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Most bees are polylectic (generalist) meaning they collect pollen from a range of flowering plants, but some are oligoleges (specialists), in that they only gather pollen from one or a few species or genera of closely related plants. In Melittidae and Apidae we also find a few genera that are highly specialized for collecting plant oils both in addition to, and instead of, nectar, which is mixed with pollen as larval food. Male orchid bees in some species gather aromatic compounds from orchids, which is one of the few cases where male bees are effective pollinators. Bees are able to sense the presence of desirable flowers through ultraviolet patterning on flowers, floral odors, and even electromagnetic fields. Once landed, a bee then uses nectar quality and pollen taste to determine whether to continue visiting similar flowers.
In rare cases, a plant species may only be effectively pollinated by a single bee species, and some plants are endangered at least in part because their pollinator is also threatened. But, there is a pronounced tendency for oligolectic bees to be associated with common, widespread plants visited by multiple pollinator species. For example, the creosote bush in the arid parts of the United States southwest is associated with some 40 oligoleges.
As mimics and models
Many bees are aposematically colored, typically orange and black, warning of their ability to defend themselves with a powerful sting. As such they are models for Batesian mimicry by non-stinging insects such as bee-flies, robber flies and hoverflies, all of which gain a measure of protection by superficially looking and behaving like bees.
Bees are themselves Müllerian mimics of other aposematic insects with the same color scheme, including wasps, lycid and other beetles, and many butterflies and moths (Lepidoptera) which are themselves distasteful, often through acquiring bitter and poisonous chemicals from their plant food. All the Müllerian mimics, including bees, benefit from the reduced risk of predation that results from their easily recognized warning coloration.
Bees are also mimicked by plants such as the bee orchid which imitates both the appearance and the scent of a female bee; male bees attempt to mate (pseudocopulation) with the furry lip of the flower, thus pollinating it.
As brood parasites | Bee | Wikipedia | 480 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Brood parasites occur in several bee families including the apid subfamily Nomadinae. Females of these species lack pollen collecting structures (the scopa) and do not construct their own nests. They typically enter the nests of pollen collecting species, and lay their eggs in cells provisioned by the host bee. When the "cuckoo" bee larva hatches, it consumes the host larva's pollen ball, and often the host egg also. In particular, the Arctic bee species, Bombus hyperboreus is an aggressive species that attacks and enslaves other bees of the same subgenus. However, unlike many other bee brood parasites, they have pollen baskets and often collect pollen.
In Southern Africa, hives of African honeybees (A. mellifera scutellata) are being destroyed by parasitic workers of the Cape honeybee, A. m. capensis. These lay diploid eggs ("thelytoky"), escaping normal worker policing, leading to the colony's destruction; the parasites can then move to other hives.
The cuckoo bees in the Bombus subgenus Psithyrus are closely related to, and resemble, their hosts in looks and size. This common pattern gave rise to the ecological principle "Emery's rule". Others parasitize bees in different families, like Townsendiella, a nomadine apid, two species of which are cleptoparasites of the dasypodaid genus Hesperapis, while the other species in the same genus attacks halictid bees.
Nocturnal bees
Four bee families (Andrenidae, Colletidae, Halictidae, and Apidae) contain some species that are crepuscular. Most are tropical or subtropical, but some live in arid regions at higher latitudes. These bees have greatly enlarged ocelli, which are extremely sensitive to light and dark, though incapable of forming images. Some have refracting superposition compound eyes: these combine the output of many elements of their compound eyes to provide enough light for each retinal photoreceptor. Their ability to fly by night enables them to avoid many predators, and to exploit flowers that produce nectar only or also at night.
Predators, parasites and pathogens | Bee | Wikipedia | 456 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Vertebrate predators of bees include bee-eaters, shrikes and flycatchers, which make short sallies to catch insects in flight. Swifts and swallows fly almost continually, catching insects as they go. The honey buzzard attacks bees' nests and eats the larvae. The greater honeyguide interacts with humans by guiding them to the nests of wild bees. The humans break open the nests and take the honey and the bird feeds on the larvae and the wax. Among mammals, predators such as the badger dig up bumblebee nests and eat both the larvae and any stored food.
Specialist ambush predators of visitors to flowers include crab spiders, which wait on flowering plants for pollinating insects; predatory bugs, and praying mantises, some of which (the flower mantises of the tropics) wait motionless, aggressive mimics camouflaged as flowers. Beewolves are large wasps that habitually attack bees; the ethologist Niko Tinbergen estimated that a single colony of the beewolf Philanthus triangulum might kill several thousand honeybees in a day: all the prey he observed were honeybees. Other predatory insects that sometimes catch bees include robber flies and dragonflies. Honey bees are affected by parasites including tracheal and Varroa mites. However, some bees are believed to have a mutualistic relationship with mites.
Some mites of genus Tarsonemus are associated with bees. They live in bee nests and ride on adult bees for dispersal. They are presumed to feed on fungi, nest materials or pollen. However, the impact they have on bees remains uncertain.
Relationship with humans
In mythology and folklore
Homer's Hymn to Hermes describes three bee-maidens with the power of divination and thus speaking truth, and identifies the food of the gods as honey. Sources associated the bee maidens with Apollo and, until the 1980s, scholars followed Gottfried Hermann (1806) in incorrectly identifying the bee-maidens with the Thriae. Honey, according to a Greek myth, was discovered by a nymph called Melissa ("Bee"); and honey was offered to the Greek gods from Mycenean times. Bees were also associated with the Delphic oracle and the prophetess was sometimes called a bee. | Bee | Wikipedia | 464 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The image of a community of honey bees has been used from ancient to modern times, in Aristotle and Plato; in Virgil and Seneca; in Erasmus and Shakespeare; Tolstoy, and by political and social theorists such as Bernard Mandeville and Karl Marx as a model for human society. In English folklore, bees would be told of important events in the household, in a custom known as "Telling the bees".
In art and literature
Some of the oldest examples of bees in art are rock paintings in Spain which have been dated to 15,000 BC.
W. B. Yeats's poem The Lake Isle of Innisfree (1888) contains the couplet "Nine bean rows will I have there, a hive for the honey bee, / And live alone in the bee loud glade." At the time he was living in Bedford Park in the West of London. Beatrix Potter's illustrated book The Tale of Mrs Tittlemouse (1910) features Babbity Bumble and her brood (pictured). Kit Williams' treasure hunt book The Bee on the Comb (1984) uses bees and beekeeping as part of its story and puzzle. Sue Monk Kidd's The Secret Life of Bees (2004), and the 2009 film starring Dakota Fanning, tells the story of a girl who escapes her abusive home and finds her way to live with a family of beekeepers, the Boatwrights.
Bees have appeared in movies, such as Jerry Seinfeld's animated Bee Movie, or Dave Goulson's A Sting in the Tale (2014). The playwright Laline Paull's fantasy The Bees (2015) tells the tale of a hive bee named Flora 717 from hatching onwards.
Beekeeping
Humans have kept honey bee colonies, commonly in hives, for millennia. Depictions of humans collecting honey from wild bees date to 15,000 years ago; efforts to domesticate them are shown in Egyptian art around 4,500 years ago. Simple hives and smoke were used. | Bee | Wikipedia | 410 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Among Classical Era authors, beekeeping with the use of smoke is described in Aristotle's History of Animals Book 9. The account mentions that bees die after stinging; that workers remove corpses from the hive, and guard it; castes including workers and non-working drones, but "kings" rather than queens; predators including toads and bee-eaters; and the waggle dance, with the "irresistible suggestion" of ("", it waggles) and ("", they watch). Beekeeping is described in detail by Virgil in his Georgics; it is mentioned in his Aeneid, and in Pliny's Natural History.
From the 18th century, European understanding of the colonies and biology of bees allowed the construction of the moveable comb hive so that honey could be harvested without destroying the colony.
As commercial pollinators
Bees play an important role in pollinating flowering plants, and are the major type of pollinator in many ecosystems that contain flowering plants. It is estimated that one third of the human food supply depends on pollination by insects, birds and bats, most of which is accomplished by bees, whether wild or domesticated.
Since the 1970s, there has been a general decline in the species richness of wild bees and other pollinators, probably attributable to stress from increased parasites and disease, the use of pesticides, and a decrease in the number of wild flowers. Climate change probably exacerbates the problem. This is a major cause of concern, as it can cause biodiversity loss and ecosystem degradation as well as increase climate change.
Contract pollination has overtaken the role of honey production for beekeepers in many countries. After the introduction of Varroa mites, feral honey bees declined dramatically in the US, though their numbers have since recovered. The number of colonies kept by beekeepers declined slightly, through urbanization, systematic pesticide use, tracheal and Varroa mites, and the closure of beekeeping businesses. In 2006 and 2007 the rate of attrition increased, and was described as colony collapse disorder. In 2010 invertebrate iridescent virus and the fungus Nosema ceranae were shown to be in every killed colony, and deadly in combination. Winter losses increased to about 1/3. Varroa mites were thought to be responsible for about half the losses. | Bee | Wikipedia | 481 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Apart from colony collapse disorder, losses outside the US have been attributed to causes including pesticide seed dressings, using neonicotinoids such as clothianidin, imidacloprid and thiamethoxam. From 2013 the European Union restricted some pesticides to stop bee populations from declining further. In 2014 the Intergovernmental Panel on Climate Change report warned that bees faced increased risk of extinction because of global warming. In 2018 the European Union decided to ban field use of all three major neonicotinoids; they remain permitted in veterinary, greenhouse, and vehicle transport usage.
Farmers have focused on alternative solutions to mitigate these problems. By raising native plants, they provide food for native bee pollinators like Lasioglossum vierecki and L. leucozonium, leading to less reliance on honey bee populations.
As food producers
Honey is a natural product produced by bees and stored for their own use, but its sweetness has always appealed to humans. Before domestication of bees was even attempted, humans were raiding their nests for their honey. Smoke was often used to subdue the bees and such activities are depicted in rock paintings in Spain dated to 15,000 BC.
Honey bees are used commercially to produce honey.
As food
Bees are considered edible insects. People in some countries eat insects, including the larvae and pupae of bees, mostly stingless species. They also gather larvae, pupae and surrounding cells, known as bee brood, for consumption. In the Indonesian dish botok tawon from Central and East Java, bee larvae are eaten as a companion to rice, after being mixed with shredded coconut, wrapped in banana leaves, and steamed.
Bee brood (pupae and larvae) although low in calcium, has been found to be high in protein and carbohydrate, and a useful source of phosphorus, magnesium, potassium, and trace minerals iron, zinc, copper, and selenium. In addition, while bee brood was high in fat, it contained no fat soluble vitamins (such as A, D, and E) but it was a good source of most of the water-soluble B vitamins including choline as well as vitamin C. The fat was composed mostly of saturated and monounsaturated fatty acids with 2.0% being polyunsaturated fatty acids.
As alternative medicine | Bee | Wikipedia | 477 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Apitherapy is a branch of alternative medicine that uses honey bee products, including raw honey, royal jelly, pollen, propolis, beeswax and apitoxin (Bee venom). The claim that apitherapy treats cancer, which some proponents of apitherapy make, remains unsupported by evidence-based medicine.
Stings
The painful stings of bees are mostly associated with the poison gland and the Dufour's gland which are abdominal exocrine glands containing various chemicals. In Lasioglossum leucozonium, the Dufour's Gland mostly contains octadecanolide as well as some eicosanolide. There is also evidence of n-triscosane, n-heptacosane, and 22-docosanolide. | Bee | Wikipedia | 161 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Hawaiian honeycreepers are a group of small birds endemic to Hawaii. They are members of the finch family Fringillidae, closely related to the rosefinches (Carpodacus), but many species have evolved features unlike those present in any other finch. Their great morphological diversity is the result of adaptive radiation in an insular environment. Many have been driven to extinction since the first humans arrived in Hawaii, with extinctions increasing over the last two centuries following European discovery of the islands, with habitat destruction and especially invasive species being the main causes.
Taxonomy
Before the introduction of molecular phylogenetic techniques, the relationship of the Hawaiian honeycreepers to other bird species was controversial. The honeycreepers were sometimes categorized as a family Drepanididae, other authorities considered them a subfamily, Drepanidinae, of Fringillidae, the finch family. The entire group was also called Drepanidini in treatments where buntings and American sparrows (Passerellidae) were included in the finch family; this term is preferred for just one subgroup of the birds today. Most recently, the entire group has been subsumed into the finch subfamily Carduelinae.
The Hawaiian honeycreepers are the sister taxon to the Carpodacus rosefinches. Their ancestors are thought to have been from Asia and diverged from Carpodacus about 7.2 million years ago, and they are thought to have first arrived and radiated on the Hawaiian Islands between 5.7-7.2 million years ago, which was roughly the same time that the islands of Ni'ihau and Kauai formed. The lineage of the recently extinct po'ouli (Melamprosops) was the most ancient of the Hawaiian honeycreeper lineages to survive to recent times, diverging about 5.7-5.8 million years ago. The lineage containing Oreomystis and Paroreomyza was the second to diverge, diverging about a million years after the po'ouli's lineage. Most of the other lineages with highly distinctive morphologies are thought to have originated in the mid-late Pliocene, after the formation of Oahu but prior to the formation of Maui. Due to this, Oahu likely played a key role in the formation of diverse morphologies among honeycreepers, allowing for cycles of colonization and speciation between Kauai and Oahu. | Hawaiian honeycreeper | Wikipedia | 496 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
A phylogenetic tree of the recent Hawaiian honeycreeper lineages is shown here. Genera or clades with question marks (?) are of controversial or uncertain taxonomic placement.
The classification of Paroreomyza and Oreomystis as sister genera and forming the second most basal group is based on genetic and molecular evidence, and has been affirmed by numerous studies; however, when morphological evidence only is used, Paroreomyza is instead the second most basal genus, with Oreomystis being the third most basal genus and more closely allied with the derived Hawaiian honeycreepers, as Oreomystis shares traits with the derived honeycreepers, such as a squared-off tongue and a distinct musty odor, that Paroreomyza does not. This does not align with the genetic evidence supporting Paroreomyza and Oreomystis as sister genera, and it would be seemingly impossible for only Paroreomyza to have lost the distinctive traits but Oreomystis and all core honeycreepers to have retained or convergently evolved them, thus presenting a taxonomic conundrum.
Viridonia (containing the greater ʻamakihi) may be associated with or even synonymous with the genus Aidemedia (containing the prehistoric icterid-like and sickle-billed gapers), and has the most debated taxonomy; it was long classified within the "greater Hemignathus" radiation (a now-paraphyletic grouping containing species formerly lumped within Hemignathus, including Hemignathus, Akialoa, and Chlorodrepanis) and while some sources speculate it as being sister to Chlorodrepanis (containing the lesser ʻamakihis), other sources speculate it may be a sister genus to the genus Loxops (containing the 'akepas, ʻakekeʻe and ʻalawī).
Characteristics
Nearly all species of Hawaiian honeycreepers have been noted as having a unique odor to their plumage, described by many researchers as "rather like that of old canvas tents". | Hawaiian honeycreeper | Wikipedia | 419 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Today, the flowers of the native ōhia (Metrosideros polymorpha) are favored by a number of nectarivorous honeycreepers. The wide range of bill shapes in this group, from thick, finch-like bills to slender, down-curved bills for probing flowers have arisen through adaptive radiation, where an ancestral finch has evolved to fill a large number of ecological niches. Some 20 species of Hawaiian honeycreeper have become extinct in the recent past, and many more in earlier times, following the arrival of humans who introduced non-native animals (ex: rats, pigs, goats, cows) and converted habitat for agriculture.
Genera and species
The term "prehistoric" indicates species that became extinct between the initial human settlement of Hawaii (i.e., from the late 1st millennium AD on) and European contact in 1778.
Subfamily Carduelinae | Hawaiian honeycreeper | Wikipedia | 178 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Drepanidini
Genus Aidemedia Olson & James, 1991 – straight thin bills, insectivores
Aidemedia chascax Olson & James, 1991 – Oahu icterid-like gaper (prehistoric)
Aidemedia lutetiae Olson & James, 1991 – Maui Nui icterid-like gaper (prehistoric)
Aidemedia zanclops Olson & James, 1991 – sickle-billed gaper (prehistoric)
Genus Akialoa Olson & James, 1995 – pointed, long and down-curved bills, insectivorous or nectarivorous
Akialoa ellisiana Gray, 1859 – Oʻahu ʻakialoa (extinct, 1940)
Akialoa lanaiensis Rothschild, 1893 – Maui Nui ʻakialoa (extinct, 1892)
Akialoa stejnegeri Wilson, 1889 – Kauaʻi ʻakialoa (extinct, 1969)
Akialoa obscura Cabanis, 1889 – lesser ʻakialoa (extinct, 1940)
Akialoa upupirostris – hoopoe-billed ʻakialoa (prehistoric)
Genus Chloridops Wilson, 1888 – thick-billed, hard seed (e.g. Myoporum sandwicense) specialist
Chloridops kona Wilson, 1888 – Kona grosbeak (extinct, 1894)
Chloridops regiskongi – King Kong grosbeak (prehistoric)
Chloridops wahi – wahi grosbeak (prehistoric)
Genus Chlorodrepanis Olson & James, 1995 – pointed bills, insectivorous and nectarivorous
Chlorodrepanis stejnegeri Pratt, 1989 – Kauaʻi ʻamakihi
Chlorodrepanis flava Bloxam, 1827 – Oʻahu ʻamakihi
Chlorodrepanis virens Cabanis, 1851 – Hawaiʻi ʻamakihi
Genus Ciridops Newton, 1892 – finch-like, fed on fruit of Pritchardia species
Ciridops anna Dole, 1879 – ʻula-ʻai-hāwane (extinct, 1892 or 1937)
Ciridops tenax Olson & James, 1991 stout-legged finch (prehistoric)
Genus Drepanis Temminck, 1820 – down-curved bills, nectarivores
Drepanis funerea Newton, 1894 – black mamo (extinct, 1907) | Hawaiian honeycreeper | Wikipedia | 493 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Drepanis pacifica Gmelin, 1788 – Hawaiʻi mamo (extinct, 1898)
Drepanis coccinea Forster, 1780 – ʻiʻiwi
Genus Dysmorodrepanis Perkins, 1919 – pincer-like bill, possibly snail specialist
Dysmorodrepanis munroi Perkins, 1919 – Lanaʻi hookbill (extinct, 1918)
Genus Hemignathus Lichtenstein, 1839 – pointed or long and down-curved bills, insectivorous
Hemignathus affinis – Maui nukupuʻu (extinct, 1995–1998)
Hemignathus hanapepe – Kauaʻi nukupuʻu (extinct, 1998)
Hemignathus lucidus – Oʻahu nukupuʻu (extinct, 1837)
Hemignathus vorpalis James & Olson, 2003 – giant nukupu'u (prehistoric)
Hemignathus wilsoni Rothschild, 1893 – ʻakiapolaʻau
Genus Himatione – thin-billed, nectarivorous
Himatione sanguinea Gmelin, 1788 – ʻapapane
Himatione fraithii – Laysan honeycreeper (extinct, 1923)
Genus Loxioides Oustalet, 1877 – finch-like, Fabales seed specialists
Loxioides bailleui Oustalet, 1877 – palila
Loxioides kikuichi Olson & James, 2006 – Kaua'i palila (prehistoric, possibly survived to the early 18th century)
Genus Loxops – small pointed bills with the tips slightly crossed, insectivorous
Loxops caeruleirostris Wilson, 1890 – ‘akeke‘e
Loxops coccineus Gmelin, 1789 – Hawaiʻi ʻakepa
Loxops ochraceus Rothschild, 1893 - Maui ʻakepa (extinct, 1988)
Loxops wolstenholmei Rothschild, 1895 – Oʻahu ʻakepa (extinct, 1990s)
Loxops mana Wilson, 1891 – Hawaiʻi creeper
Genus Magumma - small pointed bills, insectivorous and nectarivorous
Magumma parva Stejneger, 1887 - ʻanianiau
Genus Melamprosops Casey & Jacobi, 1974 – short pointed bill, insectivorous and snail specialist
Melamprosops phaeosoma Casey & Jacobi, 1974 – poʻouli (extinct, 2004)
Genus Oreomystis Wilson, 1891 – short pointed bills, insectivorous | Hawaiian honeycreeper | Wikipedia | 510 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Oreomystis bairdi Stejneger, 1887 – ʻakikiki
Genus Orthiospiza – large weak bill, possibly soft seed or fruit specialist?
