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The Caesar cipher is named after Julius Caesar, who, according to Suetonius, used it with a shift of three (A becoming D when encrypting, and D becoming A when decrypting) to protect messages of military significance. While Caesar's was the first recorded use of this scheme, other substitution ciphers are known to have... | Caesar cipher | Wikipedia | 455 | 48405 | https://en.wikipedia.org/wiki/Caesar%20cipher | Technology | Computer security | null | vital_articles |
The Vigenère cipher uses a Caesar cipher with a different shift at each position in the text; the value of the shift is defined using a repeating keyword. If the keyword is as long as the message, is chosen at random, never becomes known to anyone else, and is never reused, this is the one-time pad cipher, proven unbre... | Caesar cipher | Wikipedia | 494 | 48405 | https://en.wikipedia.org/wiki/Caesar%20cipher | Technology | Computer security | null | vital_articles |
Another approach is to match up the frequency distribution of the letters. By graphing the frequencies of letters in the ciphertext, and by knowing the expected distribution of those letters in the original language of the plaintext, a human can easily spot the value of the shift by looking at the displacement of parti... | Caesar cipher | Wikipedia | 318 | 48405 | https://en.wikipedia.org/wiki/Caesar%20cipher | Technology | Computer security | null | vital_articles |
A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geop... | Terrestrial planet | Wikipedia | 459 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
The Solar System has four terrestrial planets under the dynamical definition: Mercury, Venus, Earth and Mars. The Earth's Moon as well as Jupiter's moons Io and Europa would also count geophysically, as well as perhaps the large protoplanet-asteroids Pallas and Vesta (though those are borderline cases). Among these bod... | Terrestrial planet | Wikipedia | 499 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
Density trends
The uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. A greater uncompressed density indicates a greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within pla... | Terrestrial planet | Wikipedia | 460 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
When 51 Pegasi b, the first planet found around a star still undergoing fusion, was discovered, many astronomers assumed it to be a gigantic terrestrial, because it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. It was later found to be a gas giant.
In 2005, the first planets ... | Terrestrial planet | Wikipedia | 480 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
In 2016, statistical modeling of the relationship between a planet's mass and radius using a broken power law appeared to suggest that the transition point between rocky, terrestrial worlds and mini-Neptunes without a defined surface was in fact very close to Earth and Venus's, suggesting that rocky worlds much larger ... | Terrestrial planet | Wikipedia | 477 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
Estimates show that about 80% of potentially habitable worlds are covered by land, and about 20% are ocean planets. Planets with rations more like those of Earth, which was 30% land and 70% ocean, only make up 1% of these worlds.
Types
Several possible classifications for solid planets have been proposed.
Silicate ... | Terrestrial planet | Wikipedia | 436 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
A theoretical type of solid planet that consists of silicate rock but has no metallic core, i.e. the opposite of an iron planet. Although the Solar System contains no coreless planets, chondrite asteroids and meteorites are common in the Solar System. Ceres and Pallas have mineral compositions similar to carbonaceous c... | Terrestrial planet | Wikipedia | 100 | 48510 | https://en.wikipedia.org/wiki/Terrestrial%20planet | Physical sciences | Planetary science | null | vital_articles |
The term antelope refers to numerous extant or recently extinct species of the ruminant artiodactyl family Bovidae that are indigenous to most of Africa, India, the Middle East, Central Asia, and a small area of Eastern Europe. Antelopes do not form a monophyletic group, as some antelopes are more closely related to ot... | Antelope | Wikipedia | 444 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
The English word "antelope" first appeared in 1417 and is derived from the Old French antelop, itself derived from Medieval Latin ant(h)alopus, which in turn comes from the Byzantine Greek word ἀνθόλοψ, anthólops, first attested in Eustathius of Antioch (), according to whom it was a fabulous animal "haunting the banks... | Antelope | Wikipedia | 500 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
No antelope species is native to Australasia or Antarctica, nor do any extant species occur in the Americas, though the nominate saiga subspecies occurred in North America during the Pleistocene. North America is currently home to the native pronghorn, which taxonomists do not consider a member of the antelope group, b... | Antelope | Wikipedia | 422 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
Not surprisingly for animals with long, slender yet powerful legs, many antelope have long strides and can run fast. Some (e.g. klipspringer) are also adapted to inhabiting rock koppies and crags. Both dibatags and gerenuks habitually stand on their two hind legs to reach acacia and other tree foliage. Different antelo... | Antelope | Wikipedia | 407 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
