title
stringlengths 1
149
⌀ | section
stringlengths 1
1.9k
⌀ | text
stringlengths 13
73.5k
|
|---|---|---|
Glass
|
Physical properties
|
Optical Glass is in widespread use in optical systems due to its ability to refract, reflect, and transmit light following geometrical optics. The most common and oldest applications of glass in optics are as lenses, windows, mirrors, and prisms. The key optical properties refractive index, dispersion, and transmission, of glass are strongly dependent on chemical composition and, to a lesser degree, its thermal history. Optical glass typically has a refractive index of 1.4 to 2.4, and an Abbe number (which characterises dispersion) of 15 to 100. Refractive index may be modified by high-density (refractive index increases) or low-density (refractive index decreases) additives.Glass transparency results from the absence of grain boundaries which diffusely scatter light in polycrystalline materials. Semi-opacity due to crystallization may be induced in many glasses by maintaining them for a long period at a temperature just insufficient to cause fusion. In this way, the crystalline, devitrified material, known as Réaumur's glass porcelain is produced. Although generally transparent to visible light, glasses may be opaque to other wavelengths of light. While silicate glasses are generally opaque to infrared wavelengths with a transmission cut-off at 4 μm, heavy-metal fluoride and chalcogenide glasses are transparent to infrared wavelengths of 7 to 18 μm. The addition of metallic oxides results in different coloured glasses as the metallic ions will absorb wavelengths of light corresponding to specific colours.
|
Glass
|
Physical properties
|
Other In the manufacturing process, glasses can be poured, formed, extruded and moulded into forms ranging from flat sheets to highly intricate shapes. The finished product is brittle but can be laminated or tempered to enhance durability. Glass is typically inert, resistant to chemical attack, and can mostly withstand the action of water, making it an ideal material for the manufacture of containers for foodstuffs and most chemicals. Nevertheless, although usually highly resistant to chemical attack, glass will corrode or dissolve under some conditions. The materials that make up a particular glass composition have an effect on how quickly the glass corrodes. Glasses containing a high proportion of alkali or alkaline earth elements are more susceptible to corrosion than other glass compositions.The density of glass varies with chemical composition with values ranging from 2.2 grams per cubic centimetre (2,200 kg/m3) for fused silica to 7.2 grams per cubic centimetre (7,200 kg/m3) for dense flint glass. Glass is stronger than most metals, with a theoretical tensile strength for pure, flawless glass estimated at 14 to 35 gigapascals (2,000,000 to 5,100,000 psi) due to its ability to undergo reversible compression without fracture. However, the presence of scratches, bubbles, and other microscopic flaws lead to a typical range of 14 to 175 megapascals (2,000 to 25,400 psi) in most commercial glasses. Several processes such as toughening can increase the strength of glass. Carefully drawn flawless glass fibres can be produced with strength of up to 11.5 gigapascals (1,670,000 psi).
|
Glass
|
Physical properties
|
Reputed flow The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another. This assumption is incorrect, as once solidified, glass stops flowing. The sags and ripples observed in old glass were already there the day it was made; manufacturing processes used in the past produced sheets with imperfect surfaces and non-uniform thickness (the near-perfect float glass used today only became widespread in the 1960s).A 2017 study computed the rate of flow of the medieval glass used in Westminster Abbey from the year 1268. The study found that the room temperature viscosity of this glass was roughly 1024 Pa·s which is about 1016 times less viscous than a previous estimate made in 1998, which focused on soda-lime silicate glass. Even with this lower viscosity, the study authors calculated that the maximum flow rate of medieval glass is 1nm per billion years, making it impossible to observe in a human timescale.