Orthiospiza howarthi James & Olson, 1991 - highland finch (prehistoric)
Genus Palmeria Rothschild, 1893 – thin-billed, nectarivorous, favors Metrosideros polymorpha
Palmeria dolei Wilson, 1891 – ʻakohekohe
Genus Paroreomyza – short pointed bills, insectivorous
Paroreomyza maculata Cabanis, 1850 – Oʻahu ʻalauahio (possibly extinct, early 1990s?)
Paroreomyza flammea (Wilson, 1889) – kākāwahie (extinct, 1963)
Paroreomyza
Paroreomyza Wilson, 1890 – Lana'i 'alauahio (extinct, 1937)
Paroreomyza newtoni (Rothschild, 1893) – Maui ‘alauahio
Genus Pseudonestor – parrot-like bill, probes wood for insect larvae
Pseudonestor xanthophrys Rothschild, 1893 – Maui parrotbill or kiwikiu
Genus Psittirostra – slightly hooked bill, Freycinetia arborea fruit specialist
Psittirostra psittacea Gmelin, 1789 – ʻōʻū (probably extinct, 1998?)
Genus Rhodacanthis – large-billed, granivorous, legume specialists
Rhodacanthis flaviceps Rothschild, 1892 – lesser koa-finch (extinct, 1891)
Rhodacanthis forfex James & Olson, 2005 – scissor-billed koa-finch (prehistoric)
Rhodacanthis litotes James & Olson, 2005 – primitive koa-finch (prehistoric)
Rhodacanthis palmeri Rothschild, 1892 – greater koa-finch (extinct, 1896)
Genus Telespiza Wilson, 1890 – finch-like, granivorous, opportunistic scavengers
Telespiza cantans Wilson, 1890 – Laysan finch
Telespiza persecutrix James & Olson, 1991 – Kauaʻi finch (prehistoric)
Telespiza ultima Bryan, 1917 – Nihoa finch
Telespiza ypsilon James & Olson, 1991 – Maui Nui finch (prehistoric)
Genus Vangulifer – flat rounded bills, possibly caught flying insects
Vangulifer mirandus – strange-billed finch (prehistoric) | Hawaiian honeycreeper | Wikipedia | 509 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Vangulifer neophasis – thin-billed finch (prehistoric)
Genus Viridonia
Viridonia sagittirostris Rothschild, 1892 – greater ʻamakihi (extinct, 1901)
Genus Xestospiza James & Oslon, 1991 – cone-shaped bills, possibly insectivorous
Xestospiza conica James & Olson, 1991 – cone-billed finch (prehistoric)
Xestospiza fastigialis James & Olson, 1991 – ridge-billed finch (prehistoric) | Hawaiian honeycreeper | Wikipedia | 105 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Hawaiian honeycreepers were formerly classified into three tribes – Hemignathini, Psittirostrini, and Drepanidini – but they are not currently classified as such.
Conservation | Hawaiian honeycreeper | Wikipedia | 39 | 15975113 | https://en.wikipedia.org/wiki/Hawaiian%20honeycreeper | Biology and health sciences | Passerida | Animals |
Winchester measure is a set of legal standards of volume instituted in the late 15th century (1495) by King Henry VII of England and in use, with some modifications, until the present day. It consists of the Winchester bushel and its dependent quantities, the peck, (dry) gallon and (dry) quart. They would later become known as the Winchester Standards, named because the examples were kept in the city of Winchester.
Winchester measure may also refer to:
the systems of weights and measures used in the Kingdom of Wessex during the Anglo-Saxon period, later adopted as the national standards of England, as well as the physical standards (prototypes) associated with these systems of units
a set of avoirdupois weight standards dating to the mid-14th century, in particular, the 56-pound standard commissioned by King Edward III, which served as the prototype for Queen Elizabeth I's reform of the avoirdupois weight system in 1588
a type of glass bottle, usually amber, used in the drug and chemical industry, known variously as the Boston round, Winchester bottle, or Winchester quart bottle
History
During the 10th century, the capital city of the English king, Edgar, was at Winchester and, at his direction, standards of measurement were instituted. However, nothing is known of these standards except that, following the Norman Conquest, the physical standards (prototypes) were removed to London. In 1496, a law of King Henry VII instituted the bushel that would later come to be known by the name "Winchester".
In 1588 Queen Elizabeth I, while reforming the English weight system (which, at the time, included no less than three different pounds going by the name "avoirdupois") based the new Exchequer standard on an ancient set of bronze weights found at Winchester and dating to the reign of Edward III.
These incidents have led to the widespread belief that the Winchester units of dry capacity measure, namely, the bushel and its dependent quantities the peck, gallon and quart, must have originated in the time of King Edgar. However, contemporary scholarship can find no evidence for the existence of any these units in Britain prior to the Norman Conquest. Furthermore, all of the units associated with Winchester measure (quarter, bushel, peck, gallon, pottle, quart, pint) have names of French derivation, at least suggestive of Norman origin.
Capacity measures in the Anglo-Saxon period | Winchester measure | Wikipedia | 492 | 15982783 | https://en.wikipedia.org/wiki/Winchester%20measure | Physical sciences | Measurement systems | Basics and measurement |
Prior to the Norman Conquest, the following units of capacity measure were used: sester, amber, mitta, coomb, and seam. A statute of 1196 (9 Ric. 1. c. 27) decreed: It is established that all measures of the whole of England be of the same amount, as well of corn as of vegetables and of like things, to wit, one good horse load; and that this measure be level as well in cities and boroughs as without. This appears to be a description of the seam, which would later be equated with the quarter. The word seam is of Latin derivation (from the Vulgar Latin sauma = packsaddle). Some of the other units are likewise of Latin derivation, sester from sextarius, amber from amphora. The sester could thus be taken as roughly a pint, the amber a bushel. However, the values of these units, as well as their relationships to one another, varied considerably over the centuries so that no clear definitions are possible except by specifying the time and place in which the units were used.
After the Norman Conquest
One of the earliest documents defining the gallon, bushel and quarter is the Assize of Weights and Measures, also known as the Tractatus de Ponderibus et Mensuris, sometimes attributed to Henry III or Edward I, but nowadays generally listed under Ancient Statutes of Uncertain Date and presumed to be from −1305. It states, By Consent of the whole Realm the King’s Measure was made, so that an English Penny, which is called the Sterling, round without clipping, shall weigh Thirty-two Grains of Wheat dry in the midst of the Ear; Twenty-pence make an Ounce; and Twelve Ounces make a Pound, and Eight Pounds make a Gallon of Wine; and Eight Gallons of Wine make a Bushel of London; which is the Eighth Part of a Quarter. | Winchester measure | Wikipedia | 392 | 15982783 | https://en.wikipedia.org/wiki/Winchester%20measure | Physical sciences | Measurement systems | Basics and measurement |
In 1496, An Act for Weights and Measures (12 Hen. 7. c. 5) stated That the Measure of a Bushel contain Gallons of Wheat, and that every Gallon contain of Wheat of Troy Weight, and every Pound contain Ounces of Troy Weight, and every Ounce contain Sterlings, and every Sterling be of the Weight of Corns of Wheat that grew in the Midst of the Ear of Wheat, according to the old Laws of this Land. Even though this bushel does not quite fit the description of the Winchester bushel, the national standard prototype bushel constructed the following year (and still in existence) is near enough to a Winchester bushel that it is generally considered the first, even though it was not known by that name at the time.
The Winchester bushel is first mentioned by name in a statute of 1670 entitled An Act for ascertaining the Measures of Corn and Salt (22 Cha. 2. c. 8) which states, And that if any person or persons after the time aforesaid shall sell any sort of corn or grain, ground or unground, or any kind of salt, usually sold by the bushel, either in open market, or any other place, by any other bushel or measure than that which is agreeable to the standard, marked in his Majesty's exchequer, commonly called the Winchester measure, containing eight gallons to the bushel, and no more or less, and the said bushel strucken even by the wood or brim of the same by the seller, and sealed as this act directs, he or they shall forfeit for every such offence the sum of forty shillings.
It is first defined in law by a statute of 1696–97 (8 & 9 Will. 3. c. 22 ss. 9 & 45) And to the End all His Majesties Subjects may know the Content of the Winchester Bushell whereunto this Act refers, and that all Disputes and Differences about Measure may be prevented for the future, it is hereby declared that every round Bushel with a plain and even Bottom, being Eighteen Inches and a Halfe wide throughout, & Eight Inches deep, shall be esteemed a legal Winchester Bushel according to the Standard in His Majesty's Exchequer. | Winchester measure | Wikipedia | 459 | 15982783 | https://en.wikipedia.org/wiki/Winchester%20measure | Physical sciences | Measurement systems | Basics and measurement |
In 1824 a new Act was passed in which the gallon was defined as the volume of ten pounds of pure water at with the other units of volume changing accordingly. The "Winchester bushel", which was some 3% smaller than the new bushel (eight new gallons), was retained in the English grain trade until formally abolished in 1835. In 1836, the United States Department of the Treasury formally adopted the Winchester bushel as the standard for dealing in grain and, defined as 2,150.42 cubic inches, it remains so today.
While the United Kingdom and the British Colonies changed to "Imperial" measures in 1826, the US continued to use Winchester measures and still does.
Measures in the city museum
None of Edgar's standard measures, which were probably made of wood, remain, but the city's copy of the standard yard, although stamped with the official mark of Elizabeth I, may date from the early twelfth century, during the reign of Henry I. Preserved standard weights date from 1357, and although the original bushel is lost, a standard bushel, gallon and quart made of bronze, issued in 1497 and stamped with the mark of Henry VII are still held. | Winchester measure | Wikipedia | 241 | 15982783 | https://en.wikipedia.org/wiki/Winchester%20measure | Physical sciences | Measurement systems | Basics and measurement |
Data sharing is the practice of making data used for scholarly research available to other investigators. Many funding agencies, institutions, and publication venues have policies regarding data sharing because transparency and openness are considered by many to be part of the scientific method.
A number of funding agencies and science journals require authors of peer-reviewed papers to share any supplemental information (raw data, statistical methods or source code) necessary to understand, develop or reproduce published research. A great deal of scientific research is not subject to data sharing requirements, and many of these policies have liberal exceptions. In the absence of any binding requirement, data sharing is at the discretion of the scientists themselves. In addition, in certain situations governments and institutions prohibit or severely limit data sharing to protect proprietary interests, national security, and subject/patient/victim confidentiality. Data sharing may also be restricted to protect institutions and scientists from use of data for political purposes.
Data and methods may be requested from an author years after publication. In order to encourage data sharing and prevent the loss or corruption of data, a number of funding agencies and journals established policies on data archiving. Access to publicly archived data is a recent development in the history of science made possible by technological advances in communications and information technology. To take full advantage of modern rapid communication may require consensual agreement on the criteria underlying mutual recognition of respective contributions. Models recognized for improving the timely sharing of data for more effective response to emergent infectious disease threats include the data sharing mechanism introduced by the GISAID Initiative.
Despite policies on data sharing and archiving, data withholding still happens. Authors may fail to archive data or they only archive a portion of the data. Failure to archive data alone is not data withholding. When a researcher requests additional information, an author sometimes refuses to provide it. When authors withhold data like this, they run the risk of losing the trust of the science community. A 2022 study identified about 3500 research papers which contained statements that the data was available, but upon request and further seeking the data, found that it was unavailable for 94% of papers.
Data sharing may also indicate the sharing of personal information on a social media platform.
U.S. government policies | Data sharing | Wikipedia | 444 | 10806718 | https://en.wikipedia.org/wiki/Data%20sharing | Physical sciences | Science basics | Basics and measurement |
Federal law
On August 9, 2007, President Bush signed the America COMPETES Act (or the "America Creating Opportunities to Meaningfully Promote Excellence in Technology, Education, and Science Act") requiring civilian federal agencies to provide guidelines, policies and procedures, to facilitate and optimize the open exchange of data and research between agencies, the public and policymakers. See Section 1009.
NIH data sharing policy
The NIH Final Statement of Sharing of Research Data says:
NSF Policy from Grant General Conditions
Office of Research Integrity
Allegations of misconduct in medical research carry severe consequences. The United States Department of Health and Human Services established an office to oversee investigations of allegations of misconduct, including data withholding. The website defines the mission:
Ideals in data sharing
Some research organizations feel particularly strongly about data sharing. Stanford University's WaveLab has a philosophy about reproducible research and disclosing all algorithms and source code necessary to reproduce the research. In a paper titled "WaveLab and Reproducible Research," the authors describe some of the problems they encountered in trying to reproduce their own research after a period of time. In many cases, it was so difficult they gave up the effort. These experiences are what convinced them of the importance of disclosing source code. The philosophy is described:
The idea is: An article about computational science in a scientific publication is not the scholarship itself, it is merely advertising of the scholarship. The actual scholarship is the complete software development environment and the complete set of instructions which generated the figures.
The Data Observation Network for Earth (DataONE) and Data Conservancy are projects supported by the National Science Foundation to encourage and facilitate data sharing among research scientists and better support meta-analysis. In environmental sciences, the research community is recognizing that major scientific advances involving integration of knowledge in and across fields will require that researchers overcome not only the technological barriers to data sharing but also the historically entrenched institutional and sociological barriers. Dr. Richard J. Hodes, director of the National Institute on Aging has stated, "the old model in which researchers jealously guarded their data is no longer applicable". | Data sharing | Wikipedia | 428 | 10806718 | https://en.wikipedia.org/wiki/Data%20sharing | Physical sciences | Science basics | Basics and measurement |
The Alliance for Taxpayer Access is a group of organizations that support open access to government sponsored research. The group has expressed a "Statement of Principles" explaining why they believe open access is important. They also list a number of international public access policies. This is no more so than in timely communication of essential information to effectively respond to health emergencies. While public domain archives have been embraced for depositing data, mainly post formal publication, they have failed to encourage rapid data sharing during health emergencies, among them the Ebola and Zika, outbreaks. More clearly defined principles are required to recognize the interests of those generating the data while permitting free, unencumbered access to and use of the data (pre-publication) for research and practical application, such as those adopted by the GISAID Initiative to counter emergent threats from influenza.
International policies
Australia
Austria
Europe — Commission of European Communities
Germany
United Kingdom
'Omic Data Sharing — a list of policies of major science funders FAIRsharing.org Catalogue of Data Policies
India -National Data Sharing and Accessibility Policy – Government of India
Data sharing problems in academia
Genetics
Withholding of data has become so commonplace in genetics that researchers at Massachusetts General Hospital published a journal article on the subject. The study found that "Because they were denied access to data, 28% of geneticists reported that they had been unable to confirm published research."
Psychology
In a 2006 study, it was observed that, of 141 authors of a publication from the American Psychological Association (APA) empirical articles, 103 (73%) did not respond with their data over a 6-month period. In a follow-up study published in 2015, it was found that 246 out of 394 contacted authors of papers in APA journals did not share their data upon request (62%).
Archaeology
A 2018 study reported on study of a random sample of 48 articles published during February–May 2017 in the Journal of Archaeological Science which found openly available raw data for 18 papers (53%), with compositional and dating data being the most frequently shared types. The same study also emailed authors of articles on experiments with stone artifacts that were published during 2009 and 2015 to request data relating to the publications. They contacted the authors of 23 articles and received 15 replies, resulting in a 70% response rate. They received five responses that included data files, giving an overall sharing rate of 20%. | Data sharing | Wikipedia | 483 | 10806718 | https://en.wikipedia.org/wiki/Data%20sharing | Physical sciences | Science basics | Basics and measurement |
Scientists in training
A study of scientists in training indicated many had already experienced data withholding. This study has given rise to the fear the future generation of scientists will not abide by the established practices.
Differing approaches in different fields
Requirements for data sharing are more commonly imposed by institutions, funding agencies, and publication venues in the medical and biological sciences than in the physical sciences. Requirements vary widely regarding whether data must be shared at all, with whom the data must be shared, and who must bear the expense of data sharing.
Funding agencies such as the NIH and NSF tend to require greater sharing of data, but even these requirements tend to acknowledge the concerns of patient confidentiality, costs incurred in sharing data, and the legitimacy of the request. Private interests and public agencies with national security interests (defense and law enforcement) often discourage sharing of data and methods through non-disclosure agreements.
Data sharing poses specific challenges in participatory monitoring initiatives, for example where forest communities collect data on local social and environmental conditions. In this case, a rights-based approach to the development of data-sharing protocols can be based on principles of free, prior and informed consent, and prioritise the protection of the rights of those who generated the data, and/or those potentially affected by data-sharing. | Data sharing | Wikipedia | 261 | 10806718 | https://en.wikipedia.org/wiki/Data%20sharing | Physical sciences | Science basics | Basics and measurement |
The Port of Ningbo-Zhoushan is the busiest port in the world in terms of cargo tonnage. It handled 888.96 million tons of cargo in 2015. The port is located in Ningbo and Zhoushan, on the coast of the East China Sea, in Zhejiang province on the southeast end of Hangzhou Bay, across which it faces the municipality of Shanghai.
The port is at the crossroads of the north–south inland and coastal shipping route, including canals to the important inland waterway to interior China, the Yangtze River, to the north. The port consists of several ports which are Beilun (seaport), Zhenhai (estuary port), and old Ningbo harbor (inland river port).
The operator of the port, Ningbo Zhoushan Port Co., Ltd. (NZP), is a listed company, but it is 76.31% owned by state-owned Ningbo Zhoushan Port Group Co., Ltd., .
History
Ningbo Port was established in 1738. During the Tang dynasty (618–907), it was known as one of the three major seaports for foreign trade under the name "Mingzhou", along with Yangzhou and Guangzhou.
In the Song dynasty, it became one of the three major port cities for foreign trade, together with Guangzhou and Quanzhou. It was designated as one of the "Five Treaty Ports" along with Guangzhou, Xiamen, Fuzhou and Shanghai after the 1842 Treaty of Nanking that ended the First Opium War.
In 2006, the Port of Ningbo was merged with the neighboring Port of Zhoushan to form a combined cargo handling center. The combined Ningbo-Zhoushan Port handled a total cargo volume of 744,000,000 metric tons of cargo in 2012, making it the largest port in the world in terms of cargo tonnage, surpassing the Port of Shanghai for the first time.
The port is part of the 21st Century Maritime Silk Road that runs from the Chinese coast to Singapore, towards the southern tip of India to Mombasa, from there through the Red Sea via the Suez Canal to the Mediterranean, there to the Upper Adriatic region to the northern Italian hub of Trieste with its connections to Central Europe and the North Sea. | Port of Ningbo-Zhoushan | Wikipedia | 464 | 10809525 | https://en.wikipedia.org/wiki/Port%20of%20Ningbo-Zhoushan | Technology | Specific piers and ports | null |
Economic trade
The Port of Ningbo-Zhoushan is involved in economic trade with cargo shipment, raw materials and manufactured goods from as far as North and South America and Oceania. It has economic trade with over 560 ports from more than 90 countries and regions in the world. It is one of a growing number of ports in China with a cargo throughput volume exceeding 100 million tons annually.