Many antelope are sexually dimorphic. In most species, both sexes have horns, but those of males tend to be larger. Males tend to be larger than the females, but exceptions in which the females tend to be heavier than the males include the bush duiker, dwarf antelope, Cape grysbok, and oribi, all rather small species. ... | Antelope | Wikipedia | 384 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
The size and shape of antelope horns varies greatly. Those of the duikers and dwarf antelope tend to be simple "spikes", but differ in the angle to the head from backward curved and backward pointing (e.g. yellow-backed duiker) to straight and upright (e.g. steenbok). Other groups have twisted (e.g. common eland), spir... | Antelope | Wikipedia | 496 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
Large antelope that gather in large herds, such as wildebeest, rely on numbers and running speed for protection. In some species, adults will encircle the offspring, protecting them from predators when threatened. Many forest antelope rely on cryptic coloring and good hearing to avoid predators. Forest antelope often h... | Antelope | Wikipedia | 449 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
The saiga is hunted for its horns, which are considered an aphrodisiac by some cultures. Only the males have horns, and have been so heavily hunted that some herds contain up to 800 females to one male. The species showed a steep decline and was formerly classified as critically endangered. However, the saigas have exp... | Antelope | Wikipedia | 335 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
Domestication
Domestication of animals requires certain traits in the animal that antelope do not typically display. Most species are difficult to contain in any density, due to the territoriality of the males, or in the case of oryxes (which have a relatively hierarchical social structure), an aggressive disposition; ... | Antelope | Wikipedia | 511 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
Heraldry
Antelope are a common symbol in heraldry, though they occur in a highly distorted form from nature. The heraldic antelope has the body of a stag and the tail of a lion, with serrated horns, and a small tusk at the end of its snout. This bizarre and inaccurate form was invented by European heralds in the Middle... | Antelope | Wikipedia | 185 | 48517 | https://en.wikipedia.org/wiki/Antelope | Biology and health sciences | Artiodactyla | null | vital_articles |
A highway is any public or private road or other public way on land. It includes not just major roads, but also other public roads and rights of way. In the United States, it is also used as an equivalent term to controlled-access highway, or a translation for motorway, Autobahn, autostrada, autoroute, etc.
According ... | Highway | Wikipedia | 482 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
England and Wales
The general legal definition deals with right of use, not the form of construction; this is distinct from e.g. the popular use of the word in the US. A highway is defined in English common law by a number of similarly worded definitions such as "a way over which all members of the public have the rig... | Highway | Wikipedia | 474 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Scotland
Scots law is similar to English law with regard to highways but with differing terminology and legislation. What is defined in England as a highway will often in Scotland be what is defined by s.151 Roads (Scotland) Act 1984 (but only "in this act" although other legislation could imitate) simply as a road, t... | Highway | Wikipedia | 440 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Italy was the first country in the world to build controlled-access highways reserved for fast traffic and for motor vehicles only. The Autostrada dei Laghi ("Lakes Highway"), the first built in the world, connecting Milan to Lake Como and Lake Maggiore, and now parts of the A8 and A9 highways, was devised by Piero Pu... | Highway | Wikipedia | 406 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Often reducing travel times relative to city or town streets, highways with limited access and grade separation can create increased opportunities for people to travel for business, trade or pleasure and also provide trade routes for goods. Highways can reduce commute and other travel time but additional road capacity ... | Highway | Wikipedia | 401 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
In addition to providing benefits to their users, transport networks impose both positive and negative externalities on non-users. The consideration of these externalities—particularly the negative ones—is a part of transport economics. Positive externalities of transport networks may include the ability to provide eme... | Highway | Wikipedia | 455 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
High-occupancy vehicle lanes are being added to some newer/reconstructed highways in the United States and other countries around the world to encourage carpooling and mass transit. These lanes help reduce the number of cars on the highway and thus reduces pollution and traffic congestion by promoting the use of carpoo... | Highway | Wikipedia | 459 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Longest international highway The Pan-American Highway, which connects many countries in the Americas, is nearly long . The Pan-American Highway is discontinuous because there is a significant gap in it in southeastern Panama, where the rainfall is immense and the terrain is entirely unsuitable for highway constructio... | Highway | Wikipedia | 477 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Widest highway (maximum number of through lanes) Interstate 5 along a section between Interstate 805 and California State Route 56 in San Diego, California, which was completed in April 2007, is 22 lanes wide.
