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Jaguarundi

The jaguarundi (Herpailurus yagouaroundi; or ) is a wild cat native to the Americas. Its range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes. The jaguarundi is a medium-sized cat of slender build. Its coloration is uniform with two color morphs, gray and red. It has an elongated body, with relatively short legs, a small, narrow head, small, round ears, a short snout, and a long tail, resembling mustelids in these respects. It is about twice as large as a domestic cat (Felis catus), reaching nearly 14 in at the shoulder, and weighs 3.5-7 kg.

Secretive and alert, the jaguarundi is typically solitary or forms pairs in the wild, though captive individuals are more gregarious. Unlike other sympatric cats such as the ocelot, the jaguarundi is more active during the day and hunts mainly during daytime and evening hours. Individuals live in large home ranges, and are sparsely distributed within a region. The jaguarundi is an efficient climber, but typically prefers hunting on ground. It feeds on various kinds of prey, especially ground-feeding birds, reptiles, rodents and small mammals. Mating occurs throughout the year, with peaks at different times of the year across the range. After a gestation period of 70 to 75 days, a litter of one to four kittens is born. Lifespans of up to 15 years have been recorded in captivity.

The jaguarundi inhabits a broad array of both closed and open habitats ranging from tropical rainforests and deciduous forests to deserts and thorn scrubs. It is fairly common in Brazil, Peru, and Venezuela, but may be extirpated from the United States. It is listed as Least Concern on the IUCN Red List, but populations are in decline in many parts of its range due to loss and fragmentation of habitat, as well as persecution for killing poultry.

Etymology
The common name "jaguarundi" comes from the Old Guarani word yaguarundi, similar to the Old Tupi word yawaum'di, meaning "dark jaguar". The name is pronounced  or. In some Spanish-speaking countries, the jaguarundi is also called gato colorado, gato moro, león breñero, leoncillo and tigrillo. It is also called eyra, gato-mourisco, gato-preto, gato-vermelho and maracajá-preto in Brazilian Portuguese.

Taxonomy
In 1803 Étienne Geoffroy Saint-Hilaire described two jaguarundi skins and skulls from unknown locations in Central America and proposed the scientific name Felis yagouarundi. In the 19th and 20th centuries, several more zoological specimens were described:
 * Felis eyra proposed by Gotthelf Fischer von Waldheim in 1814 was a ferruginous skin from Paraguay.
 * F. cacomitli proposed by Jean-Louis Berlandier in 1859 was a skull and a grayish skin of a female jaguarundi from the Rio Grande area in Mexico.
 * F. yagouaroundi tolteca proposed by Oldfield Thomas in 1898 was a skull and a reddish skin from Sinaloa in Mexico.
 * F. Ameghinoi proposed by Eduardo Ladislao Holmberg in 1898 for fossil cat bones, presumably of a jaguarundi, that were excavated near San Luis, Argentina.
 * F. fossata by Edgar Alexander Mearns in 1901 was a large jaguarundi skull from Yucatán.
 * F. panamensis by Joel Asaph Allen in 1904 was a dusky gray skin of a young adult female jaguarundi collected in Panama's Chiriquí Province.
 * F. yagouaroundi melantho by Oldfield Thomas in 1914 were skulls and blackish brown skins of a male and a female from Pozuzo District in Peru.

The generic name Herpailurus was proposed by Nikolai Severtzov in 1858 for the jaguarundi. Later authors classified the jaguarundi in the genus Puma along with the cougar (P. concolor). Phylogeographical analysis of jaguarundi samples from across its range found no genetic evidence for subspecies. In 2017, the IUCN Cat Specialist Group revised felid taxonomy and recognises the jaguarundi as a monotypic taxon of the genus Herpailurus.

Phylogeny and evolution
The jaguarundi is most closely related to the cougar; the jaguarundi-cougar clade is sister to the cheetah. These three species comprise the Puma lineage, one of the eight lineages of Felidae; the Puma lineage diverged from the rest. The sister group of the Puma lineage is a clade of smaller Old World cats that includes the genera Felis, Otocolobus and Prionailurus.

The three species of the Puma lineage may have had a common ancestor during the Miocene, about. Acinonyx possibly diverged from the lineage in the Americas; some authors alternatively suggest that the cheetah diverged in the Old World.

The Puma lineage appears to have migrated from Asia to North America after crossing the Bering Strait, arriving in South America via the Isthmus of Panama by the Late Pliocene or Early Pleistocene. This was possibly followed by the bifurcation of the lineage into the cougar and Herpailurus (represented by H. pumoides) in South America around between the Late Pliocene and Early Pleistocene. H. pumoides went extinct around Middle Pleistocene, around the time the modern jaguarundi came into existence; the oldest fossils of the modern jaguarundi date back to the Late Pleistocene in Brazil around. The original North American cougars were extirpated during the Pleistocene extinctions around 10,000 years ago; North America was then recolonized by South American cougars and jaguarundis 10,000–8,000 years ago. The extinct North American genus Miracinonyx is another member of this clade.

Characteristics
The jaguarundi is a medium-sized cat of slender build and uniform coloration that differs significantly from other neotropical cats—such as the small, spotted cats in the genus Leopardus—in its external appearance. This has been attributed to variations in its karyotype—the jaguarundi has 38 chromosomes, unlike the 36 in other small South American cats, and the chromosomal features resemble those of Old World cats such as the leopard cat (Prionailurus bengalensis). In fact, the jaguarundi shows several features seen in mustelids such as otters and weasels—it has an elongated body with relatively short legs, a small, narrow head, small, round ears, a short snout and a long tail. The head-and-body length is between 53 and 77 cm; the strong, muscular tail is 31 – long. Around twice as large as the domestic cat, the jaguarundi reaches nearly 14 in at the shoulder and weighs 3.5 –, though larger individuals weighing around 9 kg have been reported. Males are slightly larger than females.

The coat is uniformly colored with at most a few faint markings on the face and the belly, though kittens are spotted for a short duration. Black and white marks on the lips and the snout, similar to those of the cougar, can be clearly seen in juveniles and some adults. Two color morphs are known (though intermediate shades are also seen)—gray (blackish to brownish-gray fur with a grizzled look due to bright and dark rings on individual hairs) and red (foxy red to chestnut); earlier these morphs were considered two different species. Individuals of both colors can be born in the same litter. Blackish brown individuals superficially resemble the tayra (Eira barbara), but the latter can be told apart by the clear, yellowish patch on the throat. The red morph is seen more often in dry, open areas. Melanistic individuals have been reported, but the coat is not completely black; the head and the throat are clearly paler than the rest of the body. The widely spaced ears are 2.5-4 cm long without any spots on the back. The jaguarundi has a total of 30 teeth; the dental formula is.

Among felids, the jaguarundi is closely similar to the flat-headed cat (Prionailurus planiceps), but has a longer body and proportionately longer legs, is heavier and lacks the dark markings on the cheeks of the flat-headed cat. Tawny jaguarundis bear a similar coloration to the larger cougar.

The diploid number of chromosomes in jaguarundi is 2n=38.

Distribution and habitat
The jaguarundi inhabits a wide variety of habitats, from tropical rainforests and deciduous forests to deserts and thorn scrubs. It can also be found in cloud forests, mangroves and savannas. Unlike the sympatric margay, ocelot and oncilla, the jaguarundi can live in open areas as well. In open habitats the jaguarundi prefers areas with vegetative cover such as cacti, which would generally be difficult for potential predators to penetrate; there may be a few clearings at the periphery of such areas. Jaguarundis tend to stay close to a source of running water. The jaguarundi is noted for its resistance to environmental disturbances in its habitat; it can thrive in reforested areas. While commonly inhabiting elevations from lowlands up to 2000 m above sea level, this cat has been reported at altitudes as high as 3200 m in Colombia.

The range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes—second only to the cougar in the latitudinal extent of its distribution. However, not all parts of its range have been studied well. The jaguarundi is fairly common in Brazil, Peru, and Venezuela. It is possibly extirpated in the United States; a 1999 study refuted claims of sightings in Arizona, in the Huachuca Mountains in Santa Cruz County. The last confirmed sighting in the U.S. was of a roadkilled individual near Brownsville, Texas, in 1986.

The occurrence of the jaguarundi in Florida has remained in doubt for decades, where they have been reported since 1907. They were allegedly introduced in the region by a writer from Chiefland who at some point imported the animals from their native habitat and released them near his hometown and in other locations across the state. W. T. Neill noted that jaguarundis occurred throughout peninsular Florida in the 1950s, but the numbers had plummeted by the late 1970s. Jaguarundis were also reported in the coastal area of Alabama in the 1980s, which may be evidence of the Florida population migrating northward. The jaguarundi has also been recorded from Cerro Largo in Uruguay, where its presence was uncertain.

Behavior and ecology
The jaguarundi is shy and reclusive, and apparently very cautious of traps. There have been only a few radio telemetry studies of jaguarundis in Belize, Brazil and Mexico. Though activity has been observed throughout the day and at night, jaguarundis seem to prefer hunting during daytime and evening hours; for instance, a study in Belize reported that jaguarundis started moving before dawn and remained active through most of the day till sunset with a peak in hunting from late morning to noon. The cat appears to be more diurnal than most other cats, especially spotted cats that tend to be more active at night. The jaguarundi can swim across medium-sized rivers; one in Bolivia was recorded swimming across the Tuichi River. Jaguarundis are efficient climbers as well, but hunt mainly on ground; the coat color works as a good camouflage for terrestrial activity. They can leap up to 2 m into the air to catch birds. Predators recorded for jaguarundis include boa constrictors, cougars and domestic dogs. Parasites such as hookworms (Ancylostoma species), tapeworms (such as Spirometra and Toxocara species) and the lung fluke have been found in jaguarundis.