The water quality within Ningbo-Zhoushan Port has become badly polluted over the past ten years, due to the massive scale of maritime traffic constantly in operation.
Port infrastructure
The Port of Ningbo-Zhoushan complex is a modern multi-purpose deep water port, consisting of inland, estuary, and coastal harbors. There are a total of 191 berths including 39 deep water berths with 10,000 and more tonnage.
The larger ports include a 250,000 tonnage crude oil terminal and a 200,000+ tonnage ore loading berth. There is also a purpose-built terminal for 6th generation container vessels and a 50,000 tonnage berth dedicated for liquid chemical products.
In August 2020, the Ningbo-Zhoushan Port (NZP) Group, together with Brazilian iron ore miner Vale, inaugurated the Shulanghu () grinding hub, after a collaboration that began in 2016. This was followed in November 2020 by an
() investment deal. The Zhejiang Free Trade Zone was quoted as stating that an "iron ore storage yard, with a maximum capacity of 4.1 million tonnes, an ore blending and processing facility and two shipping berths" would be built. | Port of Ningbo-Zhoushan | Wikipedia | 321 | 10809525 | https://en.wikipedia.org/wiki/Port%20of%20Ningbo-Zhoushan | Technology | Specific piers and ports | null |
A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via inhalation, injection, smoking, ingestion, absorption via a patch on the skin, suppository, or dissolution under the tongue.
In pharmacology, a drug is a chemical substance, typically of known structure, which, when administered to a living organism, produces a biological effect. A pharmaceutical drug, also called a medication or medicine, is a chemical substance used to treat, cure, prevent, or diagnose a disease or to promote well-being. Traditionally drugs were obtained through extraction from medicinal plants, but more recently also by organic synthesis. Pharmaceutical drugs may be used for a limited duration, or on a regular basis for chronic disorders.
Classification
Pharmaceutical drugs are often classified into drug classes—groups of related drugs that have similar chemical structures, the same mechanism of action (binding to the same biological target), a related mode of action, and that are used to treat the same disease. The Anatomical Therapeutic Chemical Classification System (ATC), the most widely used drug classification system, assigns drugs a unique ATC code, which is an alphanumeric code that assigns it to specific drug classes within the ATC system. Another major classification system is the Biopharmaceutics Classification System. This classifies drugs according to their solubility and permeability or absorption properties.
Psychoactive drugs are substances that affect the function of the central nervous system, altering perception, mood or consciousness. These drugs are divided into different groups such as: stimulants, depressants, antidepressants, anxiolytics, antipsychotics, and hallucinogens. These psychoactive drugs have been proven useful in treating a wide range of medical conditions including mental disorders around the world. The most widely used drugs in the world include caffeine, nicotine and alcohol, which are also considered recreational drugs, since they are used for pleasure rather than medicinal purposes. All drugs can have potential side effects. Abuse of several psychoactive drugs can cause addiction or physical dependence. Excessive use of stimulants can promote stimulant psychosis. Many recreational drugs are illicit; international treaties such as the Single Convention on Narcotic Drugs exist for the purpose of their prohibition. | Drug | Wikipedia | 487 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
Etymology
In English, the noun "drug" is thought to originate from Old French "", possibly deriving from " ()" from Middle Dutch meaning "dry (barrels)", referring to medicinal plants preserved as dry matter in barrels.
In the 1990s however, Spanish lexicographer Federico Corriente Córdoba documented the possible origin of the word in {ḥṭr} an early romanized form of the Al-Andalus language from the northwestern part of the Iberian peninsula. The term could approximately be transcribed as حطروكة or hatruka.
The term "drug" has become a skunked term with negative connotation, being used as a synonym for illegal substances like cocaine or heroin or for drugs used recreationally. In other contexts the terms "drug" and "medicine" are used interchangeably.
Efficacy
Drug action is highly specific and their effects may only be detected in certain individuals. For instance, the 10 highest-grossing drugs in the US may help only 4-25% of people. Often, the activity of a drug depends on the genotype of a patient. For example, Erbitux (cetuximab) increases the survival rate of colorectal cancer patients if they carry a particular mutation in the EGFR gene. Some drugs are specifically approved for certain genotypes. Vemurafenib is such a case which is used for melanoma patients who carry a mutation in the BRAF gene. The number of people who benefit from a drug determines if drug trials are worth carrying out, given that phase III trials may cost between $100 million and $700 million per drug. This is the motivation behind personalized medicine, that is, to develop drugs that are adapted to individual patients.
Medication
A medication or medicine is a drug taken to cure or ameliorate any symptoms of an illness or medical condition. The use may also be as preventive medicine that has future benefits but does not treat any existing or pre-existing diseases or symptoms. Dispensing of medication is often regulated by governments into three categories—over-the-counter medications, which are available in pharmacies and supermarkets without special restrictions; behind-the-counter medicines, which are dispensed by a pharmacist without needing a doctor's prescription, and prescription only medicines, which must be prescribed by a licensed medical professional, usually a physician. | Drug | Wikipedia | 487 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
In the United Kingdom, behind-the-counter medicines are called pharmacy medicines which can only be sold in registered pharmacies, by or under the supervision of a pharmacist. These medications are designated by the letter P on the label. The range of medicines available without a prescription varies from country to country. Medications are typically produced by pharmaceutical companies and are often patented to give the developer exclusive rights to produce them. Those that are not patented (or with expired patents) are called generic drugs since they can be produced by other companies without restrictions or licenses from the patent holder.
Pharmaceutical drugs are usually categorised into drug classes. A group of drugs will share a similar chemical structure, have the same mechanism of action or the same related mode of action, or target the same illness or related illnesses. The Anatomical Therapeutic Chemical Classification System (ATC), the most widely used drug classification system, assigns drugs a unique ATC code, which is an alphanumeric code that assigns it to specific drug classes within the ATC system. Another major classification system is the Biopharmaceutics Classification System. This groups drugs according to their solubility and permeability or absorption properties.
Spiritual and religious use
Some religions, particularly ethnic religions, are based completely on the use of certain drugs, known as entheogens, which are mostly hallucinogens,—psychedelics, dissociatives, or deliriants. Some entheogens include kava which can act as a stimulant, a sedative, a euphoriant and an anesthetic. The roots of the kava plant are used to produce a drink consumed throughout the cultures of the Pacific Ocean.
Some shamans from different cultures use entheogens, defined as "generating the divine within," to achieve religious ecstasy. Amazonian shamans use ayahuasca (yagé), a hallucinogenic brew, for this purpose. Mazatec shamans have a long and continuous tradition of religious use of Salvia divinorum, a psychoactive plant. Its use is to facilitate visionary states of consciousness during spiritual healing sessions. | Drug | Wikipedia | 440 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
Silene undulata is regarded by the Xhosa people as a sacred plant and used as an entheogen. Its roots are traditionally used to induce vivid (and according to the Xhosa, prophetic) lucid dreams during the initiation process of shamans, classifying it a naturally occurring oneirogen similar to the more well-known dream herb Calea ternifolia.
Peyote, a small spineless cactus, has been a major source of psychedelic mescaline and has probably been used by Native Americans for at least five thousand years. Most mescaline is now obtained from a few species of columnar cacti in particular from San Pedro and not from the vulnerable peyote.
The entheogenic use of cannabis has also been widely practised for centuries. Rastafari use marijuana (ganja) as a sacrament in their religious ceremonies.
Psychedelic mushrooms (psilocybin mushrooms), commonly called magic mushrooms or shrooms have also long been used as entheogens.
Smart drugs and designer drugs
Nootropics, also commonly referred to as "smart drugs", are drugs that are claimed to improve human cognitive abilities. Nootropics are used to improve memory, concentration, thought, mood, and learning. An increasingly used nootropic among students, also known as a study drug, is methylphenidate branded commonly as Ritalin and used for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. At high doses methylphenidate can become highly addictive. Serious addiction can lead to psychosis, anxiety and heart problems, and the use of this drug is related to a rise in suicides, and overdoses. Evidence for use outside of student settings is limited but suggests that it is commonplace. Intravenous use of methylphenidate can lead to emphysematous damage to the lungs, known as Ritalin lung. | Drug | Wikipedia | 394 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
Other drugs known as designer drugs are produced. An early example of what today would be labelled a 'designer drug' was LSD, which was synthesised from ergot. Other examples include analogs of performance-enhancing drugs such as designer steroids taken to improve physical capabilities; these are sometimes used (legally or not) for this purpose, often by professional athletes. Other designer drugs mimic the effects of psychoactive drugs. Since the late 1990s there has been the identification of many of these synthesised drugs. In Japan and the United Kingdom this has spurred the addition of many designer drugs into a newer class of controlled substances known as a temporary class drug.
Synthetic cannabinoids have been produced for a longer period of time and are used in the designer drug synthetic cannabis.
Recreational drug use
Recreational drug use is the use of a drug (legal, controlled, or illegal) with the primary intention of altering the state of consciousness through alteration of the central nervous system in order to create positive emotions and feelings. The hallucinogen LSD is a psychoactive drug commonly used as a recreational drug.
Ketamine is a drug used for anesthesia, and is also used as a recreational drug, both in powder and liquid form, for its hallucinogenic and dissociative effects.
Some national laws prohibit the use of different recreational drugs; medicinal drugs that have the potential for recreational use are often heavily regulated. However, there are many recreational drugs that are legal in many jurisdictions and widely culturally accepted.
Cannabis is the most commonly consumed controlled recreational drug in the world (as of 2012). Its use in many countries is illegal but is legally used in several countries usually with the proviso that it can only be used for personal use. It can be used in the leaf form of marijuana (grass), or in the resin form of hashish. Marijuana is a more mild form of cannabis than hashish.
There may be an age restriction on the consumption and purchase of legal recreational drugs. Some recreational drugs that are legal and accepted in many places include alcohol, tobacco, betel nut, and caffeine products, and in some areas of the world the legal use of drugs such as khat is common.
There are a number of legal intoxicants commonly called legal highs that are used recreationally. The most widely used of these is alcohol.
Administration of drugs
All drugs have a route of administration, and many can be administered by more than one. | Drug | Wikipedia | 498 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
A bolus is the administration of a medication, drug or other compound that is given to raise its concentration in blood rapdily to an effective level, regardless of the route of administration
Control of drugs
Numerous governmental offices in many countries deal with the control and supervision of drug manufacture and use, and the implementation of various drug laws. The Single Convention on Narcotic Drugs is an international treaty brought about in 1961 to prohibit the use of narcotics save for those used in medical research and treatment. In 1971, a second treaty the Convention on Psychotropic Substances had to be introduced to deal with newer recreational psychoactive and psychedelic drugs.
The legal status of Salvia divinorum varies in many countries and even in states within the United States. Where it is legislated against, the degree of prohibition also varies.
The Food and Drug Administration (FDA) in the United States is a federal agency responsible for protecting and promoting public health through the regulation and supervision of food safety, tobacco products, dietary supplements, prescription and over-the-counter medications, vaccines, biopharmaceuticals, blood transfusions, medical devices, electromagnetic radiation emitting devices, cosmetics, animal foods and veterinary drugs.
In India, the Narcotics Control Bureau (NCB), an Indian federal law enforcement and intelligence agency under the Ministry of Home Affairs, is tasked with combating drug trafficking and assisting international use of illegal substances under the provisions of Narcotic Drugs and Psychotropic Substances Act. | Drug | Wikipedia | 298 | 9311172 | https://en.wikipedia.org/wiki/Drug | Biology and health sciences | Drugs and medication | null |
Cyclohexane conformations are any of several three-dimensional shapes adopted by cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane are important prototypes of a wide range of compounds.
The internal angles of a regular, flat hexagon are 120°, while the preferred angle between successive bonds in a carbon chain is about 109.5°, the tetrahedral angle (the arc cosine of −). Therefore, the cyclohexane ring tends to assume non-planar (warped) conformations, which have all angles closer to 109.5° and therefore a lower strain energy than the flat hexagonal shape. | Cyclohexane conformation | Wikipedia | 149 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Consider the carbon atoms numbered from 1 to 6 around the ring. If we hold carbon atoms 1, 2, and 3 stationary, with the correct bond lengths and the tetrahedral angle between the two bonds, and then continue by adding carbon atoms 4, 5, and 6 with the correct bond length and the tetrahedral angle, we can vary the three dihedral angles for the sequences (2,3,4), (3,4,5), and (4,5,6). The next bond, from atom 6, is also oriented by a dihedral angle, so we have four degrees of freedom. But that last bond has to end at the position of atom 1, which imposes three conditions in three-dimensional space. If the bond angle in the chain (6,1,2) should also be the tetrahedral angle then we have four conditions. In principle this means that there are no degrees of freedom of conformation, assuming all the bond lengths are equal and all the angles between bonds are equal. It turns out that, with atoms 1, 2, and 3 fixed, there are two solutions called chair, depending on whether the dihedral angle for (1,2,3,4) is positive or negative, and these two solutions are the same under a rotation. But there is also a continuum of solutions, a topological circle where angle strain is zero, including the twist boat and the boat conformations. All the conformations on this continuum have a twofold axis of symmetry running through the ring, whereas the chair conformations do not (they have D symmetry, with a threefold axis running through the ring). It is because of the symmetry of the conformations on this continuum that it is possible to satisfy all four constraints with a range of dihedral angles at (1,2,3,4). On this continuum the energy varies because of Pitzer strain related to the dihedral angles. The twist boat has a lower energy than the boat. In order to go from the chair conformation to a twist-boat conformation or the other chair conformation, bond angles have to be changed, leading to a high-energy half-chair conformation. So the relative stabilities are: . All relative conformational energies are shown below. At room temperature the molecule can easily move among these conformations, but only chair and twist-boat can be isolated in pure form, because the others are not at local energy minima. | Cyclohexane conformation | Wikipedia | 506 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
The boat and twist-boat conformations, as said, lie along a continuum of zero angle strain. If there are substituents that allow the different carbon atoms to be distinguished, then this continuum is like a circle with six boat conformations and six twist-boat conformations between them, three "right-handed" and three "left-handed". (Which should be called right-handed is unimportant.) But if the carbon atoms are indistinguishable, as in cyclohexane itself, then moving along the continuum takes the molecule from the boat form to a "right-handed" twist-boat, and then back to the same boat form (with a permutation of the carbon atoms), then to a "left-handed" twist-boat, and then back again to the achiral boat. The passage boat⊣twist-boat⊣boat⊣twist-boat⊣boat constitutes a pseudorotation.
Coplanar carbons
Another way to compare the stability within two molecules of cyclohexane in the same conformation is to evaluate the number of coplanar carbons in each molecule. Coplanar carbons are carbons that are all on the same plane. Increasing the number of coplanar carbons increases the number of eclipsing substituents trying to form a 120°, which is unattainable due to the overlapping hydrogens. This overlap increases the overall torsional strain and decreases the stability of the conformation. Cyclohexane diminishes the torsional strain from eclipsing substituents through adopting a conformation with a lower number of nonplanar carbons. For example, if a half-chair conformation contains four coplanar carbons and another half-chair conformation contains five coplanar carbons, the conformation with four coplanar carbons will be more stable.
Principal conformers
The different conformations are called "conformers", a blend of the words "conformation" and "isomer".
Chair conformation
The chair conformation is the most stable conformer. At , 99.99% of all molecules in a cyclohexane solution adopt this conformation. | Cyclohexane conformation | Wikipedia | 455 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
The C–C ring of the chair conformation has the same shape as the 6-membered rings in the diamond cubic lattice. This can be modeled as follows. Consider a carbon atom to be a point with four half-bonds sticking out towards the vertices of a tetrahedron. Place it on a flat surface with one half-bond pointing straight up. Looking from directly above, the other three half-bonds will appear to point outwards towards the vertices of an equilateral triangle, so the bonds will appear to have an angle of 120° between them. Arrange six such atoms above the surface so that these 120° angles form a regular hexagon. Reflecting three of the atoms to be below the surface yields the desired geometry.
All carbon centers are equivalent. They alternate between two parallel planes, one containing C1, C3 and C5, and the other containing C2, C4, and C6. The chair conformation is left unchanged after a rotation of 120° about the symmetry axis perpendicular to these planes, as well as after a rotation of 60° followed by a reflection in the midpoint plane, resulting in a symmetry group of D3d. While all C–C bonds are tilted relative to the plane, diametrically opposite bonds (such as C1–C2 and C4–C5) are parallel to each other.
Six of the twelve C–H bonds are axial, pointing upwards or downwards almost parallel to the symmetry axis. The other six C–H bonds are equatorial, oriented radially outwards with an upwards or downwards tilt. Each carbon center has one axial C–H bond (pointed alternately upwards or downwards) and one equatorial C–H bond (tilted alternately downwards or upwards), enabling each X–C–C–Y unit to adopt a staggered conformation with minimal torsional strain. In this model, the dihedral angles for series of four carbon atoms going around the ring alternate between exactly +60° (gauche+) and −60° (gauche−). | Cyclohexane conformation | Wikipedia | 412 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
The chair conformation cannot be deformed without changing bond angles or lengths. It can be represented as two linked chains, C1–C2–C3–C4 and C1–C6–C5–C4, each mirroring the other, with opposite dihedral angles. The C1–C4 distance depends on the absolute value of this dihedral angle, so in a rigid model, changing one angle requires changing the other angle. If both dihedral angles change while remaining opposites of each other, it is not possible to maintain the correct C–C–C bond angles at C1 and C4.
The chair geometry is often preserved when the hydrogen atoms are replaced by halogens or other simple groups. However, when these hydrogens are substituted for a larger group, additional strain may occur due to diaxial interactions between pairs of substituents occupying the same-orientation axial position, which are typically repulsive due to steric crowding.
Boat and twist-boat conformations
The boat conformations have higher energy than the chair conformations. The interaction between the two flagpole hydrogens, in particular, generates steric strain. Torsional strain also exists between the C2–C3 and C5–C6 bonds (carbon number 1 is one of the two on a mirror plane), which are eclipsed — that is, these two bonds are parallel one to the other across a mirror plane. Because of this strain, the boat configuration is unstable (i.e. is not a local energy minimum).
The molecular symmetry is C2v.
The boat conformations spontaneously distorts to twist-boat conformations. Here the symmetry is D2, a purely rotational point group with three twofold axes. This conformation can be derived from the boat conformation by applying a slight twist to the molecule so as to remove eclipsing of two pairs of methylene groups. The twist-boat conformation is chiral, existing in right-handed and left-handed versions.
The concentration of the twist-boat conformation at room temperature is less than 0.1%, but at it can reach 30%. Rapid cooling of a sample of cyclohexane from to will freeze in a large concentration of twist-boat conformation, which will then slowly convert to the chair conformation upon heating.
Dynamics
Chair to chair | Cyclohexane conformation | Wikipedia | 478 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
The interconversion of chair conformers is called ring flipping or chair-flipping. Carbon–hydrogen bonds that are axial in one configuration become equatorial in the other, and vice versa. At room temperature the two chair conformations rapidly equilibrate. The proton NMR spectrum of cyclohexane is a singlet at room temperature, with no separation into separate signals for axial and equatorial hydrogens.