Highest international highway The Karakoram Highway, between Pakistan and China, is at an altitude of .
Highe... | Highway | Wikipedia | 124 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Bus lane
South Korea
In South Korea, in February 1995 a bus lane (essentially an HOV-9) was established between the northern terminus and Sintanjin for important holidays and on 1 July 2008 bus lane enforcement between Seoul and Osan (Sintanjin on weekends) became daily between 6 a.m. and 10 p.m. On 1 October this wa... | Highway | Wikipedia | 365 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
Algeria East–West Highway
Autobahns of Austria
Autoput and Autocesta
Rodovia
Avtomagistrala
Highways in Canada
Expressway
Autocesta
Dálnice
Autostrada
Autoroute
Autobahns of Germany
Aftokinitodromos
Autópálya
National Highways and Expressways
Motorway
List of highways in Israel
Autostrade o... | Highway | Wikipedia | 154 | 48519 | https://en.wikipedia.org/wiki/Highway | Technology | Road transport | null | vital_articles |
In modern usage, a sloop is a sailboat with a single mast generally having only one headsail in front of the mast and one mainsail abaft (behind) the mast. It is a type of fore-and-aft rig. The mainsail may be of any type, most often Bermuda rig, but also others, such as gaff or gunter.
In naval terminology, "sloop-of... | Sloop | Wikipedia | 459 | 48520 | https://en.wikipedia.org/wiki/Sloop | Technology | Naval transport | null | vital_articles |
A sloop's headsail may be masthead-rigged or fractional-rigged. On a masthead-rigged sloop, the forestay (on which the headsail is carried) attaches at the top of the mast. On a fractional-rigged sloop, the forestay attaches to the mast at a point below the top. A sloop may use a bowsprit, a spar that projects forward ... | Sloop | Wikipedia | 90 | 48520 | https://en.wikipedia.org/wiki/Sloop | Technology | Naval transport | null | vital_articles |
Blood vessels are the tubular structures of a circulatory system that transport blood throughout a vertebrate's body. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste and carbon dioxide away from the tissues. Some tissues such as cartilage, epithelium, an... | Blood vessel | Wikipedia | 259 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
Structure
The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins:
The inner layer, tunica intima, is the thinnest layer. It is a single layer of flat cells (simple squamous epithelium) glued by a polysaccharide intercellular matrix, surrounded by a thin layer of ... | Blood vessel | Wikipedia | 504 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
Types
There are various kinds of blood vessels:
Arteries
Elastic arteries
Distributing arteries
Arterioles
Capillaries (smallest type of blood vessels)
Venules
Veins
Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein.
Venae cavae (the two largest veins, ... | Blood vessel | Wikipedia | 466 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in inflammation in response to histamine, prostaglandins and interleukins, which leads to most of the symptoms of inflammation (swelling, redness, warmth and pain).
