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Consistency
Gödel's second incompleteness theorem says that a recursively axiomatizable system that can interpret Robinson arithmetic can prove its own consistency only if it is inconsistent. Moreover, Robinson arithmetic can be interpreted in general set theory, a small fragment of ZFC. Hence the consistency of ZFC cannot be proved within ZFC itself (unless it is actually inconsistent). Thus, to the extent that ZFC is identified with ordinary mathematics, the consistency of ZFC cannot be demonstrated in ordinary mathematics. The consistency of ZFC does follow from the existence of a weakly inaccessible cardinal, which is unprovable in ZFC if ZFC is consistent. Nevertheless, it is deemed unlikely that ZFC harbors an unsuspected contradiction; it is widely believed that if ZFC were inconsistent, that fact would have been uncovered by now. This much is certain — ZFC is immune to the classic paradoxes of naive set theory: Russell's paradox, the Burali-Forti paradox, and Cantor's paradox.
studied a subtheory of ZFC consisting of the axioms of extensionality, union, powerset, replacement, and choice. Using models, they proved this subtheory consistent, and proved that each of the axioms of extensionality, replacement, and power set is independent of the four remaining axioms of this subtheory. If this subtheory is augmented with the axiom of infinity, each of the axioms of union, choice, and infinity is independent of the five remaining axioms. Because there are non-well-founded models that satisfy each axiom of ZFC except the axiom of regularity, that axiom is independent of the other ZFC axioms.
If consistent, ZFC cannot prove the existence of the inaccessible cardinals that category theory requires. Huge sets of this nature are possible if ZF is augmented with Tarski's axiom. Assuming that axiom turns the axioms of infinity, power set, and choice (7 – 9 above) into theorems. | Zermelo–Fraenkel set theory | Wikipedia | 416 | 152214 | https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel%20set%20theory | Mathematics | Axiomatic systems | null |
Independence
Many important statements are independent of ZFC. The independence is usually proved by forcing, whereby it is shown that every countable transitive model of ZFC (sometimes augmented with large cardinal axioms) can be expanded to satisfy the statement in question. A different expansion is then shown to satisfy the negation of the statement. An independence proof by forcing automatically proves independence from arithmetical statements, other concrete statements, and large cardinal axioms. Some statements independent of ZFC can be proven to hold in particular inner models, such as in the constructible universe. However, some statements that are true about constructible sets are not consistent with hypothesized large cardinal axioms.
Forcing proves that the following statements are independent of ZFC:
Axiom of constructibility (V=L) (which is also not a ZFC axiom)
Continuum hypothesis
Diamond principle
Martin's axiom (which is not a ZFC axiom)
Suslin hypothesis
Remarks:
The consistency of V=L is provable by inner models but not forcing: every model of ZF can be trimmed to become a model of ZFC + V=L.
The diamond principle implies the continuum hypothesis and the negation of the Suslin hypothesis.
Martin's axiom plus the negation of the continuum hypothesis implies the Suslin hypothesis.
The constructible universe satisfies the generalized continuum hypothesis, the diamond principle, Martin's axiom and the Kurepa hypothesis.
The failure of the Kurepa hypothesis is equiconsistent with the existence of a strongly inaccessible cardinal.
A variation on the method of forcing can also be used to demonstrate the consistency and unprovability of the axiom of choice, i.e., that the axiom of choice is independent of ZF. The consistency of choice can be (relatively) easily verified by proving that the inner model L satisfies choice. (Thus every model of ZF contains a submodel of ZFC, so that Con(ZF) implies Con(ZFC).) Since forcing preserves choice, we cannot directly produce a model contradicting choice from a model satisfying choice. However, we can use forcing to create a model which contains a suitable submodel, namely one satisfying ZF but not C. | Zermelo–Fraenkel set theory | Wikipedia | 465 | 152214 | https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel%20set%20theory | Mathematics | Axiomatic systems | null |
Another method of proving independence results, one owing nothing to forcing, is based on Gödel's second incompleteness theorem. This approach employs the statement whose independence is being examined, to prove the existence of a set model of ZFC, in which case Con(ZFC) is true. Since ZFC satisfies the conditions of Gödel's second theorem, the consistency of ZFC is unprovable in ZFC (provided that ZFC is, in fact, consistent). Hence no statement allowing such a proof can be proved in ZFC. This method can prove that the existence of large cardinals is not provable in ZFC, but cannot prove that assuming such cardinals, given ZFC, is free of contradiction.
Proposed additions
The project to unify set theorists behind additional axioms to resolve the continuum hypothesis or other meta-mathematical ambiguities is sometimes known as "Gödel's program". Mathematicians currently debate which axioms are the most plausible or "self-evident", which axioms are the most useful in various domains, and about to what degree usefulness should be traded off with plausibility; some "multiverse" set theorists argue that usefulness should be the sole ultimate criterion in which axioms to customarily adopt. One school of thought leans on expanding the "iterative" concept of a set to produce a set-theoretic universe with an interesting and complex but reasonably tractable structure by adopting forcing axioms; another school advocates for a tidier, less cluttered universe, perhaps focused on a "core" inner model.
Criticisms
ZFC has been criticized both for being excessively strong and for being excessively weak, as well as for its failure to capture objects such as proper classes and the universal set.
Many mathematical theorems can be proven in much weaker systems than ZFC, such as Peano arithmetic and second-order arithmetic (as explored by the program of reverse mathematics). Saunders Mac Lane and Solomon Feferman have both made this point. Some of "mainstream mathematics" (mathematics not directly connected with axiomatic set theory) is beyond Peano arithmetic and second-order arithmetic, but still, all such mathematics can be carried out in ZC (Zermelo set theory with choice), another theory weaker than ZFC. Much of the power of ZFC, including the axiom of regularity and the axiom schema of replacement, is included primarily to facilitate the study of the set theory itself. | Zermelo–Fraenkel set theory | Wikipedia | 506 | 152214 | https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel%20set%20theory | Mathematics | Axiomatic systems | null |
On the other hand, among axiomatic set theories, ZFC is comparatively weak. Unlike New Foundations, ZFC does not admit the existence of a universal set. Hence the universe of sets under ZFC is not closed under the elementary operations of the algebra of sets. Unlike von Neumann–Bernays–Gödel set theory (NBG) and Morse–Kelley set theory (MK), ZFC does not admit the existence of proper classes. A further comparative weakness of ZFC is that the axiom of choice included in ZFC is weaker than the axiom of global choice included in NBG and MK.
There are numerous mathematical statements independent of ZFC. These include the continuum hypothesis, the Whitehead problem, and the normal Moore space conjecture. Some of these conjectures are provable with the addition of axioms such as Martin's axiom or large cardinal axioms to ZFC. Some others are decided in ZF+AD where AD is the axiom of determinacy, a strong supposition incompatible with choice. One attraction of large cardinal axioms is that they enable many results from ZF+AD to be established in ZFC adjoined by some large cardinal axiom. The Mizar system and metamath have adopted Tarski–Grothendieck set theory, an extension of ZFC, so that proofs involving Grothendieck universes (encountered in category theory and algebraic geometry) can be formalized. | Zermelo–Fraenkel set theory | Wikipedia | 300 | 152214 | https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel%20set%20theory | Mathematics | Axiomatic systems | null |
The persimmon () is the edible fruit of a number of species of trees in the genus Diospyros. The most widely cultivated of these is the kaki persimmon, Diospyros kaki Diospyros is in the family Ebenaceae, and a number of non-persimmon species of the genus are grown for ebony timber. In 2022, China produced 77% of the world total of persimmons.
Description
Like the tomato, the persimmon is not a berry in the general culinary sense, but its morphology as a single fleshy fruit derived from the ovary of a single flower means it is a berry in the botanical sense. The tree Diospyros kaki is the most widely cultivated species of persimmon. Typically the tree reaches in height and is round-topped. It usually stands erect, but sometimes can be crooked or have a willowy appearance.
The leaves are long, and are oblong in shape with brown-hairy petioles in length. They are leathery and glossy on the upper surface, brown and silky underneath. The leaves are deciduous and bluish-green in color. In autumn, they turn to yellow, orange, or red.
Persimmon trees are typically dioecious, meaning male and female flowers are produced on separate trees. Some trees have both male and female flowers and in rare cases may bear a perfect flower, which contains both male and female reproductive organs in one flower. Male flowers are pink and appear in groups of three. They have a four-parted calyx, a corolla, and 24 stamens in two rows. Female flowers are creamy-white and appear singly. They have a large calyx, a four-parted, yellow corolla, eight undeveloped stamens, and a rounded ovary bearing the style and stigma. 'Perfect' flowers are a cross between the two. | Persimmon | Wikipedia | 392 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
Persimmon fruit matures late in the fall and can stay on the tree until winter. In color, the ripe fruit of the cultivated strains range from glossy light yellow-orange to dark red-orange depending on the species and variety. They similarly vary in size from in diameter, and in shape the varieties may be spherical, acorn-, or pumpkin-shaped. The flesh is astringent until fully ripe and is yellow, orange, or dark-brown in color. The calyx generally remains attached to the fruit after harvesting, but becomes easy to remove once the fruit is ripe. The ripe fruit is high in sucrose, mainly in the form of fructose and glucose content, and is sweet in taste.
Chemistry
Persimmon fruits contain phytochemicals, such as catechin, gallocatechin and betulinic acid.
Taxonomy
Selected species
While many species of Diospyros bear fruit inedible to humans or only occasionally gathered, the following are grown for their edible fruit:
Diospyros kaki (Oriental persimmon)
Oriental persimmon, Chinese persimmon or Japanese persimmon (Diospyros kaki) is the most commercially important persimmon. It is native to China, Northeast India and northern Indochina. It was first cultivated in China more than 2,000 years ago, and introduced to Japan in the 7th century and to Korea in the 14th century. China, Japan and South Korea are also the top producers of persimmon. It is known as shi (柿) in Chinese, kaki (柿) in Japanese and gam (감) in Korean and also known as Korean mango. It is known as haluwabed (हलुवाबेद) in Nepal and it is used for various culinary purposes and eaten as a seasonal fruit. In Nepal, it is one of the most popular fruits and has been consumed for a very long time. It was introduced to California and southern Europe in the 1800s and to Brazil in the 1890s, in the State of São Paulo, afterwards spreading across Brazil with Japanese immigrants; the State of São Paulo is still the greatest producer within Brazil, with an area of dedicated to persimmon culture in 2003; It is deciduous, with broad, stiff leaves. Its fruits are sweet and slightly tangy with a soft to occasionally fibrous texture.
Varieties | Persimmon | Wikipedia | 486 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
Numerous cultivars have been selected. Some varieties are edible in the crisp, firm state but it has its best flavor when allowed to rest and soften slightly after harvest. The Japanese cultivar 'Hachiya' is widely grown. The fruit has a high tannin content, which makes the unripe fruit astringent and bitter. The tannin levels are reduced as the fruit matures. Persimmons like 'Hachiya' must be completely ripened before consumption. When ripe, this fruit consists of thick, pulpy jelly encased in a waxy thin-skinned shell.
Commercially and in general, there are two types of persimmon fruit: astringent and non-astringent. | Persimmon | Wikipedia | 151 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
The heart-shaped Hachiya is the most common variety of astringent persimmon. Astringent persimmons contain very high levels of soluble tannins and are unpalatable if eaten before completely softened. The astringency of tannins is removed in various ways. Examples include ripening by exposure to light for several days and wrapping the fruit in paper (probably because this increases the ethylene concentration of the surrounding air). Ethylene ripening can be increased in reliability and evenness, and the process can be greatly accelerated by adding ethylene gas to the atmosphere in which the fruit is stored. For domestic purposes, the most convenient and effective process is to store the ripening persimmons in a clean, dry container together with other varieties of fruit that give off particularly large quantities of ethylene while they are ripening; apples and related fruits such as pears are effective, as well as bananas and several others. Other chemicals are used commercially in artificially ripening persimmons or delaying their ripening. Examples include alcohol and carbon dioxide, which change tannin into the insoluble form. Such bletting processes sometimes are jump-started by exposing the fruit to cold or frost. The resultant cell damage stimulates the release of ethylene, which promotes cellular wall breakdown. Astringent varieties of persimmons also can be prepared for commercial purposes by drying. Tanenashi fruit will occasionally contain a seed or two, which can be planted and will yield a larger, more vertical tree than when merely grafted onto the D. virginiana rootstock most commonly used in the U.S. Such seedling trees may produce fruit that bears more seeds, usually six to eight per fruit, and the fruit itself may vary slightly from the parent tree. Seedlings are said to be more susceptible to root nematodes.
The non-astringent persimmon is squat like a tomato and is most commonly sold as fuyu. Non-astringent persimmons are not actually free of tannins as the term suggests but rather are far less astringent before ripening and lose more of their tannic quality sooner. Non-astringent persimmons may be consumed when still very firm and remain edible when very soft. | Persimmon | Wikipedia | 482 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
There is a third type, less commonly available, the pollination-variant non-astringent persimmons. When fully pollinated, the flesh of these fruit is brown inside—known as goma in Japan—and the fruit can be eaten when firm. These varieties are highly sought after. Tsurunoko, sold as "chocolate persimmon" for its dark brown flesh, Maru, sold as "cinnamon persimmon" for its spicy flavor, and Hyakume, sold as "brown sugar", are the three best known.
Diospyros lotus (date-plum)
Date-plum (Diospyros lotus), also known as lotus persimmon, is native to temperate Asia and southeast Europe. Its English name probably derives from Persian Khormaloo خرمالو literally "date-plum", referring to the taste of this fruit, which is reminiscent of both plums and dates.
Diospyros decandra
Diospyros decandra is native to Mainland Southeast Asia and its fruit peel is golden yellow.
Diospyros virginiana (American persimmon)
American persimmon (Diospyros virginiana) is native to the eastern United States. Harvested in the fall or after the first frost, its fruit is eaten fresh, in baked goods, in steamed puddings, and to make a mildly alcoholic beverage called persimmon beer.
Varieties
Prok
Killen
Claypool
I-115
Dollywood
100-42
100-43
100-45
Early Golden
John Rick
C-100
JF-I
Diospyros blancoi (velvet persimmon)
The Mabolo or velvet-apple (Diospyros blancoi; syn. Diospyros discolor) is native to Taiwan, the Philippines and Borneo.
Diospyros texana (Texas persimmon)
Texas persimmon (Diospyros texana) is native to central and west Texas and southwest Oklahoma in the United States, and eastern Chihuahua, Coahuila, Nuevo León, and Tamaulipas in northeastern Mexico. The fruit of D. texana are black, subglobose berries with a diameter of that ripen in August.
The fleshy berries become edible when they turn dark purple or black, at which point they are sweet and can be eaten from the hand or made into pudding or custard.
Etymology | Persimmon | Wikipedia | 491 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
The word persimmon is derived from putchamin, pasiminan, pechimin or pessamin, from Powhatan, an Algonquian language of the southern and eastern United States, meaning "a dry fruit". Other sources have suggested that the word "persimmon" comes from a Persian word meaning date-plum. It was first used in English in the early 17th century.
Production
In 2022, world production of persimmons was 4.44 million tonnes, led by China with 77% of the total (table).
In China, the Taiqiu persimmon variety yields approximately 30 tonnes of fruit per year at full production.
Australia
The persimmon was introduced to Australia by Chinese immigrants in the 1850s. Only astringent varieties were cultivated until the introduction of non-astringent varieties from Japan in the 1970s. In 2022 the vast majority of persimmons sold domestically in Australia were non-astringent varieties.
Azerbaijan
Persimmons are one of Azerbaijan's most important non-petroleum exports. The main export markets are Russia, Ukraine, Belarus, Iran, Kazakhstan and the United Arab Emirates.
India
Persimmons have various local names across India, including japani phal or amar phal in Uttar Pradesh, amlok in Assam, lukum in Manipur, and Seemai Panichai in Tamilnadu. They are grown in Jammu & Kashmir, Himachal Pradesh, Tamil Nadu, Uttarakhand, Sikkim, Darjeeling Region of West Bengal & Arunachal Pradesh.
Israel
The primary variety produced in Israel is the Sharon fruit. Israel produces of Sharon fruit a year.
"Sharon fruit" (named after the Sharon plain in Israel) is the marketing name for the Israeli-bred cultivar 'Triumph'. As with most commercial pollination-variant-astringent persimmons, the fruit are ripened off the tree by exposing them to carbon dioxide. The "sharon fruit" has no core, is seedless and particularly sweet, and can be eaten whole.
Spain
The primary variety produced in Spain is the Rojo Brillante. Spain produces 400,000 tons of Rojo Brillante a year. | Persimmon | Wikipedia | 457 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
In the Valencia region of Spain, there is a production area of kaki called the "Ribera del Xùquer" which has a protected label and where only persimmons of the variety "Rojo Brillante" or derived mutations are cultivated. The largest part of these astringent type persimmons are CO2 treated to remove astringency and marketed as "Persimon" with one "m", which is a registered trademark.
United States
California produces of Fuyu a year. Most persimmons produced in California are seedless. California and Florida account for most commercial production. The first commercial orchards in Florida were planted in the 1870s and production peaked in the 1990s before declining. Most persimmon orchards in the US are small scale (70% less than and 90% less than ).
Toxicity
Unripe persimmons contain the soluble tannin shibuol, which, upon contact with a weak acid, polymerizes in the stomach and forms a gluey coagulum, a "foodball" or phytobezoar, that can affix with other stomach matter. These phytobezoars are often very hard and almost woody in consistency. More than 85% of phytobezoars are caused by ingestion of unripened persimmons. Persimmon bezoars (diospyrobezoars) often occur in epidemics in regions where the fruit is grown.
Uses
Persimmons are eaten fresh, dried, raw or cooked. When eaten fresh, they are usually eaten whole like an apple in bite-size slices and may be peeled, although the skin is edible. One way to consume ripe persimmons, which may have soft texture, is to remove the top leaf with a paring knife and scoop out the flesh with a spoon. Riper persimmons can also be eaten by removing the top leaf, breaking the fruit in half, and eating from the inside out. The flesh ranges from firm to mushy, and, when firm owing to being unripe, has an apple-like crunch. Some varieties are completely inedible until they are fully ripe, such as American persimmons (Diospyros virginiana) and Diospyros digyna. The leaves can be used to make a tisane and the seeds can be roasted. | Persimmon | Wikipedia | 491 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
In Korea, dried persimmon fruits are used to make the traditional Korean spicy punch sujeonggwa, while the matured, fermented fruit is used to make a persimmon vinegar called gamsikcho.
In Taiwan, fruits of astringent varieties are sealed in jars filled with limewater to get rid of bitterness. Slightly hardened in the process, they are sold under the name "crisp persimmon" (cuishi) or "water persimmon" (shuishizi). Preparation time is dependent upon temperature (5 to 7 days at .
For centuries, Japanese have consumed persimmon leaf tea (Kaki-No-Ha Cha) made from the dried leaves of "kaki" persimmons (Diospyros kaki). In some areas of Manchuria and Korea, the dried leaves of the fruit are used for making tea. The Korean name for this tea is gamnip cha.
In the US from Ohio southward, persimmons are harvested and used in a variety of dessert dishes, most notably pies. They can be used in cookies, cakes, puddings, salads, curries and as a topping for breakfast cereal. Persimmon pudding is a baked dessert made with fresh persimmons that has the consistency of pumpkin pie but resembles a brownie and is almost always topped with whipped cream. An annual persimmon festival, featuring a persimmon pudding contest, is held every September in Mitchell, Indiana.
Persimmons may be stored at room temperature where they will continue to ripen. In northern China, unripe persimmons are frozen outdoors during winter to speed up the ripening process.
Ripe persimmons can be refrigerated for as long as a couple of weeks, though extreme temperature changes may contribute to a mushy texture. It is recommended to store persimmons stem end down.
Persimmons can also be fermented in the manner of black garlic.
Dried | Persimmon | Wikipedia | 416 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
In China, Korea, Japan and Vietnam, persimmons after harvesting are prepared using traditional hand-drying techniques outdoors for two to three weeks. The fruit is then further dried by exposure to heat over several days before being shipped to market, to be sold as dried fruit. In Japan, the dried persimmon fruit is called hoshigaki, in China shìbǐng (柿餠), in Korea gotgam or Geonsi (乾枾), and in Vietnam hồng khô (紅枯). It is eaten as a snack or dessert and used for other culinary purposes.
