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Volcanic ash is further divided into fine ash, with particle sizes smaller than 0.0625 mm in diameter, and coarse ash, with particle sizes between 0.0625 mm and 2 mm in diameter. Tuff is correspondingly divided into coarse tuff (coarse ash tuff) and fine tuff (fine ash tuff or dust tuff). Consolidated tephra composed m... | Tuff | Wikipedia | 474 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Particles of volcanic ash that are sufficiently hot will weld together after settling to the surface, producing a welded tuff. Welding requires temperatures in excess of . If the rock contains scattered, pea-sized fragments or fiamme in it, it is called a welded lapilli tuff. Welded tuffs (and welded lapilli tuffs) can... | Tuff | Wikipedia | 482 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
High-silica volcanism
Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with quartz, alkali feldspar, biotite, etc. Iceland, Lipari, Hungary, the Basin and Range of the American southwest, and New Zealand are among the areas where such tuffs are prominent. In the ancient rocks of Wales, Charnwood, et... | Tuff | Wikipedia | 496 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Intermediate volcanism
Andesitic tuffs are exceedingly common. They occur along the whole chain of the Cordilleras and Andes, in the West Indies, New Zealand, Japan, etc. In the Lake District, North Wales, Lorne, the Pentland Hills, the Cheviots, and many other districts of Great Britain, ancient rocks of exactly simil... | Tuff | Wikipedia | 391 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Basaltic tuffs are also found in Skye, Mull, Antrim, and other places, where Paleogene volcanic rocks are found; in Scotland, Derbyshire, and Ireland among the Carboniferous strata, and among the still older rocks of the Lake District, the southern uplands of Scotland, and Wales. They are black, dark green, or red in c... | Tuff | Wikipedia | 489 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Komatiites
Komatiite tuffs are found, for example, in the greenstone belts of Canada and South Africa.
Folding and metamorphism
In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become sheared and cleaved. Many of the green slates of the English L... | Tuff | Wikipedia | 477 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Peperino has been used in Rome and Naples as a building stone, is a trachyte tuff. Pozzolana also is a decomposed tuff, but of basic character, originally obtained near Naples and used as a cement, but this name is now applied to a number of substances not always of identical character. In the historical architecture o... | Tuff | Wikipedia | 433 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
Tuffs are deposited geologically instantaneously and often over a large region. This makes them highly useful as time-stratigraphic markers. The use of tuffs and other tephra deposits in this manner is known as tephrochronology and is particularly useful for Quaternary chronostratigraphy. Individual tuff beds can be "f... | Tuff | Wikipedia | 207 | 44481 | https://en.wikipedia.org/wiki/Tuff | Physical sciences | Petrology | null |
A linear motor is an electric motor that has had its stator and rotor "unrolled", thus, instead of producing a torque (rotation), it produces a linear force along its length. However, linear motors are not necessarily straight. Characteristically, a linear motor's active section has ends, whereas more conventional moto... | Linear motor | Wikipedia | 510 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
Synchronous
In this design the rate of movement of the magnetic field is controlled, usually electronically, to track the motion of the rotor. For cost reasons synchronous linear motors rarely use commutators, so the rotor often contains permanent magnets, or soft iron. Examples include coilguns and the motors used on... | Linear motor | Wikipedia | 439 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
In a single sided version the magnetic repulsion forces the conductor away from the stator, levitating it, and carrying it along in the direction of the moving magnetic field. He called the later versions of it magnetic river. The technologies would later be applied, in the 1984, Air-Rail Link shuttle, between Birmingh... | Linear motor | Wikipedia | 439 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
The United States Navy is also using linear induction motors in the Electromagnetic Aircraft Launch System that will replace traditional steam catapults on future aircraft carriers. They have also been suggested for use in spacecraft propulsion. In this context they are usually called mass drivers. The simplest way to ... | Linear motor | Wikipedia | 475 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
Industrial automation
The combination of high precision, high velocity, high force, and long travel makes brushless linear motors attractive for driving industrial automations equipment. They serve industries and applications such as semiconductor steppers, electronics surface-mount technology, automotive cartesian co... | Linear motor | Wikipedia | 373 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
Japanese Linear Metro
One of the biggest challenges faced by Japanese railway engineers in the 1970s to the 1980s was the ever increasing construction costs of subways. In response, the Japan Subway Association began studying on the feasibility of the "mini-metro" for meeting urban traffic demand in 1979. In 1981, the... | Linear motor | Wikipedia | 470 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
High-speed trains:
Transrapid: first commercial use in Shanghai (opened in 2004)
SCMaglev, under construction in Japan (fastest train in the world, planned to open by 2027)
Rapid transit:
Birmingham Airport, UK (opened 1984, closed 1995)
M-Bahn in Berlin, Germany (opened in 1989, closed in 1991)
Daejeon EXPO, Kor... | Linear motor | Wikipedia | 456 | 44495 | https://en.wikipedia.org/wiki/Linear%20motor | Technology | Engines | null |
Till or glacial till is unsorted glacial sediment.
Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.
Till is classified into primary deposits, laid down directly by glaciers, and se... | Till | Wikipedia | 435 | 44545 | https://en.wikipedia.org/wiki/Till | Physical sciences | Sedimentology | Earth science |
The term till comes from an old Scottish name for coarse, rocky soil. It was first used to describe primary glacial deposits by Archibald Geikie in 1863. Early researchers tended to prefer the term boulder clay for the same kind of sediments, but this has fallen into disfavor. Where it is unclear whether a poorly sorte... | Till | Wikipedia | 455 | 44545 | https://en.wikipedia.org/wiki/Till | Physical sciences | Sedimentology | Earth science |
The different types of till can be categorized between subglacial (beneath) and supraglacial (surface) deposits. Subglacial deposits include lodgement, subglacial meltout, and deformation tills. Supraglacial deposits include supraglacial meltout and flow till. Supraglacial deposits and landforms are widespread in areas... | Till | Wikipedia | 468 | 44545 | https://en.wikipedia.org/wiki/Till | Physical sciences | Sedimentology | Earth science |
Subglacial lodgement tills are deposits beneath the glacier that are forced, or "lodged" into the bed below. As glaciers advance or retreat, the clasts that are deposited by the ice may have a lower velocity than the ice itself. When the friction between the clast and the bed exceeds the forces of the ice flowing above... | Till | Wikipedia | 465 | 44545 | https://en.wikipedia.org/wiki/Till | Physical sciences | Sedimentology | Earth science |
Supraglacial flow tills refer to tills that are subject to a dense concentration of clasts and debris from meltout. These debris localities are then subsequently affected by ablation. Due to their unstable nature, they are subject to downslope flow, and thus named "flow till." Properties of flow tills vary, and can dep... | Till | Wikipedia | 406 | 44545 | https://en.wikipedia.org/wiki/Till | Physical sciences | Sedimentology | Earth science |
A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat non-vascular autotrophs such as mosses, algae and lichens, but do not include thos... | Herbivore | Wikipedia | 364 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Definition and related terms
Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in general are known as primary consumers.
Herbivory is usually limited to animals that eat plants. Ins... | Herbivore | Wikipedia | 450 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Herbivory among four-limbed terrestrial vertebrates, the tetrapods, developed in the Late Carboniferous (307–299 million years ago). The oldest known example being Desmatodon hesperis. Early tetrapods were large amphibious piscivores. While amphibians continued to feed on fish and insects, some reptiles began exploring... | Herbivore | Wikipedia | 452 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Two herbivore feeding strategies are grazing (e.g. cows) and browsing (e.g. moose). For a terrestrial mammal to be called a grazer, at least 90% of the forage has to be grass, and for a browser at least 90% tree leaves and twigs. An intermediate feeding strategy is called "mixed-feeding". In their daily need to take up... | Herbivore | Wikipedia | 465 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
This model has been criticized as circular and untestable. Critics have pointed out that its proponents use examples that fit the theory, but do not use the model when it does not fit the reality. Other critics point out that animals do not have the ability to assess and maximize their potential gains, therefore the op... | Herbivore | Wikipedia | 481 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Plant-herbivore interactions
Interactions between plants and herbivores can play a prevalent role in ecosystem dynamics such community structure and functional processes. Plant diversity and distribution is often driven by herbivory, and it is likely that trade-offs between plant competitiveness and defensiveness, and ... | Herbivore | Wikipedia | 346 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Abiotic factors such as climate and biogeographical features also impact plant-herbivore communities and interactions. For example, in temperate freshwater wetlands herbivorous waterfowl communities change according to season, with species that eat above-ground vegetation being abundant during summer, and species that ... | Herbivore | Wikipedia | 501 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Plant modification occurs when herbivores manipulate their plant prey to increase feeding. For example, some caterpillars roll leaves to reduce the effectiveness of plant defenses activated by sunlight.