Constriction
Arteries—and veins to a degree—c... | Blood vessel | Wikipedia | 493 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa). In the arterial system, this is usually around 120 mmHg systolic (high pressure wave due to contraction of the heart) and 80 mmHg diastolic (low pressure wave). In contrast, pressures in the venous system are con... | Blood vessel | Wikipedia | 443 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
Blood vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to hemorrhage due to mechanical damage to the vessel endothelium. In contrast, occlusion of the blood vessel by atherosclerotic plaque, an embolised blood clot or a foreign body leads to downstream ischemia (insuffi... | Blood vessel | Wikipedia | 260 | 48530 | https://en.wikipedia.org/wiki/Blood%20vessel | Biology and health sciences | Circulatory system | Biology | vital_articles |
Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 80% of the catecholamine content in the brain. It is an amine synthesized by remov... | Dopamine | Wikipedia | 379 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Outside the central nervous system, dopamine functions primarily as a local paracrine messenger. In blood vessels, it inhibits norepinephrine release and acts as a vasodilator; in the kidneys, it increases sodium excretion and urine output; in the pancreas, it reduces insulin production; in the digestive system, it red... | Dopamine | Wikipedia | 416 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Structure
A dopamine molecule consists of a catechol structure (a benzene ring with two hydroxyl side groups) with one amine group attached via an ethyl chain. As such, dopamine is the simplest possible catecholamine, a family that also includes the neurotransmitters norepinephrine and epinephrine. The presence ... | Dopamine | Wikipedia | 509 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
L-Phenylalanine is converted into L-tyrosine by the enzyme phenylalanine hydroxylase, with molecular oxygen (O2) and tetrahydrobiopterin as cofactors. L-Tyrosine is converted into L-DOPA by the enzyme tyrosine hydroxylase, with tetrahydrobiopterin, O2, and iron (Fe2+) as cofactors. L-DOPA is converted into dopamine by ... | Dopamine | Wikipedia | 508 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
In clinical research on schizophrenia, measurements of homovanillic acid in plasma have been used to estimate levels of dopamine activity in the brain. A difficulty in this approach however, is separating the high level of plasma homovanillic acid contributed by the metabolism of norepinephrine.
Although dopamine is n... | Dopamine | Wikipedia | 472 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Inside the brain, dopamine functions as a neurotransmitter and neuromodulator, and is controlled by a set of mechanisms common to all monoamine neurotransmitters. After synthesis, dopamine is transported from the cytosol into secretory vesicles, including synaptic vesicles, small and large dense core vesicles by a solu... | Dopamine | Wikipedia | 459 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
In the brain the level of extracellular dopamine is modulated by two mechanisms: phasic and tonic transmission. Phasic dopamine release, like most neurotransmitter release in the nervous system, is driven directly by action potentials in the dopamine-containing cells. Tonic dopamine transmission occurs when small amoun... | Dopamine | Wikipedia | 419 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
The substantia nigra is a small midbrain area that forms a component of the basal ganglia. This has two parts—an input area called the pars reticulata and an output area called the pars compacta. The dopaminergic neurons are found mainly in the pars compacta (cell group A8) and nearby (group A9). In humans, the project... | Dopamine | Wikipedia | 394 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
The arcuate nucleus and the periventricular nucleus of the hypothalamus have dopamine neurons that form an important projection—the tuberoinfundibular pathway which goes to the pituitary gland, where it influences the secretion of the hormone prolactin. Dopamine is the primary neuroendocrine inhibitor of the secretion ... | Dopamine | Wikipedia | 462 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Progress in understanding the functions of the basal ganglia has been slow. The most popular hypotheses, broadly stated, propose that the basal ganglia play a central role in action selection. The action selection theory in its simplest form proposes that when a person or animal is in a situation where several behavior... | Dopamine | Wikipedia | 434 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