Nutrition
Persimmons have higher levels of dietary fiber and some dietary minerals than apples, but overall are not a significant source of micronutrients, except for manganese (17% of the Daily Value, DV) and provitamin A beta-carotene (10% DV, table for raw Japanese persimmons per 100-gram amount). Raw American persimmons are a rich source of vitamin C (80% DV per 100g) and iron (19% DV).
Culture
In Ozark folklore, the severity of the upcoming winter is said to be predictable by slicing a persimmon seed and seeing whether it is shaped like a knife, fork, or spoon within. According to the Missouri Department of Conservation, this is not a reliable method.
In Korean folklore the dried persimmon (gotgam, Korean: 곶감) has a reputation for scaring away tigers.
In Malaysia and Singapore, large persimmons are viewed as a status symbol.
Diseases
In 1999, the first report of leaf blight on sweet persimmon tree by fungal pathogen Pestalotiopsis theae in Spain was documented. | Persimmon | Wikipedia | 356 | 152288 | https://en.wikipedia.org/wiki/Persimmon | Biology and health sciences | Tropical and tropical-like fruit | Plants |
The bulbuls are members of a family, Pycnonotidae, of medium-sized passerine songbirds, which also includes greenbuls, brownbuls, leafloves, and bristlebills. The family is distributed across most of Africa and into the Middle East, tropical Asia to Indonesia, and north as far as Japan. A few insular species occur on the tropical islands of the Indian Ocean. There are 166 species in 32 genera. While different species are found in a wide range of habitats, the African species are predominantly found in rainforest, whereas Asian bulbuls are predominantly found in more open areas.
Taxonomy
The family Pycnonotidae was introduced by the English zoologist George Robert Gray in 1840 as a subfamily Pycnonotinae of the thrush family Turdidae.
The Arabic word bulbul (بلبل) is sometimes used to refer to the "nightingale" as well as the bulbul, but the English word bulbul refers to the birds discussed in this article.
A few species that were previously considered to be members of the Pycnonotidae have been moved to other families. Several Malagasy species that were formerly placed in the genus Phyllastrephus are now placed in the family Bernieridae. In addition, the genus Nicator containing three African species is now placed in a separate family Nicatoridae.
A study published in 2007 by Ulf Johansson and colleagues using three nuclear markers found that the genus Andropadus was non-monophyletic. In the subsequent revision, species were moved to three resurrected genera: Arizelocichla, Stelgidillas and Eurillas. Only the sombre greenbul (Andropadus importunus), was retained in Andropadus. A study by Subir Shakya and Frederick Shelden published in 2017 found that species in the large genus Pycnonotus formed several deeply divergent clades. The genus was split and six genera were resurrected to accommodate these clades.
The family forms two main clades. One clade contains species that are only found in Africa; many of these have greenbul in the common name. The second clade contains mostly Asian species but includes a few species that are found in Africa.
List of genera
Currently, there are 167 recognized species in 32 genera: | Bulbul | Wikipedia | 481 | 152393 | https://en.wikipedia.org/wiki/Bulbul | Biology and health sciences | Passerida | null |
Genus Andropadus – sombre greenbul (formerly contained many species)
Genus Stelgidillas – slender-billed greenbul (formerly in Andropadus)
Genus Calyptocichla – golden greenbul
Genus Neolestes – black-collared bulbul
Genus Bleda – bristlebills (5 species)
Genus Atimastillas – greenbuls (2 species)
Genus Ixonotus – spotted greenbul
Genus Thescelocichla – swamp palm bulbul
Genus Chlorocichla – greenbuls (5 species)
Genus Baeopogon – greenbuls (2 species)
Genus Arizelocichla – greenbuls (11 species) (formerly in Andropadus)
Genus Criniger – greenbuls (5 species)
Genus Eurillas – greenbuls (5 species) (formerly in Andropadus)
Genus Phyllastrephus – greenbuls and brownbuls (21 species)
Genus Tricholestes – hairy-backed bulbul
Genus Setornis – hook-billed bulbul
Genus Alophoixus – 8 species (formerly in Criniger)
Genus Alcurus – striated bulbul
Genus Iole – 7 species
Genus Hemixos – 4 species
Genus Acritillas – yellow-browed bulbul
Genus Ixos – 5 species
Genus Hypsipetes – 26 species (includes 3 species formerly in Thapsinillas, one formerly in Cerasophila and one formerly in Microscelis)
Genus Euptilotus – puff-backed bulbul (formerly in Pycnonotus)
Genus Microtarsus – black-and-white bulbul (formerly in Pycnonotus)
Genus Poliolophus – yellow-wattled bulbul (formerly in Pycnonotus)
Genus Brachypodius – 4 species (formerly in Pycnonotus)
Genus Ixodia – 3 species (formerly in Pycnonotus)
Genus Rubigula – 5 species (formerly in Pycnonotus)
Genus Nok – bare-faced bulbul (genus introduced in 2017)
Genus Spizixos – finchbills (2 species)
Genus Pycnonotus – 34 species (substantially reduced from earlier classification)
Cladogram | Bulbul | Wikipedia | 483 | 152393 | https://en.wikipedia.org/wiki/Bulbul | Biology and health sciences | Passerida | null |
Description
Bulbuls are short-necked slender passerines. The tails are long and the wings short and rounded. In almost all species the bill is slightly elongated and slightly hooked at the end. They vary in length from 13 cm and for the tiny greenbul to 29 cm and in the straw-headed bulbul. Overall the sexes are alike, although the females tend to be slightly smaller. In a few species the differences are so great that they have been described as functionally different species. The soft plumage of some species is colorful with yellow, red or orange vents, cheeks, throat or supercilia, but most are drab, with uniform olive-brown to black plumage. Species with dull coloured eyes often sport contrasting eyerings. Some have very distinct crests. Bulbuls are highly vocal, with the calls of most species being described as nasal or gravelly. One author described the song of the brown-eared bulbul as "one of the most unattractive noises made by any bird".
Behaviour and ecology
Breeding
The bulbuls are generally monogamous. One unusual exception is the yellow-whiskered greenbul which at least over part of its range appears to be polygamous and engage in a lekking system. Some species also have alloparenting arrangements, where non-breeders, usually the young from earlier clutches, help raise the young of a dominant breeding pair. Up to five speckled eggs are laid in open tree nests and incubated by the female. Incubation usually lasts between 11 and 14 days, and chicks fledge after 12–16 days.
Feeding
Bulbuls eat a wide range of foods, ranging from fruit to seeds, nectar, small insects and other arthropods and even small vertebrates. The majority of species are frugivorous and supplement their diet with some insects, although there is a significant minority of specialists, particularly in Africa. Open country species in particular are generalists. Bulbuls in the genus Criniger and bristlebills in the genus Bleda will join mixed-species feeding flocks.
Relationship to humans
The red-whiskered bulbuls and red-vented bulbuls have been captured for the pet trade in great numbers and have been widely introduced to tropical and subtropical areas, for example, southern Florida, Fiji, Australia and Hawaii. Some species are regarded as crop pests, particularly in orchards. | Bulbul | Wikipedia | 495 | 152393 | https://en.wikipedia.org/wiki/Bulbul | Biology and health sciences | Passerida | null |
In general, bulbuls and greenbuls are resistant to human pressures on the environment and are tolerant of disturbed habitat. Around 13 species are considered threatened by human activities, mostly specialised forest species that are threatened by habitat loss. | Bulbul | Wikipedia | 45 | 152393 | https://en.wikipedia.org/wiki/Bulbul | Biology and health sciences | Passerida | null |
In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements. It explains why the observed abundances of elements change over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret and Geoffrey Burbidge, William Alfred Fowler and Fred Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history.
Stars evolve because of changes in their composition (the abundance of their constituent elements) over their lifespans, first by burning hydrogen (main sequence star), then helium (horizontal branch star), and progressively burning higher elements. However, this does not by itself significantly alter the abundances of elements in the universe as the elements are contained within the star. Later in its life, a low-mass star will slowly eject its atmosphere via stellar wind, forming a planetary nebula, while a higher–mass star will eject mass via a sudden catastrophic event called a supernova. The term supernova nucleosynthesis is used to describe the creation of elements during the explosion of a massive star or white dwarf.
The advanced sequence of burning fuels is driven by gravitational collapse and its associated heating, resulting in the subsequent burning of carbon, oxygen and silicon. However, most of the nucleosynthesis in the mass range (from silicon to nickel) is actually caused by the upper layers of the star collapsing onto the core, creating a compressional shock wave rebounding outward. The shock front briefly raises temperatures by roughly 50%, thereby causing furious burning for about a second. This final burning in massive stars, called explosive nucleosynthesis or supernova nucleosynthesis, is the final epoch of stellar nucleosynthesis. | Stellar nucleosynthesis | Wikipedia | 444 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
A stimulus to the development of the theory of nucleosynthesis was the discovery of variations in the abundances of elements found in the universe. The need for a physical description was already inspired by the relative abundances of the chemical elements in the solar system. Those abundances, when plotted on a graph as a function of the atomic number of the element, have a jagged sawtooth shape that varies by factors of tens of millions (see history of nucleosynthesis theory). This suggested a natural process that is not random. A second stimulus to understanding the processes of stellar nucleosynthesis occurred during the 20th century, when it was realized that the energy released from nuclear fusion reactions accounted for the longevity of the Sun as a source of heat and light.
History
In 1920, Arthur Eddington, on the basis of the precise measurements of atomic masses by F.W. Aston and a preliminary suggestion by Jean Perrin, proposed that stars obtained their energy from nuclear fusion of hydrogen to form helium and raised the possibility that the heavier elements are produced in stars. This was a preliminary step toward the idea of stellar nucleosynthesis. In 1928 George Gamow derived what is now called the Gamow factor, a quantum-mechanical formula yielding the probability for two contiguous nuclei to overcome the electrostatic Coulomb barrier between them and approach each other closely enough to undergo nuclear reaction due to the strong nuclear force which is effective only at very short distances. In the following decade the Gamow factor was used by Atkinson and Houtermans and later by Edward Teller and Gamow himself to derive the rate at which nuclear reactions would occur at the high temperatures believed to exist in stellar interiors. | Stellar nucleosynthesis | Wikipedia | 344 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
In 1939, in a Nobel lecture entitled "Energy Production in Stars", Hans Bethe analyzed the different possibilities for reactions by which hydrogen is fused into helium. He defined two processes that he believed to be the sources of energy in stars. The first one, the proton–proton chain reaction, is the dominant energy source in stars with masses up to about the mass of the Sun. The second process, the carbon–nitrogen–oxygen cycle, which was also considered by Carl Friedrich von Weizsäcker in 1938, is more important in more massive main-sequence stars. These works concerned the energy generation capable of keeping stars hot. A clear physical description of the proton–proton chain and of the CNO cycle appears in a 1968 textbook. Bethe's two papers did not address the creation of heavier nuclei, however. That theory was begun by Fred Hoyle in 1946 with his argument that a collection of very hot nuclei would assemble thermodynamically into iron. Hoyle followed that in 1954 with a paper describing how advanced fusion stages within massive stars would synthesize the elements from carbon to iron in mass.
Hoyle's theory was extended to other processes, beginning with the publication of the 1957 review paper "Synthesis of the Elements in Stars" by Burbidge, Burbidge, Fowler and Hoyle, more commonly referred to as the B2FH paper. This review paper collected and refined earlier research into a heavily cited picture that gave promise of accounting for the observed relative abundances of the elements; but it did not itself enlarge Hoyle's 1954 picture for the origin of primary nuclei as much as many assumed, except in the understanding of nucleosynthesis of those elements heavier than iron by neutron capture. Significant improvements were made by Alastair G. W. Cameron and by Donald D. Clayton. In 1957 Cameron presented his own independent approach to nucleosynthesis, informed by Hoyle's example, and introduced computers into time-dependent calculations of evolution of nuclear systems. Clayton calculated the first time-dependent models of the s-process in 1961 and of the r-process in 1965, as well as of the burning of silicon into the abundant alpha-particle nuclei and iron-group elements in 1968, and discovered radiogenic chronologies for determining the age of the elements.
Key reactions | Stellar nucleosynthesis | Wikipedia | 476 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
The most important reactions in stellar nucleosynthesis:
Hydrogen fusion:
Deuterium fusion
The proton–proton chain
The carbon–nitrogen–oxygen cycle
Helium fusion:
The triple-alpha process
The alpha process
Fusion of heavier elements:
Lithium burning: a process found most commonly in brown dwarfs
Carbon-burning process
Neon-burning process
Oxygen-burning process
Silicon-burning process
Production of elements heavier than iron:
Neutron capture:
The r-process
The s-process
Proton capture:
The rp-process
The p-process
Photodisintegration
Hydrogen fusion
Hydrogen fusion (nuclear fusion of four protons to form a helium-4 nucleus) is the dominant process that generates energy in the cores of main-sequence stars. It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere. There are two predominant processes by which stellar hydrogen fusion occurs: proton–proton chain and the carbon–nitrogen–oxygen (CNO) cycle. Ninety percent of all stars, with the exception of white dwarfs, are fusing hydrogen by these two processes.
In the cores of lower-mass main-sequence stars such as the Sun, the dominant energy production process is the proton–proton chain reaction. This creates a helium-4 nucleus through a sequence of reactions that begin with the fusion of two protons to form a deuterium nucleus (one proton plus one neutron) along with an ejected positron and neutrino. In each complete fusion cycle, the proton–proton chain reaction releases about 26.2 MeV. Proton-proton chain with a dependence of approximately T^4, meaning the reaction cycle is highly sensitive to temperature; a 10% rise of temperature would increase energy production by this method by 46%, hence, this hydrogen fusion process can occur in up to a third of the star's radius and occupy half the star's mass. For stars above 35% of the Sun's mass, the energy flux toward the surface is sufficiently low and energy transfer from the core region remains by radiative heat transfer, rather than by convective heat transfer. As a result, there is little mixing of fresh hydrogen into the core or fusion products outward. | Stellar nucleosynthesis | Wikipedia | 450 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
In higher-mass stars, the dominant energy production process is the CNO cycle, which is a catalytic cycle that uses nuclei of carbon, nitrogen and oxygen as intermediaries and in the end produces a helium nucleus as with the proton–proton chain. During a complete CNO cycle, 25.0 MeV of energy is released. The difference in energy production of this cycle, compared to the proton–proton chain reaction, is accounted for by the energy lost through neutrino emission. CNO cycle is highly sensitive to temperature, with rates proportional to T^{16-20}, a 10% rise of temperature would produce a 350% rise in energy production. About 90% of the CNO cycle energy generation occurs within the inner 15% of the star's mass, hence it is strongly concentrated at the core. This results in such an intense outward energy flux that convective energy transfer becomes more important than does radiative transfer. As a result, the core region becomes a convection zone, which stirs the hydrogen fusion region and keeps it well mixed with the surrounding proton-rich region. This core convection occurs in stars where the CNO cycle contributes more than 20% of the total energy. As the star ages and the core temperature increases, the region occupied by the convection zone slowly shrinks from 20% of the mass down to the inner 8% of the mass. The Sun produces on the order of 1% of its energy from the CNO cycle.
The type of hydrogen fusion process that dominates in a star is determined by the temperature dependency differences between the two reactions. The proton–proton chain reaction starts at temperatures about , making it the dominant fusion mechanism in smaller stars. A self-maintaining CNO chain requires a higher temperature of approximately , but thereafter it increases more rapidly in efficiency as the temperature rises, than does the proton–proton reaction. Above approximately , the CNO cycle becomes the dominant source of energy. This temperature is achieved in the cores of main-sequence stars with at least 1.3 times the mass of the Sun. The Sun itself has a core temperature of about . As a main-sequence star ages, the core temperature will rise, resulting in a steadily increasing contribution from its CNO cycle.
Helium fusion | Stellar nucleosynthesis | Wikipedia | 456 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
Main sequence stars accumulate helium in their cores as a result of hydrogen fusion, but the core does not become hot enough to initiate helium fusion. Helium fusion first begins when a star leaves the red giant branch after accumulating sufficient helium in its core to ignite it. In stars around the mass of the Sun, this begins at the tip of the red giant branch with a helium flash from a degenerate helium core, and the star moves to the horizontal branch where it burns helium in its core. More massive stars ignite helium in their core without a flash and execute a blue loop before reaching the asymptotic giant branch. Such a star initially moves away from the AGB toward bluer colours, then loops back again to what is called the Hayashi track. An important consequence of blue loops is that they give rise to classical Cepheid variables, of central importance in determining distances in the Milky Way and to nearby galaxies. Despite the name, stars on a blue loop from the red giant branch are typically not blue in colour but are rather yellow giants, possibly Cepheid variables. They fuse helium until the core is largely carbon and oxygen. The most massive stars become supergiants when they leave the main sequence and quickly start helium fusion as they become red supergiants. After the helium is exhausted in the core of a star, helium fusion will continue in a shell around the carbon–oxygen core.
In all cases, helium is fused to carbon via the triple-alpha process, i.e., three helium nuclei are transformed into carbon via 8Be. This can then form oxygen, neon, and heavier elements via the alpha process. In this way, the alpha process preferentially produces elements with even numbers of protons by the capture of helium nuclei. Elements with odd numbers of protons are formed by other fusion pathways.
Reaction rate
The reaction rate density between species A and B, having number densities nA,B, is given by:
where k is the reaction rate constant of each single elementary binary reaction composing the nuclear fusion process:
here, σ(v) is the cross-section at relative velocity v, and averaging is performed over all velocities.
Semi-classically, the cross section is proportional to , where is the de Broglie wavelength. Thus semi-classically the cross section is proportional to . | Stellar nucleosynthesis | Wikipedia | 478 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
However, since the reaction involves quantum tunneling, there is an exponential damping at low energies that depends on Gamow factor EG, giving an Arrhenius equation:
where S(E) depends on the details of the nuclear interaction, and has the dimension of an energy multiplied for a cross section.
One then integrates over all energies to get the total reaction rate, using the Maxwell–Boltzmann distribution and the relation:
where is the reduced mass.
Since this integration has an exponential damping at high energies of the form and at low energies from the Gamow factor, the integral almost vanished everywhere except around the peak, called Gamow peak, at E0, where:
Thus:
The exponent can then be approximated around E0 as:
And the reaction rate is approximated as:
Values of S(E0) are typically , but are damped by a huge factor when involving a beta decay, due to the relation between the intermediate bound state (e.g. diproton) half-life and the beta decay half-life, as in the proton–proton chain reaction. Note that typical core temperatures in main-sequence stars give kT of the order of keV.
Thus, the limiting reaction in the CNO cycle, proton capture by , has S(E0) ~ S(0) = 3.5keV·b, while the limiting reaction in the proton–proton chain reaction, the creation of deuterium from two protons, has a much lower S(E0) ~ S(0) = 4×10−22keV·b. Incidentally, since the former reaction has a much higher Gamow factor, and due to the relative abundance of elements in typical stars, the two reaction rates are equal at a temperature value that is within the core temperature ranges of main-sequence stars. | Stellar nucleosynthesis | Wikipedia | 383 | 152440 | https://en.wikipedia.org/wiki/Stellar%20nucleosynthesis | Physical sciences | Stellar astronomy | Astronomy |
Nuclides (or nucleides, from nucleus, also known as nuclear species) are a class of atoms characterized by their number of protons, Z, their number of neutrons, N, and their nuclear energy state.
The word nuclide was coined by the American nuclear physicist Truman P. Kohman in 1947. Kohman defined nuclide as a "species of atom characterized by the constitution of its nucleus" containing a certain number of neutrons and protons. The term thus originally focused on the nucleus.
Nuclides vs isotopes
A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon-13 with 6 protons and 7 neutrons. The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, while the isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear. The neutron number has large effects on nuclear properties, but its effect on chemical reactions is negligible for most elements. Even in the case of the very lightest elements, where the ratio of neutron number to atomic number varies the most between isotopes, it usually has only a small effect, but it matters in some circumstances. For hydrogen, the lightest element, the isotope effect is large enough to affect biological systems strongly. In the case of helium, helium-4 obeys Bose–Einstein statistics, while helium-3 obeys Fermi–Dirac statistics. Since isotope is the older term, it is better known than nuclide, and is still occasionally used in contexts in which nuclide might be more appropriate, such as nuclear technology and nuclear medicine.