In one chair form, the dihedral angle of the chain of carbon atoms (1,2,3,4) is positive whereas that of the chain (1,6,5,4) is negative, but in the other chair form, the situation is the opposite. So both these chains have to undergo a reversal of dihedral angle. When one of these two four-atom chains flattens to a dihedral angle of zero, we have the half-chair conformation, at a maximum energy along the conversion path. When the dihedral angle of this chain then becomes equal (in sign as well as magnitude) to that of the other four-atom chain, the molecule has reached the continuum of conformations, including the twist boat and the boat, where the bond angles and lengths can all be at their normal values and the energy is therefore relatively low. After that, the other four-carbon chain has to switch the sign of its dihedral angle in order to attain the target chair form, so again the molecule has to pass through the half-chair as the dihedral angle of this chain goes through zero. Switching the signs of the two chains sequentially in this way minimizes the maximum energy state along the way (at the half-chair state) — having the dihedral angles of both four-atom chains switch sign simultaneously would mean going through a conformation of even higher energy due to angle strain at carbons 1 and 4.
The detailed mechanism of the chair-to-chair interconversion has been the subject of much study and debate. The half-chair state (D, in figure below) is the key transition state in the interconversion between the chair and twist-boat conformations. The half-chair has C2 symmetry. The interconversion between the two chair conformations involves the following sequence: chair → half-chair → twist-boat → half-chair′ → chair′. | Cyclohexane conformation | Wikipedia | 472 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Twist-boat to twist-boat
The boat conformation (C, below) is a transition state, allowing the interconversion between two different twist-boat conformations. While the boat conformation is not necessary for interconversion between the two chair conformations of cyclohexane, it is often included in the reaction coordinate diagram used to describe this interconversion because its energy is considerably lower than that of the half-chair, so any molecule with enough energy to go from twist-boat to chair also has enough energy to go from twist-boat to boat. Thus, there are multiple pathways by which a molecule of cyclohexane in the twist-boat conformation can achieve the chair conformation again.
Substituted derivatives
In cyclohexane, the two chair conformations have the same energy. The situation becomes more complex with substituted derivatives.
Monosubstituted cyclohexanes
A monosubstituted cyclohexane is one in which there is one non-hydrogen substituent in the cyclohexane ring. The most energetically favorable conformation for a monosubstituted cyclohexane is the chair conformation with the non-hydrogen substituent in the equatorial position because it prevents high steric strain from 1,3 diaxial interactions. In methylcyclohexane the two chair conformers are not isoenergetic. The methyl group prefers the equatorial orientation. The preference of a substituent towards the equatorial conformation is measured in terms of its A value, which is the Gibbs free energy difference between the two chair conformations. A positive A value indicates preference towards the equatorial position. The magnitude of the A values ranges from nearly zero for very small substituents such as deuterium, to about 5 kcal/mol (21 kJ/mol) for very bulky substituents such as the tert-butyl group. Thus, the magnitude of the A value will also correspond to the preference for the equatorial position. Though an equatorial substituent has no 1,3 diaxial interaction that causes steric strain, it has a Gauche interaction in which an equatorial substituent repels the electron density from a neighboring equatorial substituent. | Cyclohexane conformation | Wikipedia | 470 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Disubstituted cyclohexanes
For 1,2- and 1,4-disubstituted cyclohexanes, a cis configuration leads to one axial and one equatorial group. Such species undergo rapid, degenerate chair flipping. For 1,2- and 1,4-disubstituted cyclohexane, a trans configuration, the diaxial conformation is effectively prevented by its high steric strain. For 1,3-disubstituted cyclohexanes, the cis form is diequatorial and the flipped conformation suffers additional steric interaction between the two axial groups. trans-1,3-Disubstituted cyclohexanes are like cis-1,2- and cis-1,4- and can flip between the two equivalent axial/equatorial forms.
Cis-1,4-Di-tert-butylcyclohexane has an axial tert-butyl group in the chair conformation and conversion to the twist-boat conformation places both groups in more favorable equatorial positions. As a result, the twist-boat conformation is more stable by at as measured by NMR spectroscopy.
Also, for a disubstituted cyclohexane, as well as more highly substituted molecules, the aforementioned A values are additive for each substituent. For example, if calculating the A value of a dimethylcyclohexane, any methyl group in the axial position contributes 1.70 kcal/mol- this number is specific to methyl groups and is different for each possible substituent. Therefore, the overall A value for the molecule is 1.70 kcal/mol per methyl group in the axial position.
1,3 diaxial interactions and gauche interactions
1,3 Diaxial interactions occur when the non-hydrogen substituent on a cyclohexane occupies the axial position. This axial substituent is in the eclipsed position with the axial substituents on the 3-carbons relative to itself (there will be two such carbons and thus two 1,3 diaxial interactions). This eclipsed position increases the steric strain on the cyclohexane conformation and the confirmation will shift towards a more energetically favorable equilibrium. | Cyclohexane conformation | Wikipedia | 483 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Gauche interactions occur when a non-hydrogen substituent on a cyclohexane occupies the equatorial position. The equatorial substituent is in a staggered position with the 2-carbons relative to itself (there will be two such carbons and thus two 1,2 gauche interactions). This creates a dihedral angle of ~60°. This staggered position is generally preferred to the eclipsed positioning.
Effects of substituent size on stability
Once again, the conformation and position of groups (ie. substituents) larger than a singular hydrogen are critical to the overall stability of the molecule. The larger the group, the less likely to prefer the axial position on its respective carbon. Maintaining said position with a larger size costs more energy from the molecule as a whole because of steric repulsion between the large groups' nonbonded electron pairs and the electrons of the smaller groups (ie. hydrogens). Such steric repulsions are absent for equatorial groups. The cyclohexane model thus assesses steric size of functional groups on the basis of gauche interactions. The gauche interaction will increase in energy as the size of the substituent involved increases. For example, a t-butyl substituent would sustain a higher energy gauche interaction as compared to a methyl group, and therefore, contribute more to the instability of the molecule as a whole.
In comparison, a staggered conformation is thus preferred; the larger groups would maintain the equatorial position and lower the energy of the entire molecule. This preference for the equatorial position among bulkier groups lowers the energy barriers between different conformations of the ring. When the molecule is activated, there will be a loss in entropy due to the stability of the larger substituents. Therefore, the preference of the equatorial positions by large molecules (such as a methyl group) inhibits the reactivity of the molecule and thus makes the molecule more stable as a whole. | Cyclohexane conformation | Wikipedia | 403 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Effects on conformational equilibrium
Conformational equilibrium is the tendency to favor the conformation where cyclohexane is the most stable. This equilibrium depends on the interactions between the molecules in the compound and the solvent. Polarity and nonpolarity are the main factors in determining how well a solvent interacts with a compound. Cyclohexane is considered nonpolar, meaning that there is no electronegative difference between its bonds and its overall structure is symmetrical. Due to this, when cyclohexane is immersed in a polar solvent, it will have less solvent distribution, which signifies a poor interaction between the solvent and solute. This produces a limited catalytic effect. Moreover, when cyclohexane comes into contact with a nonpolar solvent, the solvent distribution is much greater, showing a strong interaction between the solvent and solute. This strong interaction yields a heighten catalytic effect.
Heterocyclic analogs
Heterocyclic analogs of cyclohexane are pervasive in sugars, piperidines, dioxanes, etc. They exist generally follow the trends seen for cyclohexane, i.e. the chair conformer being most stable. The axial–equatorial equilibria (A values) are however strongly affected by the replacement of a methylene by O or NH. Illustrative are the conformations of the glucosides. 1,2,4,5-Tetrathiane ((SCH2)3) lacks the unfavorable 1,3-diaxial interactions of cyclohexane. Consequently its twist-boat conformation is populated; in the corresponding tetramethyl structure, 3,3,6,6-tetramethyl-1,2,4,5-tetrathiane, the twist-boat conformation dominates. | Cyclohexane conformation | Wikipedia | 388 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
Historical background
In 1890, , a 28-year-old assistant in Berlin, published instructions for folding a piece of paper to represent two forms of cyclohexane he called symmetrical and asymmetrical (what we would now call chair and boat). He clearly understood that these forms had two positions for the hydrogen atoms (again, to use modern terminology, axial and equatorial), that two chairs would probably interconvert, and even how certain substituents might favor one of the chair forms (). Because he expressed all this in mathematical language, few chemists of the time understood his arguments. He had several attempts at publishing these ideas, but none succeeded in capturing the imagination of chemists. His death in 1893 at the age of 31 meant his ideas sank into obscurity. It was only in 1918 that , based on the molecular structure of diamond that had recently been solved using the then very new technique of X-ray crystallography, was able to successfully argue that Sachse's chair was the pivotal motif. Derek Barton and Odd Hassel shared the 1969 Nobel Prize in Chemistry for work on the conformations of cyclohexane and various other molecules.
Practical applications
Cyclohexane is the most stable of the cycloalkanes, due to the stability of adapting to its chair conformer. This conformer stability allows cyclohexane to be used as a standard in lab analyses. More specifically, cyclohexane is used as a standard for pharmaceutical reference in solvent analysis of pharmaceutical compounds and raw materials. This specific standard signifies that cyclohexane is used in quality analysis of food and beverages, pharmaceutical release testing, and pharmaceutical method development; these various methods test for purity, biosafety, and bioavailability of products. The stability of the chair conformer of cyclohexane gives the cycloalkane a versatile and important application when regarding the safety and properties of pharmaceuticals. | Cyclohexane conformation | Wikipedia | 402 | 1524030 | https://en.wikipedia.org/wiki/Cyclohexane%20conformation | Physical sciences | Stereochemistry | Chemistry |
The blue spruce (Picea pungens), also commonly known as Colorado spruce or Colorado blue spruce, is a species of spruce tree native to North America in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming. It is noted for its blue-green colored needles, and has therefore been used as an ornamental tree in many places far beyond its native range.
Description
In the wild, Picea pungens grows to as much as in height, but more typically tall. When planted in parks and gardens it most often grows tall with a spread of . It has scaly grey-brown bark with a slight amount of a cinnamon-red undertone on its trunk, not as rough as an Engelmann spruce. On older trees the trunk bark will be deeply furrowed and scaly. The diameter of the trunk may reach as much as .
Blue spruces are conifers with a pyramidal or conical crown when young, but more open and irregular in shape as they become older. The stout branches grow out horizontally in well defined whorls, but lower branches droop downwards as trees age. Young twigs never hang downwards and are yellow-brown in color.
The narrow, needle-like, evergreen leaves are quite sharply pointed and may be dull green, blue, or pale white. Each of the needles is four sided with stomata on every side, stiff, and long. The needles are attached radially to their shoots, but curve upward. The leaf buds are golden brown and cone shaped. The buds may be in size and the tip may either be blunt or pointed.
The pollen producing cones, more properly strobili, develop throughout the crown of blue spruce trees, but are more common in the upper half of the crown. Pollen cones are mainly yellow with a touch of red and average long. The seed cones begin growing in May or June and release their mature seeds in the autumn of the same year in which they start to grow. When young they are purple-brown in color. When fully mature they are light brown with thin, papery scales and are often curved. Overall they are longer than they are wide, between long, and circular in cross section. The seed cones are only found at the top of the tree. This helps to facilitate cross-pollination.
The seeds are dark brown. They average 4 mm in length with the papery wing extending beyond the tip almost twice this length. | Blue spruce | Wikipedia | 487 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Chemistry
The phytochemistry of the blue spruce is relatively little studied. The ripe seeds have a 1.17% yield of essential oils while the cones produce only 0.38% when steam distilled for four hours. The main component, over 40%, of the essential oils is limonene with β-Pinene and α-Pinene the next most significant.
Taxonomy
Picea pungens was given its first valid scientific description by George Engelmann in 1879. He had previously named it Abies menziesii in 1862 and then as Picea menziesii in 1863 after, but both those names had already been used making them illegitimate names.
Names
Picea, the genus name, is thought to come from the Latin word pix meaning "pitch", a reference to the typical sticky resin in spruce bark. The specific epithet pungens means "sharply pointed", referring to the leaves.
The most frequently used common name in English is blue spruce. It was first used for other trees in 1817 and is still used for any spruce tree with a glaucous blue color to their needles, but most frequently meaning Picea pungens. Though this is the most common name, in the wild only part of the population has the waxy blue-gray coating for which the tree is named. Less frequently, but still common, is Colorado blue spruce, a name first used in 1912. The usage of Colorado spruce dates to 1881, but is less frequent than the longer alternate. Occasionally encountered are the names Parry's spruce, prickly spruce, silver spruce, and white spruce. Blue spruces are also rarely called silvertip fir, but this name is also applied to Abies magnifica especially when sold as Christmas trees. In addition it is sometimes labeled as "Colorado green spruce" or "green spruce" by plant nurseries or tree farms.
Similar to the meaning of the scientific name, the Navajo name for this species is a compound c’ó deniní with c’ó meaning spruce and deniní meaning "it is sharp". | Blue spruce | Wikipedia | 420 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Ecology
Blue Spruce occurs at high elevations, in the forests of the South Central Rockies and in the Southern Rocky Mountains. It grows in mesic montane conifer forests, often associating with Douglas-fir, ponderosa pine, or white fir. It has a riparian affinity, preferring moist soils such as those along streams or at the edges of wet meadows. The Douglas-fir or ponderosa pine only become associated with streams at lower, warmer elevations. It also may be found alongside the quaking aspen (Populus tremuloides) in the high mountain habitats of desert ranges in the Intermountain West.
Climate
Blue spruce usually grows in cool and humid climatic zones where the annual precipitation mainly occurs in the summer.
Blue spruce is most common in Colorado and the Southwest. The annual average temperature ranges from 3.9 to 6.1 degrees C (39 to 43 degrees F). And ranges from - 3.9 to - 2.8 degrees C (25 to 27 degrees F) in January. In July, the average temperature ranges from 13.9 to 15.0 degrees C (57 to 59 degrees F). The average minimum temperature in January ranges from - 11.1 to 8.9 degrees C (12 to 16 degrees F), and the average maximum temperature in July ranges from 21.1 to 22.2 C (70 to 72 degrees F). There is a frost-free period of about 55 to 60 days from June to August.
Annual mean precipitation generally vary from 460 to 610 mm (18 to 24 in). Winter is the season with the poorest rainfall, the precipitation is usually less than 20 percent of the annual moisture falling from December to March. Fifty percent of the annual precipitation occurs during the growing season of the plants.
Blue spruce is generally considered to grow best with abundant moisture. Nevertheless, this species can withstand drought better than any other spruce. It can withstand extremely low temperatures (-40 degrees C) as well. Furthermore, this species is more resistant to high insolation and frost damage compared to other associated species.
Distributed soil types and topography
Blue spruce generally exists on gentle uplands and sub irrigated slopes, in well-watered tributary drainage, extending down intermittent streams, and on lower northerly slopes.
Blue spruce always grow naturally in the soils which are in the order Mollisols, and the soil will also be in the orders histosols and inceptisols in a lesser extent.
Blue spruce is considered as a pioneer tree species in moist soil in Utah. | Blue spruce | Wikipedia | 512 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Rooting habits
Blue spruce seedlings have shallow roots that penetrate approximately into the soil during the first year of growth. Although freezing can't damage much in blue spruce, frost heaving will cause seedling loss. Shadows in late spring and early autumn minimize this frost heaving loss. Despite the shallow roots, blue spruce is able to resist strong winds. Five years before transplanting, the total root surface area of 2-meter-high trees was doubled by pruning the roots of blue spruce. It also increases the root concentration in drip irrigation pipeline from 40% to 60%, which is an advantage in landscape greening.
Pests and diseases
The blue spruce is attacked by two species of Adelges, an aphid-like insect that causes galls to form. Nymphs of the pineapple gall adelgid form galls at the base of twigs which resemble miniature pineapples and those of the Cooley's spruce gall adelgid cause cone-shaped galls at the tips of branches. The larva of the spruce budworm eat the buds and growing shoots while the spruce needle miner hollows out the needles and makes them coalesce in a webbed mass. An elongated white scale insect, the pine needle scale feeds on the needles causing fluffy white patches on the twigs and aphids also suck sap from the needles and may cause them to fall and possibly dieback. Mites can also infest the blue spruce, especially in a dry summer, causing yellowing of the oldest needles. Another insect pest is the spruce beetle (Dendroctonus rufipennis) which bores under the bark. It often first attacks trees which have blown over by the wind and when the larvae mature two years afterwards, a major outbreak occurs and vast numbers of beetles attack nearby standing trees.
The blue spruce is susceptible to several needle casting diseases which cause the needles to turn yellow, mottled or brown before they fall off. Various rust diseases also affect the tree causing yellowing of the needles as well as needle fall. Canker caused by Cytospora attacks one of the lower branches first and progressively makes its way higher up the tree. The first symptom is the needles turning reddish-brown and falling off. Meanwhile, patches of white resin appear on the bark and the branch eventually dies.
It is also relatively intolerant of light pollution and when planted near street lights or other outdoor lighting its preparation for winter can be delayed and parts of the tree may be damaged. | Blue spruce | Wikipedia | 508 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Range
The native range of the blue spruce is largely in the Central and Southern Rocky Mountains and moist mountain valleys and canyons to the west. In New Mexico it only grows naturally in the higher mountain ranges of the state such as the Sandia–Manzano Mountains, Sangre de Cristo Mountains, and San Juan Mountains, as well as on Sierra Blanca Peak to the south. In Arizona the range is even more limited, growing in just Coconio and Apache counties. In Apache County it is found in the White Mountains in central eastern Arizona and the Lukachukai Mountains in the northeastern corner of the state. In Coconino County they only grow on the Kaibab Plateau. The blue spruce grows in every county in the western two-thirds of Colorado; approximately half of natural range of the species is in the mountains of Colorado. In Utah they are a locally common part of forests in the Uinta Mountains. West of the Uintas blue spruces are less frequent in canyons south of Salt Lake City.
The blue spruce has become naturalized outside of its native range. In North America has escaped from cultivation in the states of Minnesota and New York. It has also become established to some extent in many western and northern European countries including Iceland, Norway, Sweden, the United Kingdom, France, and Belgium. In middle and southern Europe it is found in Germany, Switzerland, Austria, the former Czechoslovakia, and mainland Italy. To the east it grows in European portions of Russia, the Caucasus, and Bulgaria.
Notable trees
The tallest documented blue spruce tree is an individual in the San Juan Mountains of southern Colorado in the Hermosa Creek area. When measured by Matt Markworth in 2015 it was tall. Just three years later in 2018 it was threatened by the 416 Fire. Though the fire killed a shorter American champion tree with a larger trunk and crown spread the tall tree was spared due to being located in a sheltered valley.
Cultivation
Picea pungens and its many cultivars are often grown as ornamental trees in gardens and parks. It is also grown for the Christmas tree industry. It grows best in USDA growing zones 1 through 7, though it also does well in zones warmer than 7 where summer heat is moderate, as at San Francisco. | Blue spruce | Wikipedia | 454 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Common cultivars (those marked have gained the Royal Horticultural Society's Award of Garden Merit):
'Baby Blue Eyes', 'Baby Blueeyes', or 'Baby Blue' – This is a semi-dwarf cultivar that grows slowly, but may eventually reach in height. It has a pyramidal shape and holds its color well.
'Fat Albert' – compact perfect cone to of a silver blue color
'Globosa' – shrub from in height
'Hoopsii' – A full size variety with a dense pyramidal habit known for "excellent" silver-blue color of its foliage. It reaches tall when full grown.
'Koster' – A medium sized cultivar that will reach
'Montgomery' – a slow growing dwarf variety. It will typically only grow tall in eight years, but may eventually reach a height of over .
'Pendula' – drooping branches, spreads to about wide by tall
'Sester's Dwarf' – denser foliage than the species, slowly grows to about tall
Culture
The Navajo and Keres Native Americans use this tree as a traditional medicinal plant and a ceremonial item, and twigs are given as gifts to bring good fortune. In traditional medicine, an infusion of the needles is used to treat colds and settle the stomach. This liquid is also used externally for rheumatic pains.