Plant defense
A plant defense is a trait that increases plant fitness when faced with herbivory. This is measured r... | Herbivore | Wikipedia | 441 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Carbon-based defenses include terpenes and phenolics. Terpenes are derived from 5-carbon isoprene units and comprise essential oils, carotenoids, resins, and latex. They can have several functions that disrupt herbivores such as inhibiting adenosine triphosphate (ATP) formation, molting hormones, or the nervous system.... | Herbivore | Wikipedia | 464 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Several factors play into these fluctuating populations and help stabilize predator-prey dynamics. For example, spatial heterogeneity is maintained, which means there will always be pockets of plants not found by herbivores. This stabilizing dynamic plays an especially important role for specialist herbivores that feed... | Herbivore | Wikipedia | 475 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Trophic cascades and environmental degradation
When herbivores are affected by trophic cascades, plant communities can be indirectly affected. Often these effects are felt when predator populations decline and herbivore populations are no longer limited, which leads to intense herbivore foraging which can suppress pla... | Herbivore | Wikipedia | 368 | 44568 | https://en.wikipedia.org/wiki/Herbivore | Biology and health sciences | Ethology | null |
Big O notation is a mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity. Big O is a member of a family of notations invented by German mathematicians Paul Bachmann, Edmund Landau, and others, collectively called Bachmann–Landau notation... | Big O notation | Wikipedia | 511 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
And in both of these definitions the limit point (whether or not) is a cluster point of the domains of and i. e., in every neighbourhood of there have to be infinitely many points in common. Moreover, as pointed out in the article about the limit inferior and limit superior, the (at least on the extended real num... | Big O notation | Wikipedia | 502 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
There are two formally close, but noticeably different, usages of this notation:
infinite asymptotics
infinitesimal asymptotics.
This distinction is only in application and not in principle, however—the formal definition for the "big O" is the same for both cases, only with different limits for the function argument... | Big O notation | Wikipedia | 490 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
In particular, if a function may be bounded by a polynomial in , then as tends to infinity, one may disregard lower-order terms of the polynomial. The sets and are very different. If is greater than one, then the latter grows much faster. A function that grows faster than for any is called superpolynomial. One ... | Big O notation | Wikipedia | 498 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
whenever either or holds. This definition allows all of the coordinates of to increase to infinity. In particular, the statement
(i.e., ) is quite different from
(i.e., ).
Under this definition, the subset on which a function is defined is significant when generalizing statements from the univariate setting to t... | Big O notation | Wikipedia | 414 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
Example
Suppose an algorithm is being developed to operate on a set of n elements. Its developers are interested in finding a function T(n) that will express how long the algorithm will take to run (in some arbitrary measurement of time) in terms of the number of elements in the input set. The algorithm works by fir... | Big O notation | Wikipedia | 470 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
Here is a list of classes of functions that are commonly encountered when analyzing the running time of an algorithm. In each case, c is a positive constant and n increases without bound. The slower-growing functions are generally listed first.
The statement is sometimes weakened to to derive simpler formulas for a... | Big O notation | Wikipedia | 487 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
The Hardy–Littlewood definition is used mainly in analytic number theory, and the Knuth definition mainly in computational complexity theory; the definitions are not equivalent.