|
Glass
|
Types
|
Silicate Silicon dioxide (SiO2) is a common fundamental constituent of glass. Fused quartz is a glass made from chemically pure silica. It has very low thermal expansion and excellent resistance to thermal shock, being able to survive immersion in water while red hot, resists high temperatures (1000–1500 °C) and chemical weathering, and is very hard. It is also transparent to a wider spectral range than ordinary glass, extending from the visible further into both the UV and IR ranges, and is sometimes used where transparency to these wavelengths is necessary. Fused quartz is used for high-temperature applications such as furnace tubes, lighting tubes, melting crucibles, etc. However, its high melting temperature (1723 °C) and viscosity make it difficult to work with. Therefore, normally, other substances (fluxes) are added to lower the melting temperature and simplify glass processing.
|
Glass
|
Types
|
Soda–lime Sodium carbonate (Na2CO3, "soda") is a common additive and acts to lower the glass-transition temperature. However, sodium silicate is water-soluble, so lime (CaO, calcium oxide, generally obtained from limestone), along with magnesium oxide (MgO), and aluminium oxide (Al2O3), are commonly added to improve chemical durability. Soda–lime glasses (Na2O) + lime (CaO) + magnesia (MgO) + alumina (Al2O3) account for over 75% of manufactured glass, containing about 70 to 74% silica by weight. Soda–lime–silicate glass is transparent, easily formed, and most suitable for window glass and tableware. However, it has a high thermal expansion and poor resistance to heat. Soda–lime glass is typically used for windows, bottles, light bulbs, and jars.
|
Glass
|
Types
|
Borosilicate Borosilicate glasses (e.g. Pyrex, Duran) typically contain 5–13% boron trioxide (B2O3). Borosilicate glasses have fairly low coefficients of thermal expansion (7740 Pyrex CTE is 3.25×10−6/°C as compared to about 9×10−6/°C for a typical soda–lime glass). They are, therefore, less subject to stress caused by thermal expansion and thus less vulnerable to cracking from thermal shock. They are commonly used for e.g. labware, household cookware, and sealed beam car head lamps.
|
Glass
|
Types
|
Lead The addition of lead(II) oxide into silicate glass lowers melting point and viscosity of the melt. The high density of lead glass (silica + lead oxide (PbO) + potassium oxide (K2O) + soda (Na2O) + zinc oxide (ZnO) + alumina) results in a high electron density, and hence high refractive index, making the look of glassware more brilliant and causing noticeably more specular reflection and increased optical dispersion. Lead glass has a high elasticity, making the glassware more workable and giving rise to a clear "ring" sound when struck. However, lead glass cannot withstand high temperatures well. Lead oxide also facilitates solubility of other metal oxides and is used in coloured glass. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glass); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda–lime glass (108.5 vs 106.5 Ω⋅cm, DC at 250 °C).
|
Glass
|
Types
|
Aluminosilicate Aluminosilicate glass typically contains 5–10% alumina (Al2O3). Aluminosilicate glass tends to be more difficult to melt and shape compared to borosilicate compositions, but has excellent thermal resistance and durability. Aluminosilicate glass is extensively used for fiberglass, used for making glass-reinforced plastics (boats, fishing rods, etc.), top-of-stove cookware, and halogen bulb glass.
|
Glass
|
Types
|
Other oxide additives The addition of barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses. Iron can be incorporated into glass to absorb infrared radiation, for example in heat-absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs ultraviolet wavelengths. Fluorine lowers the dielectric constant of glass. Fluorine is highly electronegative and lowers the polarizability of the material. Fluoride silicate glasses are used in manufacture of integrated circuits as an insulator.
|
Glass
|
Types
|
Glass-ceramics Glass-ceramic materials contain both non-crystalline glass and crystalline ceramic phases. They are formed by controlled nucleation and partial crystallisation of a base glass by heat treatment. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. Glass-ceramics exhibit advantageous thermal, chemical, biological, and dielectric properties as compared to metals or organic polymers.The most commercially important property of glass-ceramics is their imperviousness to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking and industrial processes. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.
|
Glass
|
Types
|
Fibreglass Fibreglass (also called glass fibre reinforced plastic, GRP) is a composite material made by reinforcing a plastic resin with glass fibres. It is made by melting glass and stretching the glass into fibres. These fibres are woven together into a cloth and left to set in a plastic resin.
