in very frigid waters. One individual was found actively hunting in waters where temperatures were as low as . Following each foraging dive, the leatherback would return to warmer () surface waters to regain body heat before continuing to dive into near freezing waters. Leatherback turtles are known to pursue prey deeper than 1000 m—beyond the physiological limits of all other diving tetrapods except for beaked whales and sperm whales.
Their favored breeding beaches are mainland sites facing the deep water, and they seem to avoid those sites protected by coral reefs.
Feeding
Adult D. coriacea turtles subsist almost entirely on jellyfish. Due to their obligate feeding nature, leatherbacks help control jellyfish populations. Leatherbacks also feed on other soft-bodied organisms, such as other cnidarians (siphonophores), tunicates (salps and pyrosomas) and cephalopods (squid). They are also believed to feed on small crustaceans (amphipods and crabs), fish (possibly symbiotes with jellies), sea urchins, snails, seagrasses, and algae.
Pacific leatherbacks migrate about across the Pacific from their nesting sites in Indonesia to eat California jellyfish. During these long traveling periods, Remora remora (common Remoras) will latch onto leatherbacks and display phoresis behavior or 'hitchhiking' this represents commensalism, where one species is benefiting, while the other species is not gaining or losing anything. One cause for their endangered state is plastic bags floating in the ocean. Pacific leatherback sea turtles mistake these plastic bags for jellyfish; an estimated one-third of adults have ingested plastic. Plastic enters the oceans along the west coast of urban areas, where leatherbacks forage, with Californians using upward of 19 billion plastic bags every year. Plastic bags were banned in California in 2016.
Several species of sea turtles commonly ingest plastic marine debris, and even small quantities of debris can kill sea turtles by obstructing their digestive tracts. Nutrient dilution, which occurs when plastics displace food in the gut, affects the nutrient gain and consequently the growth of sea turtles. Ingestion of marine debris and slowed nutrient gain leads to increased time for sexual maturation that may affect future reproductive behaviors. These turtles have the highest risk of encountering and ingesting plastic bags offshore of San Francisco Bay, the Columbia River mouth, and Puget Sound.
Lifespan
Very little is known of the species' lifespan. Some reports claim "30 years or more", while others state "50 years or more" and upper estimates exceed 100 years.
In 2020, researchers from CSIRO, Australia's National Science Agency, developed a method to calculate the natural lifespan of vertebrate animals by leveraging genetic markers and known lifespans of various species. From the genomic sequencing of DNA samples taken from five different marine turtle species, the natural lifespan of the Leatherback turtle was calculated at 90.4 years.
Death and decomposition
Dead leatherbacks that wash ashore are microecosystems while decomposing. In 1996, a drowned carcass held sarcophagid and calliphorid flies after being picked open by a pair of Coragyps atratus vultures. Infestation by carrion-eating beetles of the families Scarabaeidae, Carabidae, and Tenebrionidae soon followed. After days of decomposition, beetles from the families Histeridae and Staphylinidae and anthomyiid flies invaded the corpse, as well. Organisms from more than a dozen families took part in consuming the carcass.
Life history
Predation
Leatherback turtles face many predators in their early lives. Eggs may be preyed on by a diversity of coastal predators, including ghost crabs, monitor lizards, raccoons, coatis, dogs, coyotes, genets, mongooses, and shorebirds ranging from small plovers to large gulls. Many of the same predators feed on baby turtles as they try to get to the ocean, as well as frigatebirds and varied raptors. Once in the ocean, young leatherbacks face predation from cephalopods, requiem sharks, and various large fish. Despite their lack of a hard shell, the huge adults face fewer serious predators, though they are occasionally overwhelmed and preyed on by very large marine predators such as killer whales, great white sharks, and tiger sharks. Nesting females have been preyed upon by jaguars in the American tropics. Nesting females in Papua New Guinea are also attacked by saltwater crocodiles.
The adult leatherback has been observed aggressively defending itself at sea from predators. A medium-sized adult was observed chasing a shark that had attempted to bite it and then turned its aggression and attacked the boat containing the humans observing the prior interaction. Dermochelys juveniles spend more of their time in tropical waters than do adults.
Adults are prone to long-distance migration. Migration occurs between the cold waters where mature leatherbacks feed, to the tropical and subtropical beaches in the regions where they hatch. In the Atlantic, females tagged in French Guiana have been recaptured on the other side of the ocean in Morocco and Spain.
Mating
Mating takes place at sea. Males never leave the water once they enter it, unlike females, which nest on land. After encountering a female (which possibly exudes a pheromone to signal her reproductive status), the male uses head movements, nuzzling, biting, or flipper movements to determine her receptiveness. Males can mate every year but the females mate every two to three years. Fertilization is internal, and multiple males usually mate with a single female. This polyandry does not provide the offspring with any special advantages.
Female leatherbacks are known to nest up to 10 times in a single nesting season giving them the shortest internesting interval of all sea turtles.
Offspring
While other sea turtle species almost always return to their hatching beach, leatherbacks may choose another beach within the region. They choose beaches with soft sand because their softer shells and plastrons are easily damaged by hard rocks. Nesting beaches also have shallower approach angles from the sea. This is a vulnerability for the turtles because such beaches easily erode. They nest at night when the risk of predation and heat stress is lowest. As leatherback turtles spend the vast majority of their lives in the ocean, their eyes are not well adapted to night vision on land. The typical nesting environment includes a dark forested area adjacent to the beach. The contrast between this dark forest and the brighter, moonlit ocean provides directionality for the females. They nest towards the dark and then return to the ocean and the light. The mean time it takes to complete a nesting event from landing to departure is 108.1 minutes.
Females excavate a nest above the high-tide line with their flippers. One female may lay as many as nine clutches in one breeding season. About nine days pass between nesting events. Average clutch size is around 110 eggs, 85% of which are viable. After laying, the female carefully back-fills the nest, disguising it from predators with a scattering of sand. With the average clutch size being around 110, around 50 percent of the eggs do not even develop into hatchlings. This only causes more concern for the species, because it makes management much harder to determine.
Development of offspring
Cleavage of the cell begins within hours of fertilization, but development is suspended during the gastrulation period of movements and infoldings of embryonic cells, while the eggs are being laid. Development then resumes, but embryos remain extremely susceptible to movement-induced mortality until the membranes fully develop after incubating for 20 to 25 days. The structural differentiation of body and organs (organogenesis) soon follows. The eggs hatch in about 60 to 70 days. As with other reptiles, the nest's ambient temperature determines the sex of the hatchings. After nightfall, the hatchings dig to the surface and walk to the sea. The morphology of offspring has been found to vary with nest incubation temperatures. Higher temperatures resulted in lower mass, smaller appendages, narrower carapace widths, and shorter flipper lengths while lower temperatures resulted in greater mass, wider appendage widths, wider carapace widths, and longer flipper lengths.
Leatherback nesting seasons vary by location; it occurs from February to July in Parismina, Costa Rica. Farther east in French Guiana, nesting is from March to August. Atlantic leatherbacks nest between February and July from South Carolina in the United States to the United States Virgin Islands in the Caribbean and to Suriname and Guyana.
Importance to humans
People around the world still harvest sea turtle eggs. Asian exploitation of turtle nests has been cited as the most significant factor for the species' global population decline. In Southeast Asia, egg harvesting in countries such as Thailand and Malaysia has led to a near-total collapse of local nesting populations. In Malaysia, where the turtle is practically locally extinct, the eggs are considered a delicacy. In the Caribbean, some cultures consider the eggs to be aphrodisiacs.
They are also a major jellyfish predator, which helps keep populations in check. This bears importance to humans, as jellyfish diets consist largely of larval fish, the adults of which are commercially fished by humans.
Cultural significance
The turtle is known to be of cultural significance to tribes all over the world. The Seri people, from the Mexican state of Sonora, find the leatherback sea turtle culturally significant because it is one of their five main creators. The Seri people devote ceremonies and fiestas to the turtle when one is caught and then released back into the environment. The Seri people have noticed the drastic decline in turtle populations over the years and created a conservation movement to help this. The group, made up of both youth and elders from the tribe, is called Grupo Tortuguero Comaac. They use both traditional ecological knowledge and Western technology to help manage the turtle populations and protect the turtle's natural environment.
In the Malaysian state of Terengganu, the turtle is the state's main animal and is usually seen in tourism ads.
On the South Island of New Zealand's Banks Peninsula the leatherback turtle has great spiritual significance to the Koukourārata hapū of te Rūnanga o Ngāi Tahu, as well as wider significance in Te Ao Māori and to the peoples of greater Polynesia according to the protocols of each rohe. In 2021, a leatherback sea turtle was laid to rest by New Zealand's Department of Conservation in a hilltop cave on the Peninsula's Horomaka Island dug by hapū and in accordance with their rohe's ley lines, according to New Zealand's state broadcaster, Radio New Zealand.
Conservation
Leatherback turtles have few natural predators once they mature; they are most vulnerable to predation in their early life stages. Birds, small mammals, and other opportunists dig up the nests of turtles and consume eggs. Shorebirds and crustaceans prey on the hatchlings scrambling for the sea. Once they enter the water, they become prey to predatory fish and cephalopods.
Leatherbacks have slightly fewer human-related threats than other sea turtle species, however, turtle-fishery interactions may play a larger role than previously recognized. Their flesh contains too much oil and fat to be considered palatable, reducing the demand. However, human activity still endangers leatherback turtles in direct and indirect ways. Directly, a few are caught for their meat by subsistence fisheries. Nests are raided by humans in places such as Southeast Asia. In the state of Florida, there have been 603 leatherback strandings between 1980 and 2014. Almost one-quarter (23.5%) of leatherback strandings are due to vessel-strike injuries, which is the highest cause of strandings.
Light pollution is a serious threat to sea turtle hatchlings which have a strong attraction to light. Human-generated light from streetlights and buildings causes hatchlings to become disoriented, crawling toward the light and away from the beach. Hatchlings are attracted to light because the lightest area on a natural beach is the horizon over the ocean, the darkest area is the dunes or forest. On Florida's Atlantic coast, some beaches with high turtle nesting density have lost thousands of hatchlings due to artificial light.
Many human activities indirectly harm Dermochelys populations. As a pelagic species, D. coriacea is occasionally caught as bycatch. Entanglement in lobster pot ropes is another hazard the animals face. As the largest living sea turtles, turtle excluder devices can be ineffective with mature adults. In the eastern Pacific alone, a reported average of 1,500 mature females were accidentally caught annually in the 1990s. Pollution, both chemical and physical, can also be fatal. Many turtles die from malabsorption and intestinal blockage following the ingestion of balloons and plastic bags which resemble their jellyfish prey. Chemical pollution also has an adverse effect on Dermochelys. A high level of phthalates has been measured in their eggs' yolks. Leatherback sea turtles ranging from 1885 to 2007 were autopsied for the existence of plastic in the gastrointestinal tract. It was discovered that 34% of the cases had plastic blockage.
Due to their diet consisting of gelatinous zooplankton, the leatherback sea turtle consumes high amounts of salt. Different life stages of dead individuals from the western Atlantic Ocean were used to test the concentrations of various contaminants found in the salt glands and red blood cells. These contaminants include arsenic, cadmium, lead, mercury, and selenium. The contaminants were found in higher concentrations in the blood compared to the salt gland secretions. The length of the curve in the carapace of a turtle had a direct correlation with cadmium and mercury concentrations. Salt glands and red blood cells are potentially susceptible to high levels of contaminants being found in the oceans.
Global initiatives
D. coriacea is listed on CITES Appendix I, which makes export/import of this species (including parts) illegal. It has been listed as an EDGE species by the Zoological Society of London.
The species is listed in the IUCN Red List of Threatened Species as VU (Vulnerable), and additionally with the following infraspecific taxa assessments:
East Pacific Ocean subpopulation: CR (Critically Endangered)
Northeast Indian Ocean subpopulation: DD (Data Deficient)
Northwest Atlantic Ocean subpopulation: EN (Endangered)
Southeast Atlantic Ocean subpopulation: DD (Data Deficient)
Southwest Atlantic Ocean subpopulation CR (Critically Endangered)
Southwest Indian Ocean subpopulation CR (Critically Endangered)
West Pacific Ocean subpopulation CR (Critically Endangered)
Conserving Pacific and Eastern Atlantic populations were included among the top-ten issues in turtle conservation in the first State of the World's Sea Turtles report published in 2006. The report noted significant declines in the Mexican, Costa Rican, and Malaysian populations. The eastern Atlantic nesting population was threatened by increased fishing pressures from eastern South American countries.
The Leatherback Trust was founded specifically to conserve sea turtles, specifically its namesake. The foundation established a sanctuary in Costa Rica, the Parque Marino Las Baulas.
National and local initiatives
The leatherback sea turtle is subject to different conservation laws in various countries.
The United States listed it as an endangered species on 2 June 1970. The passing of the Endangered Species Act of 1973 ratified its status. In 2012, the National Oceanic and Atmospheric Administration designated 41,914 square miles of Pacific Ocean along California, Oregon, and Washington as "critical habitat". In Canada, the Species at Risk Act made it illegal to exploit the species in Canadian waters. The Committee on the Status of Endangered Wildlife in Canada classified it as endangered. Ireland and Wales initiated a joint leatherback conservation effort between Swansea University and University College Cork. Funded by the European Regional Development Fund, the Irish Sea Leatherback Turtle Project focuses on research such as tagging and satellite tracking of individuals.
Earthwatch Institute, a global nonprofit that teams volunteer with scientists to conduct important environmental research, launched a program called "Trinidad's Leatherback Sea Turtles". This program strives to help save the world's largest turtle from extinction in Matura Beach, Trinidad, as volunteers work side by side with leading scientists and a local conservation group, Nature Seekers. This tropical island off the coast of Venezuela is known for its vibrant ethnic diversity and rich cultural events. It is also the site of one of the most important nesting beaches for endangered leatherback turtles, enormous reptiles that can weigh a ton and dive deeper than many whales. Each year, more than 2,000 female leatherbacks haul themselves onto Matura Beach to lay their eggs. With leatherback populations declining more quickly than any other large animal in modern history, each turtle is precious. On this research project, Dennis Sammy of Nature Seekers and Scott Eckert of Wider Caribbean Sea Turtle Conservation Network work alongside a team of volunteers to help prevent the extinction of leatherback sea turtles.
Several Caribbean countries started conservation programs, such as the St. Kitts Sea Turtle Monitoring Network, focused on using ecotourism to highlight the leatherback's plight. On the Atlantic coast of Costa Rica, the village of Parismina has one such initiative. Parismina is an isolated sandbar where a large number of leatherbacks lay eggs, but poachers abound. Since 1998, the village has been assisting turtles with a hatchery program. The Parismina Social Club is a charitable organization backed by American tourists and expatriates, which collects donations to fund beach patrols. In Dominica, patrollers from DomSeTCo protect leatherback nesting sites from poachers.
Mayumba National Park in Gabon, Central Africa, was created to protect Africa's most important nesting beach. More than 30,000 turtles nest on Mayumba's beaches between September and April each year.
In mid-2007, the Malaysian Fisheries Department revealed a plan to clone leatherback turtles to replenish the country's rapidly declining population. Some conservation biologists, however, are skeptical of the proposed plan because cloning has only succeeded on mammals such as dogs, sheep, cats, and cattle, and uncertainties persist about cloned animals' health and lifespans. Leatherbacks used to nest in the thousands on Malaysian beaches, including those at Terengganu, where more than 3,000 females nested in the late 1960s. The last official count of nesting leatherback females on that beach was recorded to be a mere two females in 1993.
In Brazil, reproduction of the leatherback turtle is being assisted by the Brazilian Institute of Environment and Renewable Natural Resources' projeto TAMAR (TAMAR project), which works to protect nests and prevent accidental kills by fishing boats. The last official count of nesting leatherback females in Brazil yielded only seven females. In January 2010, one female at Pontal do Paraná laid hundreds of eggs. Since leatherback sea turtles had been reported to nest only at Espírito Santo's shore, but never in the state of Paraná, this unusual act brought much attention to the area, biologists have been protecting the nests and checking their eggs' temperature, although it might be that none of the eggs are fertile.
Australia's Environment Protection and Biodiversity Conservation Act 1999 lists D. coriacea as vulnerable, while Queensland's Nature Conservation Act 1992 lists it as endangered.
| Biology and health sciences | Turtles | Animals |
322604 | https://en.wikipedia.org/wiki/Agamidae | Agamidae | Agamidae is a family containing 64 genera, 582 species of iguanian lizards indigenous to Africa, Asia, Australia, and a few in Southern Europe. Many species are commonly called dragons or dragon lizards.
Overview
Phylogenetically, they may be sister to the Iguanidae, and have a similar appearance. Agamids usually have well-developed, strong legs. Their tails cannot be shed and regenerated like those of geckos (and several other families such as skinks), though a certain amount of regeneration is observed in some. Many agamid species are capable of limited change of their colours to regulate their body temperature. In some species, males are more brightly coloured than females, and colours play a part in signaling and reproductive behaviours. Although agamids generally inhabit warm environments, ranging from hot deserts to tropical rainforests, at least one species, the mountain dragon, is found in cooler regions. They are particularly diverse in Australia.
This group of lizards includes some more popularly known, such as the domesticated bearded dragon, Chinese water dragon, and Uromastyx species.
One of the key distinguishing features of the agamids is their teeth, which are borne on the outer rim of their mouths (acrodonts), rather than on the inner side of their jaws (pleurodonts). This feature is shared with the chameleons and the tuatara, but is otherwise unusual among lizards. Agamid lizards are generally diurnal, with good vision, and include a number of arboreal species, in addition to ground- and rock-dwellers. Most need to bask in the sun to maintain elevated body temperatures, meaning they are heliothermic. They generally feed on insects and other arthropods (such as spiders), although for some larger species, their diet may include small reptiles or mammals, nestling birds, and flowers or other vegetable matter.
Reproduction
The great majority of agamid species are oviparous. The eggs are mostly found in damp soil or rotting logs to retain enough moisture during the incubation period. The clutch size varies from four to 10 eggs for most species, and incubation period lasts around 6–8 weeks. Specifically in the Leiolepidinae subfamily of agamids, all species use a burrowing system that reaches moist soil, where eggs are deposited in late spring/early summer or at the beginning of the dry season. The Leiolepidinae burrow system is also used for daily or seasonal retreats, as it allows them to regulate their body temperature or act as a refuge from predators.
Systematics and distribution
Very few studies of Agamidae have been conducted. The first comprehensive assessment was by Moody (1980) followed by a more inclusive assessment by Frost and Etheridge (1989). Subsequent studies were based on mitochondrial DNA loci by Macey et al. (2000) and Honda et al. (2000) and also by sampling across the Agamidae by Joger (1991). Few other studies focused on clades within the family, and Agamidae have not been as well investigated as Iguanidae.
The agamids show a curious distribution. They are found over much of the Old World, including continental Africa, Australia, southern Asia, and sparsely in warmer regions of Europe. They are absent from Madagascar and the New World. The distribution is the opposite of that of the iguanids, which are found in just these areas, but absent in areas where agamids are found. A similar faunal divide is found in between the boas and pythons.
Further classification
Among Agamidae, six subfamilies are generally recognized:
Agaminae (Africa, Europe and south Asia)
Amphibolurinae (Australia and New Guinea, one species in Southeast Asia)
Draconinae (South and Southeast Asia)
Hydrosaurinae (Hydrosaurus, Papua New Guinea, the Philippines, and Indonesia)
Leiolepidinae (Leiolepis, Southeast Asia)
Uromastycinae (Saara and Uromastyx, Africa and South Asia)
These can be further split into 64 genera, as follows:
Acanthocercus (15 species)
Acanthosaura (20 species)
Agama (47 species)
Agasthyagama (2 species)
Amphibolurus (4 species)
Aphaniotis (3 species)
Bronchocela (15 species)
Bufoniceps (1 species)
Calotes (29 species)
Ceratophora (6 species)
Chelosania (1 species)
Chlamydosaurus (1 species)
Complicitus (1 species)
Cophotis (2 species)
Coryphophylax (2 species)
Cristidorsa (2 species)
Cryptagama (1 species)
Ctenophorus (38 species)
Dendragama (4 species)
Diploderma (47 species)
Diporiphora (28 species)
Draco (41 species)
Gonocephalus (17 species)
Gowidon (1 species)
Harpesaurus (6 species)
Hydrosaurus (5 species)
Hypsicalotes (1 species)
Hypsilurus (18 species)
Intellagama (1 species)
Japalura (8 species)
Laodracon (1 species)
Laudakia (13 species)
Leiolepis (10 species)
Lophocalotes (2 species)
Lophognathus (2 species)
Lophosaurus (3 species)
Lyriocephalus (1 species)
Malayodracon (1 species)
Mantheyus (1 species)
Microauris (1 species)
Moloch (1 species)
Monilesaurus (4 species)
Otocryptis (2 species)
Paralaudakia (8 species)
Pelturagonia (5 species)
Phoxophrys (1 species)
Phrynocephalus (36 species)
Physignathus (1 species)
Pogona (6 species)
Psammophilus (2 species)
Pseudocalotes (23 species)
Pseudocophotis (2 species)
Pseudotrapelus (6 species)
Ptyctolaemus (3 species)
Rankinia (1 species)
Saara (3 species)
Salea (2 species)
Sarada (3 species)
Sitana (15 species)
Trapelus (13 species)
Tropicagama (1 species)
Tympanocryptis (23 species)
Uromastyx (15 species)
Xenagama (4 species)
Evolutionary history
The oldest known unambiguous agamid is Protodraco from the mid-Cretaceous (early Cenomanian) aged Burmese amber of Myanmar, dating to around 99 million years ago. It is similar to primitive living Southeast Asian agamids. Gueragama from the Late Cretaceous of Brazil may also be an agamid. Jeddaherdan, a supposed agamid from the Late Cretaceous of Morocco, was later shown to be actually a young subfossil of the living genus Uromastyx.
Predator responses
Body temperature helps determine the physiological state of agamids and affects their predator responses. A positive correlation is seen between a flight response (running speed) and body temperature of various agamid species. At higher body temperatures, these lizards tend to flee quickly from predators, whereas at lower temperatures, they tend to have a reduced running speed and show an increased fight response, where they are more likely to be aggressive and attack predators.
Certain physical features of some lizards of these species, such as frilled-neck lizards, play a role in their defensive responses, as well. During the mating season, males tend to display more of their frill, and give fight responses more often. Both males and females display their frills when they are threatened by predators, and during social interactions.
| Biology and health sciences | Iguania | Animals |
322628 | https://en.wikipedia.org/wiki/Basiliscus%20%28lizard%29 | Basiliscus (lizard) | Basiliscus is a genus of large corytophanid lizards, commonly known as basilisks, which are endemic to southern Mexico, Central America, and northern South America. The genus contains four species, which are commonly known as the Jesus Christ lizard, or simply the Jesus lizard, due to their ability to run across water for significant distances before sinking due to the large surface area of their feet.
Taxonomy and etymology
Both the generic name, Basiliscus, and the common name, "basilisk", derive from the Greek basilískos (βασιλίσκος) meaning "little king". The specific epithet, vittatus, which is Latin for "striped", was given in Carl Linnæus' 10th edition of Systema Naturæ.
Description
Basilisks on average measure in total length (including tail). Their growth is perpetual, fast when they are young and nonlinear for mature basilisks. Their skin is shed in pieces.
Basilisks are oviparous and lay 8–18 eggs.
Running on water
Basilisks sometimes run bipedally. Basilisks have the ability to "run" on water, and because of this, they have been dubbed the "Jesus Christ lizard" in reference to the biblical passage of Jesus walking on water. On water, basilisks can run at a velocity of per second for approximately before sinking on all fours and swimming. Flaps between their toes help support basilisks, creating a larger surface and pockets of air, giving them the ability to run across water.
A similar behavior, running bipedally across water, is known from the sailfin lizards and a few species of anole lizards.
Other defense mechanisms
Basilisks can burrow into sand to hide from predators; a ring of muscles around both nostrils prevents sand from entering the nose.
Habitat and geographic range
Basilisks are abundant in the tropical rain forests of Central and South America, from southern Mexico to Ecuador and Venezuela.
Invasive species
The species Basiliscus vittatus (brown basilisk) has been introduced to Florida. It has adapted to the colder winters by burrowing into leaf litter for warmth. Current reports sight the brown basilisk as far north as Fort Pierce, on the state's East Coast, where small groups have crept up the North Fork of the Saint Lucie River. Mainly it has been seen in Boca Raton and other cities in Palm Beach County. as seen in this photo taken in West Palm Beach, Florida.
Classification
Genus Basiliscus has four extant species:
| Biology and health sciences | Iguania | Animals |
322654 | https://en.wikipedia.org/wiki/Dactyloidae | Dactyloidae | Dactyloidae are a family of lizards commonly known as anoles () and native to warmer parts of the Americas, ranging from southeastern United States to Paraguay. Instead of treating it as a family, some authorities prefer to treat it as a subfamily, Dactyloinae, of the family Iguanidae. In the past they were included in the family Polychrotidae together with Polychrus (bush anoles), but the latter genus is not closely related to the true anoles.
Anoles are small to fairly large lizards, typically green or brownish, but their color varies depending on species and many can also change it. In most species at least the male has a dewlap, an often brightly colored flap of skin that extends from the throat and is used in displays. Anoles share several characteristics with geckos, including details of the foot structure (for climbing) and the ability to voluntarily break off the tail (to escape predators), but they are only very distantly related, anoles being part of Iguania.
Anoles are active during the day and feed mostly on small animals such as insects, but some will also take fruits, flowers, and nectar. Almost all species are fiercely territorial. After mating, the female lays an egg (occasionally two); in many species she may do so every few days or weeks. The egg is typically placed on the ground, but in some species it is placed at higher levels.
Anoles are widely studied in fields such as ecology, behavior, and evolution, and some species are commonly kept in captivity as pets. Anoles can function as a biological pest control by eating insects that may harm humans or plants, but represent a serious risk to small native animals and ecosystems if introduced to regions outside their home range.
Distribution and habitat
Anoles are a very diverse and plentiful group of lizards. They are native to tropical and subtropical South America, Central America, Mexico, the offshore East Pacific Cocos, Gorgona and Malpelo Islands, the West Indies and southeastern United States.
A particularly high species richness exists in Cuba (more than 60 species), Hispaniola (more than 55), Mexico (more than 50), Central America, Colombia (more than 75), and Ecuador (at least 40). Fewer live in eastern and central South America (for example, less than 20 species are known from huge Brazil), Contiguous United States (1 native species), and the Lesser Antilles (about 25 species in total, with 1–2 species on each island). However, the Lesser Antilles are relatively rich compared to their very small land area and their species are all highly localized endemics, each only found on one or a few diminutive islands. In South America, the diversity is considerably higher west of the Andes (Tumbes-Chocó-Magdalena region) than east (Amazon basin), as well illustrated in Ecuador where about of the anole species live in the former region and in the latter.
The only species native to the contiguous United States is the Carolina (or green) anole, which ranges as far west as central Texas, and north to Oklahoma, Tennessee and Virginia. Its northern limit is likely related to cold winter temperatures. Several anole species have been introduced to the contiguous US, mostly Florida, but also other Gulf Coast states and California. The most prevalent of these introductions is the brown anole. In contrast to the contiguous United States, Puerto Rico and the Virgin Islands are home to 16 native species, all endemic.
Anoles inhabit a wide range of habitats, from highlands (up to at least above sea level) to the coast, and rainforest to desert scrub. A few live in limestone karst habitats and at least two of these, the Cuban cave anole and Mexican cave anole, will enter caves, sometimes occurring as much as from the entrance. Some species live close to humans and may use fences or walls of building as perches, even inhabiting gardens or trees along roads in large cities like Miami. Most anoles are arboreal or semi-arboreal, but there are also terrestrial and semiaquatic species. They are often, especially in the Caribbean, grouped into six ecomorphs—crown giant, trunk crown, trunk, trunk ground, twig, and grass bush—that inhabit specific niches. Other less widely used groups are ground, ground bush, twig giant, saxicolous, and riparian (alternatively semi-aquatic). However, the species within each ecomorph group are not entirely alike and there are variations in the details of their niches, including both widespread generalists and more restricted specialists. The niche differentiation allows several anoles to inhabit the same locality, with up to 15 species at a single site.
Appearance and behavior
Anoles vary in size. Males generally reach a larger size than females, but in a few species it is the other way around. Adults of most anoles are between in snout-to-vent length, and between in total length, including the tail. In the smallest, the five-striped grass anole, the snout-to-vent length is about in females and males respectively, but it is a relatively long-tailed species. There are several large species that are more than in snout-to-vent length. Males of the largest, the knight anole, reach up to about in snout-to-vent length, in total length, and in weight. There are both robust and gracile species, and the head shape varies from relatively broad to elongate.
The tail of anoles varies, but mostly it is longer than the snout-to-vent length. Depending on exact species it can range from slightly shorter to about three times the snout-to-vent. The Caribbean twig ecomorph anoles, proboscis anole and "Phenacosaurus" anoles have a prehensile tail. Semi-aquatic anoles tend to have relatively tall, vertically flattened tails that aid in swimming, and their skin has certain microstructures that make it hydrophobic, resulting in a thin film of air on the skin surface when submerged and preventing water from staying on when exiting the water.
Underneath an anole's toes are pads that have several to a dozen flaps of skin (adhesive lamellae) going horizontally and covered in microscopic hairlike protrusions (setae) that allow them to cling to many different surfaces, similar to but not quite as efficient as a gecko. Despite this similarity, they are very distantly related and the adaptions are the result of convergent evolution in the two groups. The extent of these structures and clinging ability varies, being more developed in anole species that live high in the tree canopy than ones living at lower levels. In one extreme are anoles that easily can run up windows. In the opposite end of the spectrum is the bulky anole of arid coastal Venezuela and adjacent Colombia, which is the only species completely lacking the specialized toe pad structures. The relative length of the limbs vary, mainly between different species, but to some extent also between different populations of a single species. This depends on things like the preferred perch size and whether there are ground-living predators in a habitat.
Despite having relatively small eyes, their primary sense is sight, which is excellent and in color. Their pupils are round or nearly round. The Guantanamo anole and Cuban cave anole have a transparent "window" in their lower eyelid, allowing them to see even with closed eyes, but why they have this adaption is unclear. Anoles have a good directional hearing, which is able to detect frequencies between 1000 and 7000 Hz and relatively low intensity sounds like the click of a camera.
Anoles are diurnal—active during the daytime—but can also be active during bright moonlit nights and may forage near artificial lights. Many species frequently bask in the sun to increase their temperature, but others are shade-living and do not.
Colors
Most anoles are brownish or green, but there are extensive variations depending on the exact species. The majority can change their color depending on things like emotions (for example, aggression or stress), activity level, levels of light and as a social signal (for example, displaying dominance), but evidence showing that they do it in response to the color of the background (camouflage) is lacking. Whether they do it in response to temperature (thermoregulation) is less clear, with studies supporting it and contradicting it. The extent and variations of this color changing ability differ widely throughout the individual species. For example, the Carolina (or green) anole can change its color from a bright, leafy green to a dull brown color, while the brown anole can only change its shade, ranging from pale gray-brown to very dark brown. Even the distinct green-to-brown change in the Carolina anole can happen in only a few minutes. The colors are the result of their skin pigment cells, the chromatophores, of which they have three main types, but the change occurs only in the melanophores. When triggered by melanophore-stimulating hormone and other hormones, the melanosomes of the melanophores partially cover the other skin pigment cells, giving the anole a darker or browner color. In most cases stress results in a darker/browner color, but in the aquatic anole, a species that is dark brown with a barred pattern and light brown stripes on the sides of its body and head, stress results in paler brown upper parts and the stripes turn pale blue-green.
Their colors during the night when sleeping often differ distinctly from their colors during the day where awake. Among these are some species that otherwise do not drastically change their colors, including certain anoles that generally are brown during the day changing to greenish or whitish when sleeping at night, and certain anoles that generally are green during the day changing to brown when sleeping at night.
Disregarding color change, minor individual variations in the basic color and pattern, mostly related to sex or age, are common. In some anole species this variation is more pronounced and not only related to sex and age. An example of this is the basic color of the Cayman blue-throated anole, which varies geographically, roughly matching the main habitat at a location. In others it occurs at the same location. This includes the extensive individual variations in the Guadeloupean anole, which however also shows some geographic variations, but possibly not consistent enough (due in part to clines) to make the typically recognized subspecies valid. In the Puerto Rican giant anole, a species only able to perform minor color changes (essentially lightness/darkness), juveniles are gray-brown and adults typically green, but an uncommon morph maintains a gray-brown color into adulthood. Similarly, rare morphs of the usually green Carolina anole lack certain pigment cells, giving them a mainly turquoise-blue or yellow color.
Dewlap
Most—but not all—anole species have dewlaps, made of erectile cartilage (modified from the hyoid) and covered in skin, that extend from their throat areas. When not in use and closed it lies inconspicuously along the throat and chest. The size, shape, color and pattern of the dewlap vary extensively depending on species, and often it differs between the sexes, being smaller (in some absent) or less colorful in females. In a few species, including the Carolina, bark, Cochran's gianthead and slender anoles, it varies geographically in color depending on subspecies or morph. Very locally, distinct morphs of a single species that differ in dewlap colors (not just differences between sexes) may occur together. In addition to colors that are visible to humans, dewlaps can have ultraviolet reflectance, which is visible to anoles. The striped anole is the only species where it is asymmetrically colored, being brighter on one side than the other. In some species even juveniles have a dewlap. The West Cuban and Cuban stream anoles are the only where both sexes lack a dewlap, but it is reduced and diminutive in about a dozen other species.
The dewlap serves as a signal for attracting partners, territoriality, deterring predators and communicating condition. When several anoles live together the species almost always differ in their dewlap, indicating that it plays a role in species recognition. Studies however reveal a more complex pattern: The bark anole and short nosed anole species complex (which includes the Webster's and Cochran's gianthead anoles) are closely related and both vary in their dewlap color. In places where their ranges overlap their dewlaps often differ and there is little hybridization, but in some locations their dewlaps are alike. Where alike there can be higher levels of hybridization (indicating that they are more likely to confuse each other) or levels can be as low as regions where they differ (indicating that something else allows them to separate each other). Another example is the red-fanned stout and large-headed anoles, which are sister species that overlap in range and are very similar except for their dewlap color. They are highly aggressive to individuals of their own species, but not the other. When one species has its dewlap color modified to resemble the other, only a relatively minor or no increase in aggression occurs, indicating that they still can separate each other.
Several other Iguania genera, Draco, Otocryptis, Polychrus, Sarada and Sitana, have evolved relatively large, movable dewlaps independently of the anoles.
Sexual dimorphism
In some anoles the sexes are very similar and difficult to separated under normal viewing conditions, but most species exhibit clear sexual dimorphism, which allows one to fairly easily discern between adult males and females. In a few species the female is slightly larger than the male, but in others the sexes are about the same size. However, in most the males are larger, in some more than three times the mass of females. This size difference can result in differences in the microhabitat (for example, males using larger branches than females) and feeding (males on average eating large prey) between the sexes of a single species. Males of some species have proportionally far longer heads than females, but in others it is nearly alike. The crest along the nape, back and/or tail is larger in the males. In species with tall crests this difference can be obvious, but in small-crested species it is often inconspicuous and easily overlooked, especially when not raised. The dewlap is often larger in males; in some species only the male has a dewlap. In a few there are differences in the shape of the nose, but this is only known to be prominent in the proboscis and leaf-nosed anoles, which both have long-nosed males and more normal looking females (it is likely that something similar can be seen in smooth anole, but the female of that species is still unknown). A less obvious difference between anole sexes is the enlarged post-cloacal scales in males.
The males of many species are overall more brightly colored, while females are duller, more cryptic, and sometimes their upperparts have striped or lined patterns that serve to break up the outline of the anole. In general, the juvenile colors and pattern resemble those of the adult female. The dewlap tends to be more colorful in males, with clear differences being common among anoles of the mainland of the Americas and comparatively rarer in the Caribbean species.
Territoriality and breeding
Almost all anole species are highly territorial, at least the males, but a few exceptions do exist, including the rock-living Agassiz's and Taylor's anoles where males do not defend a territory, and the grass anole where dominant males accept subordinant non-territorial males within their territory. Territorial anoles will fan their dewlap, bob their head, perform "push-ups", raise their crest and do a wide range of other behaviors to scare away potential competitors. If this does not scare off the intruder, a fight proceeds in which the two anoles attempt to bite each other. During fights some species of anoles are known to vocalize. In addition to the behaviors indicating dominance, anoles may move their head up and down in a head-nod display (not to be confused with the head-bob display where entire frontal part of body is moved through "push-ups"), which is a submissive sign. Females maintain a feeding territory. Males maintain a larger breeding territory, which overlaps with the feeding territory of one or several females. The home range is generally larger in males than in females, and larger in large anole species than in smaller. In a very small species like the Bahoruco long-snouted anole the home range can be as little is about and in a female and male, compared to a large species like the knight anole where they average about and . If removed from its territory an anole will usually be able to find its way back home in a relatively short time, but exactly how they do this is unclear. Generally being highly solitary animals, anoles will only infrequently congregate, but in colder regions individuals may rest adjacent to each other in groups during the winter.
In addition to differences in the appearance of the dewlap, the frequency of the dewlap opening/closing and the frequency and amplitude of the head bobbing differ between species, allowing them to separate each other. Territoriality is typically aimed at other individuals of the same species, but in a few cases it is also directed towards other anoles, as can be seen between the crested and Cook's anoles. Unlike most anoles with widely overlapping ranges, these two inhabit very similar niches and directly compete for resources.
The breeding period varies. In species or populations living in highly seasonal regions it is generally relatively short, typically during the wet season. It is prolonged, often even year-round, in species or populations living in regions with less distinct seasons. In some species where it is year-round the egg production is however higher during the rainy season than the dry season, and in many where it is prolonged but not year-round, it begins in the spring and ends in the fall. Males attract and court females by performing a range of behaviors, often mirroring those used to scare away competitors, including extending their dewlap and bobbing their heads. During mating the male inserts one of his hemipenes into the female's cloaca, fertilizing the egg inside the oviduct. The female may mate with multiple males, but is also able to store sperm inside her body for fertilization of eggs several months after mating. A female anole produces an egg in each ovary, meaning that when one is maturing in one of her follicles the yolk of another is forming in the other. The white shell only forms when the egg has been fertilized and females will sometimes lay infertile, unshelled yellowish eggs known as "slugs". The female lays one (occasionally two) eggs per time, which typically is placed casually on the ground among leaf-litter, under debris, logs or rocks, or in a small hole. In some species it is placed at higher levels in a bromeliad, tree hole or rock crevice. A small number of species lay their eggs together, forming a communal nest. Among these is the unusual Cuban cave anole where as many as 25 eggs may be glued together in a small cavity on the side of a cave wall. A nest that contained eggs from the bay anole and the geckos Sphaerodactylus armasi and Tarentola crombiei represents the only known multi-species communal nest for an anole and the only known communal nest involving more than one family of lizard. Although typically only laying a single egg per time (clutch), females of many anole species can lay an egg every five days to four weeks. Some only have a single clutch per year, while other species may have as many as 20 on average. Depending on species, anole eggs hatch after about 30–70 days.
Feeding
Anoles are opportunistic feeders, and may attempt to eat any attractive meal that is of the right size. They primarily feed on insects like flies, grasshoppers, crickets, caterpillars, moths, butterflies, beetles and ants, and arachnids like spiders. Several species will also eat small vertebrates such as mice, small birds (including nestlings), lizards (including other anole species and Cannibalism of their own) and frogs. The slow-moving Cuban false chameleon anoles ("Chamaeleolis") are specialized snail-eaters, and a few semi-aquatic species like the Cuban stream anole may catch prey in water such as shrimp and small fish. In some species the average prey-size varies with the individual anole's size, age and sex, with juvenile anoles eating the smallest prey, adult females taking intermediate-sized prey and adult males the largest prey. In other species there are no clear differences in the preferred prey size, regardless of an individual's size and sex.
Hunting is done by sight, and they generally show a strong preference for moving prey over non-moving. Many will chase down or sneak up to a potential prey item, while others are sit-and-wait predators that pounce on prey when it gets close to the anole. Anoles have numerous small, sharp and pointed teeth that allow them to efficiently grab their prey. They are heterodonts with each tooth in the frontal half of the jaw having a single tip (unicuspid) and each in the rear half having three tips (tricuspid); one in the middle and a smaller behind and in front of it. Unusually, the Cuban false chameleon anoles have enlarged and blunt, molar-like teeth in the rear part of their jaw, allowing them to crush the shells of their snail prey.
In addition to animal prey, many anole species will take plant material, notably fruits, flowers and nectar, and overall they are best described as omnivorous. Some fruit-eating species, like the knight anole, may function as seed dispersers. Anoles have been recorded drinking sweetened water from hummingbird feeders. Anoles are vulnerable to drying out and generally need access to water for drinking, like dew or rain on leaves, although some species are less susceptible to water loss than others and are able to live in relatively arid places.
Predator avoidance and deterrence
A wide range of animals will eat anoles, such as large spiders, centipedes, predatory katydids, snakes, large frogs, lizards, birds, monkeys, bats and carnivoran mammals. At least in part of their range, snakes may be the most significant predator of anoles. For example, the Caribbean Alsophis and Borikenophis racers, and the Mexican, Central American and South American Oxybelis vine snakes feed mostly on lizards like anoles. Some reptile-eating snakes have a specialized venom that has little effect on humans, but it rapidly kills an anole. On some Caribbean Islands anoles make up as much as 40–75% of the diet of American kestrels. Large anoles may eat smaller individuals of other anole species and cannibalism—eating smaller individuals of their own species—is also widespread. There is a documented case of a small anole being captured and killed by an outside potted Venus flytrap plant.
Anoles mainly detect potential enemies by sight, but their hearing range also closely matches the typical vocal range of birds. If hearing a predatory bird, like a kestrel or hawk, they increase their vigilance. When hearing a non-predatory bird little or no change happens. Most anole species will try to escape from a predator by rapidly running or climbing away, but some will move to the opposite side of a tree trunk (facing away from the would-be attacker), jump to the ground from their perch, or freeze when disturbed, hoping the adversary does not spot it. Some anole species will show their fitness by displaying their dewlap when encountering a predator; the greater the endurance of the anole, the greater the display. Conversely, when suddenly forced to share their habitat with an efficient anole predator like the northern curly-tailed lizard (for example, if it is introduced to a place where formerly not present), the anoles may decrease the amplitude of their head bobbing, making them less conspicuous, and may become slower to emerge from hiding (less willing to take a risk) after having been scared by a predator. Slow-moving anoles, like the twig ecomorphs of the Caribbean and many Dactyloa species of mainland Central and South America, are generally cryptically colored and often coordinate their movements with the wind, resembling the surrounding vegetation. A few semi-aquatic species will attempt to escape from predators by diving into water or running bipedally across it, similar to basilisks. However, the anoles lack the specialized toe fringes that helps basilisks when doing this.
Anole tails often have the ability to break off at special segments, which is known as autotomy. The tail continues to wriggle for a period after detaching, attracting the attention of the predator and commonly allowing the anole to escape. The tail is regenerated, but it takes more than two months to complete this process. About two dozen anoles, including almost all members of the latifrons species group, all in the chamaeleonidae species group and the La Palma anole, do not have the ability to autotomize the tail.
If caught or cornered, anoles will bite in self-defense. This can be relatively effective against some predators. When fighting back and biting, sometimes for as much as 20 minutes, Puerto Rican crested anoles escape from more than of all attacks by Puerto Rican racer snakes. Some species of anoles will vocalize (typically growls, chirps or squeals) when caught.
Evolution
The evolution of anoles has been widely studied, and they have been described as a "textbook example of adaptive radiation and convergent evolution". Especially the widespread convergent evolution seen in anoles living in the Greater Antilles has attracted the attention of scientists, and resulted in comparisons with the Darwin's finches of the Galápagos Islands, lemurs of Madagascar and cichlid fish in the African Great Lakes.
Ecomorphs and origin
On each major Greater Antillean Island (Cuba, Hispaniola, Puerto Rico and Jamaica), there are anole species that have adapted to specific niches and are referred to as ecomorphs: crown giant, trunk crown, trunk, trunk ground, twig and grass bush (a few additional, less widely used ecomorphs also exist). However, even within the Greater Antilles there are differences depending on island size and the amount of available habitats. The largest, Cuba and Hispaniola, have all six primary ecomorphs, while the smaller Puerto Rico and Jamaica have five and four respectively. Species living in a specific niche on each island tend to resemble each other in both appearance and behavior. For example, the Escambray twig anole of Cuba closely resembles the Puerto Rican twig and Jamaican twig anoles, as well as several species of twig ecomorphs from Hispaniola. Despite this they are not closely related and have adapted to their specific niche independently of each other. At least four of the six primary ecomorphs are of ancient origin as they have been documented in amber fossils from Hispaniola that are about 15–20 million years old (the two missing ecomorphs are crown giant and grass bush). Otherwise there are few known fossils, but early phylogenetic and immunological studies indicate that anoles originated 40–66 million years ago, first inhabitant Central or South America, and then came to the Caribbean (initially likely Cuba or Hispaniola). A more recent phylogenetic study, published in 2012, indicated that anoles originated in South America and diverged from other reptiles far earlier, about 95 million years ago. While a South American origin has been generally accepted, the very high age has been controversial and other studies published in 2011–2014 arrived at a lower age, estimating that anoles diverged from other reptiles 23–75, 53–72 or 81–83 million years ago, while a comprehensive study from 2017 estimated about 46–65 million years ago. This indicates that early anoles arrived on the Greater Antillean Islands in the Caribbean from the mainland of the Americas via rafting rather than overland via ancient (now submerged) land bridges. After arriving in the Caribbean they diversified into several new groups and one of these, the Norops lineage, later made its way back to mainland of the Americas.
Species and adaptability
Species level evolution in anoles can be very slow. Martinique originally consisted of four tiny islands, which then merged into a single as a result of uplifting. Anoles lived on each of the tiny ancient islands and were isolated six to eight million years ago. Despite this long separation, they did not experience allopatric speciation, as mixed couples of the different Martinique anole populations can successfully reproduce and remain part of a single species. The Barbados anole is part of the same group, but Barbados remains a separate, isolated island. The genetic divergence between the different Martinique anole populations is similar to that between other Lesser Antillean anoles consistently recognized as separate species. Another Lesser Antillean species, the Guadeloupean anole, has several distinct populations that generally are recognized as subspecies. However, Guadeloupean anoles exhibit high individual variability and the populations widely intergrade, something that possibly has been enhanced by habitat changes by humans (allowing populations to easier come into contact with each other) and translocations of individuals. This indicates that the subspecies are invalid today. Genetic studies confirm that strong assortative mating between the different Guadeloupean anole populations does not exist, despite their distinct differences in appearance and them having separated about 650,000 years ago (confidence interval starting at 351,000 years). Hybridization between different anole species has rarely been documented.
In contrast to this, anoles can change rapidly in response to changes, which is an example of microevolution. They are one of the few known examples of "visible evolution" (i.e., where changes happen at a speed where they can be observed within a human lifetime), together with groups like stickleback fish, guppies and Peromyscus beach mice. In studies of brown anoles introduced to Florida it has been seen that they can become longer-legged in a single generation when living with the predatory, ground-living northern curly-tailed lizard (shorter-legged anoles are slower and easier to catch for the curly-tailed lizard). Over a longer period, however, their legs become shorter, which are better suited for perching on smaller branches higher off the ground, out of reach for the curly-tailed lizard. When brown anoles are introduced to small islands with low vegetation, their legs become shorter, better suited for rapidly moving among the shrunken shrubbery to catch insects and avoid predatory birds. Furthermore, in a study where brown anoles were introduced to seven small, anole-free Bahaman islands (anoles had disappeared because of Hurricane Frances), it was seen that—although all populations became shorter-legged within a few years—this was proportional to the leg-size of the founders. In other words: The few founder brown anoles introduced to one island were shorter-legged than the few introduced to another. Both populations became shorter-legged over time, but the first remained shorter-legged than the second. This is an example of the founder effect. Similarly, when brown anoles were introduced to Florida, the native Carolina (or green) anoles moved to higher perches and gained larger toe pads better suited for those perches. This adaptation occurred in just 20 generations. Anoles are also adapting to life with humans: Puerto Rican crested anoles living in cities have developed more adhesive lamellae on their toe pads than ones living in forests, reflecting the need for being able to climb very smooth surfaces like windows in the former habitat. In contrast to these fast changes, anole's adaptability to temperature changes has traditionally been considered relatively minor. Nevertheless, when Puerto Rican crested anoles in Florida (where introduced in the 1970s) were compared to the original, native population in Puerto Rico, it was discovered that the former had become adapted to colder temperatures, by about 3 °C (5.4 °F). An even faster adaption was observed in Carolina anoles from Texas during the unusually cold winter of 2013–2014. Carolina anoles living in central Texas and further north were already adapted to relatively cold temperatures, but those of southern Texas were not. However, after the winter of 2013–2014, the cold tolerance of the southern Texan populations had increased by as much as 1.5 °C (2.7 °F) and their genomic profiles had changed to more closely resemble the more northerly living Carolina anoles.