The Hardy–Littlewood definition
In 1914 G.H. Hardy and J.E. Littlewood introduced the new symbol which is defined as follows:
as if
Th... | Big O notation | Wikipedia | 443 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
Informally, especially in computer science, the big O notation often can be used somewhat differently to describe an asymptotic tight bound where using big Theta Θ notation might be more factually appropriate in a given context. For example, when considering a function T(n) = 73n3 + 22n2 + 58, all of the following are ... | Big O notation | Wikipedia | 410 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
Extensions to the Bachmann–Landau notations
Another notation sometimes used in computer science is Õ (read soft-O), which hides polylogarithmic factors. There are two definitions in use: some authors use f(n) = Õ(g(n)) as shorthand for for some k, while others use it as shorthand for . When is polynomial in n, there... | Big O notation | Wikipedia | 468 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
The symbol O was first introduced by number theorist Paul Bachmann in 1894, in the second volume of his book Analytische Zahlentheorie ("analytic number theory"). The number theorist Edmund Landau adopted it, and was thus inspired to introduce in 1909 the notation o; hence both are now called Landau symbols. These nota... | Big O notation | Wikipedia | 477 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
The big-O originally stands for "order of" ("Ordnung", Bachmann 1894), and is thus a Latin letter. Neither Bachmann nor Landau ever call it "Omicron". The symbol was much later on (1976) viewed by Knuth as a capital omicron, probably in reference to his definition of the symbol Omega. The digit zero should not be used. | Big O notation | Wikipedia | 84 | 44578 | https://en.wikipedia.org/wiki/Big%20O%20notation | Mathematics | Algorithms | null |
In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs, heart, and other vital organs ... | Rib | Wikipedia | 510 | 44593 | https://en.wikipedia.org/wiki/Rib | Biology and health sciences | Skeletal system | Biology |
The neck of the rib is a flattened part that extends laterally from the head. The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest (cris... | Rib | Wikipedia | 479 | 44593 | https://en.wikipedia.org/wiki/Rib | Biology and health sciences | Skeletal system | Biology |
The rib cage is separated from the lower abdomen by the thoracic diaphragm which controls breathing. When the diaphragm contracts, the thoracic cavity is expanded, reducing intra-thoracic pressure and drawing air into the lungs. This happens through one of two actions (or a mix of the two): when the lower ribs the diap... | Rib | Wikipedia | 415 | 44593 | https://en.wikipedia.org/wiki/Rib | Biology and health sciences | Skeletal system | Biology |
In jawed fish, there are often two sets of ribs attached to the vertebral column. One set, the dorsal ribs, are found in the dividing septum between the upper and lower parts of the main muscle segments, projecting roughly sideways from the vertebral column. The second set, the ventral ribs arise from the vertebral col... | Rib | Wikipedia | 488 | 44593 | https://en.wikipedia.org/wiki/Rib | Biology and health sciences | Skeletal system | Biology |
Ribs as food are widely used from many animals. The ribs are the less meaty part of the meat chop and they are often cooked as part of a slab; five or more is known as a rack, as in a rack of lamb. Short ribs are ribs of beef either served singly or several as a plate. A rib steak from beef is a popular choice used in ... | Rib | Wikipedia | 96 | 44593 | https://en.wikipedia.org/wiki/Rib | Biology and health sciences | Skeletal system | Biology |
Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending o... | Positronium | Wikipedia | 479 | 44596 | https://en.wikipedia.org/wiki/Positronium | Physical sciences | Atomic physics | Physics |
Positronium in the 2S state is metastable having a lifetime of against annihilation. The positronium created in such an excited state will quickly cascade down to the ground state, where annihilation will occur more quickly.