Studies have mostly observed jaguarundis alone or in pairs; pairs could probably be formed between mothers and older kittens or between individuals of opposite sexes during the mating season. Individuals in captivity have been found to be more gregarious. Home ranges tend to be large; a study in Brazil recorded home ranges 1.4-18 sqkm in size for females, while those of males measured 8.5-25.3 sqkm in area. Two males in Belize were recorded to have exceptionally large home ranges spanning an area of 88 sqkm and 100 sqkm, while the home range of a female in the same region measured 13-20 sqkm in size. Population densities are typically low, around 0.01 to 0.05 /sqkm in Brazil, though Tamaulipas (Mexico) and the Llanos in Costa Rica and Venezuela have recorded figures as high as 0.2 /sqkm.

Marking behavior could serve as a means of olfactory or visual communication among jaguarundis; individuals in captivity have been observed scraping areas with their hind feet (sometimes with urination), clawing on logs, rubbing objects with their heads and leaving feces uncovered. Social behavior such as grooming, growling and sniffing has been recorded. The jaguarundi has a broad vocal repertoire; 13 different calls have been recorded including chattering, purring, screaming, a 'wah-wah' call, whistling, yapping and a peculiar bird-like chirp. In captivity, females in estrus have been observed making faint sounds as they scent mark the area around their enclosures.

Diet
The jaguarundi typically feed on small-sized prey weighing less than 1 kg, including ground-feeding birds, reptiles, frogs, arthropods, rodents and small mammals. Jaguarundis will also take larger prey such as domestic poultry, fish, marmosets, rabbits and opossums; a study recorded small deer (possibly carrion) in the diet. Vegetation such as grasses have also been recorded in their diet. A study showed jaguarundis take 400 g vertebrate prey on an average every day. The broad array of prey recorded for the jaguarundi across its range and varying proportions of different prey in its diet could indicate that the cat tends to feed on the most abundant and easily catchable prey in the area.

Reproduction
Jaguarundis have been observed mating all year round, with peaks at different times of the year across the range; for instance, in Mexico breeding peaks in January and March. Estrus lasts three to five days, marked by the female regularly rolling onto her back and spraying urine. Sexually mature males will pursue the female, not reacting to any aggressive behavior from her side. As in many other felids, the male bites the fur on the female's neck on mounting; the female lets out a loud scream on penetration.

After a gestation period of 70 to 75 days, a litter of one to four kittens is born in a den constructed in a dense thicket, hollow tree, or similar cover. The kittens are covered well with fur and the underside is marked with spots, which disappear as they age; the coat color gradually changes as the kittens grow older. The mother starts bringing solid food for the kittens when they are around three weeks old, but they simply play with it until the mother ultimately ingests it. Kittens are capable of taking solid food like birds and guinea pigs at around six weeks. Jaguarundis become sexually mature at one to three years of age. Lifespan up to 15 years has been recorded in captivity.

Threats and conservation
The jaguarundi has been listed as Least Concern on the IUCN Red List since 2002. Mexican populations, except those in the northeast, appear to be stable. The huge protected areas in the Amazon Basin are probably the only conservation units that can sustain long-term viable populations. IUCN Red List assessors noted that it should be listed as Near Threatened, but the data were not sufficient to extend this classification throughout the jaguarundi's range. The jaguarundi is not particularly sought after for its fur due to its poor quality and low value, but it is suffering decline due to habitat loss.

Other threats include risks of habitat fragmentation and persecution for killing poultry. The North and Central American jaguarundi populations are listed in CITES Appendix I and all the other populations are listed in CITES Appendix II. Populations in the US are protected under the Endangered Species Act; the Texas Parks and Wildlife Department has expressed concern that its presence in South Texas may be imperiled due to loss of the cat's native habitat. Populations in Mexico are listed under the Mexican Official Norm NOM-059-SEMARNAT-2010.

Hunting jaguarundi is restricted in Peru and banned in Argentina, Belize, Brazil, Bolivia, Colombia, Costa Rica, French Guiana, Guatemala, Honduras, Mexico, Panama, Paraguay, Suriname, Uruguay, United States, and Venezuela.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Jaguarundi


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2000 in science

The year 2000 in science and technology involved some significant events.

Astronomy and space exploration

 * May 4 – A rare astronomical conjunction occurs on the new moon including all seven of the traditional celestial bodies known from ancient times until the discovery of Uranus in 1781; this conjunction consists of the Sun and Moon, Mercury, Venus, Mars, Jupiter and Saturn.
 * August 10 – Publication of the M–sigma relation in The Astrophysical Journal.

Biology

 * June 26 – 'Rough draft' of the human genome is announced jointly by President of the United States Bill Clinton and British Prime Minister Tony Blair.
 * December 14 – The full genome sequence of the flowering plant Arabidopsis thaliana is published in Nature.
 * 10-year Census of Marine Life launched.
 * A population of the Siamese crocodile, previously believed extinct in the wild since 1992, is located in the Cardamom Mountains of Cambodia.

Computer science

 * January 1 – Year 2000 problem proves to be of little global significance.
 * March 4 – Sony Computer Entertainment releases the PlayStation 2 sixth generation home video game console in Japan.
 * March 14 – Stephen King's horror story Riding the Bullet is published in e-book format only, the world's first mass-market electronic book.
 * September – First system enabling the selection, automatic downloading and storage of serial episodic audio content on PCs and portable devices, origin of the podcast, is launched by early MP3 player manufacturer i2Go.

Earth sciences

 * March – Iceberg B-15, with a surface area of 11,000 km2 (4,200 sq mi), calves from the Ross Ice Shelf of Antarctica.
 * April – Cave of the Crystals discovered at the Naica Mine in Mexico.

Mathematics

 * Omer Reingold, Salil Vadhan and Avi Wigderson introduce the zig-zag product.

Medicine

 * January – Douglas Hanahan and Robert Weinberg publish "The Hallmarks of Cancer".
 * January 31 – English doctor Harold Shipman is found guilty of killing fifteen of his elderly patients by lethal injections of diamorphine, the only British physician ever convicted of murdering his patients; he is actually considered to have killed at least 215.

Paleontology

 * First fossil of Orrorin, an early species of Homininae, discovered in the Tugen Hills of Kenya.

Institutions

 * November 13 – Museu de les Ciències Príncipe Felipe in Valencia, Spain, opens to the public.

Awards

 * Nobel Prizes
 * Physics – Zhores Alferov, Herbert Kroemer - Jack Kilby
 * Chemistry – Alan J Heeger, Alan G MacDiarmid, Hideki Shirakawa
 * Medicine – Arvid Carlsson, Paul Greengard, Eric R. Kandel
 * Turing Award: Andrew Yao
 * Wollaston Medal for Geology: William Sefton Fyfe

Deaths

 * January 12 – Margaret Hutchinson Rousseau (b. 1910), American chemical engineer
 * January 19 – G. Ledyard Stebbins (b. 1906), American botanist and geneticist
 * March 7 – W. D. Hamilton (b. 1936), English evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century
 * March 10 – Nim Chimpsky (b. 1973), chimpanzee
 * May 6 – John Clive Ward (b. 1924), English-born physicist
 * May 19 – Yevgeny Khrunov (b. 1933), cosmonaut
 * June 14 – Elsie Widdowson (b. 1908), English nutritionist
 * July 8 – W. David Kingery (b. 1926), American materials scientist specializing in ceramic materials
 * July 14 – Sir Mark Oliphant (b. 1901), Australian nuclear physicist
 * July 29 – René Favaloro (b. 1923), Argentine cardiac surgeon
 * September 20 – Gherman Titov (b. 1935), cosmonaut
 * October 4 – Michael Smith (b. 1932), English-born Canadian chemist, 1993 Nobel Prize winner
 * November 20 – Nikolay Dollezhal (b. 1899), a key figure in Soviet atomic bomb project and chief designer of nuclear reactors

title: 2000 in science


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Gordon Onslow Ford

Gordon Onslow Ford (26 December 1912 – 9 November 2003) was one of the last surviving members of the 1930s Paris surrealist group surrounding André Breton.

Born in the English town of Wendover in 1912 to a family of artists, Onslow Ford began painting at an early age. His grandfather, Edward Onslow Ford, was a Victorian sculptor. At the age of 11, he began painting landscapes under the guidance of his uncle. Following the death of his father at age 14, he was sent to the Royal Naval College at Dartmouth. The ocean affected him deeply and his early works depicted ocean scenes. The metaphor of taking a "voyage" later became an important aspect of his paintings.

Paris
While in the Navy, Onslow Ford visited Paris several times. In 1937, he resigned as a naval officer and moved to Paris to pursue painting full-time. He studied with André L’hote for five weeks and studied with Fernand Léger for a short time. He continued visiting Léger, bringing his work to him often for critique.

Soon he met the Chilean architect Roberto Matta. Matta, who was working with Le Corbusier, was an accomplished draftsman and was making small drawings on the side. Onslow Ford, with his keen sense of seeing, admired Matta's drawings as "the most exciting images" he had seen in Paris. He encouraged Matta to continue with his drawings, which eventually inspired Matta to shift his direction from architecture to painting.

Onslow Ford and Matta became close friends, meeting and traveling frequently. They developed an ongoing dialogue about their ideas on art and metaphysics. They were also inspired by the 1937 exhibit of Mathematical Objects in Paris in which one aspect of the Mathematical Object was visible while another aspect was left to the imagination of the viewer.

In 1938, André Breton invited Onslow Ford to join the surrealist group in Paris and attend their meetings in Café deux Magots. Onslow Ford then became friends with Pierre Mabille, André Breton, Yves Tanguy, Esteban Frances, Wolfgang Paalen, Max Ernst and Victor Brauner among others. His love of painting also led him to collect paintings and frequently visit the studios of Picasso, Miró, de Chirico and André Masson.

In the summer of 1939, Onslow Ford rented a chateau at Chemilleu near the border of Switzerland, and invited several of his friends to stay for a couple of months. Among the friends were André Breton, Jacqueline Lamba, Yves Tanguy, Roberto Matta, Esteban Frances, and Kay Sage. They spent the summer painting, exchanging ideas and reading poetry. They were visited regularly by their friend and neighbor Gertrude Stein.