The blue spruce is the state tree of Colorado. It officially became Colorado's state tree on 7 March 1939 when House Joint Resolution 7 was enacted by the legislature. Previously a vote of the state's school children was taken on Arbor Day in 1892 expressing their preference for the blue spruce as the state tree.
From 1933 until 2014 the blue spruce was also the state tree of Utah. It was replaced by the quaking aspen because the aspen is a great deal more common than the blue spruce in Utah, making up 10% of the state's tree cover.
Gallery | Blue spruce | Wikipedia | 389 | 1526695 | https://en.wikipedia.org/wiki/Blue%20spruce | Biology and health sciences | Pinaceae | Plants |
Percussion is a technique of clinical examination.
Overview
Percussion is a method of tapping on a surface to determine the underlying structures, and is used in clinical examinations to assess the condition of the thorax or abdomen. It is one of the four methods of clinical examination, together with inspection, palpation, auscultation, and inquiry. It is done with the middle finger of one hand tapping on the middle finger of the other hand using a wrist action. The nonstriking finger (known as the pleximeter) is placed firmly on the body over tissue. When percussing boney areas such as the clavicle, the pleximeter can be omitted and the bone is tapped directly such as when percussing an apical cavitary lung lesion typical of tuberculosis.
There are two types of percussion: direct, which uses only one or two fingers; and indirect, which uses only the middle/flexor finger. Broadly classifying, there are four types of percussion sounds: resonant, hyper-resonant, stony dull or dull. A dull sound indicates the presence of a solid mass under the surface. A more resonant sound indicates hollow, air-containing structures. As well as producing different notes which can be heard they also produce different sensations in the pleximeter finger.
Percussion was at first used to distinguish between empty and filled barrels of liquor, and Dr. Leopold Auenbrugger is said to be the person who introduced the technique to modern medicine, although this method was used by Avicenna about 1000 years before that for medical practice such as using percussion over the stomach to show how full it is, and to distinguish between ascites and tympanites.
Of the thorax
It is used to diagnose pneumothorax, emphysema and other diseases. It can be used to assess the respiratory mobility of the thorax.
Of the abdomen
It is used to find whether any organ is enlarged and similar (assessing for organomegaly). It is based on the principle of setting tissue and spaces in between at vibration. The sound thus generated is used to determine if the tissue is healthy or pathological. | Percussion (medicine) | Wikipedia | 446 | 1527059 | https://en.wikipedia.org/wiki/Percussion%20%28medicine%29 | Biology and health sciences | Diagnostics | Health |
In programming and software design, a binding is an application programming interface (API) that provides glue code specifically made to allow a programming language to use a foreign library or operating system service (one that is not native to that language).
Characteristics
Binding generally refers to a mapping of one thing to another. In the context of software libraries, bindings are wrapper libraries that bridge two programming languages, so that a library written for one language can be used in another language. Many software libraries are written in system programming languages such as C or C++. To use such libraries from another language, usually of higher-level, such as Java, Common Lisp, Scheme, Python, or Lua, a binding to the library must be created in that language, possibly requiring recompiling the language's code, depending on the amount of modification needed. However, most languages offer a foreign function interface, such as Python's and OCaml's ctypes, and Embeddable Common Lisp's cffi and uffi.
For example, Python bindings are used when an extant C library, written for some purpose, is to be used from Python. Another example is libsvn which is written in C to provide an API to access the Subversion software repository. To access Subversion from within Java code, libsvnjavahl can be used, which depends on libsvn being installed and acts as a bridge between the language Java and libsvn, thus providing an API that invokes functions from libsvn to do the work.
Major motives to create library bindings include software reuse, to reduce reimplementing a library in several languages, and the difficulty of implementing some algorithms efficiently in some high-level languages.
Runtime environment
Object models
Common Object Request Broker Architecture (CORBA) – cross-platform-language model
Component Object Model (COM) – Microsoft Windows only cross-language model
Distributed Component Object Model (DCOM) – extension enabling COM to work over networks
Cross Platform Component Object Model (XPCOM) – Mozilla applications cross-platform model
Common Language Infrastructure – .NET Framework cross-platform-language model
Freedesktop.org D-Bus – open cross-platform-language model
Virtual machines
Comparison of application virtual machines
Porting
Portable object – cross-platform-language object model definition | Language binding | Wikipedia | 478 | 3002110 | https://en.wikipedia.org/wiki/Language%20binding | Technology | Programming languages | null |
Mesosaurus (meaning "middle lizard") is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with it, the genera Brazilosaurus and Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was long thought to have been one of the first marine reptiles, although new data suggests that at least those of Uruguay inhabited a hypersaline water body, rather than a typical marine environment. In any case, it had many adaptations to a fully aquatic lifestyle. It is usually considered to have been anapsid, although Friedrich von Huene considered it to be a synapsid. Recent study of Mesosauridae phylogeny places the group as either the basal most clade within Parareptilia or the basal most clade within Sauropsida (with the latter being the less supported position) despite the skull of Mesosaurus possessing the "Synapsid condition" of one temporal fenestra.
Discovery and naming
The holotype of M. tenuidens, MNHN 1865-77, is nicknamed the "Griqua Mesosaurus" and it was found in a Griqua hut in South Africa, likely in Kimberley, Northern Cape around 1830 and was being used as a pot lid. The circumstances of its discovery and how it was taken from its previous owners in South Africa are unknown, but what is known is that the specimen eventually surfaced in the collection of the French palaeontologist Paul Gervais during the 1860s and he designated it as the holotype of a new genus and species he named Mesosaurus tenuidens in 1865.
Since then, Mesosaurus remains have also been identified from South America and were first identified in 1908 as belonging to a second species, M. brasiliensis, by J. H. MacGregor. Later studies have shown that M. brasiliensis was the same animal as M. tenuidens, which remains as the single valid species of Mesosaurus to this day.
Two other species of mesosaurids have since been described, which are Stereosternum and Brazilosaurus, which are also considered to be synonyms of Mesosaurus tenuidens according to Piñeiro et al. (2021). | Mesosaurus | Wikipedia | 468 | 5492915 | https://en.wikipedia.org/wiki/Mesosaurus | Biology and health sciences | Prehistoric marine reptiles | Animals |
Description
Mesosaurus had a long skull that was larger than that of Stereosternum and had longer teeth. The teeth are angled outwards, especially those at the tips of the jaws.The bones of the postcranial skeleton are thick, having undergone pachyostosis. Mesosaurus is unusual among reptiles in that it possesses a cleithrum, usually found in more primitive bony fish and tetrapods. The head of the interclavicle of Mesosaurus is triangular, unlike those of other early reptiles, which are diamond-shaped.
The nostrils were located at the top, allowing the creature to breathe with only the upper side of its head breaking the surface, in a similar manner to a modern crocodile.
Palaeobiology
Diet
Mesosaurus had a small skull with long jaws. The teeth were originally thought to have been straining devices for the filter feeding of planktonic organisms. However, this idea was based on the assumption that the teeth of Mesosaurus were numerous and close together in the jaws. Newly examined remains of Mesosaurus show that it had fewer teeth and that the dentition was suitable for catching small nektonic prey such as crustaceans.
Locomotion
Mesosaurus was one of the first reptiles known to have returned to the water after early tetrapods came to land in the Late Devonian or later in the Paleozoic. It was around in length, with webbed feet, a streamlined body, and a long tail that may have supported a fin. It probably propelled itself through the water with its long hind legs and flexible tail. Its body was also flexible and could easily move sideways, but it had heavily thickened ribs, which would have prevented it from twisting its body. The pachyostosis seen in the bones of Mesosaurus may have enabled it to reach neutral buoyancy in the upper few meters of the water column. The additional weight may have stabilized the animal at the water's surface. Alternatively, it could have given Mesosaurus greater momentum when gliding underwater. | Mesosaurus | Wikipedia | 414 | 5492915 | https://en.wikipedia.org/wiki/Mesosaurus | Biology and health sciences | Prehistoric marine reptiles | Animals |
While many features suggest a wholly aquatic lifestyle, Mesosaurus may have been able to move onto land for short periods of time. Its elbows and ankles were restricted in their movement, making walking appear impossible. It is more likely that if Mesosaurus moved onto land, it would push itself forward in a similar way to living female sea turtles when nesting on beaches. A study on vertebral column proportions suggested that, while young Mesosaurus might have been fully aquatic, adult animals spent some time on land. This is supported by the rarity of adult animals in aquatic settings, and a coprolite possessing drying fractures. However, how terrestrial these animals were is difficult to say, as their pachyostosis and other adaptations for an aquatic lifestyle would have made foraging on land difficult.
Reproduction
Clearly amniote-type fossil embryos of Mesosaurus in an advanced stage of development (i.e. fetuses) have been discovered in Uruguay and Brazil. These fossils are the earliest record of amniote fetuses, although amniotes are inferred to have had their typical reproductive strategy since their first appearance in the Late Carboniferous. Prior to their description, the oldest known amniote fetuses were from the Triassic.
One isolated coiled fetus called FC-DPV 2504 is not surrounded by calcareous eggshells, suggesting that the glands in the oviduct of Mesosaurus and probably all Paleozoic amniotes were not able to secrete calcium carbonate, in contrast to post-paleozoic archosaurs. This would explain the scarcity of egg fossils in the paleozoic amniote fossil record.
One Mesosaurus specimen called MCN-PV 2214 comprises a medium-size adult with a small individual in its rib cage which is interpreted as a fetus ‘in utero’, even suggesting that Mesosaurus like many other marine reptiles, gave live birth. If this interpretation is correct, this specimen would represent the earliest known example of viviparity in the fossil record. The isolated fetus FC-DPV 2504, however, rather points to an ovoviviparous reproduction strategy in Mesosaurus. | Mesosaurus | Wikipedia | 453 | 5492915 | https://en.wikipedia.org/wiki/Mesosaurus | Biology and health sciences | Prehistoric marine reptiles | Animals |
Distribution
Mesosaurus was significant in providing evidence for the theory of continental drift, because its remains were found in southern Africa, Whitehill Formation, and eastern South America (Melo Formation, Uruguay and Irati Formation, Brazil), two widely separated regions. As Mesosaurus was a coastal animal, and therefore less likely to have crossed the Atlantic Ocean, this distribution indicated that the two continents used to be joined together.
Gallery | Mesosaurus | Wikipedia | 86 | 5492915 | https://en.wikipedia.org/wiki/Mesosaurus | Biology and health sciences | Prehistoric marine reptiles | Animals |
In mathematics, stability theory addresses the stability of solutions of differential equations and of trajectories of dynamical systems under small perturbations of initial conditions. The heat equation, for example, is a stable partial differential equation because small perturbations of initial data lead to small variations in temperature at a later time as a result of the maximum principle. In partial differential equations one may measure the distances between functions using Lp norms or the sup norm, while in differential geometry one may measure the distance between spaces using the Gromov–Hausdorff distance.
In dynamical systems, an orbit is called Lyapunov stable if the forward orbit of any point is in a small enough neighborhood or it stays in a small (but perhaps, larger) neighborhood. Various criteria have been developed to prove stability or instability of an orbit. Under favorable circumstances, the question may be reduced to a well-studied problem involving eigenvalues of matrices. A more general method involves Lyapunov functions. In practice, any one of a number of different stability criteria are applied.
Overview in dynamical systems
Many parts of the qualitative theory of differential equations and dynamical systems deal with asymptotic properties of solutions and the trajectories—what happens with the system after a long period of time. The simplest kind of behavior is exhibited by equilibrium points, or fixed points, and by periodic orbits. If a particular orbit is well understood, it is natural to ask next whether a small change in the initial condition will lead to similar behavior. Stability theory addresses the following questions: Will a nearby orbit indefinitely stay close to a given orbit? Will it converge to the given orbit? In the former case, the orbit is called stable; in the latter case, it is called asymptotically stable and the given orbit is said to be attracting.
An equilibrium solution to an autonomous system of first order ordinary differential equations is called:
stable if for every (small) , there exists a such that every solution having initial conditions within distance i.e. of the equilibrium remains within distance i.e. for all .
asymptotically stable if it is stable and, in addition, there exists such that whenever then as . | Stability theory | Wikipedia | 453 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
Stability means that the trajectories do not change too much under small perturbations. The opposite situation, where a nearby orbit is getting repelled from the given orbit, is also of interest. In general, perturbing the initial state in some directions results in the trajectory asymptotically approaching the given one and in other directions to the trajectory getting away from it. There may also be directions for which the behavior of the perturbed orbit is more complicated (neither converging nor escaping completely), and then stability theory does not give sufficient information about the dynamics.
One of the key ideas in stability theory is that the qualitative behavior of an orbit under perturbations can be analyzed using the linearization of the system near the orbit. In particular, at each equilibrium of a smooth dynamical system with an n-dimensional phase space, there is a certain n×n matrix A whose eigenvalues characterize the behavior of the nearby points (Hartman–Grobman theorem). More precisely, if all eigenvalues are negative real numbers or complex numbers with negative real parts then the point is a stable attracting fixed point, and the nearby points converge to it at an exponential rate, cf Lyapunov stability and exponential stability. If none of the eigenvalues are purely imaginary (or zero) then the attracting and repelling directions are related to the eigenspaces of the matrix A with eigenvalues whose real part is negative and, respectively, positive. Analogous statements are known for perturbations of more complicated orbits.
Stability of fixed points in 2D
The paradigmatic case is the stability of the origin under the linear autonomous differential equation where and is a 2-by-2 matrix.
We would sometimes perform change-of-basis by for some invertible matrix , which gives . We say is " in the new basis". Since and , we can classify the stability of origin using and , while freely using change-of-basis.
Classification of stability types
If , then the rank of is zero or one. | Stability theory | Wikipedia | 424 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
If the rank is zero, then , and there is no flow.
If the rank is one, then and are both one-dimensional.
If , then let span , and let be a preimage of , then in basis, , and so the flow is a shearing along the direction. In this case, .
If , then let span and let span , then in basis, for some nonzero real number .
If , then it is unstable, diverging at a rate of from along parallel translates of .
If , then it is stable, converging at a rate of to along parallel translates of .
If , we first find the Jordan normal form of the matrix, to obtain a basis in which is one of three possible forms:
where .
If , then . The origin is a source, with integral curves of form
Similarly for . The origin is a sink.
If or , then , and the origin is a saddle point. with integral curves of form .
where . This can be further simplified by a change-of-basis with , after which . We can explicitly solve for with . The solution is with . This case is called the "degenerate node". The integral curves in this basis are central dilations of , plus the x-axis.
If , then the origin is an degenerate source. Otherwise it is a degenerate sink.
In both cases,
where . In this case, .
If , then this is a spiral sink. In this case, . The integral lines are logarithmic spirals.
If , then this is a spiral source. In this case, . The integral lines are logarithmic spirals.
If , then this is a rotation ("neutral stability") at a rate of , moving neither towards nor away from origin. In this case, . The integral lines are circles.
The summary is shown in the stability diagram on the right. In each case, except the case of , the values allows unique classification of the type of flow.
For the special case of , there are two cases that cannot be distinguished by . In both cases, has only one eigenvalue, with algebraic multiplicity 2. | Stability theory | Wikipedia | 442 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
If the eigenvalue has a two-dimensional eigenspace (geometric multiplicity 2), then the system is a central node (sometimes called a "star", or "dicritical node") which is either a source (when ) or a sink (when ).
If it has a one-dimensional eigenspace (geometric multiplicity 1), then the system is a degenerate node (if ) or a shearing flow (if ).
Area-preserving flow
When , we have , so the flow is area-preserving. In this case, the type of flow is classified by .
If , then it is a rotation ("neutral stability") around the origin.
If , then it is a shearing flow.
If , then the origin is a saddle point.
Stability of fixed points
The simplest kind of an orbit is a fixed point, or an equilibrium. If a mechanical system is in a stable equilibrium state then a small push will result in a localized motion, for example, small oscillations as in the case of a pendulum. In a system with damping, a stable equilibrium state is moreover asymptotically stable. On the other hand, for an unstable equilibrium, such as a ball resting on a top of a hill, certain small pushes will result in a motion with a large amplitude that may or may not converge to the original state.
There are useful tests of stability for the case of a linear system. Stability of a nonlinear system can often be inferred from the stability of its linearization.
Maps
Let be a continuously differentiable function with a fixed point , . Consider the dynamical system obtained by iterating the function :
The fixed point is stable if the absolute value of the derivative of at is strictly less than 1, and unstable if it is strictly greater than 1. This is because near the point , the function has a linear approximation with slope :
Thus
which means that the derivative measures the rate at which the successive iterates approach the fixed point or diverge from it. If the derivative at is exactly 1 or −1, then more information is needed in order to decide stability. | Stability theory | Wikipedia | 438 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
There is an analogous criterion for a continuously differentiable map with a fixed point , expressed in terms of its Jacobian matrix at , . If all eigenvalues of are real or complex numbers with absolute value strictly less than 1 then is a stable fixed point; if at least one of them has absolute value strictly greater than 1 then is unstable. Just as for =1, the case of the largest absolute value being 1 needs to be investigated further — the Jacobian matrix test is inconclusive. The same criterion holds more generally for diffeomorphisms of a smooth manifold.
Linear autonomous systems
The stability of fixed points of a system of constant coefficient linear differential equations of first order can be analyzed using the eigenvalues of the corresponding matrix.
An autonomous system
where and is an matrix with real entries, has a constant solution
(In a different language, the origin is an equilibrium point of the corresponding dynamical system.) This solution is asymptotically stable as ("in the future") if and only if for all eigenvalues of , . Similarly, it is asymptotically stable as ("in the past") if and only if for all eigenvalues of , . If there exists an eigenvalue of with then the solution is unstable for .
Application of this result in practice, in order to decide the stability of the origin for a linear system, is facilitated by the Routh–Hurwitz stability criterion. The eigenvalues of a matrix are the roots of its characteristic polynomial. A polynomial in one variable with real coefficients is called a Hurwitz polynomial if the real parts of all roots are strictly negative. The Routh–Hurwitz theorem implies a characterization of Hurwitz polynomials by means of an algorithm that avoids computing the roots.
Non-linear autonomous systems
Asymptotic stability of fixed points of a non-linear system can often be established using the Hartman–Grobman theorem.
Suppose that is a -vector field in which vanishes at a point , . Then the corresponding autonomous system
has a constant solution
Let be the Jacobian matrix of the vector field at the point . If all eigenvalues of have strictly negative real part then the solution is asymptotically stable. This condition can be tested using the Routh–Hurwitz criterion.
Lyapunov function for general dynamical systems | Stability theory | Wikipedia | 489 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
A general way to establish Lyapunov stability or asymptotic stability of a dynamical system is by means of Lyapunov functions. | Stability theory | Wikipedia | 31 | 5493795 | https://en.wikipedia.org/wiki/Stability%20theory | Mathematics | Dynamical systems | null |
In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point. In SI base units, the electric current density is measured in amperes per square metre.
Definition
Assume that (SI unit: m2) is a small surface centered at a given point and orthogonal to the motion of the charges at . If (SI unit: A) is the electric current flowing through , then electric current density at is given by the limit:
with surface remaining centered at and orthogonal to the motion of the charges during the limit process.
The current density vector is the vector whose magnitude is the electric current density, and whose direction is the same as the motion of the positive charges at .
At a given time , if is the velocity of the charges at , and is an infinitesimal surface centred at and orthogonal to , then during an amount of time , only the charge contained in the volume formed by and will flow through . This charge is equal to where is the charge density at . The electric current is , it follows that the current density vector is the vector normal (i.e. parallel to ) and of magnitude
The surface integral of over a surface , followed by an integral over the time duration to , gives the total amount of charge flowing through the surface in that time ():
More concisely, this is the integral of the flux of across between and .