Measurements
Measurements of these lifetimes and energy levels have been used in precision t... | Positronium | Wikipedia | 470 | 44596 | https://en.wikipedia.org/wiki/Positronium | Physical sciences | Atomic physics | Physics |
The lowest energy level of positronium () is . The next level is . The negative sign is a convention that implies a bound state. Positronium can also be considered by a particular form of the two-body Dirac equation; Two particles with a Coulomb interaction can be exactly separated in the (relativistic) center-of-mome... | Positronium | Wikipedia | 204 | 44596 | https://en.wikipedia.org/wiki/Positronium | Physical sciences | Atomic physics | Physics |
Formation and decay in materials
After a radioactive atom in a material undergoes a β+ decay (positron emission), the resulting high-energy positron slows down by colliding with atoms, and eventually annihilates with one of the many electrons in the material. It may however first form positronium before the annihilati... | Positronium | Wikipedia | 462 | 44596 | https://en.wikipedia.org/wiki/Positronium | Physical sciences | Atomic physics | Physics |
A discrepancy known as the ortho-positronium lifetime puzzle persisted for some time, but was resolved with further calculations and measurements. Measurements were in error because of the lifetime measurement of unthermalised positronium, which was produced at only a small rate. This had yielded lifetimes that were to... | Positronium | Wikipedia | 411 | 44596 | https://en.wikipedia.org/wiki/Positronium | Physical sciences | Atomic physics | Physics |
Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure o... | Chalcedony | Wikipedia | 505 | 44599 | https://en.wikipedia.org/wiki/Chalcedony | Physical sciences | Silicate minerals | Earth science |
Chrysoprase (also spelled chrysophrase) is a green variety of chalcedony, which has been colored by nickel oxide. (The darker varieties of chrysoprase are also referred to as prase. However, the term prase is also used to describe green quartz and to a certain extent is a color-descriptor, rather than a rigorously defi... | Chalcedony | Wikipedia | 441 | 44599 | https://en.wikipedia.org/wiki/Chalcedony | Physical sciences | Silicate minerals | Earth science |
In Greenland, white to greyish chalcedony is known from volcanic strata of the Paleocene, in the Disko-Nuussuaq area (West Greenland) and from the Scoresby Sound area (East Greenland). A light blue variety of chalcedony is known from Illorsuit, formed in the volcanic rocks along the southern coast of the island. Becaus... | Chalcedony | Wikipedia | 489 | 44599 | https://en.wikipedia.org/wiki/Chalcedony | Physical sciences | Silicate minerals | Earth science |
In the 19th century, Idar-Oberstein, Germany, became the world's largest chalcedony processing center, working mostly on agates. Most of these agates were from Latin America, in particular Brazil. Originally the agate carving industry around Idar and Oberstein was driven by local deposits that were mined in the 15th ce... | Chalcedony | Wikipedia | 394 | 44599 | https://en.wikipedia.org/wiki/Chalcedony | Physical sciences | Silicate minerals | Earth science |
Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral cha... | Carnelian | Wikipedia | 474 | 44600 | https://en.wikipedia.org/wiki/Carnelian | Physical sciences | Silicate minerals | Earth science |
There is a Neo-Assyrian seal made of carnelian in the Western Asiatic Seals collection of the British Museum that shows Ishtar-Gula as a star goddess. She is holding a ring of royal authority and is seated on a throne. She is shown with the spade of Marduk (his symbol), Sibbiti (seven) gods, the stylus of Nabu and a wo... | Carnelian | Wikipedia | 429 | 44600 | https://en.wikipedia.org/wiki/Carnelian | Physical sciences | Silicate minerals | Earth science |
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, ... | Calcite | Wikipedia | 505 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
Properties
The diagnostic properties of calcite include a defining Mohs hardness of 3, a specific gravity of 2.71 and, in crystalline varieties, a vitreous luster. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with im... | Calcite | Wikipedia | 398 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
Single calcite crystals display an optical property called birefringence (double refraction). This strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect (using calcite) was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength ... | Calcite | Wikipedia | 446 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
If the amount of dissolved carbon dioxide drops, the reaction reverses to precipitate calcite. As a result, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on such factors as the water temperature, pH, and dissolved ion concentrations. When conditions are right for precipitation... | Calcite | Wikipedia | 510 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
St. Andreasberg, Harz Mountains, and Freiberg, Saxony can find calcite.