The second important effect of dopamine is as a "teaching" signal. When an action is followed by an increase in dopamine activity, the basal ganglia circuit is altered in a way that makes the same response easier to evoke when similar situations arise in the future. This is a form of operant conditioning, in which dopa... | Dopamine | Wikipedia | 354 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Within the brain, dopamine functions partly as a global reward signal. An initial dopamine response to a rewarding stimulus encodes information about the salience, value, and context of a reward. In the context of reward-related learning, dopamine also functions as a reward prediction error signal, that is, the degree ... | Dopamine | Wikipedia | 483 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Pleasure
While dopamine has a central role in causing "wanting," associated with the appetitive or approach behavioral responses to rewarding stimuli, detailed studies have shown that dopamine cannot simply be equated with hedonic "liking" or pleasure, as reflected in the consummatory behavioral response. Dopamine neur... | Dopamine | Wikipedia | 414 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
A clinical study from January 2019 that assessed the effect of a dopamine precursor (levodopa), dopamine antagonist (risperidone), and a placebo on reward responses to music – including the degree of pleasure experienced during musical chills, as measured by changes in electrodermal activity as well as subjective ratin... | Dopamine | Wikipedia | 381 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Dopamine does not cross the blood–brain barrier, so its synthesis and functions in peripheral areas are to a large degree independent of its synthesis and functions in the brain. A substantial amount of dopamine circulates in the bloodstream, but its functions there are not entirely clear. Dopamine is found in blood pl... | Dopamine | Wikipedia | 492 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
In the immune system dopamine acts upon receptors present on immune cells, especially lymphocytes. Dopamine can also affect immune cells in the spleen, bone marrow, and circulatory system. In addition, dopamine can be synthesized and released by immune cells themselves. The main effect of dopamine on lymphocytes is to ... | Dopamine | Wikipedia | 429 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
The pancreatic islets make up the endocrine part of the pancreas, and synthesize and secrete hormones including insulin into the bloodstream. There is evidence that the beta cells in the islets that synthesize insulin contain dopamine receptors, and that dopamine acts to reduce the amount of insulin they release. The s... | Dopamine | Wikipedia | 425 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Side effects of dopamine include negative effects on kidney function and irregular heartbeats. The LD50, or lethal dose which is expected to prove fatal in 50% of the population, has been found to be: 59 mg/kg (mouse; administered intravenously); 95 mg/kg (mouse; administered intraperitoneally); 163 mg/kg (rat; adminis... | Dopamine | Wikipedia | 438 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Parkinson's disease is an age-related disorder characterized by movement disorders such as stiffness of the body, slowing of movement, and trembling of limbs when they are not in use. In advanced stages it progresses to dementia and eventually death. The main symptoms are caused by the loss of dopamine-secreting cells ... | Dopamine | Wikipedia | 501 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Dopaminergic medications that are used to treat Parkinson's disease are sometimes associated with the development of a dopamine dysregulation syndrome, which involves the overuse of dopaminergic medication and medication-induced compulsive engagement in natural rewards like gambling and sexual activity. The latter beha... | Dopamine | Wikipedia | 469 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
A variety of addictive drugs produce an increase in reward-related dopamine activity. Stimulants such as nicotine, cocaine and methamphetamine promote increased levels of dopamine which appear to be the primary factor in causing addiction. For other addictive drugs such as the opioid heroin, the increased levels of dop... | Dopamine | Wikipedia | 344 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Psychiatrists in the early 1950s discovered that a class of drugs known as typical antipsychotics (also known as major tranquilizers), were often effective at reducing the psychotic symptoms of schizophrenia. The introduction of the first widely used antipsychotic, chlorpromazine (Thorazine), in the 1950s, led to the r... | Dopamine | Wikipedia | 472 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Attention deficit hyperactivity disorder