The area required to calculate the flux is real or imaginary, flat or curved, either as a cross-sectional area or a surface. For example, for charge carriers passing through an electrical conductor, the area is the cross-section of the conductor, at the section considered.
The vector area is a combination of the magnitude of the area through which the charge carriers pass, , and a unit vector normal to the area, The relation is
The differential vector area similarly follows from the definition given above:
If the current density passes through the area at an angle to the area normal then | Current density | Wikipedia | 442 | 5498706 | https://en.wikipedia.org/wiki/Current%20density | Physical sciences | Electrodynamics | Physics |
where is the dot product of the unit vectors. That is, the component of current density passing through the surface (i.e. normal to it) is , while the component of current density passing tangential to the area is , but there is no current density actually passing through the area in the tangential direction. The only component of current density passing normal to the area is the cosine component.
Importance
Current density is important to the design of electrical and electronic systems.
Circuit performance depends strongly upon the designed current level, and the current density then is determined by the dimensions of the conducting elements. For example, as integrated circuits are reduced in size, despite the lower current demanded by smaller devices, there is a trend toward higher current densities to achieve higher device numbers in ever smaller chip areas. See Moore's law.
At high frequencies, the conducting region in a wire becomes confined near its surface which increases the current density in this region. This is known as the skin effect.
High current densities have undesirable consequences. Most electrical conductors have a finite, positive resistance, making them dissipate power in the form of heat. The current density must be kept sufficiently low to prevent the conductor from melting or burning up, the insulating material failing, or the desired electrical properties changing. At high current densities the material forming the interconnections actually moves, a phenomenon called electromigration. In superconductors excessive current density may generate a strong enough magnetic field to cause spontaneous loss of the superconductive property.
The analysis and observation of current density also is used to probe the physics underlying the nature of solids, including not only metals, but also semiconductors and insulators. An elaborate theoretical formalism has developed to explain many fundamental observations.
The current density is an important parameter in Ampère's circuital law (one of Maxwell's equations), which relates current density to magnetic field.
In special relativity theory, charge and current are combined into a 4-vector.
Calculation of current densities in matter
Free currents
Charge carriers which are free to move constitute a free current density, which are given by expressions such as those in this section.
Electric current is a coarse, average quantity that tells what is happening in an entire wire. At position at time , the distribution of charge flowing is described by the current density: | Current density | Wikipedia | 476 | 5498706 | https://en.wikipedia.org/wiki/Current%20density | Physical sciences | Electrodynamics | Physics |
where
is the current density vector;
is the particles' average drift velocity (SI unit: m∙s−1);
is the charge density (SI unit: coulombs per cubic metre), in which
is the number of particles per unit volume ("number density") (SI unit: m−3);
is the charge of the individual particles with density (SI unit: coulombs).
A common approximation to the current density assumes the current simply is proportional to the electric field, as expressed by:
where is the electric field and is the electrical conductivity.
Conductivity is the reciprocal (inverse) of electrical resistivity and has the SI units of siemens per metre (S⋅m−1), and has the SI units of newtons per coulomb (N⋅C−1) or, equivalently, volts per metre (V⋅m−1).
A more fundamental approach to calculation of current density is based upon:
indicating the lag in response by the time dependence of , and the non-local nature of response to the field by the spatial dependence of , both calculated in principle from an underlying microscopic analysis, for example, in the case of small enough fields, the linear response function for the conductive behaviour in the material. See, for example, Giuliani & Vignale (2005) or Rammer (2007). The integral extends over the entire past history up to the present time.
The above conductivity and its associated current density reflect the fundamental mechanisms underlying charge transport in the medium, both in time and over distance.
A Fourier transform in space and time then results in:
where is now a complex function.
In many materials, for example, in crystalline materials, the conductivity is a tensor, and the current is not necessarily in the same direction as the applied field. Aside from the material properties themselves, the application of magnetic fields can alter conductive behaviour.
Polarization and magnetization currents
Currents arise in materials when there is a non-uniform distribution of charge.
In dielectric materials, there is a current density corresponding to the net movement of electric dipole moments per unit volume, i.e. the polarization :
Similarly with magnetic materials, circulations of the magnetic dipole moments per unit volume, i.e. the magnetization , lead to magnetization currents:
Together, these terms add up to form the bound current density in the material (resultant current due to movements of electric and magnetic dipole moments per unit volume):
Total current in materials | Current density | Wikipedia | 506 | 5498706 | https://en.wikipedia.org/wiki/Current%20density | Physical sciences | Electrodynamics | Physics |
The total current is simply the sum of the free and bound currents:
Displacement current
There is also a displacement current corresponding to the time-varying electric displacement field :
which is an important term in Ampere's circuital law, one of Maxwell's equations, since absence of this term would not predict electromagnetic waves to propagate, or the time evolution of electric fields in general.
Continuity equation
Since charge is conserved, current density must satisfy a continuity equation. Here is a derivation from first principles.
The net flow out of some volume (which can have an arbitrary shape but fixed for the calculation) must equal the net change in charge held inside the volume:
where is the charge density, and is a surface element of the surface enclosing the volume . The surface integral on the left expresses the current outflow from the volume, and the negatively signed volume integral on the right expresses the decrease in the total charge inside the volume. From the divergence theorem:
Hence:
This relation is valid for any volume, independent of size or location, which implies that:
and this relation is called the continuity equation.
In practice
In electrical wiring, the maximum current density (for a given temperature rating) can vary from 4 A⋅mm−2 for a wire with no air circulation around it, to over 6 A⋅mm−2 for a wire in free air. Regulations for building wiring list the maximum allowed current of each size of cable in differing conditions. For compact designs, such as windings of SMPS transformers, the value might be as low as 2 A⋅mm−2. If the wire is carrying high-frequency alternating currents, the skin effect may affect the distribution of the current across the section by concentrating the current on the surface of the conductor. In transformers designed for high frequencies, loss is reduced if Litz wire is used for the windings. This is made of multiple isolated wires in parallel with a diameter twice the skin depth. The isolated strands are twisted together to increase the total skin area and to reduce the resistance due to skin effects.
For the top and bottom layers of printed circuit boards, the maximum current density can be as high as 35 A⋅mm−2 with a copper thickness of 35 μm. Inner layers cannot dissipate as much heat as outer layers; designers of circuit boards avoid putting high-current traces on inner layers. | Current density | Wikipedia | 476 | 5498706 | https://en.wikipedia.org/wiki/Current%20density | Physical sciences | Electrodynamics | Physics |
In the semiconductors field, the maximum current densities for different elements are given by the manufacturer. Exceeding those limits raises the following problems:
The Joule effect which increases the temperature of the component.
The electromigration effect which will erode the interconnection and eventually cause an open circuit.
The slow diffusion effect which, if exposed to high temperatures continuously, will move metallic ions and dopants away from where they should be. This effect is also synonymous with ageing.
The following table gives an idea of the maximum current density for various materials.
Even if manufacturers add some margin to their numbers, it is recommended to, at least, double the calculated section to improve the reliability, especially for high-quality electronics. One can also notice the importance of keeping electronic devices cool to avoid exposing them to electromigration and slow diffusion.
In biological organisms, ion channels regulate the flow of ions (for example, sodium, calcium, potassium) across the membrane in all cells. The membrane of a cell is assumed to act like a capacitor.
Current densities are usually expressed in pA⋅pF−1 (picoamperes per picofarad) (i.e., current divided by capacitance). Techniques exist to empirically measure capacitance and surface area of cells, which enables calculation of current densities for different cells. This enables researchers to compare ionic currents in cells of different sizes.
In gas discharge lamps, such as flashlamps, current density plays an important role in the output spectrum produced. Low current densities produce spectral line emission and tend to favour longer wavelengths. High current densities produce continuum emission and tend to favour shorter wavelengths. Low current densities for flash lamps are generally around 10 A⋅mm−2. High current densities can be more than 40 A⋅mm−2. | Current density | Wikipedia | 373 | 5498706 | https://en.wikipedia.org/wiki/Current%20density | Physical sciences | Electrodynamics | Physics |
Carya laciniosa, the shellbark hickory, in the Juglandaceae or walnut family is also called kingnut, big, bottom, thick, or western shellbark, attesting to some of its characteristics. It is a slow-growing, long-lived tree, hard to transplant because of its long taproot, and subject to insect damage. The nuts, largest of all hickory nuts, are sweet and edible. Wildlife and people harvest most of them; those remaining produce seedling trees readily. The wood is hard, heavy, strong, and very flexible, making it a favored wood for tool handles. A specimen tree has been reported in Missouri with diameter at breast height, tall, and a spread of .
Description
Sapling and pole stages to maturity
Growth and yield: The hickories as a group grow slowly in diameter, and shellbark hickory is no exception. Sapling size trees average per year in diameter growth, increasing to per year as poles and sawtimber. Second-growth trees show growth rates of per year. Shellbark hickory occasionally grows to a height of and a diameter of .
Rooting habit: Shellbark hickory develops a large taproot that penetrates deeply into the soil. Lateral roots emerge at nearly right angles to the taproot, spreading horizontally through the soil. Major distinct lateral roots usually develop 12 inches or more below ground level and appear only after taproot is well formed. In Illinois, root growth was rapid in April, slowed during July and August, increased again in September, and ended in late November.
Mycorrhizal associations are formed when trees are young. The only specific fungus identified from shellbark hickory roots is an ectotrophic mycorrhiza, Laccaria ochropurpurea.
Reaction to competition: Shellbark hickory is very shade-tolerant, exceeded only by sugar maple (Acer saccharum) and beech (Fagus grandifolia). It grows slowly under a dense canopy, however. In stands with only partial shade, it reproduces well. It is a very strong competitor in most of the species associations in which it is found.
Under forest conditions, shellbark hickory often develops a clear bole for half its length and has a narrow, oblong crown. Open-grown trees have egg-shaped crowns. Heavy release sometimes results in epicormic branching. | Carya laciniosa | Wikipedia | 488 | 11794177 | https://en.wikipedia.org/wiki/Carya%20laciniosa | Biology and health sciences | Fagales | Plants |
On mature trees, the bark peels away from the trunk in long, sometimes broad, strips. This gives the trees a “shaggy” appearance that is easily confused with that of the Shagbark hickory (Carya ovata). That close similarity is the reason Shellbark hickories are frequently misidentified. A closer examination of other traits is usually needed to distinguish the two species.
Damaging agents: Although numerous insects and diseases affect hickories, shellbark hickory has no enemies that seriously threaten its development or perpetuation as a species. Seed production can be reduced significantly, however, through attack by several insects. Two of the most important are the pecan weevil (Curculio caryae) and the hickory shuckworm (Laspeyresia caryana).
The hickory bark beetle (Scolytus quadrispinosus) feeds in the cambium and seriously weakens or even kills some trees. Adults of the hickory spiral borer (Agrilus arcuatus torquatus) feed on leaves, but the larvae feed beneath the bark and can be very destructive to hickory seedlings. The flatheaded appletree borer (Chrysobothris femorata) likewise is a foliage-feeder as an adult, but its larvae feed on the phloem and outer sapwood.
The living-hickory borer (Goes pulcher) feeds in the trunks and branches of trees. A twig girdler (Oncideres cingulata) can seriously affect reproduction by killing back the tops of seedlings and sprouts. Both standing dead trees and freshly cut logs are highly susceptible to attacks by numerous species of wood borers.
A large number of insect species feed on hickory foliage. None of them causes serious problems for shellbark hickory, although they may be responsible for some stem deformity and growth loss.
Shellbark hickory is free of serious diseases, but it is a host species for a variety of fungi. More than 130 fungi have been identified from species of Carya. These include leaf disease, stem canker, wood rot, and root rot-causing fungi. Specific information for shellbark hickory is not available.
Shellbark hickory is susceptible to bole injury from fire, and fire injuries are often invaded by wood rot fungi. It is resistant to snow and ice damage, but is susceptible to frost damage. | Carya laciniosa | Wikipedia | 492 | 11794177 | https://en.wikipedia.org/wiki/Carya%20laciniosa | Biology and health sciences | Fagales | Plants |
Distribution and habitat
Shellbark hickory is widely distributed, but is common nowhere. The range extends from western New York through southern Michigan to southeast Iowa, south through eastern Kansas into northern Oklahoma, and eastward through Tennessee into Pennsylvania. This species is most prominent in the lower Ohio River region and south along the Mississippi River to central Arkansas. It is frequently found in the great river swamps of central Missouri and the Wabash River region in Indiana and Ohio.
It's also found scattered in the Hudson valley in New York state
In part due to the activities of humans, shellbark hickory has become rare in its natural range. The heavy seeds do not travel far from the parent tree and many stands have been lost to forest clearing and lumber harvesting. It is also not planted much as an ornamental due to its slow growth and difficulty of transplanting.
Climate
The mean length of the frost-free period within the range of shellbark hickory is from 150 to 210 days. The average January temperature is between , and for July the mean temperature is from . An average minimum temperature of occurs in the northern part of the range, and an average maximum temperature of is found throughout the range. Precipitation varies between per year including of snow.
Soils and topography
Shellbark hickory grows best on deep, fertile, moist soils, most typical of the order Alfisols. It does not thrive in heavy clay soils, but grows well on heavy loams or silt loams. Shellbark hickory requires moister situations than do pignut, mockernut, or shagbark hickories (Carya glabra, C. alba, or C. ovata), although it is sometimes found on dry, sandy soils. Specific nutrient requirements are not known, but generally the hickories grow best on neutral or slightly alkaline soils.
The species is essentially a bottomland species and is often found on river terraces and second bottoms. Land subject to shallow inundations for a few weeks early in the growing season is favorable for shellbark. However, the tree will grow on a wide range of topographic and physiographic sites. | Carya laciniosa | Wikipedia | 432 | 11794177 | https://en.wikipedia.org/wiki/Carya%20laciniosa | Biology and health sciences | Fagales | Plants |
Associated forest cover
Shellbark hickory may be found in pure groups of several trees but is more frequent singly in association with other hardwoods. The species is a minor component of the forest cover types bur oak (Society of American Foresters type 42), pin oak–sweetgum (type 65), and swamp chestnut oak–cherrybark oak (type 91). It may also be found in one or more of the types in which hickories are included, but it is not identified at the species level.
Shellbark hickory commonly grows in association with American elm (Ulmus americana), slippery (U. rubra), and winged elms (U. alata), white (Fraxinus americana) and green ash (F. pennsylvanica), basswood (Tilia americana), American hornbeam (Carpinus caroliniana), red maple (Acer rubrum), blackgum (Nyssa sylvatica), sweetgum (Liquidambar styraciflua), and cottonwood (Populus deltoides). It is found in association with four other hickories–shagbark, mockernut, bitternut (Carya cordiformis), and water (C. aquatica), and numerous oak species, including swamp white (Quercus bicolor), pin (Q. palustris), white (Q. alba), Shumard (Q. shumardii), water (Q. nigra), Delta post (Q. stellata var. paludosa), swamp chestnut (Q. michauxii), and Nuttall (Q. nuttallii).
The herbaceous stratum includes numerous sedges and grasses. The shrub and small tree layer may be composed of painted buckeye (Aesculus sylvatica), pawpaw (Asimina triloba), flowering dogwood (Cornus florida), eastern redbud (Cercis canadensis), possumhaw (Ilex decidua), poison ivy (Toxicodendron radicans), and trumpet-creeper (Campsis radicans). | Carya laciniosa | Wikipedia | 459 | 11794177 | https://en.wikipedia.org/wiki/Carya%20laciniosa | Biology and health sciences | Fagales | Plants |
Uses
The seeds within shellbark hickory nuts are edible and consumed by ducks, quail, wild turkeys, squirrels, chipmunks, deer, foxes, raccoons, and white-footed mice. A few plantations of shellbark hickory have been established for nut production, but the nuts are difficult to crack, though the kernel is sweet. The wood is used for furniture, tool handles, sporting goods, veneer, fuelwood, charcoal, and drum sticks.
Genetics
Shellbark hickory hybridizes with the pecan, Carya illinoensis (C. x nussbaumeri Sarg.), and shagbark hickory, C. ovata (C. x dunbarii Sarg.). Shellbark hickory has 32 chromosomes. In general, species within the genus with the same chromosome number are able to cross. Numerous hybrids among the Carya species with 32 chromosomes (pecan, bitternut, shellbark, and shagbark) have been described.
Gallery | Carya laciniosa | Wikipedia | 205 | 11794177 | https://en.wikipedia.org/wiki/Carya%20laciniosa | Biology and health sciences | Fagales | Plants |
Carya tomentosa, commonly known as mockernut hickory, mockernut, white hickory, whiteheart hickory, hognut, bullnut, is a species of tree in the walnut family Juglandaceae. The most abundant of the hickories, and common in the eastern half of the United States, it is long lived, sometimes reaching the age of 500 years. A straight-growing hickory, a high percentage of its wood is used for products where strength, hardness, and flexibility are needed. The wood makes excellent fuel wood, as well.
Description
Reproduction and early growth
Flowering and fruiting
Mockernut hickory is monoecious - male and female flowers are produced on the same tree. Mockernut male flowers are catkins about long and may be produced on branches from axils of leaves of the previous season or from the inner scales of the terminal buds at the base of the current growth. The female flowers appear in short spikes on peduncles terminating in shoots of the current year. Flowers bloom in the spring from April to May, depending on latitude and weather. Usually the male flowers emerge before the female flowers. Hickories produce very large amounts of pollen that is dispersed by the wind.
Fruits are solitary or paired and globose, ripening in September and October, and are about long with a short necklike base. The fruit has a thick, four-ribbed husk thick that usually splits from the middle to the base. The nut is distinctly four-angled with a reddish-brown, very hard shell thick containing a small edible kernel.
Seed production and dissemination
The seed is dispersed from September through December. Mockernut hickory requires a minimum of 25 years to reach commercial seed-bearing age. Optimum seed production occurs from 40 to 125 years, and the maximum age listed for commercial seed production is 200 years.
Good seed crops occur every two to three years with light seed crops in intervening years. Around 50 to 75% of fresh seed will germinate. Fourteen mockernut hickory trees in southeastern Ohio produced an average annual crop of 6,285 nuts for 6 years; about 39% were sound, 48% aborted, and 13% had insect damage. Hickory shuckworm (Laspeyresia caryana) is probably a major factor in reducing germination. | Carya tomentosa | Wikipedia | 469 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Mockernut hickory produces one of the heaviest seeds of the hickory species; cleaned seeds range from 70 to 250 seeds/kg (32 to 113/lb). Seed is disseminated mainly by gravity and wildlife, particularly squirrels. Birds also help disperse seed. Wildlife such as squirrels and chipmunks often bury the seed at some distance from the seed-bearing tree.
Seedling development
Hickory seeds show embryo dormancy that can be overcome by stratification in a moist medium at for 30 to 150 days. When stored for a year or more, seed may require stratification for only 30 to 60 days. Hickory nuts seldom remain viable in the ground for more than one year. Hickory species normally require a moderately moist seedbed for satisfactory seed germination, and mockernut hickory seems to reproduce best in moist duff. Germination is hypogeal.
Mockernut seedlings are not fast-growing. The height growth of mockernut seedlings observed in the Ohio Valley in the open or under light shade on red clay soil was:
Vegetative reproduction
True hickories sprout prolifically from stumps after cutting and fire. As the stumps increase in size, the number of stumps that produce sprouts decreases; age is probably directly correlated to stump size and sprouting. Coppice management is a possibility with true hickories. True hickories are difficult to reproduce from cuttings. Madden discussed the techniques for selecting, packing, and storing hickory propagation wood. Reed indicated that the most tested hickory species for root stock for pecan hickory grafts were mockernut and water hickory (Carya aquatica).