Use and applications
Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. Many other cultures have used the material for similar car... | Calcite | Wikipedia | 470 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
Calcite can be used to alleviate water pollution caused by the excessive growth of cyanobacteria. Lakes and rivers can lead to cyanobacteria blooms due to eutrophication, which pollutes water resources. Phosphorus (P) is the leading cause of excessive growth of cyanobacteria. As an active capping material, calcite can ... | Calcite | Wikipedia | 507 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
Calcite formation can proceed by several pathways, from the classical terrace ledge kink model to the crystallization of poorly ordered precursor phases like amorphous calcium carbonate (ACC) via an Ostwald ripening process, or via the agglomeration of nanocrystals.
The crystallization of ACC can occur in two stages. ... | Calcite | Wikipedia | 477 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
In Earth history
Calcite seas existed in Earth's history when the primary inorganic precipitate of calcium carbonate in marine waters was low-magnesium calcite (lmc), as opposed to the aragonite and high-magnesium calcite (hmc) precipitated today. Calcite seas alternated with aragonite seas over the Phanerozoic, bein... | Calcite | Wikipedia | 428 | 44603 | https://en.wikipedia.org/wiki/Calcite | Physical sciences | Minerals | Earth science |
Ultramarine is a deep blue color pigment which was originally made by grinding lapis lazuli into a powder. Its lengthy grinding and washing process makes the natural pigment quite valuable—roughly ten times more expensive than the stone it comes from and as expensive as gold.
The name ultramarine comes from the Latin ... | Ultramarine | Wikipedia | 508 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
Natural production
Historically, lapis lazuli stone was mined in Afghanistan and shipped overseas to Europe.
A method to produce ultramarine from lapis lazuli was introduced and later described by Cennino Cennini in the 15th century. This process consisted of grinding the lapis lazuli mineral, mixing the ground mater... | Ultramarine | Wikipedia | 434 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
The preparation is typically made in steps:
The first part of the process takes place at 700 to 750 °C in a closed furnace, so that sulfur, carbon and organic substances give reducing conditions. This yields a yellow-green product sometimes used as a pigment.
In the second step, air or sulfur dioxide at 350 to 450 °C... | Ultramarine | Wikipedia | 444 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
Ultramarine is the aluminosilicate zeolite with a sodalite structure. Sodalite consists of interconnected aluminosilicate cages. Some of these cages contain polysulfide () groups that are the chromophore (color centre). The negative charge on these ions is balanced by ions that also occupy these cages.
The chromophor... | Ultramarine | Wikipedia | 460 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
During the Renaissance, ultramarine was the finest and most expensive blue that could be used by painters. Color infrared photogenic studies of ultramarine in 13th and 14th-century Sienese panel paintings have revealed that historically, ultramarine has been diluted with white lead pigment in an effort to use the color... | Ultramarine | Wikipedia | 491 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
17th and 18th centuries
Johannes Vermeer made extensive use of ultramarine in his paintings. The turban of the Girl with a Pearl Earring is painted with a mixture of ultramarine and lead white, with a thin glaze of pure ultramarine over it. In Lady Standing at a Virginal, the young woman's dress is painted with a mixt... | Ultramarine | Wikipedia | 422 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
A plague known as "ultramarine sickness" has occasionally been observed among ultramarine oil paintings as a grayish or yellowish gray discoloration of the paint surface. This can occur with artificial ultramarine that is used industrially. The cause of this has been debated among experts, however, potential causes inc... | Ultramarine | Wikipedia | 474 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
The term "ultramarine green" indicates a dark green while barium chromate is sometimes referred to as "ultramarine yellow". Ultramarine pigment has also been termed "Gmelin's Blue," "Guimet's Blue," "New blue," "Oriental Blue," and "Permanent Blue". | Ultramarine | Wikipedia | 67 | 44633 | https://en.wikipedia.org/wiki/Ultramarine | Physical sciences | Colors | Physics |
Lazurite, old name Azure spar is a tectosilicate mineral with sulfate, sulfur and chloride with formula . It is a feldspathoid and a member of the sodalite group. Lazurite crystallizes in the isometric system although well‐formed crystals are rare. It is usually massive and forms the bulk of the gemstone lapis lazuli.