Types of nuclides
Although the words nuclide and isotope are often used interchangeably, being isotopes is actually only one relation between nuclides. The following table names some other relations. | Nuclide | Wikipedia | 382 | 152464 | https://en.wikipedia.org/wiki/Nuclide | Physical sciences | Chemistry: General | null |
A set of nuclides with equal proton number (atomic number), i.e., of the same chemical element but different neutron numbers, are called isotopes of the element. Particular nuclides are still often loosely called "isotopes", but the term "nuclide" is the correct one in general (i.e., when Z is not fixed). In similar manner, a set of nuclides with equal mass number A, but different atomic number, are called isobars (isobar = equal in weight), and isotones are nuclides of equal neutron number but different proton numbers. Likewise, nuclides with the same neutron excess (N − Z) are called isodiaphers. The name isotone was derived from the name isotope to emphasize that in the first group of nuclides it is the number of neutrons (n) that is constant, whereas in the second the number of protons (p).
See Isotope#Notation for an explanation of the notation used for different nuclide or isotope types.
Nuclear isomers are members of a set of nuclides with equal proton number and equal mass number (thus making them by definition the same isotope), but different states of excitation. An example is the two states of the single isotope shown among the decay schemes. Each of these two states (technetium-99m and technetium-99) qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes (an isotope may consist of several different nuclides of different excitation states).
The longest-lived non-ground state nuclear isomer is the nuclide tantalum-180m (), which has a half-life in excess of 1,000 trillion years. This nuclide occurs primordially, and has never been observed to decay to the ground state. (In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to 180Hf (86%) or 180W (14%).) | Nuclide | Wikipedia | 449 | 152464 | https://en.wikipedia.org/wiki/Nuclide | Physical sciences | Chemistry: General | null |
There are 251 nuclides in nature that have never been observed to decay. They occur among the 80 different elements that have one or more stable isotopes. See stable nuclide and primordial nuclide. Unstable nuclides are radioactive and are called radionuclides. Their decay products ('daughter' products) are called radiogenic nuclides.
Origins of naturally occurring radionuclides
Natural radionuclides may be conveniently subdivided into three types. First, those whose half-lives t1/2 are at least 2% as long as the age of the Earth (for practical purposes, these are difficult to detect with half-lives less than 10% of the age of the Earth) (). These are remnants of nucleosynthesis that occurred in stars before the formation of the Solar System. For example, the isotope (t1/2 = ) of uranium is still fairly abundant in nature, but the shorter-lived isotope (t1/2 = ) is 138 times rarer. About 34 of these nuclides have been discovered (see List of nuclides and Primordial nuclide for details).
The second group of radionuclides that exist naturally consists of radiogenic nuclides such as (t1/2 = ), an isotope of radium, which are formed by radioactive decay. They occur in the decay chains of primordial isotopes of uranium or thorium. Some of these nuclides are very short-lived, such as isotopes of francium. There exist about 51 of these daughter nuclides that have half-lives too short to be primordial, and which exist in nature solely due to decay from longer lived radioactive primordial nuclides.
The third group consists of nuclides that are continuously being made in another fashion that is not simple spontaneous radioactive decay (i.e., only one atom involved with no incoming particle) but instead involves a natural nuclear reaction. These occur when atoms react with natural neutrons (from cosmic rays, spontaneous fission, or other sources), or are bombarded directly with cosmic rays. The latter, if non-primordial, are called cosmogenic nuclides. Other types of natural nuclear reactions produce nuclides that are said to be nucleogenic nuclides. | Nuclide | Wikipedia | 480 | 152464 | https://en.wikipedia.org/wiki/Nuclide | Physical sciences | Chemistry: General | null |
An example of nuclides made by nuclear reactions, are cosmogenic (radiocarbon) that is made by cosmic ray bombardment of other elements, and nucleogenic which is still being created by neutron bombardment of natural as a result of natural fission in uranium ores. Cosmogenic nuclides may be either stable or radioactive. If they are stable, their existence must be deduced against a background of stable nuclides, since every known stable nuclide is present on Earth primordially.
Artificially produced nuclides
Beyond the naturally occurring nuclides, more than 3000 radionuclides of varying half-lives have been artificially produced and characterized.
The known nuclides are shown in Table of nuclides. A list of primordial nuclides is given sorted by element, at List of elements by stability of isotopes. List of nuclides is sorted by half-life, for the 905 nuclides with half-lives longer than one hour.
Summary table for numbers of each class of nuclides
This is a summary table for the 905 nuclides with half-lives longer than one hour, given in list of nuclides. Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.
Nuclear properties and stability | Nuclide | Wikipedia | 284 | 152464 | https://en.wikipedia.org/wiki/Nuclide | Physical sciences | Chemistry: General | null |
Atomic nuclei other than hydrogen have protons and neutrons bound together by the residual strong force. Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart, reducing the electrostatic repulsion between the protons, and they exert the attractive nuclear force on each other and on protons. For this reason, one or more neutrons are necessary for two or more protons to be bound into a nucleus. As the number of protons increases, so does the ratio of neutrons to protons necessary to ensure a stable nucleus (see graph). For example, although the neutron–proton ratio of is 1:2, the neutron–proton ratio of is greater than 3:2. A number of lighter elements have stable nuclides with the ratio 1:1 (). The nuclide (calcium-40) is observationally the heaviest stable nuclide with the same number of neutrons and protons. All stable nuclides heavier than calcium-40 contain more neutrons than protons.
Even and odd nucleon numbers
The proton–neutron ratio is not the only factor affecting nuclear stability. It depends also on even or odd parity of its atomic number Z, neutron number N and, consequently, of their sum, the mass number A. Oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei, generally, less stable. This remarkable difference of nuclear binding energy between neighbouring nuclei, especially of odd-A isobars, has important consequences: unstable isotopes with a nonoptimal number of neutrons or protons decay by beta decay (including positron decay), electron capture or more exotic means, such as spontaneous fission and cluster decay.
The majority of stable nuclides are even-proton–even-neutron, where all numbers Z, N, and A are even. The odd-A stable nuclides are divided (roughly evenly) into odd-proton–even-neutron, and even-proton–odd-neutron nuclides. Odd-proton–odd-neutron nuclides (and nuclei) are the least common. | Nuclide | Wikipedia | 456 | 152464 | https://en.wikipedia.org/wiki/Nuclide | Physical sciences | Chemistry: General | null |
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.
Structure
The optic nerve has been classified as the second of twelve paired cranial nerves, but it is technically a myelinated tract of the central nervous system, rather than a classical nerve of the peripheral nervous system because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development. As a consequence, the fibers of the optic nerve are covered with myelin produced by oligodendrocytes, rather than Schwann cells of the peripheral nervous system, and are encased within the meninges. Peripheral neuropathies like Guillain–Barré syndrome do not affect the optic nerve. However, most typically, the optic nerve is grouped with the other eleven cranial nerves and is considered to be part of the peripheral nervous system.
The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fiber tracts of the mammalian central nervous system have only limited regenerative capabilities compared to the peripheral nervous system. Therefore, in most mammals, optic nerve damage results in irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex.
The optic nerve is composed of retinal ganglion cell axons and glia. Each human optic nerve contains between 770,000 and 1.7 million nerve fibers, which are axons of the retinal ganglion cells of one retina. In the fovea, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells; in other areas of the retina, they connect to thousands of photoreceptors. | Optic nerve | Wikipedia | 502 | 152465 | https://en.wikipedia.org/wiki/Optic%20nerve | Biology and health sciences | Visual system | Biology |
The optic nerve leaves the orbit (eye socket) via the optic canal, running postero-medially towards the optic chiasm, where there is a partial decussation (crossing) of fibers from the temporal visual fields (the nasal hemi-retina) of both eyes. The proportion of decussating fibers varies between species, and is correlated with the degree of binocular vision enjoyed by a species. Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex, while other axons terminate in the pretectal area and are involved in reflexive eye movements. Other axons terminate in the suprachiasmatic nucleus and are involved in regulating the sleep-wake cycle. Its diameter increases from about 1.6 mm within the eye to 3.5 mm in the orbit to 4.5 mm within the cranial space. The optic nerve component lengths are 1 mm in the globe, 24 mm in the orbit, 9 mm in the optic canal, and 16 mm in the cranial space before joining the optic chiasm. There, partial decussation occurs, and about 53% of the fibers cross to form the optic tracts. Most of these fibers terminate in the lateral geniculate body.
Based on this anatomy, the optic nerve may be divided into four parts as indicated in the image at the top of this section (this view is from above as if you were looking into the orbit after the top of the skull had been removed): 1. the optic head (which is where it begins in the eyeball (globe) with fibers from the retina); 2. orbital part (which is the part within the orbit); 3. intracanicular part (which is the part within a bony canal known as the optic canal); and, 4. cranial part (the part within the cranial cavity, which ends at the optic chiasm).
From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. In more specific terms, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the calcarine fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly, to the cuneus. | Optic nerve | Wikipedia | 494 | 152465 | https://en.wikipedia.org/wiki/Optic%20nerve | Biology and health sciences | Visual system | Biology |
Function
The optic nerve transmits all visual information including brightness perception, color perception and contrast (visual acuity). It also conducts the visual impulses that are responsible for two important neurological reflexes: the light reflex and the accommodation reflex. The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye. The accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object (for example: when reading, the lens adjusts to near vision).
The eye's blind spot is a result of the absence of photoreceptors in the area of the retina where the optic nerve leaves the eye.
Clinical significance
Disease
Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as well as an abnormal pupillary reflex, which is important for the diagnosis of nerve damage.
The type of visual field loss will depend on which portions of the optic nerve were damaged. In general, the location of the damage in relation to the optic chiasm (see diagram above) will affect the areas of vision loss. Damage to the optic nerve that is anterior, or in front of the optic chiasm (toward the face) causes loss of vision in the eye on the same side as the damage. Damage at the optic chiasm itself typically causes loss of vision laterally in both visual fields or bitemporal hemianopsia (see image to the right). Such damage may occur with large pituitary tumors, such as pituitary adenoma. Finally, damage to the optic tract, which is posterior to, or behind the chiasm, causes loss of the entire visual field from the side opposite the damage, e.g. if the left optic tract were cut, there would be a loss of vision from the entire right visual field.
Injury to the optic nerve can be the result of congenital or inheritable problems like Leber's hereditary optic neuropathy, glaucoma, trauma, toxicity, inflammation, ischemia, infection (very rarely), or compression from tumors or aneurysms. By far, the three most common injuries to the optic nerve are from glaucoma; optic neuritis, especially in those younger than 50 years of age; and anterior ischemic optic neuropathy, usually in those older than 50. | Optic nerve | Wikipedia | 487 | 152465 | https://en.wikipedia.org/wiki/Optic%20nerve | Biology and health sciences | Visual system | Biology |
Glaucoma is a group of diseases involving loss of retinal ganglion cells causing optic neuropathy in a pattern of peripheral vision loss, initially sparing central vision. Glaucoma is frequently associated with increased intraocular pressure that damages the optic nerve as it exits the eyeball. The trabecular meshwork assists the drainage of aqueous humor fluid. The presence of excess aqueous humor, increases IOP, yielding the diagnosis and symptoms of glaucoma.
Optic neuritis is inflammation of the optic nerve. It is associated with a number of diseases, the most notable one being multiple sclerosis. The patient will likely experience varying vision loss and eye pain. The condition tends to be episodic.
Anterior ischemic optic neuropathy is commonly known as a "stroke of the optic nerve" and affects the optic nerve head (where the nerve exits the eyeball). There is usually a sudden loss of blood supply and nutrients to the optic nerve head. Vision loss is typically sudden and most commonly occurs upon waking up in the morning. This condition is most common in diabetic patients 40–70 years old.
Other optic nerve problems are less common. Optic nerve hypoplasia is the underdevelopment of the optic nerve resulting in little to no vision in the affected eye. Tumors, especially those of the pituitary gland, can put pressure on the optic nerve causing various forms of visual loss. Similarly, cerebral aneurysms, a swelling of blood vessel(s), can also affect the nerve. Trauma can cause serious injury to the nerve. Direct optic nerve injury can occur from a penetrating injury to the orbit, but the nerve can also be injured by indirect trauma in which severe head impact or movement stretches or even tears the nerve.
Ophthalmologists and optometrists can detect and diagnose some optic nerve diseases but neuro-ophthalmologists are often best suited to diagnose and treat diseases of the optic nerve. The International Foundation for Optic Nerve Diseases (IFOND) sponsors research and provides information on a variety of optic nerve disorders.
Additional images | Optic nerve | Wikipedia | 440 | 152465 | https://en.wikipedia.org/wiki/Optic%20nerve | Biology and health sciences | Visual system | Biology |
Metastasis is a pathogenic agent's spreading from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, are metastases (mets). It is generally distinguished from cancer invasion, which is the direct extension and penetration by cancer cells into neighboring tissues.
Cancer occurs after cells are genetically altered to proliferate rapidly and indefinitely. This uncontrolled proliferation by mitosis produces a primary heterogeneic tumour. The cells which constitute the tumor eventually undergo metaplasia, followed by dysplasia then anaplasia, resulting in a malignant phenotype. This malignancy allows for invasion into the circulation, followed by invasion to a second site for tumorigenesis.
Some cancer cells, known as circulating tumor cells (CTCs), are able to penetrate the walls of lymphatic or blood vessels, and circulate through the bloodstream to other sites and tissues in the body. This process, known respectively as lymphatic or hematogenous spread, allows not only single cells but also groups of cells, or CTC clusters, to travel. Evidence suggests that CTC clusters may retain their multicellular configuration throughout metastasis, enhancing their ability to establish secondary tumors. This perspective aligns with the cancer exodus hypothesis, which posits that maintaining this cluster structure contributes to a higher metastatic potential. Metastasis is one of the hallmarks of cancer, distinguishing it from benign tumors. Most cancers can metastasize, although in varying degrees. Basal cell carcinoma for example rarely metastasizes.
When tumor cells metastasize, the new tumor is called a secondary or metastatic tumor, and its cells are similar to those in the original or primary tumor. This means that if breast cancer metastasizes to the lungs, the secondary tumor is made up of abnormal breast cells, not of abnormal lung cells. The tumor in the lung is then called metastatic breast cancer, not lung cancer. Metastasis is a key element in cancer staging systems such as the TNM staging system, where it represents the "M". In overall stage grouping, metastasis places a cancer in Stage IV. The possibilities of curative treatment are greatly reduced, or often entirely removed when a cancer has metastasized.
Signs and symptoms | Metastasis | Wikipedia | 503 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Initially, nearby lymph nodes are struck early. The lungs, liver, brain, and bones are the most common metastasis locations from solid tumors.
In lymph node metastasis, a common symptom is lymphadenopathy
Lung metastasis: cough, hemoptysis and dyspnea (shortness of breath)
Liver metastasis: hepatomegaly (enlarged liver), nausea and jaundice
Bone metastasis: bone pain, fracture of affected bones
Brain metastasis: neurological symptoms such as headaches, seizures, and vertigo
Although advanced cancer may cause pain, it is often not the first symptom.
Some patients, however, do not show any symptoms.
When the organ gets a metastatic disease it begins to shrink until its lymph nodes burst, or undergo lysis.
Pathophysiology
Metastatic tumors are very common in the late stages of cancer. The spread of metastasis may occur via the blood or the lymphatics or through both routes. The most common sites of metastases are the lungs, liver, brain, and the bones
Currently, three main theories have been proposed to explain the metastatic pathway of cancer: the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) hypothesis (1), the cancer stem cell hypothesis (2), and the macrophage–cancer cell fusion hybrid hypothesis (3). Some new hypotheses were suggested as well, i.e., under the effect of particular biochemical and/or physical stressors, cancer cells can undergo nuclear expulsion with subsequent macrophage engulfment and fusion, with the formation of cancer fusion cells (CFCs). Understanding the enigma of cancer cell spread to distant sites, which accounts for over 90% of cancer-related deaths, necessitates comprehensive investigation. Key outstanding questions revolve around the survival and migration of cancer cells, such as the nucleus, as they face challenges in passage through capillary valves and hydrodynamic shear forces in the circulation system, making CTCs an unlikely source of metastasis. Moreover, understanding how cancer cells adapt to the metastatic niche and remain dormant (tumor dormancy) for extended periods presents difficult questions that require further investigation. | Metastasis | Wikipedia | 482 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Factors involved
Metastasis involves a complex series of steps in which cancer cells leave the original tumor site and migrate to other parts of the body via the bloodstream, via the lymphatic system, or by direct extension. To do so, malignant cells break away from the primary tumor and attach to and degrade proteins that make up the surrounding extracellular matrix (ECM), which separates the tumor from adjoining tissues. By degrading these proteins, cancer cells are able to breach the ECM and escape. The location of the metastases is not always random, with different types of cancer tending to spread to particular organs and tissues at a rate that is higher than expected by statistical chance alone. Breast cancer, for example, tends to metastasize to the bones and lungs. This specificity seems to be mediated by soluble signal molecules such as chemokines and transforming growth factor beta. The body resists metastasis by a variety of mechanisms through the actions of a class of proteins known as metastasis suppressors, of which about a dozen are known.
Human cells exhibit different kinds of motion: collective motility, mesenchymal-type movement, and amoeboid movement. Cancer cells often opportunistically switch between different kinds of motion. Some cancer researchers hope to find treatments that can stop or at least slow down the spread of cancer by somehow blocking some necessary step in one or more kinds of motion.
All steps of the metastatic cascade involve a number of physical processes. Cell migration requires the generation of forces, and when cancer cells transmigrate through the vasculature, this requires physical gaps in the blood vessels to form. Besides forces, the regulation of various types of cell-cell and cell-matrix adhesions is crucial during metastasis. | Metastasis | Wikipedia | 369 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
The metastatic steps are critically regulated by various cell types, including the blood vessel cells (endothelial cells), immune cells or stromal cells. The growth of a new network of blood vessels, called tumor angiogenesis, is a crucial hallmark of cancer. It has therefore been suggested that angiogenesis inhibitors would prevent the growth of metastases. Endothelial progenitor cells have been shown to have a strong influence on metastasis and angiogenesis. Endothelial progenitor cells are important in tumor growth, angiogenesis and metastasis, and can be marked using the Inhibitor of DNA Binding 1 (ID1). This novel finding meant that investigators gained the ability to track endothelial progenitor cells from the bone marrow to the blood to the tumor-stroma and even incorporated in tumor vasculature. Endothelial progenitor cells incorporated in tumor vasculature suggests that this cell type in blood-vessel development is important in a tumor setting and metastasis. Furthermore, ablation of the endothelial progenitor cells in the bone marrow can lead to a significant decrease in tumor growth and vasculature development. Therefore, endothelial progenitor cells are important in tumor biology and present novel therapeutic targets. The immune system is typically deregulated in cancer and affects many stages of tumor progression, including metastasis.
Epigenetic regulation also plays an important role in the metastatic outgrowth of disseminated tumor cells. Metastases display alterations in histone modifications, such as H3K4-methylation and H3K9-methylation, when compared to matching primary tumors. These epigenetic modifications in metastases may allow the proliferation and survival of disseminated tumor cells in distant organs.
A recent study shows that PKC-iota promotes melanoma cell invasion by activating Vimentin during EMT. PKC-iota inhibition or knockdown resulted in an increase in E-cadherin and RhoA levels while decreasing total Vimentin, phosphorylated Vimentin (S39) and Par6 in metastatic melanoma cells. These results suggested that PKC-ι is involved in signaling pathways which upregulate EMT in melanoma thereby directly stimulates metastasis. | Metastasis | Wikipedia | 485 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Recently, a series of high-profile experiments suggests that the co-option of intercellular cross-talk mediated by exosome vesicles is a critical factor involved in all steps of the invasion-metastasis cascade.
Routes
Metastasis occurs by the following four routes:
Transcoelomic
The spread of a malignancy into body cavities can occur via penetrating the surface of the peritoneal, pleural, pericardial, or subarachnoid spaces. For example, ovarian tumors can spread transperitoneally to the surface of the liver.
Lymphatic spread
Lymphatic spread allows the transport of tumor cells to regional lymph nodes near the primary tumor and ultimately, to other parts of the body. This is called nodal involvement, positive nodes, or regional disease. "Positive nodes" is a term that would be used by medical specialists to describe regional lymph nodes that tested positive for malignancy. It is common medical practice to test by biopsy at least one lymph node near a tumor site when carrying out surgery to examine or remove a tumor. This lymph node is then called a sentinel lymph node.