Taxonomy
The name for this group of lizards originates from the Carib anoli. It was modified and used in French Creole, and then transferred to English via the genus name Anolis, coined by French zoologist François Marie Daudin in 1802.
Several family names have been used for the anoles in recent decades. Initially they were placed in Iguanidae. This family, then comprising several very different groups, was split into eight families in 1989, with anoles being part of Polychrotidae together with Polychrus (bush anoles). However, genetic studies have shown that Polychrus is closer to Hoplocercidae than the true anoles. The true anoles are closer to Corytophanidae (basilisks and relatives). The true anoles have therefore been transferred to their own family Dactyloidae, alternatively listed as subfamily Dactyloinae of family Iguanidae. The name Anolidae (Cope, 1864) has sometimes been used, but it is a junior synonym of Dactyloidae (Fitzinger, 1843).
More than 425 species of true anoles are known. New species are regularly described, including 12 in 2016 alone. Most of the recent discoveries have been from the mainland of the Americas, with fewer new anoles described from the comparatively better-known Caribbean Islands.
Genera
Traditionally, all the true anoles were included in the genus Anolis and some continue to use this treatment, in which case it is the largest genus of reptile. An attempt of dividing this huge genus was already made in 1959–1960, when they were placed in two major groups, the so-called "alpha anoles" (comprising most anole subgroups) and "beta anoles" (equalling today's Norops). In the following decades other changes were recommended. This included a proposal to recognize four genera, Anolis, Chamaeleolis, Chamaelinorops and Phenacosaurus, in 1976. In 1986, it was proposed that eight should be recognized: the four from 1976, and Ctenonotus, Dactyloa, Norops and Semiurus (the last was later replaced by its senior synonym Xiphosurus). These changes were adopted by some and rejected by others, who continued placing all in Anolis. In 1998–1999, the first comprehensive molecular studies of the anoles were published, confirming the earlier suspicion that the so-called "beta anoles" are a monophyletic group, but the "alpha anoles" are not. Furthermore, the genus splits proposed in 1976 and 1986 caused problems, as the narrowly defined Anolis was not monophyletic. In 2004, a major review based on several types of data (both molecular and morphological) revealed several groups and partially confirmed the genetic results from 1998 to 1999. No major changes were proposed and all anoles were maintained in a broadly defined Anolis. Two recent studies, primarily genetic and published in 2012 and 2017, confirmed several of the groups found in earlier studies, but rejected others. They found that the anoles fall into eight primary clades. Some of these can be further subdivided: For example, Chamaeleolis (from Cuba) is one of two subclades within Xiphosurus and it is sometimes considered a valid genus (in which case Xiphosurus is restricted to Hispaniola, Puerto Rico and nearby smaller islands). In contrast, the earlier proposed genus Phenacosaurus (from the Andes and tepui highlands in northwestern South America) is now included in Dactyloa. The phylogenetic position of most species is clear, but in a few the available evidence is conflicting and/or labelled with considerable statistic uncertainty.
The relationship of Dactyloidae can be described with a cladogram. Whether the eight groups are best recognized as separate genera or only as clades within a single genus, Anolis, is disputed. A few families between Polychrotidae and Corytophanidae+Dactyloidae are not shown:
Relationship with humans
Anoles are model organisms often studied in fields such as ecology, behavior, physiology and evolution. The Carolina (or green) anole is the most-studied anole species, with the earliest dedicated studies being more than 100 years old, from the late 1800s. The Carolina anole was the first reptile where the entire genome was sequenced.
Anoles are harmless to humans, but if caught or cornered they will bite in self-defense. As typical of animals, the bite force is strongly correlated to the size of the anole. It causes little pain in the smaller anoles which usually do not break the skin. Large species have relatively strong jaws lined with small, sharp teeth, and their bite can be painful and result in a superficial wound, but it is still essentially harmless.
Some anole species are commonly kept in captivity as pets and especially the Carolina (or green) anole is often described as a good "beginner's reptile", but it too requires specialized care.
Anoles can function as a biological pest control by eating pest insects that may harm humans or plants. Anole abundances can be considerably higher in diversified agroecosystems (multiple different plant types) than high-intensity agroecosystems (typically only one or very few plant types, and regular use of agrochemicals), making the former particularly suitable for this type of pest control. However, because of their potential of becoming invasive species, releasing anoles outside their native range is strongly discouraged and often illegal, even if the species occurs elsewhere in a country (for example, it is illegal to release Carolina anoles in California, as its native range is in the Southeastern United States).
Conservation
The willingness of many anoles of living close to humans in heavily altered habitats have made them common. Some anoles can occur in very high densities, as illustrated by the Saint Vincent bush, Puerto Rican bush and spotted anoles where it has been estimated that there locally are almost 28,000 individuals per hectare (11,500 per acre) in the first species and at least 20,000–21,000 per hectare (8,000–8,500 per acre) in the last two. However, in most species the density is lower and in rare anoles it can be well below 100 individuals per hectare (40 per acre). Some are restricted to specific habitats such as primary rainforest, making them more vulnerable. In a review in 2017, it was found that more than 50 anole species had a known total range that covered or less around their type locality. , only 90 anoles, equalling less than one-quarter of the total number of recognized species, had been rated by the IUCN. Most of these are either least concern (not threatened) or data deficient (limited available data prevents an assessment), but 7 are considered vulnerable, 14 endangered and 1 critically endangered. Typical threats to these are habitat loss from both humans and extreme weather, or competition/predation by introduced species. For example, the Finca Ceres anole, a critically endangered species only known from a single unprotected location in Matanzas Province, Cuba, has suffered habitat loss both due to hurricanes and expanding agricultural land. A. amplisquamosus, a critically endangered species only known from highland forest in the Cusuco National Park region of Honduras, was common in the early 2000s, but by 2006 it had experienced a drastic decline and was only infrequently encountered. A clear explanation for this is lacking, although it may be related to habitat loss due to human development and agriculture. Similarly, A. landestoyi, which only was described in 2016 and has not been rated by the IUCN, is restricted to the Loma Charco Azul reserve in Hispaniola, but it is seriously threatened by continuing illegal habitat destruction by slash-and-burn agriculture, livestock grazing and production of wood charcoal. Certain highly localized species can be threatened by other anoles. The Cook's anole, found only in southwestern Puerto Rico and considered endangered by the Puerto Rico Department of Natural and Environmental Resources, faces habitat loss and fragmentation from human development, predation by introduced species (especially cats and rats) and direct competition from a more widespread native, the Puerto Rican crested anole. The Puerto Rican crested anole has also been introduced to Dominica where it locally is outcompeting the endemic Dominican anole, having already largely displaced the South Caribbean ecotype (traditionally subspecies Anolis o. oculatus), which possibly may require a captive breeding program to ensure its survival.
Nevertheless, anoles overall do not appear to have experienced the widespread extinctions and extirpations prevalent among larger Caribbean reptiles. The Culebra Island giant anole is the only anole considered possibly extinct in recent history (other extinct anoles are prehistoric and only known from fossil remains that are millions of years old). Locals reported sighting of the Culebra Island giant anole as recent as the 1980s, but this likely involved misidentifications of young green iguanas. Others, at least the Morne Constant anole, do not grow as large today as they once did.
Species restricted to a specific habitat in relatively remote regions, infrequently visited by biologists looking for reptiles, are often virtually unknown and rarely recorded. In a review in 2017, it was found that 15 anole species only were known from their holotype. These may truly be rare and seriously threatened, as the proboscis anole, a species that only was known from a single specimen collected in 1953 until it was rediscovered in cloud forests of Ecuador in 2004. In others with few records, like the Neblina anole, this is not the case. It was initially known from six 1980s specimens from the remote Neblina highlands in Venezuela, but when the Brazilian part of these highlands were visited in 2017 it was discovered that the species was locally abundant. Some species are easily overlooked, even if common. For example, if searching for Orces' Andes anole during the night when asleep they can be fairly easy to find, but if visiting the same location during the day it can be very difficult to find any.
As introduced species
When introduced to regions outside their native range by humans, anoles may become invasive and represent a serious threat to small local animals. Such introductions may happen by mistake (for example, as "stowaways" on garden plants) or deliberately (as predators introduced to combat insects or release of pet anoles people no longer want).
In the contiguous United States, the Carolina anole has been introduced to California, the brown anole has been introduced to the Gulf Coast states and California, and the knight, Jamaican giant, bark, large-headed, Puerto Rican crested, Cuban green and Hispaniolan green anoles have been introduced to Florida. The Barbados and Morne Constant anoles have also been recorded in Florida, but do not appear to have become established. There are indications that the invasive brown anole is displacing the native Carolina anole in Florida and Texas by outcompeting it and eating its young. In the most disturbed habitats the Carolina anole may disappear entirely, but in less disturbed habitats where there is more cover (allowing young to avoid predation) it may remain fairly common, although it is forced to occur higher in trees where less visible to humans. Regardless, the Carolina anole is common and widespread overall, and it has itself been introduced to several regions outside its native range, including California, Kansas, Hawaii, Guam, Palau, the Bahamas, Cayman Islands, Anguilla, Belize, Tamaulipas in Mexico, and Japan's Okinawa and Ogasawara (Bonin) Islands. Although there are several records from Spain (both the mainland and the Canary Islands), none of these have become established. In Japan's Ogasawara Islands, the introduced Carolina anoles have caused declines in native lizards and diurnal insects, including the near-extinction of five endemic dragonfly species and the likely extinction of the Celastrina ogasawaraensis butterfly. This may be due to the ecological naïveté of the insects (before the introduction, there were no diurnal, highly arboreal lizards) and a very high anole density on these Japanese islands, as similar insect declines have not been reported from the Bahamas (which already had diurnal, arboreal lizards), or Guam, Saipan and Hawaii (where the anole density is lower). In addition to Florida, the Cuban green anole has been introduced to the Dominican Republic, São Paulo (Brazil) and Tenerife (Spain). In Florida and the Dominican Republic it competes with native anoles (Carolina anole and Hispaniolan green anole, respectively) and it is feared that something similar may happen in São Paulo. The same pattern can be seen in Dominica where the introduced Puerto Rican crested anole locally has displaced the endemic Dominican anole. The brown anole and Graham's anole have both been introduced to Bermuda where they threaten the very rare Bermuda rock lizard. This problem has not been reported for the Leach's and Barbados anoles, the other species introduced to Bermuda. In the Cayman Islands the endemic Cayman blue-throated anole has moved to higher perched in places where the introduced brown anole is present (similar to the Carolina anole in places where brown anoles are present). Outside the Americas, the brown anole has been introduced to Hawaii, Tenerife, Singapore and Taiwan, and it is able to change ant communities on the last of these islands.
| Biology and health sciences | Iguania | Animals |
322664 | https://en.wikipedia.org/wiki/Iguanidae | Iguanidae | The Iguanidae is a family of lizards composed of the iguanas, chuckwallas, and their prehistoric relatives, including the widespread green iguana.
Taxonomy
Iguanidae is thought to be the sister group to the collared lizards (family Crotaphytidae); the two groups likely diverged during the Late Cretaceous, as that is when Pristiguana and Pariguana, the two earliest fossil genera, are known from. The subfamily Iguaninae, which contains all modern genera, likely originated in the earliest Paleocene, at about 62 million years ago. The most basal extant genus, Dipsosaurus, diverged from the rest of Iguaninae during the late Eocene, about 38 million years ago, with Brachylophus following a few million years later at about 35 million years ago, presumably after its dispersal event to the Pacific. All other modern iguana genera formed in the Neogene period.
A phylogenetic tree of Iguaninae is shown here:
Description
Iguanas and iguana-type species are diverse in terms of size, appearance, and habitat. They typically flourish in tropical, warm climates, such as regions of South America and islands in the Caribbean and in the Pacific. Iguanas typically possess dorsal spines across their back, a dewlap on the neck, sharp claws, a long whip-like tail, and a stocky, squat build. Most iguanas are arboreal, living in trees, but some species tend to be more terrestrial, which means they prefer the ground. Iguanas are typically herbivores and their diets vary based on what plant life is available within their habitat. Iguanas across many species remain oviparious, and exhibit little to no parental care when their eggs hatch. They do, however, display nest-guarding behavior. Like all extant non-avian reptiles, they are poikilothermic, and also rely on regular periods of basking under the sun to thermoregulate.
Distribution
All but one of modern iguana genera are native to the Americas, ranging from the deserts of the Southwestern United States through Mexico, Central America, and the Caribbean, to throughout South America down to northernmost Argentina. Some iguanas like I. iguana have spread from their native regions of Central and South America into many Pacific Islands, and even to Fiji, Japan, and Hawai'i, due to the exotic pet trade and illegal introductions into the ecosystems. Other iguanas, like the Galapagos pink iguana (C. marthae) are endemic only to specific regions on the Galapagos islands. The Grand Cayman blue iguana, C. lewisi, is endemic only to the Grand Cayman island, limited to a small wildlife reserve. The only non-American iguana species are the members of the genus Brachylophus and the extinct Lapitiguana, which are found on Fiji and formerly Tonga; their distribution is thought to be the result of the longest overwater dispersal event ever recorded for a vertebrate species, with them rafting over 8000 km across the Pacific from the Americas to the Fiji and Tonga.
Extant genera
Fossils
Cretaceous Pristiguana brasiliensis and Pariguana lancensis are later excluded from the family.
Classification
Several classification schemes have been used to define the structure of this family. The "historical" classification recognized all New World iguanians, plus Brachylophus and the Madagascar oplurines, as informal groups and not as formal subfamilies.
Frost and Etheridge (1989) formally recognized these informal groupings as families.
Macey et al. (1997), in their analysis of molecular data for iguanian lizards recovered a monophyletic Iguanidae and formally recognized the eight families proposed by Frost and Etheridge (1989) as subfamilies of Iguanidae.
Schulte et al. (2003) reanalyzed the morphological data of Frost and Etheridge in combination with molecular data for all major groups of Iguanidae and recovered a monophyletic Iguanidae, but the subfamilies Polychrotinae and Tropidurinae were not monophyletic.
Townsend et al. (2011), Wiens et al. (2012) and Pyron et al. (2013), in the most comprehensive phylogenies published to date, recognized most groups at family level, resulting in a narrower definition of Iguanidae.
Historical classification
Family Iguanidae
Informal grouping anoloids: anoles, leiosaurs, Polychrus
Informal grouping basiliscines: casquehead lizards
Informal grouping crotaphytines: collared and leopard lizards
Informal grouping iguanines: marine, Fijian, Galapagos land, spinytail, rock, desert, green, and chuckwalla iguanas
Informal grouping morunasaurs: wood lizards, clubtails
Informal grouping oplurines: Madagascan iguanids
Informal grouping sceloporines: earless, spiny, tree, side-blotched and horned lizards
Informal grouping tropidurines: curly-tailed lizards, South American swifts, neotropical ground lizards
Frost et al. (1989) classification of iguanas
Family Corytophanidae
Family Crotaphytidae
Family Hoplocercidae
Family Iguanidae
Genus Amblyrhynchus – marine iguana
Genus Brachylophus – Fijian/Tongan iguanas
Genus Cachryx – spinytail iguanas
Genus Conolophus – Galápagos land iguanas
Genus Ctenosaura – spinytail iguanas
Genus Cyclura – West Indian rock iguanas
Genus Dipsosaurus – desert iguana
Genus Iguana – green and Lesser Antillean iguanas
Genus Sauromalus – chuckwallas
Genus Armandisaurus (extinct chuckwalla)
Genus Lapitiguana (extinct giant Fijian iguana)
Genus Pumilia (extinct Palm Springs iguana)
Genus Pristiguana (Cretaceous Brazilian iguana)
Family Opluridae
Family Phrynosomatidae
Family Polychridae
Family Tropiduridae
Macey et al. (1997) classification of Iguanidae
Family Iguanidae
Subfamily Corytophaninae: casquehead lizards
Subfamily Crotaphytinae: collared and leopard lizards
Subfamily Hoplocercinae: wood lizards, clubtails
Subfamily Iguaninae: marine, Fijian, Galapagos land, spinytail, rock, desert, green, and chuckwalla iguanas
Subfamily Oplurinae: Madagascan iguanids
Subfamily Phrynosomatinae: earless, spiny, tree, side-blotched and horned lizards
Subfamily Polychrotinae: anoles, leiosaurs, Polychrus
Subfamily Tropidurinae: curly-tailed lizards, neotropical ground lizards, South American swifts
Schulte et al. (2003) classification of Iguanidae
Here families and subfamilies are proposed as clade names, but may be recognized under the traditional Linnean nomenclature.
Iguanidae
Corytophaninae: casquehead lizards
Crotaphytinae: collared and leopard lizards
Hoplocercinae: wood lizards, clubtails
Iguaninae: marine, Fijian, Galapagos land, spinytail, rock, desert, green, and chuckwalla iguanas
Oplurinae: Madagascan iguanids
Phrynosomatinae: earless, spiny, tree, side-blotched and horned lizards
Polychrotinae: anoles, leiosaurs, Polychrus
subclade of Polychrotinae Anolis: anoles
subclade of Polychrotinae Leiosaurini: leiosaurs
subclade of Leiosaurini Leiosaurae:
subclade of Leiosaurini Anisolepae:
subclade of Polychrotinae Polychrus
Tropidurinae: curly-tailed lizards, neotropical ground lizards, South American swifts
subclade of Tropidurinae Leiocephalus: curly-tailed lizards
subclade of Tropidurinae Liolaemini: South American swifts
subclade of Tropidurinae Tropidurini: neotropical ground lizards
Townsend et al. (2011), Wiens et al. (2012) and Pyron et al. (2013) classification of Iguanidae
Family Corytophanidae
Family Crotaphytidae
Family Dactyloidae
Family Hoplocercidae
Family Iguanidae
Family Leiocephalidae
Family Leiosauridae
Family Liolaemidae
Family Opluridae
Family Phrynosomatidae
Family Polychrotidae
Family Tropiduridae
| Biology and health sciences | Iguania | Animals |
322730 | https://en.wikipedia.org/wiki/Dibamidae | Dibamidae | Dibamidae or blind skinks is a family of lizards characterized by their elongated cylindrical body and an apparent lack of limbs. Female dibamids are entirely limbless and the males retain small flap-like hind limbs, which they use to grip their partner during mating. They have a rigidly fused skull, lack pterygoid teeth and external ears. Their eyes are greatly reduced, and covered with a scale.
They are small insectivorous lizards, with long, slender bodies, adapted for burrowing into the soil. They usually lay one egg with a hard, calcified shell, rather than the leathery shells typical of many other reptile groups.
The family Dibamidae has two genera, Dibamus with 23 species native to Southeast Asia, Indonesia, the Philippines, and western New Guinea and the monotypic Anelytropsis native to Mexico. Recent phylogenetic analyses place the dibamids as the sister clade to all the other lizards and snakes or classify them as sharing a common ancestor with the infraorder Gekkota, with Dibamidae and Gekkota forming the sister clade to all other squamates. Hoeckosaurus from the Oligocene of Mongolia represents the only fossil record of the group.
Characteristics
General appearance
Dibamids are burrower lizards characterized by their elongated bodies with blunt head and tail, and an apparent lack of limbs. Relatively small, blind skinks can reach a maximum length of 250 mm (9.8 in) from head to tail and the snout vent length (SVL) is variable between both genus Anelytropsis and Dibamus. In Anelytropsis, the tail is longer than in Dibamus and represents between 34 and the 38% of the snout vent length which can range from 77 to 180 mm (3 to 7 in). In Dibamus, the tail corresponds to 9 to 25% of the SVL that varies from 52 to 203 mm (2 to 8 in).
Usually dibamids are dark colored, from brown to dark purple, with little to no variation along their body and frequently lack elaborate patterns. It is common to find a color gradation from the darker back towards a lighter ventral side. Scales are shiny and smooth and very similar and overlapping along with some variation in number and shape in the head and anal regions where males usually have additional scales to cover anal pores. Scale row counts varies between both genera; Anelytropsis has 19 to 25 rows whereas Dibamus has 18 to 33. In both groups osteoderms are absent.
General characteristics of the soft tissue includes a tongue that is covered in lamellae except in the tip, heavily modified ears without external openings or middle ear cavity or eustachian tubes, and highly reduced eyes that are covered by a scale and lack internal structure, particularly in Dibamus.
Limbs
Dibamids are lizards with highly reduced limbs but they are not completely limbless. Males and females have rudimentary poorly developed hind limbs containing a femur, tibia and fibula in males, and distal cartilage cap. These elements are more developed on Dibamus than in Anelytropsis. Female Dibamus lack the tibia and the fibula.
Skull
The skull is approximately 5 – 7 mm in length with reduced kinesis and a more rigid skull for burrowing. The combination of fossorial habits and small size, contributes to the development of a skull configuration that is frequently found in other groups of burrowers and miniaturized species. Among those characteristics are the closure of the supratemporal fenestra and the post-temporal fenestra, the relative large braincase, tubular or scroll-like palatines and modified jaw suspension mechanism with the quadrate articulating with the lateral wall of the braincase.
Other characteristics of the skull of blind skinks include the absence of a parietal foramen, a well developed secondary palate formed by three different bones, the maxillae, vomers and palatines which are expanded ventromedially to form a scroll, and the lack of palatal teeth. Nasal and frontal bones are paired and contact each other in a W-shape suture with no overlap between the two bones, and several bones are lost (lacrimal, postorbital and jugal) or highly reduced (supratemporal and squamosal). The main cranial differences, besides sizes, between Anelytropsis and Dibamus is the presence of epipterygoid and postfrontal in the Central American genus.
The mandible of Dibamidae bears less than 10 teeth and is composed of only three bones, the dentary, the coronoid and the compound bone. A remnant of the splenial bone is only present in one species of Dibamus, Dibamus novaeguineae.
Classification
The family Dibamidae contains two genera, Anelytropsis and Dibamus, and the close relationship of the genera was based on two morphological characteristics that are unique to these groups, the secondary palate and the lamellae covering the tongue, and additional cranial characteristics that can be shared with other groups of lizards.
The anatomical characteristics that dibamids share with other squamates contributed to the formulation of different taxonomic hypothesis. Dibamids, and particularly Dibamus was considered to be part of geckos and precisely the family of legless geckos; snakes, considering the organization of the skull and jaw muscles; or was proposed to be closely related to a group of fossorial skinks with elongated bodies and reduced limbs.
Phylogeny
Relationships among Dibamidae
The relationships within Dibamidae have only be assessed until recently in a phylogenetic analysis that included DNA sequences from seven nuclear genes and one mitochondrial gene for 8 species, seven species of Dibamus and the one species of Anelytropsis. This analysis shows that there are two major clades within Dibamidae, one that includes the one species form the genus Anelytropsis, Analytropsis papillous, and the species of Dibamus that are distributed along continental Southeast Asia (Dibamus greeri, Dibamus montanus, and Dibamus bourreti). The other clade includes species that are currently distributed in the peninsular Southeast Asia and Islands (Dibamus tiomanensis, Dibamus novaeguineae, Dibamus seramensis, and Dibamus celebensis). These clades diverged 72 million years ago. Anelytropsis diverged from all mainland Dibamus at approximately 69.2 million years ago.
Dibamidae and its relationship with Squamata
The relationship of Dibamidae with other Squamata (lizards and snakes) has a long history of phylogenetic studies in which the morphological characteristics are used to determine those relationships. Those analyses found close relationships between Dibamidae and all other lizards with elongated bodies, limb reduction and usually, a fossorial habit like amphisbaenians, snakes or fossorial skinks. In morphology based phylogenies, dibamids are sister taxa to amphisbaenians and the clade that includes amphisbaenians and Dibamidae is sister to all snakes. The close relationships of this groups are the result of convergent evolution among these groups since some of the morphological traits have evolved independently in different groups.
More recent phylogenies using DNA sequences of nuclear and mitochondrial genes include a large taxonomic sample of squamates and place dibamids as the sister group to all other lizards and snakes, or with Gekkota as the sister group to all other squamates. Phylogenetic evidence supports dibamids being the most basal squamates, being sister to all other lizards and snakes, and indicates that they diverged during the late Triassic, around 210 million years ago.
Biodiversity
There are two recognized genera within the family, Anelytropsis and Dibamus. According to The Reptile Database, Anelytropsis is monotypic and Dibamus includes 23 species:
Anelytropsis
Anelytropsis papillosus
Dibamus
Dibamus alfredi
Dibamus bogadeki
Dibamus booliati
Dibamus bourreti
Dibamus celebensis
Dibamus dalaiensis
Dibamus deharvengi
Dibamus dezwaani
Dibamus floweri
Dibamus greeri
Dibamus ingeri
Dibamus kondaoensis
Dibamus leucurus
Dibamus montanus
Dibamus nicobaricum
Dibamus novaeguineae
Dibamus seramensis
Dibamus smithi
Dibamus somsaki
Dibamus taylori
Dibamus tebal
Dibamus tiomanensis
Dibamus vorisi
For additional details, see here
An extinct monotypic genus, Hoeckosaurus was recently proposed from the description of fossil material from the early Oligocene of the Valley of Lakes in Central Mongolia.
Hoeckosaurus mongoliensis sp. nov.
Biogeography
Dibamids have a disjunct distribution with one genus living in Northern Mexico, Anelytropsis, and the other one, Dibamus, living in South East Asia. Biogeographical studies suggest that the separation between Anelytropsis and Dibamus, specifically the clade with species that are distributed in continental South East Asia, occurred approximately 69 million years ago during the late Cretaceous and the migration from Asia to North America took place during the Late Paleocene or Eocene through Beringia.
Biology
Blind skinks are insectivorous and feed on arthropods and earthworms. Blind skinks are characterized by their fossorial or burrowing habits. They can dig their own burrows, use old burrows or other openings in the ground, or dwell under the leaf litter or logs.
Species of the genus Dibamus are frequently found in primary and secondary forests in a wide range of altitudinal variation (from the sea level to approximately 1300 meters above sea level). Anelytropsis is found in drier environments and is adapted to xeric conditions of different environments in northern Mexico.
Little is known about the reproduction of this group of lizards, but the inspection of female specimens from herpetological collections indicate that dibamids lays single egg with hardened shell, and eggs are laid frequently, at least in Dibamus.
Conservation
None of the species of Dibamidae are listed as endangered species in the Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES.
The International Union for Conservation of Nature (IUCN) include some of the species of the genus Dibamus and the single species of Anelytropsis in the red list of endangered species, most are in the category of least concern, and two species, Dibamus kondaoensis and Dibamus tiomanensis are listed as nearly threatened and endangered respectively.
| Biology and health sciences | Lizards and other Squamata | Animals |
322739 | https://en.wikipedia.org/wiki/Lacertidae | Lacertidae | The Lacertidae are the family of the wall lizards, true lizards, or sometimes simply lacertas, which are native to Afro-Eurasia. It is a diverse family with at about 360 species in 39 genera. They represent the dominant group of reptiles found in Europe.
Habitat
The European and Mediterranean species of lacertids live mainly in forest and scrub habitats. Eremias and Ophisops species replace these in the grassland and desert habitats of Asia. African species usually live in rocky, arid areas. Holaspis species are among the few arboreal lacertids, and its two species, Holaspis guentheri and Holaspis laevis, are gliders (although apparently poor ones), using their broad tail and flattened body as an aerofoil.
Description
Lacertids are small to medium-sized lizards. Most species are less than 9cm long, excluding the tail. The largest living species, Gallotia stehlini, reaches 46cm, and some extinct forms were larger still. They are primarily insectivorous. An exception is Meroles anchietae, one of the few wall lizards that regularly eat seeds – an appropriate food for a lizard of the harsh Namib Desert.
Lacertids are remarkably similar in form, with slender bodies and long tails, but have highly varied patterns and colours, even within the same species. Their scales are large on the head, which often also has osteoderms, small and granular on the back, and rectangular on the underside. Most species are sexually dimorphic, with the males and females having different patterns.
At least eight species from the Caucasus are parthenogenetic, and three species give birth to live young, including the viviparous lizard, Zootoca vivipara.
Evolutionary history
Lacertids are suspected to have originated in Europe, due to their earliest fossils being found in the region, alongside those of their sister group, the extinct Eolacertidae. Fossils possibly attributable to lacertids are known from the Paleocene of France and Belgium. The oldest definitive lacertid is known from the early Eocene (Ypresian) in Mutigny, France in the Paris Basin. Lacertids dispersed into Asia by the early Oligocene. The timing of the colonisation of Africa is uncertain, ranging from the Eocene to the Miocene.
Classification
The classification into subfamilies and tribes below follows one presented by Arnold et al., 2007, based on their phylogenetic analysis.
Family Lacertidae
Subfamily Gallotiinae
Genus Gallotia (8 species)
Genus Psammodromus (8 species)
Subfamily Lacertinae
Tribe Eremiadini
Genus Acanthodactylus (45 species)
Genus Adolfus (6 species)
Genus Australolacerta (1 species)
Genus Congolacerta (2 species)
Genus Eremias (42 species)
Genus Gastropholis (4 species)
Genus Heliobolus (6 species)
Genus Holaspis (2 species)
Genus Ichnotropis (6 species)
Genus Latastia (10 species)
Genus Meroles (8 species)
Genus Mesalina (20 species)
Genus Nucras (13 species)
Genus Ophisops (11 species)
Genus Pedioplanis (16 species)
Genus Philochortus (7 species)
Genus Poromera (1 species)
Genus Pseuderemias (7 species)
Genus Tropidosaura (4 species)
Tribe Lacertini
Genus Algyroides (4 species)
Genus Anatololacerta (4 species)
Genus Apathya (2 species)
Genus Archaeolacerta (1 species)
Genus Atlantolacerta (1 species)
Genus Dalmatolacerta (1 species)
Genus Darevskia (35 species)
Genus Dinarolacerta (2 species)
Genus Hellenolacerta (1 species)
Genus Iberolacerta (8 species)
Genus Iranolacerta (2 species)
Genus Lacerta (10 species)
Genus Omanosaura (2 species)
Genus Parvilacerta (2 species)
Genus Phoenicolacerta (4 species)
Genus Podarcis (26 species)
Genus Scelarcis (1 species)
Genus Takydromus (24 species)
Genus Teira (1 species)
Genus Timon (6 species)
Genus Vhembelacerta (1 species)
Genus Zootoca (2 species)
The latest extensive phylogenetic lacertid tree was made by Baeckens et al. in 2015.
Extinct genera
†Succinilacerta Baltic amber, Eocene
†Plesiolacerta Europe, Eocene-Oligocene
†Dracaenosaurus France, Oligocene
†Maioricalacerta Mallorca, Pliocene
†Quercycerta France, Eocene
†Janosikia Germany, Miocene
†Escampcerta France, Eocene
†Mediolacerta France, Germany, Oligocene
†Pseudeumeces France, Germany, Spain, Oligocene-Miocene
†Amblyolacerta France, Czech Republic, Miocene
†Ligerosaurus France, Miocene
†Miolacerta Germany, Austria, Czech Republic, Oligocene-Miocene
†Edlartetia Augé and Rage 2000 Germany, France Austria, Miocene
†Escampcerta France, Eocene
†Cernaycerta? France, Paleocene (questioned by some authors)
†Dormaalisaurus France, Belgium, Spain, Eocene
| Biology and health sciences | Lizards and other Squamata | Animals |
322882 | https://en.wikipedia.org/wiki/Teiidae | Teiidae | Teiidae is a family of Lacertoidean lizards native to the Americas. Members of this family are generally known as whiptails or racerunners; however, tegus also belong to this family. Teiidae is sister to the Gymnopthalmidae, and both families comprise the Teiioidea. The Teiidae includes several parthenogenic species – a mode of clonal reproduction. Presently, the Teiidae consists of approximately 150 species in eighteen genera.
Morphology and behavior
Teiids can be distinguished from other lizards by the following characteristics: large rectangular scales that form distinct transverse rows ventrally and generally small granular scales dorsally, head scales that are separate from the skull bones, and teeth that are solid at the base and "glued" to the jaw bones. Additionally, all teiids have a forked, snake-like tongue. They all possess well-developed limbs.
Teiids are all terrestrial (few are semi-aquatic) and diurnal, and are primarily carnivorous or insectivorous. Most teiids forage quite actively within their ideal temperature range, quickly skirting between cover objects. Some will include a small amount of plant matter in their diet. They are oviparous, and some species lay very large clutches.
Parthenogenesis
Several species of whiptail lizards are entirely female and no males are known. These all-female species reproduce by obligate parthenogenesis (obligate, because the lizards do not involve males and cannot reproduce sexually). Like all squamate obligate parthenogenetic lineages, parthenogenetic teiids are hybrids. Two or more species rarely hybridize and the offspring are thought to occasionally be capable of reproduction without sperm. The meiotic mechanism for bypassing fertilization is an ongoing area of research.
Primarily known from lab studies of parthenogenetic Aspidoscelis neomexicanus, simulated mating behavior can increase fertility. In this behavior known as pseudocopulation, one female assumes a male-like role and the other a female-like role. Individuals can switch roles throughout their life. The claim of pseudocopulation was initially met with hesitation by some researchers, and the behavior has not been observed in all parthenogenetic varieties. Since at least some all-female lineages exhibit pseudocopulation, these lizards can be considered to reproduce unisexually (in contrast to asexually).
Fossil record
Teiids are known to have briefly occurred in Europe during the Late Eocene based on fragmentary fossil material non-diagnostic to the genus level found in the Quercy Phosphorites Formation of France dating to the MP 17 zone.
Taxonomy
The Teiidae contains approximately 150 species divided into two subfamilies and 18 genera. This assessment includes several recent changes: three resurrected genera, five newly described genera, and the large genus Cnemidophorus split into Aspidoscelis and Cnemidophorus. In some technical literature, the Teiidae are referred to as macroteiids (in opposition to the microteiids, which are members of a sister family Gymnopthalmidae). Parthenogenetic lineages are generally referred to as species, though the concept of a species is meant loosely. Other terms include array, clone, type, or morph.
Subfamily Teiinae:
Ameiva – junglerunners (14 species)
Ameivula – (11 species)
Aspidoscelis – North American whiptail lizards (46 species)
Aurivela – (2 species)
Cnemidophorus – South American whiptail lizards (19 species)
Contomastix – (6 species)
Dicrodon – desert tegus (3 species)
Glaucomastix – (5 species)
Holcosus – (18 species)
Kentropyx – (9 species)
Medopheos – (1 species)
Pholidoscelis – (20 species)
Teius – (3 species)
Subfamily Tupinambinae:
Callopistes – false monitors (4 species)
Crocodilurus – the crocodile tegu (1 species)
Dracaena – caiman lizards (3 species)
Salvator – (3 species)
Tupinambis – tegus (8 species)
| Biology and health sciences | Lizards and other Squamata | Animals |
322886 | https://en.wikipedia.org/wiki/Cordylidae | Cordylidae | Cordylidae is a family of small- to medium-sized lizards that occur in southern and eastern Africa. They are commonly known as girdled lizards, spinytail lizards, or girdle-tail lizards.
Cordylidae is closely related to the family Gerrhosauridae, occurring in Africa and Madagascar. These two scientific families of lizards, known as Cordyliformes or Cordyloidea, are sometimes combined into a larger concept of Cordylidae. Recent molecular analyses confirm the clade made up of Cordylidae and Gerrhosauridae (Cordyloidea) and place it in a larger clade including Xantusiidae (Cordylomorpha Vidal & Hedges, 2009).
Description and behavior
Girdled lizards are diurnal and insectivorous. They are terrestrial, mostly inhabiting crevices in rocky terrain, although at least one species digs burrows and another lives under exfoliating bark on trees. They have flattened heads and bodies, and are distinguished by a heavy armour of osteoderms and large, rectangular, scales, arranged in regular rows around the body and tail. Many species have rings of spines on the tail, that aid in wedging the animal into sheltering crevices, and also in dissuading predators.
Most species have four limbs, but those in the genus Chamaesaura are almost entirely limbless, with only tiny spikes in place of the hind limbs. The family includes both egg-laying and ovoviviparous species.
Genera
| Biology and health sciences | Lizards and other Squamata | Animals |
323221 | https://en.wikipedia.org/wiki/Sun%20dog | Sun dog | A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in atmospheric science, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° halo.
The sun dog is a member of the family of halos caused by the refraction of sunlight by ice crystals in the atmosphere. Sun dogs typically appear as a pair of subtly colored patches of light, around 22° to the left and right of the Sun, and at the same altitude above the horizon as the Sun. They can be seen anywhere in the world during any season, but are not always obvious or bright. Sun dogs are best seen and most conspicuous when the Sun is near the horizon.
Formation and characteristics
Sun dogs are commonly caused by the refraction and scattering of light from horizontally oriented plate-shaped hexagonal ice crystals either suspended in high and cold cirrus or cirrostratus clouds, or drifting in freezing moist air at low levels as diamond dust. The crystals act as prisms, bending the light rays passing through them with a minimum deflection of 22°. As the crystals gently float downwards with their large hexagonal faces almost horizontal, sunlight is refracted horizontally, and sun dogs are seen to the left and right of the Sun. Larger plates wobble more, and thus produce taller sun dogs.
Sun dogs are red-colored at the side nearest the Sun; farther out the colors grade through oranges to blue. The colors overlap considerably and are muted, never pure or saturated. The colors of the sun dog finally merge into the white of the parhelic circle (if the latter is visible).
The same plate-shaped ice crystals that cause sun dogs are also responsible for the colorful circumzenithal arc, meaning that these two types of halo tend to co-occur. The latter is often missed by viewers, since it is located more or less directly overhead. Another halo variety often seen together with sun dogs is the 22° halo, which forms a ring at roughly the same angular distance from the sun as the sun dogs, thus appearing to interconnect them. As the Sun rises higher, the rays passing through the plate crystals are increasingly skewed from the horizontal plane, causing their angle of deviation to increase and the sun dogs to move farther from the 22° halo, while staying at the same elevation.
It is possible to predict the forms of sun dogs as would be seen on other planets and moons. Mars might have sun dogs formed by both water-ice and CO2-ice. On the giant planets—Jupiter, Saturn, Uranus, and Neptune—other crystals form clouds of ammonia, methane, and other substances that can produce halos with four or more sun dogs.
A related phenomenon, the Crown flash is also known as a "leaping Sundog".
Terminology
A somewhat common misconception among the general public is to refer to any member of the ice halo family as a "sun dog" (especially the 22° halo, being one of the most common varieties). However, sun dogs represent just one of many different types of halos. For referring to the atmospheric phenomenon in general, the term (ice crystal) halo(s) is more appropriate.
Etymology
The exact etymology of sun dog largely remains a mystery. The Oxford English Dictionary says it is "of obscure origin".
In Abram Palmer's 1882 book Folk-etymology: A Dictionary of Verbal Corruptions Or Words Perverted in Form Or Meaning, by False Derivation Or Mistaken Analogy, sun-dogs are defined:
(Dog in English as a verb can mean "hunt, track, or follow", so Dog the true [sun] has meant track the true [sun] since the 1510s.)
Alternatively, Jonas Persson suggested that out of Norse mythology and archaic names — (sun dog), (sun dog), (sun wolf) — in the Scandinavian languages, constellations of two wolves hunting the Sun and the Moon, one after and one before, may be a possible origin for the term.
Parhelion (plural parhelia) comes from (, 'beside the sun'; from (, 'beside') and (, 'sun')).
In the Anglo-Cornish dialect of Cornwall, United Kingdom, sun dogs are known as weather dogs (described as "a short segment of a rainbow seen on the horizon, foreshowing foul weather"). It is also known as a lagas in the sky which comes from the Cornish language term for the sun dog meaning 'weather's eye' (, 'eye' and , 'weather/wind'). This is in turn related to the Anglo-Cornish term cock's eye for a halo round the Sun or the Moon, also a portent of bad weather.
History
Antiquity
Aristotle (Meteorology III.2, 372a14) notes that "two mock suns rose with the sun and followed it all through the day until sunset." He says that "mock suns" are always to the side, never above or below, most commonly at sunrise or sunset, more rarely in the middle of the day.
The poet Aratus (Phaenomena, lines 880–891) mentions parhelia as part of his catalogue of Weather Signs; according to him, they can indicate rain, wind, or an approaching storm.
Artemidorus in his Oneirocritica ('On the Interpretation of Dreams') included the mock suns amongst a list of celestial deities.
A passage in Cicero's On the Republic (54–51 BC) is one of many Roman authors who refer to sun dogs and similar phenomena:
Seneca makes an incidental reference to sun dogs in the first book of his Naturales Quaestiones.
The 2nd-century Roman writer and philosopher Apuleius in his Apologia says "What is the cause of the prismatic colours of the rainbow, or of the appearance in heaven of two rival images of the sun, with sundry other phenomena treated in a monumental volume by Archimedes of Syracuse."
Fulcher of Chartres, writing in Jerusalem in the early twelfth century, notes in his Historia Hierosolymitana (1127) that on February 23, 1106
Wars of the Roses
The prelude to the Battle of Mortimer's Cross in Herefordshire, England in 1461 is supposed to have involved the appearance of a halo display with three "suns". The Yorkist commander, later Edward IV of England, convinced his initially frightened troops that it represented the three sons of the Duke of York, and Edward's troops won a decisive victory. The event was dramatized by William Shakespeare in King Henry VI, Part 3, and by Sharon Kay Penman in The Sunne In Splendour.
Early modern era
Another early clear description of sun dogs is by Jacob Hutter, who wrote in his Brotherly Faithfulness: Epistles from a Time of Persecution:
The observation most likely occurred in Auspitz (Hustopeče), Moravia on 31 October 1533. The original was written in German and is from a letter originally sent in November 1533 from Auspitz in Moravia to the Adige Valley in South Tyrol. The Kuntz Maurer and Michel Schuster mentioned in the letter left Hutter on the Thursday after the feast day of Simon and Jude, which is 28 October. The Thursday after was 30 October. It is likely that the "two rainbows with their backs turned toward each other, almost touching" involved two further halo phenomena, possibly a circumzenithal arc (prone to co-occur with sun dogs) together with a partial 46° halo or supralateral arc.
While mostly known and often quoted for being the oldest color depiction of the city of Stockholm, Vädersolstavlan (Swedish; "The Sundog Painting", literally "The Weather Sun Painting") is arguably also one of the oldest known depictions of a halo display, including a pair of sun dogs. For two hours in the morning of 20 April 1535, the skies over the city were filled with white circles and arcs crossing the sky, while additional suns (i.e., sun dogs) appeared around the sun. The phenomenon quickly resulted in rumours of an omen of God's forthcoming revenge on King Gustav Vasa (1496–1560) for having introduced Protestantism during the 1520s and for being heavy-handed with his enemies allied with the Danish king.
Hoping to end speculations, the Chancellor Olaus Petri (1493–1552), a Lutheran scholar, ordered a painting to be produced documenting the event. When confronted with the painting, the King, however, interpreted it as a conspiracy — the real sun, of course, being himself —threatened by competing fake suns, one being Olaus Petri and the other the clergyman and scholar Laurentius Andreae (1470–1552). Both were thus accused of treachery, but eventually escaped capital punishment. The original painting is lost, but a copy from the 1630s survives and can still be seen in the church Storkyrkan in central Stockholm.
A series of complex parhelia displays in Rome in 1629, and again in 1630, were described by Christoph Scheiner in his book Parhelia, one of the earliest works on the subject. It had a profound effect, causing René Descartes to interrupt his metaphysical studies and led to his work of natural philosophy called The World.
On 20 February 1661 the people of Gdańsk witnessed a complex halo display, described by Georg Fehlau in a pamphlet, the Sevenfold Sun Miracle, and again the following year by Johannes Hevelius in his book, Mercurius in Sole visus Gedani.
On 18 June 1790 Johann Tobias Lowitz, in Saint Petersburg, Russia, observed a complex display of haloes and parhelia which included his Lowitz arcs.
Late modern era to current day
In 1843, winter in the British Colony of Newfoundland was referred to as the 'Winter of Three Suns' and was unusually cold with 15 days of temperatures between 3–10 degrees below zero.
"Part of the time we marched in the teeth of a biting storm of snow, and at every hour of the day the sun could be discerned sulking behind soft grey mists in company with rivals, known in the language of the plains as 'Sun-dogs', whose parahelic splendors warned the traveler of the approach of the ever-to-be-dreaded 'blizzard'."
On 14 February 2020, the people of Inner Mongolia Autonomous Region witnessed a different complex halo display called the Five-fold sun miracle, in which all five sun halos were linked to each other by rays, forming a circle among them.
| Physical sciences | Atmospheric optics | Earth science |
14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Napa cabbage | Napa cabbage (Brassica rapa subsp. pekinensis, or Brassica rapa Pekinensis Group) is a type of Chinese cabbage originating near the Beijing region of China that is widely used in East Asian cuisine. Since the 20th century, it has also become a widespread crop in Europe, the Americas, and Australia. In much of the world, it is referred to as "Chinese cabbage".
Names
The word "napa" in the name napa cabbage comes from colloquial and regional Japanese, where nappa () refers to the leaves of any vegetable, especially when used as food. The Japanese name for this specific variety of cabbage is hakusai (), a Sino-Japanese reading of the Chinese name báicài (), literally "white vegetable". The Korean name for napa cabbage, baechu (), is a nativized word from the Sino-Korean reading, , of the same Chinese character sets. Today in Mandarin Chinese, napa cabbage is known as dàbáicài (), literally "big white vegetable", as opposed to the "small white vegetable" that is known in English as bok choy.
Outside of Asia, this vegetable is also referred to as Chinese cabbage or sometimes celery cabbage. It is also known as siu choy (Cantonese ), wombok in Australia and wong bok or won bok in New Zealand, all corruptions of wong ngaa baak (Cantonese ). In the United Kingdom this vegetable is known as Chinese leaf or winter cabbage, and in the Philippines as petsay (from Hokkien, ) or pechay baguio. Another name used in English is petsai or pe-tsai. In Ukraine it is called (), and in Poland - , literally "Beijing cabbage". In Sweden it is known as (salad cabbage) or sometimes (china cabbage).
Origin
The first records of napa cabbage cultivation date back to the 15th century in the Yangtze River region in China. From China it later spread to Korea and Japan. Beginning in the 19th century with the Chinese diaspora, it was distributed to the rest of Asia, Europe, America as well as Australia. During the 19th century napa cabbage was first introduced to America from Europe and the supply of seed materials from Europe continued until World War I. After the blockade of the European seed supply, US government research institutes and the seed industry developed new seed stocks for vegetable crops. Oregon and California were the cabbage seed production areas during that time. Today it is cultivated and eaten throughout the world.
Napa cabbage might have originated from natural hybridization between turnip (Brassica rapa subsp. rapa) and pak-choi (Brassica rapa subsp. chinensis). Artificial crosses between these two subspecies, as well as molecular data, strengthen this suggestion.
Description
The leaves, which are the harvested organ, lay side by side densely, are lime green coloured with white leaf veins and have a smooth surface. The vegetable has an oval form and weighs . The leaves are organized in basal rosettes. The flowers are yellow and have a typical Brassicaceae cross-linked arrangement, hence the name Crucifereae, which means “cross-bearing”. Because the plant is harvested in an earlier stage than flowering, normally the flowers are not visible on the field.
It develops similar to other head-forming leaf vegetables, for example cabbage lettuce. The chronological stages on the BBCH-scale are germination, leaf formation, vegetative growth (head-forming), appearance of the sprout that bears the flowers, flowering, fruit development, seed ripening and senescence.