|
Glass
|
Types
|
Fibreglass has the properties of being lightweight and corrosion resistant, and is a good insulator enabling its use as building insulation material and for electronic housing for consumer products. Fibreglass was originally used in the United Kingdom and United States during World War II to manufacture radomes. Uses of fibreglass include building and construction materials, boat hulls, car body parts, and aerospace composite materials.Glass-fibre wool is an excellent thermal and sound insulation material, commonly used in buildings (e.g. attic and cavity wall insulation), and plumbing (e.g. pipe insulation), and soundproofing. It is produced by forcing molten glass through a fine mesh by centripetal force, and breaking the extruded glass fibres into short lengths using a stream of high-velocity air. The fibres are bonded with an adhesive spray and the resulting wool mat is cut and packed in rolls or panels.
|
Glass
|
Types
|
Non-silicate Besides common silica-based glasses many other inorganic and organic materials may also form glasses, including metals, aluminates, phosphates, borates, chalcogenides, fluorides, germanates (glasses based on GeO2), tellurites (glasses based on TeO2), antimonates (glasses based on Sb2O3), arsenates (glasses based on As2O3), titanates (glasses based on TiO2), tantalates (glasses based on Ta2O5), nitrates, carbonates, plastics, acrylic, and many other substances. Some of these glasses (e.g. Germanium dioxide (GeO2, Germania), in many respects a structural analogue of silica, fluoride, aluminate, phosphate, borate, and chalcogenide glasses) have physico-chemical properties useful for their application in fibre-optic waveguides in communication networks and other specialised technological applications.Silica-free glasses may often have poor glass forming tendencies. Novel techniques, including containerless processing by aerodynamic levitation (cooling the melt whilst it floats on a gas stream) or splat quenching (pressing the melt between two metal anvils or rollers), may be used to increase cooling rate, or to reduce crystal nucleation triggers.
|
Glass
|
Types
|
Amorphous metals In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk.A number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs.
|
Glass
|
Types
|
Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.Experimental evidence indicates that the system Al-Fe-Si may undergo a first-order transition to an amorphous form (dubbed "q-glass") on rapid cooling from the melt. Transmission electron microscopy (TEM) images indicate that q-glass nucleates from the melt as discrete particles with a uniform spherical growth in all directions. While x-ray diffraction reveals the isotropic nature of q-glass, a nucleation barrier exists implying an interfacial discontinuity (or internal surface) between the glass and melt phases.
|
Glass
|
Types
|
Polymers Important polymer glasses include amorphous and glassy pharmaceutical compounds. These are useful because the solubility of the compound is greatly increased when it is amorphous compared to the same crystalline composition. Many emerging pharmaceuticals are practically insoluble in their crystalline forms. Many polymer thermoplastics familiar from everyday use are glasses. For many applications, like glass bottles or eyewear, polymer glasses (acrylic glass, polycarbonate or polyethylene terephthalate) are a lighter alternative to traditional glass.
|
Glass
|
Types
|
Molecular liquids and molten salts Molecular liquids, electrolytes, molten salts, and aqueous solutions are mixtures of different molecules or ions that do not form a covalent network but interact only through weak van der Waals forces or through transient hydrogen bonds. In a mixture of three or more ionic species of dissimilar size and shape, crystallization can be so difficult that the liquid can easily be supercooled into a glass. Examples include LiCl:RH2O (a solution of lithium chloride salt and water molecules) in the composition range 4<R<8. sugar glass, or Ca0.4K0.6(NO3)1.4. Glass electrolytes in the form of Ba-doped Li-glass and Ba-doped Na-glass have been proposed as solutions to problems identified with organic liquid electrolytes used in modern lithium-ion battery cells.
|
Glass
|
Production
|
Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda–lime glass for mass production is melted in glass melting furnaces. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.