Lymphatic spread is the most common route of initial metastasis for carcinomas. In contrast, it is uncommon for a sarcoma to metastasize via this route. Localized spread to regional lymph nodes near the primary tumor is not normally counted as a metastasis, although this is a sign of a worse outcome.
The lymphatic system does eventually drain from the thoracic duct and right lymphatic duct into the systemic venous system at the venous angle and into the brachiocephalic veins, and therefore these metastatic cells can also eventually spread through the haematogenous route.
Hematogenous spread
This is typical route of metastasis for sarcomas, but it is also the favored route for certain types of carcinoma, such as renal cell carcinoma originating in the kidney and follicular carcinomas of the thyroid. Because of their thinner walls, veins are more frequently invaded than are arteries, and metastasis tends to follow the pattern of venous flow. That is, hematogenous spread often follows distinct patterns depending on the location of the primary tumor. For example, colorectal cancer spreads primarily through the portal vein to the liver.
Canalicular spread | Metastasis | Wikipedia | 508 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Some tumors, especially carcinomas may metastasize along anatomical canalicular spaces. These spaces include for example the bile ducts, the urinary system, the airways and the subarachnoid space. The process is similar to that of transcoelomic spread. However, often it remains unclear whether simultaneously diagnosed tumors of a canalicular system are one metastatic process or in fact independent tumors caused by the same agent (field cancerization).
Organ-specific targets
There is a propensity for certain tumors to seed in particular organs. This was first discussed as the seed and soil theory by Stephen Paget in 1889. The propensity for a metastatic cell to spread to a particular organ is termed 'organotropism'. For example, prostate cancer usually metastasizes to the bones. In a similar manner, colon cancer has a tendency to metastasize to the liver. Stomach cancer often metastasises to the ovary in women, when it is called a Krukenberg tumor.
According to the seed and soil theory, it is difficult for cancer cells to survive outside their region of origin, so in order to metastasize they must find a location with similar characteristics. For example, breast tumor cells, which gather calcium ions from breast milk, metastasize to bone tissue, where they can gather calcium ions from bone. Malignant melanoma spreads to the brain, presumably because neural tissue and melanocytes arise from the same cell line in the embryo.
In 1928, James Ewing challenged the seed and soil theory, and proposed that metastasis occurs purely by anatomic and mechanical routes. This hypothesis has been recently utilized to suggest several hypotheses about the life cycle of circulating tumor cells (CTCs) and to postulate that the patterns of spread could be better understood through a 'filter and flow' perspective. However, contemporary evidences indicate that the primary tumour may dictate organotropic metastases by inducing the formation of pre-metastatic niches at distant sites, where incoming metastatic cells may engraft and colonise. Specifically, exosome vesicles secreted by tumours have been shown to home to pre-metastatic sites, where they activate pro-metastatic processes such as angiogenesis and modify the immune contexture, so as to foster a favourable microenvironment for secondary tumour growth. | Metastasis | Wikipedia | 499 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Metastasis and primary cancer
It is theorized that metastasis always coincides with a primary cancer, and, as such, is a tumor that started from a cancer cell or cells in another part of the body. However, over 10% of patients presenting to oncology units will have metastases without a primary tumor found. In these cases, doctors refer to the primary tumor as "unknown" or "occult," and the patient is said to have cancer of unknown primary origin (CUP) or unknown primary tumors (UPT). It is estimated that 3% of all cancers are of unknown primary origin. Studies have shown that, if simple questioning does not reveal the cancer's source (coughing up blood—"probably lung", urinating blood—"probably bladder"), complex imaging will not either. In some of these cases a primary tumor may appear later.
The use of immunohistochemistry has permitted pathologists to give an identity to many of these metastases. However, imaging of the indicated area only occasionally reveals a primary. In rare cases (e.g., of melanoma), no primary tumor is found, even on autopsy. It is therefore thought that some primary tumors can regress completely, but leave their metastases behind. In other cases, the tumor might just be too small and/or in an unusual location to be diagnosed.
Diagnosis
The cells in a metastatic tumor resemble those in the primary tumor. Once the cancerous tissue is examined under a microscope to determine the cell type, a doctor can usually tell whether that type of cell is normally found in the part of the body from which the tissue sample was taken.
For instance, breast cancer cells look the same whether they are found in the breast or have spread to another part of the body. So, if a tissue sample taken from a tumor in the lung contains cells that look like breast cells, the doctor determines that the lung tumor is a secondary tumor. Still, the determination of the primary tumor can often be very difficult, and the pathologist may have to use several adjuvant techniques, such as immunohistochemistry, FISH (fluorescent in situ hybridization), and others. Despite the use of techniques, in some cases the primary tumor remains unidentified. | Metastasis | Wikipedia | 467 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
Metastatic cancers may be found at the same time as the primary tumor, or months or years later. When a second tumor is found in a patient that has been treated for cancer in the past, it is more often a metastasis than another primary tumor.
It was previously thought that most cancer cells have a low metastatic potential and that there are rare cells that develop the ability to metastasize through the development of somatic mutations. According to this theory, diagnosis of metastatic cancers is only possible after the event of metastasis. Traditional means of diagnosing cancer (e.g. a biopsy) would only investigate a subpopulation of the cancer cells and would very likely not sample from the subpopulation with metastatic potential.
The somatic mutation theory of metastasis development has not been substantiated in human cancers. Rather, it seems that the genetic state of the primary tumor reflects the ability of that cancer to metastasize. Research comparing gene expression between primary and metastatic adenocarcinomas identified a subset of genes whose expression could distinguish primary tumors from metastatic tumors, dubbed a "metastatic signature." Up-regulated genes in the signature include: SNRPF, HNRPAB, DHPS and securin. Actin, myosin and MHC class II down-regulation was also associated with the signature. Additionally, the metastatic-associated expression of these genes was also observed in some primary tumors, indicating that cells with the potential to metastasize could be identified concurrently with diagnosis of the primary tumor. Recent work identified a form of genetic instability in cancer called chromosome instability (CIN) as a driver of metastasis. In aggressive cancer cells, loose DNA fragments from unstable chromosomes spill in the cytosol leading to the chronic activation of innate immune pathways, which are hijacked by cancer cells to spread to distant organs.
Expression of this metastatic signature has been correlated with a poor prognosis and has been shown to be consistent in several types of cancer. Prognosis was shown to be worse for individuals whose primary tumors expressed the metastatic signature. Additionally, the expression of these metastatic-associated genes was shown to apply to other cancer types in addition to adenocarcinoma. Metastases of breast cancer, medulloblastoma and prostate cancer all had similar expression patterns of these metastasis-associated genes. | Metastasis | Wikipedia | 495 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
The identification of this metastasis-associated signature provides promise for identifying cells with metastatic potential within the primary tumor and hope for improving the prognosis of these metastatic-associated cancers. Additionally, identifying the genes whose expression is changed in metastasis offers potential targets to inhibit metastasis.
Management
Treatment and survival is determined, to a great extent, by whether or not a cancer remains localized or spreads to other locations in the body. If the cancer metastasizes to other tissues or organs it usually dramatically increases a patient's likelihood of death. Some cancers—such as some forms of leukemia, a cancer of the blood, or malignancies in the brain—can kill without spreading at all.
Once a cancer has metastasized it may still be treated with radiosurgery, chemotherapy, radiation therapy, biological therapy, hormone therapy, surgery, or a combination of these interventions ("multimodal therapy"). The choice of treatment depends on many factors, including the type of primary cancer, the size and location of the metastases, the patient's age and general health, and the types of treatments used previously. In patients diagnosed with CUP it is often still possible to treat the disease even when the primary tumor cannot be located.
Current treatments are rarely able to cure metastatic cancer though some tumors, such as testicular cancer and thyroid cancer, are usually curable.
Palliative care, care aimed at improving the quality of life of people with major illness, has been recommended as part of management programs for metastasis. Results from a systematic review of the literature on radiation therapy for brain metastases found that there is little evidence to inform comparative effectiveness and patient-centered outcomes on quality of life, functional status, and cognitive effects.
Research
Although metastasis is widely accepted to be the result of the tumor cells migration, there is a hypothesis saying that some metastases are the result of inflammatory processes by abnormal immune cells. The existence of metastatic cancers in the absence of primary tumors also suggests that metastasis is not always caused by malignant cells that leave primary tumors. | Metastasis | Wikipedia | 430 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
The research done by Sarna's team proved that heavily pigmented melanoma cells have Young's modulus about 4.93, when in non-pigmented ones it was only 0.98. In another experiment they found that elasticity of melanoma cells is important for its metastasis and growth: non-pigmented tumors were bigger than pigmented and it was much easier for them to spread. They showed that there are both pigmented and non-pigmented cells in melanoma tumors, so that they can both be drug-resistant and metastatic.
History
The first physician to report the possibility of local metastasis from a primary cancerous source to nearby tissues was Ibn Sina. He described a case of breast cancer and metastatic condition in The Canon of Medicine. His hypothesis was based on clinical course of the patient.
In March 2014 researchers discovered the oldest complete example of a human with metastatic cancer. The tumors had developed in a 3,000-year-old skeleton found in 2013 in a tomb in Sudan dating back to 1200 BC. The skeleton was analyzed using radiography and a scanning electron microscope. These findings were published in the Public Library of Science journal.
Etymology
Metastasis is a Greek word meaning "displacement", from μετά, meta, "next", and στάσις, stasis, "placement". | Metastasis | Wikipedia | 285 | 152509 | https://en.wikipedia.org/wiki/Metastasis | Biology and health sciences | Cancer | Health |
In geometry, bisection is the division of something into two equal or congruent parts (having the same shape and size). Usually it involves a bisecting line, also called a bisector. The most often considered types of bisectors are the segment bisector, a line that passes through the midpoint of a given segment, and the angle bisector, a line that passes through the apex of an angle (that divides it into two equal angles).
In three-dimensional space, bisection is usually done by a bisecting plane, also called the bisector.
Perpendicular line segment bisector
Definition
The perpendicular bisector of a line segment is a line which meets the segment at its midpoint perpendicularly.
The perpendicular bisector of a line segment also has the property that each of its points is equidistant from segment AB's endpoints:
(D).
The proof follows from and Pythagoras' theorem:
Property (D) is usually used for the construction of a perpendicular bisector:
Construction by straight edge and compass
In classical geometry, the bisection is a simple compass and straightedge construction, whose possibility depends on the ability to draw arcs of equal radii and different centers:
The segment is bisected by drawing intersecting circles of equal radius , whose centers are the endpoints of the segment. The line determined by the points of intersection of the two circles is the perpendicular bisector of the segment.
Because the construction of the bisector is done without the knowledge of the segment's midpoint , the construction is used for determining as the intersection of the bisector and the line segment.
This construction is in fact used when constructing a line perpendicular to a given line at a given point : drawing a circle whose center is such that it intersects the line in two points , and the perpendicular to be constructed is the one bisecting segment .
Equations
If are the position vectors of two points , then its midpoint is and vector is a normal vector of the perpendicular line segment bisector. Hence its vector equation is . Inserting and expanding the equation leads to the vector equation
(V)
With one gets the equation in coordinate form:
(C)
Or explicitly:
(E),
where , , and . | Bisection | Wikipedia | 470 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
Applications
Perpendicular line segment bisectors were used solving various geometric problems:
Construction of the center of a Thales' circle,
Construction of the center of the Excircle of a triangle,
Voronoi diagram boundaries consist of segments of such lines or planes.
Perpendicular line segment bisectors in space
The perpendicular bisector of a line segment is a plane, which meets the segment at its midpoint perpendicularly.
Its vector equation is literally the same as in the plane case:
(V)
With one gets the equation in coordinate form:
(C3)
Property (D) (see above) is literally true in space, too:
(D) The perpendicular bisector plane of a segment has for any point the property: .
Angle bisector
An angle bisector divides the angle into two angles with equal measures. An angle only has one bisector. Each point of an angle bisector is equidistant from the sides of the angle.
The 'interior' or 'internal bisector' of an angle is the line, half-line, or line segment that divides an angle of less than 180° into two equal angles. The 'exterior' or 'external bisector' is the line that divides the supplementary angle (of 180° minus the original angle), formed by one side forming the original angle and the extension of the other side, into two equal angles.
To bisect an angle with straightedge and compass, one draws a circle whose center is the vertex. The circle meets the angle at two points: one on each leg. Using each of these points as a center, draw two circles of the same size. The intersection of the circles (two points) determines a line that is the angle bisector.
The proof of the correctness of this construction is fairly intuitive, relying on the symmetry of the problem. The trisection of an angle (dividing it into three equal parts) cannot be achieved with the compass and ruler alone (this was first proved by Pierre Wantzel).
The internal and external bisectors of an angle are perpendicular. If the angle is formed by the two lines given algebraically as and then the internal and external bisectors are given by the two equations
Triangle
Concurrencies and collinearities
The bisectors of two exterior angles and the bisector of the other interior angle are concurrent. | Bisection | Wikipedia | 485 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
Three intersection points, each of an external angle bisector with the opposite extended side, are collinear (fall on the same line as each other).
Three intersection points, two of them between an interior angle bisector and the opposite side, and the third between the other exterior angle bisector and the opposite side extended, are collinear.
Angle bisector theorem
The angle bisector theorem is concerned with the relative lengths of the two segments that a triangle's side is divided into by a line that bisects the opposite angle. It equates their relative lengths to the relative lengths of the other two sides of the triangle.
Lengths
If the side lengths of a triangle are , the semiperimeter and A is the angle opposite side , then the length of the internal bisector of angle A is
or in trigonometric terms,
If the internal bisector of angle A in triangle ABC has length and if this bisector divides the side opposite A into segments of lengths m and n, then
where b and c are the side lengths opposite vertices B and C; and the side opposite A is divided in the proportion b:c.
If the internal bisectors of angles A, B, and C have lengths and , then
No two non-congruent triangles share the same set of three internal angle bisector lengths.
Integer triangles
There exist integer triangles with a rational angle bisector.
Quadrilateral
The internal angle bisectors of a convex quadrilateral either form a cyclic quadrilateral (that is, the four intersection points of adjacent angle bisectors are concyclic), or they are concurrent. In the latter case the quadrilateral is a tangential quadrilateral.
Rhombus
Each diagonal of a rhombus bisects opposite angles.
Ex-tangential quadrilateral
The excenter of an ex-tangential quadrilateral lies at the intersection of six angle bisectors. These are the internal angle bisectors at two opposite vertex angles, the external angle bisectors (supplementary angle bisectors) at the other two vertex angles, and the external angle bisectors at the angles formed where the extensions of opposite sides intersect.
Parabola
The tangent to a parabola at any point bisects the angle between the line joining the point to the focus and the line from the point and perpendicular to the directrix.
Bisectors of the sides of a polygon
Triangle | Bisection | Wikipedia | 511 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
Medians
Each of the three medians of a triangle is a line segment going through one vertex and the midpoint of the opposite side, so it bisects that side (though not in general perpendicularly). The three medians intersect each other at a point which is called the centroid of the triangle, which is its center of mass if it has uniform density; thus any line through a triangle's centroid and one of its vertices bisects the opposite side. The centroid is twice as close to the midpoint of any one side as it is to the opposite vertex.
Perpendicular bisectors
The interior perpendicular bisector of a side of a triangle is the segment, falling entirely on and inside the triangle, of the line that perpendicularly bisects that side. The three perpendicular bisectors of a triangle's three sides intersect at the circumcenter (the center of the circle through the three vertices). Thus any line through a triangle's circumcenter and perpendicular to a side bisects that side.
In an acute triangle the circumcenter divides the interior perpendicular bisectors of the two shortest sides in equal proportions. In an obtuse triangle the two shortest sides' perpendicular bisectors (extended beyond their opposite triangle sides to the circumcenter) are divided by their respective intersecting triangle sides in equal proportions.
For any triangle the interior perpendicular bisectors are given by and where the sides are and the area is
Quadrilateral
The two bimedians of a convex quadrilateral are the line segments that connect the midpoints of opposite sides, hence each bisecting two sides. The two bimedians and the line segment joining the midpoints of the diagonals are concurrent at a point called the "vertex centroid" and are all bisected by this point.
The four "maltitudes" of a convex quadrilateral are the perpendiculars to a side through the midpoint of the opposite side, hence bisecting the latter side. If the quadrilateral is cyclic (inscribed in a circle), these maltitudes are concurrent at (all meet at) a common point called the "anticenter". | Bisection | Wikipedia | 461 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
Brahmagupta's theorem states that if a cyclic quadrilateral is orthodiagonal (that is, has perpendicular diagonals), then the perpendicular to a side from the point of intersection of the diagonals always bisects the opposite side.
The perpendicular bisector construction forms a quadrilateral from the perpendicular bisectors of the sides of another quadrilateral.
Area bisectors and perimeter bisectors
Triangle
There is an infinitude of lines that bisect the area of a triangle. Three of them are the medians of the triangle (which connect the sides' midpoints with the opposite vertices), and these are concurrent at the triangle's centroid; indeed, they are the only area bisectors that go through the centroid. Three other area bisectors are parallel to the triangle's sides; each of these intersects the other two sides so as to divide them into segments with the proportions . These six lines are concurrent three at a time: in addition to the three medians being concurrent, any one median is concurrent with two of the side-parallel area bisectors.
The envelope of the infinitude of area bisectors is a deltoid (broadly defined as a figure with three vertices connected by curves that are concave to the exterior of the deltoid, making the interior points a non-convex set). The vertices of the deltoid are at the midpoints of the medians; all points inside the deltoid are on three different area bisectors, while all points outside it are on just one.
The sides of the deltoid are arcs of hyperbolas that are asymptotic to the extended sides of the triangle. The ratio of the area of the envelope of area bisectors to the area of the triangle is invariant for all triangles, and equals i.e. 0.019860... or less than 2%.
A cleaver of a triangle is a line segment that bisects the perimeter of the triangle and has one endpoint at the midpoint of one of the three sides. The three cleavers concur at (all pass through) the center of the Spieker circle, which is the incircle of the medial triangle. The cleavers are parallel to the angle bisectors. | Bisection | Wikipedia | 486 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
A splitter of a triangle is a line segment having one endpoint at one of the three vertices of the triangle and bisecting the perimeter. The three splitters concur at the Nagel point of the triangle.
Any line through a triangle that splits both the triangle's area and its perimeter in half goes through the triangle's incenter (the center of its incircle). There are either one, two, or three of these for any given triangle. A line through the incenter bisects one of the area or perimeter if and only if it also bisects the other.
Parallelogram
Any line through the midpoint of a parallelogram bisects the area and the perimeter.
Circle and ellipse
All area bisectors and perimeter bisectors of a circle or other ellipse go through the center, and any chords through the center bisect the area and perimeter. In the case of a circle they are the diameters of the circle.
Bisectors of diagonals
Parallelogram
The diagonals of a parallelogram bisect each other.
Quadrilateral
If a line segment connecting the diagonals of a quadrilateral bisects both diagonals, then this line segment (the Newton Line) is itself bisected by the vertex centroid.
Volume bisectors
A plane that divides two opposite edges of a tetrahedron in a given ratio also divides the volume of the tetrahedron in the same ratio. Thus any plane containing a bimedian (connector of opposite edges' midpoints) of a tetrahedron bisects the volume of the tetrahedron | Bisection | Wikipedia | 337 | 152547 | https://en.wikipedia.org/wiki/Bisection | Mathematics | Other | null |
Rutabaga (; North American English) or swede (English and some Commonwealth English) is a root vegetable, a form of Brassica napus (which also includes rapeseed). Other names include Swedish turnip, neep (Scots), and turnip (Scottish and Canadian English, Irish English and Manx English, as well as some dialects of English in Northern England). However, elsewhere, the name turnip usually refers to the related white turnip. The species Brassica napus originated as a hybrid between the cabbage (Brassica oleracea) and the turnip (Brassica rapa). Rutabaga roots are eaten as human food in various ways, and the leaves can be eaten as a leaf vegetable. The roots and tops are also used for livestock, fed directly in the winter or foraged in the field during the other seasons. Scotland, Northern and Western England, Wales, the Isle of Man, and Ireland had a tradition of carving the roots into Jack-o'-lanterns at Halloween.
Etymology
Rutabaga has many national and regional names. Rutabaga is the common North American term for the plant. This comes from the Swedish dialectal word , from 'root' + 'lump, bunch'. In the U.S., the plant is also known as Swedish turnip or yellow turnip.