Napa cabbage is an annual plant that reaches the generative period in the first year. It must be consumed in its vegetative period, so there is a challenge in cultivation not to reach the stadium of flowering. The stadium of flowering can be initiated by cold temperatures or the length of the day. Napa cabbage reproduces mainly by allogamy. Napa cabbage produces more leaves, bigger leaves and a higher biomass under long day conditions than under short day conditions.
Uses
Culinary
Napa cabbage is a cool season annual vegetable which grows best when the days are short and mild. The plant grows to an oblong shaped head consisting of tightly arranged crinkly, thick, light-green leaves with prominent white veins. Innermost layer leaves feature light yellow color.
Napa cabbage belongs to the family Brassicaceae, commonly called the mustard or cabbage family. As a cruciferous plant it is closely related to species of Brassica like broccoli, bok choy and cauliflower.
Napa cabbage is widely used in China, Japan, and Korea. Napa cabbage is used as a sign of prosperity in China, and often appears as a symbol in glass and porcelain figures. The Jadeite Cabbage sculpture of Taiwan's National Palace Museum is a carving of a napa cabbage variety. It is also found in North American and Australian cities after Asian immigrants settled in the regions.
Fermented Napa cabbage (suan cai/sauerkraut) is a traditional food in Northeast China.
In Korean cuisine, napa cabbage is the main ingredient of baechu-kimchi, the most common type of kimchi, but is also eaten raw as a wrap for pork or oysters, dipped in gochujang. The outer, tougher leaves are used in soups. It can be used in stir-fry with other ingredients, such as tofu, mushroom and zucchini. It is also eaten with hot pot meals. Napa cabbage is particularly popular in South Korea's northern Gangwon Province. In European, American and Australian kitchens, it is more common to eat it cooked or raw as salad.
The vegetable is rich in vitamin C (26 mg/100g) and has a fair amount of calcium (40 mg/100g). It tastes mildly aromatic.
Cultivation
Napa cabbage can be cultivated in many different areas of the world, the main area of diversification represents Asia.
Soil requirements
Napa cabbage requires deeply loosened medium heavy soil. There must not be any compaction due to plowing. The crop achieves particularly high yields on sandy loam. Extremely sandy or claylike soils are not suitable.
The crop prefers a pH range from 6.0 to 6.2, a high organic matter content and good moisture holding capacity of the soil. Lower pH or droughty soil can lead to calcium or magnesium deficiency and internal quality defects.
Climate requirements
Napa cabbage needs much water during the whole growth period. Often an irrigation system is needed, especially for August and September. The required amount of water depends on the stage of crop growth, weather conditions, and soil type. The most critical stage after establishment is when the head is forming. Inadequate water at this time will result in reduced uptake of calcium. This condition causes dead leaf tips within the head which makes it unmarketable. During head formation, of water per week is needed to maintain sustained growth rates.
Temperature requirements are low. Temperatures below are tolerated for short time periods; persistent frosts below are not endured. Too low temperature can induce premature bolting. The plants perform best under temperatures between , but depending on the cultivar.
Seedbed requirements & sowing
Napa cabbage has very small seeds with a thousand kernel weight of about 2.5 to 2.8 g. For professional cultivation it is recommended to use disinfected seeds to prevent onset diseases. With the single-grain sowing technique, about 400 to 500 g of seeds per hectare is required; with the normal sowing technique, about 1 kg per hectare. If the normal sowing technique is used, the seedlings must be thinned out after two to four weeks. The seeds should be deposited deep, with a row width of and distance between the seeds.
The seedlings can be grown in the greenhouse and then transplanted into the field after two to three weeks. Earlier harvest can be achieved with this method. Seventy thousand to 80,000 seedlings per hectare are required. The transplanting method is normally used for the spring crop and the seeding technique for the fall crop.
Fertilization, field management
The nutrient removal of napa cabbage is high:
150–200 kg N per hectare
80–120 kg P2O5 per hectare
180–250 kg K2O per hectare
110–150 kg Ca per hectare
20–40 kg Mg per hectare
Fertilizer recommendations are in the range of the nutrient removal. Organic fertilizer must be applied before sowing due to the short cultivation time of napa cabbage and the slow availability of organic fertilizers. Synthetic N fertilizer should be applied in three equal doses. The last application must happen before two thirds of the cultivation time is over to avoid quality losses during storage.
Weeds should be controlled mechanically or chemically.
Harvest, storage and yield
Napa cabbage can be harvested 8–12 weeks after sowing. The harvest work is mostly done by hand. The plant is cut above the ground. It is usual to harvest several times per field to achieve consistent cabbage quality. Cabbages will keep in good condition for three to four months in cool stores at and 85 to 90 percent relative humidity. Napa cabbage achieves a yield of 4 to 5 kg/m2.
Breeding
Brassica rapa species are diploid and have 10 chromosomes. A challenge for breeding of napa cabbage is the variable self-incompatibility. The self-incompatibility activity was reported to change by temperature and humidity. In vitro pollination with 98% relative humidity proved to be the most reliable as compared to greenhouse pollination.
A lot of work has already been done on breeding of napa cabbage. In the 21st century, 880 varieties of Napa cabbage were registered by the Korea Seed and Variety Service.
Breeding of napa cabbage was started by the Korean government research station of horticultural demonstration in 1906 to overcome starvation. As napa cabbage and radish are the main vegetables for kimchi, research focused on increasing yield. The most important person for this process was Dr. Woo Jang-choon who bred hybrid cultivars with self-incompatibility and contributed to commercial breeding by developing valuable materials and educating students. The main purpose of the hybrid cultivar was high yield and year-round production of napa cabbage after 1960.
To enable year round production of napa cabbage, it has to be modified to tolerate high and low temperatures. Normally, sowing in the late summer and harvesting in late autumn can produce high quality vegetables. As an example, a summer cultivar called “Nae-Seo-beak-ro” was developed 1973 by a commercial seed company. It tolerates high temperatures, could endure high humidity in the monsoon, and showed resistance to viral disease, soft rot and downy mildew. The low temperature in early spring reduces the quality of the vegetable and it cannot be used for kimchi. In the 1970s the developing of winter cultivars started. The majority of new cultivars could not endure the cold winter conditions and disappeared. The cultivar “Dong-Pung” (meaning “east wind”) was developed in 1992 and showed a high resistance to cold temperature. It is mostly used in Korea, where fresh napa cabbage is nowadays cultivated year round.
In the 1970s, one seed company developed the rose-shape heading variety while other seed companies focused on the semi-folded heading type. As a result of continuous breeding in the commercial seed companies and the government research stations, farmers could now select what they wanted from among various high quality hybrids of Chinese cabbage. The fall season cultivar 'Yuki', with white ribs and tight leaf folding, gained the RHS's Award of Garden Merit (AGM) in 2003.
In 1988, the first cultivar with yellow inner leaf was introduced. This trait has prevailed until today.
A very important breeding aim is to get varieties with resistance to pests and diseases. There exist varieties with resistance to turnip mosaic virus but as mentioned above, there exist numerous other diseases. There have been attempts to breed varieties with clubroot resistance or powdery mildew resistance but the varieties failed due to bad leaf texture traits or broken resistances.
Pests and diseases
Fungal diseases
Alternaria diseases are caused by the organisms Alternaria brassicae, Alternaria brassicicola and Alternaria japonica. Their English names are black spot (not to be confused with midrib 'pepper spots' which are physiological in origin and often result from improper storage), pod spot, gray leaf spot, dark leaf spot or Alternaria blight. The symptoms can be seen on all aboveground plant parts as dark spots. The infected plants are shrivelled and smaller than normal. Alternaria diseases infect almost all brassica plants, the most important hosts are oilseed brassicas.
The fungus is a facultative parasite, what means that it can survive on living hosts as well as on dead plant tissue. Infected plant debris is in most circumstances the primary source of inoculum. The spores can be dispersed by wind to host plants in the field or to neighbouring brassica crops. This is why cross infections often occur in areas where different brassica crops are cultivated in close proximity. The disease spreads especially fast when the weather is wet and the plants have reached maturity.
Alternaria brassicae is well adapted to temperate regions while Alternaria brassicicola occurs primarily in warmer parts of the world. Temperature requirement for Alternaria japonica is intermediate.
There exist some wild accessions of Brassica rapa subsp. pekinensis with resistance to Alternaria brassicae but not on commercial cultivars. These resistances should be included to breeding programmes. Alternaria epidemics are best avoided by management practices like at least 3 years non-host crops between brassica crops, incorporation of plant debris into the soil to accelerate decomposition and usage of disease-free seeds.
Anhracnose is a brassica disease caused by Colletotrichum higginsianum that is especially damaging on napa cabbage, pak choi, turnip, rutabaga and tender green mustard. The symptoms are dry pale gray to straw spots or lesions on the leaves. The recommended management practices are the same as for Alternaria diseases.
Black root is a disease that infects mainly radish, but it also occurs on many other brassica vegetables inclusively napa cabbage. It caused by the fungus Aphanomyces raphani. The pathogen can persist for long times in the soil, therefore crop rotations are an essential management tool.
White leaf spot is found primarily in temperate climate regions and is important on vegetable brassicas and oilseed rape. The causal organism is Mycosphaerella capsellae. The symptoms are white spots on leaves, stems and pods and can thus easily be confused with those of downy mildew. The disease spreads especially fast with rain or moisture and temperature is between .
Yellows, also called Fusarium wilt, is another Brassica disease that infects oilseed rape, cabbage, mustards, Napa cabbage and other vegetable brassicas. It is only a problem in regions with warm growing seasons where soil temperatures are in the range of 18 to 32 °C. The causal organism is Fusarium oxysporum f. sp. conlutinans. Napa cabbage is relatively tolerant to the disease; mostly the only external symptoms are yellowing of lower, older leaves. The disease is soil borne and can survive for many years in the absence of a host. Most cruciferous weeds can serve as alternate hosts.
Damping-Off is a disease in temperate areas caused by soil inhabiting oomycetes like Phytophthora cactorum and Pythium spp. The disease concerns seedlings, which often collapse and die.
Other diseases that infect napa cabbage:
black leg or phoma stem cancer: Leptosphaeria maculans
clubroot: Plasmodiophora brassicae
Downy mildew: Hyaloperonospora brassicae
Powdery mildew: Erysiphe cruciferarum
Rhizoctonia solani
Sclerotinia sclerotiorum
Bacterial diseases
Bacterial soft rot is considered one of the most important diseases of vegetable brassicas. The disease is particularly damaging in warm humid climate. The causal organisms are Erwinia carotovora var. carotovora and Pseudomonas marginalis pv. marginalis. The rot symptoms can occur in the field, on produce transit or in storage.
Bacteria survive mainly on plant residues in the soil. They are spread by insects and by cultural practices, such as irrigation water and farm machinery. The disease is tolerant to low temperatures; it can spread in storages close to 0 °C, by direct contact and by dripping onto the plants below.
Bacterial soft rot is more severe on crops which have been fertilized too heavily with nitrogen, had late nitrogen applications, or are allowed to become over-mature before harvesting.
Black rot, the most important disease of vegetable brassicas, is caused by Xanthomonas campestris pv. campestris.
Virus diseases
source:
Cucumber mosaic virus
Radish mosaic virus
Ribgrass mosaic virus
Turnip crinkle virus
Cardamine chlorotic fleck virus
Turnip mosaic virus
Turnip yellow mosaic virus
Insect pests
source:
large white butterfly (Pieris brassicae)
cabbage root fly (Delia radicum)
cabbage seed weevil (Ceutorhynchus assimilis)
cabbage looper
cabbage beetle (Colaphellus bowringi)
diamondback moth
small white butterfly (Pieris rapae)
aphids
cucumber beetles
stink bugs
Vegetable weevils
Mole crickets
cutworms
Other pests and diseases
Aster yellows is a disease caused by a phytoplasm.
Nematodes are disease agents that are often overlooked but they can cause considerable yield losses. The adult nematodes have limited active movement but their eggs contained within cysts (dead females) are readily spread with soil, water, equipment or seedlings.
Parasitic nematode species that cause damage on napa cabbage:
Heterodera schachtii
Meloidogyne hapla
Nacobbus batatiformis
Rotylenchulus reniformis
| Biology and health sciences | Leafy vegetables | Plants |
10802532 | https://en.wikipedia.org/wiki/Palaeotheriidae | Palaeotheriidae | Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia, from the mid-Eocene to the early Oligocene. They are classified in Equoidea, along with the living family Equidae (which includes zebras, horses and asses).
Morphology
Palaeotheres ranged widely in size, from small species like Palaeotherium lautricense, which is estimated to have only weighed to large species like Palaeotherium magnum, which are comparable in size to living equines, with body masses over . Their teeth are brachydont (low crowned). According to Danilo et al. 2013., paleotheriids are distinguished from other equoids by one unambiguous synapomorphy "the nasal notch opening distally to the canine, above the postcanine diastema" and two unambiguous character state changes "an average metaconule on [the fourth premolar]" and "an oblique metastyle on [the first and second molars]".
Taxonomy
Palaeotheriidae is generally divided into the subfamilies Palaeotheriinae and ‘Pachynolophinae'. The two groups are distinguished by the morphology of their upper molars, with mesostyles being at least moderately developed in those Palaeotheriinae, but generally weakly developed or absent in those of 'Pachylophinae'. 'Pachylophinae' is controversial with regards to its definition and phylogenetic placement. 'Pachylophinae', along with the genus Pachynolophus has been argued to be a paraphyletic group that is ancestral to Palaeotheriinae.
Ecology
Early members of the family are suggested to have been frugivores, with later, larger members suggested to be browsers.
Extinction
Evidence suggests that palaeotheriids went extinct in Eurasia during the Early Oligocene, approximately 33 Ma, as part of a faunal turnover event known as the Grande Coupure. The Eocene-Oligocene transition marked a significant global cooling event caused by the onset of Antarctic glaciation. This resulted in drier and more open habitats dominating the early Oligocene, and the loss of the dense forests that characterised the Eocene epoch. This environmental change, coupled with the arrival of new and better-adapted mammalian groups from Asia, triggered a decline in endemic European mammal groups such as Palaeotheriidae and Anoplotheriidae. In the Hampshire Basin of southern England the last record of Palaeotheriidae is from the Lower Hamstead Mbr. of the Bouldnor Formation, dating to approximately 33.6 Ma.
Fossil distribution
Creechbarrow Hill Site, Dorset, England
Geiseltal, Mittelkohle, Zone III, Saxony-Anhalt, Germany
Egerkingen, Alpha & Beta fissures, Baselland, Switzerland
La Debruge, Provence-Alpes-Côte d'Azur Region, France
The Caucasus Mountains in Georgia
| Biology and health sciences | Perissodactyla | Animals |
10802893 | https://en.wikipedia.org/wiki/Protoceratidae | Protoceratidae | Protoceratidae is an extinct family of herbivorous North American artiodactyls (even-toed ungulates) that lived during the Eocene through Pliocene. While early members of the group were hornless, in later members males developed elaborate cranial ornamentation. They are variously allied with Ruminantia or Tylopoda.
Classification
Protoceratidae was erected by Othniel Charles Marsh in 1891, with the type genus Protoceras and assigned to the Artiodactyla. It was later assigned to Pecora, and more recently to Ruminantia or Tylopoda. However, recently a relationship to chevrotains in the infraorder Tragulina has been proposed.
Morphology
When alive, protoceratids would have resembled deer, though they were not directly related. Protoceratids ranged from 1 to 2 m in length, from about the size of a roe deer to an elk. Unlike many modern ungulates, they lacked cannon bones in their legs. Their dentition was similar to that of modern deer and cattle, suggesting they fed on tough grasses and similar foods, with a complex stomach similar to that of camels. At least some forms are believed to have lived in herds.
The most dramatic feature of the protoceratids, however, were the horns of the males. In addition to having horns in the more usual place, protoceratids had additional, rostral horns above their noses. These horns were either paired, as in Syndyoceras, or fused at the base, and branching into two near the tip, as in Synthetoceras. In life, the horns were probably covered with skin, much like the ossicones of a giraffe. The females were either hornless, or had far smaller horns than the males. Horns were therefore probably used in sexual display or competition for mates. In later forms, the horns were large enough to have been used in sparring between males, much as with the antlers of some modern deer.
Genera by epoch
Eocene
Heteromeryx
Leptoreodon
Leptotragulus
Poabromylus
Pseudoprotoceras
Toromeryx
Trigenicus
Oligocene
Protoceras
Miocene
Paratoceras
Lambdoceras
Prosynthetoceras
Synthetoceras
Syndyoceras
Pliocene
Kyptoceras
| Biology and health sciences | Other artiodactyla | Animals |
1519419 | https://en.wikipedia.org/wiki/Arroyo%20%28watercourse%29 | Arroyo (watercourse) | An arroyo ( (from Spanish arroyo (, "brook"))) or wash is a dry watercourse that temporarily or seasonally fills and flows after sufficient rain. Flash floods are common in arroyos following thunderstorms. It's akin to the Catalan rambla, which stems from the Arabic rámla, "dry river".
Similar landforms are referred to as wadi (in North Africa and Western Asia), chapp in the Gobi, laagate in the Kalahari, donga in South Africa, nullah in India, fiumare in Italy, and dry valley in England.
The desert dry wash biome is restricted to the arroyos of the southwestern United States. Arroyos provide a water source to desert animals.
Types and processes
Arroyos can be natural fluvial landforms or constructed flood control channels. The term usually applies to a sloped or mountainous terrain in xeric and desert climates. In addition: in many rural communities arroyos are also the principal transportation routes; and in many urban communities arroyos are also parks and recreational locations, often with linear multi-use bicycle, pedestrian, and equestrian trails. Flash flooding can cause the deep arroyos or deposition of sediment on flooded lands. This can lower the groundwater level of the surrounding area, making it unsuitable for agriculture. However a shallow water table lowered in desert arroyo valleys can reduce saline seeping and alkali deposits in the topsoil, making it suitable for irrigated farming.
Natural
The Doña Ana County Flood Commission in the U.S. state of New Mexico defines an arroyo as "a watercourse that conducts an intermittent or ephemeral flow, providing primary drainage for an area of land of or larger; or a watercourse which would be expected to flow in excess of one hundred cubic feet per second as the result of a 100 year storm event." Research has been conducted in the hydrological modeling relative to arroyos.
Natural arroyos are made through the process known as arroyo-cutting. This occurs in arid regions, such as New Mexico, where heavy rains can lead to enlargement of rivers cutting into surrounding rock creating ravines which are dry under normal weather conditions.
It is argued, however, whether these excessively stormy periods are the sole cause of arroyo-cutting as other factors such as long-term climate changes must also be taken into account. Further, overgrazing by livestock throughout the 20th century and today has removed vast amounts of surface vegetation which decreases ground infiltration of precipitation and increased runoff, increasing speed and energy of high flow rain events. Coupled with groundwater pumping this increases downcutting in arroyos as well. Arroyo cutting which occurred in the 1900s in the southwestern United States caused serious farming issues such as a lowered water table and the destruction of agriculture lands.
Constructed
In agricultural areas in climates needing irrigation, farmers traditionally relied on small constructed arroyos, acequias, zanjas or aqueduct channels and ditches for the distribution of water.
An example of larger constructed arroyos is in Albuquerque, New Mexico. There are several miles of open-air concrete lined drainage channels that drain an area into the main North Diversion Channel, a tributary of the Rio Grande joining upstream of Albuquerque. After the San Juan Project Water Treatment Plant here, the Rio Grande's flow exceeding that needed for the river's silvery minnow habitat is available for municipal water supply diversion. Signs are posted at the constructed arroyos warning to keep out due to danger of flash flooding.
The Arroyo Seco and Los Angeles River are more famous examples in Southern California of former natural arroyo seasonal watercourses that became constructed open drainage system arroyos.
| Physical sciences | Hydrology | Earth science |
1520435 | https://en.wikipedia.org/wiki/Common%20seadragon | Common seadragon | The common seadragon or weedy seadragon (Phyllopteryx taeniolatus) is a marine fish of the order Syngnathiformes, which also includes the similar pipefishes, seahorses, and trumpetfishes among other species. Adult common seadragons are a reddish colour, with yellow and purple striped markings; they have small, leaf-like appendages that resemble kelp or seaweed fronds, providing camouflage, as well as a number of short spines for protection. As with seahorses and the other syngnathids, the seadragon has a similarly tubular snout and a fused, toothless jaw into which it captures small invertebrate prey at lightning speed. Males have narrower bodies and are darker than females. Seadragons have a long dorsal fin along the back and small pectoral fins on either side of the neck, which provide balance. Weedy seadragons can reach in length.
The seadragon is the marine emblem of the Australian state of Victoria.
Range and habitat
The common seadragon is endemic to Australian and insular coastal waters of the eastern Indian Ocean northern Southern Ocean and the southwestern Pacific Ocean. It can generally be found along the entire southern coastline of the Australian continent, including Tasmania and other offshore islands. It can be observed regularly from around Port Stephens, New South Wales to Geraldton, Western Australia, as well as off the coast of South Australia and the Great Australian Bight.
The common seadragon inhabits coastal waters down around to deep. It is associated with rocky reefs, seaweed beds, seagrass meadows and structures colonised by seaweed.
Biology
The seadragons are slow-moving and, like most of their relatives, rely on excellent camouflage—the mimicry of seaweed, in this case—as a defense against predators. They lack the prehensile tail that many seahorses and pipefishes have evolved as anchors, to clasp and steady themselves; seadragons, instead, drift in the water among kelp and seaweed masses, which they blend-into with their leafy-looking appendages.
Individuals are observed either on their own or in pairs, feeding on tiny crustaceans and other zooplankton by sucking prey into their toothless mouths. As with most other syngnathids, seadragon males are the sex that cares for the developing eggs. Females lay around 120 eggs onto the brood patch located on the underside of the male's tail. The eggs are fertilised and carried by the male for around a month before the hatchlings emerge. The young are independent at birth, beginning to eat shortly after. Common seadragons take about 28 months to reach sexual maturity, and may live for up to six years.
Mating in captivity is relatively rare since researchers have yet to understand what biological or environmental factors trigger them to reproduce. The survival rate for young common seadragons is low in the wild, but it is about 60% in captivity.
The Aquarium of the Pacific (in Long Beach, California) and the Tennessee Aquarium (in Chattanooga, Tennessee), in the US, and Melbourne Aquarium in Melbourne, Australia are among the few facilities in the world to have successfully bred common seadragons in captivity, though others occasionally report egg-laying. In March 2012, Georgia Aquarium (in Atlanta) announced a successful breeding event of common seadragons. In July of the same year, Monterey Bay Aquarium, on California's central coast, successfully bred and hatched-out common seadragons, on-exhibit. Most recently, Birch Aquarium (in La Jolla, San Diego, California) successfully bred and hatched common seadragon fry in early 2023.
Aquarium keepers must make adjustments to the water, food, tank setup, and captivity procedures, as many studies have shown that sea dragons are prone to diseases and infections such as scuticociliatosis, myxozoanosis, fungal infections, intestinal coccidiosis, neoplasia, and swim bladder issues, which can result from parasites growing in their bodies due to their captive environment.
Threats
The common seadragon is classified as Least Concern (LC) on the IUCN Red List. While the common seadragon is a desired species in the international aquarium trade, the volume of wild-caught individuals is small and therefore not currently a major threat. Instead, habitat loss and degradation due to human activities and pollution threaten common seadragons most.
The loss of suitable seagrass beds and loss of canopy seaweed from inshore rock reefs, coupled with natural history traits that make them poor dispersers, put the future of seadragon populations at risk. This species is not at present a victim of bycatch or a target of trade in traditional Chinese medicine, two activities which are currently a threat to many related seahorse and pipefish populations.
More recent research suggests that the weedy seadragon may be far more endangered than initially assumed as a result of climate change-induced marine heatwaves on the Great Southern Reef. Edgar et al (2023) documented a population decline of 59% between 2011 and 2021, a period of frequent and extensive marine heatwaves. This would be enough to classify it as Endangered on the IUCN Red List.
Conservation
It is illegal to take or export these species in most of the states within which they occur. A database of seadragon sightings, known as 'Dragon Search' has been established with support from the Marine Life Society of South Australia Inc., ('Dragon Search' arose as the logical progression of a similar project initiated by the MLSSA, which was the first community group or indeed organisation of any type to adopt the common seadragon's close relative, the leafy seadragon, as part of its logo), the Marine and Coastal Community Network (MCCN), the Threatened Species Network (TSN) and the Australian Marine Conservation Society (AMCS), which encourages divers to report sightings. Monitoring of populations may provide indications of local water quality and seadragons could also become an important 'flagship' species for the often-overlooked richness of the unique flora and fauna of Australia's south coast.
Captive breeding programs are in place for the weedy seadragon, headed up by Sea Life Melbourne Aquarium. The dragon has been difficult to breed in captivity, though in 2015, research observing the creatures in the wild and trying to replicate the conditions in captivity had researchers making changes to the light, water temperature and water flow proving to be key.
In December 2015, the Melbourne aquarium hatched eggs and the aquarium's weedy seadragon population significantly increased. The aquarium reported in March 2016 that 45 fry were still going strong, a 95% survival rate.
Related species
The common seadragon is in the subfamily Syngnathinae, which contains all pipefish. It is most closely related to the other member of its genus, the ruby seadragon (Phyllopteryx dewysea), and also the leafy seadragon (Phycodurus eques). Haliichthys taeniophorus, sometimes referred to as the "ribboned seadragon" is not closely related (it does not form a true monophyletic clade with weedy and leafy seadragons).
The common seadragon was previously the only member of its genus until the description of the ruby seadragon in 2015.
Ongoing research
In the November 2006 issue of National Geographic magazine, marine biologist Greg Rouse is reported as investigating the DNA variation of the two seadragon species across their ranges.
| Biology and health sciences | Acanthomorpha | Animals |
1521467 | https://en.wikipedia.org/wiki/Caribbean%20plate | Caribbean plate | The Caribbean plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the northern coast of South America.
Roughly in area, the Caribbean plate borders the North American plate, the South American plate, the Nazca plate and the Cocos plate. These borders are regions of intense seismic activity, including frequent earthquakes, occasional tsunamis, and volcanic eruptions.
Boundary types
The northern boundary with the North American plate is a transform or strike-slip boundary that runs from the border area of Belize, Guatemala (Motagua Fault), and Honduras in Central America, eastward through the Cayman trough along the Swan Islands Transform Fault before joining the southern boundary of the Gonâve microplate. East of the Mid-Cayman Rise this continues as the Walton fault zone and the Enriquillo–Plantain Garden fault zone into eastern Hispaniola. From there it continues into Puerto Rico, and the Virgin Islands. Part of the Puerto Rico Trench, the deepest part of the Atlantic Ocean (roughly ), lies along this border. The Puerto Rico Trench is at a complex transition from the subduction boundary to the south and the transform boundary to the west.
The eastern boundary is a subduction zone, the Lesser Antilles subduction zone, where oceanic crust of the South American plate is being subducted under the Caribbean plate. Subduction forms the volcanic islands of the Lesser Antilles Volcanic Arc from the Virgin Islands in the north to the islands off the coast of Venezuela in the south. This boundary contains seventeen active volcanoes, most notably Soufriere Hills on Montserrat; Mount Pelée on Martinique; La Grande Soufrière on Guadeloupe; Soufrière Saint Vincent on Saint Vincent; and the submarine volcano Kick 'em Jenny which lies about 10 km north of Grenada. Large historical earthquakes in 1839 and 1843 in this region are possibly megathrust earthquakes.
Along the geologically complex southern boundary, the Caribbean plate interacts with the South American plate forming Barbados, Trinidad and Tobago (all on the Caribbean plate), and islands off the coast of Venezuela (including the Leeward Antilles) and Colombia. This boundary is in part the result of transform faulting, along with thrust faulting and some subduction. The rich Venezuelan petroleum fields possibly result from this complex plate interaction. The Caribbean plate is moving eastward about per year in relation to the South American plate. In Venezuela, much of the movement between the Caribbean plate and the South American plate occurs along the faults of Boconó, El Pilar, and San Sebastián.
The western portion of the plate is occupied by Central America. The Cocos plate in the Pacific Ocean is subducted beneath the Caribbean plate, just off the western coast of Central America. This subduction forms the volcanoes of Guatemala, El Salvador, Nicaragua, and Costa Rica, also known as the Central America Volcanic Arc.
Origin
The usual theory of the origin of the Caribbean plate was confronted by a contrasting theory in 2002.
The mainstream theory holds that it is the Caribbean large igneous province (CLIP) which formed in the Pacific Ocean tens of millions of years ago, perhaps originating at the Galápagos hotspot. As the Atlantic Ocean widened, North America and South America were pushed westward, separated for a time by oceanic crust. The Pacific Ocean floor subducted under this oceanic crust between the continents. The CLIP drifted into the same area, but as it was less dense and thicker than the surrounding oceanic crust, it did not subduct, but rather overrode the ocean floor, continuing to move eastward relative to North America and South America. With the formation of the Isthmus of Panama 3 million years ago, it ultimately lost its connection to the Pacific.
The more recent theory asserts that the Caribbean plate came into being from an Atlantic hotspot which no longer exists. This theory points to evidence of the absolute motion of the Caribbean plate which indicates that it moves westward, not east, and that its apparent eastward motion is only relative to the motions of the North American plate and the South American plate.
First American land bridge
The Caribbean plate began its eastward migration (Ma) during the Late Cretaceous. This migration eventually resulted in a volcanic arc stretching from northwestern South America to the Yucatán Peninsula, today represented by the Aves Islands and the Lesser and Greater Antilles. This arc was the subject of constant tectonism and sea-level fluctuation, but lasted until the mid-Eocene and intermittently formed a land bridge along the eastern and northern boundaries of the Caribbean plate. What would eventually become present-day Central America, part of the western plate boundary, was still isolated in the Pacific.
, during the Late Paleocene, a local sea-level low-stand assisted by the continental uplift of the western margin of South America, resulted in a fully operative land bridge over which several groups of mammals apparently took part in an interchange. For example, specimens have been assigned to xenarthra, didelphidae, and phorusrhacidae from Eocene North America and Europe (although these have been criticized), and Peradectes from Paleocene South America.
Great American Interchange
The Great American Interchange in which land and freshwater fauna migrated between North America and South America via the uplifted western margin of the Caribbean plate (Central America) was a later event, which peaked dramatically around 2.6 million years (Ma) ago during the Piacenzian age.
| Physical sciences | Tectonic plates | Earth science |
1522271 | https://en.wikipedia.org/wiki/Epsilon%20Canis%20Majoris | Epsilon Canis Majoris | Epsilon Canis Majoris is a binary star system and the second-brightest star in the constellation of Canis Major. Its name is a Bayer designation that is Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is the 22nd-brightest star in the night sky with an apparent magnitude of 1.50. About 4.7 million years ago, it was the brightest star in the night sky, with an apparent magnitude of −3.99. Based upon parallax measurements obtained during the Hipparcos mission, it is about 405 light-years distant.
The two components are designated ε Canis Majoris A, officially named Adhara – the traditional name of the system, and B.
Nomenclature
ε Canis Majoris (Latinised to Epsilon Canis Majoris) is the binary system's Bayer designation. The designations of the two components as ε Canis Majoris A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
ε Canis Majoris bore the traditional name Adhara (sometimes spelled Adara, Adard, Udara or Udra), derived from the Arabic word عذارى 'aðāra', "virgins". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire star systems. It approved the name Adhara for the star ε Canis Majoris A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.
In the 17th-century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Adzari (أول العذاري awwal al-adhara), which was translated into Latin as Prima Virginum, meaning First of the Virgins. Along with δ Canis Majoris (Wezen), η Canis Majoris (Aludra) and ο2 Canis Majoris (Thanih al Adzari), these stars were Al ʽAdhārā (العذاري), 'the Virgins'.
In Chinese, (), meaning Bow and Arrow, refers to an asterism consisting of ε Canis Majoris, δ Canis Majoris, η Canis Majoris, κ Canis Majoris, ο Puppis, π Puppis, χ Puppis, c Puppis and k Puppis. Consequently, ε Canis Majoris itself is known as (, ).
Physical properties
ε Canis Majoris is a binary star. The primary, ε Canis Majoris A, has an apparent magnitude of +1.5 and belongs to the spectral classification B2. Its color is blue or blueish-white, due to the surface temperature of . It emits a total radiation equal to 38,700 times that of the Sun. This star is the brightest source of extreme ultraviolet in the night sky. It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud. Its rotation period is estimated to be about 5 days.
The exact evolutionary status of is uncertain. Spectroscopically it has been given the class B2 II, with the luminosity class of II indicating that is a bright giant, more luminous than a typical giant (luminosity class III). However, it appear less luminous than the expected for this luminosity class, and is more likely of class B2 III-II. Two studies suggest is still in the late main sequence (TAMS), rather than being a giant. One of these even suggested it could be the final product of a stellar merger.
The +7.5-magnitude (the absolute magnitude amounts to +1.9) companion star, ε Canis Majoris B, is away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the primary is approximately 250 times brighter than its companion.
A few million years ago, ε Canis Majoris was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4.4 million years ago, Adhara was light-years from the Sun, and was the brightest star in the sky with a magnitude of . The values adoptedNo other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.
In culture
USS Adhara (AK-71) was a U.S. Navy Crater-class cargo ship named after the star.
ε Canis Majoris appears on the national flag of Brazil, symbolising the state of Tocantins.
| Physical sciences | Notable stars | Astronomy |
1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Soil horizon | A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below.
The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed.
In most soil classification systems, horizons are used to define soil types. The German system uses entire horizon sequences for definition. Other systems pick out certain horizons, the "diagnostic horizons", for the definition; examples are the World Reference Base for Soil Resources (WRB), the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are usually indicated with names, e.g. the "cambic horizon" or the "spodic horizon". The WRB lists 40 diagnostic horizons. In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. Some soils do not have a clear development of horizons.
A soil horizon is a result of soil-forming processes (pedogenesis). Layers that have not undergone such processes may be simply called "layers".
Horizon sequence
Many soils have an organic surface layer, which is denominated with a capital letter "O" (letters may differ depending on the system). The mineral soil usually starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is generally called a B horizon. An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is mostly denominated R. Most individual systems defined more horizons and layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil.
Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons almost completely. When examining soils in the field, attention must be paid to the local geomorphology and the historical uses to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons.
Examples of soil profiles
Horizons and layers according to the World Reference Base for Soil Resources
The designations are found in Chapter 10 of the World Reference Base for Soil Resources Manual, 4th edition (2022). The chapter starts with some general definitions:
The fine earth comprises the soil constituents ≤ 2 mm. The whole soil comprises fine earth, coarse fragments, artefacts, cemented parts, and dead plant residues of any size.
A litter layer is a loose layer that contains > 90% (by volume, related to the fine earth plus all dead plant residues) recognizable dead plant tissues (e.g. undecomposed leaves). Dead plant material still connected to living plants (e.g. dead parts of Sphagnum mosses) is not regarded to form part of a litter layer. The soil surface (0 cm) is by convention the surface of the soil after removing, if present, the litter layer and, if present, below a layer of living plants (e.g. living mosses). The mineral soil surface is the upper limit of the uppermost layer consisting of mineral material.
A soil layer is a zone in the soil, approximately parallel to the soil surface, with properties different from layers above and/or below it. If at least one of these properties is the result of soil-forming processes, the layer is called a soil horizon. In the following, the term layer is used to indicate the possibility that soil-forming processes did not occur.
The following layers are distinguished (see Chapter 3.3 of the WRB Manual):
Organic layers consist of organic material: Have ≥ 20% organic carbon, not consisting of artefacts (related to the fine earth plus the dead plant residues of any length and a diameter ≤ 5 mm) and do not form part of a litter layer.
Organotechnic layers consist of organotechnic material: Have ≥ 35% (by volume, related to the whole soil) artefacts containing ≥ 20% organic carbon; and < 20% organic carbon, not consisting of artefacts (related to the fine earth plus the dead plant residues of any length and a diameter ≤ 5 mm).
Mineral layers are all other layers.
The designation consists of a capital letter (master symbol), which in most cases is followed by one or more lowercase letters (suffixes).
Master symbols
H:
Organic or organotechnic layer, not forming part of a litter layer;
water saturation > 30 consecutive days in most years or drained;
generally regarded as peat layer or organic limnic layer.
O:
Organic horizon or organotechnic layer, not forming part of a litter layer;
water saturation ≤ 30 consecutive days in most years and not drained;
generally regarded as non-peat and non-limnic horizon.
A:
Mineral horizon at the mineral soil surface or buried;
contains organic matter that has at least partly been modified in-situ;
soil structure and/or structural elements created by cultivation in ≥ 50% (by volume, related to the fine earth), i.e. rock structure, if present, in < 50% (by volume).
E:
Mineral horizon;
has lost by downward movement within the soil (vertically or laterally) one or more of the following: Fe, Al, and/or Mn species; clay minerals; organic matter.
B:
Mineral horizon that has (at least originally) formed below an A or E horizon;
rock structure, if present, in < 50% (by volume, related to the fine earth);
one or more of the following processes of soil formation:
formation of soil aggregate structure
formation of clay minerals and/or oxides
accumulation by illuviation processes of one or more of the following: Fe, Al, and/or Mn species; clay minerals; organic matter; silica; carbonates; gypsum
removal of carbonates or gypsum.
B horizons may show other accumulations as well.
C:
Mineral layer;
unconsolidated (can be cut with a spade when moist), or consolidated and more fractured than the R layer;
no soil formation, or soil formation that does not meet the criteria of the A, E, and B horizon.
R:
Consolidated rock;
air-dry or drier specimens, when placed in water, will not slake within 24 hours;
fractures, if present, occupy < 10% (by volume, related to the whole soil);
not resulting from the cementation of a soil horizon.
I:
≥ 75% ice (by volume, related to the whole soil), permanent, below an H, O, A, E, B or C layer.
W:
Permanent water above the soil surface or between layers, may be seasonally frozen.
Suffixes
This is the list of suffixes to the master symbols. In brackets is indicated to which master symbols the suffixes can be added. The suffixes e and i have different meanings for organic and mineral layers.
a: Organic material in an advanced state of decomposition [a like advanced] (H, O).
b: Buried horizon; first, the horizon has formed, and then, it was buried by mineral material [b like buried] (H, O, A, E, B).
c: Concretions and/or nodules [c like concretion]; only used if following another suffix (k, q, v, y) that indicates the accumulated substance.
d: Drained [d like drained] (H).
e: Organic material in an intermediate state of decomposition [e like intermediate] (H, O).
e: Saprolite [e like saprolite] (C).
f: Permafrost [f like frost] (H, O, A, E, B, C).
g: Accumulation of Fe and/or Mn oxides predominantly inside soil aggregates, if present, and loss of these oxides on aggregate surfaces (A, B, C), or loss of Fe and/or Mn by lateral subsurface flow and pale colours in ≥ 50% of the exposed area (E); transport in reduced form [g like stagnic].
h: Significant amount of organic matter; in A horizons at least partly modified in situ; in B horizons predominantly by illuviation; in C horizons forming part of the parent material [h like humus] (A, B, C).
i: Organic material in an initial state of decomposition; [i like initial] (H, O).
j: Accumulation of jarosite and/or schwertmannite [j like jarosite] (H, O, A, E, B, C).
k: Accumulation of secondary carbonates [k like German Karbonat] (H, O, A, E, B, C).
l: Accumulation of Fe and/or Mn in reduced form by upward-moving capillary water with subsequent oxidation: accumulation predominantly at soil aggregate surfaces, if present, and reduction of these oxides inside the aggregates [l like capillary] (H, A, B, C).
m: Pedogenic cementation in ≥ 50% of the volume; cementation class: at least moderately cemented; only used if following another suffix (k, l, q, s, v, y, z) that indicates the cementing agent [m like cemented].
n: Exchangeable sodium percentage ≥ 6% [n like natrium] (E, B, C).
o: Residual accumulation of large amounts of pedogenic oxides in strongly weathered horizons [o like oxide] (B).
p: Modification by cultivation (e.g. ploughing); mineral layers are designated A, even if they belonged to another layer before cultivation [p like plough] (H, O, A).
q: Accumulation of secondary silica [q like quartz] (A, E, B, C).
r: Strong reduction [r like reduction] (A, E, B, C).
s: Accumulation of Fe oxides, Mn oxides and/or Al by vertical illuviation processes from above [s like sesquioxide]. (B, C).
ss: Slickensides and/or wedge-shaped aggregates [ss like "s"licken"s"ide] (B).
t: Accumulation of clay minerals by illuviation processes [t like German Ton, clay]. (B, C).
u: Containing artefacts or consisting of artefacts [u like urban] (H, O, A, E, B, C, R).
v: Plinthite [the suffix v has no connotation] (B, C).
w: Formation of soil structure and/or oxides and/or clay minerals (layer silicates, allophanes and/or imogolites) [w like weathered] (B).
x: Fragic characteristics [the x refers to the impossibility of roots to enter the aggregates] (E, B, C).
y: Accumulation of secondary gypsum [y like gypsum or Spanish yeso] (A, E, B, C).
z: Presence of readily soluble salts [z like Dutch zout] (H, O, A, E, B, C).
@: cryogenic alteration (H, O, A, E, B, C).
α: Presence of primary carbonates (in R layers related to the rock, in all other layers related to the fine earth) [α like carbonate] (H, A, E, B, C, R).
β: Bulk density ≤ 0.9 kg dm-3 [β like bulk density] (B).
γ: Containing ≥ 5% (by grain count) volcanic glasses in the fraction between > 0.02 and ≤ 2 mm [γ like glass] (H, O, A, E, B, C).
δ: High bulk density (natural or anthropogenic), so that roots cannot enter, except along cracks [δ like dense] (A, E, B, C).
λ: Deposited in a body of water (limnic) [λ like limnic] (H, A. C).
ρ: Relict features (only used if following another suffix (g, k, l, p, r, @) that indicates the relict feature) [ρ like relict].
σ: Permanent water saturation and no redoximorphic features [σ like saturation] (A, D, B, C)
τ: Human-transported natural material (related to the whole soil) [τ like transported] ((H, O, A, B, C).
φ: Accumulation of Fe and/or Mn in reduced form by lateral subsurface flow with subsequent oxidation [φ like flow] (A, B, C).
I and W layers have no suffixes.
Combination of suffixes:
1. The c follows the suffix that indicates the substance that forms the concretions or nodules; if this is true for more than one suffix, each one is followed by the c.
2. The m follows the suffix that indicates the substance that is the cementing agent; if this is true for more than one suffix, each one is followed by the m.
3. The ρ follows the suffix that indicates the relict features; if this is true for more than one suffix, each one is followed by the ρ.
4. If two suffixes belong to the same soil-forming process, they follow each other immediately; in the combination of t and n, the t is written first; rules 1, 2 and 3 have to be followed, if applicable.
Examples: Btn, Bhs, Bsh, Bhsm, Bsmh.
5. If in a B horizon the characteristics of the suffixes g, h, k, l, o, q, s, t, v, or y are strongly expressed, the suffix w is not used, even if its characteristics are present; if the characteristics of the mentioned suffixes are weakly expressed and the characteristics of the suffix w are present as well, the suffixes are combined.
6. In H and O layers, the i, e or a is written first.
7. The @, f and b are written last, if b occurs together with @ or f (only if other suffixes are present as well): @b, fb.
8. Besides that, combinations must be in the sequence of dominance, the dominant one first. Examples: Btng, Btgb, Bkcyc.
Transitional layers
If the characteristics of two or more master layers are superimposed to each other, the master symbols are combined without anything in between, the dominant one first, each one followed by its suffixes.
Examples: AhBw, BwAh, AhE, EAh, EBg, BgE, BwC, CBw, BsC, CBs.
If the characteristics of two or more master layers occur in the same depth range, but occupy distinct parts clearly separated from each other, the master symbols are combined with the slash (/), the dominant one first, each one followed by its suffixes.
Examples:
Bt/E (interfingering of E material into a Bt horizon),
C/Bt (Bt horizon forming lamellae within a C layer).
W cannot be combined with other master symbols. H, O, I, and R can only be combined using the slash.
Layer sequences
The sequence of the layers is from top to down with a hyphen in between.
If lithic discontinuities occur, the strata are indicated by preceding figures, starting with the second stratum. I and W layers are not considered as strata. All layers of the respective stratum are indicated by the figure:
Example: Oi-Oe-Ah-E-2Bt-2C-3R.
If two or more layers with the same designation occur, the letters are followed by figures. The sequence of figures continues across different strata.
Examples:
Oi-Oe-Oa-Ah-Bw1-Bw2-2Bw3-3Ahb1-3Eb-3Btb-4Ahb2-4C,
Oi-He-Ha-Cr1-2Heb-2Hab-2Cr2-3Crγ.
Horizons and layers according to the FAO Guidelines for Soil Description (2006)
Source:
Master horizons and layers
H horizons or layers:
These are layers of organic material. Organic material is defined by having a certain minimum content of soil organic carbon. In the WRB, this is 20% (by weight). The H horizon is formed from organic residues that are not incorporated into the mineral soil. The residues may be partially altered by decomposition. Contrary to the O horizons, the H horizons are saturated with water for prolonged periods, or were once saturated but are now drained artificially. In many H horizons, the residues are predominantly mosses. Although these horizons form above the mineral soil surface, they may be buried by mineral soil and therefore be found at greater depth. H horizons may be overlain by O horizons that especially form after drainage.
O horizons or layers:
These are layers of organic material. Organic material is defined by having a certain minimum content of soil organic carbon. In the WRB, this is 20% (by weight). The O horizon is formed from organic residues that are not incorporated into the mineral soil. The residues may be partially altered by decomposition. Contrary to the H horizons, the O horizons are not saturated with water for prolonged periods and not drained artificially. In many O horizons, the residues are leaves, needles, twigs, moss, and lichens. Although these horizons form above the mineral soil surface, they may be buried by mineral soil and therefore be found at greater depth.
A horizons:
These are mineral horizons that formed at the surface or below an O horizon. All or much of the original rock structure has been obliterated. Additionally, they are characterized by one or more of the following:
an accumulation of humified organic matter, intimately mixed with the mineral fraction, and not displaying properties characteristic of E or B horizons (see below);
properties resulting from cultivation, pasturing, or similar kinds of disturbance;
a morphology that is different from the underlying B or C horizon, resulting from processes related to the surface.
If a surface horizon has properties of both A and E horizons but the dominant feature is an accumulation of humified organic matter, it is designated an A horizon.
E horizons:
These are mineral horizons in which the main feature is loss of clay minerals, iron, aluminium, organic matter or some combination of these, leaving a concentration of sand and silt particles. However, pedogenesis is advanced, because the lost substances first have been formed or accumulated there. All or much of the original rock structure is obliterated. An E horizon is usually, but not necessarily, lighter in colour than an underlying B horizon. In some soils, the colour is that of the sand and silt particles. An E horizon is most commonly differentiated from an underlying B horizon: by colour of higher value or lower chroma, or both; by coarser texture; or by a combination of these properties. An E horizon is commonly near to the surface, below an O or A horizon, and above a B horizon. However, the symbol E may be used without regard to the position in the profile for any horizon that meets the requirements and that has resulted from soil genesis.
B horizons:
These are horizons that formed below an A, E, H, or O horizon, and in which the dominant features are the obliteration of all or much of the original rock structure, together with one or a combination of the following:
residual concentration of oxides (especially iron oxides) and/or clay minerals;
evidence of removal of carbonates or gypsum;
illuvial concentration, alone or in combination, of clay minerals, iron, aluminium, organic matter, carbonates, gypsum or silica;
coatings of oxides that make the horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons without apparent illuviation of iron;
alteration that forms clay minerals or liberates oxides or both and that forms a granular, blocky or prismatic structure if volume changes accompany changes in moisture content;
brittleness.
All kinds of B horizons are or were originally subsurface horizons.
Examples of layers that are not B horizons are: layers in which clay films either coat rock fragments or are found on finely stratified unconsolidated sediments, whether the films were formed in place or by illuviation; layers into which carbonates have been illuviated but that are not contiguous to an overlying genetic horizon; and layers with gleying but no other pedogenic changes.