However, mockernut root stock grew slowly and reduced the growth of pecan tops. Also, this graft seldom produced a tree that bore well or yielded large nuts.
Sapling and pole stages to maturity
Growth and yield
Mockernut hickory is a large, true hickory with a dense crown. This species occasionally grows to about tall and in diameter at breast height (dbh), but heights and diameters usually range from about , respectively.
The relation of height to age is: | Carya tomentosa | Wikipedia | 437 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
The current annual growth of mockernut hickory on dry sites is estimated at 1.0 m3/ha (15 ft3/acre). In fully stocked stands on moderately fertile soil2.1 m3 /ha (30 ft3 /acre) is estimated, though annual growth rates of 3.1 m3/ha (44 ft3/acre) were reported in Ohio (26). Greenwood and bark weights for commercial-size mockernut trees from mixed hardwoods in Georgia are available for total tree and saw-log stems to a 4-inch top for trees 5 to 22 inches d.b.h..
Available growth data and other research information are summarized for hickory species, not for individual species. Trimble compared growth rates of various Appalachian hardwoods including a hickory species category dominant-codominant hickory trees in dbh on good oak sites grew slowly compared to northern red oak, yellow-poplar, black cherry (Prunus serotina), and sugar maple (Acer saccharum). Hickories were in the white oak, sweet birch (Betula lenta), and American beech (Fagus grandifolia) growth-rate category. Dominant-codominant hickory trees grew about dbh per year compared to for the moderate-growth species (black cherry) and for the faster-growing species (yellow-poplar and red oak). Equations are available for predicting merchantable gross volumes from hickory stump diameters in Ohio. Also, procedures are described for predicting diameters and heights and for developing volume tables to any merchantable top diameter for hickory species in southern Illinois and West Virginia. Generally, epicormic branching is not a problem with hickory species, but a few branches do occur.
The leaves turn yellow in Autumn.
Rooting habit
True hickories such as mockernut develop a long taproot with few laterals. Early root growth is primarily into the taproot, which typically reaches a depth of during the first year. Small laterals originate along the taproot, but many die back during the fall. During the second year, the taproot may reach a depth of , and the laterals grow rapidly. After 5 years, the root system attains its maximum depth, and the horizontal spread of the roots is about double that of the crown. By age 10, the height is four times the depth of the taproot.
Etymology | Carya tomentosa | Wikipedia | 490 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
The species' name comes from the Latin word tomentum, meaning "stuffing", referring to the underside of the leaves, which are covered with dense, short hairs, which help identify the species. Also called the white hickory due to the light color of the wood, the common name mockernut likely refers to the would-be nut eater, who would struggle to crack the thick shell only to find a small, unrewarding nut inside.
Distribution and habitat
Native range
Mockernut hickory, a true hickory, grows from Massachusetts and New York west to southern Ontario, and northern Illinois; then to southeastern Iowa, Missouri, and eastern Kansas, south to eastern Texas and east to northern Florida. This species is not present in Michigan, New Hampshire and Vermont as previously mapped by Little. Mockernut hickory is most abundant southward through Virginia, North Carolina, and Florida, where it is the most common of the hickories. It is also abundant in the lower Mississippi Valley and grows largest in the lower Ohio River Basin and in Missouri and Arkansas.
Climate
The climate where mockernut hickory grows is usually humid. Within its range, the mean annual precipitation measures from in the north to in the south. During the growing season (April through September), annual precipitation varies from . About of annual snowfall is common in the northern part of the range, but snow is rare in the southern portion.
Annual temperatures range from . Monthly average temperatures range from in July and from in January. Temperature extremes are well above and below . The growing season is about 160 days in the northern part of the range and up to 320 days in the southern part of the range.
Soils and topography
In the north, mockernut hickory is found on drier soils of ridges and hillsides and less frequently on moist woodlands and alluvial bottoms. The species grows and develops best on deep, fertile soils. In the Cumberland Mountains and hills of southern Indiana, it grows on dry sites such as south and west slopes or dry ridges. In Alabama and Mississippi, it grows on sandy soils with shortleaf pine (Pinus echinata) and loblolly pine (P taeda). However, most of the merchantable mockernut grows on moderately fertile upland soils. | Carya tomentosa | Wikipedia | 454 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Mockernut hickory grows primarily on ultisols occurring on an estimated 65% of its range, including much of the southern to northeastern United States. These soils are low in nutrients and usually moist, but during the warm season, they are dry part of the time. Along the mid-Atlantic and in the southern and western range, mockernut hickory grows on a variety of soils on slopes of 25% or less, including combinations of fine to coarse loams, clays, and well-drained quartz sands. On slopes steeper than 25%, mockernut often grows on coarse loams.
Mockernut grows on inceptisols in an estimated 15% of its range. These clayey soils are moderate to high in nutrients and are primarily in the Appalachians on gentle to moderate slopes, where water is available to plants during the growing season. In the northern Appalachians on slopes of 25% or less, mockernut hickory grows on poorly drained loams with a fragipan. In the central and southern Appalachians on slopes 25% or less, mockernut hickory grows on fine loams. On steeper slopes, it grows on coarse loams.
In the northwestern part of the range, mockernut grows on mollisols. These soils have a deep, fertile surface horizon greater than thick. Mollisols characteristically form under grass in climates with moderate to high seasonal precipitation.
Mockernut grows on a variety of soils including wet, fine loams, sandy textured soils that often have been burned, plowed, and pastured. Alfisols are also present in these areas and contain a medium to high supply of nutrients. Water is available to plants more than half the year or more than three consecutive months during the growing season. On slopes of 25% or less, mockernut grows on wet to moist, fine loam soils with a high carbonate content.
Ecology
Mockernuts are preferred mast for wildlife, particularly squirrels, which eat green nuts. Black bears, foxes, rabbits, beavers, and white-footed mice feed on the nuts, and sometimes the bark. The white-tailed deer browse on foliage and twigs and also feed on nuts. Hickory nuts are a minor source of food for ducks, quail, and turkey. | Carya tomentosa | Wikipedia | 463 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Mockernut hickory nuts are consumed by many species of birds and other animals, including wood duck, red-bellied woodpecker, red fox, squirrels, beaver, eastern cottontail, eastern chipmunk, turkey, white-tailed deer, white-footed mice, and others. Many insect pests eat hickory leaves and bark. Mockernut hickories also provide cavities for animals to live in, such as woodpeckers, black rat snakes, raccoons, Carolina chickadees, and more. They are also good nesting trees, providing cover for birds with their thick foliage. Animals help disperse seeds so that new hickories can grow elsewhere. Chipmunks, squirrels, and birds do this best. Some fungi grow on mockernut hickory roots, sharing nutrients from the soil.
Reaction to competition
At certain times during its life, mockernut hickory may be variously classified as tolerant to intolerant. Overall it is classified as intolerant of shade. It recovers rapidly from suppression and is probably a climax species on moist sites.
Silvicultural practices for managing the oak-hickory type have been summarized. Establishing the seedling origin of hickory trees is difficult because of seed predators. Although infrequent bumper seed crops usually provide some seedlings, seedling survival is poor under a dense canopy. Because of prolific sprouting ability, hickory reproduction can survive browsing, breakage, drought, and fire. Top dieback and resprouting may occur several times, each successive shoot reaching a larger size and developing a stronger root system than its predecessors. By this process, hickory reproduction gradually accumulates and grows under moderately dense canopies, especially on sites dry enough to restrict reproduction of more tolerant, but more fire or drought-sensitive species.
Wherever adequate hickory advance reproduction occurs, clearcutting results in new sapling stands containing some hickories. Reproduction is difficult to attain if advance hickory regeneration is inadequate, though; then clearcutting will eliminate hickories except for stump sprouts. In theory, light thinnings or shelterwood cuts can be used to create advance hickory regeneration, but this has not been demonstrated. | Carya tomentosa | Wikipedia | 445 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Damaging agents
Mockernut hickory is extremely sensitive to fire because of the low insulating capacity of the hard, flinty bark. It is not subject to severe loss from disease. The main fungus of hickory is Poria spiculosa, a trunk rot. This fungus kills the bark, which produces a canker, causes heart rot and decay, and can seriously degrade the tree. Mineral streaks and sapsucker-induced streaks also degrade the lumber. In general, the hard, strong, and durable wood of hickories makes them relatively resistant to decay fungi. Most fungi cause little, if any, decay in small, young trees.
Common foliage diseases include leaf mildew and witches' broom (Microstroma juglandis), leaf blotch (Mycosphaerella dendroides), and pecan scab (Cladosporium effusum). Mockernut hickory is host to anthracnose (Gnomonia caryae).
Nuts of all hickory species are susceptible to attack by the hickory nut weevil (Curculio caryae). Another weevil (Conotrachelus aratus) attacks young shoots and leaf petioles. The Curculio species are the most damaging and can destroy 65% of the hickory nut crop. Hickory shuckworms also damage nuts.
The bark beetle (Scolytus quadrispinosus) attacks mockernut hickory, especially in drought years and where hickory species are growing rapidly. The hickory spiral borer (Argilus arcuatus torquatus) and the pecan carpenterworm (Cossula magnifica) are also serious insect enemies of mockernut. The hickory bark beetle probably destroys more sawtimber-size mockernut trees than any other insect. The hickory spiral borer kills many seedlings and young trees, and the pecan carpenterworm degrades both trees and logs. The twig girdler (Oncideres cingulata) attacks both small and large trees; it seriously deforms trees by sawing branches. Sometimes, these girdlers cut hickory seedlings near ground level. | Carya tomentosa | Wikipedia | 444 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Two casebearers (Acrobasis caryivorella and A. juglandis) feed on buds and leaves; later, they bore into succulent hickory shoots. Larvae of A. caryivorella may destroy entire nut sets. The living-hickory borer (Goes pulcher) feeds on hickory boles and branches throughout the East. Borers commonly found on dying or dead hickory trees or cut logs include:
Banded hickory borer (Knulliana cincta)
Long-horned beetle (Saperda discoidea)
Apple twig borer (Amphicerus bicaudatus)
Flatheaded ambrosia beetle (Platypus compositus)
Redheaded ash borer (Neoclytus acuminatus)
False powderpost beetle (Scobicia bidentata)
Severe damage to hickory lumber and manufactured hickory products is caused by powderpost beetles (Lyctus spp. and Polycanon stoutii). Gall insects (Caryomyia spp.) commonly infest leaves. The fruit-tree leafroller (Archips argyrospila) and the hickory leafroller (Argyrotaenia juglandana) are the most common leaf feeders. The giant bark aphid (Longistigma caryae) is common on hickory bark. This aphid usually feeds on twigs and can cause branch mortality. The European fruit lecanium (Parthnolecanium corni) is common on hickories.
Mockernut is not easily injured by ice glaze or snow, but young seedlings are very susceptible to frost damage. Many birds and animals feed on the nuts of mockernut hickory. This feeding combined with insect and disease problems eliminates the annual nut production, except during bumper seed crop years.
Associated forest cover
Mockernut hickory is associated with the eastern oak-hickory forest and the beech-maple forest. The species does not exist in sufficient numbers to be included as a title species in the Society of American Foresters forest cover types. Nevertheless, it is identified as an associated species in eight cover types. Three of the upland oak types and the bottom land type are subclimax to climax.
In the central forest upland oak types, mockernut is commonly associated with: | Carya tomentosa | Wikipedia | 465 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
pignut hickory (Carya glabra)
shagbark hickory (C. ovata)
bitternut hickory (C. cordiformis)
black oak (Quercus velutina)
scarlet oak (Q. coccinea)
post oak (Q. stellata)
bur oak (Q. macrocarpa)
blackgum (Nyssa sylvatica)
yellow-poplar (Liriodendron tulipifera)
maples (Acer spp.)
white ash (Fraxinus americana)
eastern white pine (Pinus strobus)
eastern hemlock (Tsuga canadensis)
Common understory vegetation includes:
flowering dogwood (Cornus florida)
sumac (Rhus spp.)
sassafras (Sassafras albidum)
sourwood (Oxydendrum arboreum)
downy serviceberry (Amelanchier spp.)
redbud (Cercis canadensis)
eastern hophornbeam (Ostrya virginiana)
American hornbeam (Carpinus caroliniana)
Mockernut is also associated with:
wild grapes (Vitis spp.)
rosebay rhododendron (Rhododendron maximum)
mountain-laurel (Kalmia latifolia)
greenbriers (Smilax spp.)
blueberries (Vaccinium spp.)
witch-hazel (Hamamelis virginiana)
spicebush (Lindera benzoin)
New Jersey tea (Ceanothus americanus)
wild hydrangea (Hydrangea arborescens)
tick-trefoil (Desmodium spp.)
bluestem (Andropogon spp.)
poverty oatgrass (Danthonia spicata)
sedges (Carex spp.)
pussytoes (Antennaria spp.)
goldenrod (Solidago spp.)
asters (Aster or other genera, depending on the classification).
In the southern forest, mockernut grows with:
shortleaf pine
loblolly pine
pignut hickory
gums
oaks
sourwood
winged elm (Ulmus alata)
flowering dogwood
redbud
sourwood
persimmon (Diospyros virginiana)
eastern redcedar (Juniperus virginiana)
sumacs
hawthorns (Crataegus spp.)
blueberries
honeysuckle (Lonicera spp.)
mountain-laurel
viburnums
greenbriers
grapes | Carya tomentosa | Wikipedia | 491 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
In the loblolly pine-hardwood type in the southern forest, mockernut commonly grows in the upland and drier sites with:
white oak (Quercus alba)
post oak
northern red oak (Q. rubra)
southern red oak (Q. falcata)
scarlet oak
shagbark and pignut hickories
blackgum
flowering dogwood
hawthorn
sourwood
greenbrier
grape
honeysuckle
blueberry
In the southern bottom lands, mockernut occurs in the swamp chestnut oak-cherrybark oak type along with:
green ash (Fraxinus pennsylvanica)
white ash
shagbark
shellbark hickory (Carya laciniosa)
bitternut hickories
white oak
delta post oak (Quercus stellata var. paludosa)
Shumard oak (Q. shumardii)
blackgum.
Understory trees include:
American pawpaw (Asimina triloba)
flowering dogwood
painted buckeye (Aesculus sylvatica)
American hornbeam
devils-walking stick (Aralia spinosa)
redbud
American holly (Ilex opaca)
Dwarf palmetto (Sabal minor)
Coastal plain willow (Salix caroliniana)
Uses
True hickories provide a large portion of the high-grade hickory used by industry. Mockernut is used for lumber, pulpwood, charcoal, and other fuelwood products. Hickory species are preferred species for fuelwood consumption. Mockernut has the second-highest heating value among the species of hickories. It can be used for veneer, but the low supply of logs of veneer quality is a limiting factor.
Mockernut hickory is used for tool handles requiring high shock resistance. It is used for ladder rungs, athletic goods, agricultural implements, dowels, gymnasium apparatus, poles, shafts, well pumps, and furniture. Lower-grade lumber is used for pallets, blocking, etc. Hickory sawdust, chips, and some solid wood are often used by packing companies to smoke meats; mockernut is the preferred wood for smoking hams. Though mockernut kernels are edible, they are rarely eaten by humans because of their size and because they are eaten by squirrels and other wildlife. | Carya tomentosa | Wikipedia | 456 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Genetics
Mockernut is a 64-chromosome species, so rarely crosses with 32-chromosome species such as pecan or shellbark hickory. No published information exists concerning population or other genetic studies of this species. Efforts are currently underway to map the genome of pecan in a collaborative effort. The genome map at some point may expand to cover other hickory species.
Hickories are noted for their variability, with many natural hybrids known among North American Carya species. Hickories usually can be crossed successfully within the genus. Geneticists recognize that mockernut hickory hybridizes naturally with C. illinoensis (Carya x schneckii Sarg.) and C. ovata (Carya x collina Laughlin). Mockernut readily hybridizes with tetraploid C. texana. Hybrids generally are shy nut producers or produce nuts that are not filled with a kernel. Numerous exceptions to this rule are known.
Gallery | Carya tomentosa | Wikipedia | 193 | 11794330 | https://en.wikipedia.org/wiki/Carya%20tomentosa | Biology and health sciences | Fagales | Plants |
Caninae (whose members are known as canines () is the only living subfamily within Canidae, alongside the extinct Borophaginae and Hesperocyoninae. They first appeared in North America, during the Oligocene around 35 million years ago, subsequently spreading to Asia and elsewhere in the Old World at the end of the Miocene, some 7 million to 8 million years ago.
Taxonomy and lineage
The genus Leptocyon (Greek: leptos slender + cyon dog) includes 11 species and was the first primitive canine. They were small and weighed around 2 kg. They first appeared in Sioux County, Nebraska in the Orellan era 34-32 million years ago, which was the beginning of the Oligocene. This was the same time as the appearance of the Borophaginae with whom they share features, indicating that these were two sister groups. Borophaginae skull and dentition were designed for a powerful killing bite compared with the Leptocyon which were designed for snatching small, fast-moving prey. The species L. delicatus is the smallest canid to have existed. At the close of their genus 9 million years ago one Leptocyon lineage resembled the modern fox. The various species of Leptocyon branched 11.9 Mya into Vulpini (foxes) and Canini (canines).
The canines spent two-thirds of their history in North America, before dispersing 7 million years ago into Asia, Europe, and Africa. One of the characteristics that distinguished them from the Borophaginae and Hesperocyoninae was their possession of less weight in their limbs and more length in their legs, which may have aided their dispersion. The first canine to arrive in Eurasia was the coyote-sized Canis cipio, whose scant fossils were found in Spain. However, the assignment of C. cipio within the canines to the genus Canis or genus Eucyon is not clear.
Phylogenetic relationships
The results of allozyme and chromosome analyses have previously suggested several phylogenetic divisions: | Caninae | Wikipedia | 428 | 11795855 | https://en.wikipedia.org/wiki/Caninae | Biology and health sciences | Canines | Animals |
DNA analysis shows that the first three form monophyletic clades. The wolf-like canines and the South American canines together form the tribe Canini. Molecular data imply a North American origin of living Canidae some 10 Mya and an African origin of wolf-like canines (Canis, Cuon, and Lycaon), with the jackals being the most basal of this group.
The South American clade is rooted by the maned wolf and bush dog, and the fox-like canines by the fennec fox and Blanford's fox. The gray fox and island fox are basal to the other clades; however, this topological difference is not strongly supported.
The cladogram below is based on the phylogeny of Lindblad-Toh (2005) modified to incorporate recent findings on Canis, Vulpes, Lycalopex species, and Dusicyon. | Caninae | Wikipedia | 193 | 11795855 | https://en.wikipedia.org/wiki/Caninae | Biology and health sciences | Canines | Animals |
NGC 6302 (also known as the Bug Nebula, Butterfly Nebula, or Caldwell 69) is a bipolar planetary nebula in the constellation Scorpius. The structure in the nebula is among the most complex ever seen in planetary nebulae. The spectrum of Butterfly Nebula shows that its central star is one of the hottest stars known, with a surface temperature in excess of 250,000 degrees Celsius, implying that the star from which it formed must have been very large.
The central star, a white dwarf, was identified in 2009, using the upgraded Wide Field Camera 3 on board the Hubble Space Telescope. The star has a current mass of around 0.64 solar masses. It is surrounded by a dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star's outflows to form a bipolar structure similar to an hourglass. This bipolar structure shows features such as ionization walls, knots and sharp edges to the lobes.
Observation history
As it is included in the New General Catalogue, this object has been known since at least 1888. The earliest-known study of NGC 6302 is by Edward Emerson Barnard, who drew and described it in 1907.
The nebula featured in some of the first images released after the final servicing mission of the Hubble Space Telescope in September 2009.