The term swede (from "Swedish turnip") is used in many Commonwealth Nations, including much of the United Kingdom, Australia, and New Zealand. The name turnip is also used in parts of Northern and Midland England, the West Country (particularly Cornwall), Ireland, the Isle of Man, and Canada. In Wales, according to region, it is variously known as , , or in Welsh, and as swede or turnip in English.
In Scotland, it is known as turnip, tumshie (also used as a pejorative term for a foolish or stupid person), or neep (from Old English , Latin ). Some areas of south-east Scotland, such as Berwickshire and Roxburghshire, still use the term baigie, possibly a derivative of the Swedish dialectal word . The term turnip is also used for the white turnip (Brassica rapa ssp rapa). | Rutabaga | Wikipedia | 474 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Some will also refer to both swede and (white) turnip as just turnip (this word is also derived from ). In north-east England, turnips and swedes are colloquially called snannies snadgers, snaggers (archaic) or narkies. Rutabaga is also known as moot in the Isle of Man and the Manx language word for turnip is .
History
The first known printed reference to the rutabaga comes from the Swiss botanist Gaspard Bauhin in 1620, where he notes that it was growing wild in Sweden. It is often considered to have originated in Scandinavia, Finland or Russia. According to the Natural Resources Institute Finland (now Luke), rutabaga or was most likely bred on more than one occasion in Northern Europe around the 16th century. Studies by its research institute have shown that was developed independently in Finland and Sweden from turnip and cabbage in connection with seed cultivation. There are contradictory accounts of how rutabaga arrived in England. Some sources say it arrived in England from Germany, while other accounts support Swedish origins. According to John Sinclair, the root vegetable arrived in England from Germany around 1750. Rutabaga arrived in Scotland by way of Sweden around 1781.
An article in The Gardeners' Chronicle suggests that the rutabaga was introduced more widely to England in 1790. Introduction to North America came in the early 19th century with reports of rutabaga crops in Illinois as early as 1817. In 1835, a rutabaga fodder crop was recommended to New York farmers in the Genesee River valley.
Rutabaga was once considered a food of last resort in both Germany and France due to its association with food shortages in World War I and World War II. Boiled stew with rutabaga and water as the only ingredients (Steckrübeneintopf) was a typical food in Germany during the famines and food shortages of World War I caused by the Allied blockade (the or Turnip Winter of 1916–17) and between 1945 and 1949. As a result, many older Germans had unhappy memories of this food. | Rutabaga | Wikipedia | 440 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Botanical history
Rutabaga has a complex taxonomic history. The earliest account comes from the Swiss botanist Gaspard Bauhin, who wrote about it in his 1620 Prodromus. Brassica napobrassica was first validly published by Carl Linnaeus in his 1753 work Species Plantarum as a variety of B. oleracea: B. oleracea var. napobrassica. It has since been moved to other taxa as a variety, subspecies, or elevated to species rank. In 1768, a Scottish botanist promoted Linnaeus' variety to species rank as Brassica napobrassica in The Gardeners Dictionary.
Rutabaga has a chromosome number of 2n = 38. It originated from a cross between turnip (Brassica rapa) and Brassica oleracea. The resulting cross doubled its chromosomes, becoming an allopolyploid. This relationship was first published by Woo Jang-choon in 1935 and is known as the Triangle of U.
Cuisine
Europe
Netherlands
In the Netherlands, rutabaga is traditionally served boiled and mashed. Adding mashed potatoes (and, in some recipes, similarly mashed vegetables or fruits) makes 'mash pot', a dish often served alongside smoked sausage. Similar dishes are known in the Southern low countries, down to and including Brussels, as stoemp.
Poland
During the difficult days of World War II, rutabaga and rutabaga juice were an important part of the local diet, and were consumed in large quantities.
Scandinavia
Sweden and Norway
In Sweden and Norway, rutabaga is cooked with potato and sometimes carrot, and mashed with butter and either stock or, occasionally, milk or cream, to create a puree called (Swedish, literally 'root mash') or (Norwegian). Onion is occasionally added. In Norway, is an obligatory accompaniment to many festive dishes, including , , and salted herring. In Sweden, is often eaten together with cured and boiled ham hock, accompanied by mustard. This classic Swedish dish is called .
Finland
Finns eat and cook rutabaga in a variety of ways. Rutabaga is the major ingredient in the popular Christmas dish lanttulaatikko (rutabaga casserole), one of the three main casseroles served during Finnish Christmas, alongside the potato and carrot casseroles. | Rutabaga | Wikipedia | 487 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Uncooked and thinly julienned rutabaga is often served as a side dish salad in school and workplace lunches. Raisins or canned pineapple in light syrup are often added to the rutabaga salad. Sometimes, thinly sliced raw carrots are mixed with rutabaga.
Finns use rutabaga in most dishes that call for a root vegetable. Many Finnish soup bases consist of potatoes, carrots, and rutabagas.
Finnish cuisine also roasts, bakes, boils, and grills rutabagas. Oven-baked root vegetables are another home-cooking classic in Finland: rutabaga, carrots, beetroots, and potatoes are roasted in the oven with salt and oil. Karelian hot pot () is a popular slow-cooking stew with root vegetables and meat cooked for a long time in a Dutch oven.
Finnish supermarkets sell alternative potato chips made from root vegetables, such as rutabagas, beetroots and carrots.
Rutabagas are also an ingredient in (rutabaga-, a traditional Savonian and Karelian dish).
United Kingdom
England
In England, swede is boiled with carrots and mashed or pureed with butter and ground pepper. The flavoured cooking water is often retained for soup or as an addition to gravy. Swede is also a component of the popular condiment Branston Pickle. The swede is also one of the four traditional ingredients of the pasty originating in Cornwall.
Scotland
In Scotland, separately boiled and mashed, swede (neeps) and potatoes are served as "neeps and " ( being the Scots word for potatoes), in a traditional Burns supper, together with the main course of haggis (the Scottish national dish). Neeps mashed with potatoes are called clapshot. Roughly equal quantities of neeps and tatties are boiled in salted water and mashed with butter. Seasoning can be augmented with black pepper. Onions are never used. Regionally, neeps are a common ingredient in soups and stews.
Wales
Swede is an essential vegetable component of the traditional Welsh lamb broth called cawl. A mash produced using just potato and swede is known as in the North-East of the country, as on the Llyn peninsula and as in other parts.
Outside Europe | Rutabaga | Wikipedia | 490 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Australia
In Australia, swedes are used as a flavour enhancer in casseroles, stews, and soups.
Canada
In Canada, they are considered winter vegetables, as, along with similar vegetables, they can be kept in a cold area or cellar for several months. They are primarily used as a side dish. They are also used as filler in foods such as mincemeat and Christmas cake. In Newfoundland, it is served with Jiggs dinner.
New Zealand
In New Zealand, they are more commonly available in winter but can be easily purchased for much of the year. It is thought they best grow in Southland, where the winters are colder. They are usually served mashed with butter but are often added to other dishes like casseroles or bakes.
United States
In the US, rutabagas are not widely eaten but may be found as part of stews or casseroles, served mashed with carrots, or baked in a pasty. They are sometimes included in the New England boiled dinner.
Phytochemistry
Rutabaga and other cyanoglucoside-containing foods (including cassava, maize (corn), bamboo shoots, sweet potatoes, and lima beans) release cyanide, which is subsequently detoxified into thiocyanate. Thiocyanate inhibits thyroid iodide transport and, at high doses, competes with iodide in the organification process within thyroid tissue. Goitres may develop when there is a dietary imbalance of thiocyanate-containing food in excess of iodine consumption, and these compounds can contribute to hypothyroidism. Yet, there have been no reports of ill effects in humans from the consumption of glucosinolates from normal amounts of Brassica vegetables. Glucosinolate content in Brassica vegetables is around one percent of dry matter. These compounds also cause the bitter taste of rutabaga. | Rutabaga | Wikipedia | 401 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
As with watercress, mustard greens, turnip, broccoli, and horseradish, human perception of bitterness in rutabaga is governed by a gene affecting the TAS2R bitter receptor, which detects the glucosinolates in rutabaga. Sensitive individuals with the genotype PAV/PAV (supertasters) find rutabaga twice as bitter as insensitive subjects (AVI/AVI). The difference for the mixed type (PAV/AVI) is insignificant for rutabaga. As a result, sensitive individuals may find some rutabagas too bitter to eat.
Other chemical compounds that contribute to flavour and odour include glucocheirolin, glucobrassicanapin, glucoberteroin, gluconapoleiferin, and glucoerysolin. Several phytoalexins that aid in defence against plant pathogens have also been isolated from the rutabaga, including three novel phytoalexins that were reported in 2004.
Rutabaga contains significant amounts of vitamin C: 100 g contains 25 mg, 30% of the daily recommended dose.
Other uses
Livestock
The roots and tops of "swedes" came into use as a forage crop in the early nineteenth century, used as winter feed for livestock. They may be fed directly (chopped or from a hopper), or animals may be allowed to forage the plants directly in the field.
Halloween
People in Northern England, West England, Ireland, and Scotland have long carved turnips and often use them as lanterns to ward off harmful spirits. In the Middle Ages, rowdy bands of children roamed the streets in masks carrying carved turnips known in Scotland as "tumshie heads". In modern times, turnips are often carved to look as sinister and threatening as possible and are put in the window or on the doorstep of a house on Halloween to ward off evil spirits. | Rutabaga | Wikipedia | 413 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Since pumpkins became readily available in Europe in the 1980s, they have taken over this role to a large extent. In the Isle of Man, turnip lanterns are still carved at Hop-tu-Naa (Manx equivalent of Halloween), lit with a candle or electric torch, and carried from house to house by some children, with the accompanying Hop tu Naa song; hoping for money or treats of food. The smell of burning turnip is an evocative part of the event.
Festivals
A local farmers' market in the town of Ithaca, New York, organizes what it calls the International Rutabaga Curling Championship annually on the last day of the market season. The villages of Askov, Minnesota, and Cumberland, Wisconsin, both hold annual rutabaga festivals in August. | Rutabaga | Wikipedia | 162 | 152561 | https://en.wikipedia.org/wiki/Rutabaga | Biology and health sciences | Brassicales | null |
Cellular differentiation is the process in which a stem cell changes from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover. Some differentiation occurs in response to antigen exposure. Differentiation dramatically changes a cell's size, shape, membrane potential, metabolic activity, and responsiveness to signals. These changes are largely due to highly controlled modifications in gene expression and are the study of epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself. Metabolic composition, however, gets dramatically altered where stem cells are characterized by abundant metabolites with highly unsaturated structures whose levels decrease upon differentiation. Thus, different cells can have very different physical characteristics despite having the same genome.
A specialized type of differentiation, known as terminal differentiation, is of importance in some tissues, including vertebrate nervous system, striated muscle, epidermis and gut. During terminal differentiation, a precursor cell formerly capable of cell division permanently leaves the cell cycle, dismantles the cell cycle machinery and often expresses a range of genes characteristic of the cell's final function (e.g. myosin and actin for a muscle cell). Differentiation may continue to occur after terminal differentiation if the capacity and functions of the cell undergo further changes. | Cellular differentiation | Wikipedia | 318 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Among dividing cells, there are multiple levels of cell potency, which is the cell's ability to differentiate into other cell types. A greater potency indicates a larger number of cell types that can be derived. A cell that can differentiate into all cell types, including the placental tissue, is known as totipotent. In mammals, only the zygote and subsequent blastomeres are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques. A cell that can differentiate into all cell types of the adult organism is known as pluripotent. Such cells are called meristematic cells in higher plants and embryonic stem cells in animals, though some groups report the presence of adult pluripotent cells. Virally induced expression of four transcription factors Oct4, Sox2, , and Klf4 (Yamanaka factors) is sufficient to create pluripotent (iPS) cells from adult fibroblasts. A multipotent cell is one that can differentiate into multiple different, but closely related cell types. Oligopotent cells are more restricted than multipotent, but can still differentiate into a few closely related cell types. Finally, unipotent cells can differentiate into only one cell type, but are capable of self-renewal. In cytopathology, the level of cellular differentiation is used as a measure of cancer progression. "Grade" is a marker of how differentiated a cell in a tumor is.
Mammalian cell types
Three basic categories of cells make up the mammalian body: germ cells, somatic cells, and stem cells. Each of the approximately 37.2 trillion (3.72x1013) cells in an adult human has its own copy or copies of the genome except certain cell types, such as red blood cells, that lack nuclei in their fully differentiated state. Most cells are diploid; they have two copies of each chromosome. Such cells, called somatic cells, make up most of the human body, such as skin and muscle cells. Cells differentiate to specialize for different functions. | Cellular differentiation | Wikipedia | 430 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Germ line cells are any line of cells that give rise to gametes—eggs and sperm—and thus are continuous through the generations. Stem cells, on the other hand, have the ability to divide for indefinite periods and to give rise to specialized cells. They are best described in the context of normal human development.
Development begins when a sperm fertilizes an egg and creates a single cell that has the potential to form an entire organism. In the first hours after fertilization, this cell divides into identical cells. In humans, approximately four days after fertilization and after several cycles of cell division, these cells begin to specialize, forming a hollow sphere of cells, called a blastocyst. The blastocyst has an outer layer of cells, and inside this hollow sphere, there is a cluster of cells called the inner cell mass. The cells of the inner cell mass go on to form virtually all of the tissues of the human body. Although the cells of the inner cell mass can form virtually every type of cell found in the human body, they cannot form an organism. These cells are referred to as pluripotent. | Cellular differentiation | Wikipedia | 232 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Pluripotent stem cells undergo further specialization into multipotent progenitor cells that then give rise to functional cells. Examples of stem and progenitor cells include:
Radial glial cells (embryonic neural stem cells) that give rise to excitatory neurons in the fetal brain through the process of neurogenesis.
Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets.
Mesenchymal stem cells (adult stem cells) from the bone marrow that give rise to stromal cells, fat cells, and types of bone cells
Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells
Muscle satellite cells (progenitor cells) that contribute to differentiated muscle tissue.
A pathway that is guided by the cell adhesion molecules consisting of four amino acids, arginine, glycine, asparagine, and serine, is created as the cellular blastomere differentiates from the single-layered blastula to the three primary layers of germ cells in mammals, namely the ectoderm, mesoderm and endoderm (listed from most distal (exterior) to proximal (interior)). The ectoderm ends up forming the skin and the nervous system, the mesoderm forms the bones and muscular tissue, and the endoderm forms the internal organ tissues.
Dedifferentiation
Dedifferentiation, or integration, is a cellular process seen in the more basal life forms in animals, such as worms and amphibians where a differentiated cell reverts to an earlier developmental stageusually as part of a regenerative process. Dedifferentiation also occurs in plant cells. And, in cell culture in the laboratory, cells can change shape or may lose specific properties such as protein expressionwhich processes are also termed dedifferentiation.
Some hypothesize that dedifferentiation is an aberration that likely results in cancers, but others explain it as a natural part of the immune response that was lost to humans at some point of evolution. | Cellular differentiation | Wikipedia | 451 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
A newly discovered molecule dubbed reversine, a purine analog, has proven to induce dedifferentiation in myotubes. These manifestly dedifferentiated cellsnow performing essentially as stem cellscould then redifferentiate into osteoblasts and adipocytes.
Mechanisms
Each specialized cell type in an organism expresses a subset of all the genes that constitute the genome of that species. Each cell type is defined by its particular pattern of regulated gene expression. Cell differentiation is thus a transition of a cell from one cell type to another and it involves a switch from one pattern of gene expression to another. Cellular differentiation during development can be understood as the result of a gene regulatory network. A regulatory gene and its cis-regulatory modules are nodes in a gene regulatory network; they receive input and create output elsewhere in the network. The systems biology approach to developmental biology emphasizes the importance of investigating how developmental mechanisms interact to produce predictable patterns (morphogenesis). However, an alternative view has been proposed recently. Based on stochastic gene expression, cellular differentiation is the result of a Darwinian selective process occurring among cells. In this frame, protein and gene networks are the result of cellular processes and not their cause.
While evolutionarily conserved molecular processes are involved in the cellular mechanisms underlying these switches, in animal species these are very different from the well-characterized gene regulatory mechanisms of bacteria, and even from those of the animals' closest unicellular relatives. Specifically, cell differentiation in animals is highly dependent on biomolecular condensates of regulatory proteins and enhancer DNA sequences.
Cellular differentiation is often controlled by cell signaling. Many of the signal molecules that convey information from cell to cell during the control of cellular differentiation are called growth factors. Although the details of specific signal transduction pathways vary, these pathways often share the following general steps. A ligand produced by one cell binds to a receptor in the extracellular region of another cell, inducing a conformational change in the receptor. The shape of the cytoplasmic domain of the receptor changes, and the receptor acquires enzymatic activity. The receptor then catalyzes reactions that phosphorylate other proteins, activating them. A cascade of phosphorylation reactions eventually activates a dormant transcription factor or cytoskeletal protein, thus contributing to the differentiation process in the target cell. Cells and tissues can vary in competence, their ability to respond to external signals. | Cellular differentiation | Wikipedia | 504 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Signal induction refers to cascades of signaling events, during which a cell or tissue signals to another cell or tissue to influence its developmental fate. Yamamoto and Jeffery investigated the role of the lens in eye formation in cave- and surface-dwelling fish, a striking example of induction. Through reciprocal transplants, Yamamoto and Jeffery found that the lens vesicle of surface fish can induce other parts of the eye to develop in cave- and surface-dwelling fish, while the lens vesicle of the cave-dwelling fish cannot.
Other important mechanisms fall under the category of asymmetric cell divisions, divisions that give rise to daughter cells with distinct developmental fates. Asymmetric cell divisions can occur because of asymmetrically expressed maternal cytoplasmic determinants or because of signaling. In the former mechanism, distinct daughter cells are created during cytokinesis because of an uneven distribution of regulatory molecules in the parent cell; the distinct cytoplasm that each daughter cell inherits results in a distinct pattern of differentiation for each daughter cell. A well-studied example of pattern formation by asymmetric divisions is body axis patterning in Drosophila. RNA molecules are an important type of intracellular differentiation control signal. The molecular and genetic basis of asymmetric cell divisions has also been studied in green algae of the genus Volvox, a model system for studying how unicellular organisms can evolve into multicellular organisms. In Volvox carteri, the 16 cells in the anterior hemisphere of a 32-cell embryo divide asymmetrically, each producing one large and one small daughter cell. The size of the cell at the end of all cell divisions determines whether it becomes a specialized germ or somatic cell.
Epigenetic control
Since each cell, regardless of cell type, possesses the same genome, determination of cell type must occur at the level of gene expression. While the regulation of gene expression can occur through cis- and trans-regulatory elements including a gene's promoter and enhancers, the problem arises as to how this expression pattern is maintained over numerous generations of cell division. As it turns out, epigenetic processes play a crucial role in regulating the decision to adopt a stem, progenitor, or mature cell fate This section will focus primarily on mammalian stem cells. | Cellular differentiation | Wikipedia | 465 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
In systems biology and mathematical modeling of gene regulatory networks, cell-fate determination is predicted to exhibit certain dynamics, such as attractor-convergence (the attractor can be an equilibrium point, limit cycle or strange attractor) or oscillatory.
Importance of epigenetic control
The first question that can be asked is the extent and complexity of the role of epigenetic processes in the determination of cell fate. A clear answer to this question can be seen in the 2011 paper by Lister R, et al. on aberrant epigenomic programming in human induced pluripotent stem cells. As induced pluripotent stem cells (iPSCs) are thought to mimic embryonic stem cells in their pluripotent properties, few epigenetic differences should exist between them. To test this prediction, the authors conducted whole-genome profiling of DNA methylation patterns in several human embryonic stem cell (ESC), iPSC, and progenitor cell lines.