C horizons or layers:
These are horizons or layers, excluding hard bedrock, that are little affected by pedogenic processes and lack properties of H, O, A, E or B horizons. Most are mineral layers, but some siliceous and calcareous layers, such as shells, coral, and diatomaceous earth, are included. The material of C layers may be either like or unlike that from which the overlying solum presumably formed. Plant roots can penetrate C horizons, which provide an important growing medium. Included as C layers are sediments, saprolite, non-indurated bedrock, and other geological materials that commonly slake within 24 hours when air-dry or drier chunks are placed in water, and that, when moist, can be dug with a spade. Some soils form in material that is already highly weathered, and if such material does not meet the requirements of A, E, or B horizons, it is designated C. Changes not considered pedogenic are those not related to overlying horizons. Layers having accumulations of silica, carbonates, or gypsum, even if indurated, may be included in C horizons, unless the layer is obviously affected by pedogenic processes; then it is a B horizon.
R layers:
These consist of hard bedrock underlying the soil. Granite, basalt, quartzite, and indurated limestone or sandstone are examples of bedrock that are designated R. Air-dry or drier chunks of an R layer, when placed in water, will not slake within 24 hours. The R layer is sufficiently coherent when moist to make hand digging with a spade impractical. The bedrock may contain cracks, but these are so few and so small that few roots can penetrate. The cracks may be coated or filled with soil material.
I layers:
These are ice lenses and wedges that contain at least 75 per cent ice (by volume) and that distinctly separate layers (organic or mineral) in the soil.
L layers:
These are sediments deposited in a body of water. They may be organic or mineral. Limnic material is either: (i) deposited by precipitation or through action of aquatic organisms, such as algae, especially diatoms; or (ii) derived from underwater and floating aquatic plants and subsequently modified by aquatic animals. L layers include coprogenous earth or sedimentary peat (mostly organic), diatomaceous earth (mostly siliceous), and marl (mostly calcareous).
W layers:
These are either water layers in soils or water layers submerging soils. The water is present either permanently or cyclic within the time frame of 24 hours. Some organic soils float on water. In other cases, shallow water (i.e. water not deeper than 1 m) may cover the soil permanently, as in the case of shallow lakes, or cyclic, as in tidal flats. The occurrence of tidal water can be indicated by the letter W in brackets: (W).
Transitional horizons and layers
A horizon that combines the characteristics of two master horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If discrete, intermingled bodies of two master horizons occur together, the horizon symbols are combined using a slash (/). Example: A/B and B/A. The master horizon symbols may be followed by the lowercase letters indicating subordinate characteristics (see below). Example: AhBw. The I, L and W symbols are not used in transitional horizon designations.
Subordinate characteristics
This is the list of suffixes to the master horizons. After the hyphen, it is indicated to which master horizons the suffixes can be added.
a: Highly decomposed organic material—H and O horizons.
b: Buried genetic horizon—mineral horizons, not cryoturbated.
c: Concretions or nodules—mineral horizons.
c: Coprogenous earth—L horizon.
d: Dense layer (physically root restrictive)—mineral horizons, not with m.
d: Diatomaceous earth—L horizon.
e: Moderately decomposed organic material—H and O horizons.
f: Frozen soil—not in I and R horizons.
g: Stagnic conditions—no restriction.
h: Accumulation of organic matter—mineral horizons.
i: Slickensides—mineral horizons.
i: Slightly decomposed organic material—H and O horizons.
j: Jarosite accumulation—no restriction.
k: Accumulation of pedogenic carbonates—no restriction.
l: Mottling due to upmoving groundwater (gleying)—no restriction.
m: Strong cementation or induration (pedogenic, massive)—mineral horizons.
m: Marl—L horizon.
n: Pedogenic accumulation of exchangeable sodium—no restriction.
o: Residual accumulation of sesquioxides (pedogenic)—no restriction.
p: Ploughing or other human disturbance—no restriction; ploughed E, B, or C horizons are referred to as Ap.
q: Accumulation of pedogenic silica—no restriction.
r: Strong reduction—no restriction.
s: Illuvial accumulation of sesquioxides—B horizons.
t: Illuvial accumulation of clay minerals—B and C horizons.
u: Urban and other human-made materials (artefacts—H, O, A, E, B and C horizons.
v: Occurrence of plinthite—no restriction.
w: Development of colour or structure—B horizons.
x: Fragipan characteristics—no restriction.
y: Pedogenic accumulation of gypsum—no restriction.
z: Pedogenic accumulation of salts more soluble than gypsum—no restriction.
@: Evidence of cryoturbation—no restriction.
Discontinuities and vertical subdivisions
Numerical prefixes are used to denote lithic discontinuities. By convention, 1 is not shown. Numerical suffixes are used to denote subdivisions within a horizon. The horizons in a profile are combined using a hyphen (-). Example: Ah-E-Bt1-2Bt2-2BwC-3C1-3C2.
Horizons and layers according to the USDA Field Book for Describing and Sampling Soils (2012)
Source:
Master horizons and layers
O: Organic soil materials (not limnic).
A: Mineral; organic matter (humus) accumulation.
E: Mineral; some loss of Fe, Al, clay, or organic matter.
B: Subsurface accumulation of clay, Fe, Al, Si, humus, CaCO3, CaSO4; or loss of CaCO3; or accumulation of sesquioxides; or subsurface soil structure.
C: Little or no pedogenic alteration, unconsolidated earthy material, soft bedrock.
L: Limnic soil materials.
W: A layer of liquid water (W) or permanently frozen water (Wf) within or beneath the soil (excludes water/ice above soil).
M: Root-limiting subsoil layers of human-manufactured materials.
R: Bedrock, strongly cemented to indurated.
Transitional horizons and layers
A horizon that combines the characteristics of two master horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If discrete, intermingled bodies of two master horizons occur together, the horizon symbols are combined using a slash (/). Example: A/B and B/A.
Horizon suffixes
a: Highly decomposed organic matter (used only with O).
aa: (proposed) Accumulation of anhydrite (CaSO4).
b: Buried genetic horizon (not used with C horizons).
c: Concretions or nodules.
co: Coprogenous earth (used only with L).
d: Densic layer (physically root restrictive).
di: Diatomaceous earth (used only with L).
e: Moderately decomposed organic matter (used only with O).
f: Permanently frozen soil or ice (permafrost); continuous subsurface ice; not seasonal ice.
ff: Permanently frozen soil ("dry" permafrost); no continuous ice; not seasonal ice.
g: Strong gley.
h: Illuvial organic matter accumulation.
i: Slightly decomposed organic matter (used only with O).
j: Jarosite accumulation.
jj: Evidence of cryoturbation.
k: Pedogenic CaCO3 accumulation (<50% by vol.).
kk: Major pedogenic CaCO3 accumulation (≥50% by vol.).
m: Continuous cementation (pedogenic).
ma: Marl (used only with L).
n: Pedogenic, exchangeable sodium accumulation.
o: Residual sesquioxide accumulation (pedogenic).
p: Plow layer or other artificial disturbance.
q: Secondary (pedogenic) silica accumulation.
r: Weathered or soft bedrock.
s: Illuvial sesquioxide and organic matter accumulation.
se: Presence of sulfides (in mineral or organic horizons).
ss: Slickensides.
t: Illuvial accumulation of silicate clay.
u: Presence of human-manufactured materials (artifacts).
v: Plinthite.
w: Weak color or structure within B (used only with B).
x: Fragipan characteristics.
y: Accumulation of gypsum.
yy: Dominance of gypsum (≈≥50% by vol.).
z: Pedogenic accumulation of salt more soluble than gypsum.
Other horizon modifiers
Numerical prefixes are used to denote lithologic discontinuities. By convention, 1 is not shown. Numerical suffixes are used to denote subdivisions within a master horizon. Example: A, E, Bt1, 2Bt2, 2BC, 3C1, 3C2.
Horizons according to the Australian Soil and Land Survey Field Handbook (2009)
Source:
Horizons
O horizon
The "O" stands for organic matter. It is a surface layer, dominated by the presence of large amounts of organic matter in varying stages of decomposition. In the Australian system, the O horizon should be considered distinct from the layer of leaf litter covering many heavily vegetated areas, which contains no weathered mineral particles and is not part of the soil itself. O horizons may be divided into O1 and O2 categories, whereby O1 horizons contain undecomposed matter whose origin can be spotted on sight (for instance, fragments of leaves), and O2 horizons contain organic debris in various stages of decomposition, the origin of which is not readily visible. O horizons contain ≥ 20% organic carbon.
P horizon
These horizons are also heavily organic but are distinct from O horizons in that they form under waterlogged conditions. The "P" designation comes from their common name, peats. They may be divided into P1 and P2 in the same way as O horizons. P horizons contain ≥ 12 to 18% organic carbon, depending on the clay content.
A horizon
The A horizon is the top layer of the mineral soil horizons, often referred to as 'topsoil'. This layer contains dark decomposed organic matter, which is called "humus". The technical definition of an A horizon may vary between the systems, but it is most commonly described in terms relative to deeper layers. "A" horizons may be darker in colour than deeper layers and contain more organic matter, or they may be lighter but contain less clay or pedogenic oxides. The A is a surface horizon, and as such is also known as the zone in which most biological activity occurs. Soil organisms such as earthworms, potworms (enchytraeids), arthropods, nematodes, fungi, and many species of bacteria and archaea are concentrated here, often in close association with plant roots. Thus, the A horizon may be referred to as the biomantle. However, since biological activity extends far deeper into the soil, it cannot be used as a chief distinguishing feature of an A horizon. The A horizon may be further subdivided into A1 (dark, maximum biologic activity), A2 (paler), and A3 (transitional to the B horizon).
E horizon (not used in the Australian system)
"E", being short for eluviated, is most commonly used to label a horizon that has been significantly leached of its mineral and/or organic content, leaving a pale layer largely composed of silicates or silica. These are present only in older, well-developed soils, and generally occur between the A and B horizons. In systems where (like in the Australian system) this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, and then appended with the designation "e" (see the section below on horizon suffixes). In soils that contain gravels, due to animal bioturbation, a stonelayer commonly forms near or at the base of the E horizon.
B horizon
The B horizon is commonly referred to as "subsoil" and consists of mineral layers which are significantly altered by pedogenesis, mostly with the formation of iron oxides and clay minerals. It is usually brownish or reddish due to the iron oxides, which increases the chroma of the subsoil to a degree that it can be distinguished from the other horizons. The weathering may be biologically mediated. In addition, the B horizon is defined as having a distinctly different structure or consistency than the horizon(s) above and the horizon(s) below.
The B horizon can also accumulate minerals and organic matter that are migrating downwards from the A and E horizons. If so, this layer is also known as the illuviated or illuvial horizon.
As with the A horizon, the B horizon may be divided into B1, B2, and B3 types under the Australian system. B1 is a transitional horizon of the opposite nature to an A3 – dominated by the properties of the B horizons below it, but containing some A-horizon characteristics. B2 horizons have a high concentration of clay minerals or oxides. B3 horizons are transitional between the overlying B layers and the material beneath it, whether C or D horizon.
The A3, B1, and B3 horizons are not tightly defined, and their use is generally at the discretion of the individual worker.
Plant roots penetrate throughout this layer, but it has very little humus.
The A/E/B horizons are referred to collectively as the "solum", the surface depth of the soil where biologically activity and climate effects drives pedogenesis. The layers below the solum have no collective name but are distinct in that they are noticeably less affected by surface soil-forming processes.
C horizon
The C horizon is below the solum horizons. This layer is little affected by pedogenesis. Clay illuviation, if present, is not significant. The absence of solum-type development (pedogenesis) is one of the defining attributes. The C horizon forms either in deposits (e.g., loess, flood deposits, landslides) or it formed from weathering of residual bedrock. The C horizon may be enriched with carbonates carried below the solum by leaching. If there is no lithologic discontinuity between the solum and the C horizon and no underlying bedrock present, the C horizon resembles the parent material of the solum.
D horizon
D horizons are not universally distinguished, but in the Australian system refer to "any soil material below the solum that is unlike the solum in its general character, is not C horizon, and cannot be given reliable horizon designation… [it] may be recognized by the contrast in pedologic organization between it and the overlying horizons" (National Committee on Soil and Terrain, 2009, p. 151).
R horizon
R horizons denote the layer of partially weathered or unweathered bedrock at the base of the soil profile. Unlike the above layers, R horizons largely comprise continuous masses (as opposed to boulders) of hard rock that cannot be excavated by hand. If there is no lithologic discontinuity between the solum and the R horizon, the R horizon resembles the parent material of the solum.
L horizon (not used in the Australian system)
L (Limnic) horizons or layers indicate mineral or organic material that has been deposited in water by precipitation or through the actions of aquatic organisms. Included are coprogenous earth (sedimentary peat), diatomaceous earth, and marl; and is usually found as a remnant of past bodies of standing water.
Transitional horizons
A horizon that combines the characteristics of two horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If distinct parts have properties of two kinds of horizons, the horizon symbols are combined using a slash (/). Example: A/B and B/A.
Horizon suffixes
In addition to the main descriptors above, several modifiers exist to add necessary detail to each horizon. Firstly, each major horizon may be divided into sub-horizons by the addition of a numerical subscript, based on minor shifts in colour or texture with increasing depth (e.g., B21, B22, B23 etc.). While this can add necessary depth to a field description, workers should bear in mind that excessive division of a soil profile into narrow sub-horizons should be avoided. Walking as little as ten metres in any direction and digging another hole can often reveal a very different profile in regards to the depth and thickness of each horizon. Over-precise description can be a waste of time. In the Australian system, as a rule of thumb, layers thinner than 5 cm (2 inches) or so are best described as pans or segregations within a horizon rather than as a distinct layer.
Suffixes describing particular features of a horizon may also be added. The Australian system provides the following suffixes:
b: buried horizon.
c: presence of mineral concretions or nodules, perhaps of iron, aluminium, or manganese.
d: root restricting layer.
e: conspicuously bleached.
f: faunal accumulations in A horizons.
g: gleyed horizon.
h: accumulation of organic matter.
j: sporadically bleached.
k: accumulation of carbonates, commonly calcium carbonate.
m: strong cementation or induration.
p: disturbed by ploughing or other tillage practices (A horizons only).
q: accumulation of secondary silica.
r: weathered, digable rock.
s: sesquioxide accumulation.
t: accumulation of clay minerals.
w: weak development.
x: fragipan.
y: accumulation of calcium sulfate (gypsum).
z: accumulation of salts more soluble than calcium sulfate.
Buried soils
Soil formation is often described as occurring in situ: Rock breaks down, weathers and is mixed with other materials, or loose sediments are transformed by weathering. But the process is often far more complicated. For instance, a fully formed profile may have developed in an area only to be buried by wind- or water-deposited sediments which later formed into another soil profile. This sort of occurrence is most common in coastal areas, and descriptions are modified by numerical prefixes. Thus, a profile containing a buried sequence could be structured O, A1, A2, B2, 2A2, 2B21, 2B22, 2C with the buried profile commencing at 2A2.
Diagnostic soil horizons
Many soil classification systems have diagnostic horizons. A diagnostic horizon is a horizon used to define soil taxonomic units (e.g., to define soil types). A taxonomic unit is determined by the presence or absence of one or more diagnostic horizons in a required depth. In addition, most classification systems use other soil characteristics to define taxonomic units. The diagnostic horizons need to be thoroughly characterized by a set of criteria. When allocating soil (a pedon, a soil profile) to a taxonomic unit, one has to check every horizon of this soil and decide whether or not the horizon fulfills the criteria of a diagnostic horizon. Based on the identified diagnostic horizons, one can proceed with the allocation of the soil to a taxonomic unit. The following lists the diagnostic horizons of two soil classification systems.
Diagnostic horizons in the World Reference Base for Soil Resources (WRB)
Source:
Albic horizon
Anthraquic horizon
Argic horizon
Calcic horizon
Cambic horizon
Chernic horizon
Cohesic horizon
Cryic horizon
Duric horizon
Ferralic horizon
Ferric horizon
Folic horizon
Fragic horizon
Gypsic horizon
Histic horizon
Hortic horizon
Hydragric horizon
Irragric horizon
Limonic horizon
Mollic horizon
Natric horizon
Nitic horizon
Panpaic horizon
Petrocalcic horizon
Petroduric horizon
Petrogypsic horizon
Petroplinthic horizon
Pisoplinthic horizon
Plaggic horizon
Plinthic horizon
Pretic horizon
Protovertic horizon
Salic horizon
Sombric horizon
Spodic horizon
Terric horizon
Thionic horizon
Tsitelic horizon
Umbric horizon
Vertic horizon
Diagnostic horizons in the USDA soil taxonomy (ST)
Source:
Diagnostic surface horizons
Anthropic epipedon
Folistic epipedon
Histic epipedon
Melanic epipedon
Mollic epipedon (see Mollisols)
Ochric epipedon
Plaggen epipedon
Umbric epipedon
Diagnostic subsurface horizons
Agric horizon
Albic horizon
Anhydric horizon
Argillic horizon
Calcic horizon
Cambic horizon
Duripan layer
Fragipan layer
Glossic horizon
Gypsic horizon
Kandic horizon
Natric horizon
Nitic horizon
Ortstein layer
Oxic horizon
Petrocalcic Horizon
Petrogypsic horizon
Petroplinthic horizon
Placic horizon
Salic horizon
Sombric horizon
Spodic horizon
| Physical sciences | Soil science | Earth science |
6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Fracture (geology) | A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.
Brittle deformation
Fractures are forms of brittle deformation. There are two types of primary brittle deformation processes. Tensile fracturing results in joints. Shear fractures are the first initial breaks resulting from shear forces exceeding the cohesive strength in that plane.
After those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults.
Most often, fracture profiles will look like either a blade, ellipsoid, or circle.
Causes
Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults. Fractures may also be a result from shear or tensile stress. Some of the primary mechanisms are discussed below.
Modes
First, there are three modes of fractures that occur (regardless of mechanism):
Mode I crack – Opening mode (a tensile stress normal to the plane of the crack)
Mode II crack – Sliding mode (a shear stress acting parallel to the plane of the crack and perpendicular to the crack front)
Mode III crack – Tearing mode (a shear stress acting parallel to the plane of the crack and parallel to the crack front)
For more information on this, see fracture mechanics.
Tensile fractures
Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined.
The first form is in axial stretching. In this case a remote tensile stress, σn, is applied, allowing microcracks to open slightly throughout the tensile region. As these cracks open up, the stresses at the crack tips intensify, eventually exceeding the rock strength and allowing the fracture to propagate. This can occur at times of rapid overburden erosion. Folding also can provide tension, such as along the top of an anticlinal fold axis. In this scenario the tensile forces associated with the stretching of the upper half of the layers during folding can induce tensile fractures parallel to the fold axis.
Another, similar tensile fracture mechanism is hydraulic fracturing. In a natural environment, this occurs when rapid sediment compaction, thermal fluid expansion, or fluid injection causes the pore fluid pressure, σp, to exceed the pressure of the least principal normal stress, σn. When this occurs, a tensile fracture opens perpendicular to the plane of least stress.[4]
Tensile fracturing may also be induced by applied compressive loads, σn, along an axis such as in a Brazilian disk test. This applied compression force results in longitudinal splitting. In this situation, tiny tensile fractures form parallel to the loading axis while the load also forces any other microfractures closed. To picture this, imagine an envelope, with loading from the top. A load is applied on the top edge, the sides of the envelope open outward, even though nothing was pulling on them. Rapid deposition and compaction can sometimes induce these fractures.
Tensile fractures are almost always referred to as joints, which are fractures where no appreciable slip or shear is observed.
To fully understand the effects of applied tensile stress around a crack in a brittle material such a rock, fracture mechanics can be used. The concept of fracture mechanics was initially developed by A. A. Griffith during World War I. Griffith looked at the energy required to create new surfaces by breaking material bonds versus the elastic strain energy of the stretched bonds released. By analyzing a rod under uniform tension Griffith determined an expression for the critical stress at which a favorably orientated crack will grow. The critical stress at fracture is given by,
where γ = surface energy associated with broken bonds, E = Young's modulus, and a = half crack length. Fracture mechanics has generalized to that γ represents energy dissipated in fracture not just the energy associated with creation of new surfaces
Linear elastic fracture mechanics
Linear elastic fracture mechanics (LEFM) builds off the energy balance approach taken by Griffith but provides a more generalized approach for many crack problems. LEFM investigates the stress field near the crack tip and bases fracture criteria on stress field parameters. One important contribution of LEFM is the stress intensity factor, K, which is used to predict the stress at the crack tip. The stress field is given by
where is the stress intensity factor for Mode I, II, or III cracking and is a dimensionless quantity that varies with applied load and sample geometry. As the stress field gets close to the crack tip, i.e. , becomes a fixed function of . With knowledge of the geometry of the crack and applied far field stresses, it is possible to predict the crack tip stresses, displacement, and growth. Energy release rate is defined to relate K to the Griffith energy balance as previously defined. In both LEFM and energy balance approaches, the crack is assumed to be cohesionless behind the crack tip. This provides a problem for geological applications such a fault, where friction exists all over a fault. Overcoming friction absorbs some of the energy that would otherwise go to crack growth. This means that for Modes II and III crack growth, LEFM and energy balances represent local stress fractures rather than global criteria.
Crack formation and propagation
Cracks in rock do not form smooth path like a crack in a car windshield or a highly ductile crack like a ripped plastic grocery bag. Rocks are a polycrystalline material so cracks grow through the coalescing of complex microcracks that occur in front of the crack tip. This area of microcracks is called the brittle process zone. Consider a simplified 2D shear crack as shown in the image on the right. The shear crack, shown in blue, propagates when tensile cracks, shown in red, grow perpendicular to the direction of the least principal stresses. The tensile cracks propagate a short distance then become stable, allowing the shear crack to propagate. This type of crack propagation should only be considered an example. Fracture in rock is a 3D process with cracks growing in all directions. It is also important to note that once the crack grows, the microcracks in the brittle process zone are left behind leaving a weakened section of rock. This weakened section is more susceptible to changes in pore pressure and dilatation or compaction. Note that this description of formation and propagation considers temperatures and pressures near the Earth's surface. Rocks deep within the earth are subject to very high temperatures and pressures. This causes them to behave in the semi-brittle and plastic regimes which result in significantly different fracture mechanisms. In the plastic regime cracks acts like a plastic bag being torn. In this case stress at crack tips goes to two mechanisms, one which will drive propagation of the crack and the other which will blunt the crack tip. In the brittle-ductile transition zone, material will exhibit both brittle and plastic traits with the gradual onset of plasticity in the polycrystalline rock. The main form of deformation is called cataclastic flow, which will cause fractures to fail and propagate due to a mixture of brittle-frictional and plastic deformations.
Joint types
Describing joints can be difficult, especially without visuals. The following are descriptions of typical natural fracture joint geometries that might be encountered in field studies:
Plumose Structures are fracture networks that form at a range of scales, and spread outward from a joint origin. The joint origin represents a point at which the fracture begins. The mirror zone is the joint morphology closest to the origin that results in very smooth surfaces. Mist zones exist on the fringe of mirror zones and represent the zone where the joint surface slightly roughens. Hackle zones predominate after mist zones, where the joint surface begins to get fairly rough. This hackle zone severity designates barbs, which are the curves away from the plume axis.
Orthogonal Joints occur when the joints within the system occur at mutually perpendicular angles to each other.
Conjugate Joints occur when the joints intersect each other at angles significantly less than ninety degrees.
Systematic Joints are joint systems in which all the joints are parallel or subparallel, and maintain roughly the same spacing from each other.
Columnar Joints are joints that cut the formation vertically in (typically) hexagonal columns. These tend to be a result of cooling and contraction in hypabyssal intrusions or lava flows.
Desiccation cracks are joints that form in a layer of mud when it dries and shrinks. Like columnar joints, these tend to be hexagonal in shape.
Sigmoidal Joints are joints that run parallel to each other, but are cut by sigmoidal (stretched S) joints in between.
Sheeting joints are joints that often form near surface, and as a result form parallel to the surface. These can also be recognized in exfoliation joints.
In joint systems where relatively long joints cut across the outcrop, the throughgoing joints act as master joints and the short joints that occur in between are cross joints.
Poisson effect is the creation of vertical contraction fractures that are a result of the relief of overburden over a formation.
Pinnate joints are joints that form immediately adjacent to and parallel to the shear face of a fault. These joints tend to merge with the faults at an angle between 35 and 45 degrees to the fault surface.
Release joints are tensile joints that form as a change in geologic shape results in the manifestation of local or regional tension that can create Mode I tensile fractures.
Concurrent joints that display a ladder pattern are interior regions with one set of joints that are fairly long, and the conjugate set of joints for the pattern remain relatively short, and terminate at the long joint.
Sometimes joints can also display grid patterns, which are fracture sets that have mutually crosscutting fractures.
An en echelon or stepped array represents a set of tensile fractures that form within a fault zone parallel to each other.
Faults and shear fractures
Faults are another form of fracture in a geologic environment. In any type of faulting, the active fracture experiences shear failure, as the faces of the fracture slip relative to each other. As a result, these fractures seem like large scale representations of Mode II and III fractures, however that is not necessarily the case.
On such a large scale, once the shear failure occurs, the fracture begins to curve its propagation towards the same direction as the tensile fractures. In other words, the fault typically attempts to orient itself perpendicular to the plane of least principal stress. This results in an out-of-plane shear relative to the initial reference plane. Therefore, these cannot necessarily be qualified as Mode II or III fractures.
An additional, important characteristic of shear-mode fractures is the process by which they spawn wing cracks, which are tensile cracks that form at the propagation tip of the shear fractures. As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the σh-max, which is the direction of maximum principal stress.
Shear-failure criteria is an expression that attempts to describe the stress at which a shear rupture creates a crack and separation. This criterion is based largely off of the work of Charles Coulomb, who suggested that as long as all stresses are compressive, as is the case in shear fracture, the shear stress is related to the normal stress by:
σs= C+μ(σn-σf),
where C is the cohesion of the rock, or the shear stress necessary to cause failure given the normal stress across that plane equals 0. μ is the coefficient of internal friction, which serves as a constant of proportionality within geology. σn is the normal stress across the fracture at the instant of failure, σf represents the pore fluid pressure. It is important to point out that pore fluid pressure has a significant impact on shear stress, especially where pore fluid pressure approaches lithostatic pressure, which is the normal pressure induced by the weight of the overlying rock.
This relationship serves to provide the coulomb failure envelope within the Mohr-Coulomb Theory.
Frictional sliding is one aspect for consideration during shear fracturing and faulting. The shear force parallel to the plane must overcome the frictional force to move the faces of the fracture across each other. In fracturing, frictional sliding typically only has significant effects on the reactivation on existing shear fractures. For more information on frictional forces, see friction.
The shear force required to slip fault is less than force required to fracture and create new faults as shown by the Mohr-Coulomb diagram. Since the earth is full of existing cracks and this means for any applied stress, many of these cracks are more likely to slip and redistribute stress than a new crack is to initiate. The Mohr's Diagram shown, provides a visual example. For a given stress state in the earth, if an existing fault or crack exists orientated anywhere from −α/4 to +α/4, this fault will slip before the strength of the rock is reached and a new fault is formed. While the applied stresses may be high enough to form a new fault, existing fracture planes will slip before fracture occurs.
One important idea when evaluating the friction behavior within a fracture is the impact of asperities, which are the irregularities that stick out from the rough surfaces of fractures. Since both faces have bumps and pieces that stick out, not all of the fracture face is actually touching the other face. The cumulative impact of asperities is a reduction of the real area of contact''', which is important when establishing frictional forces.
Subcritical crack growth
Sometimes, it is possible for fluids within the fracture to cause fracture propagation with a much lower pressure than initially required. The reaction between certain fluids and the minerals the rock is composed of can lower the stress required for fracture below the stress required throughout the rest of the rock. For instance, water and quartz can react to form a substitution of OH molecules for the O molecules in the quartz mineral lattice near the fracture tip. Since the OH bond is much lower than that with O, it effectively reduces the necessary tensile stress required to extend the fracture.
Engineering considerations
In geotechnical engineering a fracture forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel, foundation, or slope construction.
Fractures also play a significant role in minerals exploitation. One aspect of the upstream energy sector is the production from naturally fractured reservoirs. There are a good number of naturally fractured reservoirs in the United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production.
The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates. One of the most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas. The chalk had very little porosity, and even less permeability. However, tectonic stresses over time created one of the most extensive fractured reservoirs in the world. By predicting the location and connectivity of fracture networks, geologists were able to plan horizontal wellbores to intersect as many fracture networks as possible. Many people credit this field for the birth of true horizontal drilling in a developmental context. Another example in South Texas is the Georgetown and Buda limestone formations.
Furthermore, the recent uprise in prevalence of unconventional reservoirs is actually, in part, a product of natural fractures. In this case, these microfractures are analogous to Griffith Cracks, however they can often be sufficient to supply the necessary productivity, especially after completions, to make what used to be marginally economic zones commercially productive with repeatable success.
However, while natural fractures can often be beneficial, they can also act as potential hazards while drilling wells. Natural fractures can have very high permeability, and as a result, any differences in hydrostatic balance down the well can result in well control issues. If a higher pressured natural fracture system is encountered, the rapid rate at which formation fluid can flow into the wellbore can cause the situation to rapidly escalate into a blowout, either at surface or in a higher subsurface formation. Conversely, if a lower pressured fracture network is encountered, fluid from the wellbore can flow very rapidly into the fractures, causing a loss of hydrostatic pressure and creating the potential for a blowout from a formation further up the hole.
Fracture modeling
Since the mid-1980s, 2D and 3D computer modeling of fault and fracture networks has become common practice in Earth Sciences. This technology became known as "DFN" (discrete fracture network") modeling, later modified into "DFFN" (discrete fault and fracture network") modeling.
The technology consists of defining the statistical variation of various parameters such as size, shape, and orientation and modeling the fracture network in space in a semi-probabilistic way in two or three dimensions. Computer algorithms and speed of calculation have become sufficiently capable of capturing and simulating the complexities and geological variabilities in three dimensions, manifested in what became known as the "DMX Protocol".
Fracture terminology
A list of fracture related terms:asperities – tiny bumps and protrusions along the faces of fracturesaxial stretching – fracture mechanism resulting from a remote applied tensile force that creates fractures perpendicular to the tensile load axiscataclastic flow – microscopic ductile flow resulting from small grain-scale fracturing and frictional sliding distributed across a large area.*fracture – any surface of discontinuity within a layer of rockdike – a fracture filled with sedimentary or igneous rock not originating in the fracture formationfault – (in a geologic sense) a fracture surface upon which there has been slidingfissure – a fracture with walls that have separated and opened significantlyfracture front – the line separating the rock that has been fractured from the rock that has notfracture tip – the point at which the fracture trace terminates on the surfacefracture trace – the line representing the intersection of the fracture plane with the surfaceGriffith cracks – preexisting microfractures and flaws in the rockjoint – a natural fracture in the formation in which there is no measureable shear displacementKIC – critical stress intensity factor, aka fracture toughness – the stress intensity at which tensile fracture propagation may occurlithostatic pressure – the weight of the overlying column of rocklongitudinal splitting – fracture mechanism resulting from compression along an axis that creates fractures parallel to the load axispore fluid pressure – the pressure exerted by the fluid within the rock poresshear fracture – fractures across which shear displacement has occurredvein – a fracture filled with minerals precipitated out of an aqueous solutionwing cracks'' – tensile fractures created as a result of propagating shear fractures
| Physical sciences | Structural geology | Earth science |
979990 | https://en.wikipedia.org/wiki/Secondary%20color | Secondary color | A secondary color is a color made by mixing two primary colors of a given color model in even proportions. Combining two secondary colors in the same manner produces a tertiary color. Secondary colors are special in traditional color theory, but have no special meaning in color science.
Overview
Primary color
In traditional color theory, it is believed that all colors can be mixed from 3 universal primary - or pure - colors, which were originally believed to be red, yellow and blue pigments (representing the RYB color model). However, modern color science does not recognize universal primary colors and only defines primary colors for a given color model or color space. RGB and CMYK color models are popular color models in modern color science, but are only chosen as efficient primaries, in that their combination leads to a large gamut. However, any three primaries can produce a viable color gamut. The RYB model continues to be used and taught as a color model for practical color mixing in the visual arts.
Secondary color
A secondary color is an even mixture of two primary colors. For a given color model, secondary colors have no special meaning, but are useful when comparing additive and subtractive color models.
Intermediate color
An intermediate color is any mixture of a secondary and a primary color. They are often visualized as even mixtures, but intermediate colors can arise from any mixture proportion. Therefore any color that is not a secondary or primary color is an intermediate color.
Tertiary color
Tertiary color has two common, conflicting definitions, depending on context.
In traditional color theory, which applies mostly to practical painting, a tertiary color is an even mixture between two secondary colors, i.e. a mixture of three primaries in 1:2:1 proportion. This definition is used by color theorists, such as Moses Harris and Josef Albers. The result is approximately a less saturated form of the dominant primary color of the mixture. Under this definition, a color model has 3 tertiary colors.
More recently, an alternative definition has emerged that is more applicable to digital media, where a tertiary color is an intermediate color resulting from an even mixture of a primary and a secondary color, i.e. a mixture of the primaries in 3:1:0 proportion. The result yields a maximum saturation for a given hue. Under this definition, a color model has 6 tertiary colors.
Quaternary color
A quaternary color is a seldom-used descriptor that is the conceptual extension of a tertiary color. Quaternary colors have no special use or status in color theory or color science.
Under the traditional definition, a quaternary color is the even mixture of two tertiary colors, as demonstrated by Charles Hayter. These quaternary colors have contributions from all three primaries in 3-3-2 proportions, so are very desaturated (even mixtures of three primaries gives a neutral color: zero saturation). Under this definition, a color model has 3 quaternary colors.
Under the modern definition, a quaternary color is the even mixture of a tertiary color with either a secondary or primary color. Quaternary colors are sometimes given a maximum saturation for their hue. Under this definition, a color model has 12 quaternary colors.
RGB and CMYK
The RGB color model is an additive mixing model, used to estimate the mixing of colored light, with primary colors red, green, and blue. The secondary colors are yellow, cyan and magenta as demonstrated here:
The CMY color model is an analogous subtractive mixing color model, used to estimate the mixing of colored pigments, with primary colors cyan, magenta, and yellow, equivalent to the secondary colors of the RGB color model. The secondary colors of the CMY model are blue, red and green, equivalent to the primary colors of the RGB model, as demonstrated here:
Under the modern definition, the 6 tertiary colors are conceptually equivalent between the color models, and can be described by the even combinations of a primary and a secondary color:
A color model is a conceptual model and does not have specifically defined primary colors. A color space based on the RGB color model, most commonly sRGB, has defined primaries and can be used to visualize the color mixing and yield approximate tertiary colors. Also note that the color terms applied to tertiary and quaternary colors are not well-defined.
RYB color model
RYB is a subtractive mixing color model, used to estimate the mixing of pigments (e.g. paint) in traditional color theory, with primary colors red, yellow, and blue. The secondary colors are green, purple, and orange as demonstrated here:
Under the modern definition (as even combinations of a primary and a secondary color), tertiary colors are typically named by combining the names of the adjacent primary and secondary color. However, these tertiary colors have also been ascribed with common names: amber/marigold (yellow-orange), vermilion/cinnabar (red-orange), magenta (red-purple), violet (blue-purple), teal/aqua (blue-green), and chartreuse/lime green (yellow-green). The 6 tertiary colors are given:
Approximate colors and color names are given for the tertiary and quaternary colors. However, the names for the twelve quaternary colors are quite variable, and defined here only as an approximation.
Under the traditional definition, there are three tertiary colors, approximately named russet (orange–purple), slate (purple–green), and citron (green–orange), with the corresponding three quaternary colors plum (russet–slate), sage (slate–citron), buff (citron–russet) (with olive sometimes used for either slate or citron). In every level of mixing, saturation of the resultant decreases and mixing two quaternary colors approaches gray.
The RYB color terminology outlined above and in the color samples shown below is ultimately derived from the 1835 book Chromatography, an analysis of the RYB color wheel by George Field, a chemist who specialized in pigments and dyes.
| Physical sciences | Basics | Physics |
980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Humphead wrasse | The humphead wrasse (Cheilinus undulatus) is a large species of wrasse mainly found on coral reefs in the Indo-Pacific region. It is also known as the Māori wrasse, Napoleon wrasse, Napoleon fish, so mei 蘇眉 (Cantonese), mameng (Filipino), and merer in the Pohnpeian language of the Caroline Islands.
Description
The humphead wrasse is the largest extant member of the family Labridae. Males, typically larger than females, are capable of reaching up to 2 meters and weighing up to 180 kg, but the average length is a little less than 1 meter. Females rarely grow larger than one meter. This species can be easily identified by its large size, thick lips, two black lines behind its eyes, and the hump on the foreheads of larger adults. Its color can vary between dull blue-green to more vibrant shades of green and purplish-blue. Adults are usually observed living singly, but are also seen in male/female pairs and in small groups.
Habitat
The humphead wrasses can be found on the east coast of Africa around the mouth of the Red Sea, and in some areas of the Indian and Pacific Oceans. Juveniles are usually found in shallow, sandy ranges bordering coral reef waters, while adults are found mostly in offshore and deeper areas of coral reefs, typically in outer-reef slopes and channels, but also in lagoons.
Reproduction
The humphead wrasse is long-lived, but has a very slow breeding rate. Individuals become sexually mature at five to seven years, and are known to live for around 30 years. They are protogynous hermaphrodites, with some becoming male at about 9 years old. The factors controlling the timing of sex change are not yet known. At certain times of year, adults move to the down-current end of the reef and form local spawning aggregations (groups). They likely do not travel very far for their spawning aggregations.
The pelagic eggs and larvae ultimately settle on or near coral reef habitats. Eggs are 0.65 mm in diameter and spherical, with no pigment.
Ecology
Very opportunistic predators, C. undulatus preys primarily on invertebrates such as mollusks (particularly gastropods, as well as pelecypods, echinoids, crustaceans, and annelids) other fish, and even the highly venomous Crown-of-thorns starfish. Because half of echinoids and most pelecypods hide under the sand, wrasses may rely on fish excavators like stingrays, or they themselves may excavate by ejecting water to displace sand and nosing around for prey. Like many other Red Sea wrasses, humphead wrasses often crack sea urchins (echinoids) by carrying them to a rock in their mouths and striking them against the rock with brisk, sideways head movements.
They sometimes engage in cooperative hunting with the roving coral grouper.
Adults are commonly found on steep coral reef slopes, channel slopes, and lagoon reefs in water deep.
The species actively selects branching hard and soft corals and seagrasses at settlement. Juveniles tend to prefer a more cryptic existence in areas of dense branching corals, bushy macroalgae, or seagrasses, while larger individuals and adults prefer limited home ranges in more open habitat on the edges of reefs, channels, and reef passes.
Conservation
The humphead wrasse is listed as endangered on the IUCN Red list and in Appendix II of CITES. Its numbers have declined due to multiple threats, including:
Intensive, species-specific removal by the live reef food-fish trade throughout its core range in Southeast Asia
Destructive fishing techniques, including bombs and cyanide
Habitat loss and degradation
Local consumption, and its perception as a delicacy to locals and tourists
A developing export market for juveniles for the marine aquarium trade
Lack of coordinated, consistent national and regional management
Inadequate knowledge of the species
Illegal, unreported and unregulated fishing
Unsustainable and severe overfishing within the live reef food fish trade is the primary threat. Sabah, on Borneo Island, is a major source of humphead wrasses. The fishing industry is vital to this state because of its severe poverty. The export of humphead wrasses out of Sabah has led to a roughly 99% decline in the area's population. In an effort to protect it, export of the humphead wrasse out of Sabah has been banned; however, it has not prevented illegal, unreported and unregulated activities. Protection by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is managed in this area by the federal Department of Fisheries Malaysia, , which issues permits to regulate fishing activity. Two pieces of legislation have also been implemented to protect the species: The Fisheries Act 1985 controls the transport of live fish and prohibits destructive fishing techniques; and the International Trade in Endangered Species Act 2008 supports Malaysia's adoption of CITES.
The humphead wrasse is considered an umbrella species, which means many other species are sympatric with it and have much smaller ranges—thus the conservation of the humphead wrasse's habitat would benefit these other species as well. Understanding the concept of an umbrella species can lead to a better understanding of endangered species protection.
The humphead wrasse has historically been fished commercially in northern Australia, but has been protected in Queensland since 2003 and in Western Australia since 1998.
In Guangdong Province, southern mainland China, permits are required for the sale of the species. Indonesia allows fishing only for research, mariculture and licensed artisanal fishing. The Maldives instituted an export ban in 1995; Papua New Guinea prohibits export of fish over ; and Niue has banned all fishing for this species.
The U.S. National Marine Fisheries Service has classified the humphead wrasse as a species of concern—one about which it has concerns, but for which it has insufficient information to list under the Endangered Species Act.
In Taiwan it is a protected species with fines of between NT$300,000 and $1.5 million and jail sentences of between 6 months and 5 years under the Wildlife Conservation act for hunting or killing of the species having been added to the protection list in 2014.
Population conservation by genetics
In 1996, following a decade of rapid population decline, the humphead wrasse was placed on the IUCN Red List of endangered species. The wrasse's genomes must be analyzed to help keep the species alive.
Since so little was known about the wrasse's genetic relationships at a geographical scale, researchers utilized a test using microsatellite loci to facilitate population genetic studies. (DNA markers could not be used for testing, as the humphead wrasse lack such markers.) Of the 15 microsatellite loci used in the test, only four seemed to have different outcomes than the other 11. These loci were all prone to null alleles. However, with the presence of these null alleles, the results may have been slightly biased, or they may be related to a particularity of the C. undulatus, which are highly restricted to coral reef habitats.
Illegal, unregulated and unreported activities
The Philippines, Indonesia, and Sabah Malaysia are the three largest exporters of the humphead wrasse. It has one of the highest retail values in Asia, especially when caught alive, and it is considered a delicacy in places like Malaysia. Illegal, unregulated, and unreported activities have been identified as the major factor for the failure of conservation efforts. Although the Convention on International Trade in Endangered Species of Wild Fauna and Flora has banned its export, the fish are still smuggled across the Malaysia–Philippines border.
Four main factors have allowed illegal, unregulated and unreported activities to persist:
Lack of capacity – A lack exists of formal procedures and personnel to monitor fishing activities and enforce fishing regulations
Lack of disincentives – Fishers do not have alternatives for the humphead wrasse, due to its value, and sanctions for illegal fishing are not harsh enough to discourage them
Weak accountability systems – Because a number of people are involved in the species's trade, it is difficult to trace its source; and importers and consumers cannot be held responsible for illegal exportation.
Absent domestic trade controls – Domestic catching, possession, and trade are not sufficiently restricted. Fishers may illegally source the fish or intend to illegally trade it, but cannot be prosecuted if they are in Malaysian waters with appropriate permits.
Most exports of the humphead wrasse in Malaysia occur in Sandakan, Papar, and Tawau, where the fish could recently be purchased for between US$45.30 and $69.43, with its retail price ranging from $60.38 to $120.36.
| Biology and health sciences | Acanthomorpha | Animals |
980257 | https://en.wikipedia.org/wiki/Diospyros | Diospyros | Diospyros is a genus of over 700 species of deciduous and evergreen trees and shrubs. The majority are native to the tropics, with only a few species extending into temperate regions. Individual species valued for their hard, heavy, dark timber, are commonly known as ebony trees, while others are valued for their fruit and known as persimmon trees. Some are useful as ornamentals and many are of local ecological importance. Species of this genus are generally dioecious, with separate male and female plants.
Taxonomy and etymology
The generic name Diospyros comes from a Latin name for the Caucasian persimmon (D. lotus), derived from the Greek διόσπυρος : dióspyros, from diós () and pyrós (). The Greek name literally means "Zeus's wheat" but more generally intends "divine food" or "divine fruit".
The genus is a large one and the number of species has been estimated variously, depending on the date of the source. The Royal Botanic Gardens, Kew, list has over 1000 entries, including synonyms and items of low confidence. Over 700 species are marked as being assigned with high confidence.
The oldest fossils of the genus date to the Eocene, which indicate by that time Diospyros was widely distributed over the Northern Hemisphere.
Chemotaxonomy
The leaves of Diospyros blancoi have been shown to contain isoarborinol methyl ether (also called cylindrin) and fatty esters of α- and β-amyrin. Both isoarborinol methyl ether and the amyrin mixture demonstrated antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Staphylococcus aureus, and Trichophyton interdigitale. Anti-inflammatory and analgesic properties have also been shown for the isolated amyrin mixture.
Ecology
Diospyros species are important and conspicuous trees in many of their native ecosystems, such as lowland dry forests of the former Maui Nui in Hawaii, Caspian Hyrcanian mixed forests, Khathiar–Gir dry deciduous forests, Louisiade Archipelago rain forests, Madagascar lowland forests, Narmada Valley dry deciduous forests, New Caledonian sclerophytic vegetation, New Guinea mangroves or South Western Ghats montane rain forests.
The green fruits are avoided by most herbivores, perhaps because they are rich in tannins. When ripe, they are eagerly eaten by many animals however, such as (in East Africa) the rare Aders' duiker (Cephalophus adersi). The foliage is used as food by the larvae of numerous Lepidoptera species:
Arctiidae:
Eupseudosoma aberrans
Eupseudosoma involutum (snowy eupseudosoma)
Hypercompe indecisa
Geometridae:
Gymnoscelis rufifasciata (double-striped pug) – recorded on persimmons
Limacodidae:
Monema flavescens
Lycaenidae:
Neopithecops zalmora (Quaker)
Nymphalidae:
Charaxes khasianus (Kihansi charaxes) – recorded on D. natalensis
Dophla evelina (redspot duke) – recorded on D. candolleana
Saturniidae:
Actias luna (Luna moth) – recorded on persimmons
Callosamia promethea (promethea silkmoth) – recorded on persimmons
Citheronia regalis (regal moth) – recorded on American persimmon (D. virginiana)
Tortricidae:
"Cnephasia" jactatana (black-lyre leafroller moth)
An economically significant plant pathogen infecting many Diospyros species – D. hispida, kaki persimmon (D. kaki), date-plum (D. lotus), Texas persimmon (D. texana), Coromandel ebony (D. melanoxylon) and probably others – is the sac fungus Pseudocercospora kaki, which causes a leaf spot disease.
Use by humans
The genus includes several plants of commercial importance, either for their edible fruit (persimmons) or for their timber (ebony). The latter are divided into two groups in trade: the pure black ebony (notably from D. ebenum, but also several other species), and the striped ebony or calamander wood (from D. celebica, D. mun and others). Most species in the genus produce little to none of this black ebony-type wood; their hard timber (e.g. of American persimmon, D. virginiana) may still be used on a more limited basis.
Leaves of the Coromandel ebony (D. melanoxylon) are used to roll South Asian beedi cigarettes. Several species are used in herbalism, and D. leucomelas yields the versatile medical compound betulinic acid. Extracts from Diospyros plants have also been proposed as novel anti-viral treatment. Though bees do not play a key role as pollinators, in plantations Diospyros may be of some use as honey plants. D. mollis, locally known as mặc nưa, is used in Vietnam to dye the famous black lãnh Mỹ A silk of Tân Châu district.
The reverence of these trees in their native range is reflected by their use as floral emblems. In Indonesia, D. celebica (Makassar ebony, known locally as eboni) is the provincial tree of Central Sulawesi, while ajan kelicung (D. macrophylla) is that of West Nusa Tenggara. The emblem of the Japanese island of Ishigaki is the Yaeyama kokutan (D. ferrea). The Gold apple (D. decandra), called "Trái thị" in Vietnamese, is a tree in the Tấm Cám fable. It is also the provincial tree of Chanthaburi as well as Nakhon Pathom Provinces in Thailand, while the black-and-white ebony (D. malabarica) is that of Ang Thong Province. The name of the Thai district Amphoe Tha Tako, literally means "District of the Diospyros pier", the latter being a popular local gathering spot.