Altered dopamine neurotransmission is implicated in attention deficit hyperactivity disorder (ADHD), a condition associated with impaired cognitive control, in turn leading to problems with regulating attention (attentional control), inhibiting behaviors (inhibitory control), an... | Dopamine | Wikipedia | 486 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Simultaneous positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), have shown that the amount of dopamine release is dependent on the strength of conditioned fear response and is linearly coupled to learning-induced activity in the amygdala. Dopamine is generally linked to reward learning... | Dopamine | Wikipedia | 510 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Dopamine has also consistently been shown to play a role in reward learning, in all animal groups. As in all vertebrates – invertebrates such as roundworms, flatworms, molluscs and common fruit flies can all be trained to repeat an action if it is consistently followed by an increase in dopamine levels. In fruit flies,... | Dopamine | Wikipedia | 496 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Dopamine consumed in food cannot act on the brain, because it cannot cross the blood–brain barrier. However, there are also a variety of plants that contain L-DOPA, the metabolic precursor of dopamine. The highest concentrations are found in the leaves and bean pods of plants of the genus Mucuna, especially in Mucuna p... | Dopamine | Wikipedia | 492 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
Dopamine was first synthesized in 1910 by George Barger and James Ewens at Wellcome Laboratories in London, England and first identified in the human brain by Katharine Montagu in 1957. It was named dopamine because it is a monoamine whose precursor in the Barger-Ewens synthesis is 3,4-dihydroxyphenylalanine (levodopa ... | Dopamine | Wikipedia | 448 | 48548 | https://en.wikipedia.org/wiki/Dopamine | Biology and health sciences | Biochemistry and molecular biology | null | vital_articles |
In graph theory, a tree is an undirected graph in which any two vertices are connected by path, or equivalently a connected acyclic undirected graph. A forest is an undirected graph in which any two vertices are connected by path, or equivalently an acyclic undirected graph, or equivalently a disjoint union of trees.... | Tree (graph theory) | Wikipedia | 357 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
Tree
A tree is an undirected graph that satisfies any of the following equivalent conditions:
is connected and acyclic (contains no cycles).
is acyclic, and a simple cycle is formed if any edge is added to .
is connected, but would become disconnected if any single edge is removed from .
is connected and the c... | Tree (graph theory) | Wikipedia | 460 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
A (or directed tree or oriented tree or singly connected network) is a directed acyclic graph (DAG) whose underlying undirected graph is a tree. In other words, if we replace its directed edges with undirected edges, we obtain an undirected graph that is both connected and acyclic.
Some authors restrict the phrase "d... | Tree (graph theory) | Wikipedia | 499 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
In a rooted tree, the parent of a vertex is the vertex connected to on the path to the root; every vertex has a unique parent, except the root has no parent. A child of a vertex is a vertex of which is the parent. An ascendant of a vertex is any vertex that is either the parent of or is (recursively) an ascendant... | Tree (graph theory) | Wikipedia | 505 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
Properties
Every tree is a bipartite graph. A graph is bipartite if and only if it contains no cycles of odd length. Since a tree contains no cycles at all, it is bipartite.
Every tree with only countably many vertices is a planar graph.
Every connected graph G admits a spanning tree, which is a tree that contains e... | Tree (graph theory) | Wikipedia | 451 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
A more general problem is to count spanning trees in an undirected graph, which is addressed by the matrix tree theorem. (Cayley's formula is the special case of spanning trees in a complete graph.) The similar problem of counting all the subtrees regardless of size is #P-complete in the general case ().