Female adipose cells, lung fibroblasts, and foreskin fibroblasts were reprogrammed into induced pluripotent state with the OCT4, SOX2, KLF4, and MYC genes. Patterns of DNA methylation in ESCs, iPSCs, somatic cells were compared. Lister R, et al. observed significant resemblance in methylation levels between embryonic and induced pluripotent cells. Around 80% of CG dinucleotides in ESCs and iPSCs were methylated, the same was true of only 60% of CG dinucleotides in somatic cells. In addition, somatic cells possessed minimal levels of cytosine methylation in non-CG dinucleotides, while induced pluripotent cells possessed similar levels of methylation as embryonic stem cells, between 0.5 and 1.5%. Thus, consistent with their respective transcriptional activities, DNA methylation patterns, at least on the genomic level, are similar between ESCs and iPSCs. | Cellular differentiation | Wikipedia | 422 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
However, upon examining methylation patterns more closely, the authors discovered 1175 regions of differential CG dinucleotide methylation between at least one ES or iPS cell line. By comparing these regions of differential methylation with regions of cytosine methylation in the original somatic cells, 44-49% of differentially methylated regions reflected methylation patterns of the respective progenitor somatic cells, while 51-56% of these regions were dissimilar to both the progenitor and embryonic cell lines. In vitro-induced differentiation of iPSC lines saw transmission of 88% and 46% of hyper and hypo-methylated differentially methylated regions, respectively.
Two conclusions are readily apparent from this study. First, epigenetic processes are heavily involved in cell fate determination, as seen from the similar levels of cytosine methylation between induced pluripotent and embryonic stem cells, consistent with their respective patterns of transcription. Second, the mechanisms of reprogramming (and by extension, differentiation) are very complex and cannot be easily duplicated, as seen by the significant number of differentially methylated regions between ES and iPS cell lines. Now that these two points have been established, we can examine some of the epigenetic mechanisms that are thought to regulate cellular differentiation.
Mechanisms of epigenetic regulation | Cellular differentiation | Wikipedia | 277 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Pioneer factors (Oct4, Sox2, Nanog)
Three transcription factors, OCT4, SOX2, and NANOG – the first two of which are used in induced pluripotent stem cell (iPSC) reprogramming, along with Klf4 and c-Myc – are highly expressed in undifferentiated embryonic stem cells and are necessary for the maintenance of their pluripotency. It is thought that they achieve this through alterations in chromatin structure, such as histone modification and DNA methylation, to restrict or permit the transcription of target genes. While highly expressed, their levels require a precise balance to maintain pluripotency, perturbation of which will promote differentiation towards different lineages based on how the gene expression levels change. Differential regulation of Oct-4 and SOX2 levels have been shown to precede germ layer fate selection. Increased levels of Oct4 and decreased levels of Sox2 promote a mesendodermal fate, with Oct4 actively suppressing genes associated with a neural ectodermal fate. Similarly, increased levels of Sox2 and decreased levels of Oct4 promote differentiation towards a neural ectodermal fate, with Sox2 inhibiting differentiation towards a mesendodermal fate. Regardless of the lineage cells differentiate down, suppression of NANOG has been identified as a necessary prerequisite for differentiation.
Polycomb repressive complex (PRC2)
In the realm of gene silencing, Polycomb repressive complex 2, one of two classes of the Polycomb group (PcG) family of proteins, catalyzes the di- and tri-methylation of histone H3 lysine 27 (H3K27me2/me3). By binding to the H3K27me2/3-tagged nucleosome, PRC1 (also a complex of PcG family proteins) catalyzes the mono-ubiquitinylation of histone H2A at lysine 119 (H2AK119Ub1), blocking RNA polymerase II activity and resulting in transcriptional suppression. PcG knockout ES cells do not differentiate efficiently into the three germ layers, and deletion of the PRC1 and PRC2 genes leads to increased expression of lineage-affiliated genes and unscheduled differentiation. Presumably, PcG complexes are responsible for transcriptionally repressing differentiation and development-promoting genes. | Cellular differentiation | Wikipedia | 499 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Trithorax group proteins (TrxG)
Alternately, upon receiving differentiation signals, PcG proteins are recruited to promoters of pluripotency transcription factors. PcG-deficient ES cells can begin differentiation but cannot maintain the differentiated phenotype. Simultaneously, differentiation and development-promoting genes are activated by Trithorax group (TrxG) chromatin regulators and lose their repression. TrxG proteins are recruited at regions of high transcriptional activity, where they catalyze the trimethylation of histone H3 lysine 4 (H3K4me3) and promote gene activation through histone acetylation. PcG and TrxG complexes engage in direct competition and are thought to be functionally antagonistic, creating at differentiation and development-promoting loci what is termed a "bivalent domain" and rendering these genes sensitive to rapid induction or repression.
DNA methylation
Regulation of gene expression is further achieved through DNA methylation, in which the DNA methyltransferase-mediated methylation of cytosine residues in CpG dinucleotides maintains heritable repression by controlling DNA accessibility. The majority of CpG sites in embryonic stem cells are unmethylated and appear to be associated with H3K4me3-carrying nucleosomes. Upon differentiation, a small number of genes, including OCT4 and NANOG, are methylated and their promoters repressed to prevent their further expression. Consistently, DNA methylation-deficient embryonic stem cells rapidly enter apoptosis upon in vitro differentiation.
Nucleosome positioning
While the DNA sequence of most cells of an organism is the same, the binding patterns of transcription factors and the corresponding gene expression patterns are different. To a large extent, differences in transcription factor binding are determined by the chromatin accessibility of their binding sites through histone modification and/or pioneer factors. In particular, it is important to know whether a nucleosome is covering a given genomic binding site or not. This can be determined using a chromatin immunoprecipitation assay. | Cellular differentiation | Wikipedia | 430 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Histone acetylation and methylation
DNA-nucleosome interactions are characterized by two states: either tightly bound by nucleosomes and transcriptionally inactive, called heterochromatin, or loosely bound and usually, but not always, transcriptionally active, called euchromatin. The epigenetic processes of histone methylation and acetylation, and their inverses demethylation and deacetylation primarily account for these changes. The effects of acetylation and deacetylation are more predictable. An acetyl group is either added to or removed from the positively charged Lysine residues in histones by enzymes called histone acetyltransferases or histone deactylases, respectively. The acetyl group prevents Lysine's association with the negatively charged DNA backbone. Methylation is not as straightforward, as neither methylation nor demethylation consistently correlate with either gene activation or repression. However, certain methylations have been repeatedly shown to either activate or repress genes. The trimethylation of lysine 4 on histone 3 (H3K4Me3) is associated with gene activation, whereas trimethylation of lysine 27 on histone 3 represses genes
In stem cells
During differentiation, stem cells change their gene expression profiles. Recent studies have implicated a role for nucleosome positioning and histone modifications during this process. There are two components of this process: turning off the expression of embryonic stem cell (ESC) genes, and the activation of cell fate genes. Lysine specific demethylase 1 (KDM1A) is thought to prevent the use of enhancer regions of pluripotency genes, thereby inhibiting their transcription. It interacts with Mi-2/NuRD complex (nucleosome remodelling and histone deacetylase) complex, giving an instance where methylation and acetylation are not discrete and mutually exclusive, but intertwined processes.
Role of signaling in epigenetic control | Cellular differentiation | Wikipedia | 425 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
A final question to ask concerns the role of cell signaling in influencing the epigenetic processes governing differentiation. Such a role should exist, as it would be reasonable to think that extrinsic signaling can lead to epigenetic remodeling, just as it can lead to changes in gene expression through the activation or repression of different transcription factors. Little direct data is available concerning the specific signals that influence the epigenome, and the majority of current knowledge about the subject consists of speculations on plausible candidate regulators of epigenetic remodeling. We will first discuss several major candidates thought to be involved in the induction and maintenance of both embryonic stem cells and their differentiated progeny, and then turn to one example of specific signaling pathways in which more direct evidence exists for its role in epigenetic change.
The first major candidate is Wnt signaling pathway. The Wnt pathway is involved in all stages of differentiation, and the ligand Wnt3a can substitute for the overexpression of c-Myc in the generation of induced pluripotent stem cells. On the other hand, disruption of β-catenin, a component of the Wnt signaling pathway, leads to decreased proliferation of neural progenitors.
Growth factors comprise the second major set of candidates of epigenetic regulators of cellular differentiation. These morphogens are crucial for development, and include bone morphogenetic proteins, transforming growth factors (TGFs), and fibroblast growth factors (FGFs). TGFs and FGFs have been shown to sustain expression of OCT4, SOX2, and NANOG by downstream signaling to Smad proteins. Depletion of growth factors promotes the differentiation of ESCs, while genes with bivalent chromatin can become either more restrictive or permissive in their transcription.
Several other signaling pathways are also considered to be primary candidates. Cytokine leukemia inhibitory factors are associated with the maintenance of mouse ESCs in an undifferentiated state. This is achieved through its activation of the Jak-STAT3 pathway, which has been shown to be necessary and sufficient towards maintaining mouse ESC pluripotency. Retinoic acid can induce differentiation of human and mouse ESCs, and Notch signaling is involved in the proliferation and self-renewal of stem cells. Finally, Sonic hedgehog, in addition to its role as a morphogen, promotes embryonic stem cell differentiation and the self-renewal of somatic stem cells. | Cellular differentiation | Wikipedia | 510 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
The problem, of course, is that the candidacy of these signaling pathways was inferred primarily on the basis of their role in development and cellular differentiation. While epigenetic regulation is necessary for driving cellular differentiation, they are certainly not sufficient for this process. Direct modulation of gene expression through modification of transcription factors plays a key role that must be distinguished from heritable epigenetic changes that can persist even in the absence of the original environmental signals. Only a few examples of signaling pathways leading to epigenetic changes that alter cell fate currently exist, and we will focus on one of them.
Expression of Shh (Sonic hedgehog) upregulates the production of BMI1, a component of the PcG complex that recognizes H3K27me3. This occurs in a Gli-dependent manner, as Gli1 and Gli2 are downstream effectors of the Hedgehog signaling pathway. In culture, Bmi1 mediates the Hedgehog pathway's ability to promote human mammary stem cell self-renewal. In both humans and mice, researchers showed Bmi1 to be highly expressed in proliferating immature cerebellar granule cell precursors. When Bmi1 was knocked out in mice, impaired cerebellar development resulted, leading to significant reductions in postnatal brain mass along with abnormalities in motor control and behavior. A separate study showed a significant decrease in neural stem cell proliferation along with increased astrocyte proliferation in Bmi null mice.
An alternative model of cellular differentiation during embryogenesis is that positional information is based on mechanical signalling by the cytoskeleton using Embryonic differentiation waves. The mechanical signal is then epigenetically transduced via signal transduction systems (of which specific molecules such as Wnt are part) to result in differential gene expression.
In summary, the role of signaling in the epigenetic control of cell fate in mammals is largely unknown, but distinct examples exist that indicate the likely existence of further such mechanisms. | Cellular differentiation | Wikipedia | 407 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Effect of matrix elasticity
In order to fulfill the purpose of regenerating a variety of tissues, adult stems are known to migrate from their niches, adhere to new extracellular matrices (ECM) and differentiate. The ductility of these microenvironments are unique to different tissue types. The ECM surrounding brain, muscle and bone tissues range from soft to stiff. The transduction of the stem cells into these cells types is not directed solely by chemokine cues and cell to cell signaling. The elasticity of the microenvironment can also affect the differentiation of mesenchymal stem cells (MSCs which originate in bone marrow.) When MSCs are placed on substrates of the same stiffness as brain, muscle and bone ECM, the MSCs take on properties of those respective cell types.
Matrix sensing requires the cell to pull against the matrix at focal adhesions, which triggers a cellular mechano-transducer to generate a signal to be informed what force is needed to deform the matrix. To determine the key players in matrix-elasticity-driven lineage specification in MSCs, different matrix microenvironments were mimicked. From these experiments, it was concluded that focal adhesions of the MSCs were the cellular mechano-transducer sensing the differences of the matrix elasticity. The non-muscle myosin IIa-c isoforms generates the forces in the cell that lead to signaling of early commitment markers. Nonmuscle myosin IIa generates the least force increasing to non-muscle myosin IIc. There are also factors in the cell that inhibit non-muscle myosin II, such as blebbistatin. This makes the cell effectively blind to the surrounding matrix. Researchers have achieved some success in inducing stem cell-like properties in HEK 239 cells by providing a soft matrix without the use of diffusing factors. The stem-cell properties appear to be linked to tension in the cells' actin network. One identified mechanism for matrix-induced differentiation is tension-induced proteins, which remodel chromatin in response to mechanical stretch. The RhoA pathway is also implicated in this process.
Evolutionary history | Cellular differentiation | Wikipedia | 456 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
A billion-years-old, likely holozoan, protist, Bicellum brasieri with two types of cells, shows that the evolution of differentiated multicellularity, possibly but not necessarily of animal lineages, occurred at least 1 billion years ago and possibly mainly in freshwater lakes rather than the ocean. | Cellular differentiation | Wikipedia | 65 | 152611 | https://en.wikipedia.org/wiki/Cellular%20differentiation | Biology and health sciences | Cell processes | Biology |
Radiology ( ) is the medical specialty that uses medical imaging to diagnose diseases and guide treatment within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiation), but today it includes all imaging modalities. This includes technologies that use no ionizing electromagnetic radiation, such as ultrasonography and magnetic resonance imaging), as well as others that do use radiation, such as computed tomography (CT), fluoroscopy, and nuclear medicine including positron emission tomography (PET). Interventional radiology is the performance of usually minimally invasive medical procedures with the guidance of imaging technologies such as those mentioned above.
The modern practice of radiology involves a team of several different healthcare professionals. A radiologist, who is a medical doctor with specialized post-graduate training, interprets medical images, communicates these findings to other physicians through reports or verbal communication, and uses imaging to perform minimally invasive medical procedures The nurse is involved in the care of patients before and after imaging or procedures, including administration of medications, monitoring of vital signs and monitoring of sedated patients. The radiographer, also known as a "radiologic technologist" in some countries such as the United States and Canada, is a specially trained healthcare professional that uses sophisticated technology and positioning techniques to produce medical images for the radiologist to interpret. Depending on the individual's training and country of practice, the radiographer may specialize in one of the above-mentioned imaging modalities or have expanded roles in image reporting.
Diagnostic imaging modalities
Projection (plain) radiography
Radiographs (originally called roentgenographs, named after the discoverer of X-rays, Wilhelm Conrad Röntgen) are produced by transmitting X-rays through a patient. The X-rays are projected through the body onto a detector; an image is formed based on which rays pass through (and are detected) versus those that are absorbed or scattered in the patient (and thus are not detected). Röntgen discovered X-rays on November 8, 1895, and received the first Nobel Prize in Physics for his discovery in 1901. | Radiology | Wikipedia | 444 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
In film-screen radiography, an X-ray tube generates a beam of X-rays, which is aimed at the patient. The X-rays that pass through the patient are filtered through a device called a grid or X-ray filter, to reduce scatter, and strike an undeveloped film, which is held tightly to a screen of light-emitting phosphors in a light-tight cassette. The film is then developed chemically and an image appears on the film. Film-screen radiography is being replaced by phosphor plate radiography but more recently by digital radiography (DR) and the EOS imaging. In the two latest systems, the X-rays strike sensors that converts the signals generated into digital information, which is transmitted and converted into an image displayed on a computer screen. In digital radiography the sensors shape a plate, but in the EOS system, which is a slot-scanning system, a linear sensor vertically scans the patient.
Plain radiography was the only imaging modality available during the first 50 years of radiology. Due to its availability, speed, and lower costs compared to other modalities, radiography is often the first-line test of choice in radiologic diagnosis. Also despite the large amount of data in CT scans, MR scans and other digital-based imaging, there are many disease entities in which the classic diagnosis is obtained by plain radiographs. Examples include various types of arthritis and pneumonia, bone tumors (especially benign bone tumors), fractures, congenital skeletal anomalies, and certain kidney stones.
Mammography and DXA are two applications of low energy projectional radiography, used for the evaluation for breast cancer and osteoporosis, respectively.
Fluoroscopy | Radiology | Wikipedia | 356 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Fluoroscopy and angiography are special applications of X-ray imaging, in which a fluorescent screen and image intensifier tube is connected to a closed-circuit television system. This allows real-time imaging of structures in motion or augmented with a radiocontrast agent. Radiocontrast agents are usually administered by swallowing or injecting into the body of the patient to delineate anatomy and functioning of the blood vessels, the genitourinary system, or the gastrointestinal tract (GI tract). Two radiocontrast agents are presently in common use. Barium sulfate (BaSO4) is given orally or rectally for evaluation of the GI tract. Iodine, in multiple proprietary forms, is given by oral, rectal, vaginal, intra-arterial or intravenous routes. These radiocontrast agents strongly absorb or scatter X-rays, and in conjunction with the real-time imaging, allow demonstration of dynamic processes, such as peristalsis in the digestive tract or blood flow in arteries and veins. Iodine contrast may also be concentrated in abnormal areas more or less than in normal tissues and make abnormalities (tumors, cysts, inflammation) more conspicuous. Additionally, in specific circumstances, air can be used as a contrast agent for the gastrointestinal system and carbon dioxide can be used as a contrast agent in the venous system; in these cases, the contrast agent attenuates the X-ray radiation less than the surrounding tissues.
Computed tomography
CT imaging uses X-rays in conjunction with computing algorithms to image the body.
In CT, an X-ray tube opposite an X-ray detector (or detectors) in a ring-shaped apparatus rotate around a patient, producing a computer-generated cross-sectional image (tomogram). CT is acquired in the axial plane, with coronal and sagittal images produced by computer reconstruction. Radiocontrast agents are often used with CT for enhanced delineation of anatomy. Although radiographs provide higher spatial resolution, CT can detect more subtle variations in attenuation of X-rays (higher contrast resolution). CT exposes the patient to significantly more ionizing radiation than a radiograph. | Radiology | Wikipedia | 457 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Spiral multidetector CT uses 16, 64, 254 or more detectors during continuous motion of the patient through the radiation beam to obtain fine detail images in a short exam time. With rapid administration of intravenous contrast during the CT scan, these fine detail images can be reconstructed into three-dimensional (3D) images of carotid, cerebral, coronary or other arteries.
The introduction of computed tomography in the early 1970s revolutionized diagnostic radiology by providing front-line clinicians with detailed images of anatomic structures in three dimensions. CT scanning has become the test of choice in diagnosing some urgent and emergent conditions, such as cerebral hemorrhage, pulmonary embolism (clots in the arteries of the lungs), aortic dissection (tearing of the aortic wall), appendicitis, diverticulitis, and obstructing kidney stones. Before the development of CT imaging, risky and painful exploratory surgery was often the only way to obtain a definitive diagnosis of the cause of severe abdominal pain which could not be otherwise ascertained from external observation. Continuing improvements in CT technology, including faster scanning times and improved resolution, have dramatically increased the accuracy and usefulness of CT scanning, which may partially account for increased use in medical diagnosis.
Ultrasound
Medical ultrasonography uses ultrasound (high-frequency sound waves) to visualize soft tissue structures in the body in real time. No ionizing radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person (ultrasonographer) performing the exam and the patient's body size. Examinations of larger, overweight patients may have a decrease in image quality as their subcutaneous fat absorbs more of the sound waves. This results in fewer sound waves penetrating to organs and reflecting back to the transducer, resulting in loss of information and a poorer quality image. Ultrasound is also limited by its inability to image through air pockets (lungs, bowel loops) or bone. Its use in medical imaging has developed mostly within the last 30 years. The first ultrasound images were static and two-dimensional (2D), but with modern ultrasonography, 3D reconstructions can be observed in real time, effectively becoming "4D". | Radiology | Wikipedia | 467 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Because ultrasound imaging techniques do not employ ionizing radiation to generate images (unlike radiography, and CT scans), they are generally considered safer and are therefore more common in obstetrical imaging. The progression of pregnancies can be thoroughly evaluated with less concern about damage from the techniques employed, allowing early detection and diagnosis of many fetal anomalies. Growth can be assessed over time, important in patients with chronic disease or pregnancy-induced disease, and in multiple pregnancies (twins, triplets, etc.). Color-flow Doppler ultrasound measures the severity of peripheral vascular disease and is used by cardiologists for dynamic evaluation of the heart, heart valves and major vessels. Stenosis, for example, of the carotid arteries may be a warning sign for an impending stroke. A clot, embedded deep in one of the inner veins of the legs, can be found via ultrasound before it dislodges and travels to the lungs, resulting in a potentially fatal pulmonary embolism. Ultrasound is useful as a guide to performing biopsies to minimize damage to surrounding tissues and in drainages such as thoracentesis. Small, portable ultrasound devices now replace peritoneal lavage in trauma wards by non-invasively assessing for the presence of internal bleeding and any internal organ damage. Extensive internal bleeding or injury to the major organs may require surgery and repair.