New York City
At the outset of World War II, the Society for the Preservation of European Culture invited Onslow Ford to join the surrealists in New York. Onslow Ford, one of the few surrealists who was an English speaker, was invited to give a series of lectures at the New School for Social Research and organized four important surrealist shows in 1941. Those lectures and exhibitions are said to have influenced artists such as Jackson Pollock, Robert Motherwell, and others who would go on to create Abstract Expressionism.

Mexico
Onslow Ford met the American writer Jacqueline Johnson at his lectures in New York and they married in 1941. That same year, they moved to Mexico where he had previously visited his surrealist friends Wolfgang Paalen, Remedios Varo and Esteban Frances who were all living there.

For six years (1941–1947) Onslow Ford and Johnson lived in Erongaricuaro, a remote village populated by the Purépecha Indians and located on the shores of Lake Patzcuaro. While living there, they created, studied, and learned the native way of living and participated in some native ceremonies. They stayed in constant connection with Wolfgang Paalen with Johnson assisting Paalen in editing his journal DYN as well as contributing writings for the journal. During their stay they were also visited by many Surrealist friends including Roberto Matta, Wolfgang Paalen, Remedios Varo, Esteban Frances, Eva Sulzer, Alice Rahon, William Fett, Pierre Mabille, Benjamin Péret, and the poet César Moro.

San Francisco
In 1947, Onslow Ford and Johnson moved to California, choosing the San Francisco Bay Area as the fertile soil where their new ideas would have a chance to grow. While in San Francisco, he was invited to give a retrospective show at the San Francisco Museum of Art (1948). The title of the exhibit and the catalogue, Towards a New Subject in Painting, spoke to the fact that he was moving in a new direction in his art.

While living in San Francisco, Onslow Ford met the Greek poet Jean Varda and together they acquired the ferryboat Vallejo, which they docked in Sausalito and converted into their studios. For many years the ferryboat was an inspiring haven for painters and artists and became a small cultural center on the waterfront. In 1951, Onslow Ford with his friends Wolfgang Paalen, Lee Mullican, and Jacqueline Johnson created an exhibition at the San Francisco Museum of Art called Dynaton.

In the early 1950s, Onslow Ford was introduced to Asian philosophy and studied Hinduism with Haridas Chaudhuri and Buddhist scholar Alan Watts at the newly formed Asian Academy (now called the California Institute of Integral Studies) in San Francisco. Around this time he also met the venerable Zen master Hodo Tobase of the Soto Zen sect and began studying Chinese calligraphy (1952–57). This entrance into Asian thought and practice had a profound influence on his paintings. Buddhist teachings of the Void and Emptiness as well as the practice of calligraphy initiated him into an exploration of the depths of the Mind and its images.

Inverness
In 1957, Onslow Ford and Johnson acquired a large body of virgin woodlands in the hills of Inverness, California. Ten years later they gave the majority of the land to the Nature Conservancy for the sake of preserving it. At this time, Onslow Ford began writing and, in 1964, he published his first book entitled Painting in the Instant. Johnson died in 1976 as he was working on his second book, Creation, which was published in 1978. In 1977, he had a major retrospective of his work at the Oakland Museum of California. After this, he assumed a more solitary life, focusing more deeply on his painting.

In 1989, he met Fariba Bogzaran, an artist, lucid dream researcher, and faculty member at John F. Kennedy University. They began a series of dialogues on arts and consciousness. In her research, Bogzaran found a connection between Onslow Ford's paintings, lucid dreaming, and meditation. Onslow Ford collaborated with her on several of his books including Insights (1991), Ecomorphology (1994) and Once Upon a Time (1999).

In 1998, Onslow Ford, Bogzaran, and Robert Anthoine cofounded the nonprofit organization Lucid Art Foundation in order to explore the relationship between art, consciousness, and nature through art exhibitions, publications, and seminars for artists.

Exhibitions
In the 1990s,Onslow Ford has had several retrospectives and solo exhibitions in the United States, Germany, Chile, and Spain. In 1996, he inaugurated the John F. Kennedy University Arts and Consciousness Gallery and M.F.A. program in Berkeley, California, and received an honorary doctorate degree in Fine Arts from the university in 1997. His paintings are in the collections of the Whitney Museum of American Art, the Solomon R. Guggenheim Museum, the Tate Britain, de Young Museum, Oakland Museum of California, San Francisco Museum of Modern Art, and the Los Angeles County Museum of Art. In 2010, Francis M. Naumann Fine Art showed Paintings and Works on Paper: 1939-1951, the first solo show of Onslow Ford's work in New York since 1946.

Onslow Ford died peacefully in his home on 9 November 2003. He was 90. He left his legacy to the Lucid Art Foundation.

title: Gordon Onslow Ford


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User:Egon

My name is Egon and I am from Estonia, but I've been a year and a half in South Korea. So I found that it is cool and useful to have this kind of free encyclopedia. I firstly start to use and edit estonian wikipedia, but now I try to write some articles here too, although, my english is not so correct.

So please forgive me, if I will have some mistakes.

All the best to all of You!...

title: User:Egon


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True frog

True frogs is the common name for the frog family Ranidae. They have the widest distribution of any frog family. They are abundant throughout most of the world, occurring on all continents except Antarctica. The true frogs are present in North America, northern South America, Europe, Africa (including Madagascar), and Asia. The Asian range extends across the East Indies to New Guinea and a single species, the Australian wood frog (Hylarana daemelii), has spread into the far north of Australia.

Typically, true frogs are smooth and moist-skinned, with large, powerful legs and extensively webbed feet. The true frogs vary greatly in size, ranging from small—such as the wood frog (Lithobates sylvatica)—to large.

Many of the true frogs are aquatic or live close to water. Most species lay their eggs in the water and go through a tadpole stage. However, as in most families of frogs, there is large variation of habitat within the family. There are also arboreal species of true frogs, and the family includes some of the very few amphibians that can live in brackish water.

Evolution
The Ranidae are related to several other frog families that have Eurasian and Indian origins, including Rhacophoridae, Dicroglossidae, Nyctibatrachidae, Micrixalidae, and Ranixalidae. They are thought to be most closely related to the Indian-endemic Nyctibatrachidae, from which they diverged in the early Eocene. However, other studies recover a closer relationship with the Dicroglossidae.

It was previously thought that the Ranidae and their closest relatives were of Gondwanan origins, having evolved on Insular India during the Cretaceous. They were then entirely restricted to the Indian subcontinent until the late Eocene, when India collided with Asia, allowing the Ranidae to colonize Eurasia and eventually the rest of the world. However, more recent studies instead propose that the Ranidae originated in Eurasia, and their close relationship with India-endemic frog lineages is due to those lineages colonizing India from Eurasia during the Paleogene.

Systematics
The subdivisions of the Ranidae are still a matter of dispute, although most are coming to an agreement. Several former subfamilies are now recognised as separate families (Petropedetidae, Cacosterninae, Mantellidae, and Dicroglossidae). The genus Rana has now been split up and is much reduced in size.

While too little of the vast diversity of true frogs has been subject to recent studies to say something definite, as of mid-2008, studies are going on, and several lineages are recognizable. The following phylogeny of some genera was recovered by Che et al., 2007 using mitochondrial genes.
 * The genus Staurois is probably a very ancient offshoot of the main Raninae lineage.
 * Amolops has been generally delimited as a monophyletic group.
 * Odorrana and Rana plus some proposed minor genera (which probably ought to be included in the latter) form another group.
 * A group including Clinotarsus, Huia in the strict sense and Meristogenys
 * An ill-defined assemblage of Babina, Glandirana, Hylarana, Pulchrana, Sanguirana, and Sylvirana, as well as Hydrophylax and Pelophylax, which are probably not monophyletic. Some authorities have treated them as junior synonyms of the genus Hylarana.

Genera
Most of the subfamilies formerly included under Ranidae are now treated as separate families, leaving only Raninae remaining. The following genera are recognised in the family Ranidae:

In 2023, Amphibian Species of the World tentatively synonymized Amnirana, Chalcorana, Humerana, Hydrophylax, Indosylvirana, Papurana, Pulchrana, and Sylvirana into Hylarana until significant taxonomic confusion surrounding the group could be cleared up. These changes are not recognized by AmphibiaWeb.
 * Abavorana Oliver, Prendini, Kraus, and Raxworthy, 2015 (three species)
 * Amnirana Dubois, 1992 (11 species)
 * Amolops Cope, 1865 (80 species)
 * Babina Thompson, 1912 (two species)
 * Chalcorana Dubois, 1992 (nine species)
 * Clinotarsus Mivart 1869 (three species)
 * Glandirana Fei, Ye, and Huang, 1990 (six species)
 * Huia Yang, 1991 (monotypic)
 * Humerana Dubois, 1992 (four species)
 * Hydrophylax Fitzinger, 1843 (four species)
 * Hylarana Tschudi 1838 (four species)
 * Indosylvirana Oliver, Prendini, Kraus, and Raxworthy, 2015 (13 species)
 * Lithobates Fitzinger, 1843 (55 species)
 * Meristogenys Yang, 1991 (13 species)
 * Nidirana Dubois, 1992 (19 species)
 * Odorrana Fei, Ye, and Huang, 1990 (64 species)
 * Papurana Dubois, 1992 (19 species)
 * Pelophylax Fitzinger 1843 (19 species)
 * Pseudorana Fei, Ye, and Huang, 1990 (monotypic)
 * Pterorana Kiyasetuo and Khare, 1986 (monotypic)
 * Pulchrana Dubois, 1992 (18 species)
 * Rana Linnaeus, 1758 (58 species)
 * Sanguirana Dubois, 1992 (six species)
 * Staurois Cope, 1865 (six species)
 * Sumaterana Arifin, Smart, Hertwig, Smith, Iskandar, and Haas, 2018 (three species)
 * Sylvirana Dubois, 1992 (12 species)
 * Wijayarana Arifin, Chan, Smart, Hertwig, Smith, Iskandar, and Haas, 2021 (five species)

Incertae sedis
A number of taxa are placed in Ranidae incertae sedis, that is, their taxonomic status is too uncertain to allow more specific placement.
 * "Hylarana" chitwanensis (Das, 1998)
 * "Hylarana" garoensis (Boulenger, 1920)
 * "Hylarana" latouchii (Boulenger, 1899)
 * "Hylarana" margariana Anderson, 1879
 * "Hylarana" montivaga (Smith, 1921)
 * "Hylarana" persimilis (Van Kampen, 1923)

title: True frog


text:
User:Maj~enwiki

Hi, I'm Maj, one of the founders of Wikitravel.