Unlabeled tre... | Tree (graph theory) | Wikipedia | 463 | 48560 | https://en.wikipedia.org/wiki/Tree%20%28graph%20theory%29 | Mathematics | Graph theory | null | vital_articles |
Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC is to prevent collisions, organize and expedi... | Air traffic control | Wikipedia | 370 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
In the United States, air traffic control developed three divisions. The first of several air mail radio stations (AMRS) was created in 1922, after World War I, when the U.S. Post Office began using techniques developed by the U.S. Army to direct and track the movements of reconnaissance aircraft. Over time, the AMRS m... | Air traffic control | Wikipedia | 390 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
The primary method of controlling the immediate airport environment is visual observation from the airport control tower. The tower is typically a tall, windowed structure, located within the airport grounds. The air traffic controllers, usually abbreviated 'controller', are responsible for separation and efficient m... | Air traffic control | Wikipedia | 452 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Ground control (sometimes known as , GMC) is responsible for the airport areas, as well as areas not released to the airlines or other users. This generally includes all taxiways, inactive runways, holding areas, and some transitional aprons or intersections where aircraft arrive, having vacated the runway or departu... | Air traffic control | Wikipedia | 447 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Within the tower, a highly disciplined communications process between the air control and ground control is an absolute necessity. Air control must ensure that ground control is aware of any operations that will impact the taxiways, and work with the approach radar controllers to create in the arrival traffic; to all... | Air traffic control | Wikipedia | 439 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Flight data (which is routinely combined with clearance delivery) is the position that is responsible for ensuring that both controllers and pilots have the most current information: pertinent weather changes, outages, airport ground delays / ground stops, runway closures, etc. Flight data may inform the pilots using ... | Air traffic control | Wikipedia | 505 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Area control centre / en-route centre
Air traffic control also provides services to aircraft in flight between airports. Pilots fly under one of two sets of rules for separation: visual flight rules (VFR), or instrument flight rules (IFR). Air traffic controllers have different responsibilities to aircraft operating... | Air traffic control | Wikipedia | 418 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Centre controllers are responsible for issuing instructions to pilots to climb their aircraft to their assigned altitude, while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in its immediate area. Additionally, the aircraft must be placed in a flow consistent with the airc... | Air traffic control | Wikipedia | 397 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by radar, and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by aircraft, due to high terrain or distance from radar facilities. A centre may require numerous radar systems to cover the air... | Air traffic control | Wikipedia | 275 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Some air navigation service providers (e.g., Airservices Australia, the U.S. Federal Aviation Administration, Nav Canada, etc.) have implemented automatic dependent surveillance – broadcast (ADS-B) as part of their surveillance capability. This newer technology reverses the radar concept. Instead of radar 'finding' a... | Air traffic control | Wikipedia | 441 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Flight traffic mapping
The mapping of flights in real-time is based on the air traffic control system, and volunteer ADS-B receivers. In 1991, data on the location of aircraft was made available by the Federal Aviation Administration to the airline industry. The National Business Aviation Association (NBAA), the Gene... | Air traffic control | Wikipedia | 276 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
The day-to-day problems faced by the air traffic control system are primarily related to the volume of air traffic demand placed on the system, and weather. Several factors dictate the amount of traffic that can land at an airport in a given amount of time. Each landing aircraft must touch down, slow, and exit the ru... | Air traffic control | Wikipedia | 474 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
In Area Control Centres, a major weather problem is thunderstorms, which present a variety of hazards to aircraft. Airborne aircraft will deviate around storms, reducing the capacity of the en-route system, by requiring more space per aircraft, or causing congestion, as many aircraft try to move through a single hole ... | Air traffic control | Wikipedia | 363 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Call signs
A prerequisite to safe air traffic separation is the assignment and use of distinctive call signs. These are permanently allocated by ICAO on request, usually to scheduled flights, and some air forces and other military services for military flights. There are written call signs with a two or three letter ... | Air traffic control | Wikipedia | 342 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Before around 1980, International Air Transport Association (IATA) and ICAO were using the same two-letter call signs. Due to the larger number of new airlines after deregulation, the ICAO established the three-letter call signs as mentioned above. The IATA call signs are currently used in aerodromes on the announcem... | Air traffic control | Wikipedia | 462 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Usually, a flight data processing system manages all the flight plan related data, incorporating, in a low or high degree, the information of the track once the correlation between them (flight plan and track) is established. All this information is distributed to modern operational display systems, making it availabl... | Air traffic control | Wikipedia | 175 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Some tools are available in different domains to help the controller further:
Flight data processing systems: this is the system (usually one per centre) that processes all the information related to the flight (the flight plan), typically in the time horizon from gate to gate (airport departure / arrival gates). It u... | Air traffic control | Wikipedia | 445 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Passive final approach spacing tool (pFAST): a CTAS tool, provides runway assignment and sequence number advisories to terminal controllers to improve the arrival rate at congested airports. pFAST was deployed and operational at five US TRACONs before being cancelled. NASA research included an active FAST capability ... | Air traffic control | Wikipedia | 466 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
In Europe, several MTCD tools are available: (National Air Traffic Services), VAFORIT (Deutsche Flugsicherung), new FDPS (Maastricht Upper Area Control). The Single European Sky ATM Research (SESAR) programme should soon launch new MTCD concepts.