|
Glass
|
Production
|
After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish. Container glass for common bottles and jars is formed by blowing and pressing methods. This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance.
|
Glass
|
Production
|
Once the desired form is obtained, glass is usually annealed for the removal of stresses and to increase the glass's hardness and durability. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition). Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating selenium dioxide (SeO2). Also, more readily reacting raw materials may be preferred over relatively inert ones, such as aluminum hydroxide (Al(OH)3) over alumina (Al2O3). Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.
|
Glass
|
Production
|
Colour Colour in glass may be obtained by addition of homogenously distributed electrically charged ions (or colour centres). While ordinary soda–lime glass appears colourless in thin section, iron(II) oxide (FeO) impurities produce a green tint in thick sections. Manganese dioxide (MnO2), which gives glass a purple colour, may be added to remove the green tint given by FeO. FeO and chromium(III) oxide (Cr2O3) additives are used in the production of green bottles. Iron (III) oxide, on the other-hand, produces yellow or yellow-brown glass. Low concentrations (0.025 to 0.1%) of cobalt oxide (CoO) produces rich, deep blue cobalt glass. Chromium is a very powerful colourising agent, yielding dark green.Sulphur combined with carbon and iron salts produces amber glass ranging from yellowish to almost black. A glass melt can also acquire an amber colour from a reducing combustion atmosphere. Cadmium sulfide produces imperial red, and combined with selenium can produce shades of yellow, orange, and red. The additive Copper(II) oxide (CuO) produces a turquoise colour in glass, in contrast to Copper(I) oxide (Cu2O) which gives a dull brown-red colour.
|
Glass
|
Uses
|
Architecture and windows Soda–lime sheet glass is typically used as transparent glazing material, typically as windows in external walls of buildings. Float or rolled sheet glass products is cut to size either by scoring and snapping the material, laser cutting, water jets, or diamond bladed saw. The glass may be thermally or chemically tempered (strengthened) for safety and bent or curved during heating. Surface coatings may be added for specific functions such as scratch resistance, blocking specific wavelengths of light (e.g. infrared or ultraviolet), dirt-repellence (e.g. self-cleaning glass), or switchable electrochromic coatings.Structural glazing systems represent one of the most significant architectural innovations of modern times, where glass buildings now often dominate skylines of many modern cities. These systems use stainless steel fittings countersunk into recesses in the corners of the glass panels allowing strengthened panes to appear unsupported creating a flush exterior. Structural glazing systems have their roots in iron and glass conservatories of the nineteenth century Tableware Glass is an essential component of tableware and is typically used for water, beer and wine drinking glasses. Wine glasses are typically stemware, i.e. goblets formed from a bowl, stem, and foot. Crystal or Lead crystal glass may be cut and polished to produce decorative drinking glasses with gleaming facets. Other uses of glass in tableware include decanters, jugs, plates, and bowls.
|
Glass
|
Uses
|
Packaging The inert and impermeable nature of glass makes it a stable and widely used material for food and drink packaging as glass bottles and jars. Most container glass is soda–lime glass, produced by blowing and pressing techniques. Container glass has a lower magnesium oxide and sodium oxide content than flat glass, and a higher silica, calcium oxide, and aluminum oxide content. Its higher content of water-insoluble oxides imparts slightly higher chemical durability against water, which is advantageous for storing beverages and food. Glass packaging is sustainable, readily recycled, reusable and refillable.For electronics applications, glass can be used as a substrate in the manufacture of integrated passive devices, thin-film bulk acoustic resonators, and as a hermetic sealing material in device packaging, including very thin solely glass based encapsulation of integrated circuits and other semiconductors in high manufacturing volumes.