I thought I'd try my hand at some Wikipedia-ing between travel articles. You can find out more about me at my Wikitravel user page or at my site, Majink

Interests:
 * Hawaii
 * Victoria Ka'iulani (my first article!)
 * Linguistics
 * Library Science
 * Languages
 * Parenting -- Full disclosure, I'm a follower of "practical" Attachment Parenting

title: User:Maj~enwiki


text:
User talk:Oaaltone

Hi, you shouldn't create a personal page in the main article namespace, but you are free to put the info from Oliver Aaltonen on your user page. Adam Bishop 20:50, 25 Nov 2003 (UTC)

title: User talk:Oaaltone


text:
User talk:Nguyenr22

Hello, welcome to Wikipedia. Here are some useful links in case you haven't already found them;

 * How to edit a page
 * How to write a great article
 * Naming conventions
 * Manual of Style

If you have any questions, see the help pages, add a question to the village pump or ask me on my talk page. I hope you enjoy editing here and being a Wikipedian!

snoyes 20:51, 25 Nov 2003 (UTC)

Please do not remove the existing information from Lung cancer. If you wish to add information, then please do that, though bear in mind that you need to follow a neutral point of view. You should not delete large sections of a page without first discussing it on the talk page. For example Talk:Lung cancer. Angela 21:18, 25 Nov 2003 (UTC)

title: User talk:Nguyenr22


text:
Kuressaare

Kuressaare is a town on the island of Saaremaa in Estonia. It is the administrative centre of Saaremaa Municipality and the seat of Saare County. Kuressaare is the westernmost town in Estonia. The recorded population on 1 January 2018 was 13,276.

The town is situated on the southern coast of Saaremaa island, facing the Gulf of Riga of the Baltic Sea, and is served by the Kuressaare Airport, Roomassaare harbour, and Kuressaare yacht harbour.

Names
Kuressaare's historic name Arensburg (from Middle High German a(a)r: eagle, raptor) renders the Latin denotation arx aquilae for the city's castle. The fortress and the eagle, tetramorph symbol of Saint John the Evangelist, are also depicted on Kuressaare's coat of arms.

The town, which grew around the fortress, was simultaneously known as Arensburg and Kuressaare linn; the latter name being a combination of Kuressaare—an ancient name of the Saaremaa Island—and linn, which means town. Alternatively, the town's name may come from kurg (crane) and saare (island), a name that may have come from the city's German name and coat of arms, or may have existed before German settlers arrived. Eventually, the town's name shortened to Kuressaare and became official in 1918 after Estonia had declared its independence from Bolshevist Russia. Under Soviet rule, the town was renamed Kingissepa in 1952. This name came from the Bolshevik Kuressaare-native Viktor Kingissepp executed in 1922. The name Kuressaare was restored in 1988.

History
The town first appeared on maps around 1154. The island of Saaremaa (German, Ösel) was conquered by the Livonian Brothers of the Sword under Volkwin of Naumburg in 1227, who merged with the Teutonic Knights shortly afterwards. The first documentation of the castle (arx aquilae) was found in Latin texts written in 1381 and 1422. Over time, a town, which became known as Arensburg or Kuressaarelinn, grew and flourished around the fortress. It became the see of the Bishopric of Ösel-Wiek established by Albert of Riga in 1228, part of the Terra Mariana.

Johann von Münchhausen, bishop since 1542, converted to Protestantism. With the advance of the troops of Tsar Ivan IV of Russia in the course of the Livonian War, Münchhausen sold his lands to King Frederick II of Denmark in 1559 and returned to Germany. Frederick sent his younger brother Prince Magnus to Kuressaare where he was elected bishop the following year. It was through his influence that the city obtained its civic charter in 1563, modeled after that of Riga. The bishopric was finally secularised in 1572 and Kuressaare fell to the Danish Crown.

In 1645, it passed to Swedish control through the Treaty of Brömsebro after the Danish defeat in the Torstenson War. Queen Christina of Sweden granted her favourite, Magnus Gabriel de la Gardie, the title of Count of Arensburg, the German and Swedish name for Kuressaare at that time. The city was burnt to the ground by Russian troops in 1710 during the Great Northern War and suffered heavily from the plague. Abandoned by the Swedes, it was incorporated into the Governorate of Livonia of the Russian Empire through the Treaty of Nystad in 1721.

During the 19th century Kuressaare became a popular seaside resort on the Baltic coast. During World War I, between September and October 1917, German land and naval forces occupied Saaremaa with Operation Albion. During World War II, the Battle of Tehumardi took place. In October 1990, Kuressaare was the first town in Estonia to regain its self-governing status.

Tourism
Kuressaare is a well-known summer and resort town. The city is one of the most visited tourist centers in Estonia. The first known tourist group visited Kuressaare almost 165 years ago.

History
In the middle of the 19th century, Kuressaare became a spa town when large reserves of healing mud were discovered near the town. The first mud spa was built in 1840, but healing with mud baths has been tested on the west coast of Saaremaa since the mid-1820s. It was the health mud that became Kuressaare's key word. New sanatoriums and boarding houses were created, the order was considerably improved and the number of visitors continued to grow.

Between 1918 and 1940, the resort's heyday continued. The share of Russians among visitors decreased, giving way to Latvians, Finns and Swedes.

The development of tourism slowed down from the beginning of the Second World War until the end of the Soviet occupation, when the entire Saaremaa was declared a closed border zone, which excluded all foreign tourism. Only strictly limited and controlled domestic tourism was allowed.

Today, Kuressaare is once again a resort town. New health facilities and hotels have been built, and historical monuments have been restored. Two thirds of the current visitors to the city are mainland Estonians, the remaining visitors are mainly from Finland, Sweden and Latvia.

Sights
In the old town of Kuressaare, mainly the 18th and 19th centuries have been preserved. historical buildings from the 19th century, but there are also older ones. In the old town there are, for example, St. Nicholas Church and Laurentius Church, a goods yard, an old mill (1899), a harbor yard (1663) and residential buildings. The baroque town hall and council house date from the Swedish era in the 17th century, while the building of the Saaremaa Knights, located next to the Kuressaare town hall, dates from the 18th century. Among the oldest preserved buildings are also the parsonage building at Kauba tänav 5 and the Põlluvahi house at the corner of Kitsa and Kitzbergi streets.

Kuressaare bishop castle
The city's biggest attraction is the Kuressaare Bishop's Castle, which mainly dates from the 14th century, and currently houses the Saaremaa Museum. The square-shaped fortress consists of four building wings around the courtyard. On the northeast side are the gate and two towers: Pikk Hermann and Sturvolt. 17-18 are also important. The powerful earthen fortifications of the Kuressaare fortress around the medieval fortress core date from the 19th century. Kuressaare Castle is one of the best preserved in the Baltic States. It has been restored several times since the beginning of the 20th century. Since 2001, Kuressaare Castle Days have been organized every summer with knight tournaments, theatrical tours and processions, and other medieval attractions.

To the south-west of the castle is Tori bay, where the port of Kuressaare is located.

Kuressaare Castle Park and the historicist-style Kuressaare Kursaal are the center of resort life. Both were founded in the second half of the 19th century.

At the beginning of Lossi Street, in the former fish market, there is a monument to those who fell in the Estonian War of Independence.

Neighborhoods of Kuressaare
There are nine neighborhoods of Kuressaare:
 * Ida-Niidu
 * Kesklinn
 * Kellamäe
 * Marientali
 * Põllu alev
 * Roomassaare
 * Smuuli
 * Suuremõisa
 * Tori.

Landmarks and culture

The medieval episcopal Kuressaare Castle today houses the Saaremaa Regional Museum. The original wooden castle was constructed between 1338 and 1380, although other sources claim a fortress was built in Kuressaare as early as 1260. In 1968, architect began studies on Kuressaare Castle.

The town hall was originally built in 1654, and restored, retaining classicist and baroque features. It was last restored in the 1960s with dolomite stairs at the front. St Nicolaus Church was built in 1790.

The annual Saaremaa Opera Days (Saaremaa Ooperipäevad) have been held in Kuressaare each summer since 1999. Other festivals include Kuressaare Chamber Music Days (Kuressaare Kammermuusika Päevad), held since 1995 and Kuressaare Maritime Festival (Kuressaare Merepäevad), held since 1998.

Kuressaare also hosts the FC Kuressaare football club.

Transportation
Kuressaare is served by Kuressaare Airport, located on a peninsula southeast of the town. There is regular traffic to Tallinn, as well as seasonal flights to the island of Ruhnu.

There are bus connections around the island, as well as with Kuivastu on Muhu Island, a ferry terminal with connection to the mainland.

In 1917, during the German occupation, an urban railway was built in Kuressaare, and in 1918, it was transferred to the town administration. It connected the port with the city center/ One of the stations was provisionally located in Kurhouse, and in 1924, the dedicated Park Station was built. The railway functioned until the 1930s when it was gradually disused and mostly dismantled. An attempt to revive the railway in the beginning of the 1950s, during the Soviet period, was unsuccessful, and ended up with rails fully removed from the streets.