Selected species
Diospyros abyssinica
Diospyros acuminata
Diospyros alatella
Diospyros andamanica
Diospyros apiculata
Diospyros areolata
Diospyros artanthifolia
Diospyros atrata
Diospyros attenuata
Diospyros australis – yellow persimmon, black plum, "grey plum"
Diospyros beccarioides
Diospyros borneensis
Diospyros britannoborneensis
Diospyros buxifolia
Diospyros cambodiana
Diospyros candolleana
Diospyros celebica – Makassar ebony
Diospyros chaetocarpa
Diospyros chamaethamnus – sand apple
Diospyros chloroxylon
Diospyros clementium
Diospyros confertiflora
Diospyros cordata
Diospyros coriacea
Diospyros crassiflora – Gaboon ebony, Gabon ebony, African ebony, West African ebony, Benin ebony
Diospyros crockerensis
Diospyros curranii
Diospyros daemona
Diospyros decandra – gold apple
Diospyros dichrophylla
Diospyros dictyoneura
Diospyros diepenhorstii
Diospyros discocalyx
Diospyros discolor – kamagong, mabolo, butter fruit, velvet-apple
Diospyros duclouxii
Diospyros ebenum – Ceylon ebony, India ebony, "ebony"
Diospyros elliptifolia
Diospyros eriantha
Diospyros eucalyptifolia
Diospyros euphlehia
Diospyros evena
Diospyros everettii
Diospyros fasciculosa
Diospyros ferox
Diospyros ferrea
Diospyros ferruginescens
Diospyros foxworthyi
Diospyros frutescens
Diospyros fusiformis
Diospyros geminata
Diospyros hallieri
Diospyros havilandii
Diospyros hebecarpa
Diospyros hillebrandii
Diospyros hirsuta
Diospyros humilis – Queensland ebony
Diospyros inconstans
Diospyros insignis
Diospyros insularis – Papua ebony
Diospyros kaki – Japanese persimmon, kaki persimmon, Asian persimmon
Diospyros keningauensis
Diospyros korthalsiana
Diospyros kurzii – Andaman marblewood
Diospyros lanceifolia
Diospyros lateralis
Diospyros leucomelas
Diospyros longibracteata
Diospyros lotus – date-plum, Caucasian persimmon, lilac persimmon
Diospyros lunduensis
Diospyros lycioides – bushveld bluebush
subsp. guerkei
subsp. nitens
subsp. sericea
Diospyros mabacea – red-fruited ebony
Diospyros macrophylla
Diospyros maingayi
Diospyros major
Diospyros malabarica – black-and-white ebony, pale moon ebony, Malabar ebony, gaub tree
Diospyros maritima
Diospyros marmorata – marblewood ebony, "marblewood"
Diospyros melanoxylon – Coromandel ebony, East Indian ebony
var. tupru
Diospyros mespiliformis – jackalberry, "African ebony"
Diospyros mindanaensis
Diospyros montana
Diospyros mun – mun ebony
Diospyros muricata
Diospyros neurosepala
Diospyros nigra – black sapote, chocolate pudding fruit, "black persimmon"
Diospyros oligantha
Diospyros oocarpa
Diospyros oppositifolia
Diospyros ovalifolia
Diospyros parabuxifolia
Diospyros pendula
Diospyros penibukanensis
Diospyros pentamera – myrtle ebony, grey persimmon, black myrtle, grey plum
Diospyros perfida
Diospyros pilosanthera
Diospyros piscicapa
Diospyros plectosepala
Diospyros puncticulosa
Diospyros pyrrhocarpa
Diospyros quaesita
Diospyros racemosa
Diospyros revaughanii
Diospyros rhombifolia
Diospyros ridleyi
Diospyros rigida
Diospyros rufa
Diospyros sandwicensis
Diospyros seychellarum
Diospyros siamang
Diospyros simaloerensis
Diospyros singaporensis
Diospyros squamifolia
Diospyros squarrosa – rigid star-berry
Diospyros styraciformis
Diospyros subrhomboidea
Diospyros subtruncata
Diospyros sulcata
Diospyros sumatrana
Diospyros tessellaria – Mauritius ebony
Diospyros texana – Texas persimmon, Mexican persimmon, "black persimmon"
Diospyros thwaitesii
Diospyros tuberculata
Diospyros ulo
Diospyros venosa
var. olivacea
Diospyros virginiana – American persimmon, eastern persimmon, common persimmon, possumwood, "simmon", "sugar-plum"
Diospyros walkeri
Diospyros wallichii
Diospyros whyteana – Cape ebony
| Biology and health sciences | Ericales | null |
980345 | https://en.wikipedia.org/wiki/Espalier | Espalier | Espalier ( or ) is the horticultural and ancient agricultural practice of controlling woody plant growth for the production of fruit, by pruning and tying branches to a frame. Plants are frequently shaped in formal patterns, flat against a structure such as a wall, fence, or trellis, and also plants which have been shaped in this way.
Espaliers, trained into flat two-dimensional forms, are used not only for decorative purposes, but also for gardens in which space is limited. In a temperate climate, espaliers may be trained next to a wall that can reflect more sunlight and retain heat overnight or oriented so that they absorb maximum sunlight by training them parallel to the equator. These two strategies allow the season to be extended so that fruit has more time to mature.
A restricted form of training consists of a central stem and a number of paired horizontal branches all trained in the same plane. The most important advantage is that of being able to increase the growth of a branch by training it vertically. Later, one can decrease growth while increasing fruit production by training it horizontally.
History
The word is French, coming from the Italian , meaning "something to rest the shoulder () against." During the 17th century, the word initially referred only to the actual trellis or frame on which such a plant was trained to grow, but over time it has come to be used to describe both the practice and the plants themselves.
Espalier as a technique seems to have started with the ancient Romans. In the Middle Ages the Europeans refined it into an art. The practice was popularly used in Europe to produce fruit inside the walls of a typical castle courtyard without interfering with the open space and to decorate solid walls by planting flattened trees near them. Vineyards have used the technique in the training of grapes for hundreds or perhaps even thousands of years.
Belgian fence
A Belgian fence is created by cutting back an unbranched, slender tree to between above the ground. The topmost three buds are allowed to form; one in the middle is trained vertically while two others are trained into a V shape. Any other buds are rubbed away. Removing the vertical stem completes the individual V-shaped espalier. By placing many similarly trained trees in a line two feet apart with their branches trained to the same plane, a Belgian fence is created.
The Belgian fence is an intermediary form that can then be used to train onward to many other forms of espalier, including: Step-over, where the branches are lowered down to the horizontal in autumn while still flexible enough and tied to a trellis; Fan, where the branches are lowered and cut back then trained further; Horizontal T, where the branches are trained to horizontal as with step-over but the vertical stem is trained up to another level and cut usually in spring of the second year, where another V shape is created and the resulting branches finally being lowered to another wire in autumn of the second year. Multiple levels of horizontal branching can be trained in this way.
Species choices
Certain types of trees adapt better to espalier than others, but almost any woody plant can be trained to grow along a flat plane by removing growth outside that plane.
Horizontal T training of an apple or pear tree is a good example of the ideal species for espalier. In the spring, the tree is pruned to the lowest wire perhaps above the ground. During the summer, buds lengthen into branches; one trained vertically to the next wire while others are trained along the wires. Unnecessary buds are removed by rubbing them away with a thumb. In autumn, the side branches are lowered and tied to the wires completing the level. The following year another level is created.
Examples of species for espalier include:
Trees:
Acer palmatum Japanese Maple
Cercis canadensis Redbud
Citrus spp. Lemon, Orange, Tangerine, etc.
Coccoloba uvifera Sea grape
Eriobotrya japonica Loquat
Euonymus alata Winged Euonymus
Ficus carica Fig
Forsythia intermedia Forsythia
Ilex spp. Hollies, esp. Ilex cornuta 'Burford Burford holly
Lagerstroemia indica Crape myrtle
Magnolia grandiflora Southern magnolia
Magnolia stellata Star Magnolia
Malus spp. Apple, Crabapple, etc.
Olea europia Olive
Prunus spp. Peach, Nectarine, Plum, Almond, etc.
Pyrus spp. Pear
Taxus sp. YewShrubs:Camellia japonica and C. sasanqua Camellia
Carissa grandiflora Natal plum
Chaenomeles lagenaria Chinese flowering quince
Cotoneaster sp. Cotoneaster
Gardenia jasminoides Gardenia
Juniperus spp. Juniper, esp. Juniperus × pfitzeriana''' Pfitzer juniperLigustrum japonicum PrivetOsmanthus fragrans Sweet OlivePhotinia glabra Redtip photiniaPhotinia serrulata Chinese PhotiniaPodocarpus spp. PodocarpusPyracantha spp. Firethorn, esp. Pyracantha coccinea Pyracantha coccinea
Stewartia Koreana Korean Stewartia
Viburnum sp. ViburnumWoody vines:'''Allamanda cathartica AllamandaFicus pumila Creeping figJasminum nudiflorum Winter JasminePyrostegia venusta Flame vineTrachelospermum jasminoides'' Confederate jasmine
Designs
Espalier design often uses traditional formal patterns developed over hundreds of years, but can also employ more modern informal designs. A stunted or deformed plant, or one that already has interesting or unique characteristics, might be just right for an informal espalier.
Common formal patterns include the following styles.
V-shaped: Tree is cut to a low wire from the ground; two buds lengthen into branches which are attached to canes that keep them straight, and the canes are attached to another wire that maintains a V shape. The V shape is the first step in producing many other formal patterns.
Belgian fence: More than one V-shaped espaliers are planted two feet apart, so their branches cross, and are tied to a trellis.
Stepover: A Horizontal espalier with only one set of branches tied to a wire around above the ground. Start with a V shape until desired branch length is attained, but lower branches to the bottom wire by autumn of the first year. Takes only one year to produce the design from a well-rooted unbranched tree (it may take somewhat longer for it to start producing fruit).
Horizontal T, also referred to as a horizontal cordon: Branches are trained horizontally along evenly spaced wires. Start with a V shape where a third bud is trained straight up to another wire. Train other two branches to stepover. In spring of second year prune the vertical stem to the second wire and again train to a V shape, etc. It takes one year per each level.
Palmette or fan: Branches grow in a radiating pattern created when the branches of a V-shaped espalier are cut back and lowered slightly. Multiple buds are coaxed to form branches that are tied to a trellis in a radiating pattern.
Baldassari palmette: A palmette design created around 1950, used primarily for training peaches.
Cordon: Consists of a main stem with short fruiting spurs tied to a fence or a wire trellis. Probably the simplest and quickest espalier is the single vertical or angled cordon. The weakness of the vertical cordon is that it is difficult to rein in the vigor of the tree. An angled cordon reduces the vigor of its growth and increases fruit production.
Verrier candelabra is a type of vertical cordon with multiple upright stems that usually starts from a V shape.
Drapeau marchand: A cordon trained at an angle with the branches on its upper side trained to a right angle from the main stem.
U double and other U-shaped espalier is just another way of referring to a double vertical cordon.
Plant selection, installation, and maintenance
Espalier plants on solid walls are usually installed from the base of that wall, to allow space below ground for roots to grow in all directions as well as space above ground for good air circulation and pest control. Supports for wire guides, which are generally necessary to train an espalier into a design, are installed first, directly into a wall constructed of suitable material. Masonry walls are ideal for placing U-bolts, eye bolts, or eye screws, anchored with either plastic plugs or expandable lead shields, directly into the mortar joints. Wooden walls may be better fitted with galvanized nipples, using turnbuckles for adjustment of the wire tautness.
Suitable, established and healthy plants, three to four feet tall and perhaps in three-gallon containers, are available from most nurseries. Some may even have trellises already installed. These plants could also be good candidates for espalier treatment if their form is similar to the intended design, as they frequently have already been pruned into a flattened overall plant shape. All that is required for such specimens is transplanting. Unpruned plants benefit from being allowed to become well established following transplant, before pruning them gradually into their flattened profile and training them as designed. Any major pruning needed is generally accomplished either while the plant is dormant or, for flowering plants, during the proper season for pruning that species. Bending and training of the limbs that will remain in the design is done during the progression of the summer season, when they are most flexible.
Related tree shaping practices
Bonsai: A small tree shaped to mimic the form of a full grown tree
Grafting: A horticultural technique of joining two or more plants together
Pleaching: Way of creating a hedge with plants for stock control
Topiary: The clipping of foliage of perennial plants into clearly defined shapes
Tree Shaping: Creating with living trees structures and art
| Technology | Horticulture | null |
980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | White rhinoceros | The white rhinoceros, white rhino or square-lipped rhinoceros (Ceratotherium simum) is the largest extant species of rhinoceros. It has a wide mouth used for grazing and is the most social of all rhino species. The white rhinoceros consists of two subspecies: the southern white rhinoceros, with an estimated 16,803
wild-living animals, and the much rarer northern white rhinoceros. The northern subspecies has very few remaining individuals, with only two confirmed left in 2018 (two females: Fatu, 24 and Najin, 29, both in captivity at Ol Pejeta). Sudan, the world's last known male northern white rhinoceros, died in Kenya on 19 March 2018 at age 45.
Naming
A popular albeit widely discredited theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English. The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English. The word "wide" refers to the width of the rhinoceros' mouth. So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino. This suggests the origin of the word was before codification by Dutch writers. A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word wijd was ever used to describe the rhino outside of oral use.
An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros. The white rhinoceros' generic name, Ceratotherium, given by the zoologist John Edward Gray in 1868, is derived from the Greek terms keras (κέρας) "horn" and thērion (θηρίον) "beast". Simum, is derived from the Greek term simos (σιμός), meaning "flat nosed".
Taxonomy and evolution
The white rhinoceros of today was said to be likely descended from Ceratotherium praecox, which lived around 7 million years ago. Remains of this white rhino have been found at Langebaanweg near Cape Town. A review of fossil rhinos in Africa by Denis Geraads has suggested, however, that the species from Langebaanweg is of the genus Ceratotherium, but not Ceratotherium praecox, as the type specimen of Ceratotherium praecox should, in fact, be Diceros praecox, given that it shows closer affinities with the black rhinoceros Diceros bicornis. It has been suggested that the modern white rhino's skull, which is longer than that of Ceratotherium praecox, evolved in order to facilitate consumption of shorter grasses that resulted from the long-term trend to drier conditions in Africa. However, if Ceratotherium praecox is in fact Diceros praecox, then the shorter skull could indicate a browsing species. Teeth of fossils assigned to Ceratotherium found at Makapansgat in South Africa were analysed for carbon isotopes, and the researchers concluded that these animals consumed more than 30% browse in their diet, suggesting that these are not the fossils of the extant Ceratotherium simum, which only eats grass. It is suggested that the real lineage of the white rhino should be: Ceratotherium neumayri → Ceratotherium mauritanicum → C. simum, with the Langebaanweg rhinos being Ceratotherium sp. (as yet unnamed), and with black rhinos being descended from C. neumayri via Diceros praecox.
Recently, an alternative scenario has been proposed under which the earliest African Ceratotherium is considered to be Ceratotherium efficax (now synonymous with C. mauritanicum), known from the Late Pliocene of Ethiopia and the Early Pleistocene of Tanzania. This species is proposed to have been diversified into the Middle Pleistocene species C. mauritanicum in northern Africa, C. germanoafricanum in East Africa, and the extant C. simum. The first two of these are extinct; however, C. germanoafricanum is very similar to C. simum and has often been considered a fossil and ancestral subspecies to the latter. The study also doubts the ancestry of C. neumayri from the Miocene of southern Europe to the African species.
The ancestor of both the black and the white rhino was likely a mixed feeder, with the two lineages then specializing in browsing and grazing, respectively. The oldest definitive record of the white rhinoceros is during the mid-Early Pleistocene at Olduvai Gorge in Tanzania, around 1.8 Ma.
Southern white rhinoceros
As of 2021, there were an estimated 15,940 southern white rhinos in the wild, making them by far the most abundant subspecies of rhino in the world. The number of southern white rhinos outnumbers all other rhino subspecies combined. South Africa is the stronghold for this subspecies, with 12,968 individuals recorded in 2021. There are smaller reintroduced populations within the historical range of the species in Namibia, Botswana, Zimbabwe, Uganda and Eswatini, while a small population survives in Mozambique. Populations have also been introduced outside of the former range of the species to Kenya and Zambia.
Northern white rhinoceros
The northern white rhinoceros or northern square-lipped rhinoceros (Ceratotherium simum cottoni) is considered critically endangered and possibly extinct in the wild. Formerly found in several countries in East and Central Africa south of the Sahara, this subspecies is a grazer in grasslands and savanna woodlands.
Initially, six northern white rhinoceros lived in the Dvůr Králové Zoo in the Czech Republic. Four of the six rhinos (which were also the only reproductive animals of this subspecies) were transported to Ol Pejeta Conservancy in Kenya, where scientists hoped they would successfully breed and save this subspecies from extinction. One of the two remaining in the Czech Republic died in late May 2011. Both of the last two bulls capable of natural mating died in 2014 (one in Kenya on 18 October and one in San Diego on 15 December). In 2015, the Kenyan government placed the last remaining bull of the subspecies at Ol Pejeta under 24-hour armed guard to deter poachers, but he was put down on 19 March 2018 due to multiple health problems caused by old age, leaving just two cows alive which reside at the Ol Pejeta complex. Staff hope to inseminate the remaining cows with the last bull's semen, although the semen is not preferable due to the age of the rhino.
Following the phylogenetic species concept, recent research has led to the hypothesis that the northern white rhinoceros is a different species, rather than a subspecies of white rhinoceros as was previously thought, in which case the correct scientific name for the former should be Ceratotherium cottoni. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years. However, the results of the research were not universally accepted by other scientists.
Description
The white rhinoceros is the largest of the five living species of rhinoceros. By mean body mass, the white rhinoceros falls behind only the three extant species of elephant as the largest land animal and terrestrial mammal alive today. It weighs slightly more on average than a hippopotamus despite a considerable mass overlap between these two species. It has a massive body and large head, a short neck and broad chest.
The head and body length is in bulls and in cows, with the tail adding another , and the shoulder height is in the bull and in the cow. The bull, averaging about is heavier than the cow, at an average of about . The largest size the species can attain is not definitively known; specimens of up to are considered reliable, while larger sizes up to have been claimed but are not verified. On its snout it has two horn-like growths, one behind the other. These are made of solid keratin, in which they differ from the horns of bovids (cattle and their relatives), which are keratin with a bony core, and deer antlers, which are solid bone. The average weight of a horn is about 4.0 kilograms (8.8 pounds).
The front horn is larger and averages in length, reaching as much as but only in cows. The white rhinoceros also has a noticeable hump on the back of its neck. Each of the four stumpy feet has three toes. The color of the body ranges from yellowish-brown to slate grey. Its only hair is the ear fringes and tail bristles. White rhinos have a distinctive broad, straight mouth which is used for grazing. Its ears can move independently to pick up sounds, but it depends most of all on its sense of smell. The olfactory passages that are responsible for smelling are larger than their entire brain. The white rhinoceros has the widest set of nostrils of any land-based animal.
Genome
The genome size of the white rhinoceros is 2581.22 Mb. A diploid cell has 2 x 40 autosomals and 2 sex chromosomes (XX or XY).
Behavior and ecology
White rhinos are grazing herbivores. They are found in grassland and savannah habitat. Preferring the shortest grains, the white rhinoceros is one of the largest pure grazers. It drinks twice a day if water is available, but if conditions are dry it can live four or five days without water. It spends about half of the day eating, one-third resting, and the rest of the day doing various other things. Like all species of rhinoceros, white rhinos enjoy wallowing in mud holes to cool down. The white rhinoceros is thought to have changed the structure and ecology of the savanna's grasslands. Comparatively, based on studies of the African elephant, scientists believe the white rhino is a driving factor in its ecosystem. The destruction of the megaherbivore could have serious cascading effects on the ecosystem and harm other animals.
White rhinos produce sounds that include a panting contact call, grunts and snorts during courtship, squeals of distress, and deep bellows or growls when threatened. Threat displays (in bulls mostly) include wiping its horn on the ground and a head-low posture with ears back, combined with snarl threats and shrieking if attacked. The vocalizations of the two species differ between each other, and the panting contact calls between individual white rhinos in each species can vary as well. The differences in these calls aid the white rhinos in identifying each other and communicating over long distances. The white rhinoceros is quick and agile and can run .
White rhinos live in crashes or herds of up to 14 animals (usually mostly cows). Sub-adult bulls will congregate, often in association with an adult cow. Most adult bulls are solitary. Dominant bulls mark their territory with excrement and urine. The dung is laid in well defined piles. It may have 20 to 30 of these piles to alert passing white rhinos that it is his territory. Another way of marking their territory is wiping their horns on bushes or the ground and scraping with their feet before urine spraying. They do this around ten times an hour while patrolling territory. The same ritual as urine marking except without spraying is also commonly used. The territorial bull will scrape-mark every 30 m (100 ft) or so around his territory boundary. Subordinate bulls do not mark territory. The most serious fights break out over mating rights with a cow. Cow territory overlaps extensively, and they do not defend it.
Reproduction
Cows reach sexual maturity at 6–7 years of age while bulls reach sexual maturity between 10 and 12 years of age. Courtship is often a difficult affair. The bull stays beyond the point where the cow acts aggressively and will give out a call when approaching her. The bull chases and or blocks the way of the cow while squealing or wailing loudly if the cow tries to leave his territory. When ready to mate, the cow curls her tail and gets into a stiff stance during the half-hour copulation. Breeding pairs stay together between 5–20 days before they part their separate ways. The gestation period of a white rhino is 16 months. A single calf is born and usually weighs . Calves are unsteady for their first two to three days of life. When threatened, the baby will run in front of the mother, which is very protective of her calf and will fight for it vigorously. Weaning starts at two months, but the calf may continue suckling for over 12 months. The birth interval for the white rhino is between two and three years. Before giving birth, the mother will chase off her current calf. White rhinos can live to be up to 40–50 years old.
Due to their size, adult white rhinos have no natural predators (other than humans), and even young rhinos are rarely attacked or preyed on due to the mother's presence and their tough skin. One exceptional, successful attack was perpetrated by a lion pride on a sick bull white rhinoceros, which weighed , and occurred in Mala Mala Game Reserve, South Africa.
Distribution
The southern white rhino lives in Southern Africa. About 98.5% of white rhinos live in just five countries (South Africa, Namibia, Zimbabwe, Kenya, and Uganda). Almost at the edge of extinction in the early 20th century, the southern subspecies have made a tremendous comeback. In 2001, it was estimated that there were 11,670 white rhinos in the wild, with a further 777 in captivity worldwide, making it the most common rhino in the world. By the end of 2007, wild-living southern white rhinos had increased to an estimated 17,480 animals (IUCN 2008).
The northern white rhino (Ceratotherium simum cottoni) formerly ranged over parts of northwestern Uganda, southern Chad, southwestern Sudan, the eastern part of Central African Republic, and northeastern Democratic Republic of the Congo (DRC). The last surviving population of wild northern white rhinos are or were in Garamba National Park, Democratic Republic of the Congo (DRC) but in August 2005, ground and aerial surveys conducted under the direction of African Parks Foundation and the African Rhino Specialist Group (ARSG) only found four animals: a solitary adult male and a group of one adult male and two adult females. In June 2008, it was reported that the species may have gone extinct in the wild.
Like the black rhino, the white rhino is under threat from habitat loss and poaching, most recently by Janjaweed. Although there are no measurable health benefits, the horn is sought after for traditional medicine and jewelry.
Poaching
Historically, the major factor in the decline of white rhinos was uncontrolled hunting in the colonial era, but now poaching for their horn is the primary threat. The white rhino is particularly vulnerable to hunting because it is a large and relatively unaggressive animal with very poor eyesight and generally living in herds.
Despite the lack of scientific evidence, the rhino horn is highly prized in traditional Asian medicine, where it is ground into a fine powder or manufactured into tablets to be used as a treatment for a variety of illnesses such as nosebleeds, strokes, convulsions, and fevers. Due to this demand, several highly organized and very profitable international poaching syndicates came into being and would carry out their poaching missions with advanced technologies ranging from night vision scopes, silenced weapons, darting equipment, and even helicopters. The ongoing conflict in the Democratic Republic of Congo and incursions by poachers, primarily coming from Sudan, have further disrupted efforts to protect the few remaining northern rhinos.
In 2013, poaching rates for white rhinos nearly doubled from the previous year. As a result, the white rhino has now received Near Threatened status as its total population tops out at 20,000 members. Poaching of the animal has gone virtually unchecked in most of Africa, and the non-violent nature of the rhinoceros makes it susceptible to poaching. Mozambique, one of the four main countries in which the white rhino lives, is used by poachers as a passageway to South Africa, which holds a fairly large number of white rhinos. Here, rhinos are regularly killed and their horns are smuggled out of the country. As of 2014, Mozambique labels white rhino poaching as a misdemeanor. The white rhino population in South Africa's Kruger National Park fell by 60% between 2013 and 2021, to an estimated 3,529 individuals.
In March 2017, poachers broke into the Thoiry Zoo, which is located in France. A southern white rhinoceros named Vince was found shot dead in his enclosure; the poachers had removed one of his horns and had attempted to remove his second horn. This is believed to be the first time that a rhinoceros had been killed in a European zoo.
Even with increased anti-poaching efforts in many African countries, many poachers are still willing to risk death or prison time because of the tremendous amount of money that they stand to make. Rhino horn can fetch tens of thousands of dollars per kilogram on the black market in Asia, and, depending on the exact price, can be worth more than its weight in gold. Poachers are also starting to use social media sites for obtaining information on the location of rhino in popular tourist attractions (such as Kruger National Park) by searching for geotagged photographs posted online by unsuspecting tourists. By using GPS coordinates of rhinos in recent photographs, poachers can more easily find and kill their targets.
Modern conservation tactics
The northern white rhino is critically endangered to the point that only two of these rhinos are known to remain in the world, both in captivity. Several conservation tactics have been taken to prevent this subspecies from disappearing from the planet. Perhaps the most notable type of conservation effort for these rhinos is having moved them from Dvur Kralove Zoo in the Czech Republic to Kenya's Ol Pejeta Conservancy on 20 December 2009, where they have been under constant watch every day, and have been given favorable climate and diet, to which they have adapted well, to boost their chances of reproducing.
To save the northern white rhino from extinction, Ol Pejeta Conservancy announced that it would introduce a fertile southern white rhino from Lewa Wildlife Conservancy in February 2014. They placed the male rhino in an enclosure with both female northern white rhinos in hopes to cross-breed the subspecies. Having the male rhino with two female rhinos was expected to increase competition for the female rhinos and, in theory, should result in more mating experiences. Ol Pejeta Conservancy did not announce any news of rhino mating.
On 22 August 2019, using (ICSI), eggs from Fatu and Najin "were successfully inseminated" using the seminal fluid from Saut and Suni. The male Sudan's sperm was harvested before his death and is still in Kenya. On 11 September 2019, it was announced that "two embryos" were generated and will be kept in a frozen state, until placed in a surrogate female. On 15 January 2020, it was announced that "another embryo" was created using the same techniques; all three embryos are "from Fatu".
In captivity
Most white rhinos in zoos are southern white rhinos; in 2021, it was estimated that there were over 1,000 southern white rhinos in captivity worldwide.
Wild-caught southern whites will readily breed in captivity given appropriate amounts of space and food, as well as the presence of other female rhinos of breeding age. However, for reasons that are not currently understood, the rate of reproduction is extremely low among captive-born southern white females.
The San Diego Zoo Safari Park in San Diego, California, United States, had two northern white rhinos, one of which was wild-caught. On 22 November 2015, a 41-year-old female named Nola (born in 1974), which had been on loan from the Dvůr Králové Zoo in Dvůr Králové, Czech Republic) since 1989, was euthanized after experiencing a downturn in health. On 14 December 2014, a 44-year-old male named Angalifu died of old age at the San Diego Zoo. The other four captive northern white rhinos were loaned to Ol Pejeta Conservancy in Kenya, and only two remain alive. Females Najin and Fatu are still living, while males Suni and Sudan died in 2014 and 2018, respectively. The northern white rhinos had been transferred to Ol Pejeta Conservancy from the Dvůr Králové Zoo in 2009 in an attempt to protect the taxa in their natural habitat. The only two northern white rhinos left are maintained under 24-hour armed guard in Kenya.
| Biology and health sciences | Perissodactyla | Animals |
981252 | https://en.wikipedia.org/wiki/Oceanic%20crust | Oceanic crust | Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.
Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter.
The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier injections, forming magma lenses that are the source of the sheeted dikes that feed the overlying pillow lavas. As the lavas cool they are, in most instances, modified chemically by seawater. These eruptions occur mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. But most magma crystallises at depth, within the lower oceanic crust. There, newly intruded magma can mix and react with pre-existing crystal mush and rocks.
Composition
Although a complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. Estimations of composition are based on analyses of ophiolites (sections of oceanic crust that are thrust onto and preserved on the continents), comparisons of the seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from the ocean floor by submersibles, dredging (especially from ridge crests and fracture zones) and drilling. Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. According to mineral physics experiments, at lower mantle pressures, oceanic crust becomes denser than the surrounding mantle.
Layer 1 is on an average 0.4 km thick. It consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Near the continental margins sediment is terrigenous, meaning derived from the land, unlike deep sea sediments which are made of tiny shells of marine organisms, usually calcareous and siliceous, or it can be made of volcanic ash and terrigenous sediments transported by turbidity currents.
Layer 2 could be divided into two parts: layer 2A – 0.5 km thick uppermost volcanic layer of glassy to finely crystalline basalt usually in the form of pillow basalt, and layer 2B – 1.5 km thick layer composed of diabase dikes.
Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbro and cumulate ultramafic rocks. It constitutes over two-thirds of oceanic crust volume with almost 5 km thickness.
Geochemistry
The most voluminous volcanic rocks of the ocean floor are the mid-oceanic ridge basalts, which are derived from low-potassium tholeiitic magmas. These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements. There can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland.
Prior to the Neoproterozoic Era 1000 Ma ago the world's oceanic crust was more mafic than present-days'. The more mafic nature of the crust meant that higher amounts of water molecules (OH) could be stored the altered parts of the crust. At subduction zones this mafic crust was prone to metamorphose into greenschist instead of blueschist at ordinary blueschist facies.
Life cycle
Oceanic crust is continuously being created at mid-ocean ridges. As continental plates diverge at these ridges, magma rises into the upper mantle and crust. As the continental plates move away from the ridge, the newly formed rocks cool and start to erode with sediment gradually building up on top of them. The youngest oceanic rocks are at the oceanic ridges, and they get progressively older away from the ridges.
As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr−1 half-rate) produce thinner crust (4–5 km thick) as the mantle has a chance to cool on upwelling and so it crosses the solidus and melts at lesser depth, thereby producing less melt and thinner crust. An example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a greater depth, creating more melt and a thicker crust. An example of this is Iceland which has crust of thickness ~20 km.
The age of the oceanic crust can be used to estimate the (thermal) thickness of the lithosphere, where young oceanic crust has not had enough time to cool the mantle beneath it, while older oceanic crust has thicker mantle lithosphere beneath it. The oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another. In the second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old.
The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson Cycle.
The oldest large-scale oceanic crust is in the west Pacific and north-west Atlantic — both are about up to 180-200 million years old. However, parts of the eastern Mediterranean Sea could be remnants of the much older Tethys Ocean, at about 270 and up to 340 million years old.
Magnetic anomalies
The oceanic crust displays a pattern of magnetic lines, parallel to the ocean ridges, frozen in the basalt. A symmetrical pattern of positive and negative magnetic lines emanates from the mid-ocean ridge. New rock is formed by magma at the mid-ocean ridges, and the ocean floor spreads out from this point. When the magma cools to form rock, its magnetic polarity is aligned with the then-current positions of the magnetic poles of the Earth. New magma then forces the older cooled magma away from the ridge. This process results in parallel sections of oceanic crust of alternating magnetic polarity.
| Physical sciences | Tectonics | Earth science |
981546 | https://en.wikipedia.org/wiki/Astoria%E2%80%93Megler%20Bridge | Astoria–Megler Bridge | The Astoria–Megler Bridge is a steel cantilever through-truss bridge in the Pacific Northwest region of the United States that spans the lower Columbia River. It carries a section of U.S. Route 101 from Astoria, Oregon, to Point Ellice near Megler, Washington. Opened in 1966, it is the longest continuous truss bridge in North America.
The bridge is from the mouth of the river at the Pacific Ocean. The bridge is in length, and was the final segment of U.S. Route 101 to be completed between Olympia, Washington, and Los Angeles, California.
History
Ferry service between Astoria and the Washington side of the Columbia River began in 1926. The Oregon Department of Transportation purchased the ferry service in 1946. This ferry service did not operate during inclement weather and the half-hour travel time caused delays. In order to allow faster and more reliable crossings near the mouth of the river, a bridge was planned. The bridge was built jointly by the Oregon Department of Transportation and Washington State Department of Transportation. Following construction, the Oregon Department of Transportation became the lead agency responsible for maintenance and operating the structure.
Construction on the structure began on November 5, 1962, and the concrete piers were cast at Tongue Point, upriver. The steel structure was built in segments at Vancouver, Washington, upriver, then barged downstream where hydraulic jacks lifted them into place. The bridge opened to traffic on July 29, 1966, marking the completion of U.S. Route 101 and becoming the seventh major bridge built by Oregon in the 1950s–1960s; ferry service ended the night before. On August 27, 1966, Governors Mark Hatfield of Oregon and Dan Evans of Washington dedicated the bridge by cutting a ceremonial ribbon. The four-day ceremony was celebrated by 30,000 attendees who participated in parades, drives, and a marathon boat race from Portland to Astoria. The cost of the project was $24 million, equivalent to $ million in dollars, and was paid for by tolls that were removed on December 24, 1993, more than two years early.
Details
The bridge is in length and carries one lane of traffic in each direction. The cantilever-span section, which is closest to the Oregon side, is long, and its main (central) span measures . It was built to withstand wind gusts and river water speeds of . As of 2004, an average of 7,100 vehicles per day used the Astoria–Megler Bridge. Designed by William Adair Bugge construction of the cantilever truss bridge was completed by the DeLong Corporation, the American Bridge Company, and Pomeroy Gerwick.
The south end has the former toll plaza, at the end of a inclined ramp which forms a spiral bridge, going through a full 360-degree loop while gaining elevation over land to provide almost of clearance over the shipping channel (similarly to the Lincoln Tunnel Helix in Weehawken, New Jersey). The north end is an at-grade intersection with State Route 401. Since most of the northern portion of the bridge is over shallow, non-navigable water, it is low to the water.
Repainting the bridge was planned for May 2009 through 2011 and budgeted at $20 million, to be shared by the states of Oregon and Washington. A four-year planned paint stripping and repainting project was planned for March 2012 through December 2016.
In 2016, a colony of double-crested cormorants moved from nearby East Sand Island to the bridge, where they began nesting. Their presence caused issues with bridge inspections, as bird droppings and guano covered visual cracks, and nests obscured navigational lights used by ship traffic. The population of cormorants increased to 5,000 breeding pairs in 2020, prompting efforts by the Army Corps of Engineers to scare the birds from the bridge and relocate them back to East Sand Island.
Pedestrians
Normally, only motor vehicles and bicycles are allowed on the bridge—not pedestrians. There is no sidewalk and the shoulders are too narrow for pedestrians adjacent to traffic. However, one day a year—usually in October—the bridge is host to the Great Columbia Crossing. Participants are taken by shuttle to the Washington side, from where they run or walk to the Oregon side on a route across the bridge. Motor traffic is allowed to use only one lane (of two lanes) and is advised to expect delays during the two-hour event. For the first time, during the 2018 event, the Oregon Department of Transportation announced that the bridge would be closed to motor traffic.
Popular culture
The bridge itself is featured prominently in the movies Short Circuit, Kindergarten Cop, Free Willy 2: The Adventure Home, The Goonies, and Sometimes I Think About Dying. It stands in for the doomed fictional Madison Bridge in Irwin Allen's 1979 made-for-TV disaster movie The Night the Bridge Fell Down. Songwriter Sufjan Stevens most likely references the bridge in his song "Should Have Known Better" off his 2015 album Carrie & Lowell as a metaphor for dealing with his grief from the death of his mother.
Images
| Technology | Bridges | null |
983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Ankylosaurus | Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
Possibly the largest known ankylosaurid, Ankylosaurus is estimated to have been between long and to have weighed between . It was quadrupedal, with a broad, robust body. It had a wide, low skull, with two horns pointing backward from the back of the head, and two horns below these that pointed backward and down. Unlike other ankylosaurs, its nostrils faced sideways rather than towards the front. The front part of the jaws was covered in a beak, with rows of small, leaf-shaped teeth farther behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name.
Ankylosaurus is a member of the family Ankylosauridae, and its closest relatives appear to be Anodontosaurus and Euoplocephalus. Ankylosaurus is thought to have been a slow-moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or may have played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. Specimens of Ankylosaurus have been found in the Hell Creek, Lance, Scollard, Frenchman, and Ferris formations, but it appears to have been rare in its environment. Although it lived alongside a nodosaurid ankylosaur, their ranges and ecological niches do not appear to have overlapped, and Ankylosaurus may have inhabited upland areas. Ankylosaurus also lived alongside dinosaurs such as Tyrannosaurus, Triceratops, and Edmontosaurus.
History of discovery
In 1906, an American Museum of Natural History expedition led by American paleontologist Barnum Brown discovered the type specimen of Ankylosaurus magniventris (AMNH 5895) in the Hell Creek Formation, near Gilbert Creek, Montana. The specimen (found by collector Peter Kaisen) consisted of the upper part of a skull, two teeth, part of the shoulder girdle, cervical, dorsal, and caudal vertebrae, ribs, and more than thirty osteoderms (armor plates). Brown scientifically described the animal in 1908; the generic name is derived from the Greek words ('bent' or 'crooked'), referring to the medical term ankylosis, the stiffness produced by the fusion of bones in the skull and body, and ('lizard'). The name can be translated as "fused lizard", "stiff lizard", or "curved lizard". The type species name, magniventris, is derived from the ('great') and ('belly'), referring to the great width of the animal's body.
The skeletal reconstruction accompanying the 1908 description restored the missing parts in a fashion similar to Stegosaurus, and Brown likened the result to the extinct armored mammal Glyptodon. In contrast to modern depictions, Brown's stegosaur-like reconstruction showed robust forelimbs, a strongly arched back, a pelvis with prongs projecting forwards from the ilium and pubis, as well as a short, drooping tail without a tail club, which was unknown at the time. Brown also reconstructed the armor plates in parallel rows running down the back; this arrangement was purely hypothetical. Brown's reconstruction became highly influential, and restorations of the animal based on his diagram were published as late as the 1980s. In a 1908 review of Brown's Ankylosaurus description, the American paleontologist Samuel Wendell Williston criticized the skeletal reconstruction as being based on too few remains, and claimed that Ankylosaurus was merely a synonym of the genus Stegopelta, which Williston had named in 1905. Williston also stated that a skeletal reconstruction of the related Polacanthus by Hungarian paleontologist Franz Nopcsa was a better example of how ankylosaurs would have appeared in life. The claim of synonymy was not accepted by other researchers, and the two genera are now considered distinct.
Brown had collected 77 osteoderms while excavating a Tyrannosaurus specimen in the Lance Formation of Wyoming in 1900. He mentioned these osteoderms (specimen AMNH 5866) in his description of Ankylosaurus but thought they belonged to the Tyrannosaurus instead. Paleontologist Henry Fairfield Osborn also expressed this view when he described the Tyrannosaurus specimen as the now synonymous genus Dynamosaurus in 1905. More recent examination has shown them to be similar to those of Ankylosaurus; it seems that Brown had compared them with some Euoplocephalus osteoderms, which had been erroneously cataloged as belonging to Ankylosaurus at the AMNH.
In 1910, another AMNH expedition led by Brown discovered an Ankylosaurus specimen (AMNH 5214) in the Scollard Formation by the Red Deer River in Alberta, Canada. This specimen included a complete skull, mandibles, the first and only tail club known of this genus, as well as ribs, vertebrae, limb bones, and armor. In 1947 the American fossil collectors Charles M. Sternberg and T. Potter Chamney collected a skull and mandible (specimen CMN 8880, formerly NMC 8880), north of where the 1910 specimen was found. This is the largest-known Ankylosaurus skull, but it is damaged in places. A section of caudal vertebrae (specimen CCM V03) was discovered in the 1960s in the Powder River drainage, Montana, part of the Hell Creek Formation. In addition to these five incomplete specimens, many other isolated osteoderms and teeth have been found.
In 1990, American paleontologist Walter P. Coombs pointed out that the teeth of two skulls assigned to A. magniventris differed from those of the holotype specimen in some details, and though he expressed a "considerate temptation" to name a new species of Ankylosaurus for these, he refrained from doing so, as the range of variation in the species was not completely documented. He also raised the possibility that the two teeth associated with the holotype specimen perhaps did not belong to it, as they were found in matrix within the nasal chambers. The American paleontologist Kenneth Carpenter accepted the teeth as belonging to A. magniventris in 2004, and that all the specimens belonged to the same species, noting that the teeth of other ankylosaurs are highly variable.
Most of the known Ankylosaurus specimens were not scientifically described at length, though several paleontologists planned to do so until Carpenter redescribed the genus in 2004. In 2017 the Canadian paleontologists Victoria M. Arbour and Jordan Mallon redescribed the genus in light of newer ankylosaur discoveries, including elements of the holotype that had not been previously mentioned in the literature (such as parts of the skull and the cervical half-rings). They concluded that though Ankylosaurus is the best-known member of its group, it was bizarre in comparison to related ankylosaurs, and therefore not representative of the group. In spite of its familiarity, it is known from far fewer remains than its closest relatives.
Description
Ankylosaurus was the largest-known ankylosaurine dinosaur and possibly the largest ankylosaurid. In 2004 Carpenter estimated that the individual with the largest-known skull (specimen CMN 8880), which is long and wide, was about long and had a hip height of about . The smallest-known skull (specimen AMNH 5214) is long and wide, and Carpenter estimated that it measured about long and about tall at the hips. The English paleontologist Roger B. J. Benson and colleagues estimated the weight for AMNH 5214 at in 2014.
In 2017, based on comparisons with more complete ankylosaurines, Arbour and Mallon estimated a length of for CMN 8880, and for AMNH 5214. Though the latter is the smallest specimen of Ankylosaurus, its skull is still larger than those of any other ankylosaurins. A few other ankylosaurs reached about in length. Because the vertebrae of AMNH 5214 are not significantly larger than those of other ankylosaurines, Arbour and Mallon considered their upper range estimate of nearly for large Ankylosaurus too long, and suggested a length of instead. Arbour and Mallon estimated a weight of for AMNH 5214, and tentatively estimated the weight of CMN 8880 at .
Skull
The three known Ankylosaurus skulls differ in various details; this is thought to be the result of taphonomy (changes happening during decay and fossilization of the remains) and individual variation. The skull was low and triangular in shape, and wider than it was long; the back of the skull was broad and low. The skull had a broad beak on the premaxillae. The orbits (eye sockets) were almost round to slightly oval and did not face directly sideways because the skull tapered towards the front. The braincase was short and robust, as in other ankylosaurines. Crests above the orbits merged into the upper squamosal horns (their shape has been described as "pyramidal"), which pointed backwards to the sides from the back of the skull. The crest and horn were probably separate elements originally, as seen in the related Pinacosaurus and Euoplocephalus. Below the upper horns, jugal horns were present, which pointed backward and down. The horns may have originally been osteoderms that fused to the skull. The scale-like cranial ornamentation on the surfaces of ankylosaurs skulls is called "", and were the result of remodeling of the skull itself. This obliterated the sutures between skull elements, which is common for adult ankylosaurs. The caputegulum pattern of the skull was variable between specimens, though some details are shared. The caputegulae are named according to their position on the skull, and those of Ankylosaurus include a relatively large, hexagonal (or diamond-shaped) nasal caputegulum at the front of the snout between the nostrils, which had a loreal caputegulum on each side, an anterior and posterior supraorbital caputegulum above each orbit, and a ridge of nuchal caputegulae at the back of the skull.
The snout region of Ankylosaurus was unique among ankylosaurs, and had undergone an "extreme" transformation compared to its relatives. The snout was arched and truncated at the front, and the nostrils were elliptical and were directed downward and outward, unlike in all other known ankylosaurids where they faced obliquely forward or upward. Additionally, the nostrils were not visible from the front because the sinuses were expanded to the sides of the premaxilla bones, to a larger extent than seen in other ankylosaurs. Large loreal caputegulae—strap-like, side osteoderms of the snout—completely roofed the enlarged opening of the nostrils, giving a bulbous appearance. The nostrils also had an intranarial septum, which separated the nasal passage from the sinus. Each side of the snout had five sinuses, four of which expanded into the maxilla bone. The nasal cavities (or chambers) of Ankylosaurus were elongated and separated by a septum at the midline, which divided the inside of the snout into two mirrored halves. The nasal chambers had two openings, including the choanae (internal nostrils), and the air passage was looped. The maxillae expanded to the sides, giving the impression of a bulge, which may have been due to the sinuses inside. The maxillae had a ridge that may have been the attachment site for fleshy cheeks; the presence of cheeks in ornithischians is controversial, but some nodosaurs had armor plates that covered the cheek region, which may have been embedded in the flesh.
Specimen AMNH 5214 has 34–35 dental alveoli (tooth sockets) in the maxilla. The tooth rows in the maxillae of this specimen are about long. Each alveolus had a foramen (opening) near its side where a replacement tooth could be seen. Compared to other ankylosaurs, the mandible of Ankylosaurus was low in proportion to its length, and, when seen from the side, the tooth row was almost straight instead of arched. The mandibles are completely preserved only in the smallest specimen (AMNH 5214) and are about long. The incomplete mandible of the largest specimen (CMN 8880) is the same length. AMNH 5214 has 35 dental alveoli in the left dentary bone () and 36 in the right, for a total of 71. The predentary bone of the tip of the mandibles has not yet been found. Like other ankylosaurs, Ankylosaurus had small, phylliform (leaf-shaped) teeth, which were compressed sideways. The teeth were mostly taller than they were wide, and were very small; their size in proportion to the skull meant that the jaws of Ankylosaurus could accommodate more teeth than other ankylosaurines. The teeth of the largest Ankylosaurus skull are smaller than those of the smallest skull in the absolute sense. Some teeth from behind in the tooth row curved backwards, and tooth crowns were usually flatter on one side than the other. Ankylosaurus teeth are diagnostic and can be distinguished from the teeth of other ankylosaurids based on their smooth sides. The denticles were large, their number ranging from six to eight on the front part of the tooth, and five to seven behind.
Postcranial skeleton
The structure of much of the skeleton of Ankylosaurus, including most of the pelvis, tail, and feet, is still unknown. It was quadrupedal, and its hind limbs were longer than its forelimbs. In the holotype specimen, the scapula (shoulder blade) measures long and was fused with the coracoid (a rectangular bone connected to the lower end of the scapula). It also had entheses (connective tissue) for various muscle attachments. The humerus (upper arm bone) of AMNH 5214 was short, very broad and about long. The femur (thigh bone), also from AMNH 5214, was long and very robust. While the feet of Ankylosaurus are incompletely known, the hindfeet probably had three toes, as is the case in advanced ankylosaurids.
The cervical vertebrae had broad neural spines that increased in height towards the body. The front part of the neural spines had well-developed entheses, which was common among adult dinosaurs, and indicates the presence of large ligaments, which helped support the massive head. The dorsal vertebrae had centra (or bodies) that were short relative to their width, and their neural spines were short and narrow. The dorsal vertebrae were tightly spaced, which limited the downwards movement of the back. The neural spines had ossified (turned to bone) tendons, which also overlapped some of the vertebrae. The ribs of the last four back vertebrae were fused to the and (the structures that articulated the ribs with the vertebrae), and the ribcage was very broad in this part of the body. The caudal vertebrae had centra that were slightly amphicoelous, meaning they were concave on both sides.
Armor
A prominent feature of Ankylosaurus was its armor, consisting of knobs and plates of bone known as osteoderms, or scutes, embedded in the skin. These have not been found in articulation, so their exact placement on the body is unknown, though inferences can be made based on related animals, and various configurations have been proposed. The osteoderms ranged from in diameter to in length, and varied in shape. The osteoderms of Ankylosaurus were generally thin walled and hollowed on the underside. Compared to Euoplocephalus, the osteoderms of Ankylosaurus were smoother. Many smaller osteoderms and ossicles probably occupied the space between the larger ones, as in other ankylosaurids. The osteoderms covering the body were very flat, though with a low keel at one margin. In contrast, the nodosaurid Edmontonia had high keels stretching from one margin to the other on the midline of its osteoderms. Ankylosaurus had some smaller osteoderms with a keel across the midline.