Characteristics
NGC 6302 has a complex structure, which may be approximated as bipolar with two primary lobes, though there is evidence for a second pair of lobes that may have belonged to a previous phase of mass loss. A dark lane runs through the waist of the nebula obscuring the central star at all wavelengths.
The nebula contains a prominent northwest lobe which extends up to 3.0′ away from the central star and is estimated to have formed from an eruptive event around 1,900 years ago. It has a circular part whose walls are expanding such that each part has a speed proportional to its distance from the central star. At an angular distance of 1.71′ from the central star, the flow velocity of this lobe is measured to be 263 km/s. At the extreme periphery of the lobe, the outward velocity exceeds 600 km/s. The western edge of the lobe displays characteristics suggestive of a collision with pre-existing globules of gas which modified the outflow in that region. | NGC 6302 | Wikipedia | 472 | 4117384 | https://en.wikipedia.org/wiki/NGC%206302 | Physical sciences | Notable nebulae | Astronomy |
Central star
The central star, among the hottest stars known, had escaped detection because of a combination of its high temperature (meaning that it radiates mainly in the ultraviolet), the dusty torus (which absorbs a large fraction of the light from the central regions, especially in the ultraviolet) and the bright background from the star. It was not seen in the first Hubble Space Telescope images; the improved resolution and sensitivity of the new Wide Field Camera 3 of the same telescope later revealed the faint star at the centre. A temperature of 200,000 Kelvin is indicated, and a mass of 0.64 solar masses. The original mass of the star was much higher, but most was ejected in the event which created the planetary nebula. The luminosity and temperature of the star indicate it has ceased nuclear burning and is on its way to becoming a white dwarf, fading at a predicted rate of 1% per year.
Dust chemistry
The prominent dark lane that runs through the centre of the nebula has been shown to have an unusual composition, showing evidence for multiple crystalline silicates, crystalline water ice and quartz, with other features which have been interpreted as the first extra-solar detection of carbonates. This detection has been disputed, due to the difficulties in forming carbonates in a non-aqueous environment. The dispute remains unresolved.
One of the characteristics of the dust detected in NGC 6302 is the existence of both oxygen-bearing silicate molecules and carbon-bearing polycyclic aromatic hydrocarbons (PAHs). Stars are usually either oxygen-rich or carbon-rich, the change from the former to the latter occurring late in the evolution of the star due to nuclear and chemical changes in the star's atmosphere. NGC 6302 belongs to a group of objects where hydrocarbon molecules formed in an oxygen-rich environment. | NGC 6302 | Wikipedia | 375 | 4117384 | https://en.wikipedia.org/wiki/NGC%206302 | Physical sciences | Notable nebulae | Astronomy |
A computer network is a set of computers sharing resources located on or provided by network nodes. Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies.
The nodes of a computer network can include personal computers, servers, networking hardware, or other specialized or general-purpose hosts. They are identified by network addresses and may have hostnames. Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying the nodes by communication protocols such as the Internet Protocol.
Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth, communications protocols to organize network traffic, the network size, the topology, traffic control mechanisms, and organizational intent.
Computer networks support many applications and services, such as access to the World Wide Web, digital video and audio, shared use of application and storage servers, printers and fax machines, and use of email and instant messaging applications.
History
Computer networking may be considered a branch of computer science, computer engineering, and telecommunications, since it relies on the theoretical and practical application of the related disciplines. Computer networking was influenced by a wide array of technological developments and historical milestones. | Computer network | Wikipedia | 281 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In the late 1950s, a network of computers was built for the U.S. military Semi-Automatic Ground Environment (SAGE) radar system using the Bell 101 modem. It was the first commercial modem for computers, released by AT&T Corporation in 1958. The modem allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 110 bits per second (bit/s).
In 1959, Christopher Strachey filed a patent application for time-sharing in the United Kingdom and John McCarthy initiated the first project to implement time-sharing of user programs at MIT. Strachey passed the concept on to J. C. R. Licklider at the inaugural UNESCO Information Processing Conference in Paris that year. McCarthy was instrumental in the creation of three of the earliest time-sharing systems (the Compatible Time-Sharing System in 1961, the BBN Time-Sharing System in 1962, and the Dartmouth Time-Sharing System in 1963).
In 1959, Anatoly Kitov proposed to the Central Committee of the Communist Party of the Soviet Union a detailed plan for the re-organization of the control of the Soviet armed forces and of the Soviet economy on the basis of a network of computing centers. Kitov's proposal was rejected, as later was the 1962 OGAS economy management network project.
In 1960, the commercial airline reservation system semi-automatic business research environment (SABRE) went online with two connected mainframes.
In 1963, J. C. R. Licklider sent a memorandum to office colleagues discussing the concept of the "Intergalactic Computer Network", a computer network intended to allow general communications among computer users.
In 1965, Western Electric introduced the first widely used telephone switch that implemented computer control in the switching fabric.
Throughout the 1960s, Paul Baran and Donald Davies independently invented the concept of packet switching for data communication between computers over a network. Baran's work addressed adaptive routing of message blocks across a distributed network, but did not include routers with software switches, nor the idea that users, rather than the network itself, would provide the reliability. Davies' hierarchical network design included high-speed routers, communication protocols and the essence of the end-to-end principle. The NPL network, a local area network at the National Physical Laboratory (United Kingdom), pioneered the implementation of the concept in 1968-69 using links. Both Baran's and Davies' inventions were seminal contributions that influenced the development of computer networks. | Computer network | Wikipedia | 506 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In 1969, the first four nodes of the ARPANET were connected using circuits between the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, and the University of Utah. Designed principally by Bob Kahn, the network's routing, flow control, software design and network control were developed by the IMP team working for Bolt Beranek & Newman. In the early 1970s, Leonard Kleinrock carried out mathematical work to model the performance of packet-switched networks, which underpinned the development of the ARPANET. His theoretical work on hierarchical routing in the late 1970s with student Farouk Kamoun remains critical to the operation of the Internet today.
In 1972, commercial services were first deployed on experimental public data networks in Europe.
In 1973, the French CYCLADES network, directed by Louis Pouzin was the first to make the hosts responsible for the reliable delivery of data, rather than this being a centralized service of the network itself.
In 1973, Peter Kirstein put internetworking into practice at University College London (UCL), connecting the ARPANET to British academic networks, the first international heterogeneous computer network.
In 1973, Robert Metcalfe wrote a formal memo at Xerox PARC describing Ethernet, a networking system that was based on the Aloha network, developed in the 1960s by Norman Abramson and colleagues at the University of Hawaii. Metcalfe, with John Shoch, Yogen Dalal, Ed Taft, and Butler Lampson also developed the PARC Universal Packet for internetworking.
In 1974, Vint Cerf and Bob Kahn published their seminal 1974 paper on internetworking, A Protocol for Packet Network Intercommunication. Later that year, Cerf, Yogen Dalal, and Carl Sunshine wrote the first Transmission Control Protocol (TCP) specification, , coining the term Internet as a shorthand for internetworking.
In July 1976, Robert Metcalfe and David Boggs published their paper "Ethernet: Distributed Packet Switching for Local Computer Networks" and collaborated on several patents received in 1977 and 1978.
Public data networks in Europe, North America and Japan began using X.25 in the late 1970s and interconnected with X.75. This underlying infrastructure was used for expanding TCP/IP networks in the 1980s.
In 1976, John Murphy of Datapoint Corporation created ARCNET, a token-passing network first used to share storage devices. | Computer network | Wikipedia | 493 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In 1977, the first long-distance fiber network was deployed by GTE in Long Beach, California.
In 1979, Robert Metcalfe pursued making Ethernet an open standard.
In 1980, Ethernet was upgraded from the original protocol to the 10 Mbit/s protocol, which was developed by Ron Crane, Bob Garner, Roy Ogus, and Yogen Dalal.
In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s. By 1998, Ethernet supported transmission speeds of 1 Gbit/s. Subsequently, higher speeds of up to 400 Gbit/s were added (). The scaling of Ethernet has been a contributing factor to its continued use. | Computer network | Wikipedia | 142 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Use
Computer networks enhance how users communicate with each other by using various electronic methods like email, instant messaging, online chat, voice and video calls, and video conferencing. Networks also enable the sharing of computing resources. For example, a user can print a document on a shared printer or use shared storage devices. Additionally, networks allow for the sharing of files and information, giving authorized users access to data stored on other computers. Distributed computing leverages resources from multiple computers across a network to perform tasks collaboratively.
Network packet
Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network.
Packets consist of two types of data: control information and user data (payload). The control information provides data the network needs to deliver the user data, for example, source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers, with payload data in between.
With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched. When one user is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link is not overused. Often the route a packet needs to take through a network is not immediately available. In that case, the packet is queued and waits until a link is free.
The physical link technologies of packet networks typically limit the size of packets to a certain maximum transmission unit (MTU). A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message.
Network topology
The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks, a single failure can cause the network to fail entirely. In general, the more interconnections there are, the more robust the network is; but the more expensive it is to install. Therefore, most network diagrams are arranged by their network topology which is the map of logical interconnections of network hosts. | Computer network | Wikipedia | 467 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Common topologies are:
Bus network: all nodes are connected to a common medium along this medium. This was the layout used in the original Ethernet, called 10BASE5 and 10BASE2. This is still a common topology on the data link layer, although modern physical layer variants use point-to-point links instead, forming a star or a tree.
Star network: all nodes are connected to a special central node. This is the typical layout found in a small switched Ethernet LAN, where each client connects to a central network switch, and logically in a wireless LAN, where each wireless client associates with the central wireless access point.
Ring network: each node is connected to its left and right neighbor node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards. Token ring networks, and the Fiber Distributed Data Interface (FDDI), made use of such a topology.
Mesh network: each node is connected to an arbitrary number of neighbors in such a way that there is at least one traversal from any node to any other.
Fully connected network: each node is connected to every other node in the network.
Tree network: nodes are arranged hierarchically. This is the natural topology for a larger Ethernet network with multiple switches and without redundant meshing.
The physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDI, the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrelevant, however, as common ducting and equipment locations can represent single points of failure due to issues like fires, power failures and flooding.
Overlay network
An overlay network is a virtual network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the Internet.
Overlay networks have been used since the early days of networking, back when computers were connected via telephone lines using modems, even before data networks were developed. | Computer network | Wikipedia | 495 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network. Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Address resolution and routing are the means that allow mapping of a fully connected IP overlay network to its underlying network.
Another example of an overlay network is a distributed hash table, which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map) indexed by keys.
Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP multicast have not seen wide acceptance largely because they require modification of all routers in the network. On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination.
For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes end system multicast, resilient routing and quality of service studies, among others.
Network links
The transmission media (often referred to in the literature as the physical medium) used to link devices to form a computer network include electrical cable, optical fiber, and free space. In the OSI model, the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer.
A widely adopted family that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Wireless LAN standards use radio waves, others use infrared signals as a transmission medium. Power line communication uses a building's power cabling to transmit data.
Wired
The following classes of wired technologies are used in computer networking. | Computer network | Wikipedia | 480 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second.
ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed local area network.
Twisted pair cabling is used for wired Ethernet and other standards. It typically consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 Mbit/s to 10 Gbit/s. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted-pair (STP). Each form comes in several category ratings, designed for use in various scenarios.
An optical fiber is a glass fiber. It carries pulses of light that represent data via lasers and optical amplifiers. Some advantages of optical fibers over metal wires are very low transmission loss and immunity to electrical interference. Using dense wave division multiplexing, optical fibers can simultaneously carry multiple streams of data on different wavelengths of light, which greatly increases the rate that data can be sent to up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea communications cables to interconnect continents. There are two basic types of fiber optics, single-mode optical fiber (SMF) and multi-mode optical fiber (MMF). Single-mode fiber has the advantage of being able to sustain a coherent signal for dozens or even a hundred kilometers. Multimode fiber is cheaper to terminate but is limited to a few hundred or even only a few dozens of meters, depending on the data rate and cable grade.
Wireless | Computer network | Wikipedia | 389 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Network connections can be established wirelessly using radio or other electromagnetic means of communication.
Terrestrial microwave – Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately apart.
Communications satellites – Satellites also communicate via microwave. The satellites are stationed in space, typically in geosynchronous orbit above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
Cellular networks use several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area is served by a low-power transceiver.
Radio and spread spectrum technologies – Wireless LANs use a high-frequency radio technology similar to digital cellular. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wi-Fi.
Free-space optical communication uses visible or invisible light for communications. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.
Extending the Internet to interplanetary dimensions via radio waves and optical means, the Interplanetary Internet.
IP over Avian Carriers was a humorous April fool's Request for Comments, issued as . It was implemented in real life in 2001.
The last two cases have a large round-trip delay time, which gives slow two-way communication but does not prevent sending large amounts of information (they can have high throughput).
Network nodes
Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers, repeaters, hubs, bridges, switches, routers, modems, and firewalls. Any particular piece of equipment will frequently contain multiple building blocks and so may perform multiple functions.
Network interfaces
A network interface controller (NIC) is computer hardware that connects the computer to the network media and has the ability to process low-level network information. For example, the NIC may have a connector for plugging in a cable, or an aerial for wireless transmission and reception, and the associated circuitry. | Computer network | Wikipedia | 455 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In Ethernet networks, each NIC has a unique Media Access Control (MAC) address—usually stored in the controller's permanent memory. To avoid address conflicts between network devices, the Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets. The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.
Repeaters and hubs
A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of obstruction so that the signal can cover longer distances without degradation. In most twisted-pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart.
Repeaters work on the physical layer of the OSI model but still require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters used in a network, e.g., the Ethernet 5-4-3 rule.
An Ethernet repeater with multiple ports is known as an Ethernet hub. In addition to reconditioning and distributing network signals, a repeater hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely obsoleted by modern network switches.
Bridges and switches
Network bridges and network switches are distinct from a hub in that they only forward frames to the ports involved in the communication whereas a hub forwards to all ports. Bridges only have two ports but a switch can be thought of as a multi-port bridge. Switches normally have numerous ports, facilitating a star topology for devices, and for cascading additional switches. | Computer network | Wikipedia | 413 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Bridges and switches operate at the data link layer (layer 2) of the OSI model and bridge traffic between two or more network segments to form a single local network. Both are devices that forward frames of data between ports based on the destination MAC address in each frame.
They learn the association of physical ports to MAC addresses by examining the source addresses of received frames and only forward the frame when necessary. If an unknown destination MAC is targeted, the device broadcasts the request to all ports except the source, and discovers the location from the reply.
Bridges and switches divide the network's collision domain but maintain a single broadcast domain. Network segmentation through bridging and switching helps break down a large, congested network into an aggregation of smaller, more efficient networks.
Routers
A router is an internetworking device that forwards packets between networks by processing the addressing or routing information included in the packet. The routing information is often processed in conjunction with the routing table. A router uses its routing table to determine where to forward packets and does not require broadcasting packets which is inefficient for very big networks.
Modems
Modems (modulator-demodulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Early modems modulated audio signals sent over a standard voice telephone line. Modems are still commonly used for telephone lines, using a digital subscriber line technology and cable television systems using DOCSIS technology.
Firewalls
A firewall is a network device or software for controlling network security and access rules. Firewalls are inserted in connections between secure internal networks and potentially insecure external networks such as the Internet. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks.
Communication protocols
A communication protocol is a set of rules for exchanging information over a network. Communication protocols have various characteristics. They may be connection-oriented or connectionless, they may use circuit mode or packet switching, and they may use hierarchical addressing or flat addressing. | Computer network | Wikipedia | 470 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In a protocol stack, often constructed per the OSI model, communications functions are divided up into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP (the World Wide Web protocol) running over TCP over IP (the Internet protocols) over IEEE 802.11 (the Wi-Fi protocol). This stack is used between the wireless router and the home user's personal computer when the user is surfing the web.
There are many communication protocols, a few of which are described below.
Common protocols
Internet protocol suite
The Internet protocol suite, also called TCP/IP, is the foundation of all modern networking. It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP). At its core, the protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 (IPv4) and for IPv6, the next generation of the protocol with a much enlarged addressing capability. The Internet protocol suite is the defining set of protocols for the Internet.
IEEE 802
IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides a diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at layers 1 and 2 of the OSI model.
For example, MAC bridging (IEEE 802.1D) deals with the routing of Ethernet packets using a Spanning Tree Protocol. IEEE 802.1Q describes VLANs, and IEEE 802.1X defines a port-based network access control protocol, which forms the basis for the authentication mechanisms used in VLANs (but it is also found in WLANs) – it is what the home user sees when the user has to enter a "wireless access key".
Ethernet
Ethernet is a family of technologies used in wired LANs. It is described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers.
Wireless LAN
Wireless LAN based on the IEEE 802.11 standards, also widely known as WLAN or WiFi, is probably the most well-known member of the IEEE 802 protocol family for home users today. IEEE 802.11 shares many properties with wired Ethernet. | Computer network | Wikipedia | 497 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
SONET/SDH
Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support circuit-switched digital telephony. However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames.
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells. This differs from other protocols such as the Internet protocol suite or Ethernet that use variable-sized packets or frames. ATM has similarities with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins.
ATM still plays a role in the last mile, which is the connection between an Internet service provider and the home user.
Cellular standards
There are a number of different digital cellular standards, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne, CDMA2000, Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN).
Routing
Routing is the process of selecting network paths to carry network traffic. Routing is performed for many kinds of networks, including circuit switching networks and packet switched networks. | Computer network | Wikipedia | 414 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
In packet-switched networks, routing protocols direct packet forwarding through intermediate nodes. Intermediate nodes are typically network hardware devices such as routers, bridges, gateways, firewalls, or switches. General-purpose computers can also forward packets and perform routing, though because they lack specialized hardware, may offer limited performance. The routing process directs forwarding on the basis of routing tables, which maintain a record of the routes to various network destinations. Most routing algorithms use only one network path at a time. Multipath routing techniques enable the use of multiple alternative paths.
Routing can be contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, the structured addressing used by routers outperforms unstructured addressing used by bridging. Structured IP addresses are used on the Internet. Unstructured MAC addresses are used for bridging on Ethernet and similar local area networks.
Geographic scale
Networks may be characterized by many properties or features, such as physical capacity, organizational purpose, user authorization, access rights, and others. Another distinct classification method is that of the physical extent or geographic scale.
Nanoscale network
A nanoscale network has key components implemented at the nanoscale, including message carriers, and leverages physical principles that differ from macroscale communication mechanisms. Nanoscale communication extends communication to very small sensors and actuators such as those found in biological systems and also tends to operate in environments that would be too harsh for other communication techniques.
Personal area network
A personal area network (PAN) is a computer network used for communication among computers and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with USB and FireWire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN. | Computer network | Wikipedia | 437 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
Local area network
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Wired LANs are most commonly based on Ethernet technology. Other networking technologies such as ITU-T G.hn also provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines.
A LAN can be connected to a wide area network (WAN) using a router. The defining characteristics of a LAN, in contrast to a WAN, include higher data transfer rates, limited geographic range, and lack of reliance on leased lines to provide connectivity. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to and in excess of 100 Gbit/s, standardized by IEEE in 2010.
Home area network
A home area network (HAN) is a residential LAN used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable Internet access or digital subscriber line (DSL) provider.
Storage area network
A storage area network (SAN) is a dedicated network that provides access to consolidated, block-level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the storage appears as locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments.
Campus area network
A campus area network (CAN) is made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, Cat5 cabling, etc.) are almost entirely owned by the campus tenant or owner (an enterprise, university, government, etc.).
For example, a university campus network is likely to link a variety of campus buildings to connect academic colleges or departments, the library, and student residence halls. | Computer network | Wikipedia | 475 | 4122592 | https://en.wikipedia.org/wiki/Computer%20network | Technology | Networks | null |
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