|
Glass
|
Uses
|
Laboratories Glass is an important material in scientific laboratories for the manufacture of experimental apparatus because it is relatively cheap, readily formed into required shapes for experiment, easy to keep clean, can withstand heat and cold treatment, is generally non-reactive with many reagents, and its transparency allows for the observation of chemical reactions and processes. Laboratory glassware applications include flasks, petri dishes, test tubes, pipettes, graduated cylinders, glass lined metallic containers for chemical processing, fractionation columns, glass pipes, Schlenk lines, gauges, and thermometers. Although most standard laboratory glassware has been mass-produced since the 1920s, scientists still employ skilled glassblowers to manufacture bespoke glass apparatus for their experimental requirements.
|
Glass
|
Uses
|
Optics Glass is a ubiquitous material in optics by virtue of its ability to refract, reflect, and transmit light. These and other optical properties can be controlled by varying chemical compositions, thermal treatment, and manufacturing techniques. The many applications of glass in optics includes glasses for eyesight correction, imaging optics (e.g. lenses and mirrors in telescopes, microscopes, and cameras), fibre optics in telecommunications technology, and integrated optics. Microlenses and gradient-index optics (where the refractive index is non-uniform) find application in e.g. reading optical discs, laser printers, photocopiers, and laser diodes.
|
Glass
|
Uses
|
Art Glass as art dates to least 1300 BC shown as an example of natural glass found in Tutankhamun's pectoral, which also contained vitreous enamel, that is to say, melted coloured glass used on a metal backing. Enamelled glass, the decoration of glass vessels with coloured glass paints, has existed since 1300 BC, and was prominent in the early 20th century with Art Nouveau glass and that of the House of Fabergé in St. Petersburg, Russia. Both techniques were used in stained glass, which reached its height roughly from 1000 to 1550, before a revival in the 19th century.
|
Glass
|
Uses
|
The 19th century saw a revival in ancient glassmaking techniques including cameo glass, achieved for the first time since the Roman Empire, initially mostly for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy in the first French wave of the movement, producing coloured vases and similar pieces, often in cameo glass or in lustre glass techniques.Louis Comfort Tiffany in America specialised in stained glass, both secular and religious, in panels and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. Small studios may hand-produce glass artworks. Techniques for producing glass art include blowing, kiln-casting, fusing, slumping, pâte de verre, flame-working, hot-sculpting and cold-working. Cold work includes traditional stained glass work and other methods of shaping glass at room temperature. Objects made out of glass include vessels, paperweights, marbles, beads, sculptures and installation art.
|
Natural magic
|
Natural magic
|
Natural magic in the context of Renaissance magic is that part of the occult which deals with natural forces directly, as opposed to ceremonial magic which deals with the summoning of spirits. Natural magic sometimes makes use of physical substances from the natural world such as stones or herbs.Natural magic so defined includes astrology, alchemy, and disciplines that we would today consider fields of natural science, such as astronomy and chemistry (which developed and diverged from astrology and alchemy, respectively, into the modern sciences they are today) or botany (from herbology). The Jesuit scholar Athanasius Kircher wrote that "there are as many types of natural magic as there are subjects of applied sciences".Heinrich Cornelius Agrippa discusses natural magic in his Three Books of Occult Philosophy (1533), where he calls it "nothing else but the highest power of natural sciences". The Italian Renaissance philosopher Giovanni Pico della Mirandola, who founded the tradition of Christian Kabbalah, argued that natural magic was "the practical part of natural science" and was lawful rather than heretical.
|
Applied Thermal Engineering
|
Applied Thermal Engineering
|
Applied Thermal Engineering is a peer-reviewed scientific journal covering all aspects of the thermal engineering of advanced processes, including process integration, intensification, and development, together with the application of thermal equipment in conventional process plants, which includes its use for heat recovery. The editor-in-chief is C.N. Markides. The journal was established in 1981 as Journal of Heat Recovery Systems and renamed to Heat Recovery Systems and CHP in 1987. It obtained its current title in 1996.
|
Applied Thermal Engineering
|
Applied Thermal Engineering
|
According to the Journal Citation Reports, the journal has a 2021 impact factor of 6.465.