Notable people

 * Adam Georg von Agthe (1777–1826), Russian military officer
 * Tiiu Aro (born 1952), Estonian physician and politician
 * Eugen Dücker (1841–1916), Baltic German painter
 * Maria Faust (born 1979), Estonian saxophone player and composer
 * Bernd Freytag von Loringhoven (1914–2007), German military officer
 * Louis Kahn (1901–1974), American architect
 * Madis Kallas (born 1981), Estonian decathlete and politician
 * Viktor Kingissepp (1888–1922), Estonian communist politician
 * Heli Lääts (1932–2018), Estonian singer
 * Karl Patrick Lauk (born 1997), Estonian cyclist
 * Tullio Liblik (born 1964), Estonian entrepreneur
 * Jörgen Liik (born 1990), Estonian actor
 * Ivo Linna (born 1949), Estonian singer
 * Richard Maack (1825–1886), Russian naturalist
 * Konstantin Märska (1896–1951), Estonian cinematographer and film director
 * Gerd Neggo (1891–1974), Estonian dancer and choreographer
 * Marek Niit (born 1987), Estonian sprinter
 * Sulev Nõmmik (1931–1992), Estonian actor, director, humorist and dancer
 * Tiidrek Nurme (born 1985), Estonian runner
 * Margus Oopkaup (born 1959), Estonian actor
 * Mikk Pahapill (born 1983), Estonian decathlete
 * Grete Paia (born 1995), Estonian singer and songwriter
 * Tõnis Palts (born 1953), Estonian politician and businessman
 * Jüri Pihl (1954–2019), Estonian police officer and politician
 * Keith Pupart (born 1985), Estonian volleyball player
 * Ilmar Raag (born 1968), Estonian film director and media personality
 * Mihkel Räim (born 1993), Estonian cyclist
 * Tuuli Rand (born 1990), Estonian singer
 * Getter Saar (born 1992), Estonian badminton player
 * Indrek Saar (born 1973), Estonian actor and politician
 * Benno Schotz (1891–1984), Scottish sculptor
 * Hannibal Sehested (1609–1666), Danish statesman
 * Karen Sehested (1606–1672), Danish court official
 * Adeele Sepp (born 1989), Estonian actor
 * Jaanus Tamkivi (born 1959), Estonian politician
 * Tarmo Teder (born 1958), Estonian writer and critic
 * Ivar Karl Ugi (1930–2005), German chemist
 * Voldemar Väli (1903–1997), Estonian wrestler
 * Mihail Velsvebel (1926–2008), Estonian runner
 * Alexander Vostokov (1781–1864), Russian philologist
 * Richard Otto Zöpffel (1843–1891), Baltic German theologian

Twin towns and sister cities
The former municipality of Kuressaare was twinned with:
 * 🇫🇮 Ekenäs, Finland (since 21 November 1988)
 * 🇧🇪 Kuurne, Belgium (since 9 August 1998)
 * 🇫🇮 Mariehamn, Finland (since 24 October 1991)
 * 🇩🇰 Rønne, Denmark (since 3 October 1991)
 * 🇸🇪 Skövde, Sweden (since 23 June 1993)
 * 🇱🇻 Talsi, Latvia (since 27 May 1998)
 * 🇫🇮 Turku, Finland (since 30 May 1996)
 * 🇫🇮 Vammala, Finland (since 30 June 1994)

Significant depictions in popular culture

 * Arensburg (Kuressaare) is one of the starting towns of the State of the Teutonic Order in the turn-based strategy game Medieval II: Total War: Kingdoms.

title: Kuressaare


text:
Sensory nervous system

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

The receptive field is the area of the body or environment to which a receptor organ and receptor cells respond. For instance, the part of the world an eye can see, is its receptive field; the light that each rod or cone can see, is its receptive field. Receptive fields have been identified for the visual system, auditory system and somatosensory system.

Senses and receptors
While debate exists among neurologists as to the specific number of senses due to differing definitions of what constitutes a sense, Gautama Buddha and Aristotle classified five 'traditional' human senses which have become universally accepted: touch, taste, smell, vision, and hearing. Other senses that have been well-accepted in most mammals, including humans, include pain, balance, kinaesthesia, and temperature. Furthermore, some nonhuman animals have been shown to possess alternate senses, including magnetoreception and electroreception.

Receptors
The initialization of sensation stems from the response of a specific receptor to a physical stimulus. The receptors which react to the stimulus and initiate the process of sensation are commonly characterized in four distinct categories: chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors. All receptors receive distinct physical stimuli and transduce the signal into an electrical action potential. This action potential then travels along afferent neurons to specific brain regions where it is processed and interpreted.

Chemoreceptors
Chemoreceptors, or chemosensors, detect certain chemical stimuli and transduce that signal into an electrical action potential. The two primary types of chemoreceptors are:
 * 1) Distance chemoreceptors are integral to receiving stimuli in gases in the olfactory system through both olfactory receptor neurons and neurons in the vomeronasal organ.
 * 2) Direct chemoreceptors that detect stimuli in liquids include the taste buds in the gustatory system as well as receptors in the aortic bodies which detect changes in oxygen concentration.

Photoreceptors
Photoreceptors are neuron cells and are specialized units that play the main role in initiating vision function. Photoreceptors are light-sensitive cells that capture different wavelengths of light. Different types of photoreceptors are able to respond to the varying light wavelengths in relation to color, and transduce them into electrical signals. Photoreceptors are capable of phototransduction, a process which converts light (electromagnetic radiation) into, among other types of energy, a membrane potential. There are five compartments that are present in these cells. Each compartment corresponds to differences in function and structure. The first compartment is the outer segment (OS), where it is responsible for capturing light and transducing it. The second compartment is the inner segment (IS), which includes the necessary organelles that function in cellular metabolism and biosynthesis. Mainly, these organelles include mitochondria, Golgi apparatus and endoplasmic reticulum as well as among others. The third compartment is the connecting cilium (CC). As its name suggests, CC works to connect the OS and the IS regions together for the purpose of essential protein trafficking. The fourth compartment contains the nucleus and is a continuation of the IS region, known as the nuclear region. Finally, the fifth compartment is the synaptic region, where it acts as a final terminal for the signal, consisting of synaptic vesicles. In this region, glutamate neurotransmitter is transmitted from the cell to secondary neuron cells. The three primary types of photoreceptors are: cones are photoreceptors which respond significantly to color. In humans, the three different types of cones correspond with a primary response to short wavelength (blue), medium wavelength (green), and long wavelength (yellow/red). Rods are photoreceptors which are very sensitive to the intensity of light, allowing for vision in dim lighting. The concentrations and ratio of rods to cones is strongly correlated with whether an animal is diurnal or nocturnal. In humans, rods outnumber cones by approximately 20:1, while in nocturnal animals, such as the tawny owl, the ratio is closer to 1000:1. Ganglion cells reside in the adrenal medulla and retina where they are involved in the sympathetic response. Of the ~1.3 million ganglion cells present in the retina, 1-2% are believed to be photosensitive ganglia. These photosensitive ganglia play a role in conscious vision for some animals, and are believed to do the same in humans.

Mechanoreceptors
Mechanoreceptors are sensory receptors which respond to mechanical forces, such as pressure or distortion. While mechanoreceptors are present in hair cells and play an integral role in the vestibular and auditory systems, the majority of mechanoreceptors are cutaneous and are grouped into four categories:
 * 1) Slowly adapting type 1 receptors have small receptive fields and respond to static stimulation. These receptors are primarily used in the sensations of form and roughness.
 * 2) Slowly adapting type 2 receptors have large receptive fields and respond to stretch. Similarly to type 1, they produce sustained responses to a continued stimuli.
 * 3) Rapidly adapting receptors have small receptive fields and underlie the perception of slip.
 * 4) Pacinian receptors have large receptive fields and are the predominant receptors for high-frequency vibration.

Thermoreceptors
Thermoreceptors are sensory receptors which respond to varying temperatures. While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that mammals have at least two distinct types of thermoreceptors:
 * 1) The end-bulb of Krause or bulboid corpuscle detects temperatures above body temperature.
 * 2) Ruffini's end organ detects temperatures below body temperature.

TRPV1 is a heat-activated channel that acts as a small heat detecting thermometer in the membrane which begins the polarization of the neural fiber when exposed to changes in temperature. Ultimately, this allows us to detect ambient temperature in the warm/hot range. Similarly, the molecular cousin to TRPV1, TRPM8, is a cold-activated ion channel that responds to cold. Both cold and hot receptors are segregated by distinct subpopulations of sensory nerve fibers, which shows us that the information coming into the spinal cord is originally separate. Each sensory receptor has its own "labeled line" to convey a simple sensation experienced by the recipient. Ultimately, TRP channels act as thermosensors, channels that help us to detect changes in ambient temperatures.

Nociceptors
Nociceptors respond to potentially damaging stimuli by sending signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain. They are found in internal organs, as well as on the surface of the body. Nociceptors detect different kinds of damaging stimuli or actual damage. Those that only respond when tissues are damaged are known as "sleeping" or "silent" nociceptors.
 * 1) Thermal nociceptors are activated by noxious heat or cold at various temperatures.
 * 2) Mechanical nociceptors respond to excess pressure or mechanical deformation.
 * 3) Chemical nociceptors respond to a wide variety of chemicals, some of which are signs of tissue damage. They are involved in the detection of some spices in food.

Sensory cortex
All stimuli received by the receptors listed above are transduced to an action potential, which is carried along one or more afferent neurons towards a specific area of the brain. While the term sensory cortex is often used informally to refer to the somatosensory cortex, the term more accurately refers to the multiple areas of the brain at which senses are received to be processed. For the five traditional senses in humans, this includes the primary and secondary cortices of the different senses: the somatosensory cortex, the visual cortex, the auditory cortex, the primary olfactory cortex, and the gustatory cortex. Other modalities have corresponding sensory cortex areas as well, including the vestibular cortex for the sense of balance.