URET and MTCD provide conflict advisories up to 30 minutes in advance, ... | Air traffic control | Wikipedia | 376 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
The electronic flight strip system (e-strip): a system of electronic flight strips replacing the existing paper strips is being used by several service providers, such as Nav Canada, MASUAC, DFS, DECEA. E-strips allows controllers to manage electronic flight data online without paper strips, reducing the need for manu... | Air traffic control | Wikipedia | 342 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Azerbaijan – AzərAeroNaviqasiya
Albania – Albcontrol
Algeria – Etablissement National de la Navigation Aérienne (ENNA)
Argentina – Empresa Argentina de Navegación Aérea (EANA)
Armenia – Armenian Air Traffic Services (ARMATS)
Australia – Airservices Australia (government owned corporation) and Royal Australian Air Force... | Air traffic control | Wikipedia | 503 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Fiji – Fiji Airports (fully owned government commercial company)
Finland – Finavia
France – Direction Générale de l'Aviation Civile (DGAC): Direction des Services de la Navigation Aérienne (DSNA) (government body)
Georgia – SAKAERONAVIGATSIA, Ltd. (Georgian Air Navigation)
Germany – Deutsche Flugsicherung (German ATC –... | Air traffic control | Wikipedia | 509 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Romania – Romanian Air Traffic Services Administration (ROMATSA)
Russia – Federal State Unitary Enterprise (State ATM Corporation)
Saudi Arabia – Saudi Air Navigation Services (SANS)
Seychelles – Seychelles Civil Aviation Authority (SCAA)
Singapore – Civil Aviation Authority of Singapore (CAAS)
Serbia – Serbia and Mont... | Air traffic control | Wikipedia | 321 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Proposed changes
In the United States, some alterations to traffic control procedures are being examined:
The Next Generation Air Transportation System examines how to overhaul the United States national airspace system.
Free flight is a developing air traffic control method that uses no centralised control (e.g. air t... | Air traffic control | Wikipedia | 358 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
Privatisation
Many countries have also privatised or corporatised their air navigation service providers. There are several models that can be used for ATC service providers. The first is to have the ATC services be part of a government agency as is currently the case in the United States. The problem with this mode... | Air traffic control | Wikipedia | 401 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
The Canadian system is the one most often used as a model by proponents of privatisation. Air traffic control privatisation has been successful in Canada with the creation of Nav Canada, a private non-profit organisation which has reduced costs, and has allowed new technologies to be deployed faster due to the elimina... | Air traffic control | Wikipedia | 326 | 48563 | https://en.wikipedia.org/wiki/Air%20traffic%20control | Technology | Aviation | null | vital_articles |
In number theory, a Gaussian integer is a complex number whose real and imaginary parts are both integers. The Gaussian integers, with ordinary addition and multiplication of complex numbers, form an integral domain, usually written as or
Gaussian integers share many properties with integers: they form a Euclidean ... | Gaussian integer | Wikipedia | 411 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null | vital_articles |
Gaussian integers have a Euclidean division (division with remainder) similar to that of integers and polynomials. This makes the Gaussian integers a Euclidean domain, and implies that Gaussian integers share with integers and polynomials many important properties such as the existence of a Euclidean algorithm for comp... | Gaussian integer | Wikipedia | 460 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null | vital_articles |
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