|
Uterus-like mass
|
Uterus-like mass
|
The uterus-like mass (ULM) is a tumorlike anatomical entity originally described in the ovary in 1981 and thereafter reported in several locations of the pelvis and abdominal cavity including broad ligament, greater omentum, cervix, small intestine, mesentery and conus medullaris. Basically, it is represented by a miniature uterus comprising a smooth muscle wall lined by endometrium thus outlining a uterus anatomical structure. Some of the reported cases have been associated to urinary tract and internal genitalia malformations whereas others appeared as a solitary finding. The term endomyometriosis has also been applied to this lesion.Different pathogenetic views have been suggested for this anomaly: a) a metaplastic change in endometriosis foci bringing about smooth muscle hyperplasia; b) a congenital anomaly due to fusion defects of the Müllerian ducts; and c) a sub-coelomic transformation of the mesenchyme.
|
Uterus-like mass
|
Uterus-like mass
|
ULM has also been reported associated to endometrial carcinoma and breast cancer. A clonal chromosome deletion 2p21 was found in endomyometriosis by Verhest et al. while Pai evidenced a strict relationship among ULM, breast cancer and elevated serum CA125 supporting the view of ULM being either hormone-dependent or a form of endometriosis. There have been reports of the finding of occurrence of endometriosis in leiomyomatosis peritonealis disseminata.More than 15 cases of ULM have been reported so far. A case of ULM was reported 22 years after total hysterectomy, another 17 years after. Abdominal pain and a palpable mass are among the main clinical findings.
|
Uterus-like mass
|
Uterus-like mass
|
Anyway, the phenomenon of smooth muscle cell metaplasia occurring in association with endometriosis (endomyometriosis), as well as of smooth muscle differentiation at endometrio-myometrial junction independently from actually engendering uterus-like configurations in several locations of the pelvis, have been pointed out by several authors.A magnetic resonance account of this lesion type has been provided by Menn et al.
|
Jacquet module
|
Jacquet module
|
In mathematics, the Jacquet module is a module used in the study of automorphic representations. The Jacquet functor is the functor that sends a linear representation to its Jacquet module. They are both named after Hervé Jacquet.
|
Jacquet module
|
Definition
|
The Jacquet module J(V) of a representation (π,V) of a group N is the space of co-invariants of N; or in other words the largest quotient of V on which N acts trivially, or the zeroth homology group H0(N,V). In other words, it is the quotient V/VN where VN is the subspace of V generated by elements of the form π(n)v - v for all n in N and all v in V.
|
Jacquet module
|
Definition
|
The Jacquet functor J is the functor taking V to its Jacquet module J(V).
|
Jacquet module
|
Applications
|
Jacquet modules are used to classify admissible irreducible representations of a reductive algebraic group G over a local field, and N is the unipotent radical of a parabolic subgroup of G. In the case of p-adic groups, they were studied by Hervé Jacquet (1971).
For the general linear group GL(2), the Jacquet module of an admissible irreducible representation has dimension at most two. If the dimension is zero, then the representation is called a supercuspidal representation. If the dimension is one, then the representation is a special representation. If the dimension is two, then the representation is a principal series representation.
|
Andersonite
|
Andersonite
|
Andersonite, Na2Ca(UO2)(CO3)3·6H2O, or hydrated sodium calcium uranyl carbonate is a rare uranium carbonate mineral that was first described in 1948. Named after Charles Alfred Anderson (1902–1990) of the United States Geological Survey, who first described the mineral species, it is found in sandstone-hosted uranium deposits. It has a high vitreous to pearly luster and is fluorescent. Andersonite specimens will usually glow a bright lemon yellow (or green with blue hints depending on the deposit) in ultraviolet light. It is commonly found as translucent small rhombohedral crystals that have angles close to 90 degrees although its crystal system is nominally trigonal. Its Mohs hardness is 2.5, with an average specific gravity of 2.8.