... | Lazurite | Wikipedia | 472 | 44652 | https://en.wikipedia.org/wiki/Lazurite | Physical sciences | Silicate minerals | Earth science |
Structure
Lazurite and hauyne seem to have the same structure and both are sulfate-dominant minerals. Lazurite is a pigment (opalescent) and has a bright blue streak (especially as a component of the semiprecious stone lapis lazuli). Many hauynes have a white or pale blue streak and are translucent. The difference mig... | Lazurite | Wikipedia | 91 | 44652 | https://en.wikipedia.org/wiki/Lazurite | Physical sciences | Silicate minerals | Earth science |
Porcupines are large rodents with coats of sharp spines, or quills, that protect them against predation. The term covers two families of animals: the Old World porcupines of the family Hystricidae, and the New World porcupines of the family Erethizontidae. Both families belong to the infraorder Hystricognathi within t... | Porcupine | Wikipedia | 447 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
Taxonomy
A porcupine is any of 30 species of rodents belonging to the families Erethizontidae (genera: Coendou, Erethizon, and Chaetomys) or Hystricidae (genera: Atherurus, Hystrix, and Trichys). Porcupines vary in size considerably: Rothschild's porcupine of South America weighs less than a kilogram (2.2 lb); the cres... | Porcupine | Wikipedia | 414 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
Defence
Defensive behaviour displays in a porcupine depend on sight, scent, and sound. Often, these displays are shown when a porcupine becomes agitated or annoyed. There are four main displays seen in a porcupine: (in order from least to most aggressive) quill erection, teeth clattering, odour emission, and attack. A ... | Porcupine | Wikipedia | 477 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
There are some possible antibiotic properties within the quills, specifically associated with the free fatty acids coating the quills. The antibiotic properties are believed to aid a porcupine that has suffered from self-injury.
Uses by humans
Porcupines are seldom eaten in Western culture but are eaten often in Sout... | Porcupine | Wikipedia | 477 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
Infraorder Hystricognathi
Family Hystricidae: Old World porcupines
African brush-tailed porcupine, Atherurus africanus
African crested porcupine, Hystrix cristata
Asiatic brush-tailed porcupine, Atherurus macrourus
Cape porcupine, Hystrix africaeaustralis
Indian porcupine, Hystrix indicus
Malayan porcupine, Hyst... | Porcupine | Wikipedia | 511 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
Family Hydrochaeridae: capybara
Family Caviidae: Guinea-pigs
Family Dasyproctidae: agoutis and acouchis
Superfamily Octodontoidea
Family Abrocomidae: chinchilla-rats
Family Octodontidae: degus
Family Ctenomyidae: tuco-tucos
Family Echimyidae: spiny rats
Family Myocastoridae: nutrias
Family Capromyidae: hutias
... | Porcupine | Wikipedia | 118 | 44668 | https://en.wikipedia.org/wiki/Porcupine | Biology and health sciences | Rodents | null |
The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation CMYK refers to the four ink plates used: cyan, magenta, yellow, and key (most often black).