Magnetic resonance imaging
MRI uses strong magnetic fields to align atomic nuclei (usually hydrogen protons) within body tissues, then uses a radio signal to disturb the axis of rotation of these nuclei and observes the radio frequency signal generated as the nuclei return to their baseline states. The radio signals are collected by small antennae, called coils, placed near the area of interest. An advantage of MRI is its ability to produce images in axial, coronal, sagittal and multiple oblique planes with equal ease. MRI scans give the best soft tissue contrast of all the imaging modalities. With advances in scanning speed and spatial resolution, and improvements in computer 3D algorithms and hardware, MRI has become an important tool in musculoskeletal radiology and neuroradiology. | Radiology | Wikipedia | 438 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
One disadvantage is the patient has to hold still for long periods of time in a noisy, cramped space while the imaging is performed. Claustrophobia (fear of closed spaces) severe enough to terminate the MRI exam is reported in up to 5% of patients. Recent improvements in magnet design including stronger magnetic fields (3 teslas), shortening exam times, wider, shorter magnet bores and more open magnet designs, have brought some relief for claustrophobic patients. However, for magnets with equivalent field strengths, there is often a trade-off between image quality and open design. MRI has great benefit in imaging the brain, spine, and musculoskeletal system. The use of MRI is currently contraindicated for patients with pacemakers, cochlear implants, some indwelling medication pumps, certain types of cerebral aneurysm clips, metal fragments in the eyes, some metallic hardware due to the powerful magnetic fields, and strong fluctuating radio signals to which the body is exposed. Areas of potential advancement include functional imaging, cardiovascular MRI, and MRI-guided therapy.
Nuclear medicine | Radiology | Wikipedia | 226 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Nuclear medicine imaging involves the administration into the patient of radiopharmaceuticals consisting of substances with affinity for certain body tissues labeled with radioactive tracer. The most commonly used tracers are technetium-99m, iodine-123, iodine-131, gallium-67, indium-111, thallium-201 and fludeoxyglucose (18F) (18F-FDG). The heart, lungs, thyroid, liver, brain, gallbladder, and bones are commonly evaluated for particular conditions using these techniques. While anatomical detail is limited in these studies, nuclear medicine is useful in displaying physiological function. The excretory function of the kidneys, iodine-concentrating ability of the thyroid, blood flow to heart muscle, etc. can be measured. The principal imaging devices are the gamma camera and the PET Scanner, which detect the radiation emitted by the tracer in the body and display it as an image. With computer processing, the information can be displayed as axial, coronal and sagittal images (single-photon emission computed tomography - SPECT or Positron-emission tomography - PET). In the most modern devices, nuclear medicine images can be fused with a CT scan taken quasisimultaneously, so the physiological information can be overlaid or coregistered with the anatomical structures to improve diagnostic accuracy.
Positron emission tomography (PET) scanning deals with positrons instead of gamma rays detected by gamma cameras. The positrons annihilate to produce two opposite traveling gamma rays to be detected coincidentally, thus improving resolution. In PET scanning, a radioactive, biologically active substance, most often 18F-FDG, is injected into a patient and the radiation emitted by the patient is detected to produce multiplanar images of the body. Metabolically more active tissues, such as cancer, concentrate the active substance more than normal tissues. PET images can be combined (or "fused") with anatomic (CT) imaging, to more accurately localize PET findings and thereby improve diagnostic accuracy. | Radiology | Wikipedia | 433 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
The fusion technology has gone further to combine PET and MRI similar to PET and CT. PET/MRI fusion, largely practiced in academic and research settings, could potentially play a crucial role in fine detail of brain imaging, breast cancer screening, and small joint imaging of the foot. The technology recently blossomed after passing the technical hurdle of altered positron movement in strong magnetic field thus affecting the resolution of PET images and attenuation correction.
Interventional radiology
Interventional radiology (IR or sometimes VIR for vascular and interventional radiology) is a subspecialty of radiology in which minimally invasive procedures are performed using image guidance. Some of these procedures are done for purely diagnostic purposes (e.g., angiogram), while others are done for treatment purposes (e.g., angioplasty).
The basic concept behind interventional radiology is to diagnose or treat pathologies, with the most minimally invasive technique possible. Minimally invasive procedures are currently performed more than ever before. These procedures are often performed with the patient fully awake, with little or no sedation required. Interventional radiologists and interventional radiographers diagnose and treat several disorders, including peripheral vascular disease, renal artery stenosis, inferior vena cava filter placement, gastrostomy tube placements, biliary stents and hepatic interventions. Radiographic images, fluoroscopy, and ultrasound modalities are used for guidance, and the primary instruments used during the procedure are specialized needles and catheters. The images provide maps that allow the clinician to guide these instruments through the body to the areas containing disease. By minimizing the physical trauma to the patient, peripheral interventions can reduce infection rates and recovery times, as well as hospital stays. To be a trained interventionalist in the United States, an individual completes a five-year residency in radiology and a one- or two-year fellowship in IR.
Analysis of images
Plain, or general, radiography | Radiology | Wikipedia | 414 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
The basic technique is optical density evaluation (i.e. histogram analysis). It is then described that a region has a different optical density, e.g. a cancer metastasis to bone can cause radiolucency. The development of this is the digital radiological subtraction. It consists in overlapping two radiographs of the same examined region and subtracting the optical densities Comparison of changes in dental and bone radiographic densities in the presence of different soft-tissue simulators using pixel intensity and digital subtraction analyses. The resultant image only contains the time-dependent differences between the two examined radiographs. The advantage of this technique is the precise determination of the dynamics of density changes and the place of their occurrence. However, beforehand the geometrical adjustment and general alignment of optical density should be done Noise in subtraction images made from pairs of intraoral radiographs: a comparison between four methods of geometric alignment.
Another possibility of radiographic image analysis is to study second order features, e.g. digital texture analysis Basic research Textural entropy as a potential feature for quantitative assessment of jaw bone healing process Comparative Analysis of Three Bone Substitute Materials Based on Co-Occurrence Matrix or fractal dimension Using fractal dimension to evaluate alveolar bone defects treated with various bone substitute materials. On this basis, it is possible to assess the places where bio-materials are implanted into the bone for the purpose of guided bone regeneration. They take an intact bone image sample (region of interest, ROI, reference site) and a sample of the implantation site (second ROI, test site) can be assessed numerically/objectively to what extent the implantation site imitates a healthy bone and how advanced is the process of bone regeneration Fast-Versus Slow-Resorbable Calcium Phosphate Bone Substitute Materials—Texture Analysis after 12 Months of Observation New Oral Surgery Materials for Bone Reconstruction—A Comparison of Five Bone Substitute Materials for Dentoalveolar Augmentation. It is also possible to check whether the bone healing process is influenced by some systemic factors Influence of General Mineral Condition on Collagen-Guided Alveolar Crest Augmentation.
Teleradiology | Radiology | Wikipedia | 446 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Teleradiology is the transmission of radiographic images from one location to another for interpretation by an appropriately trained professional, usually a radiologist or reporting radiographer. It is most often used to allow rapid interpretation of emergency room, ICU and other emergent examinations after hours of usual operation, at night and on weekends. In these cases, the images can be sent across time zones (e.g. to Spain, Australia, India) with the receiving Clinician working his normal daylight hours. However, at present, large private teleradiology companies in the U.S. currently provide most after-hours coverage employing night-working radiologists in the U.S. Teleradiology can also be used to obtain consultation with an expert or subspecialist about a complicated or puzzling case. In the U.S., many hospitals outsource their radiology departments to radiologists in India due to the lowered cost and availability of high speed internet access.
Teleradiology requires a sending station, a high-speed internet connection, and a high-quality receiving station. At the transmission station, plain radiographs are passed through a digitizing machine before transmission, while CT, MRI, ultrasound and nuclear medicine scans can be sent directly, as they are already digital data. The computer at the receiving end will need to have a high-quality display screen that has been tested and cleared for clinical purposes. Reports are then transmitted to the requesting clinician.
The major advantage of teleradiology is the ability to use different time zones to provide real-time emergency radiology services around-the-clock. The disadvantages include higher costs, limited contact between the referrer and the reporting Clinician, and the inability to cover for procedures requiring an onsite reporting Clinician. Laws and regulations concerning the use of teleradiology vary among the states, with some requiring a license to practice medicine in the state sending the radiologic exam. In the U.S., some states require the teleradiology report to be preliminary with the official report issued by a hospital staff radiologist. Lastly, a benefit of teleradiology is that it might be automated with modern machine learning techniques. | Radiology | Wikipedia | 449 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Patient interaction
Some radiologists, like teleradiologists, have no interaction with patients. Other radiologists, like interventional radiologists, primarily interact with patients and spend less time analyzing images. Diagnostic radiologists tend to spend the majority of their time analyzing images and a minority of their time interacting with patients. Compared to the healthcare provider who sends the patient to have images interpreted by a diagnostic radiologist, the radiologist usually does not know as much about the patient's clinical status or have as much influence on what action should be taken based on the images. Thus, the diagnostic radiologist reports image findings directly to that healthcare provider and often provides recommendations, who then takes the appropriate next steps for recommendations about medical management. Because radiologists undergo training regarding risks associated with different types of imaging tests and image-guided procedures, radiologists are the healthcare providers who generally educate patients about those risks to enable informed consent, not the healthcare provider requesting the test or procedure.
Professional training
United States
Radiology is a field in medicine that has expanded rapidly after 2000 due to advances in computer technology, which is closely linked to modern imaging techniques. Applying for residency positions in radiology has become highly competitive. Applicants are often near the top of their medical school classes, with high USMLE (board) examination scores. Diagnostic radiologists must complete prerequisite undergraduate education, four years of medical school to earn a medical degree (D.O. or M.D.), one year of internship, and four years of residency training. After residency, most radiologists pursue one or two years of additional specialty fellowship training. | Radiology | Wikipedia | 323 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
The American Board of Radiology (ABR) administers professional certification in Diagnostic Radiology, Radiation Oncology and Medical Physics as well as subspecialty certification in neuroradiology, nuclear radiology, pediatric radiology and vascular and interventional radiology. "Board Certification" in diagnostic radiology requires successful completion of two examinations. The Core Exam is given after 36 months of residency. Although previously taken in Chicago or Tucson, Arizona, beginning in February 2021, the computer test transitioned permanently to a remote format. It encompasses 18 categories. A passing score is 350 or above. A fail on one to five categories was previously a Conditioned exam, however beginning in June 2021, the conditioned category will no longer exist and the test will be graded as a whole. The Certification Exam, can be taken 15 months after completion of the Radiology residency. This computer-based examination consists of five modules and graded pass-fail. It is given twice a year in Chicago and Tucson. Recertification examinations are taken every 10 years, with additional required continuing medical education as outlined in the Maintenance of Certification document.
Certification may also be obtained from the American Osteopathic Board of Radiology (AOBR) and the American Board of Physician Specialties.
Following completion of residency training, radiologists may either begin practicing as a general diagnostic radiologist or enter into subspecialty training programs known as fellowships. Examples of subspeciality training in radiology include abdominal imaging, thoracic imaging, cross-sectional/ultrasound, MRI, musculoskeletal imaging, interventional radiology, neuroradiology, interventional neuroradiology, paediatric radiology, nuclear medicine, emergency radiology, breast imaging and women's imaging. Fellowship training programs in radiology are usually one or two years in length.
Some medical schools in the US have started to incorporate a basic radiology introduction into their core MD training. New York Medical College, the Wayne State University School of Medicine, Weill Cornell Medicine, the Uniformed Services University, and the University of South Carolina School of Medicine offer an introduction to radiology during their respective MD programs. Campbell University School of Osteopathic Medicine also integrates imaging material into their curriculum early in the first year.
Radiographic exams are usually performed by radiographers. Qualifications for radiographers vary by country, but many radiographers now are required to hold a degree. | Radiology | Wikipedia | 492 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Veterinary radiologists are veterinarians who specialize in the use of X-rays, ultrasound, MRI and nuclear medicine for diagnostic imaging or treatment of disease in animals. They are certified in either diagnostic radiology or radiation oncology by the American College of Veterinary Radiology.
United Kingdom
Radiology is an extremely competitive speciality in the UK, attracting applicants from a broad range of backgrounds. Applicants are welcomed directly from the Foundation Programme, as well as those who have completed higher training. Recruitment and selection into training post in clinical radiology posts in England, Scotland and Wales is done by an annual nationally coordinated process lasting from November to March. In this process, all applicants are required to pass a Specialty Recruitment Assessment (SRA) test. Those with a test score above a certain threshold are offered a single interview at the London and the South East Recruitment Office. At a later stage, applicants declare what programs they prefer, but may in some cases be placed in a neighbouring region.
The training programme lasts for a total of five years. During this time, doctors rotate into different subspecialities, such as paediatrics, musculoskeletal or neuroradiology, and breast imaging. During the first year of training, radiology trainees are expected to pass the first part of the Fellowship of the Royal College of Radiologists (FRCR) exam. This comprises a medical physics and anatomy examination. Following completion of their part 1 exam, they are then required to pass six written exams (part 2A), which cover all the subspecialities. Successful completion of these allows them to complete the FRCR by completing part 2B, which includes rapid reporting, and a long case discussion.
After achieving a certificate of completion of training (CCT), many fellowship posts exist in specialities such as neurointervention and vascular intervention, which would allow the doctor to work as an Interventional radiologist. In some cases, the CCT date can be deferred by a year to include these fellowship programmes.
UK radiology registrars are represented by the Society of Radiologists in Training (SRT), which was founded in 1993 under the auspices of the Royal College of Radiologists. The society is a nonprofit organisation, run by radiology registrars specifically to promote radiology training and education in the UK. Annual meetings are held by which trainees across the country are encouraged to attend. | Radiology | Wikipedia | 490 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Currently, a shortage of radiologists in the UK has created opportunities in all specialities, and with the increased reliance on imaging, demand is expected to increase in the future. Radiographers, and less frequently Nurses, are often trained to undertake many of these opportunities in order to help meet demand. Radiographers often may control a "list" of a particular set of procedures after being approved locally and signed off by a consultant radiologist. Similarly, radiographers may simply operate a list for a radiologist or other physician on their behalf. Most often if a radiographer operates a list autonomously then they are acting as the operator and practitioner under the Ionising Radiation (Medical Exposures) Regulations 2000. Radiographers are represented by a variety of bodies; most often this is the Society and College of Radiographers. Collaboration with nurses is also common, where a list may be jointly organised between the nurse and radiographer.
Germany
After obtaining medical licensure, German radiologists complete a five-year residency, culminating with a board examination (known as Facharztprüfung).
Italy
Italian radiologists complete a four-year residency program, after completing the six-year MD program.
The Netherlands
Dutch radiologists complete a five-year residency program, after completing the six-year MD program.
India
In India, one must obtain a bachelor's degree which requires 4.5 years of training, along with 1 year internship, followed by NEET PG examination which is one of the hardest examinations in India. Previous rank data shows only top rankers take radiology which means if the score is less, one might get accepted into other branches, but not radiology. The radiology program is a post graduate 3-year program (MD/DNB Radiology) or a 2-year diploma (DMRD).
Singapore
Radiologists in Singapore complete a five-year undergraduate MD program, followed by a one-year internship, and then a five-year residency program. Some radiologists may elect to complete a one or two-year fellowship for further sub-specialization in fields such as interventional radiology.
Slovenia
After finishing a six-year study of medicine and passing the emergency medicine internship, MDs can apply for radiology residency. Radiology is a five-year post-graduate program that involves all fields of radiology with a final board exam.
France | Radiology | Wikipedia | 483 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
To become a radiologist, after having validated the common core of medical studies, one must obtain a DES (Specialized Studies Diploma) in radiology and medical imaging (specialized studies in 5 years), or a DES in advanced interventional radiology (specialized studies in 6 years). At the end of his DES, once validated, the future doctor will have to defend his “practice thesis” in order to validate his DE (State Diploma) as a doctor of medicine (common to all doctors of medicine therefore) and to be able to practice in France.
Specialty training for interventional radiology
Training for interventional radiology occurs in the residency portion of medical education, and has gone through developments.
In 2000, the Society of Interventional Radiology (SIR) created a program named "Clinical Pathway in IR", which modified the "Holman Pathway" that was already accepted by the American Board of Radiology to including training in IR; this was accepted by ABR but was not widely adopted. In 2005 SIR proposed and ABR accepted another pathway called "DIRECT (Diagnostic and Interventional Radiology Enhanced Clinical Training) Pathway" to help trainees coming from other specialities learn IR; this too was not widely adopted. In 2006 SIR proposed a pathway resulting in certification in IR as a speciality; this was eventually accepted by the ABR in 2007 and was presented to the American Board of Medical Specialities (ABMS) in 2009, which rejected it because it did not include enough diagnostic radiology (DR) training. The proposal was reworked, at the same time that overall DR training was being revamped, and a new proposal that would lead to a dual DR/IR specialization was presented to the ABMS and was accepted in 2012 and eventually was implemented in 2014. By 2016 the field had determined that the old IR fellowships would be terminated by 2020.
A handful of programs have offered interventional radiology fellowships that focus on training in the treatment of children. | Radiology | Wikipedia | 399 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
In Europe the field followed its own pathway; for example in Germany the parallel interventional society began to break free of the DR society in 2008. In the UK, interventional radiology was approved as a sub-specialty of clinical radiology in 2010. While many countries have an interventional radiology society, there is also the European-wide Cardiovascular and Interventional Radiological Society of Europe, whose aim is to support teaching, science, research and clinical practice in the field by hosting meetings, educational workshops and promoting patient safety initiatives. Furthermore, the Society provides an examination, the European Board of Interventional Radiology (EBIR), which is a highly valuable qualification in interventional radiology based on the European Curriculum and Syllabus for IR. | Radiology | Wikipedia | 151 | 152623 | https://en.wikipedia.org/wiki/Radiology | Biology and health sciences | Fields of medicine | null |
Speleology () is the scientific study of caves and other karst features, as well as their composition, structure, physical properties, history, ecology, and the processes by which they form (speleogenesis) and change over time (speleomorphology). The term speleology is also sometimes applied to the recreational activity of exploring caves, but this is more properly known as caving, potholing (British English), or spelunking (United States and Canadian English). Speleology and caving are often connected, as the physical skills required for in situ study are the same.
Speleology is a cross-disciplinary field that combines the knowledge of chemistry, biology, geology, physics, meteorology, and cartography to develop portraits of caves as complex, evolving systems.
History
Before modern speleology developed, John Beaumont wrote detailed descriptions of some Mendip caves in the 1680s. The term speleology was coined by Émile Rivière in 1890.
Prior to the mid-nineteenth century the scientific value of caves was considered only in its contribution to other branches of science, and cave studies were considered part of the larger disciplines of geography, geology or archaeology. Very little cave-specific study was undertaken prior to the work of Édouard-Alfred Martel (1859–1938), the 'father of modern speleology', who through his extensive and well-publicised cave explorations introduced in France the concept of speleology as a distinct area of study. In 1895 Martel founded the Société de Spéléologie, the first organization devoted to cave science in the world. Other early speleologists include Herbert E. Balch.
An international speleological congress was proposed at a meeting in Valence-sur-Rhone, France in 1949 and first held in 1953 in Paris. The International Union of Speleology (UIS) was founded in 1965.
The growth of speleology is directly linked with that of the sport of caving, both because of the stimulation of public interest and awareness, and the fact that most speleological field-work has been conducted by sport cavers. | Speleology | Wikipedia | 439 | 152630 | https://en.wikipedia.org/wiki/Speleology | Physical sciences | Caves | Earth science |
Cave geology, hydrogeology and biology
Karst is a landscape that has limestone underneath which has been eroded. Caves are usually formed through chemical corrosion via a process of dissolution. Corrosion has several ways of doing this, it can be on carbonate rocks through chemical reactions, in gypsum and rock salt it can happen physically, and in silicate rocks and warm climate the decomposition of the materials can happen as well.
Geochemistry
Speleothems
A speleothem is a geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment. Their chemical composition, gradual growth, and preservation in caves make them useful paleoclimatic proxies.
Biochemistry
Caves have an absence of stable temperature, high relative humidity, low rates of evaporation and limited supply of organic material, which help in creating an environment which is highly favorable for the growth of microbes. Microbial assemblages in caves include archaea, bacteria, fungi and other micro-eukaryotes, these highly adapted microbial communities represent the living-backbone of cave ecosystems and play a key role in shaping structures and sustaining trophic networks.