Like other ankylosaurids, Ankylosaurus had (armor plates on the neck), but these are known only from fragments, making their exact arrangement uncertain. Carpenter suggested that when seen from above, the plates would have been paired, creating an inverted V-shape across the neck, with the midline gap probably being filled with small ossicles (round bony scutes) to allow for movement. He believed the width of this armor belt was too wide to have fitted solely on the neck, and that it covered the base of the neck and continued onto the shoulder region. Arbour and the Canadian paleontologist Philip J. Currie disagreed with Carpenter's interpretation in 2015 and pointed out that the cervical half-ring fragments of the holotype specimen did not fit together in the way proposed by Carpenter (though this could be due to breakage). They instead suggested that the fragments represented the remains of two cervical half-rings, which formed two semi-circular plates of armor around the upper part of the neck, as in the closely related Anodontosaurus and Euoplocephalus. Arbour and Mallon elaborated on this idea, describing the shape of these half-rings as "continuous U-shaped yokes" over the upper part of the neck, and suggested that Ankylosaurus had six keeled osteoderms with oval bases on each half-ring.
The first osteoderms behind the second cervical half-ring would have been similar in shape to those in the first half-ring, and the osteoderms on the back probably decreased in diameter hindwards. The largest osteoderms were probably arranged in transverse and longitudinal rows across most of the body, with four or five transverse rows separated by creases in the skin. The osteoderms on the flanks would probably have had a more square outline than those on the back. There may have been four longitudinal rows of osteoderms on the flanks. Unlike some basal ankylosaurs and many nodosaurs, ankylosaurids do not appear to have had co-ossified pelvic shields above their hips. Some osteoderms without keels may have been placed above the hip region of Ankylosaurus, as in Euoplocephalus. Ankylosaurus may have had three or four transverse rows of circular osteoderms over the pelvic region, which were smaller than those on the rest of the body, as in Scolosaurus. Smaller, triangular osteoderms may have been present on the sides of the pelvis. Flattened, pointed plates resemble those on the sides of the tail of Saichania, and may have been distributed similarly on Ankylosaurus. Osteoderms with oval keels could have been placed on the upper side of the tail or the side of the limbs. Compressed, triangular osteoderms found with Ankylosaurus specimens may have been placed on the sides of the pelvis or the tail. Ovoid, keeled, and teardrop-shaped osteoderms are known from Ankylosaurus, and may have been placed on the forelimbs, like those known from Pinacosaurus, but it is unknown whether the hindlimbs bore osteoderms.
The tail club (or tail knob) of Ankylosaurus was composed of two large osteoderms, with a row of small osteoderms at the midline, and two small osteoderms at the tip; these osteoderms obscured the last tail vertebra. As only the tail club of specimen AMNH 5214 is known, the range of variation between individuals is unknown. The tail club of AMNH 5214 is long, wide, and tall. The club of the largest specimen may have been wide. The tail club of Ankylosaurus was semicircular when seen from above, similar to those of Euoplocephalus and Scolosaurus but unlike the pointed club osteoderms of Anodontosaurus or the narrow, elongated club of Dyoplosaurus. The last seven tail vertebrae formed the "handle" of the tail club. These vertebrae were in contact, with no cartilage between them, and were sometimes co-ossified, which made them immobile. Ossified tendons attached to the vertebrae in front of the tail club, and these features together helped strengthen it. The interlocked zygapophyses (articular processes) and neural spines of the handle vertebrae were U-shaped when seen from above, whereas those of most other ankylosaurids are V-shaped, which may be due to the handle of Ankylosaurus being wider. The larger width may indicate that the tail of Ankylosaurus was shorter in relation to its body length than those of other ankylosaurids, or that it had the same proportions but with a smaller club.
Classification
Brown considered Ankylosaurus so distinct that he made it the type genus of a new family, Ankylosauridae, typified by massive, triangular skulls, short necks, stiff backs, broad bodies, and osteoderms. He also classified Palaeoscincus (only known from teeth), and Euoplocephalus (then only known from a partial skull and osteoderms) as part of the family. Due to the fragmentary condition of the remains, Brown was unable to fully distinguish between Euoplocephalus and Ankylosaurus. Having for comparison only a few, incomplete members of the family, he believed the group was part of the suborder Stegosauria. In 1923 Osborn coined the name Ankylosauria, thereby placing the ankylosaurids in their own suborder.
Ankylosauria and Stegosauria are now grouped together within the clade Thyreophora. This group first appeared in the Sinemurian age, and survived for 135 million years until disappearing in the Maastrichtian. They were widespread and inhabited a broad range of environments. As more complete specimens and new genera have been discovered, theories about ankylosaurian interrelatedness have become more complex, and hypotheses have often changed between studies. In addition to Ankylosauridae, Ankylosauria has been divided into the families Nodosauridae, and sometimes Polacanthidae (these families lacked tail clubs). Ankylosaurus is considered part of the subfamily Ankylosaurinae (members of which are called ankylosaurines) within Ankylosauridae. Ankylosaurus appears to be most closely related to Anodontosaurus and Euoplocephalus. The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:
Because Ankylosaurus and other Late Cretaceous North American ankylosaurids were grouped with Asian genera (in a tribe the authors named Ankylosaurini), Arbour and Currie suggested that earlier North American ankylosaurids had gone extinct by the late Albian or Cenomanian ages of the Middle Cretaceous. Ankylosaurids thereafter recolonized North America from Asia during the Campanian or Turonian ages of the Late Cretaceous, and there diversified again, leading to genera such as Ankylosaurus, Anodontosaurus, and Euoplocephalus. The theory explains a 30-million-year gap in the fossil record of North American ankylosaurids between the ages.
Paleobiology
Feeding
Like other ornithischians, Ankylosaurus was herbivorous. Its wide muzzle was adapted for non-selective low-browse cropping, although not to the extent seen in some related genera, especially Euoplocephalus. Though ankylosaurs may not have fed on fibrous and woody plants, they may have had a varied diet, including tough leaves and pulpy fruits. Ankylosaurus probably fed on abundant ferns and low-growing shrubs. Assuming it was endothermic, Ankylosaurus would have eaten of ferns per day, similar to the amount of dry vegetation a large elephant would consume. The requirements for nutrition could have been more effectively met if Ankylosaurus ate fruit, which its small, cusp-like teeth and the shape of its beak seem well adapted for, compared to for example Euoplocephalus. Certain invertebrates, which the small teeth may have been adapted for handling, could also have provided supplemental nutrition.
Fossils of Ankylosaurus teeth exhibit wear on the face of the crown rather than on the tip of the crown, as in nodosaurid ankylosaurs. In 1982 Carpenter ascribed to baby Ankylosaurus two very small teeth that originate from the Lance and Hell Creek Formations and measure in length, respectively. The smaller tooth is heavily worn, leading Carpenter to suggest that ankylosaurids in general or at least the young did not swallow their food whole but employed some sort of chewing. Since adult Ankylosaurus did little chewing of its food, it would have spent less time in the day foraging than an elephant. Based on the broadness of the ribcage, the digestion of unchewed food may have been facilitated by hindgut fermentation like in modern herbivorous lizards, which have several chambers in their enlarged colon.
In 1969, paleontologist Georg Haas concluded that despite the large size of ankylosaur skulls, the associated musculature was relatively weak. He also thought jaw movement was limited to up and down movements. Extrapolating from this, Haas suggested that ankylosaurs ate relatively soft non-abrasive vegetation. Later research on Euoplocephalus indicates that forward and sideways jaw movement was possible in these animals, the skull being able to withstand considerable forces. A 2016 study of the dental occlusion (contact between the teeth) of ankylosaur specimens found that the ability for backwards (palinal) jaw movement evolved independently in different ankylosaur lineages, including Late Cretaceous North American ankylosaurids like Ankylosaurus and Euoplocephalus.
The retracted position of the nostrils of Ankylosaurus were compared to those of fossorial (digging) worm lizards and blind snakes by Arbour and Mallon in 2017, and though it was probably not a burrowing animal, the snout of Ankylosaurus may indicate earth-moving behavior. These factors, as well as the low rate of tooth formation in ankylosaurs compared to other ornithischians, indicate that Ankylosaurus may have been omnivorous (eating both plant and animal matter). It may also (or alternatively) have dug in the ground for roots and tubers. A 2023 study by paleontologist Antonio Ballell and colleagues found that North American ankylosaurids from the latest Cretaceous (including Ankylosaurus) had jaws with low mechanical advantage, whereas those of earlier relatives were high to moderate. These late ankylosaurids also had tooth occlusion and complex biphasal jaw mechanisms, features shared with some Late Cretaceous nodosaurids, but those instead have jaws with high mechanical advantage. This indicates that while the two groups converged in some features, the nodosaurs had higher relative bite force, which suggests diverging jaw mechanics and dietary partitioning between the two.
Airspaces and senses
In 1977, paleontologist Teresa Maryańska proposed that the complex sinuses and nasal cavities of ankylosaurs may have lightened the weight of the skull, housed a nasal gland, or acted as a chamber for vocal resonance. Carpenter rejected these hypotheses, arguing that tetrapod animals make sounds through the larynx, not the nostrils, and that reduction in weight was minimal, as the spaces only accounted for a small percent of the skull volume. He also considered a gland unlikely and noted that the sinuses may not have had any specific function. It has also been suggested that the respiratory passages were used to perform a mammal-like treatment of inhaled air, based on the presence and arrangement of specialized bones.
A 2011 study of the nasal passages of Euoplocephalus by paleontologist Tetsuto Miyashita and colleagues supported their function as a heat and water balancing system, noting the extensive blood vessel system and an increased surface area for the mucosa membrane (used for heat and water exchange in modern animals). The researchers also supported the idea of the loops acting as a resonance chamber, comparable to the elongated nasal passages of saiga antelope and the looping trachea of cranes and swans. Reconstructions of the inner ear suggest adaptation to hearing at low frequencies, such as the low-toned resonant sounds possibly produced by the nasal passages. They disputed the possibility that the looping is related to olfaction (sense of smell) as the olfactory region is pushed to the sides of the main airway.
According to Carpenter, the shape of the nasal chambers of Ankylosaurus indicate that airflow was unidirectional (looping through the lungs during inhalation and exhalation), although it may also have been bidirectional in the posterior nasal chamber, with air directed past the olfactory lobes. The enlarged olfactory region of ankylosaurids indicates a well-developed sense of smell. Though hindwards retraction of the nostrils is seen in aquatic animals and animals with a proboscis, it is unlikely either possibility applies to Ankylosaurus, as the nostrils tend to be reduced or the premaxilla extended. In addition, though the widely separated nostrils may have allowed for stereo-olfaction (where each nostril senses smells from different directions), as has been proposed for the moose, little is known about this feature. The position of the orbits of Ankylosaurus suggest some stereoscopic vision.
Limb movements
Reconstructions of ankylosaur forelimb musculature made by Coombs in 1978 suggest that the forelimbs bore the majority of the animal's weight, and were adapted for high force delivery on the front feet, possibly for food gathering. In addition, Coombs suggested that ankylosaurs may have been capable diggers, though the hoof-like structure of the manus would have limited fossorial activity. Ankylosaurs were likely to have been slow-moving and sluggish animals, though they may have been capable of quick movements when necessary.
Growth
The squamosal horns of the largest Ankylosaurus specimen are blunter than those of the smallest specimen, which is also the case in Euoplocephalus, and this may represent ontogenetic variation (related to growth development). Studies of specimens of Pinacosaurus of different ages found that during ontogenetic development, the ribs of juvenile ankylosaurs fused with their vertebrae. The forelimbs strongly increased in robustness while the hindlimbs did not become larger relative to the rest of the skeleton, further evidence that the arms bore most of the weight. In the cervical half-rings, the underlying bone band developed outgrowths connecting it with the underlying osteoderms, which simultaneously fused to each other. On the skull, the middle bone plates first ossified at the snout and the rear rim, with ossification gradually extending towards the middle regions. On the rest of the body, ossification progressed from the neck backward in the direction of the tail.
Defense
The osteoderms of ankylosaurids were thin in comparison to those of other ankylosaurs, and appear to have been strengthened by randomly distributed cushions of collagen fibers. Structurally similar to Sharpey's fibres, they were embedded directly into the bone tissue, a feature unique to ankylosaurids. This would have provided the ankylosaurids with an armor covering that was both lightweight and highly durable, being resistant to breakage and penetration by the teeth of predators. The palpebral bones over the eyes may have provided additional protection for them. Carpenter suggested in 1982 that the heavily vascularized armor may also have had a role in thermoregulation as in modern crocodilians.
The tail club of Ankylosaurus seems to have been an active defensive weapon, capable of producing enough of an impact to break the bones of an assailant. The tendons of the tail were partially ossified and were not very elastic, allowing great force to be transmitted to the club when it was used as a weapon. Coombs suggested in 1979 that several hindlimb muscles would have controlled the swinging of the tail, and that violent thrusts of the club would have been able to break the metatarsal bones of large theropods.
A 2009 study estimated that ankylosaurids could swing their tails at 100 degrees laterally, and the mainly cancellous clubs would have had a lowered moment of inertia and been effective weapons. The study also found that while adult ankylosaurid tail clubs were capable of breaking bones, those of juveniles were not. Despite the feasibility of tail-swinging, the researchers could not determine whether ankylosaurids used their clubs for defense against potential predators, in intraspecific combat, or both. Other studies have found evidence of ankylosaurids using their tail clubs for intraspecific combat. One specimen of Tarchia showed signs of injury on both the pelvic and tail area and the club was found to be asymmetrical, a sign of being worn down by the strikes.
In 1993, Tony Thulborn proposed that the tail club of ankylosaurids primarily acted as a decoy for the head, as he thought the tail too short and inflexible to have an effective reach; the "dummy head" would lure a predator close to the tail, where it could be struck. Carpenter has rejected this idea, as tail club shape is highly variable among ankylosaurids, even in the same genus.
Paleoenvironment
Ankylosaurus existed between 68 and 66 million years ago, in the final, or Maastrichtian, stage of the Late Cretaceous Period. It was among the last dinosaur genera that appeared before the Cretaceous–Paleogene extinction event. The type specimen is from the Hell Creek Formation of Montana, while other specimens have been found in the Lance and Ferris Formations in Wyoming, the Scollard Formation in Alberta, and the Frenchman Formation in Saskatchewan, all of which date to the end of the Cretaceous.
Fossils of Ankylosaurus are rare in the sediments it is known from, and the distribution of its remains suggests that it was ecologically rare, or restricted to the uplands of the formations, where it would have been less likely to fossilize, rather than the coastal lowlands. Another ankylosaur, a nodosaur referred to as Edmontonia sp., is also found in the same formations, but according to Carpenter, the range of the two genera does not seem to have overlapped. Their remains have so far not been found in the same localities, and the nodosaur appears to have inhabited the lowlands. The narrower muzzle of the nodosaur suggests it had a more selective diet than Ankylosaurus, further indicating ecological separation, whether their range overlapped or not.
With its low center of gravity, Ankylosaurus would have been unable to knock down trees like modern elephants do. It was also incapable of chewing bark and thus unlikely to have practiced bark stripping. As an adult, Ankylosaurus does not appear to have congregated in groups (though some ankylosaurs appear to have congregated when young). It is therefore improbable that Ankylosaurus was able to modify the landscape of its ecosystem in the way elephants do; hadrosaurids may instead have had such an "ecosystem engineer" role.
The formations where Ankylosaurus fossils have been found represent different sections of the western shore of the Western Interior Seaway dividing western and eastern North America during the Cretaceous, a broad coastal plain extending westward from the seaway to the newly formed Rocky Mountains. These formations are composed largely of sandstone and mudstone, which have been attributed to floodplain environments. The regions where Ankylosaurus and other Late Cretaceous ankylosaurs have been found had a warm subtropical/temperate climate, which was monsoonal, had occasional rainfall, tropical storms, and forest fires. In the Hell Creek Formation, many types of plants were supported, primarily angiosperms, with less common conifers, ferns and cycads. An abundance of fossil leaves found at dozens of different sites indicates that the area was largely forested by small trees. Ankylosaurus shared its environment with other dinosaurs that included the ceratopsids Triceratops and Torosaurus, the hypsilophodont Thescelosaurus, the hadrosaurid Edmontosaurus, an indeterminate nodosaur, the pachycephalosaurian Pachycephalosaurus, and the theropods Struthiomimus, Ornithomimus, Pectinodon, and Tyrannosaurus.
Cultural significance
Carpenter noted in 2004 that Ankylosaurus has become the archetypal member of its group, and the best-known ankylosaur in popular culture, perhaps due to a life-sized reconstruction of the animal being featured at the 1964 World's Fair in New York City. Arbour and Mallon called Ankylosaurus an "iconic" dinosaur in 2017, and noted that the World's Fair sculpture, as well as the American artist Rudolph Zallinger's 1947 mural The Age of Reptiles and other later popular depictions, showed Ankylosaurus with a tail club, following the first discovery of the feature in 1910.
Many traditional popular depictions show Ankylosaurus in a squatting posture and with a huge tail club being dragged over the ground. Modern reconstructions show the animal with a more upright limb posture and with the tail held off the ground. Likewise, large spines projecting sideways from the body (similar to those of nodosaurid ankylosaurs) are present in many traditional depictions, but are not known from Ankylosaurus itself. The armor of Ankylosaurus has often been conflated with that of Edmontonia (earlier referred to as Palaeoscincus); in addition to Ankylosaurus being depicted with spikes, Edmontonia has also been depicted with an Ankylosaurus-like tail club (a feature nodosaurids did not have), including in a mural by the American artist Charles R. Knight from 1930. Ankylosaurus has been featured in the Jurassic Park franchise, where they are depicted as attacking with their tails and running, abilities that have been criticized as unlikely by paleontologists.
| Biology and health sciences | Ornitischians | Animals |
983423 | https://en.wikipedia.org/wiki/47%20Tucanae | 47 Tucanae | 47 Tucanae or 47 Tuc (also designated as NGC 104 and Caldwell 106) is a globular cluster located in the constellation Tucana. It is about from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.
47 Tucanae is the second brightest globular cluster after Omega Centauri, and telescopically reveals about ten thousand stars, many appearing within a small dense central core. The cluster may contain an intermediate-mass black hole.
Early history
The cluster was recorded in 1751-2 by Nicolas-Louis de Lacaille, who initially thought it was the nucleus of a bright comet. Lacaille then listed it as "Lac I-1", the first object listed in his deep-sky catalogue. The number "47" was assigned in Allgemeine Beschreibung und Nachweisung der Gestirne nebst Verzeichniss ("General description and verification of the stars and indexes"), compiled by Johann Elert Bode and published in Berlin in 1801. Bode did not observe this cluster himself, but had reordered Lacaille's catalogued stars by constellation in order of right ascension.
In the 19th century, Benjamin Apthorp Gould assigned the Greek letter ξ (Xi) to the cluster to designate it ξ Tucanae, but this was not widely adopted and it is almost universally referred to as 47 Tucanae.
Characteristics
47 Tucanae is the second brightest globular cluster in the sky (after Omega Centauri), and is noted for having a small very bright and dense core. It is one of the most massive globular clusters in the Galaxy, containing millions of stars. The cluster appears roughly the size of the full moon in the sky under ideal conditions. Though it appears adjacent to the Small Magellanic Cloud, the latter is some distant, being over fifteen times farther than 47 Tuc.
A blue giant star with a spectral class of B8III is the brightest star in visible and ultraviolet light, with a luminosity of about 1,100 times that of the Sun, and is aptly known as the "Bright Star". It is a post-AGB star, having passed the asymptotic giant branch phase of its life, and is currently fusing helium. It has an effective temperature of about 10,850 K, and is about 54% the mass of the Sun.
The core of 47 Tuc was the subject of a major survey for planets, using the Hubble Space Telescope to look for partial eclipses of stars by their planets. No planets were found, though ten to fifteen were expected based on the rate of planet discoveries around stars near the Sun. This indicates that planets are relatively rare in globular clusters. A later ground-based survey in the uncrowded outer regions of the cluster also failed to detect planets when several were expected. This strongly indicates that the low metallicity of the environment, rather than the crowding, is responsible.
47 Tucanae contains at least two stellar populations of stars, of different ages or metallicities. The dense core contains a number of exotic stars of scientific interest, including at least 21 blue stragglers. Globular clusters efficiently sort stars by mass, with the most massive stars falling to the center.
47 Tucanae contains hundreds of X-ray sources, including stars with enhanced chromospheric activity due to their presence in binary star systems, cataclysmic variable stars containing white dwarfs accreting from companion stars and low-mass X-ray binaries containing neutron stars that are not currently accreting, but can be observed by the X-rays emitted from the hot surface of the neutron star.
47 Tucanae has 35 known millisecond pulsars, the second largest population of pulsars in any globular cluster, after Terzan 5.
These pulsars are thought to be spun up by the accretion of material from binary companion stars, in a previous X-ray binary phase. The companion of one pulsar in 47 Tucanae, 47 Tuc W, seems to still be transferring mass towards its companion, indicating that this system is completing a transition from being an accreting low-mass X-ray binary to a millisecond pulsar. X-ray emission has been individually detected from most millisecond pulsars in 47 Tucanae with the Chandra X-ray Observatory, likely emission from the neutron star surface, and gamma-ray emission has been detected with the Fermi Gamma-ray Space Telescope from its millisecond pulsar population (making 47 Tucanae the first globular cluster to be detected in gamma-rays).
Possible central black hole
It is not yet clear whether 47 Tucanae hosts a central black hole. Hubble Space Telescope data constrain the mass of any possible black hole at the cluster's center to be less than approximately 1,500 solar masses. However, in February, 2017, astronomers announced that a black hole of some 2,200 solar masses may be located in the cluster; the researchers detected the black hole's signature from the motions and distributions of pulsars in the cluster. Despite this, a recent analysis of an updated and more extensive timing data set on these pulsars provides no solid evidence in favor of the existence of a black hole.
Modern discoveries
In December 2008, Ragbir Bhathal of the University of Western Sydney claimed the detection of a strong laser-like signal from the direction of 47 Tucanae.
In May 2015, the first evidence of the process of mass segregation in this globular cluster was announced. The cluster's Hertzsprung–Russell diagram suggests stars approximately 13 billion years old, which is unusually old.
| Physical sciences | Notable star clusters | Astronomy |
983904 | https://en.wikipedia.org/wiki/NGC%206946 | NGC 6946 | NGC 6946, sometimes referred to as the Fireworks Galaxy, is a face-on intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the northern constellations of Cepheus and Cygnus. Its distance from Earth is about 25.2 million light-years or 7.72 megaparsecs, similar to the distance of M101 (NGC 5457) in the constellation Ursa Major. Both were once considered to be part of the Local Group, but are now known to be among the dozen bright spiral galaxies near the Milky Way but beyond the confines of the Local Group. NGC 6946 lies within the Virgo Supercluster.
The galaxy was discovered by William Herschel on 9 September 1798. Based on an estimation by the Third Reference Catalogue of Bright Galaxies (RC3) in 1991, the galaxy has a D25 B-band isophotal diameter of . It is heavily obscured by interstellar matter due to its location close to the galactic plane of the Milky Way. Due to its prodigious star formation it has been classified as an active starburst galaxy. NGC 6946 has also been classified as a double-barred spiral galaxy, with the inner, smaller bar presumably responsible for funneling gas into its center.
Various unusual celestial objects have been observed within NGC 6946. This includes the so-called 'Red Ellipse' along one of the northern arms that looks like a super-bubble or very large supernova remnant, and which may have been formed by an open cluster containing massive stars. There are also two regions of unusual dark lanes of nebulosity, while within the spiral arms several regions appear devoid of stars and gaseous hydrogen, some spanning up to two kiloparsecs across. A third peculiar object, discovered in 1967, is now known as "Hodge's Complex". This was once thought to be a young supergiant cluster, but in 2017 it was conjectured to be an interacting dwarf galaxy superimposed on NGC 6946.
Supernovae
Ten supernovae have been observed in NGC 6946 in the 20th and early 21st century: SN 1917A, SN 1939C, SN 1948B, SN 1968D, SN 1969P, SN 1980K, SN 2002hh, SN 2004et, SN 2008S, and SN 2017eaw. For this reason, NGC 6946 has sometimes been referred to as the "Fireworks Galaxy". This is about ten times the rate observed in our Milky Way galaxy, even though the Milky Way has twice as many stars as NGC 6946.
On 27 September 2004, the Type II supernova SN 2004et was observed at magnitude 15.2 and rose to a maximum visual magnitude of 12.7. Images taken during the preceding days revealed that the supernova explosion occurred on 22 September. The progenitor of the supernova was identified on earlier images –– only the seventh time that such an event was directly identified with its host star. The red supergiant progenitor had an initial mass of about 15 in an interacting binary system shared with a blue supergiant.
During 2009, a bright star within NGC 6946 flared up over several months to become over one million times as bright as the Sun. Shortly thereafter it faded rapidly. Observations with the Hubble Space Telescope suggest that the star did not survive, although there remains some infrared emission from its position. This is thought to come from debris falling onto a black hole that formed when the star died. This potential black hole-forming star is designated N6946-BH1. The progenitor is believed to have been a yellow hypergiant star.
In May 2017, supernova SN 2017eaw was detected in the northwest region of the galaxy, and light curves obtained over the next 600 days showed that it was a Type II-P. The progenitor was determined to have been a red supergiant, with a mass of around 15.
As of 2017, more supernovae had been seen in NGC 6946 than in any other galaxy, a record that has since been surpassed by NGC 3690.
Gallery
| Physical sciences | Notable galaxies | Astronomy |
2991134 | https://en.wikipedia.org/wiki/Chinese%20water%20dragon | Chinese water dragon | Physignathus cocincinus is a species of agamid lizard native to southern China and mainland Southeast Asia. It is commonly known as the Chinese water dragon, Indochinese water dragon, Asian water dragon, Thai water dragon, or green water dragon.
Chinese water dragons are large diurnal lizards adapted for dense subtropical forests replete with unpolluted streams. They are semi-arboreal, roosting at night on branches overlooking streams, which offer an escape route when the lizards are disturbed. Arthropods are their main source of food, though worms, snails, vertebrates, and plants make up a notable portion of the diet as well. Males are territorial towards each other and bear display features such as crests and jowls. Females are oviparous and reproduce sexually in the wild, though at least one captive Chinese water dragon is known to have reproduced via parthenogenesis. Physignathus cocincinus is related to Australasian lizards in the subfamily Amphibolurinae. One amphibolurine, the Australian water dragon (Intellagama lesuerii) is so anatomically and ecologically similar to Physignathus cocincinus that it was once (erroneously) placed in the same genus.
Feral populations introduced to Hong Kong and Taiwan flourish in high densities despite countermeasures in the latter territory. Their populations are also stable (albeit not widespread) in protected areas of Thailand. However, in the rest of their native range, Chinese water dragons have seen sharp population declines in recent decades. They are listed as a Vulnerable species at risk of extinction in the future, based on current trends. The largest threat to the species is overharvesting for meat and the pet trade. Their meat is in high demand in Vietnam, and captive breeding is currently incapable of replacing wild collection by hunters and poachers. Due to their charismatic appearance, captured Chinese water dragons are sold as pets for both local and international markets. Yearly exports to the European Union and the United States number in the tens of thousands, all of which are taken from wild populations. Habitat loss is another source of pressure, as undisturbed streamside forest is converted into cropland or subjected to illegal logging and other human activities.
Taxonomy
The species and genus were first described by Georges Cuvier in 1829. Cuvier's original spelling, Phyhignat,us cocincinus, is likely a printing error. The epithet cocincinus is from the French term , for the type locality Cochin-china (an exonym of Vietnam).
During the 19th and 20th centuries, several other species of agamid lizards were placed in Cuvier's genus Physignathus. These have been reclassified into separate genera, leaving Physignathus with only the original species P. cocincinus remaining. For example, the Australian water dragon (Intellagama lesueurii) was known as Physignathus lesueurii for much of its history.
According to most genetic analyses, Physignathus cocincinus is the sister taxon or the most basal (earliest branching) species of the agamid subfamily Amphibolurinae. All other amphibolurines are native to Australia or New Guinea, including bearded dragons (Pogona spp.), the frilled lizard (Chlamydosaurus kingii), the thorny devil (Moloch horridus), the Australian water dragon, and many others. A 2000 paper estimated that Physignathus cocincinus diverged from the Australasian amphibolurines up to 120 million years ago, though subsequent studies support a more recent divergence, around 30 million years ago.
Description
Adult Chinese water dragons are large and robust lizards; males can grow up to 90 cm (3 feet) in total length, including the tail. The tail is very long, exceeding 70% of the total body length. The maximum snout-vent length (tail excluded) is about 25 cm (9.8 inches) in males and 20 cm (7.9 inches) in females. The body and tail are compressed (taller than wide) while the limbs are long and muscular, each ending at five sharp claws. In both sexes, a fringe of enlarged scales runs down the length of the spine. The tympanum (eardrum) is partially exposed, with its rim covered by scales. There is a row of 8 or 9 large white plate-like scales on the edge of the lower jaw, below the infralabials (the scale row of the lower lip).
Chinese water dragons show distinct sexual dimorphism; the males are heavier (up to 0.6 kg or 1.3 lbs) and have prominent display features. An arched crest extends along the rear of the neck onto the back, and another low crest is present at the base of the tail. The head is larger and more triangular, while the cheeks are swollen into jowls with pale tubercles (prominent pointed scales). There is no dewlap, unlike anoles and iguanas. Males have a functional series of femoral pores on the underside of the thigh, while in females these pores are little more than subtle indentations. Females reach a maximum weight 0.25 kg (0.55 lb), with a smaller head and lower crests.
Coloration is usually a shade of bright green, though they can take on a brown or grey hue when stressed. In juveniles, the body has vibrant green or turquoise diagonal stripes, which may fade with maturity. Most of the tail is ornamented with thick bands of alternating light green and dark brown. In some individuals a dark stripe stretches between the eye and the ear. In most areas the undersides are pale in color, but the throat takes on a more colorful shade of yellow or orange, especially in adult males. Scales on the cheek and lower jaw may acquire a blue or pink coloration in adults.
Distribution
Native range
Chinese water dragons are native to the subtropical forests of southern China (Guangdong, Guangxi, and Yunnan provinces) and Southeast Asia (Vietnam, Laos, portions of Cambodia, eastern Thailand). There are also unconfirmed reports from Myanmar.
Introduced populations
An introduced population of Chinese water dragons have established themselves in Hong Kong, probably from released pet animals. The first reports came from Tsing Yi Island in 2004, though the Hong Kong population likely originated from several releases. Since 2010, another breeding population has been established in New Taipei City, Taiwan. Hundreds of the lizards were culled from 2013 to 2017 over concerns about their impact on native Taiwanese wildlife. Introduced individuals (but not breeding populations) have also been reported from Malaysia and Florida.
Habitat
Chinese water dragons are most commonly found within dense closed evergreen forest along the banks of freshwater streams. They live in a humid climate with mild seasons: average humidity levels of 40–80% and temperatures ranging from 80–90 °F (26–32 °C). Their reliance on undisturbed forest streams indicates that, despite their wide extent of occurrence in southeast Asia, Chinese water dragons are a geographically restricted species. They can be found between elevations of around 50 meters (164 ft) and 820 meters (2690 ft), though their density and abundance decline strongly above around 270 meters (885 ft).
Despite their preference for undisturbed habitat, Chinese water dragons are common in the urban parks of Hong Kong. Nevertheless, they show a systematic preference for areas with streamside boulders, taller trees, and a denser canopy. Though all sampled individuals have streams within their territory, less than half of first-hand recordings occur within close proximity (< 5 meters) to a stream. Males prefer to defend wide or deep streams while female territories occupy more dry land. Rocks and concrete structures are frequented for basking spots. Orchards are avoided, since they offer no benefits for protection (relative to dense forests) or heat retention (relative to concrete).
Behavior and ecology
Chinese water dragons are diurnal (active during the day) and forage for prey within small territories in the morning and midday. They are also semi-arboreal (spending much of their time in trees or plants). Adult males in particular tend to rest during the night on tree limbs overlooking streams. If threatened, a Chinese water dragon will leap or run to the nearest stream and either swim to safety or remain submerged for up to 90 minutes.
In Hong Kong, the average territory size is about 1800 m2, with a small daily range of about 5 meters on average. Male territories generally do not overlap with each other, arguing that males are much more territorial than females. Movement and range patterns appear to be similar between the hot and wet summer and the relatively cool and dry winter, unlike most other subtropical reptiles. This may be an unintentional artefact of the fact that Hong Kong's dry season during the study interval (2015–2016) was unusually warm and wet. Captive male water dragons are very aggressive towards each other while females and juveniles are more tolerant.
Diet
Chinese water dragons are omnivorous and will readily supplement their diet with non-toxic vegetables or fruits in captivity. Nevertheless, their diet consists mainly of insects with occasional small vertebrates, eggs, and snails. Introduced Chinese water dragons in Taiwan are known to prey on native lizards, frogs, snakes, and mice.
According to a 2018 survey in Central Vietnam, Chinese water dragons persist on a diverse variety of terrestrial invertebrates. Termites, ants, orthopterans (grasshoppers and crickets), earthworms, and spiders all make up a significant portion of the diet, along with insect larvae, snails, and various other prey items. Plant material was eaten very rarely by the subjects of this study, though other accounts testify that plants make up a significant portion of the diet in the wild.
Reproduction and life history
Chinese water dragons are oviparous, with a clutch of 5 to 16 eggs buried in sandy riverbanks near the end of the dry winter. The eggs hatch two or three months later in the early part of the wet summer. Maturity is met within the first year, and the generation length is about 6 years. Captive females may breed several times per year. Healthy captive Chinese water dragons have a life expectancy of 10 to 15 years, though some can exceed 20 years of age.
Though they reproduce sexually in the wild, there is one reported case of facultative parthenogenesis in a captive individual. A female housed at the Smithsonian National Zoo produced viable offspring in 2016 and 2018, along with numerous unfertilized and nonviable eggs. The two surviving offspring are homozygous or hemizygous at seven particular microsatellite loci in the genome. This condition would be nearly impossible if sexual reproduction was involved, since at least a few of the seven microsatellite loci would be expected to be heterozygous. Physignathus cocincinus is the only agamid known to reproduce via parthenogenesis, though the low hatch rate suggests that this is an accidental occurrence rather than an ingrained evolutionary strategy.
Threats and conservation
Though locally abundant in some areas, the Chinese water dragon faces persistent unrestrained threats and a steadily declining wild population. It is listed as Vulnerable in Vietnamese conservation lists, and Endangered in Thailand and China. On an international scale, the IUCN has rated it as a Vulnerable species since 2017. In accordance with a 2022 proposal, the Chinese water dragon has been listed on CITES Appendix II (requiring a CITES-approved permit for export) since 2023.
Population dynamics
At one site in Cambodia the species experienced a 50% population decline in 18 years, while a 2007 estimate considered the entire Vietnamese population to have declined by 20% over the previous decade. Based on these estimates, the species as a whole may be declining by 30% every 18 years.
A 2017 population survey in Thua Thien Hue Province, Vietnam estimated that up to 250 individuals in total were present at the 11 sampled sites (combined). This is far below the several thousand expected to sustain long-term genetic diversity for a species restrained to narrow riparian habitats. Sites sampled in June 2017 show a slightly lower population and a higher relative proportion of females and sub-adults relative to the same sites in April 2017. Adults were uncommon in both months while juveniles were most common in April, maturing into a large sub-adult cohort by June. Chinese water dragons in Thua Thien Hue occur at moderate to high densities, up to 2.6 per 100 meters in April 2017.
Somewhat different patterns were observed in a 2014–2016 survey in Northern Vietnam. In disturbed areas, Chinese water dragons occur at very low densities (as low as 0.17 per 100 meters in 2015), and adults make up to a third of the population. Several previously reported populations were probably extirpated, as individuals could not be found at 8 of the 15 investigated stream transects. Introduced populations in Hong Kong have a much higher population density (about 114 per 100 meters) than native Vietnamese populations.
Hunting and the pet trade
The most severe threat to the species is harvesting for meat and the pet trade. According to a series of 2016 interviews with 21 rural hunter groups, water dragons are a frequent and easy target of traps and hand collecting throughout Thua Thien Hue. Hunting pressure is greatest in May and June, with adult males prioritized due to their large size and conspicuous appearance. This agrees with the decreasing proportion of adult males found in June compared to April. Water dragon meat is typically sold to local restaurants, while eggs are stored in rice wine to be used as traditional medicine. Skins and leather are also traded and exported.
Wild water dragons are captured and sold as pets on social media platforms for both Vietnamese customers and the international markets of Europe and the United States. In Vietnam, about five times as many Chinese water dragons are sold for meat compared to those sold as pets. Exports to Europe began in 1975 and have accelerated in recent decades. From 2010 to 2018, a stable average of around 7,000 live Chinese water dragons per year were exported to the European Union. Approximately 89% came from Vietnam, though information on their production (wild caught or captive bred) is available for fewer than 13% of recorded exports to Europe.
Exports to the United States are even higher despite recent declines: an average of 81,000 per year from 2002 to 2011, and around 48,000 per year from 2013 to 2017. Practically all water dragons exported to the United States are Vietnamese in origin. At least 95% are wild caught while around 3% are reportedly captive bred in Vietnam. It is probable that some individuals sourced from Vietnam were actually collected from other nations, simply using the ports of Vietnam as a transit hub. Captive breeding is a viable but limited conservation strategy; Chinese water dragons breed readily in captivity, though not at a high enough rate to counteract demand. There is no direct evidence that captive breeding programs in Vietnam are in operation, despite claims of captive-bred exports.
Habitat loss
A smaller threat, though still impactful, is degradation or removal of the forested stream habitats which water dragons rely on. In Thua Thien Hue, illegal logging and a major highway construction project are likely partially responsible for losses in the Nam Dong and A Luoi districts. These pressures are less prevalent in the uplands of Phong Dien district, which seems to not experience the same degree of population decline. Logging and expansion of agricultural and tourism infrastructure also contribute to the paucity of suitable habitats in Northern Vietnam. Coal mining, stream pollution, and climate change may also threaten the species, as reported for ecologically similar reptiles in the region, such as the Chinese crocodile lizard (Shinisaurus crocodilurus).
Despite its common name, the Chinese water dragon is exceedingly rare in China, where it is threatened by dam construction on top of the same pressures as the Vietnamese populations. Suitably undeveloped habitats are uncommon in Cambodia and Laos. The few Chinese water dragons present in Thailand are stable and locally abundant thanks to their range lining up with protected areas such as Khao Yai National Park and Namtok Phlio National Park.
Gallery
Wild individuals
Captive individuals
| Biology and health sciences | Iguania | Animals |
2992637 | https://en.wikipedia.org/wiki/Relative%20dating | Relative dating | Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e., estimated age). In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials. Though relative dating can only determine the sequential order in which a series of events occurred, not when they occurred, it remains a useful technique. Relative dating by biostratigraphy is the preferred method in paleontology and is, in some respects, more accurate. The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.
Geology
The regular order of the occurrence of fossils in rock layers was discovered around 1800 by William Smith. While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers. As he continued his job as a surveyor, he found the same patterns across England. He also found that certain animals were in only certain layers and that they were in the same layers all across England. Due to that discovery, Smith was able to recognize the order that the rocks were formed. Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.
Principles of relative dating
Methods for relative dating were developed when geology first emerged as a natural science in the 18th century. Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.
Uniformitarianism
The principle of Uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time. A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."
Intrusive relationships
The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes.
Cross-cutting relationships
The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault.
Inclusions and components
The principle of inclusions and components explains that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them.
Original horizontality
The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).
Superposition
The law of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. This is because it is not possible for a younger layer to slip beneath a layer previously deposited. The only disturbance that the layers experience is bioturbation, in which animals and/or plants move things in the layers. however, this process is not enough to allow the layers to change their positions. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.
Faunal succession
The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils may be found globally at the same time.
Lateral continuity
The principle of lateral continuity states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
Layers of sediment do not extend indefinitely; rather, the limits can be recognized and are controlled by the amount and type of sediment available and the size and shape of the sedimentary basin. Sediment will continue to be transported to an area and it will eventually be deposited. However, the layer of that material will become thinner as the amount of material lessens away from the source.
Often, coarser-grained material can no longer be transported to an area because the transporting medium has insufficient energy to carry it to that location. In its place, the particles that settle from the transporting medium will be finer-grained, and there will be a lateral transition from coarser- to finer-grained material. The lateral variation in sediment within a stratum is known as sedimentary facies.
If sufficient sedimentary material is available, it will be deposited up to the limits of the sedimentary basin. Often, the sedimentary basin is within rocks that are very different from the sediments that are being deposited, in which the lateral limits of the sedimentary layer will be marked by an abrupt change in rock type.
Inclusions of igneous rocks
Melt inclusions are small parcels or "blobs" of molten rock that are trapped within crystals that grow in the magmas that form igneous rocks. In many respects they are analogous to fluid inclusions. Melt inclusions are generally small – most are less than 100 micrometres across (a micrometre is one thousandth of a millimeter, or about 0.00004 inches). Nevertheless, they can provide an abundance of useful information. Using microscopic observations and a range of chemical microanalysis techniques geochemists and igneous petrologists can obtain a range of useful information from melt inclusions. Two of the most common uses of melt inclusions are to study the compositions of magmas present early in the history of specific magma systems. This is because inclusions can act like "fossils" – trapping and preserving these early melts before they are modified by later igneous processes. In addition, because they are trapped at high pressures many melt inclusions also provide important information about the contents of volatile elements (such as H2O, CO2, S and Cl) that drive explosive volcanic eruptions.
Sorby (1858) was the first to document microscopic melt inclusions in crystals. The study of melt inclusions has been driven more recently by the development of sophisticated chemical analysis techniques. Scientists from the former Soviet Union lead the study of melt inclusions in the decades after World War II (Sobolev and Kostyuk, 1975), and developed methods for heating melt inclusions under a microscope, so changes could be directly observed.
Although they are small, melt inclusions may contain a number of different constituents, including glass (which represents magma that has been quenched by rapid cooling), small crystals and a separate vapour-rich bubble. They occur in most of the crystals found in igneous rocks and are common in the minerals quartz, feldspar, olivine and pyroxene. The formation of melt inclusions appears to be a normal part of the crystallization of minerals within magmas, and they can be found in both volcanic and plutonic rocks.
Included fragments
The law of included fragments is a method of relative dating in geology. Essentially, this law states that clasts in a rock are older than the rock itself. One example of this is a xenolith, which is a fragment of country rock that fell into passing magma as a result of stoping. Another example is a derived fossil, which is a fossil that has been eroded from an older bed and redeposited into a younger one.
This is a restatement of Charles Lyell's original principle of inclusions and components from his 1830 to 1833 multi-volume Principles of Geology, which states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows and are incorporated later to cool in the matrix. As a result, xenoliths are older than the rock which contains them.
Planetology
Relative dating is used to determine the order of events on Solar System objects other than Earth; for decades, planetary scientists have used it to decipher the development of bodies in the Solar System, particularly in the vast majority of cases for which we have no surface samples. Many of the same principles are applied. For example, if a valley is formed inside an impact crater, the valley must be younger than the crater.
Craters are very useful in relative dating; as a general rule, the younger a planetary surface is, the fewer craters it has. If long-term cratering rates are known to enough precision, crude absolute dates can be applied based on craters alone; however, cratering rates outside the Earth-Moon system are poorly known.
Archaeology
Relative dating methods in archaeology are similar to some of those applied in geology. The principles of typology can be compared to the biostratigraphic approach in geology.
| Physical sciences | Geochronology | Earth science |
2996328 | https://en.wikipedia.org/wiki/Belostomatidae | Belostomatidae | Belostomatidae is a family of freshwater hemipteran insects known as giant water bugs or colloquially as toe-biters, Indian toe-biters, electric-light bugs (because they fly to lights in large numbers), alligator ticks, or alligator fleas (in Florida). They are the largest insects in the order Hemiptera. There are about 170 species found in freshwater habitats worldwide, with more than 110 in the Neotropics, more than 20 in Africa, almost as many in the Nearctic, and far fewer elsewhere. These predators are typically encountered in freshwater ponds, marshes and slow-flowing streams. Most species are at least long, although smaller species, down to , also exist. The largest are members of the genus Lethocerus, which can exceed and nearly reach the length of some of the largest beetles in the world. Giant water bugs are a popular food in parts of Asia.
The oldest fossil member of this family is Triassonepa from the Late Triassic-aged Cow Branch Formation of Virginia & North Carolina, USA.
Morphology
Belostomatids have a flattened, obovoid to ovoid-elongate body, and usually the legs are flattened. The head features two large compound eyes, but lacks ocelli, contrasting with many hemipterans. Short antennae are tucked in grooves behind the eyes. A short breathing tube can be retracted into its abdomen. Adults cannot breathe under water, so must periodically place the breathing tube at the surface for air (similar to a snorkel).
Their hind tarsi have two apical claws. The frontal legs are modified into raptorial appendages that they use to grab their prey, except in the African Limnogeton, which has "normal" forelegs and is a specialized snail-eater. Once caught, the prey are stabbed with their proboscis and a powerful proteolytic saliva is injected, allowing the Belostomatid to suck out the liquefied remains. Wing pads can be seen from the dorsal view. While the members of the subfamily Lethocerinae can disperse by flying, other species, including Abedus herberti, have a greatly reduced flight apparatus and are flightless. Giant Water Bugs exhibit muscle regression as they develop from nymphs to adults, adapting their musculature for a more energy-efficient predatory lifestyle, which may influence their hunting strategies and ecological interactions.
Subfamilies and genera
BioLib lists three extant subfamilies and a number of fossil taxa:
Belostomatinae
Auth. Leach, 1815
Abedus Stål, 1862
Appasus Amyot & Serville, 1843
Belostoma Latreille, 1807
Diplonychus Laporte de Castelnau, 1833 (synonym Sphaerodema Laporte, 1833)
Hydrocyrius Spinola, 1850 (synonym Poissonia Brown, 1948)
Limnogeton Mayr, 1853
Weberiella De Carlo, 1966
Fossil genera
Horvathiniinae
Auth. Lauck & Menke, 1961; South America
Horvathinia Montandon, 1911
Lethocerinae
Auth. Lauck & Menke, 1961
Benacus Stål, 1861
Kirkaldyia Montandon, 1909
Lethocerus Mayr, 1853
Fossil taxa
subfamily Stygeonepinae Popov, 1971 †
Aenictobelostoma Polhemus, 2000 †
Belostomates Schöberlin, 1888 †
Lethopterus Popov, 1989 †
Manocerus Zhang, 1989 †
Scarabaeides Germar, 1839 †
Triassonepa Criscione & Grimaldi, 2017 †
Habits
Feeding and defense
Belostomatids are aggressive predators that stalk, capture, and feed on fish, amphibians, as well as aquatic invertebrates such as snails and crustaceans. The largest species have also been found to capture and feed on baby turtles and water snakes. They often lie motionless at the bottom of a body of water, attached to various objects, where they wait for prey to come near. They then strike, injecting a venomous digestive saliva with their rostrum. Although their sting is excruciatingly painful, it is of no medical significance. Occasionally, when encountered by a larger animal or a human, they have been known to "play dead" and most species can emit a fluid from their anus. Due to this, they are assumed dead by humans only to later "come alive" with painful results.
Breeding
Belostomatids show paternal care and these aspects have been studied extensively, among others involving the North American Belostoma flumineum and the East Asian Lethocerus (Kirkaldyia) deyrollei. In species of the subfamily Belostomatinae, the eggs are typically laid on the male's wings and carried until they hatch. The male cannot mate during this period. The males invest considerable time and energy in reproduction and females take the role of actively finding males to mate. This role reversal matches the predictions of R. L. Trivers' parental investment theory. In the subfamily Lethocerinae, the eggs are laid on emergent vegetation and guarded by the male.
In Asian cuisine
Belostomatids can be found for sale in markets mainly in Southeast Asia involving the species Lethocerus indicus. In Southeast Asia they are often collected for this purpose using large floating traps on ponds, set with black lights to attract the bugs. Adults fly at night, like many aquatic insects, and are attracted to lights during the breeding season.
| Biology and health sciences | Hemiptera (true bugs) | Animals |
7143953 | https://en.wikipedia.org/wiki/Antiparasitic | Antiparasitic | Antiparasitics are a class of medications which are indicated for the treatment of parasitic diseases, such as those caused by helminths, amoeba, ectoparasites, parasitic fungi, and protozoa, among others. Antiparasitics target the parasitic agents of the infections by destroying them or inhibiting their growth; they are usually effective against a limited number of parasites within a particular class. Antiparasitics are one of the antimicrobial drugs which include antibiotics that target bacteria, and antifungals that target fungi. They may be administered orally, intravenously or topically. Overuse or misuse of antiparasitics can lead to the development of antimicrobial resistance.