The human sensory system consists of the following subsystems:
 * Visual system (Vision)
 * Auditory system (Hearing)
 * Somatosensory system (Touch/Temperature/Kinesthesia/Pain)
 * Gustatory system (Taste)
 * Olfactory system (Smell)
 * Vestibular system (Balance)

Somatosensory cortex
Located in the parietal lobe, the primary somatosensory cortex is the primary receptive area for the sense of touch and proprioception in the somatosensory system. This cortex is further divided into Brodmann areas 1, 2, and 3. Brodmann area 3 is considered the primary processing center of the somatosensory cortex as it receives significantly more input from the thalamus, has neurons highly responsive to somatosensory stimuli, and can evoke somatic sensations through electrical stimulation. Areas 1 and 2 receive most of their input from area 3. There are also pathways for proprioception (via the cerebellum), and motor control (via Brodmann area 4). See also: S2 Secondary somatosensory cortex.

Visual cortex
The visual cortex refers to the primary visual cortex, labeled V1 or Brodmann area 17, as well as the extrastriate visual cortical areas V2-V5. Located in the occipital lobe, V1 acts as the primary relay station for visual input, transmitting information to two primary pathways labeled the dorsal and ventral streams. The dorsal stream includes areas V2 and V5, and is used in interpreting visual 'where' and 'how.' The ventral stream includes areas V2 and V4, and is used in interpreting 'what.' Increases in task-negative activity are observed in the ventral attention network, after abrupt changes in sensory stimuli, at the onset and offset of task blocks, and at the end of a completed trial.

Auditory cortex
Located in the temporal lobe, the auditory cortex is the primary receptive area for sound information. The auditory cortex is composed of Brodmann areas 41 and 42, also known as the anterior transverse temporal area 41 and the posterior transverse temporal area 42, respectively. Both areas act similarly and are integral in receiving and processing the signals transmitted from auditory receptors.

Primary olfactory cortex
Located in the temporal lobe, the primary olfactory cortex is the primary receptive area for olfaction, or smell. Unique to the olfactory and gustatory systems, at least in mammals, is the implementation of both peripheral and central mechanisms of action. The peripheral mechanisms involve olfactory receptor neurons which transduce a chemical signal along the olfactory nerve, which terminates in the olfactory bulb. The chemoreceptors in the receptor neurons that start the signal cascade are G protein-coupled receptors. The central mechanisms include the convergence of olfactory nerve axons into glomeruli in the olfactory bulb, where the signal is then transmitted to the anterior olfactory nucleus, the piriform cortex, the medial amygdala, and the entorhinal cortex, all of which make up the primary olfactory cortex.

In contrast to vision and hearing, the olfactory bulbs are not cross-hemispheric; the right bulb connects to the right hemisphere and the left bulb connects to the left hemisphere.

Gustatory cortex
The gustatory cortex is the primary receptive area for taste. The word taste is used in a technical sense to refer specifically to sensations coming from taste buds on the tongue. The five qualities of taste detected by the tongue include sourness, bitterness, sweetness, saltiness, and the protein taste quality, called umami. In contrast, the term flavor refers to the experience generated through integration of taste with smell and tactile information. The gustatory cortex consists of two primary structures: the anterior insula, located on the insular lobe, and the frontal operculum, located on the frontal lobe. Similarly to the olfactory cortex, the gustatory pathway operates through both peripheral and central mechanisms. Peripheral taste receptors, located on the tongue, soft palate, pharynx, and esophagus, transmit the received signal to primary sensory axons, where the signal is projected to the nucleus of the solitary tract in the medulla, or the gustatory nucleus of the solitary tract complex. The signal is then transmitted to the thalamus, which in turn projects the signal to several regions of the neocortex, including the gustatory cortex.

The neural processing of taste is affected at nearly every stage of processing by concurrent somatosensory information from the tongue, that is, mouthfeel. Scent, in contrast, is not combined with taste to create flavor until higher cortical processing regions, such as the insula and orbitofrontal cortex.

Quiescent state
Most sensory systems have a quiescent state, that is, the state that a sensory system converges to when there is no input.

This is well-defined for a linear time-invariant system, whose input space is a vector space, and thus by definition has a point of zero. It is also well-defined for any passive sensory system, that is, a system that operates without needing input power. The quiescent state is the state the system converges to when there is no input power.

It is not always well-defined for nonlinear, nonpassive sensory organs, since they can't function without input energy. For example, a cochlea is not a passive organ, but actively vibrates its own sensory hairs to improve its sensitivity. This manifests as otoacoustic emissions in healthy ears, and tinnitus in pathological ears. There is still a quiescent state for the cochlea, since there is a well-defined mode of power input that it receives (vibratory energy on the eardrum), which provides an unambiguous definition of "zero input power".

Some sensory systems can have multiple quiescent states depending on its history, like flip-flops, and magnetic material with hysteresis. It can also adapt to different quiescent states. In complete darkness, the retinal cells become extremely sensitive, and there is noticeable "visual snow" caused by the retinal cells firing randomly without any light input. In brighter light, the retinal cells become much less sensitive, consequently decreasing visual noise.

Quiescent state is less well-defined when the sensory organ can be controlled by other systems, like a dog's ears that turn towards the front or the sides as the brain commands. Some spiders can use their nets as a large touch-organ, like weaving a skin for themselves. Even in the absence of anything falling on the net, hungry spiders may increase web thread tension, so as to respond promptly even to usually less noticeable, and less profitable prey, such as small fruit flies, creating two different "quiescent states" for the net.

Things become completely ill-defined for a system which connects its output to its own input, thus ever-moving without any external input. The prime example is the brain, with its default mode network.

Diseases

 * Amblyopia
 * Anacusis
 * Color blindness
 * Deafness

title: Sensory nervous system


text:
National Stock Exchange (Jersey City, New Jersey)

The National Stock Exchange (NSX) is an electronic stock exchange based in Jersey City, New Jersey. It was founded March 1885 in Cincinnati, Ohio, as the Cincinnati Stock Exchange.

In 1995, it moved headquarters to Chicago, Illinois, and it was renamed the National Stock Exchange in 2003. After demutualizing in 2006, it moved headquarters to Jersey City. In 2011, CBOE Stock Exchange acquired the National Stock Exchange, with both exchanges operating under separate names. The NSX ceased trading operations on February 1, 2017, when it was acquired by the New York Stock Exchange, and reopened on May 21, 2018.

Early name changes
National Stock Exchange was founded March 1885 in Cincinnati, Ohio, as the Cincinnati Stock Exchange. In 1976, it closed its physical trading floor and became an all-electronic stock market. The Cincinnati Stock Exchange moved its headquarters to Chicago in 1995, and changed its name to the National Stock Exchange – NSX – on November 7, 2003. Owned by its members since inception, it demutualized in 2006. It later moved its headquarters to Jersey City, New Jersey. In September 2011, CBOE Stock Exchange (CBSX) entered into an agreement to acquire the National Stock Exchange. The acquisition was completed on December 30, 2011, with both exchanges to operate under separate names. The National Stock Exchange continued to be based in Jersey City.

2014–2015 shutdown
In May 2014, the exchange "changed its pricing structure to charge both sides of a trade a fee for securities priced $1 or more, a departure from other public venues that usually charge one side and pay a rebate to another." With David Harris as chief executive officer, the National Stock Exchange ceased trading operations on May 30, 2014. The exchange stated in a release that it, "continues to be registered as a national securities exchange under Section 6 of the Securities Exchange Act (the "Act") and remains a self-regulatory organization. All NSX rules remain in full force and effect." The closure brought the number of active stock exchanges in the United States to 11, as the CBOE Stock Exchange had closed the month prior. Wrote Bloomberg, "just one public exchange, Chicago Stock Exchange Inc., that isn’t owned Bats, Nasdaq OMX Group Inc. or IntercontinentalExchange Group Inc." On February 24, 2015, the NSX was bought by a private entity known as National Stock Exchange Holdings. Trading resumed on December 22, 2015.

NYSE acquisition
The New York Stock Exchange announced it has entered into an agreement to acquire the NSX, subject to Securities and Exchange Commission (SEC) approval. The NSX ceased trading operations on February 1, 2017. NYSE plans to bring it back on its new trading platform Pillar, some time in the distant future.

NSX was to be renamed "NYSE National" as a result of the acquisition by NYSE.

On January 12, 2018, an SEC filing for rule changes was made to support re-activation of NYSE National, Inc. in the second quarter of 2018 (on the Pillar trading platform as previously noted). NYSE National opened for business on May 21, 2018. The difference between NYSE National and other NYSE exchanges is that it uses a taker-maker pricing model, which offers rebates for adding liquidity, rather than payment for order flow or other models.

Previous exchanges named NSX
Two previous exchanges, both located in New York City, operated as the National Stock Exchange. The first exchange operated for seven months to September 1869. The other, associated with the New York Mercantile Exchange, traded from March 7, 1962, to January 31, 1975.


text:
Schmitt trigger

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal. The circuit is named a trigger because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high. When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable multivibrator (latch or flip-flop). There is a close relation between the two kinds of circuits: a Schmitt trigger can be converted into a latch and a latch can be converted into a Schmitt trigger.

Schmitt trigger devices are typically used in signal conditioning applications to remove noise from signals used in digital circuits, particularly mechanical contact bounce in switches. They are also used in closed loop negative feedback configurations to implement relaxation oscillators, used in function generators and switching power supplies.

In signal theory, a schmitt trigger is essentially a one-bit quantizer.

History
The Schmitt trigger was invented by American scientist Otto H. Schmitt in 1934 while he was a graduate student, later described in his doctoral dissertation (1937) as a thermionic trigger. It was a direct result of Schmitt's study of the neural impulse propagation in squid nerves.

Fundamental idea
[[Image:Ideal feedback model.svg|thumb|300px|Block diagram of a Schmitt trigger circuit. It is a system with [[positive feedback]] in which the output signal fed back into the input causes the amplifier A to switch rapidly from one saturated state to the other when the input crosses a threshold.