Th... | CMYK color model | Wikipedia | 464 | 44682 | https://en.wikipedia.org/wiki/CMYK%20color%20model | Physical sciences | Basics_7 | null |
The CMYK color model is based on the CMY color model, which omits the black ink. Four-color printing uses black ink in addition to subtractive primaries for several reasons:
In traditional preparation of color separations, a red keyline on the black line art marked the outline of solid or tint color areas. In some cas... | CMYK color model | Wikipedia | 442 | 44682 | https://en.wikipedia.org/wiki/CMYK%20color%20model | Physical sciences | Basics_7 | null |
Other printer color models
CMYK, as well as all other process color printing, is contrasted with spot color printing, in which specific colored inks are used to generate the colors seen. Some printing presses are capable of printing with both four-color process inks and additional spot color inks at the same time. Hig... | CMYK color model | Wikipedia | 450 | 44682 | https://en.wikipedia.org/wiki/CMYK%20color%20model | Physical sciences | Basics_7 | null |
Spectrum of printed paper
To reproduce color, the CMYK color model codes for absorbing light rather than emitting it (as is assumed by RGB). The K component ideally absorbs all wavelengths and is therefore achromatic. The cyan, magenta, and yellow components are used for color reproduction and they may be viewed as th... | CMYK color model | Wikipedia | 499 | 44682 | https://en.wikipedia.org/wiki/CMYK%20color%20model | Physical sciences | Basics_7 | null |
Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damage may result in a lack of ability to feel pain, which can lead to the loss of parts of... | Leprosy | Wikipedia | 422 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Leprosy is not highly contagious. People with leprosy can live with their families and go to school and work. In the 1980s, there were 5.2 million cases globally, but by 2020 this decreased to fewer than 200,000. Most new cases occur in one of 14 countries, with India accounting for more than half of all new cases. In ... | Leprosy | Wikipedia | 395 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Leprosy can affect people in different ways. The average incubation period is five years. People may begin to notice symptoms within the first year or up to 20 years after infection. The first noticeable sign of leprosy is often the development of pale or pink coloured patches of skin that may be insensitive to tempera... | Leprosy | Wikipedia | 411 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Naturally occurring infections have been reported in nonhuman primates (including the African chimpanzee, the sooty mangabey, and the cynomolgus macaque), armadillos, and red squirrels. Multilocus sequence typing of the armadillo M. leprae strains suggests that they were of human origin for at most a few hundred years.... | Leprosy | Wikipedia | 469 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Leprosy is not sexually transmitted and is not spread through pregnancy to the unborn child. The majority (95%) of people who are exposed to M. leprae do not develop leprosy; casual contact such as shaking hands and sitting next to someone with leprosy does not lead to transmission. People are considered non-infectious... | Leprosy | Wikipedia | 442 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Mechanism
Most leprosy complications are the result of nerve damage. The nerve damage occurs from direct invasion by the M. leprae bacteria and a person's immune response resulting in inflammation. The molecular mechanism underlying how M. leprae produces the symptoms of leprosy is not clear, but M. leprae has been sh... | Leprosy | Wikipedia | 354 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Skin lesions can be single or many, and usually hypopigmented, although occasionally reddish or copper-colored. The lesions may be flat (macules), raised (papules), or solid elevated areas (nodular). Experiencing sensory loss at the skin lesion is a feature that can help determine if the lesion is caused by leprosy or ... | Leprosy | Wikipedia | 423 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Classification
Several different approaches for classifying leprosy exist. There are similarities between the classification approaches.
The World Health Organization (WHO) system distinguishes "paucibacillary" and "multibacillary" based on the proliferation of bacteria. ("pauci-" refers to a small quantity.)
The Ri... | Leprosy | Wikipedia | 506 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
A novel vaccine called LepVax entered clinical trials in 2017 with the first encouraging results reported on 24 participants published in 2020. If successful, this would be the first leprosy-specific vaccine available.
Treatment
Several leprostatic agents are available for treatment. A three-drug regimen of rifampi... | Leprosy | Wikipedia | 364 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Outcomes
Although leprosy has been curable since the mid-20th century, left untreated it can cause permanent physical impairments and damage to a person's nerves, skin, eyes, and limbs. Despite leprosy not being very infectious and having a low pathogenicity, there is still significant stigma and prejudice associated ... | Leprosy | Wikipedia | 400 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
The number of new leprosy cases is difficult to measure and monitor because of leprosy's long incubation period, delays in diagnosis after the onset of the disease, and lack of medical care in affected areas. The registered prevalence of the disease is used to determine disease burden. Registered prevalence is a useful... | Leprosy | Wikipedia | 486 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
The oldest strains of leprosy known from Europe are from Great Chesterford in southeast England and date back to AD 415–545. These findings suggest a different path for the spread of leprosy, meaning it may have originated in western Eurasia. This study also indicates that there were more strains in Europe at the time ... | Leprosy | Wikipedia | 477 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Treatment
Chaulmoogra tree oil was used topically to manage Hansen's disease for centuries. Chaulmoogra oil could not be taken orally without causing nausea or injected without forming an abscess. Leprosy was once believed to be highly contagious and was treated with mercury, as was syphilis, which was first described... | Leprosy | Wikipedia | 509 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
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