Broad-spectrum antiparasitics, analogous to broad-spectrum antibiotics for bacteria, are antiparasitic drugs with efficacy in treating a wide range of parasitic infections caused by parasites from different classes.
Types
Broad-spectrum
Nitazoxanide
Antiprotozoals
Melarsoprol (for treatment of sleeping sickness caused by Trypanosoma brucei)
Eflornithine (for sleeping sickness)
Metronidazole (for vaginitis caused by Trichomonas)
Tinidazole (for intestinal infections caused by Giardia lamblia)
Miltefosine (for the treatment of visceral and cutaneous leishmaniasis, currently undergoing investigation for Chagas disease)
Antihelminthic
Antinematodes
Mebendazole (for most nematode infections)
Pyrantel pamoate (for most nematode infections)
Thiabendazole (for roundworm infections)
Diethylcarbamazine (for treatment of Lymphatic filariasis)
Ivermectin (for prevention of river blindness)
Fenbendazole
Anticestodes
Niclosamide (for tapeworm infections)
Praziquantel (for tapeworm infections)
Albendazole (broad spectrum)
Antitrematodes
[Praziquantel]
Antiamoebics
Rifampin
Amphotericin B
Antifungals
Fumagillin (for microsporidiosis)
Medical uses
Antiparasitics treat parasitic diseases, which impact an estimated 2 billion people.
Administration
Antiparastics may be given via a variety of routes depending on the specific medication, including oral, topical, and intravenous.
Resistance to antiparasitics has been a growing concern, especially in veterinary medicine. The Egg hatch assay can be used to determine whether a parasite causing an infection has become resistant to standard drug treatments.
Drug development history
Early antiparasitics were ineffective, frequently toxic to patients, and difficult to administer due to the difficulty in distinguishing between the host and the parasite.
Between 1975 and 1999 only 13 of 1,300 new drugs were antiparasitics, which raised concerns that insufficient incentives existed to drive development of new treatments for diseases that disproportionately target low-income countries. This led to new public sector and public-private partnerships (PPPs), including investment by the Bill and Melinda Gates Foundation. Between 2000 and 2005, twenty new antiparasitic agents were developed or in development. Metal-containing compounds are the subject of another avenue of approach.
Research
In the last decades, triazolopyrimidines and their metal complexes have been looked at as an alternative drug to the existing commercial antimonials, searching for a decrease in side effects and the development of parasite drug resistance.
| Biology and health sciences | Antiparasitic | Health |
7149361 | https://en.wikipedia.org/wiki/Regular%20dodecahedron | Regular dodecahedron | A regular dodecahedron or pentagonal dodecahedron is a dodecahedron composed of regular pentagonal faces, three meeting at each vertex. It is an example of Platonic solids, described as cosmic stellation by Plato in his dialogues, and it was used as part of Solar System proposed by Johannes Kepler. However, the regular dodecahedron, including the other Platonic solids, has already been described by other philosophers since antiquity.
The regular dodecahedron is the family of truncated trapezohedron because it is the result of truncating axial vertices of a pentagonal trapezohedron. It is also a Goldberg polyhedron because it is the initial polyhedron to construct new polyhedrons by the process of chamfering. It has a relation with other Platonic solids, one of them is the regular icosahedron as its dual polyhedron. Other new polyhedrons can be constructed by using regular dodecahedron.
The regular dodecahedron's metric properties and construction are associated with the golden ratio. The regular dodecahedron can be found in many popular cultures: Roman dodecahedron, the children's story, toys, and painting arts. It can also be found in nature and supramolecules, as well as the shape of the universe. The skeleton of a regular dodecahedron can be represented as the graph called the dodecahedral graph, a Platonic graph. Its property of the Hamiltonian, a path visits all of its vertices exactly once, can be found in a toy called icosian game.
As a Platonic solid
The regular dodecahedron is a polyhedron with twelve pentagonal faces, thirty edges, and twenty vertices. It is one of the Platonic solids, a set of polyhedrons in which the faces are regular polygons that are congruent and the same number of faces meet at a vertex. This set of polyhedrons is named after Plato. In Theaetetus, a dialogue of Plato, Plato hypothesized that the classical elements were made of the five uniform regular solids. Plato described the regular dodecahedron, obscurely remarked, "...the god used [it] for arranging the constellations on the whole heaven". Timaeus, as a personage of Plato's dialogue, associates the other four Platonic solids—regular tetrahedron, cube, regular octahedron, and regular icosahedron—with the four classical elements, adding that there is a fifth solid pattern which, though commonly associated with the regular dodecahedron, is never directly mentioned as such; "this God used in the delineation of the universe." Aristotle also postulated that the heavens were made of a fifth element, which he called aithêr (aether in Latin, ether in American English).
Following its attribution with nature by Plato, Johannes Kepler in his Harmonices Mundi sketched each of the Platonic solids, one of them is a regular dodecahedron. In his Mysterium Cosmographicum, Kepler also proposed the Solar System by using the Platonic solids setting into another one and separating them with six spheres resembling the six planets. The ordered solids started from the innermost to the outermost: regular octahedron, regular icosahedron, regular dodecahedron, regular tetrahedron, and cube.
Many antiquity philosophers described the regular dodecahedron, including the rest of the Platonic solids. Theaetetus gave a mathematical description of all five and may have been responsible for the first known proof that no other convex regular polyhedra exist. Euclid completely mathematically described the Platonic solids in the Elements, the last book (Book XIII) of which is devoted to their properties. Propositions 13–17 in Book XIII describe the construction of the tetrahedron, octahedron, cube, icosahedron, and dodecahedron in that order. For each solid, Euclid finds the ratio of the diameter of the circumscribed sphere to the edge length. In Proposition 18 he argues that there are no further convex regular polyhedra. Iamblichus states that Hippasus, a Pythagorean, perished in the sea, because he boasted that he first divulged "the sphere with the twelve pentagons".
Relation to the regular icosahedron
The dual polyhedron of a dodecahedron is the regular icosahedron. One property of the dual polyhedron generally is that the original polyhedron and its dual share the same three-dimensional symmetry group. In the case of the regular dodecahedron, it has the same symmetry as the regular icosahedron, the icosahedral symmetry . The regular dodecahedron has ten three-fold axes passing through pairs of opposite vertices, six five-fold axes passing through the opposite faces centers, and fifteen two-fold axes passing through the opposite sides midpoints.
When a regular dodecahedron is inscribed in a sphere, it occupies more of the sphere's volume (66.49%) than an icosahedron inscribed in the same sphere (60.55%). The resulting of both spheres' volumes initially began from the problem by ancient Greeks, determining which of two shapes has a larger volume: an icosahedron inscribed in a sphere, or a dodecahedron inscribed in the same sphere. The problem was solved by Hero of Alexandria, Pappus of Alexandria, and Fibonacci, among others. Apollonius of Perga discovered the curious result that the ratio of volumes of these two shapes is the same as the ratio of their surface areas. Both volumes have formulas involving the golden ratio but are taken to different powers.
Golden rectangle may also related to both regular icosahedron and regular dodecahedron. The regular icosahedron can be constructed by intersecting three golden rectangles perpendicularly, arranged in two-by-two orthogonal, and connecting each of the golden rectangle's vertices with a segment line. There are 12 regular icosahedron vertices, considered as the center of 12 regular dodecahedron faces.
Relation to the regular tetrahedron
As two opposing tetrahedra can be inscribed in a cube, and five cubes can be inscribed in a dodecahedron, ten tetrahedra in five cubes can be inscribed in a dodecahedron: two opposing sets of five, with each set covering all 20 vertices and each vertex in two tetrahedra (one from each set, but not the opposing pair). As quoted by ,
Configuration matrix
The configuration matrix is a matrix in which the rows and columns correspond to the elements of a polyhedron as in the vertices, edges, and faces. The diagonal of a matrix denotes the number of each element that appears in a polyhedron, whereas the non-diagonal of a matrix denotes the number of the column's elements that occur in or at the row's element. The regular dodecahedron can be represented in the following matrix:
Relation to the golden ratio
The golden ratio is the ratio between two numbers equal to the ratio of their sum to the larger of the two quantities. It is one of two roots of a polynomial, expressed as . The golden ratio can be applied to the regular dodecahedron's metric properties, as well as to construct the regular dodecahedron.
The surface area and the volume of a regular dodecahedron of edge length are:
The following Cartesian coordinates define the twenty vertices of a regular dodecahedron centered at the origin and suitably scaled and oriented:
If the edge length of a regular dodecahedron is , the radius of a circumscribed sphere (one that touches the regular dodecahedron at all vertices), the radius of an inscribed sphere (tangent to each of the regular dodecahedron's faces), and the midradius (one that touches the middle of each edge) are:
Given a regular dodecahedron of edge length one, is the radius of a circumscribing sphere about a cube of edge length , and is the apothem of a regular pentagon of edge length .
The dihedral angle of a regular dodecahedron between every two adjacent pentagonal faces is , approximately 116.565°.
Other related geometric objects
The regular dodecahedron can be interpreted as a truncated trapezohedron. It is the set of polyhedrons that can be constructed by truncating the two axial vertices of a trapezohedron. Here, the regular dodecahedron is constructed by truncating the pentagonal trapezohedron.
The regular dodecahedron can be interpreted as the Goldberg polyhedron. It is a set of polyhedrons containing hexagonal and pentagonal faces. Other than two Platonic solids—tetrahedron and cube—the regular dodecahedron is the initial of Goldberg polyhedron construction, and the next polyhedron is resulted by truncating all of its edges, a process called chamfer. This process can be continuously repeated, resulting in more new Goldberg's polyhedrons. These polyhedrons are classified as the first class of a Goldberg polyhedron.
The stellations of the regular dodecahedron make up three of the four Kepler–Poinsot polyhedra. The first stellation of a regular dodecahedron is constructed by attaching its layer with pentagonal pyramids, forming a small stellated dodecahedron. The second stellation is by attaching the small stellated dodecahedron with wedges, forming a great dodecahedron. The third stellation is by attaching the great dodecahedron with the sharp triangular pyramids, forming a great stellated dodecahedron.
Appearances
In visual arts
Regular dodecahedra have been used as dice and probably also as divinatory devices. During the Hellenistic era, small hollow bronze Roman dodecahedra were made and have been found in various Roman ruins in Europe. Its purpose is not certain.
In 20th-century art, dodecahedra appear in the work of M. C. Escher, such as his lithographs Reptiles (1943) and Gravitation (1952). In Salvador Dalí's painting The Sacrament of the Last Supper (1955), the room is a hollow regular dodecahedron. Gerard Caris based his entire artistic oeuvre on the regular dodecahedron and the pentagon, presented as a new art movement coined as Pentagonism.
In toys and popular culture
In modern role-playing games, the regular dodecahedron is often used as a twelve-sided die, one of the more common polyhedral dice. The Megaminx twisty puzzle is shaped like a regular dodecahedron alongside its larger and smaller order analogues.
In the children's novel The Phantom Tollbooth, the regular dodecahedron appears as a character in the land of Mathematics. Each face of the regular dodecahedron describes the various facial expressions, swiveling to the front as required to match his mood.
In nature and supramolecules
The fossil coccolithophore Braarudosphaera bigelowii (see figure), a unicellular coastal phytoplanktonic alga, has a calcium carbonate shell with a regular dodecahedral structure about 10 micrometers across.
The hydrocarbon dodecahedrane, some quasicrystals and cages have dodecahedral shape (see figure). Some regular crystals such as garnet and diamond are also said to exhibit "dodecahedral" habit, but this statement actually refers to the rhombic dodecahedron shape.
Shape of the universe
Various models have been proposed for the global geometry of the universe. These proposals include the Poincaré dodecahedral space, a positively curved space consisting of a regular dodecahedron whose opposite faces correspond (with a small twist). This was proposed by Jean-Pierre Luminet and colleagues in 2003, and an optimal orientation on the sky for the model was estimated in 2008.
In Bertrand Russell's 1954 short story "The Mathematician's Nightmare: The Vision of Professor Squarepunt", the number 5 said: "I am the number of fingers on a hand. I make pentagons and pentagrams. And but for me dodecahedra could not exist; and, as everyone knows, the universe is a dodecahedron. So, but for me, there could be no universe."
Dodecahedral graph
According to Steinitz's theorem, the graph can be represented as the skeleton of a polyhedron; roughly speaking, a framework of a polyhedron. Such a graph has two properties. It is planar, meaning the edges of a graph are connected to every vertex without crossing other edges. It is also three-connected graph, meaning that, whenever a graph with more than three vertices, and two of the vertices are removed, the edges remain connected. The skeleton of a regular dodecahedron can be represented as a graph, and it is called the dodecahedral graph, a Platonic graph.
This graph can also be constructed as the generalized Petersen graph , where the vertices of a decagon are connected to those of two pentagons, one pentagon connected to odd vertices of the decagon and the other pentagon connected to the even vertices. Geometrically, this can be visualized as the ten-vertex equatorial belt of the dodecahedron connected to the two 5-vertex polar regions, one on each side.
The high degree of symmetry of the polygon is replicated in the properties of this graph, which are distance-transitive, distance-regular, and symmetric. The automorphism group has order a hundred and twenty. The vertices can be colored with 3 colors, as can the edges, and the diameter is five.
The dodecahedral graph is Hamiltonian, meaning a path visits all of its vertices exactly once. The name of this property is named after William Rowan Hamilton, who invented a mathematical game known as the icosian game. The game's object was to find a Hamiltonian cycle along the edges of a dodecahedron.
| Mathematics | Three-dimensional space | null |
7149700 | https://en.wikipedia.org/wiki/Thylacocephala | Thylacocephala | The Thylacocephala (from the Greek or , meaning "pouch", and or meaning "head") are group of extinct probable mandibulate arthropods, that have been considered by some researchers as having possible crustacean affinities. As a class they have a short research history, having been erected in the early 1980s.
They typically possess a large, laterally flattened carapace that encompasses the entire body. The compound eyes tend to be large and bulbous, and occupy a frontal notch on the carapace. They possess three pairs of large raptorial limbs, and the abdomen bears a battery of small swimming limbs. Their size ranges from ~15 mm to potentially up to 250 mm.
Inconclusive claims of thylacocephalans have been reported from the lower lower Cambrian (Zhenghecaris), but later study considered that genus as radiodont or arthropod with uncertain systematic position. The oldest unequivocal fossils are Upper Ordovician and Lower Silurian in age. As a group, the Thylacocephala survived to the Santonian stage of the Upper Cretaceous, around 84 million years ago.
Beyond this, there remains much uncertainty concerning fundamental aspects of the thylacocephalan anatomy, mode of life, and relationship to the Crustacea, with whom they have always been cautiously aligned.
Research history
The Thylacocephala is only recently described as a class, yet species now included within the group were first described at the turn of the century. These were typically assigned to the phyllocarids despite an apparent lack of abdomen and appendages. In 1982/83, three research groups independently created higher taxa to accommodate new species. Based on a specimen from northern Italy, Pinna et al. designated a new class, Thylacocephala, while Secrétan – studying Dollocaris ingens, a species from the La Voulte-sur-Rhône konservat-lagerstätte in France – erected the class Conchyliocarida. Briggs & Rolfe, working on fossils from Australia's Devonian deposits were unable to attribute certain specimens to a known group, and created an order of uncertain affinities, the Concavicarida, to accommodate them. It was apparent the three groups were in fact working on a single major taxon (Rolfe noted disagreements over interpretation and taxonomic placement largely resulted from a disparity of sizes and differences in preservation.) The group took the name Thylacocephala by priority, with Concavicarida and Conchyliocarida subjugated to orders, erected by Rolfe, and modified by Schram.
Taxonomy
Researchers agree the Thylacocephala represent a class. Some efforts have been made at further classification: Schram split currently known taxa into two orders:
Concavicarida Briggs & Rolfe, 1983 which possesses:
A large, well developed optic notch
A discrete compound eye
A fused rostrum
8 to 16 homologous well-demarcated trunk segments diminishing in height anteriorly and posteriorly
Order includes Ainiktozoon (Silurian), Harrycaris (Devonian), Concavicaris (Devonian to Carboniferous), Dollocaris (Jurassic).
Conchyliocarida Secrétan, 1983:
Lacks an optic notch
Eyes on a protruding sac-like cephalon
No rostrum.
Order includes Convexicaris (Carboniferous), Yangzicaris (Triassic), and Atropicaris, Austriocaris, Clausocaris, Kilianocaris, Ostenocaris, and Paraostenia from the Jurassic.
The accuracy of this scheme has been questioned in recent papers, as it stresses differences in the eyes and exoskeletal structure, which – in modern arthropods – tend to be a response to environmental conditions. Thus it has been suggested these features are too strongly controlled by external factors to be used alone to distinguish higher taxa. The problem is exacerbated by the limited number of thylacocephalan species known. More reliable anatomical indicators would include segmentation and appendage attachments (requiring the internal anatomy, currently elusive as a result of the carapace).
Genera
Class: Thylacocephala
Ainiktozoon
Ankitokazocaris
Eodollocaris
Falcatacaris
Ligulacaris
Paraostenia
Polzia
Rugocaris
Silesicaris
Thylacares
Victoriacaris
Order Concavicarida
Family Austriocarididae
Austriocaris
Yangzicaris
Family Clausocarididae
Clausocaris
Convexicaris
Family Concavicarididae
Concavicaris
Harrycaris
Paraconcavicaris
Family: Microcarididae
Atropicaris
Ferrecaris
Keelicaris
Microcaris
Thylacocephalus
Family: Protozoeidae
Globulocaris
Hamaticaris
Protozoea
Pseuderichthus
Order Conchyliocarida
Family: Dollocarididae
Dollocaris
Mayrocaris
Paradollocaris
Thylacocaris
Family: Ostenocarididae
Kilianocaris
Ostenocaris
Anatomy
Based on Vannier, modified after Schram:
The Thylacocephala are bivalved arthropods with morphology exemplified by three pairs of long raptorial (predatory) appendages and hypertrophied eyes. They have a worldwide distribution. A laterally compressed, shield−like carapace encloses the entire body, and often has an anterior rostrum−notch complex and posterior rostrum. Its lateral surface can be externally ornamented, and evenly convex or with longitudinal ridges. Spherical or drop-shaped eyes are situated in the optic notches, and are often hypertrophied, filling the notches or forming a paired, frontal globular structure. No prominent abdominal features emerge from the carapace, and the cephalon is obscured. Even so, some authors have suggested the presence of five cephalic appendages, three of which could be the very long genticulate and chelate raptorials protruding beyond the ventral margin. Alternatively these could originate from three anterior trunk segments. The posterior trunk has a series of eight to twenty styliform, filamentous pleopod-like appendages, decreasing in size posteriorly. Most Thylacocephala have eight pairs of well developed gills, found in the trunk region.
Beyond this there is a lack of knowledge about even basic thylacocephalan anatomy, including the number of posterior segments, origin of the raptorials, number of cephalic appendages, shape and attachment of gills, character of mouth, stomach and gut. This results from the class's all–encompassing carapace, which prevents the study of their internal anatomy in fossils.
Affinities
It is universally accepted that the Thylacocephala are arthropods, yet the position within this phylum is debated. It had formerly been cautiously assumed that the class was a member of the Crustacea, but no conclusive proof exists. The strongest apomorphy aligning the class with other crustaceans is the carapace. As this feature has evolved independently numerous times within the Crustacea and other arthropods, it is not a very reliable pointer, and such evidence alone remains insufficient to align the class with the crustaceans.
Of the features which could prove crustacean affinities, the arrangement of mouthparts would be the easiest to find in the Thylacocephala. The literature features some mention of such a head arrangement, but none definitive. Schram reports the discovery of mandibles in the Mazon Creek thylacocephalan Concavicaris georgeorum. Secrétan also mentions – with caution – possible mandibles in serial sections of Dollocaris ingens, and traces of small limbs in the cephalic region (not well preserved enough to assess their identity). Lange et al. report a new genus and species, Thylacocephalus cymolopos, from the Upper Cretaceous of Lebanon, which has two possible pairs of antennae, but note the possession of two pairs of antennae alone does not prove the class occupies a position in the crown-group Crustacea.
Despite a lack of evidence for a crustacean body plan, several authors have aligned the class with different groups of crustaceans. Schram provides an overview of possible affinities:
Nothing in either Uniramia or Cheliceriformes seems likely.
Conchostraca is possible, but there is no strong supporting evidence.
A maxillopodan connection is possible. Largely considered due to the Italian researchers' insistence (see disagreements).
Stomatopods show many parallels but have no comparison to cephalon or body regions.
Remipedes show some parallels.
Decapod-like gills suggest malacostracan affinities.
In these various interpretations, numerous different limb arrangements for the three raptorials have been proposed:
antennules, antennae and mandibles
antennules, antennae and maxillipeds
thoracic (in keeping with stromatopod analogies)
maxillules, maxillae, maxillipedes
Further work is necessary to provide any solid conclusions.
A study in 2022 describing a new arthropod from Wisconsin, Acheronauta, found that the Thylacocephalans occupied a position more primitive than the crustaceans and myriapods as basal stem-group mandibulates. This would place them outside of the crustaceans as a more basal branch of the arthropod family tree.
This cladogram represents the placement of the Thylacocephalans within the arthropoda as suggested by Pulsipher, 2022.
Disagreements
Numerous conflicts of opinion surround the Thylacocephala, of which the split between the “Italian school” and rest of the world is the most notable. Based on poorly preserved Ostenocaris cypriformis fossils from the Osteno deposits of Lombardy, Pinna et al. erected the class Thylacocephala. Based on inferred cirripede affinities the authors concluded the frontal lobed structure was not an eye, but a 'cephalic sac'. This opinion arose from the misinterpretation of the stomach as a reproductive organ (its contents included vertebral elements of fish, thought to be ovarian eggs). Such an arrangement is reminiscent of cirripede crustaceans, leading the authors to suggest a sessile, filter feeding mode of life, the 'cephalic sac' used to anchor the organism to the seabed. The researchers have since conceded it is highly improbable the ovaries are situated in the head, but maintain that the frontal structure is not an eye. Instead they suggest the 'cephalic sac' is covered with microsclerites, their arguments most recently presented in Alessandrello et al.
The structure is complex and "presumably multipurpose"
“Apart from a few features” it shows little affinity with a compound eye
There is a close connection with stomach residues, sac muscular system and outer hexagonal layer
Having a stomach between the eyes is unusual
Sclerites that should correspond to rhabdoms in 'eye theory' are interstitial to the hexagons, not at centre as would be expected for individual ommatidium.
Structural analogy with cirriped peduncle
Instead the authors suggest the sac is used to break down coarse chunks of food and reject indigestible portions.
All other parties interpret this as a large compound eye, the hexagons being preserved ommatidia (all researchers agree these are the same structure). This is supported by fossils of Dollocaris ingens which are so well preserved that individual retinula cells can be discerned. The preservation is so exceptional that studies have shown the species' numerous small ommatidia, distributed over the large eyes, could reduce the angle between ommatidia, thus improve their ability to detect small objects. Of the arguments above, it is posited by opponents that eyes are complex structures, and those in the Thylacocephala display clear and numerous affinities with compound eyes in other arthropod fossils, down to a cellular level of detail. The 'cephalic sac' structure itself is poorly preserved in Osteno specimens, a possible reason for interstitial 'sclerites'. The structural analogy with a cirripede peduncle lost supporting evidence when the 'ovaries' were shown to be alimentary residues, and the sac muscular system could be used to support the eyes. The unusual position of the stomach is thus the strongest inconsistency, but the Thylacocephala are defined by their unusual features, so this is not inconceivable. Further, Rolfe suggests the eyes' position can be explained if they have a large posterior area of attachment, while Schram suggests that the stomach region extending into the cephalic sac could result from an inflated foregut or anteriorly directed caecum.
Discussion of the matter has ceased in the last decade, and most researchers accept the anterior structure is an eye. Confusion is most likely the result of differing preservation in Osteno.
Mode of life
Numerous modes of life have been suggested for the Thylacocephala.
Secrétan suggested Dollocaris ingens was too large to swim, so inferred a predatory 'lurking' mode of life, lying in wait on the sea bed and then springing out to capture prey. The author also suggested it could be necrophagous, supported by Alessandrello et al., who suggest they would have been incapable of directly killing the shark remains found in the Osteno specimens' alimentary residues. Instead they surmise the Thylacocephala could have ingested shark vomit which included such remains.
Vannier et al. note the Thylacocephala possess features which would suggest adaptations for swimming in dim-light environments – a thin, non-mineralized carapace, well-developed rostral spines for possible buoyancy control in some species, a battery of pleopods for swimming, and large prominent eyes. This is supported by the Cretaceous species from Lebanon, which show adaptations for swimming, and possibly schooling.
Rolfe provides many possibilities, but concludes a realistic mode of life is mesopelagic, by analogy with hyperiid amphipods. Further suggests floor-dwelling is also possible, and that the organism could rise to catch prey during the day and return to the sea floor at night. Another notable proposal is that, like hyperiids, the class could gain oil from their food source for buoyancy, an idea supported by their diet (known from stomach residues containing shark and coleoid remains, and other Thylacocephala).
Alessandrello et al. suggest a head-down, semi-sessile life on a soft bottom, in agreement with that of Pinna et al., based on cirripede affinities. A necrophagous diet is suggested.
Briggs & Rolfe report that all the Gogo formation Thylacocephala are found in a reef formation, suggesting a shallow water environment. The authors speculate that due to the terracing of the carapace an infaunal mode of life is possible, or the ridges could provide more friction for hiding in crevices of rock.
Schram suggests a dichotomy in size of the class results from different environments; larger Thylacocephala could have lived in a fluid characterized by turbulent flow, and relied on single power stroke of trunk limbs to position themselves. He suggests that smaller forms may have resided in a viscous medium, characterized by laminar flow, and used a lever to generate the speed necessary to capture prey.
| Biology and health sciences | Fossil arthropods | Animals |
13280372 | https://en.wikipedia.org/wiki/Limb%20%28anatomy%29 | Limb (anatomy) | A limb (from Old English lim, meaning "body part") is a jointed, muscled appendage of a tetrapod vertebrate animal used for weight-bearing, terrestrial locomotion and physical interaction with other objects. The distalmost portion of a limb is known as its extremity. The limbs' bony endoskeleton, known as the appendicular skeleton, is homologous among all tetrapods, who use their limbs for walking, running and jumping, swimming, climbing, grasping, touching and striking.
All tetrapods have four limbs that are organized into two bilaterally symmetrical pairs, with one pair at each end of the torso, which phylogenetically correspond to the four paired fins (pectoral and pelvic fins) of their fish (sarcopterygian) ancestors. The cranial pair (i.e. closer to the head) of limbs are known as the forelimbs or front legs, and the caudal pair (i.e. closer to the tail or coccyx) are the hindlimbs or back legs. In animals with a more erect bipedal posture (mainly hominid primates, particularly humans), the forelimbs and hindlimbs are often called upper and lower limbs, respectively. The fore-/upper limbs are connected to the thoracic cage via the pectoral/shoulder girdles, and the hind-/lower limbs are connected to the pelvis via the hip joints. Many animals, especially the arboreal species, have prehensile forelimbs adapted for grasping and climbing, while some (mostly primates) can also use hindlimbs for grasping. Some animals (birds and bats) have expanded forelimbs (and sometimes hindlimbs as well) with specialized feathers or membranes to achieve lift and fly. Aquatic and semiaquatic tetrapods usually have limb features (such as webbings) adapted to better provide propulsion in water, while marine mammals and sea turtles have convergently evolved flattened, paddle-like limbs known as flippers.
In human anatomy, the upper and lower limbs are commonly known as the arms and legs respectively, although in academic usage, these terms refer specifically to the upper arm and lower leg (the lower arm and upper leg are instead called forearm and thigh, respectively). The human arms have relatively great ranges of motion and are highly adapted for grasping and for carrying objects. The extremity of each arm, known as the hand, has five opposable digits known as fingers (made up of metacarpal and metatarsal bones for hands and feet respectively) and specializes in intrinsic fine motor skills for precise manipulation of objects. The human legs and their extremities — the feet — are specialized for bipedal locomotion. Compared to most other mammals that walk and run on all four limbs, human limbs are proportionally weaker but very mobile and versatile, and the unique dexterity of the human upper extremities allows them to make sophisticated tools and machines that compensate for the lack of physical strength and endurance.
Anatomy
Limbs are attached to the torso via girdles, either the pectoral girdle for the forelimbs, or the pelvic girdle for the hindlimbs. In terrestrial tetrapods, the pectoral girdles are more mobile, floating over the rib cage connected only via the clavicles (to the sternum) and numerous muscles; while the pelvic girdles are typically fused together anteriorly via a fibrocartilaginous joint and posteriorly with the vertebral column (sacrum), forming an immobile ring-like pelvis. The girdles are each connected to the corresponding limb proper via a ball-and-socket synovial joint.
The overall patterns of forelimbs and hindlimbs are homologous among all tetrapods, as they all branched out of the same bottlenecked lineage of stegocephalians that survived the Late Devonian extinction. The body plan of tetrapod limbs are so similar (especially the pentadactyly) that they are given shared terminologies for each component of the appendicular skeleton.
The proximal half of the limb proper has one long bone, the stylopodium (plural: stylopodia), which may be the humerus of the upper arm (proximal forelimbs), or the femur of the thigh (proximal hindlimbs).
The distal half of the limb proper has two long bones, together termed the zeugopodium (plural: zeugopodia). These may be radius and ulna of the forearm, or the tibia and fibula of the shin.
The distalmost portion or extremity of the limb, i.e. the hand or foot, is known as the autopodium (plural: autopodia). Hands are technically known as the manus, and feet as the pes.
The proximal part of the autopodium, i.e. the wrist or ankle region, has many small nodular bones, collectively termed the mesopodium (plural: mesopodia). Wrist bones are known as the carpals, and ankle bones are known as the tarsals.
The middle part of the autopodium is the metapodium (plural: metapodia), composed of the slender long bones each called a metapodial. The metapodials of the hand are known as metacarpals, while the metapodials of the foot are known as metatarsals. The ventral (or flexor) aspect of the hand is known as the palm or , and that of the foot as the sole or .
The distalmost part of the autopodium are the digits (fingers or toes), which have multi-jointed phalanges and are highly mobile in most tetrapods. The ends of the digits are often protectively covered by hardened keratin outgrowths such as claws and nails.
Development
Limb development is controlled by Hox genes. All jawed vertebrates surveyed so far organize their developing limb buds in a similar way. Growth occurs from proximal to distal part of the limb. On the distal end, the differentiation of skeletal elements occurs in an apical ectodermal ridge (AER) which expands in rays. A Zone of Polarizing Activity (ZPA) at the rear part of the AER coordinates the differentiation of digits.
| Biology and health sciences | External anatomy and regions of the body | Biology |
13283176 | https://en.wikipedia.org/wiki/Wild%20water%20buffalo | Wild water buffalo | The wild water buffalo (Bubalus arnee), also called Asian buffalo, Asiatic buffalo and wild buffalo, is a large bovine native to the Indian subcontinent and Southeast Asia. It has been listed as Endangered in the IUCN Red List since 1986, as the remaining population totals less than 4,000. A population decline of at least 50% over the last three generations (24–30 years) is projected to continue. The global population has been estimated at 3,400 individuals, of which 95% live in India, mostly in Assam. The wild water buffalo is the most likely ancestor of the domestic water buffalo.
Taxonomy
Bos arnee was the scientific name proposed by Robert Kerr in 1792 who described a skull with horns of a buffalo zoological specimen from Bengal in northern India. The specific name arnee is derived from Hindi arnī, which referred to a female wild water buffalo; the term is related to Sanskrit áraṇya ("forest") and áraṇa ("strange, foreign.") Bubalus arnee was proposed by Charles Hamilton Smith in 1827 who introduced the generic name Bubalus for bovids with large heads, convex-shaped narrow foreheads, laterally bent flat horns, funnel-shaped ears, small dewlaps and slender tails.
Later authors subordinated the wild water buffalo under either Bos, Bubalus or Buffelus.
In 2003, the International Commission on Zoological Nomenclature placed Bubalus arnee on the Official List of Specific Names in Zoology, recognizing the validity of this name for a wild species. Most authors have adopted the binomen Bubalus arnee for the wild water buffalo as valid for the taxon.
The wild water buffalo is the most likely ancestor of the domestic water buffalo.
Only a few DNA sequences are available from wild water buffalo populations. Wild populations are considered to be the progenitor of the modern domestic water buffalo, but the genetic variation within the species is unclear, and also how it is related to the domesticated river and Carabao swamp buffaloes.
Characteristics
The wild water buffalo has an ash-gray to black skin. The moderately long, coarse and sparse hair is directed forward from the haunches to the long and narrow head. There is a tuft on the forehead, and the ears are comparatively small. Its head-to-body-length is with a long tail and a shoulder height of . Both sexes carry horns that are heavy at the base and widely spreading up to along the outer edges, exceeding in size the horns of any other living bovid. The tip of the tail is bushy; the hooves are large and splayed.
It is larger and heavier than the domestic water buffalo, and weighs from . The average weight of three captive wild water buffaloes was .
It is among the heaviest living wild bovid species, and is slightly smaller than gaur.
Distribution and habitat
The wild water buffalo occurs in India, Nepal, Bhutan, Thailand, and Cambodia, with an unconfirmed population in Myanmar. It has been extirpated in Bangladesh, Laos, Vietnam, and Sri Lanka. It is associated with wet grasslands, swamps, flood plains and densely vegetated river valleys.
India hosts 95% of the total global wild buffalo population, with over 2,600 wild water buffaloes in Assam. It is largely restricted to in and around Kaziranga, Manas and Dibru-Saikhowa National Parks, Laokhowa Wildlife Sanctuary and Bura Chapori Wildlife Sanctuary and in a few scattered pockets in Assam, and in and around D'Ering Memorial Wildlife Sanctuary in Arunachal Pradesh. A small population survives in Balphakram National Park in Meghalaya, and in Chhattisgarh in Indravati National Park and Udanti Wildlife Sanctuary. This population might extend into adjacent parts of Odisha and Gadchiroli District of Maharashtra. In the early 1990s, there may still have been about 3,300–3,500 wild water buffaloes in Assam and the adjacent states of northeast India. In 1997, the number was assessed at less than 1,500 mature individuals.
Many surviving populations are thought to have interbred with feral or domestic water buffaloes. In the late 1980s, fewer than 100 wild water buffaloes were left in Madhya Pradesh. By 1992, only 50 animals were estimated to have survived there.
Nepal's only population lives in Koshi Tappu Wildlife Reserve and has grown from 63 individuals in 1976 to 219 individuals in 2009. In 2016, 18 individuals were translocated from Koshi Tappu Wildlife Reserve to Chitwan National Park.
In and around Bhutan's Royal Manas National Park, a small number of wild water buffaloes occur. This is part of the sub-population that occurs in India's Manas National Park. In Myanmar, a few animals live in Hukaung Valley Wildlife Sanctuary.
In Thailand, wild water buffaloes have been reported to occur in small herds of less than 40 individuals. A population of 25–60 individuals inhabited lowland areas of the Huai Kha Khaeng Wildlife Sanctuary between December 1999 and April 2001. This population has not grown significantly in 15 years, and is maybe interbreeding with domestic water buffaloes.
The population in Cambodia is confined to a small area of easternmost Mondulkiri and possibly Ratanakiri Provinces. Only a few dozen individuals remain.
The wild water buffaloes in Sri Lanka are thought to be descendants of the introduced domestic water buffalo. It is unlikely that any true wild water buffaloes remain there today.
Wild-living populations found elsewhere in Asia, Australia, Argentina and Bolivia are feral domestic water buffaloes.
Ecology and behavior
Wild water buffaloes are both diurnal and nocturnal. Adult females and their young form stable clans of as many as 30 individuals which have home ranges of , including areas for resting, grazing, wallowing, and drinking. Clans are led by old cows, even when bulls accompany the group. Several clans form a herd of 30 to 500 animals that gather at resting areas. Adult males form bachelor groups of up to 10 individuals, with older males often being solitary, and spend the dry season apart from the female clans. They are seasonal breeders in most of their range, typically in October and November. However, some populations breed year round. Dominant males mate with the females of a clan who subsequently drive them off. Their gestation period is 10 to 11 months, with an inter-birth interval of one year. They typically give birth to a single offspring, although twins are possible. Age at sexual maturity is 18 months for males, and three years for females. The maximum known lifespan is 25 years in the wild. In Assam, herd sizes vary from three to 30 individuals.
They are probably grazers by preference, feeding mainly on graminoids when available, such as Bermuda grass, and Cyperus sedges, but they also eat other herbs, fruits, and bark, as well as browsing on trees and shrubs. They also feed on crops, including rice, sugarcane, and jute, sometimes causing considerable damage.
Tigers and mugger crocodiles prey on adult wild water buffaloes, and Asian black bears have also been known to kill them.
Threats
A population reduction by at least 50% over the last three generations seems likely given the severity of the threats, especially hybridization; this population trend is projected to continue into the future. The most important threats are:
interbreeding with feral and domestic water buffaloes in and around protected areas;
hunting, especially in Thailand, Cambodia, and Myanmar;
habitat loss of floodplain areas due to conversion to agriculture and hydropower development;
degradation of wetlands due to invasive species such as stem twiners and lianas;
diseases and parasites transmitted by domestic livestock;
interspecific competition for food and water between wild water buffaloes and livestock.
Conservation
Bubalus arnee is included in CITES Appendix III, and is legally protected in Bhutan, India, Nepal, and Thailand.
In 2017, 15 wild water buffaloes were reintroduced into Chitwan National Park in Nepal to establish a second viable sub-population in the country.
In 2023, 4 wild buffalos were translocated to Udanti-Sitanadi Tiger Reserve to reverse its declining population in the state.
| Biology and health sciences | Bovidae | Animals |
13288318 | https://en.wikipedia.org/wiki/Universal%20Flash%20Storage | Universal Flash Storage | Universal Flash Storage (UFS) is a flash storage specification for digital cameras, mobile phones and consumer electronic devices. It was designed to bring higher data transfer speed and increased reliability to flash memory storage, while reducing market confusion and removing the need for different adapters for different types of cards. The standard encompasses both packages permanently embedded (via ball grid array package) within a device (), and removable UFS memory cards.
Overview
UFS uses NAND flash. It may use multiple stacked 3D TLC NAND flash dies (integrated circuits) with an integrated controller.
The proposed flash memory specification is supported by consumer electronics companies such as Nokia, Sony Ericsson, Texas Instruments, STMicroelectronics, Samsung, Micron, and SK Hynix. UFS is positioned as a replacement for and SD cards. The electrical interface for UFS uses the M-PHY, developed by the MIPI Alliance, a high-speed serial interface targeting 2.9 Gbit/s per lane with up-scalability to 5.8 Gbit/s per lane. UFS implements a full-duplex serial LVDS interface that scales better to higher bandwidths than the 8-lane parallel and half-duplex interface of . Unlike eMMC, Universal Flash Storage is based on the SCSI architectural model and supports SCSI Tagged Command Queuing. The standard is developed by, and available from, the JEDEC Solid State Technology Association.
Software support
The Linux kernel supports UFS. OpenBSD 7.3 and later support UFS. Windows 10 and later support UFS.
History
In 2010, the Universal Flash Storage Association (UFSA) was founded as an open trade association to promote the UFS standard.
In September 2013, JEDEC published JESD220B UFS 2.0 (update to UFS v1.1 standard published in June 2012). JESD220B Universal Flash Storage v2.0 offers increased link bandwidth for performance improvement, a security features extension and additional power saving features over the UFS v1.1.
On 30 January 2018 JEDEC published version 3.0 of the UFS standard, with a higher 11.6 Gbit/s data rate per lane (1450 MB/s) with the use of MIPI M-PHY v4.1 and UniProSM v1.8. At the MWC 2018, Samsung unveiled embedded UFS () v3.0 and uMCP (UFS-based multi-chip package) solutions.
On 30 January 2020 JEDEC published version 3.1 of the UFS standard. UFS 3.1 introduces Write Booster, Deep Sleep, Performance Throttling Notification and Host Performance Booster for faster, more power efficient and cheaper UFS solutions. The Host Performance Booster feature is optional. Before the UFS 3.1 standard, the SLC cache feature is optional on UFS device, which is a de facto feature on personal SSDs.
In 2022 Samsung announced version 4.0 doubling from 11.6 Gbit/s to 23.2 Gbit/s with the use of MIPI M-PHY v5.0 and UniPro v2.0. UFS 4.0 introduces File Based Optimization.
As of Q2 2024, Zoned UFS (ZUFS) is in development by SK hynix.
Notable devices
In February 2013, semiconductor company Toshiba Memory (now Kioxia) started shipping samples of a 64 GB NAND flash chip, the first chip to support the then new UFS standard.
In April 2015, Samsung's Galaxy S6 family was the first phone to ship with storage using the UFS 2.0 standard.
On 7 July 2016, Samsung announced its first UFS cards, in 32, 64, 128, and 256 GB storage capacities. The cards were based on the UFS 1.0 Card Extension Standard. The 256 GB version was reported to offer sequential read performance up to 530 MB/s and sequential write performance up to 170 MB/s and random performance of 40,000 read IOPS and 35,000 write IOPS. However, they were apparently not actually released to the public.
On 17 November 2016, Qualcomm announced the Snapdragon 835 SoC with support for UFS 2.1.
On 14 May 2019, OnePlus introduced the OnePlus 7 and OnePlus 7 Pro, the first phones to feature built-in 3.0 (The Galaxy Fold, originally planned to be the first smartphone to feature UFS 3.0 was ultimately delayed after the OnePlus 7's launch).
The first UFS cards began to be publicly sold in early 2020. According to a Universal Flash Storage Association press release, Samsung planned to transition its products to UFS cards during 2020. Several consumer devices with UFS card slots have been released in 2020.
On 08 December 2022, IQOO announced the IQOO 11 which was the first phone to release with UFS 4.0 Storage. After that, other Android OEMs started using this storage solution on their flagship to upper mid-range category smartphones.
Version comparison
UFS
UFS Card
Implementation
UFS 2.0 has been implemented in Snapdragon 820 and 821. Kirin 950 and 955. Exynos 7420. NVIDIA Jetson AGX Xavier SOMs
UFS 2.1 has been implemented in Snapdragon 712 (710&720G), 730G, 732G, 835, 845 and 855. Kirin 960, 970 and 980. Exynos 9609, 9610, 9611, 9810 and 980.
UFS 3.0 has been implemented in Snapdragon 855, 855+, 860, 865, Exynos 9820–9825, and Kirin 990.
UFS 3.1 has been implemented in Snapdragon 855+/860, Snapdragon 865, Snapdragon 870, Snapdragon 888, Exynos 2100, and Exynos 2200.
UFS 4.0 has been implemented in MediaTek Dimensity 9200, MediaTek Dimensity 8300 and Snapdragon 8 Gen 2.
Complementary UFS standards
On 30 March 2016, JEDEC published version 1.0 of the UFS Card Extension Standard (JESD220-2), which offered many of the features and much of the same functionality as the existing UFS 2.0 embedded device standard, but with additions and modifications for removable cards.
Also in March 2016, JEDEC published version 1.1 of the UFS Unified Memory Extension (JESD220-1A), version 2.1 of the UFS Host Controller Interface (UFSHCI) standard (JESD223C), and version 1.1A of the UFSHCI Unified Memory Extension standard (JESD223-1A).
On January 30, 2018, the UFS Card Extension standard was updated to version 1.1 (JESD220-2A), and the UFSHCI standard was updated to version 3.0 (JESD223D), to align with UFS version 3.0.
Rewrite cycle life
A UFS drive's rewrite life cycle affects its lifespan. There is a limit to how many write/erase cycles a flash block can accept before it produces errors or fails altogether. Each write/erase cycle causes a flash memory cell's oxide layer to deteriorate. The reliability of a drive is based on three factors: the age of the drive, total terabytes written over time and drive writes per day. This is typical of flash memory in general.
| Technology | Non-volatile memory | null |
15967917 | https://en.wikipedia.org/wiki/Sodium%20citrate | Sodium citrate | Sodium citrate may refer to any of the sodium salts of citric acid (though most commonly the third):
Monosodium citrate
Disodium citrate
Trisodium citrate
The three forms of salt are collectively known by the E number E331.
Applications
Food
Sodium citrates are used as acidity regulators in food and drinks, and also as emulsifiers for oils. They enable cheeses to melt without becoming greasy and also reduce the acidity of food. They are generally considered safe and are designated GRAS by the FDA.
Blood clotting inhibitor
Sodium citrate is used to prevent donated blood from clotting in storage, and can also be used as an additive for apheresis to prevent clots forming in the tubes of the machine. By binding with calcium ions in the blood it prevents the process of coagulation. It is also used as an anticoagulant for laboratory testing, in that blood samples are collected into sodium citrate-containing tubes for tests such as the PT (INR), APTT, and fibrinogen levels. Sodium citrate is used in medical contexts as an alkalinizing agent in place of sodium bicarbonate, to neutralize excess acid in the blood and urine.
Metabolic acidosis
It has applications for the treatment of metabolic acidosis and chronic kidney disease.
Ferrous nanoparticles
Along with oleic acid, sodium citrate may be used in the synthesis of magnetic Fe3O4 nanoparticle coatings.
| Physical sciences | Citrates | Chemistry |
9293603 | https://en.wikipedia.org/wiki/Mouth | Mouth | The mouth is the body orifice through which many animals ingest food and vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also the first part of the alimentary canal, which leads to the pharynx and the gullet. In tetrapod vertebrates, the mouth is bounded on the outside by the lips and cheeks — thus the oral cavity is also known as the buccal cavity (from Latin , meaning "cheek") — and contains the tongue on the inside. Except for some groups like birds and lissamphibians, vertebrates usually have teeth in their mouths, although some fish species have pharyngeal teeth instead of oral teeth.
Most bilaterian phyla, including arthropods, molluscs and chordates, have a two-opening gut tube with a mouth at one end and an anus at the other. Which end forms first in ontogeny is a criterion used to classify bilaterian animals into protostomes and deuterostomes.
Development
In the first multicellular animals, there was probably no mouth or gut and food particles were engulfed by the cells on the exterior surface by a process known as endocytosis. The particles became enclosed in vacuoles into which enzymes were secreted and digestion took place intracellularly. The digestive products were absorbed into the cytoplasm and diffused into other cells. This form of digestion is used nowadays by simple organisms such as Amoeba and Paramecium and also by sponges which, despite their large size, have no mouth or gut and capture their food by endocytosis.
However, most animals have a mouth and a gut, the lining of which is continuous with the epithelial cells on the surface of the body. A few animals which live parasitically originally had guts but have secondarily lost these structures. The original gut of diploblastic animals probably consisted of a mouth and a one-way gut. Some modern invertebrates still have such a system: food being ingested through the mouth, partially broken down by enzymes secreted in the gut, and the resulting particles engulfed by the other cells in the gut lining. Indigestible waste is ejected through the mouth.
In animals at least as complex as an earthworm, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the formation of the gut. In deuterostomes, the blastopore becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. In the protostomes, it used to be thought that the blastopore formed the mouth (proto– meaning "first") while the anus formed later as an opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the slit-like blastopore close up in the middle, leaving openings at both ends that become the mouth and anus.
Anatomy
Invertebrates
Apart from sponges and placozoans, almost all animals have an internal gut cavity, which is lined with gastrodermal cells. In less advanced invertebrates such as the sea anemone, the mouth also acts as an anus. Circular muscles around the mouth are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape widely enough to accommodate large prey items. Food passes first into a pharynx and digestion occurs extracellularly in the gastrovascular cavity. Annelids have simple tube-like guts, and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients.
Many molluscs have a radula, which is used to scrape microscopic particles off surfaces. In invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have a range of mouthparts suited to their mode of feeding. These include mandibles, maxillae and labium and can be modified into suitable appendages for chewing, cutting, piercing, sponging and sucking. Decapods have six pairs of mouth appendages, one pair of mandibles, two pairs of maxillae and three of maxillipeds. Sea urchins have a set of five sharp calcareous plates, which are used as jaws and are known as Aristotle's lantern.