A > 1 is the amplifier gain

B < 1 is the feedback transfer function]]

Circuits with hysteresis are based on positive feedback. Any active circuit can be made to behave as a Schmitt trigger by applying a positive feedback so that the loop gain is more than one. The positive feedback is introduced by adding a part of the output voltage to the input voltage. These circuits contain an attenuator (the B box in the figure on the right) and an adder (the circle with "+" inside) in addition to an amplifier acting as a comparator. There are three specific techniques for implementing this general idea. The first two of them are dual versions (series and parallel) of the general positive feedback system. In these configurations, the output voltage increases the effective difference input voltage of the comparator by 'decreasing the threshold' or by 'increasing the circuit input voltage'; the threshold and memory properties are incorporated in one element. In the third technique, the threshold and memory properties are separated.

Dynamic threshold (series feedback): when the input voltage crosses the threshold in some direction the circuit itself changes its own threshold to the opposite direction. For this purpose, it subtracts a part of its output voltage from the threshold (it is equal to adding voltage to the input voltage). Thus the output affects the threshold and does not impact on the input voltage. These circuits are implemented by a differential amplifier with 'series positive feedback' where the input is connected to the inverting input and the output - to the non-inverting input. In this arrangement, attenuation and summation are separated: a voltage divider acts as an attenuator and the loop acts as a simple series voltage summer. Examples are the classic transistor emitter-coupled Schmitt trigger, the op-amp inverting Schmitt trigger, etc.

Modified input voltage (parallel feedback): when the input voltage crosses the threshold in some direction the circuit changes its input voltage in the same direction (now it adds a part of its output voltage directly to the input voltage). Thus the output augments the input voltage and does not affect the threshold. These circuits can be implemented by a single-ended non-inverting amplifier with 'parallel positive feedback' where the input and the output sources are connected through resistors to the input. The two resistors form a weighted parallel summer incorporating both the attenuation and summation. Examples are the less familiar collector-base coupled Schmitt trigger, the op-amp non-inverting Schmitt trigger, etc.

Some circuits and elements exhibiting negative resistance can also act in a similar way: negative impedance converters (NIC), neon lamps, tunnel diodes (e.g., a diode with an N-shaped current–voltage characteristic in the first quadrant), etc. In the last case, an oscillating input will cause the diode to move from one rising leg of the "N" to the other and back again as the input crosses the rising and falling switching thresholds.

Two different unidirectional thresholds are assigned in this case to two separate open-loop comparators (without hysteresis) driving a bistable multivibrator (latch) or flip-flop. The trigger is toggled high when the input voltage crosses down to up the high threshold and low when the input voltage crosses up to down the low threshold. Again, there is a positive feedback but now it is concentrated only in the memory cell. Examples are the 555 timer and the switch debounce circuit.

The symbol for Schmitt triggers in circuit diagrams is a triangle with a symbol inside representing its ideal hysteresis curve.

Classic emitter-coupled circuit

The original Schmitt trigger is based on the dynamic threshold idea that is implemented by a voltage divider with a switchable upper leg (the collector resistors RC1 and RC2) and a steady lower leg (RE). Q1 acts as a comparator with a differential input (Q1 base-emitter junction) consisting of an inverting (Q1 base) and a non-inverting (Q1 emitter) inputs. The input voltage is applied to the inverting input; the output voltage of the voltage divider is applied to the non-inverting input thus determining its threshold. The comparator output drives the second common collector stage Q2 (an emitter follower) through the voltage divider R1-R2. The emitter-coupled transistors Q1 and Q2 actually compose an electronic double throw switch that switches over the upper legs of the voltage divider and changes the threshold in a different (to the input voltage) direction.

This configuration can be considered as a differential amplifier with series positive feedback between its non-inverting input (Q2 base) and output (Q1 collector) that forces the transition process. There is also a smaller negative feedback introduced by the emitter resistor RE. To make the positive feedback dominate over the negative one and to obtain a hysteresis, the proportion between the two collector resistors is chosen RC1 > RC2. Thus less current flows through and less voltage drop is across RE when Q1 is switched on than in the case when Q2 is switched on. As a result, the circuit has two different thresholds in regard to ground (V− in the image).

Operation
Initial state. For the NPN transistors shown on the right, imagine the input voltage is below the shared emitter voltage (high threshold for concreteness) so that Q1 base-emitter junction is reverse-biased and Q1 does not conduct. The Q2 base voltage is determined by the mentioned divider so that Q2 is conducting and the trigger output is in the low state. The two resistors RC2 and RE form another voltage divider that determines the high threshold. Neglecting VBE, the high threshold value is approximately

 * $$V_\mathrm{HT} = \frac{R_\mathrm{E}}{R_\mathrm{E} + R_\mathrm{C2}}{V_+}$$.

The output voltage is low but well above ground. It is approximately equal to the high threshold and may not be low enough to be a logical zero for subsequent digital circuits. This may require an additional shifting circuit following the trigger circuit.

Crossing up the high threshold. When the input voltage (Q1 base voltage) rises slightly above the voltage across the emitter resistor RE (the high threshold), Q1 begins conducting. Its collector voltage goes down and Q2 begins going cut-off, because the voltage divider now provides lower Q2 base voltage. The common emitter voltage follows this change and goes down thus making Q1 conduct more. The current begins steering from the right leg of the circuit to the left one. Although Q1 is more conducting, it passes less current through RE (since RC1 > RC2); the emitter voltage continues dropping and the effective Q1 base-emitter voltage continuously increases. This avalanche-like process continues until Q1 becomes completely turned on (saturated) and Q2 turned off. The trigger is transitioned to the high state and the output (Q2 collector) voltage is close to V+. Now, the two resistors RC1 and RE form a voltage divider that determines the low threshold. Its value is approximately

 * $$V_\mathrm{LT} = \frac{R_\mathrm{E}}{R_\mathrm{E} + R_\mathrm{C1}}{V_+}$$.

Crossing down the low threshold. With the trigger now in the high state, if the input voltage lowers enough (below the low threshold), Q1 begins cutting-off. Its collector current reduces; as a result, the shared emitter voltage lowers slightly and Q1 collector voltage rises significantly. The R1-R2 voltage divider conveys this change to the Q2 base voltage and it begins conducting. The voltage across RE rises, further reducing the Q1 base-emitter potential in the same avalanche-like manner, and Q1 ceases to conduct. Q2 becomes completely turned on (saturated) and the output voltage becomes low again.

Variations

Non-inverting circuit. The classic non-inverting Schmitt trigger can be turned into an inverting trigger by taking Vout from the emitters instead of from a Q2 collector. In this configuration, the output voltage is equal to the dynamic threshold (the shared emitter voltage) and both the output levels stay away from the supply rails. Another disadvantage is that the load changes the thresholds so, it has to be high enough. The base resistor RB is obligatory to prevent the impact of the input voltage through Q1 base-emitter junction on the emitter voltage.

Direct-coupled circuit. To simplify the circuit, the R1–R2 voltage divider can be omitted connecting Q1 collector directly to Q2 base. The base resistor RB can be omitted as well so that the input voltage source drives directly Q1's base. In this case, the common emitter voltage and Q1 collector voltage are not suitable for outputs. Only Q2 collector should be used as an output since, when the input voltage exceeds the high threshold and Q1 saturates, its base-emitter junction is forward biased and transfers the input voltage variations directly to the emitters. As a result, the common emitter voltage and Q1 collector voltage follow the input voltage. This situation is typical for over-driven transistor differential amplifiers and ECL gates.

Collector-base coupled circuit

Like every latch, the fundamental collector-base coupled bistable circuit possesses a hysteresis. So, it can be converted to a Schmitt trigger by connecting an additional base resistor R to one of the inputs (Q1 base in the figure). The two resistors R and R4 form a parallel voltage summer (the circle in the block diagram above) that sums output (Q2 collector) voltage and the input voltage, and drives the single-ended transistor "comparator" Q1. When the base voltage crosses the threshold (VBE0 ∞ 0.65 V) in some direction, a part of Q2's collector voltage is added in the same direction to the input voltage. Thus the output modifies the input voltage by means of parallel positive feedback and does not affect the threshold (the base-emitter voltage).

Comparison between emitter- and collector-coupled circuit
The emitter-coupled version has the advantage that the input transistor is reverse biased when the input voltage is quite below the high threshold so the transistor is surely cut-off. It was important when germanium transistors were used for implementing the circuit and this advantage has determined its popularity. The input base resistor can be omitted since the emitter resistor limits the current when the input base-emitter junction is forward-biased.

An emitter-coupled Schmitt trigger logical zero output level may not be low enough and might need an additional output shifting circuit. The collector-coupled Schmitt trigger has extremely low (almost zero) output at logical zero.

Op-amp implementations
Schmitt triggers are commonly implemented using an operational amplifier or a dedicated comparator. An open-loop op-amp and comparator may be considered as an analog-digital device having analog inputs and a digital output that extracts the sign of the voltage difference between its two inputs. The positive feedback is applied by adding a part of the output voltage to the input voltage in series or parallel manner. Due to the extremely high op-amp gain, the loop gain is also high enough and provides the avalanche-like process.

Non-inverting Schmitt trigger

In this circuit, the two resistors R1 and R2 form a parallel voltage summer. It adds a part of the output voltage to the input voltage thus augmenting it during and after switching that occurs when the resulting voltage is near ground. This parallel positive feedback creates the needed hysteresis that is controlled by the proportion between the resistances of R1 and R2. The output of the parallel voltage summer is single-ended (it produces voltage with respect to ground) so the circuit does not need an amplifier with a differential input. Since conventional op-amps have a differential input, the inverting input is grounded to make the reference point zero volts.

The output voltage always has the same sign as the op-amp input voltage but it does not always have the same sign as the circuit input voltage (the signs of the two input voltages can differ). When the circuit input voltage is above the high threshold or below the low threshold, the output voltage has the same sign as the circuit input voltage (the circuit is non-inverting). It acts like a comparator that switches at a different point depending on whether the output of the comparator is high or low. When the circuit input voltage is between the thresholds, the output voltage is undefined and it depends on the last state (the circuit behaves as an elementary latch).