Cave cartography
The creation of an accurate, detailed map is one of the most common technical activities undertaken within a cave. Cave maps, called surveys, can be used to compare caves to each other by length, depth and volume, may reveal clues on speleogenesis, provide a spatial reference for further scientific study, and assist visitors with route-finding.
Cave biology
Caves provide a home for many unique biota. Cave ecologies are very diverse, and not sharply distinct from surface habitats. Generally however, the deeper the cave becomes, the more rarefied the ecology. | Speleology | Wikipedia | 381 | 152630 | https://en.wikipedia.org/wiki/Speleology | Physical sciences | Caves | Earth science |
Cave environments fall into three general categories:
Endogean
the parts of caves that are in communication with surface soils through cracks and rock seams, groundwater seepage, and root protrusion.
Parahypogean
the threshold regions near cave mouths that extend to the last penetration of sunlight.
Hypogean
or "true" cave environments. These can be in regular contact with the surface via wind and underground rivers, or the migration of animals, or can be almost entirely isolated. Deep hypogean environments can host autonomous ecologies whose primary source of energy is not sunlight, but chemical energy liberated from limestone and other minerals by chemoautotrophic bacteria.
Cave organisms fall into three basic classes:
There are also so-called accidental trogloxenes which are surface organisms that enter caves for no survival reason. Some may even be troglophobes (“cave haters”), which cannot survive in caves for any extended period. Examples include deer which fell through a sinkhole, frogs swept into a cave by a flash flood, etc.
The two factors that limit cave ecologies are generally energy and nutrients. To some degree moisture is always available in actively forming Karst caves. Cut off from the sunlight and steady deposition of plant detritus, caves are poor habitats in comparison with wet areas on the surface. Most of the energy in cave environments comes from the surplus of the ecosystems outside. One major source of energy and nutrients in caves is dung from trogloxenes, most of which is deposited by bats. Other sources are mentioned above.
Cave ecosystems are very fragile. Because of their rarity and position in the ecosystem they are threatened by a large number of human activities. Dam construction, limestone quarrying, water pollution and logging are just some of the disasters that can devastate or destroy underground biological communities.
Other areas of cave science
Speleologists also work with archaeologists in studying underground ruins, tunnels, sewers and aqueducts, such as the various inlets and outlets of the Cloaca Maxima in Rome. | Speleology | Wikipedia | 419 | 152630 | https://en.wikipedia.org/wiki/Speleology | Physical sciences | Caves | Earth science |
Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between parts of an electrical circuit, or between different electrical circuits, thereby joining them into a larger circuit.
The connection may be removable (as for portable equipment), require a tool for assembly and removal, or serve as a permanent electrical joint between two points. An adapter can be used to join dissimilar connectors. Most electrical connectors have a genderi.e. the male component, called a plug, connects to the female component, or socket.
Thousands of configurations of connectors are manufactured for power, data, and audiovisual applications. Electrical connectors can be divided into four basic categories, differentiated by their function:
inline or cable connectors permanently attached to a cable, so it can be plugged into another terminal (either a stationary instrument or another cable)
Chassis or panel connectors permanently attached to a piece of equipment so users can connect a cable to a stationary device
PCB mount connectors soldered to a printed circuit board, providing a point for cable or wire attachment. (e.g. pin headers, screw terminals, board-to-board connectors)
Splice or butt connectors (primarily insulation displacement connectors) that permanently join two lengths of wire or cable
In computing, electrical connectors are considered a physical interface and constitute part of the physical layer in the OSI model of networking.
Physical construction
In addition to the classes mentioned above, connectors are characterised by their pinout, method of connection, materials, size, contact resistance, insulation, mechanical durability, ingress protection, lifetime (number of cycles), and ease of use.
It is usually desirable for a connector to be easy to identify visually, rapid to assemble, inexpensive, and require only simple tooling. In some cases an equipment manufacturer might choose a connector specifically because it is not compatible with those from other sources, allowing control of what may be connected. No single connector has all the ideal properties for every application; the proliferation of types is a result of the diverse yet specific requirements of manufacturers.
Materials
Electrical connectors essentially consist of two classes of materials: conductors and insulators. Properties important to conductor materials are contact resistance, conductivity, mechanical strength, formability, and resilience. Insulators must have a high electrical resistance, withstand high temperatures, and be easy to manufacture for a precise fit | Electrical connector | Wikipedia | 511 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Electrodes in connectors are usually made of copper alloys, due to their good conductivity and malleability. Alternatives include brass, phosphor bronze, and beryllium copper. The base electrode metal is often coated with another inert metal such as gold, nickel, or tin. The use of a coating material with good conductivity, mechanical robustness and corrosion resistance helps to reduce the influence of passivating oxide layers and surface adsorbates, which limit metal-to-metal contact patches and contribute to contact resistance. For example, copper alloys have favorable mechanical properties for electrodes, but are hard to solder and prone to corrosion. Thus, copper pins are usually coated with gold to alleviate these pitfalls, especially for analog signals and high-reliability applications.
Contact carriers that hold the parts of a connector together are usually made of plastic, due to its insulating properties. Housings or backshells can be made of molded plastic and metal. Connector bodies for high-temperature use, such as thermocouples or associated with large incandescent lamps, may be made of fired ceramic material.
Failure modes
The majority of connector failures result in intermittent connections or open contacts:
Connectors are purely passive componentsthat is, they do not enhance the function of a circuitso connectors should affect the function of a circuit as little as possible. Insecure mounting of connectors (primarily chassis-mounted) can contribute significantly to the risk of failure, especially when subjected to extreme shock or vibration. Other causes of failure are connectors inadequately rated for the applied current and voltage, connectors with inadequate ingress protection, and threaded backshells that are worn or damaged.
High temperatures can also cause failure in connectors, resulting in an "avalanche" of failuresambient temperature increases, leading to a decrease in insulation resistance and increase in conductor resistance; this increase generates more heat, and the cycle repeats. | Electrical connector | Wikipedia | 391 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Fretting (so-called dynamic corrosion) is a common failure mode in electrical connectors that have not been specifically designed to prevent it, especially in those that are frequently mated and de-mated. Surface corrosion is a risk for many metal parts in connectors, and can cause contacts to form a thin surface layer that increases resistance, thus contributing to heat buildup and intermittent connections. However, remating or reseating a connector can alleviate the issue of surface corrosion, since each cycle scrapes a microscopic layer off the surface of the contact(s), exposing a fresh, unoxidised surface.
Circular connectors
Many connectors used for industrial and high-reliability applications are circular in cross section, with a cylindrical housing and circular contact interface geometries. This is in contrast to the rectangular design of some connectors, e.g. USB or blade connectors. They are commonly used for easier engagement and disengagement, tight environmental sealing, and rugged mechanical performance. They are widely used in military, aerospace, industrial machinery, and rail, where MIL-DTL-5015 and MIL-DTL-38999 are commonly specified. Fields such as sound engineering and radio communication also use circular connectors, such as XLR and BNC. AC power plugs are also commonly circular, for example, Schuko plugs and IEC 60309.
The M12 connector, specified in IEC 61076-2-101, is a circular electrical plug/receptacle pair with 12mm OD mating threads, used in NMEA 2000, DeviceNet, IO-Link, some kinds of Industrial Ethernet, etc.
A disadvantage of the circular design is its inefficient use of panel space when used in arrays, when compared to rectangular connectors.
Circular connectors commonly use backshells, which provide physical and electromagnetic protection, whilst sometimes also providing a method for locking the connector into a receptacle. In some cases, this backshell provides a hermetic seal, or some degree of ingress protection, through the use of grommets, O-rings, or potting. | Electrical connector | Wikipedia | 439 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Hybrid connectors
Hybrid connectors allow the intermixing of many connector types, usually by way of a housing with inserts. These housings may also allow intermixing of electrical and non-electrical interfaces, examples of the latter being pneumatic line connectors, and optical fiber connectors. Because hybrid connectors are modular in nature, they tend to simplify assembly, repair, and future modifications. They also allow the creation of composite cable assemblies that can reduce equipment installation time by reducing the number of individual cable and connector assemblies.
Mechanical features
Pin sequence
Some connectors are designed such that certain pins make contact before others when inserted, and break first on disconnection. This is often used in power connectors to protect equipment, e.g. connecting safety ground first. It is also employed for digital signals, as a method to sequence connections properly in hot swapping.
Keying
Many connectors are keyed with some mechanical component (sometimes called a keyway), which prevents mating in an incorrect orientation. This can be used to prevent mechanical damage to connectors, from being jammed in at the wrong angle or into the wrong connector, or to prevent incompatible or dangerous electrical connections, such as plugging an audio cable into a power outlet. Keying also prevents otherwise symmetrical connectors from being connected in the wrong orientation or polarity. Keying is particularly important for situations where there are many similar connectors, such as in signal electronics. For instance, XLR connectors have a notch to ensure proper orientation, while Mini-DIN plugs have a plastic projection that fits into a corresponding hole in the socket (they also have a notched metal skirt to provide secondary keying).
Locking mechanisms
Some connector housings are designed with locking mechanisms to prevent inadvertent disconnection or poor environmental sealing. Locking mechanism designs include locking levers of various sorts, jackscrews, screw-in shells, push-pull connector, and toggle or bayonet systems. Some connectors, particularly those with large numbers of contacts, require high forces to connect and disconnect. Locking levers and jackscrews and screw-in shells for such connectors frequently serve both to retain the connector when connected and to provide the force needed for connection and disconnection. Depending on application requirements, housings with locking mechanisms may be tested under various environmental simulations that include physical shock and vibration, water spray, dust, etc. to ensure the integrity of the electrical connection and housing seals. | Electrical connector | Wikipedia | 507 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Backshells
Backshells are a common accessory for industrial and high-reliability connectors, especially circular connectors. Backshells typically protect the connector and/or cable from environmental or mechanical stress, or shield it from electromagnetic interference. Many types of backshells are available for different purposes, including various sizes, shapes, materials, and levels of protection. Backshells usually lock onto the cable with a clamp or moulded boot, and may be threaded for attachment to a mating receptacle. Backshells for military and aerospace use are regulated by SAE AS85049 within the USA.
Hyperboloid contacts
To deliver ensured signal stability in extreme environments, traditional pin and socket design may become inadequate. Hyperboloid contacts are designed to withstand more extreme physical demands, such as vibration and shock. They also require around 40% less insertion force as low as per contact,which extends the lifespan, and in some cases offers an alternative to zero insertion force connectors.
In a connector with hyperboloid contacts, each female contact has several equally spaced longitudinal wires twisted into a hyperbolic shape. These wires are highly resilient to strain, but still somewhat elastic, hence they essentially function as linear springs. As the male pin is inserted, axial wires in the socket half are deflected, wrapping themselves around the pin to provide a number of contact points. The internal wires that form the hyperboloid structure are usually anchored at each end by bending the tip into a groove or notch in the housing.
Whilst hyperboloid contacts may be the only option to make a reliable connection in some circumstances, they have the disadvantage of taking up greater volume in a connector, which can cause problems for high-density connectors. They are also significantly more expensive than traditional pin and socket contacts, which has limited their uptake since their invention in the 1920s by Wilhelm Harold Frederick. In the 1950s, Francois Bonhomme popularised hyperboloid contacts with his "Hypertac" connector, which was later acquired by Smiths Group. During the following decades, the connectors steadily gained popularity, and are still used for medical, industrial, military, aerospace, and rail applications (particularly trains in Europe).
Pogo pins | Electrical connector | Wikipedia | 451 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Pogo pin or spring loaded connectors are commonly used in consumer and industrial products, where mechanical resilience and ease of use are priorities. The connector consists of a barrel, a spring, and a plunger. They are in applications such as the MagSafe connector where a quick disconnect is desired for safety. Because they rely on spring pressure, not friction, they can be more durable and less damaging than traditional pin and socket design, leading to their use in in-circuit testing.
Crown spring connectors
Crown spring connectors are commonly used for higher current flows and industrial applications. They have a high number of contact points, which provides a more electrically reliable connection than traditional pin and socket connectors.
Methods of connection
Whilst technically inaccurate, electrical connectors can be viewed as a type of adapter to convert between two connection methods, which are permanently connected at one end and (usually) detachable at the other end. By definition, each end of this "adapter" has a different connection methode.g. the solder tabs on a male phone connector, and the male phone connector itself. In this example, the solder tabs connected to the cable represent the permanent connection, whilst the male connector portion interfaces with a female socket forming a detachable connection.
There are many ways of applying a connector to a cable or device. Some of these methods can be accomplished without specialized tools. Other methods, while requiring a special tool, can assemble connectors much faster and more reliably, and make repairs easier.
The number of times a connector can connect and disconnect with its counterpart while meeting all its specifications is termed as mating cycles and is an indirect measure of connector lifespan. The material used for connector contact, plating type and thickness is a major factor that determines the mating cycles.
Plug and socket connectors
Plug and socket connectors are usually made up of a male plug (typically pin contacts) and a female socket (typically receptacle contacts). Often, but not always, sockets are permanently fixed to a device as in a chassis connector , and plugs are attached to a cable. | Electrical connector | Wikipedia | 432 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Plugs generally have one or more pins or prongs that are inserted into openings in the mating socket. The connection between the mating metal parts must be sufficiently tight to make a good electrical connection and complete the circuit. An alternative type of plug and socket connection uses hyperboloid contacts, which makes a more reliable electrical connection. When working with multi-pin connectors, it is helpful to have a pinout diagram to identify the wire or circuit node connected to each pin.
Some connector styles may combine pin and socket connection types in a single unit, referred to as a hermaphroditic connector. These connectors includes mating with both male and female aspects, involving complementary paired identical parts each containing both protrusions and indentations. These mating surfaces are mounted into identical fittings that freely mate with any other, without regard for gender (provided that the size and type match).
Sometimes both ends of a cable are terminated with the same gender of connector, as in many Ethernet patch cables. In other applications the two ends are terminated differently, either with male and female of the same connector (as in an extension cord), or with incompatible connectors, which is sometimes called an adapter cable.
Plugs and sockets are widely used in various connector systems including blade connectors, breadboards, XLR connectors, car power outlets, banana connectors, and phone connectors.
Jacks and plugs
A jack is a connector that installs on the surface of a bulkhead or enclosure, and mates with its reciprocal, the plug. According to the American Society of Mechanical Engineers, the stationary (more fixed) connector of a pair is classified as a jack (denoted J), usually attached to a piece of equipment as in a chassis-mount or panel-mount connector. The movable (less fixed) connector is classified as a plug (denoted P), designed to attach to a wire, cable or removable electrical assembly. This convention is currently defined in ASME Y14.44-2008, which supersedes IEEE 200-1975, which in turn derives from the long-withdrawn MIL-STD-16 (from the 1950s), highlighting the heritage of this connector naming convention. IEEE 315-1975 works alongside ASME Y14.44-2008 to define jacks and plugs. | Electrical connector | Wikipedia | 469 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
The term jack occurs in several related terms:
The registered jack or modular jack in RJ11, RJ45 and other similar connectors used for telecommunications and computer networking
The telephone jack of manual telephone switchboards, which is the socket fitting the original telephone plug
The phone jack common to many electronic applications in various configurations, sometimes referred to as a headphone jack
The RCA jack, also known as a phono jack, common to consumer audiovisual electronics
The EIAJ jack for consumer appliances requiring a power supply of less than 18.0 volts
Crimp-on connectors
Crimped connectors are a type of solderless connection, using mechanical friction and uniform deformation to secure a connector to a pre-stripped wire (usually stranded). Crimping is used in splice connectors, crimped multipin plugs and sockets, and crimped coaxial connectors. Crimping usually requires a specialised crimping tool, but the connectors are quick and easy to install and are a common alternative to solder connections or insulation displacement connectors. Effective crimp connections deform the metal of the connector past its yield point so that the compressed wire causes tension in the surrounding connector, and these forces counter each other to create a high degree of static friction. Due to the elastic element in crimped connections, they are highly resistant to vibration and thermal shock.
Crimped contacts are permanent (i.e. the connectors and wire ends cannot be reused).
Crimped plug-and-socket connectors can be classified as rear release or front release. This relates to the side of the connector where the pins are anchored:
Front release contacts are released from the front (contact side) of the connector, and removed from the rear. The removal tool engages with the front portion of the contact and pushes it through to the back of the connector.
Rear release contacts are released and removed from the rear (wire side) of the connector. The removal tool releases the contacts from the rear and pulls the contact out of the retainer.
Soldered connectors | Electrical connector | Wikipedia | 427 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Many plug and socket connectors are attached to a wire or cable by soldering conductors to electrodes on the back of the connector. Soldered joints in connectors are robust and reliable if executed correctly, but are usually slower to make than crimped connections. When wires are to be soldered to the back of a connector, a backshell is often used to protect the connection and add strain relief. Metal solder buckets or solder cups are provided, which consist of a cylindrical cavity that an installer fills with solder before inserting the wire.
When creating soldered connections, it is possible to melt the dielectric between pins or wires. This can cause problems because the thermal conductivity of metals causes heat to quickly distribute through the cable and connector, and when this heat melts plastic dielectric, it can cause short circuits or "flared" (conical) insulation. Solder joints are also more prone to mechanical failure than crimped joints when subjected to vibration and compression.
Insulation-displacement connectors
Since stripping insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors which cut the insulation as the wire is inserted. These generally take the form of a fork-shaped opening in the terminal, into which the insulated wire is pressed, which cut through the insulation to contact the conductor. To make these connections reliably on a production line, special tools accurately control the forces applied during assembly. On small scales, these tools tend to cost more than tools for crimped connections.
Insulation displacement connectors are usually used with small conductors for signal purposes and at low voltage. Power conductors carrying more than a few amperes are more reliably terminated with other means, though "hot tap" press-on connectors find some use in automotive applications for additions to existing wiring.
A common example is the multi-conductor flat ribbon cable used in computer disk drives; to terminate each of the many (approximately 40) wires individually would be slow and error-prone, but an insulation displacement connector can terminate all the wires in a single action. Another very common use is so-called punch-down blocks used for terminating unshielded twisted pair wiring.
Binding posts
Binding posts are a single-wire connection method, where stripped wire is screwed or clamped to a metal electrode. Such connectors are frequently used in electronic test equipment and audio. Many binding posts also accept a banana plug.
Screw terminals | Electrical connector | Wikipedia | 497 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Screw connections are frequently used for semi-permanent wiring and connections inside devices, due to their simple but reliable construction. The basic principle of all screw terminals involves the tip of a bolt clamping onto a stripped conductor. They can be used to join multiple conductors, to connect wires to a printed circuit board, or to terminate a cable into a plug or socket. The clamping screw may act in the longitudinal axis (parallel to the wire) or the transverse axis (perpendicular to the wire), or both. Some disadvantages are that connecting wires is more difficult than simply plugging in a cable, and screw terminals are generally not very well protected from contact with persons or foreign conducting materials.
Terminal blocks (also called terminal boards or strips) provide a convenient means of connecting individual electrical wires without a splice or physically joining the ends. Since terminal blocks are readily available for a wide range of wire sizes and terminal quantity, they are one of the most flexible types of electrical connector available. One type of terminal block accepts wires that are prepared only by stripping a short length of insulation from the end. Another type, often called barrier strips, accepts wires that have ring or spade terminal lugs crimped onto the wires.
Printed circuit board (PCB) mounted screw terminals let individual wires connect to a PCB through leads soldered to the board.
Ring and spade connectors
The connectors in the top row of the image are known as ring terminals and spade terminals (sometimes called fork or split ring terminals). Electrical contact is made by the flat surface of the ring or spade, while mechanically they are attached by passing a screw or bolt through them. The spade terminal form factor facilitates connections since the screw or bolt can be left partially screwed in as the spade terminal is removed or attached. Their sizes can be determined by the gauge of the conducting wire, and the interior and exterior diameters.
In the case of insulated crimp connectors, the crimped area lies under an insulating sleeve through which the pressing force acts. During crimping, the extended end of this insulating sleeve is simultaneously pressed around the insulated area of the cable, creating strain relief. The insulating sleeve of insulated connectors has a color that indicates the wire's cross-section area. Colors are standardized according to DIN 46245: | Electrical connector | Wikipedia | 473 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
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