Vertebrates
In vertebrates, the first part of the digestive system is the buccal cavity, commonly known as the mouth. The buccal cavity of a fish is separated from the opercular cavity by the gills. Water flows in through the mouth, passes over the gills and exits via the operculum or gill slits. Nearly all fish have jaws and may seize food with them but most feed by opening their jaws, expanding their pharynx and sucking in food items. The food may be held or chewed by teeth located in the jaws, on the roof of the mouth, on the pharynx or on the gill arches.
Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth, where they hold the prey with their jaws. They then swallow their food whole without much chewing. They typically have many small hinged pedicellate teeth, the bases of which are attached to the jaws, while the crowns break off at intervals and are replaced. Most amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians, there are also vomerine teeth attached to the bone in the roof of the mouth.
The mouths of reptiles are largely similar to those of mammals. The crocodilians are the only reptiles to have teeth anchored in sockets in their jaws. They are able to replace each of their approximately 80 teeth up to 50 times during their lives. Most reptiles are either carnivorous or insectivorous, but turtles are often herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles often have gastroliths in their stomach to further grind the plant material. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull. These modifications allow them to open their mouths wide enough to swallow their prey whole, even if it is wider than they are.
Birds do not have teeth, relying instead on other means of gripping and macerating their food. Their beaks have a range of sizes and shapes according to their diet and are composed of elongated mandibles. The upper mandible may have a nasofrontal hinge allowing the beak to open wider than would otherwise be possible. The exterior surface of beaks is composed of a thin, horny sheath of keratin. Nectar feeders such as hummingbirds have specially adapted brushy tongues for sucking up nectar from flowers.
In mammals, the buccal cavity is typically roofed by the hard and soft palates, floored by the tongue and surrounded by the cheeks, salivary glands, and upper and lower teeth. The upper teeth are embedded in the upper jaw and the lower teeth in the lower jaw, which articulates with the temporal bones of the skull. The lips are soft and fleshy folds which shape the entrance into the mouth. The buccal cavity empties through the pharynx into the oesophagus.
Other functions of the mouth
Crocodilians living in the tropics can gape with their mouths to provide cooling by evaporation from the mouth lining. Some mammals rely on panting for thermoregulation as it increases evaporation of water across the moist surfaces of the lungs, the tongue and mouth. Birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat) skin, similar to panting in mammals.
Various animals use their mouths in threat displays. They may gape widely, exhibit their teeth prominently, or flash the startling colours of the mouth lining. This display allows each potential combatant an opportunity to assess the weapons of their opponent and lessens the likelihood of actual combat being necessary.
A number of species of bird use a gaping, open beak in their fear and threat displays. Some augment the display by hissing or breathing heavily, while others clap their beaks.
Mouths are also used as part of the mechanism for producing sounds for communication. To produce sounds, air is forced from the lungs over vocal cords in the larynx. In humans, the pharynx, soft palate, hard palate, alveolar ridge, tongue, teeth and lips are termed articulators and play their part in the production of speech. Varying the position of the tongue in relation to the other articulators or moving the lips restricts the airflow from the lungs in different ways and changes the mouth's resonating properties, producing a range of different sounds. In frogs, the sounds can be amplified using sacs in the throat region. The vocal sacs can be inflated and deflated and act as resonators to transfer the sound to the outside world. A bird's song is produced by the flow of air over a vocal organ at the base of the trachea, the syrinx. For each burst of song, the bird opens its beak and closes it again afterwards. The beak may move slightly and may contribute to the resonance but the song originates elsewhere.
| Biology and health sciences | Digestive system | null |
2166413 | https://en.wikipedia.org/wiki/Rosella | Rosella | Rosellas are in a genus that consists of six species and nineteen subspecies.
These colourful parrots from Australia are in the genus Platycercus.
Platycercus means "broad-tailed" or "flat-tailed", reflecting a feature common to the rosellas and other members of the broad-tailed parrot tribe. Their diet is mainly seeds and fruit.
Taxonomy
The genus was described by naturalist Nicholas Aylward Vigors in 1825; the name Platycercus derived from the Greek platykerkos meaning "broad-" or "flat-tailed", from platys "broad, wide, level, flat" and kerkos "tail of a beast". The relationships with other parrots have been unclear, with the Australian ringneck (genus Barnardius) cited as a closest relative by some, and the genus Psephotus by others; the plumage of the western rosella seen as a link to the latter genus.Early European settlers encountered the eastern rosella at Rose Hill, New South Wales, now Parramatta, and so they called it the Rosehill parakeet which became "Rosehiller", and eventually "rosella". Vigors defined the genus Platycercus in 1825, based on
the distinctive architecture of the feathers in the tail and wing, and designated the crimson rosella Platycercus elegans (as Platycercus pennantii) as the type species. The description as a flat or broad tail follows Heinrich Kuhl, who separated his psittacine specimens to a group with tails that were "narrow and cuneated", that is, a tapering wedged outline.
There are, broadly speaking, three groups of rosella species. They are the blue-cheeked species which includes elegans and caledonicus, the white-cheeked species, eximius, adscitus and venustus and the yellow-cheeked species, icterotis. The observed difference in plumage has been reinforced by molecular studies in 1987 and 2015 that place the icterotis as a basal offshoot.
There are six species and many subspecies: Ovenden and colleagues analysed mitochondrial DNA, confirming the blue-cheeked and white-cheeked lineages. They found P. caledonicus to be basal to the other blue-cheeked forms, with P. elegans nigrescens being divergent from other subspecies of P. elegans. Also, P. venustus was basal to P. eximius and P. adscitus. However, a mitochondrial study published in 2017 found that P. eximius was the earlier offshoot of the lineage that split into P. adscitus and P. venustus, and that nonsister taxa were hence able to hybridise. In 2015, Ashlee Shipham and colleagues published a molecular study based on nuclear DNA finding that P. venustus and P. adscitus were sister species, and that P. elegans nigrescens diverged earlier than P. caledonicus.
Description
Ranging in size from , rosellas are medium-sized parrots with long tails. The feathers on their backs show an obvious scalloping appearance with colouring that differs between the species. All species have distinctive cheek patches. Sexual dimorphism is absent or slight – males and females generally have similar plumage, apart from the western rosella. The juveniles of the blue-cheeked species, and western rosella, all have a distinctive green-based plumage, while immature plumage of the white-cheeked species is merely a duller version of the adults.
Distribution and habitat
Rosellas are native to Australia and nearby islands, where they inhabit forests, woodlands, farmlands, and suburban parks and gardens. They are confined to the coastal mountains and plains and are absent from the outback. Introduced populations have also established themselves in New Zealand (notably in the North Island and in north Dunedin) and on Norfolk Island.
Behaviour and ecology
Rosellas feed predominantly on seeds and fruit, with food held in the foot. They enjoy bathing in puddles of water in the wild and in captivity. Rosellas scratch their heads with the foot behind the wing.
Mutual preening is not exhibited by the genus, and the courtship display is simple; the male waves his tail sideways, and engages in some head bobbing, and the female reciprocates.
Like most parrots, they are cavity nesters, generally nesting high in older large trees in forested areas. They generally have a clutch size of several eggs which are incubated for around 21 days by the female alone. The male feeds the female through this time and for some time after incubation concludes. Quickly covered in a white down, chicks take around five weeks to fledge.
Aviculture
The more colourful rosella species are popular as pet parrots and also as aviary birds. They can live for longer than 20 years, and they are relatively easy to breed. All have a reputation for being aggressive in captivity, and are hence recommended be kept separate from other caged birds. Their diet in aviculture includes seeds, fruit such as apple, pear, and grapes, and vegetable matter such as lettuce, grass, and silver beet.
| Biology and health sciences | Psittaciformes | Animals |
2167305 | https://en.wikipedia.org/wiki/Pareiasauria | Pareiasauria | Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct in the Permian–Triassic extinction event.
Description
Pareiasaurs ranged in size from long, with some species estimated to exceed in body mass. The limbs of many parieasaurs were extremely robust, likely to account for the increased stress on their limbs caused by their typically sprawling posture. The cow-sized Bunostegos differed from other pareiasaurs by having a more upright limb posture, being amongst the first amniotes to develop this trait. Pareiasaurs were protected by bony scutes called osteoderms that were set into the skin. Their skulls were heavily ornamented with bosses, rugose ridges, and bumps. Their leaf-shaped multi-cusped teeth resemble those of iguanas, indicating a herbivorous diet. The body probably housed an extensive digestive tract. Most authors have assumed a terrestrial lifestyle for pareiasaurs. A 2008 bone microanatomy study suggested a more aquatic, plausibly amphibious lifestyle, but a later 2019 study found that the bone histology provided no direct evidence of this lifestyle.
Evolutionary history
Pareiasaurs appear very suddenly in the fossil record. It is clear that these animals are parareptiles. As such, they are closely related to nycteroleterids. Pareiasaurs filled the large herbivore niche (or guild) that had been occupied early in the Permian period by the caseid pelycosaurs and, before them, the diadectid reptiliomorphs. They are much larger than the diadectids, more similar to the giant caseid pelycosaur Cotylorhynchus. Although the last Pareiasaurs were no larger than the first types (indeed, many of the last ones became smaller), there was a definite tendency towards increased armour as the group developed. Pareiasaurs first appeared in the fossil record in the Middle Permian (Guadalupian) of Southern Pangaea, before dispersing into Northern Pangaea and gaining a cosmopolitan distribution during the Late Permian (Lopingian).
Classification
Some paleontologists considered that pareiasaurs were direct ancestors of modern turtles. Pareiasaur skulls have several turtle-like features, and in some species the scutes have developed into bony plates, possibly the precursors of a turtle shell. Jalil and Janvier, in a large analysis of pareiasaur relationships, also found turtles to be close relatives of the "dwarf" pareiasaurs, such as Pumiliopareia. However, the discovery of Pappochelys argues against a potential pareisaurian relationship to turtles, and DNA evidence indicates that living turtles are more closely related to living archosaurs than lepidosaurs, and therefore cladistically diapsids.
Associated clades
Hallucicrania (Lee 1995): This clade was coined by MSY Lee for Lanthanosuchidae + (Pareiasauridae + Testudines). Lee's pareiasaur hypothesis has become untenable due to the diapsid features of the stem turtle Pappochelys and the potential testudinatan nature of Eunotosaurus. Recent cladistic analyses reveal that lanthanosuchids have a much more basal position in the Procolophonomorpha, and that the nearest sister taxon to the pareiasaurs are the rather unexceptional and conventional looking nycteroleterids (Müller & Tsuji 2007, Lyson et al. 2010) the two being united in the clade Pareiasauromorpha (Tsuji et al. 2012).
Pareiasauroidea (Nopcsa, 1928): This clade (as opposed to the superfamily or suborder Pareiasauroidea) was used by Lee (1995) for Pareiasauridae + Sclerosaurus. More recent cladistic studies place Sclerosaurus in the procolophonid subfamily Leptopleuroninae (Cisneros 2006, Sues & Reisz 2008), which means the similarities with pareiasaurs are the result of convergences.
Pareiasauria (Seeley, 1988): If neither Lanthanosuchidae or Testudines are included in the clade, the Pareiasauria only contains the monophyletic family Pareiasauridae.
Phylogeny
Below is a cladogram from Tsuji et al. (2013):
| Biology and health sciences | Parareptilia | Animals |
2167405 | https://en.wikipedia.org/wiki/Marine%20shrimp%20farming | Marine shrimp farming | Marine shrimp farming is an aquaculture business for the cultivation of marine shrimp or prawns for human consumption. Although traditional shrimp farming has been carried out in Asia for centuries, large-scale commercial shrimp farming began in the 1970s, and production grew steeply, particularly to match the market demands of the United States, Japan and Western Europe. The total global production of farmed shrimp reached more than 1.6 million tonnes in 2003, representing a value of nearly 9 billion U.S. dollars. About 75% of farmed shrimp is produced in Asia, in particular in China and Thailand. The other 25% is produced mainly in Latin America, where Brazil, Ecuador, and Mexico are the largest producers. The largest exporting nation is India.
Shrimp farming has changed from traditional, small-scale businesses in Southeast Asia into a global industry. Technological advances have led to growing shrimp at ever higher densities, and broodstock is shipped worldwide. Virtually all farmed shrimp are of the family Penaeidae, and just two species – Penaeus vannamei (Pacific white shrimp) and Penaeus monodon (giant tiger prawn) – account for roughly 80% of all farmed shrimp. These industrial monocultures are very susceptible to diseases, which have caused several regional wipe-outs of farm shrimp populations. Increasing ecological problems, repeated disease outbreaks, and pressure and criticism from both NGOs and consumer countries led to changes in the industry in the late 1990s and generally stronger regulation by governments. In 1999, a program aimed at developing and promoting more sustainable farming practices was initiated, including governmental bodies, industry representatives, and environmental organizations.
History and geography
Shrimp has been farmed in South East Asia and China for centuries, using traditional low-density methods. In Indonesia, the use of brackish water ponds, called tambaks, can be traced back as far as the 15th century. They used small scale ponds for monoculture or polycultured with other species, such as milkfish, or in rotation with rice, using the rice paddies for shrimp cultures during the dry season, when no rice could be grown. Such cultures often were in coastal areas or on river banks. Mangrove areas were favored because of their abundant natural shrimp. Wild juvenile shrimp were trapped in ponds and reared on naturally occurring organisms in the water until they reached the desired size for harvesting.
Industrial shrimp farming can be traced to the 1930s, when Japanese agrarians spawned and cultivated Kuruma shrimp (Penaeus japonicus) for the first time. By the 1960s, a small industry had developed in Japan. Commercial shrimp farming began to grow rapidly in the late 1960s and early 1970s. Technological advances led to more intensive forms of farming, and growing market demand led to worldwide proliferation of shrimp farms, concentrated in tropical and subtropical regions. Growing consumer demand in the early 1980s coincided with faltering wild catches, creating a booming industry. Taiwan was an early adopter and a major producer in the 1980s; its production collapsed beginning in 1988 due to poor management practices and disease. In Thailand, large-scale production expanded rapidly from 1985. In South America, Ecuador pioneered shrimp farming, where it expanded dramatically from 1978. Brazil had been active in shrimp farming since 1974, but trade boomed there only in the 1990s, making the country a major producer within a few years. Today, there are marine shrimp farms in over fifty countries.
Farming methods
When shrimp farming emerged to satisfy demand that had surpassed the wild fisheries' capacity, the subsistence farming methods of old were rapidly replaced by the more productive practices required to serve a global market. Industrial farming at first followed traditional methods, with so-called "extensive" farms, compensating for low density with increased pond sizes; instead of ponds of just a few hectares, ponds of sizes up to were used and huge areas of mangroves were cleared in some areas. Technological advances made more intensive practices possible that increase yield per area, helping reduce pressure to convert more land. Semi-intensive and intensive farms appeared, where the shrimp were reared on artificial feeds and ponds were actively managed. Although many extensive farms remain, new farms typically are of the semi-intensive kind.
Until the mid-1980s, most farms were stocked with young wild animals, called 'postlarvae', typically caught locally. Postlarvae fishing became an important economic sector in many countries. To counteract the depletion of fishing grounds and to ensure a steady supply of young shrimp, the industry started breeding shrimp in hatcheries.
Life cycle
Shrimp mature and breed only in a marine habitat. The females lay 100,000 to 500,000 eggs, which hatch after some 24 hours into tiny nauplii. These nauplii feed on yolk reserves within their bodies, and then metamorphose into zoeae. Shrimp in this second larval stage feed in the wild on algae, and after a few days, morph again into mysis larvae. The mysis larvae or myses look akin to tiny shrimp, and feed on algae and zooplankton. After another three to four days, they metamorphose a final time into postlarvae: young shrimp that have adult characteristics. The whole process takes about 12 days from hatching. In the wild, postlarvae then migrate into estuaries, which are rich in nutrients and low in salinity. They migrate back into open waters when they mature.
Supply chain
In shrimp farming, this life cycle occurs under controlled conditions. The reasons to do so include more intensive farming, improved size control resulting in more uniformly sized shrimp, and better predator control, but also the ability to accelerate growth and maturation by controlling the climate (especially in farms in the temperate zones, using greenhouses). There are three different stages:
Hatcheries breed shrimp and produce nauplii or even postlarvae, which they sell to farms. Large shrimp farms maintain their own hatcheries and sell nauplii or postlarvae to smaller farms in the region.
Nurseries grow postlarvae and accustom them to the marine conditions in the grow-out ponds.
In the grow-out ponds the shrimp are grown from juveniles to marketable size, which takes between three and six months.
Most farms produce one to two harvests a year; in tropical climates, even three are possible. Because of the need for salt water, shrimp farms are located on or near a coast. Inland shrimp farms have also been tried in some regions, but the need to ship salt water and competition for land with agricultural users led to problems. Thailand banned inland shrimp farms in 1999.
Hatcheries
Small-scale hatcheries are very common throughout Southeast Asia. Often run as family businesses and using a low-technology approach, they use small tanks (less than ten tons) and often low animal densities. They are susceptible to disease, but due to their small size, they can typically restart production quickly after disinfection. The survival rate is anywhere between zero and 90%, depending on a wide range of factors, including disease, the weather, and the experience of the operator.
Greenwater hatcheries are medium-sized hatcheries using large tanks with low animal densities. To feed the shrimp larvae, an algal bloom is induced in the tanks. The survival rate is about 40%.
Galveston hatcheries (named after Galveston, Texas, where they were developed) are large-scale, industrial hatcheries using a closed and tightly controlled environment. They breed the shrimp at high densities in large (15–30 t) tanks. Survival rates vary between 0% and 80%, but typically achieve 50%.
In hatcheries, the developing shrimp are fed on a diet of algae and later also brine shrimp nauplii, sometimes (especially in industrial hatcheries) augmented by artificial diets. The diet of later stages also includes fresh or freeze-dried animal protein, for example krill. Nutrition and medication (such as antibiotics) fed to the brine shrimp nauplii are passed on to the shrimp that eat them.
Nurseries
Many farms have nurseries where the postlarval shrimp are grown into juveniles for another three weeks in separate ponds, tanks, or so-called raceways. A raceway is a rectangular, long, shallow tank through which water flows continuously.
In a typical nursery, there are 150 to 200 animals per square metre. They are fed on a high-protein diet for at most three weeks before they are moved to the grow-out ponds. At that time, they weigh between one and two grams. The water salinity is adjusted gradually to that of the grow-out ponds.
Farmers refer to postlarvae as "PLs", with the number of days suffixed (i.e., PL-1, PL-2, etc.). They are ready to be transferred to the grow-out ponds after their gills have branched, which occurs around PL-13 to PL-17 (about 25 days after hatching). Nursing is not absolutely necessary, but is favoured by many farms because it makes for better food utilization, improves the size uniformity, helps use the infrastructure better, and can be done in a controlled environment to increase the harvest. The main disadvantage of nurseries is that some of the postlarval shrimp die upon the transfer to the grow-out pond.
Some farms do not use a nursery, but stock the postlarvae directly in the grow-out ponds after having acclimated them to the appropriate temperature and salinity levels in an acclimation tank. Over the course of a few days, the water in these tanks is changed gradually to match that of the grow-out ponds. The animal density should not exceed 500/litre for young postlarvae and 50/liter for larger ones, such as PL-15.
Grow-out
In the grow-out phase, the shrimp are grown to maturity. The postlarvae are transferred to ponds where they are fed until they reach marketable size, which takes about another three to six months. Harvesting the shrimp is done by fishing them from the ponds using nets or by draining the ponds. Pond sizes and the level of technical infrastructure vary.
Extensive shrimp farms using traditional low-density methods are invariably located on a coast and often in mangrove areas. The ponds range from just a few to more than 100 hectares; shrimp are stocked at low densities (2–3 animals per square metre, or 25,000/ha). The tides provide for some water exchange, and the shrimp feed on naturally occurring organisms. In some areas, farmers even grow wild shrimp by just opening the gates and impounding wild larvae. Prevalent in poorer or less developed countries where land prices are low, extensive farms produce annual yields from 50 to 500 kg/ha of shrimp (head-on weight). They have low production costs (US$1–3/kg live shrimp), are not very labor-intensive, and do not require advanced technical skills.
Semi-intensive farms do not rely on tides for water exchange, but use pumps and a planned pond layout. They can therefore be built above the high tide line. Pond sizes range from 2 to 30 ha; the stocking densities range from 10 to 30/square meter (100,000–300,000/ha). At such densities, artificial feeding using industrially prepared shrimp feeds and fertilizing the pond to stimulate the growth of naturally occurring organisms become a necessity. Annual yields range from 500 to 5,000 kg/ha, while production costs are in the range of US$2–6/kg live shrimp. With densities above 15 animals per square meter, aeration is often required to prevent oxygen depletion. Productivity varies depending upon water temperature, thus it is common to have larger sized shrimp in some seasons than in others.
Intensive farms use even smaller ponds () and even higher stocking densities. The ponds are actively managed: they are aerated, there is a high water exchange to remove waste products and maintain water quality, and the shrimp are fed on specially designed diets, typically in the form of formulated pellets. Such farms produce annual yields between 5,000 and 20,000 kg/ha; a few super-intensive farms can produce as much as 100,000 kg/ha. They require an advanced technical infrastructure and highly trained professionals for constant monitoring of water quality and other pond conditions; their production costs are in the range of US$4–8/kg live shrimp.
Estimates on the production characteristics of shrimp farms vary. Most studies agree that about 15-20% of all shrimp farms worldwide are extensive farms, another 25–30% are semi-intensive, and the rest are intensive farms. Regional variation is high, though, and Tacon reports wide discrepancies in the percentages claimed for individual countries by different studies.
Animal welfare
Eyestalk ablation is the removal of one (unilateral) or both (bilateral) eyestalks from a crustacean. It is routinely practiced on female shrimps (or prawns) in almost every marine shrimp maturation or reproduction facility in the world, both research and commercial. The aim of ablation under these circumstances is to stimulate the female shrimp to develop mature ovaries and spawn.
Most captive conditions for shrimp cause inhibitions in females that prevent them from developing mature ovaries. Even in conditions where a given species will develop ovaries and spawn in captivity, use of eyestalk ablation increases total egg production and increases the percentage of females in a given population that will participate in reproduction. Once females have been subjected to eyestalk ablation, complete ovarian development often ensues within as little as 3 to 10 days.
Feeding
While extensive farms mainly rely on the natural productivity of the ponds, more intensively managed farms rely on artificial shrimp feeds, either exclusively or as a supplement to the organisms that naturally occur in a pond. A food chain is established in the ponds, based on the growth of phytoplankton. Fertilizers and mineral conditioners are used to boost the growth of the phytoplankton to accelerate the growth of the shrimp. Waste from the artificial food pellets and shrimp excrement can lead to the eutrophication of the ponds.
Artificial feeds come in the form of specially formulated, granulated pellets that disintegrate quickly. Up to 70% of such pellets are wasted, as they decay before the shrimp have eaten them. They are fed two to five times daily; the feeding can be done manually either from ashore or from boats, or using mechanized feeders distributed all over a pond. The feed conversion rate (FCR), i.e. the amount of food needed to produce a unit (e.g. one kilogram) of shrimp, is claimed by the industry to be around 1.2–2.0 in modern farms, but this is an optimum value that is not always attained in practice. For a farm to be profitable, a feed conversion rate below 2.5 is necessary; in older farms or under suboptimal pond conditions, the ratio may easily rise to 4:1. Lower FCRs result in a higher profit for the farm.
Farmed species
Although there are many species of shrimp and prawn, only a few of the larger ones are actually cultivated, all of which belong to the family of penaeids (family Penaeidae), and within it to the genus Penaeus. Many species are unsuitable for farming: they are too small to be profitable, or simply stop growing when crowded together, or are too susceptible to diseases. The two species dominating the market are:
Pacific white shrimp (Litopenaeus vannamei, also called "whiteleg shrimp") is the main species cultivated in western countries. Native to the Pacific coast from Mexico to Peru, it grows to a size of 23 cm. L. vannamei accounts for 95% of the production in Latin America. It is easy to breed in captivity, but succumbs to the Taura disease.
Giant tiger prawn (P. monodon, also known as "black tiger shrimp") occurs in the wild in the Indian Ocean and in the Pacific Ocean from Japan to Australia. The largest of all the cultivated shrimp, it can grow to a length of 36 cm and is farmed in Asia. Because of its susceptibility to whitespot disease and the difficulty of breeding it in captivity, it is gradually being replaced by L. vannamei since 2001.
Together, these two species account for about 80% of the whole farmed shrimp production. Other species being bred are:
Western blue shrimp (P. stylirostris) was a popular choice for shrimp farming in the western hemisphere, until the IHHN virus wiped out nearly the whole population in the late 1980s. A few stocks survived and became resistant against this virus. When it was discovered that some of these were also resistant against the Taura virus, some farms again bred P. stylirostris from 1997 on.
Chinese white shrimp (P. chinensis, also known as the fleshy prawn) occurs along the coast of China and the western coast of Korea and is being farmed in China. It grows to a maximum length of only 18 cm, but tolerates colder water (min. 16 °C). Once a major factor on the world market, it is today used almost exclusively for the Chinese domestic market after a disease wiped out nearly all the stocks in 1993.
Kuruma shrimp (P. japonicus) is farmed primarily in Japan and Taiwan, but also in Australia; the only market is in Japan, where live Kuruma shrimp reach prices of the order of US$100 per pound ($220/kg).
Indian white shrimp (P. indicus) is a native of the coasts of the Indian Ocean and is widely bred in India, Iran and the Middle East and along the African shores.
Banana shrimp (P. merguiensis) is another cultured species from the coastal waters of the Indian Ocean, from Oman to Indonesia and Australia. It can be grown at high densities.
Several other species of Penaeus play only a very minor role in shrimp farming. Some other kinds of shrimp also can be farmed, e.g. the "Akiami paste shrimp" or Metapenaeus spp. Their total production from aquaculture is of the order of only about 25,000 tonnes per year, small in comparison to that of the penaeids.
Diseases
There are a variety of lethal viral diseases that affect shrimp. In the densely populated, monocultural farms such virus infections spread rapidly and may wipe out whole shrimp populations. A major transfer vector of many of these viruses is the water itself; and thus any virus outbreak also carries the danger of decimating shrimp living in the wild.
Yellowhead disease, called Hua leung in Thai, affects P. monodon throughout Southeast Asia. It had been reported first in Thailand in 1990. The disease is highly contagious and leads to mass mortality within 2 to 4 days. The cephalothorax of an infected shrimp turns yellow after a period of unusually high feeding activity ending abruptly, and the then moribund shrimp congregate near the surface of their pond before dying.
Early mortality syndrome (EMS) has been linked to a strain of a bacterium called Vibrio parahaemolyticus which affects the Giant Tiger Prawn and the Whiteleg Shrimp, both shrimp that are commonly farmed around the world. The strains are not harmful to humans, but are economically devastating for shrimp farmers. The spread of the bacteria is more prevalent in warmer and saltier ocean waters.
Whitespot syndrome is a disease caused by a family of related viruses. First reported in 1993 from Japanese P. japonicus cultures, it spread throughout Asia and then to the Americas. It has a wide host range and is highly lethal, leading to mortality rates of 100% within days. Symptoms include white spots on the carapace and a red hepatopancreas. Infected shrimp become lethargic before they die.
Taura syndrome was first reported from shrimp farms on the Taura river in Ecuador in 1992. The host of the virus causing the disease is P. vannamei, one of the two most commonly farmed shrimp. The disease spread rapidly, mainly through the shipping of infected animals and broodstock. Originally confined to farms in the Americas, it has also been propagated to Asian shrimp farms with the introduction of L. vannamei there. Birds are thought to be a route of infection between farms within one region.
Infectious hypodermal and hematopoietic necrosis (IHHN) is a disease that causes mass mortality among P. stylirostris (as high as 90%) and severe deformations in L. vannamei. It occurs in Pacific farmed and wild shrimp, but not in wild shrimp on the Atlantic coast of the Americas.
There are also a number of bacterial infections that are lethal to shrimp. The most common is vibriosis, caused by bacteria of the Vibrio species. The shrimp become weak and disoriented, and may have dark wounds on the cuticle. The mortality rate can exceed 70%. Another bacterial disease is necrotising hepatopancreatitis (NHP); symptoms include a soft exoskeleton and fouling. Most such bacterial infections are strongly correlated to stressful conditions, such as overcrowded ponds, high temperatures, and poor water quality, factors that positively influence the growth of bacteria. Treatment is done using antibiotics. Importing countries have repeatedly placed import bans on shrimp containing various antibiotics. One such antibiotic is chloramphenicol, which has been banned in the European Union since 1994, but continues to pose problems.
With their high mortality rates, diseases represent a very real danger to shrimp farmers, who may lose their income for the whole year if their ponds are infected. Since most diseases cannot yet be treated effectively, the industry's efforts are focused on preventing disease outbreak in the first place. Active water quality management helps avoid poor pond conditions favorable to the spread of diseases, and instead of using larvae from wild catches, specific pathogen free broodstocks raised in captivity in isolated environments and certified not to carry diseases are used increasingly. To avoid introducing diseases into such disease-free populations on a farm, there is also a trend to create more controlled environments in the ponds of semi-intensive farms, such as by lining them with plastic to avoid soil contact, and by minimizing water exchange in the ponds.
Economy
The total global production of farmed shrimp reached 2.5 million tonnes in 2005. This accounts for 42% of the total shrimp production that year (farming and wild catches combined). The largest single market for shrimp is the United States, importing between 500 – 600,000 tonnes of shrimp products yearly in the years 2003–2009. About 200,000 tonnes yearly are imported by Japan, while the European Union imported in 2006 another about 500,000 tonnes of tropical shrimps, with the largest importers being Spain and France. The EU also is a major importer of coldwater shrimp from catches, mainly common shrimp (Crangon crangon) and Pandalidae such as Pandalus borealis; in 2006, these imports accounted for about another 200,000 tonnes.
The import prices for shrimp fluctuate wildly. In 2003, the import price per kilogram shrimp in the United States was US$8.80, slightly higher than in Japan at US$8.00. The average import price in the EU was only about US$5.00/kg; this much lower value is explained by the fact that the EU imports more coldwater shrimp (from catches) that are much smaller than the farmed warm water species, and thus attain lower prices. In addition, Mediterranean Europe prefers head-on shrimp, which weigh approximately 30% more, but have a lower unit price.
About 75% of the world production of farmed shrimp comes from Asian countries; the two leading nations being China and Thailand, closely followed by Vietnam, Indonesia, and India. The other 25% are produced in the western hemisphere, where Latin American countries (Brazil, Ecuador, Mexico) dominate. In terms of export, Thailand is by far the leading nation, with a market share of more than 30%, followed by China, Indonesia, and India, accounting each for about 10%. Other major export nations are Vietnam, Bangladesh, and Ecuador. Thailand exports nearly all of its production, while China uses most of its shrimp in the domestic market. The only other major export nation that has a strong domestic market for farmed shrimp is Mexico.
Disease problems have repeatedly impacted the shrimp production negatively. Besides the near-wipeout of P. chinensis in 1993, there were outbreaks of viral diseases that led to marked declines in the per-country production in 1996/97 in Thailand and repeatedly in Ecuador. In Ecuador alone, production suffered heavily in 1989 (IHHN), 1993 (Taura), and 1999 (whitespot). Another reason for sometimes wild changes in shrimp farm output are the import regulations of the destination countries, which do not allow shrimp contaminated by chemicals or antibiotics to be imported.
In the 1980s and through much of the 1990s, shrimp farming promised high profits. The investments required for extensive farms were low, especially in regions with low land prices and wages. For many tropical countries, especially those with poorer economies, shrimp farming was an attractive business, offering jobs and incomes for poor coastal populations and has, due to the high market prices of shrimp, provided many developing countries with non-negligible foreign currency earnings. Many shrimp farms were funded initially by the World Bank or substantially subsidized by local governments.
In the late 1990s, the economic situation changed. Governments and farmers alike were under increasing pressure from NGOs and the consumer countries, who criticized the practices of the trade. International trade conflicts erupted, such as import bans by consumer countries on shrimp containing antibiotics, the United States' shrimp import ban against Thailand in 2004 as a measure against Thai shrimp fishers not using turtle excluder devices in their nets, or the "anti-dumping" case initiated by U.S. shrimp fishers in 2002 against shrimp farmers worldwide, which resulted two years later in the U.S. imposing antidumping tariffs of the order of about 10% against many producer countries (except China, which received a 112% duty). Diseases caused significant economic losses. In Ecuador, where shrimp farming was a major export sector (the other two are bananas and oil), the whitespot outbreak of 1999 caused an estimated 130,000 workers to lose their jobs. Furthermore, shrimp prices dropped sharply in 2000. All of these factors contributed to the slowly growing acceptance by farmers that improved farming practices were needed, and resulted in tighter government regulation of the business, both of which internalized some of the external costs that were ignored during the boom years.
Socioeconomic aspects
Shrimp farming offers significant employment opportunities, which may help alleviate the poverty of the local coastal populations in many areas, if it is properly managed. The published literature on that topic shows large discrepancies, and much of the available data are of anecdotal nature. Estimates of the labor intensity of shrimp farms range from about one-third to three times more than when the same area was used for rice paddies, with much regional variation and depending on the type of farms surveyed. In general, intensive shrimp farming requires more labor per unit area than extensive farming. Extensive shrimp farms cover much more land area and are often, but not always, located in areas where no agricultural land uses are possible. Supporting industries such as feed production or storage, handling, and trade companies should also not be neglected, even if not all of them are exclusive to shrimp farming.
Typically, workers on a shrimp farm can get better wages than with other employment. A global estimate from one study is that a shrimp farm worker can earn 1.5–3 times as much as in other jobs; a study from India arrived at a salary increase of about 1.6, and a report from Mexico states the lowest paid job at shrimp farms was paid in 1996 at 1.22 times the average worker salary in the country.
NGOs have frequently criticized that most of the profits went to large conglomerates instead of to the local population. While this may be true in certain regions, such as Ecuador, where most shrimp farms are owned by large companies, it does not apply in all cases. For instance in Thailand, most farms are owned by small local entrepreneurs, although there is a trend to vertically integrate the industries related to shrimp farming from feed producers to food processors and trade companies. A 1994 study reported a farmer in Thailand could increase their income by a factor of ten by switching from growing rice to farming shrimp. An Indian study from 2003 arrives at similar figures for shrimp farming in the East Godavari district in Andhra Pradesh.
Whether the local population benefits from shrimp farming is also dependent on the availability of sufficiently trained people. Extensive farms tend to offer mainly seasonal jobs during harvest that do not require much training. In Ecuador, many of these positions are known to have been filled by migrant workers. More intensive farms have a need for year-round labor in more sophisticated jobs.
Marketing
For commercialization, shrimp are graded and marketed in different categories. From complete shrimp (known as "head-on, shell-on" or HOSO) to peeled and deveined (P&D), any presentation is available in stores. The animals are graded by their size uniformity and then also by their count per weight unit, with larger shrimp attaining higher prices.
Ecological impacts
Shrimp farms of all types, from extensive to super-intensive, can cause severe ecological problems wherever they are located. For extensive farms, huge areas of mangroves were cleared, reducing biodiversity. During the 1980s and 1990s, about 35% of the world's mangrove forests had vanished. Shrimp farming was a major cause of this, accounting for over a third of it according to one study; other studies report between 5% and 10% globally, with enormous regional variability. Other causes of mangrove destruction are population pressure, logging, pollution from other industries, or conversion to other uses such as salt pans. Mangroves, through their roots, help stabilize a coastline and capture sediments; their removal has led to a marked increase of erosion and less protection against floods. Mangrove estuaries are also especially rich and productive ecosystems and provide the spawning grounds for many species of fish, including many commercially important ones. Many countries have protected their mangroves and forbidden the construction of new shrimp farms in tidal or mangrove areas. The enforcement of the respective laws is often problematic, though, and especially in the least developed countries such as Bangladesh, Myanmar, or Vietnam the conversion of mangroves to shrimp farms remains an issue for areas such as the Myanmar Coast mangroves.
Intensive farms, while reducing the direct impact on the mangroves, have other problems. Their nutrient-rich effluents (industrial shrimp feeds disintegrate quickly, as little as 30% are actually eaten by the shrimp with a corresponding economic loss to the farmer, the rest is wasted) are typically discharged into the environment, seriously upsetting the ecological balance. These waste waters contain significant amounts of chemical fertilizers, pesticides, and antibiotics that cause pollution of the environment. Furthermore, releasing antibiotics in such ways injects them into the food chain and increases the risks of bacteria becoming resistant against them. However, most aquatic bacteria, unlike bacteria associated with terrestrial animals, are not zoonotic. Only a few disease transfers from animals to humans have been reported.
Prolonged use of a pond can lead to an incremental buildup of a sludge at the pond's bottom from waste products and excrement. The sludge can be removed mechanically, or dried and plowed to allow biodecomposition, at least in areas without acid problems. Flushing a pond never completely removes this sludge, and eventually, the pond is abandoned, leaving behind a wasteland, with the soil made unusable for any other purposes due to the high levels of salinity, acidity, and toxic chemicals. A typical pond in an extensive farm can be used only a few years. An Indian study estimated the time to rehabilitate such lands to about 30 years. Thailand has banned inland shrimp farms since 1999 because they caused too much destruction of agricultural lands due to salination. A Thai study estimated 60% of the shrimp farming area in Thailand was abandoned in the years 1989–1996. Many of these problems stem from using mangrove land that has high natural pyrite content (acid sulfate soil) and poor drainage. The shift to semi-intensive farming requires higher elevations for drain harvesting and low sulfide (pyrite) content to prevent acid formation when the soils shift from anaerobic to aerobic conditions.
The global nature of the shrimp farming business, and in particular the shipment of broodstock and hatchery products, throughout the world have not only introduced various shrimp species as exotic species, but also distributed the diseases the shrimp may carry worldwide. As a consequence, most broodstock shipments require health certificates and/or to have specific pathogen free (SPF) status. Many organizations lobby actively for consumers to avoid buying farmed shrimp; some also advocate the development of more sustainable farming methods. A joint programme of the World Bank, the Network of Aquaculture Centres in Asia-Pacific (NACA), the WWF, and the FAO was established in August 1999 to study and propose improved practices for shrimp farming. Some existing attempts at sustainable export-oriented shrimp farming marketing the shrimp as "ecologically produced" are criticized by NGOs as being dishonest and trivial window-dressing.
Yet, the industry has been slowly changing since about 1999. It has adopted the "best management practices" developed by the World Bank program, for example, and others. and instituted educational programs to promote them. Due to the mangrove protection laws enacted in many countries, new farms are usually of the semi-intensive kind, which are best constructed outside mangrove areas anyway. There is a trend to create even more tightly controlled environments in these farms, with the hope to achieve better disease prevention. Waste water treatment has attracted considerable attention; modern shrimp farms routinely have effluent treatment ponds where sediments are allowed to settle at the bottom and other residuals are filtered. As such improvements are costly, the World Bank program also recommends low-intensity polyculture farming for some areas. Since it has been discovered that mangrove soils are effective in filtering waste waters and tolerate high nitrate levels, the industry has also developed an interest in mangrove reforestation, although its contributions in that area are still minor. The long-term effects of these recommendations and industry trends cannot be evaluated conclusively yet.
Still, it was reported in 2012 that one pound of frozen shrimp adds one ton of carbon dioxide to the atmosphere, more than ten times that generated to produce the same weight of beef raised on cleared rainforest land.
Social changes
Shrimp farming in many cases has far-reaching effects on the local coastal population. Especially in the boom years of the 1980s and 1990s, when the business was largely unregulated in many countries, the very fast expansion of the industry caused significant changes that sometimes were detrimental to the local population. Conflicts can be traced back to two root causes: competition for common resources such as land and water, and changes induced by wealth redistribution.
A significant problem causing much conflict in some regions, for instance in Bangladesh, are the land use rights. With shrimp farming, a new industry expanded into coastal areas and started to make exclusive use of previously public resources. In some areas, the rapid expansion resulted in the local coastal population being denied access to the coast by a continuous strip of shrimp farms with serious impacts on the local fisheries. Such problems were compounded by poor ecological practices that caused a degradation of common resources (such as excessive use of freshwater to control the salinity of the ponds, causing the water table to sink and leading to the salination of freshwater aquifers by an inflow of salt water). With growing experience, countries usually introduced stronger governmental regulations and have taken steps to mitigate such problems, for instance through land zoning legislations. Some late adopters have even managed to avoid some problems through proactive legislation, e.g. Mexico. The situation in Mexico is unique owing to the strongly government-regulated market. Even after the liberalisation in the early 1990s, most shrimp farms are still owned and controlled by locals or local co-ops ().
Social tensions have occurred due to changes in the wealth distribution within populations. The effects of this are mixed, though, and the problems are not unique to shrimp farming. Changes in the distribution of wealth tend to induce changes in the power structure within a community. In some cases, there is a widening gap between the general population and local elites who have easier access to credits, subsidies, and permits and thus are more likely to become shrimp farmers and benefit more. In Bangladesh, on the other hand, local elites were opposing shrimp farming, which was controlled largely by an urban elite. Land concentrations in a few hands has been recognized to carry an increased risk of social and economic problems developing, especially if the landowners are non-local.
In general, it has been found that shrimp farming is accepted best and introduced most easily and with the greatest benefits for the local communities if the farms are owned by local people instead of by restricted remote élites or large companies because local owners have a direct interest in maintaining the environment and good relations with their neighbors, and because it avoids the formation of large-scale land property.
Sustainable practices
Although shrimp farming has disrupted social structures, it is possible for both commercial industries and independent farmers to succeed. Closed system shrimp aquaculture for instance, is becoming widely used in the US and is making its way to Southeast Asia. This system takes place indoors in moderate sized pools which efficiently circulates the water. In some cases filter feeders such as shellfish and other fish are introduced in the system, feeding off nutrients in the water that would otherwise be cycled out. This option is more environmentally safe than large scale intensive farming practices. Unfortunately, this system is capital intensive and would be difficult for small scale, independent shrimp farmers to acquire. However, this would be an excellent alternative for larger shrimp industries in Thailand.
Another alternative would be to revert to traditional shrimp farming practices, without overstocking and the use of harmful chemicals. This would be an ideal option for small scale shrimp farmers supplying for their own community as well as creating an independent food source.
| Technology | Aquaculture | null |
2167409 | https://en.wikipedia.org/wiki/Freshwater%20prawn%20farming | Freshwater prawn farming | A freshwater prawn farm is an aquaculture business designed to raise and produce freshwater prawns or shrimp for human consumption. Freshwater prawn farming shares many characteristics with, and many of the same problems as, marine shrimp farming. Unique problems are introduced by the developmental life cycle of the main species (the giant river prawn, Macrobrachium rosenbergii).
The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tons, of which China produced some 180,000 tons, followed by India and Thailand with some 35,000 tons each. Additionally, China produced about 370,000 tons of Chinese river crab (Eriocheir sinensis).
Species
All farmed freshwater prawns today belong to the genus Macrobrachium. Until 2000, the only species farmed was the giant river prawn (Macrobrachium rosenbergii, also known as the Malaysian prawn). Since then, China has begun farming the Oriental river prawn (M. nipponense) in large quantities, and India farms a small amount of monsoon river prawn (M. malcolmsonii). In 2003, these three species accounted for all farmed freshwater prawns, about two-thirds M. rosenbergii and one-third M. nipponense.
About 200 species in the genus Macrobrachium live in the tropical and subtropical climates on all continents except Europe and Antarctica.
Biology of Macrobrachium rosenbergii
Giant river prawns live in turbid freshwater, but their larval stages require brackish water to survive.
Males can reach a body size of 32 cm; females grow to 25 cm. In mating, the male deposits spermatophores on the underside of the female's thorax, between the walking legs. The female then extrudes eggs, which pass through the spermatophores. The female carries the fertilized eggs with her until they hatch; the time may vary, but is generally less than three weeks. A large female may lay up to 100,000 eggs.
From these eggs hatch zoeae, the first larval stage of crustaceans. They drift towards brackish waters where they go through several larval stages before metamorphosing into postlarvae, at which stage they are about 8 mm long and have all the characteristics of adults. This metamorphosis usually takes place about 32 to 35 days after hatching. These postlarvae then migrate back into freshwater.
There are three different morphotypes of males. The first stage is called "small male" (SM); this smallest stage has short, nearly translucent claws. If conditions allow, small males grow and metamorphose into "orange claw" (OC) males, which have large orange claws on their second chelipeds, which may have a length of 0.8 to 1.4 times their body size. OC males later may transform into the third and final stage, the "blue claw" (BC) males. These have blue claws, and their second chelipeds may become twice as long as their body.
Male M. rosenbergii prawns have a strict hierarchy: the territorial BC males dominate the OCs, which in turn dominate the SMs. The presence of BC males inhibits the growth of SMs and delays the metamorphosis of OCs into BCs; an OC will keep growing until it is larger than the largest BC male in its neighbourhood before transforming. All three male stages are sexually active, though, and females which have undergone their premating molt will cooperate with any male to reproduce. BC males protect the females until their shells have hardened; OCs and SMs show no such behavior.
Technology
Giant river prawns have been farmed using traditional methods in Southeast Asia for a long time. First experiments with artificial breeding cultures of M. rosenbergii were done in the early 1960s in Malaysia, where it was discovered that the larvae needed brackish water for survival. Industrial-scale rearing processes were perfected in the early 1970s in Hawaii, and spread first to Taiwan and Thailand, and then to other countries.
The technologies used in freshwater prawn farming are basically the same as in marine shrimp farming. Hatcheries produce postlarvae, which then are grown and acclimated in nurseries before being transferred into growout ponds, where the prawns are then fed and grown until they reach marketable size. Harvesting is done by either draining the pond and collecting the animals ("batch" harvesting) or by fishing the prawns out of the pond using nets (continuous operation).
Due to the aggressive nature of M. rosenbergii and the hierarchy between males, stocking densities are much lower than in marine penaeid shrimp farms. Intensive farming is not possible due to the increased level of cannibalism, so all farms are either stocked semi-intensively (4 to 20 postlarvae per square metre) or, in extensive farms, at even lower densities (1 to 4/m2). The management of the growout ponds must take into account the growth characteristics of M. rosenbergii: the presence of blue-claw males inhibits the growth of small males, and delays the metamorphosis of OC males into BCs. Some farms fish off the largest prawns from the pond using seines to ensure a healthy composition of the pond's population, designed to optimize the yield, even if they employ batch harvesting. The heterogeneous individual growth of M. rosenbergii makes growth control necessary even if a pond is stocked newly, starting from scratch: some animals will grow faster than others and become dominant BCs, stunting the growth of other individuals.
The FAO considers the ecological impact of freshwater prawn farming to be less severe than in shrimp farming. The prawns are cultured at much lower densities, meaning less concentrated waste products and a lesser danger of the ponds becoming breeding places for diseases. The growout ponds do not salinate agricultural land, as do those of inland marine shrimp farms. However, the lower yield per area means that the income per Ha is also lower and a given area can support fewer humans. This limits the culture area to low value lands where intensification is not required. Freshwater prawn farms do not endanger mangroves, and are better amenable to small-scale businesses run by a family. However, like marine farmed shrimp, M. rosenbergii is also susceptible to a variety of viral or bacterial diseases, including white tail disease, also called "white muscle disease".
Economics
The global annual production of freshwater prawns in 2003 was about 280,000 tonnes, of which China produced some 180,000 tonnes, followed by India and Thailand with some 35,000 tonnes each. Other major producer countries are Taiwan, Bangladesh, and Vietnam. In the United States, only a few hundred small farms for M. rosenbergii produced about 50 tonnes in 2003.
| Technology | Aquaculture | null |
2168763 | https://en.wikipedia.org/wiki/Reyn | Reyn | In fluid dynamics, the reyn is a British unit of dynamic viscosity,
named in honour of Osbourne Reynolds, for whom the Reynolds number is also named.
Conversions
By definition,
1 reyn = 1 lbf s in−2.
It follows that the relation between the reyn and the poise is approximately
1 reyn = 6.89476 × 104 P.
In SI units, viscosity is expressed in newton-seconds per square meter, or equivalently in pascal-seconds. The conversion factor between the two is approximately
1 reyn = 6890 Pa s.
| Physical sciences | Viscosity | Basics and measurement |
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