For instance, if the Schmitt trigger is currently in the high state, the output will be at the positive power supply rail (+VS). The output voltage V+ of the resistive summer can be found by applying the superposition theorem:

 * $$V_\mathrm{+} = \frac{R_2}{R_1+R_2} \cdot V_\mathrm{in} + \frac{R_1}{R_1+R_2} \cdot V_\mathrm{s}$$

The comparator will switch when V+=0. Then $${R_2}\cdot V_\mathrm{in} = -{R_1}\cdot V_\mathrm{s}$$ (the same result can be obtained by applying the current conservation principle). So $$V_{\text{in}}$$ must drop below $$-\frac{R_1}{R_2}{V_s}$$ to get the output to switch. Once the comparator output has switched to −VS, the threshold becomes $$+\frac{R_1}{R_2}{V_s}$$ to switch back to high. So this circuit creates a switching band centered on zero, with trigger levels $$\pm\frac{R_1}{R_2}{V_s}$$ (it can be shifted to the left or the right by applying a bias voltage to the inverting input). The input voltage must rise above the top of the band, and then below the bottom of the band, for the output to switch on (plus) and then back off (minus). If R1 is zero or R2 is infinity (i.e., an open circuit), the band collapses to zero width, and it behaves as a standard comparator. The transfer characteristic is shown in the picture on the left. The value of the threshold T is given by $$\frac{R_1}{R_2}{V_s}$$ and the maximum value of the output M is the power supply rail.

A unique property of circuits with parallel positive feedback is the impact on the input source. In circuits with negative parallel feedback (e.g., an inverting amplifier), the virtual ground at the inverting input separates the input source from the op-amp output. Here there is no virtual ground, and the steady op-amp output voltage is applied through R1-R2 network to the input source. The op-amp output passes an opposite current through the input source (it injects current into the source when the input voltage is positive and it draws current from the source when it is negative).

A practical Schmitt trigger with precise thresholds is shown in the figure on the right. The transfer characteristic has exactly the same shape of the previous basic configuration, and the threshold values are the same as well. On the other hand, in the previous case, the output voltage was depending on the power supply, while now it is defined by the Zener diodes (which could also be replaced with a single double-anode Zener diode). In this configuration, the output levels can be modified by appropriate choice of Zener diode, and these levels are resistant to power supply fluctuations (i.e., they increase the PSRR of the comparator). The resistor R3 is there to limit the current through the diodes, and the resistor R4 minimizes the input voltage offset caused by the comparator's input leakage currents (see limitations of real op-amps).

Inverting Schmitt trigger

In the inverting version, the attenuation and summation are separated. The two resistors R1 and R2 act only as a "pure" attenuator (voltage divider). The input loop acts as a series voltage summer that adds a part of the output voltage in series to the circuit input voltage. This series positive feedback creates the needed hysteresis that is controlled by the proportion between the resistances of R1 and the whole resistance (R1 and R2). The effective voltage applied to the op-amp input is floating so the op-amp must have a differential input.

The circuit is named inverting since the output voltage always has an opposite sign to the input voltage when it is out of the hysteresis cycle (when the input voltage is above the high threshold or below the low threshold). However, if the input voltage is within the hysteresis cycle (between the high and low thresholds), the circuit can be inverting as well as non-inverting. The output voltage is undefined and it depends on the last state so the circuit behaves like an elementary latch.

To compare the two versions, the circuit operation will be considered at the same conditions as above. If the Schmitt trigger is currently in the high state, the output will be at the positive power supply rail (+VS). The output voltage V+ of the voltage divider is:

 * $$V_\mathrm{+} = \frac{R_1}{R_1+R_2} \cdot V_\mathrm{s}$$

The comparator will switch when Vin = V+. So $$V_{\text{in}}$$ must exceed above this voltage to get the output to switch. Once the comparator output has switched to −VS, the threshold becomes $$-\frac{R_1}{R_1+R_2}{V_s}$$ to switch back to high. So this circuit creates a switching band centered on zero, with trigger levels $$\pm\frac{R_1}{R_1 + R_2}{V_s}$$ (it can be shifted to the left or the right by connecting R1 to a bias voltage). The input voltage must rise above the top of the band, and then below the bottom of the band, for the output to switch off (minus) and then back on (plus). If R1 is zero (i.e., a short circuit) or R2 is infinity, the band collapses to zero width, and it behaves as a standard comparator.

In contrast with the parallel version, this circuit does not impact on the input source since the source is separated from the voltage divider output by the high op-amp input differential impedance.

In the inverting amplifier voltage drop across resistor (R1) decides the reference voltages i.e., upper threshold voltage (V+) and lower threshold voltages (V−) for the comparison with input signal applied. These voltages are fixed as the output voltage and resistor values are fixed.

so by changing the drop across (R1) threshold voltages can be varied. By adding a bias voltage in series with resistor (R1) drop across it can be varied, which can change threshold voltages. Desired values of reference voltages can be obtained by varying bias voltage.

The above equations can be modified as:
 * $$V_\pm = \pm V_s \frac{R_1}{R_1+R_2} + V_b \frac{R_2}{R_1+R_2}$$

Applications
Schmitt triggers are typically used in open loop configurations for noise immunity and closed loop configurations to implement function generators.
 * Analog-to-digital conversion:  The Schmitt trigger is effectively a one bit analog to digital converter. When the signal reaches a given level it switches from its low to high state.
 * Level detection:  The Schmitt trigger circuit is able to provide level detection. When undertaking this application, it is necessary that the hysteresis voltage is taken into account so that the circuit switches on the required voltage.
 * Line reception:  When running a data line that may have picked up noise into a logic gate it is necessary to ensure that a logic output level is only changed as the data changed and not as a result of spurious noise that may have been picked up. Using a Schmitt trigger broadly enables the peak to peak noise to reach the level of the hysteresis before spurious triggering may occur.

Noise immunity
One application of a Schmitt trigger is to increase the noise immunity in a circuit with only a single input threshold. With only one input threshold, a noisy input signal near that threshold could cause the output to switch rapidly back and forth from noise alone. A noisy Schmitt Trigger input signal near one threshold can cause only one switch in output value, after which it would have to move beyond the other threshold in order to cause another switch.

For example, an amplified infrared photodiode may generate an electric signal that switches frequently between its absolute lowest value and its absolute highest value. This signal is then low-pass filtered to form a smooth signal that rises and falls corresponding to the relative amount of time the switching signal is on and off. That filtered output passes to the input of a Schmitt trigger. The net effect is that the output of the Schmitt trigger only passes from low to high after a received infrared signal excites the photodiode for longer than some known period, and once the Schmitt trigger is high, it only moves low after the infrared signal ceases to excite the photodiode for longer than a similar known period. Whereas the photodiode is prone to spurious switching due to noise from the environment, the delay added by the filter and Schmitt trigger ensures that the output only switches when there is certainly an input stimulating the device.

Schmitt triggers are common in many switching circuits for similar reasons (e.g., for switch debouncing).

The following 7400 series devices include a Schmitt trigger on their input(s): (see List of 7400-series integrated circuits)
 * 7413: Dual Schmitt trigger 4-input NAND Gate
 * 7414: Hex Schmitt trigger Inverter
 * 7418: Dual Schmitt trigger 4-input NAND Gate
 * 7419: Hex Schmitt trigger Inverter
 * 74121: Monostable Multivibrator with Schmitt Trigger Inputs
 * 74132: Quad 2-input NAND Schmitt Trigger
 * 74221: Dual Monostable Multivibrator with Schmitt Trigger Input
 * 74232: Quad NOR Schmitt Trigger
 * 74310: Octal Buffer with Schmitt Trigger Inputs
 * 74340: Octal Buffer with Schmitt Trigger Inputs and three-state inverted outputs
 * 74341: Octal Buffer with Schmitt Trigger Inputs and three-state noninverted outputs
 * 74344: Octal Buffer with Schmitt Trigger Inputs and three-state noninverted outputs
 * 74(HC/HCT)7541 Octal Buffer with Schmitt Trigger Inputs and Three-State Noninverted Outputs
 * SN74LV8151 is a 10-bit universal Schmitt-trigger buffer with 3-state outputs

A number of 4000 series devices include a Schmitt trigger on their inputs(s): (see List of 4000-series integrated circuits)
 * 4017: Decade Counter with Decoded Outputs
 * 4020: 14-Stage Binary Ripple Counter
 * 4022: Octal Counter with Decoded Outputs
 * 4024: 7-Stage Binary Ripple Counter
 * 4040: 12-Stage Binary Ripple Counter
 * 4093: Quad 2-Input NAND
 * 4538: Dual Monostable Multivibrator
 * 4584: Hex inverting Schmitt trigger
 * 40106: Hex Inverter

Schmitt input configurable single-gate chips: (see List of 7400-series integrated circuits)
 * NC7SZ57 Fairchild
 * NC7SZ58 Fairchild
 * SN74LVC1G57 Texas Instruments
 * SN74LVC1G58 Texas Instruments

Use as an oscillator

A Schmitt trigger is a bistable multivibrator, and it can be used to implement another type of multivibrator, the relaxation oscillator. This is achieved by connecting a single RC integrating circuit between the output and the input of an inverting Schmitt trigger. The output will be a continuous square wave whose frequency depends on the values of R and C, and the threshold points of the Schmitt trigger. Since multiple Schmitt trigger circuits can be provided by a single integrated circuit (e.g. the 4000 series CMOS device type 40106 contains 6 of them), a spare section of the IC can be quickly pressed into service as a simple and reliable oscillator with only two external components.

Here, a comparator-based Schmitt trigger is used in its inverting configuration. Additionally, slow negative feedback is added with an integrating RC network. The result, which is shown on the right, is that the output automatically oscillates from VSS to VDD as the capacitor charges from one Schmitt trigger threshold to the other.

title: Schmitt trigger


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