|
Andersonite
|
Andersonite
|
It occurs in the oxidized zone of uranium-bearing polymetallic ore deposits. It also may occur as an efflorescent crust on the walls and timbers of uranium mines. As this mineral is water-soluble, samples must be stored in dry conditions. It occurs with schrockingerite, bayleyite, schwarzites, boltwoodite, liebigite and gypsum.It was first described in 1948 for an occurrence in the Hillside Mine near Bagdad, Eureka District, Yavapai County, Arizona.
|
JR Ogura Station
|
JR Ogura Station
|
JR Ogura Station (JR小倉駅, JR Ogura-eki) is a train station Uji, Kyoto Prefecture, Japan, operated by West Japan Railway Company (JR West).
|
JR Ogura Station
|
Lines
|
JR Ogura Station is served by the Nara Line.
|
JR Ogura Station
|
Station Layout
|
The station has two side platforms serving one track each.
Platforms
|
JR Ogura Station
|
Passenger statistics
|
According to the Kyoto Prefecture statistical report, the average number of passengers per day is as follows.
|
JR Ogura Station
|
History
|
The station opened on 3 March 2001. It opened at the same time as the double track between Uji Station and Shinden Station on the Nara Line. The IC card ticket "ICOCA" can be used since 1 November 2003. Station numbering was introduced in March 2018 with JR Fujinomori being assigned station number JR-D10.
|
100,000
|
100,000
|
100,000 (one hundred thousand) is the natural number following 99,999 and preceding 100,001. In scientific notation, it is written as 105.
|
100,000
|
Terms for 100,000
|
In Bangladesh, India, Pakistan and South Asia, one hundred thousand is called a lakh, and is written as 1,00,000. The Thai, Lao, Khmer and Vietnamese languages also have separate words for this number: แสน, ແສນ, សែន (all saen), and ức respectively. The Malagasy word is hetsy.In Cyrillic numerals, it is known as the legion (легион): or .
|
100,000
|
Values of 100,000
|
In astronomy, 100,000 metres, 100 kilometres, or 100 km (62 miles) is the altitude at which the Fédération Aéronautique Internationale (FAI) defines spaceflight to begin.
In the Irish language, céad míle fáilte (pronounced [ˌceːd̪ˠ ˈmʲiːlʲə ˈfˠaːlʲtʲə]) is a popular greeting meaning "a hundred thousand welcomes".
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
100,001 to 199,999 100,003 = smallest 6-digit prime number 100,128 = smallest triangular number with 6 digits and the 447th triangular number 100,151 = twin prime with 100,153 100,153 = twin prime with 100,151 100,255 = Friedman number 100,489 = 3172, the smallest 6-digit square 101,101 = smallest palindromic Carmichael number 101,723 = smallest prime number whose square is a pandigital number containing each digit from 0 to 9 102,564 = The smallest parasitic number 103,049 = little Schroeder number 103,680 = highly totient number 103,769 = the number of combinatorial types of 5-dimensional parallelohedra 103,823 = 473, the smallest 6-digit cube and nice Friedman number (−1 + 0 + 3×8×2)3 104,480 = number of non-isomorphic set-systems of weight 14.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
104,723 = the 9,999th prime number 104,729 = the 10,000th prime number 104,869 = the smallest prime number containing every non-prime digit 104,976 = 184, 3-smooth number 105,071 = number of triangle-free graphs on 11 vertices 105,664 = harmonic divisor number 109,376 = 1-automorphic number 110,880 = highly composite number 111,111 = repunit 111,777 = smallest natural number requiring 17 syllables in American English, 19 in British English 113,634 = Motzkin number for n = 14 114,243/80,782 ≈ √2 114,689 = prime factor of F12 115,975 = Bell number 116,281 = 3412, square number, centered decagonal number, 18-gonal number 117,067 = first vampire prime 117,649 = 76 117,800 = harmonic divisor number 120,284 = Keith number 120,960 = highly totient number 121,393 = Fibonacci number 124,000 = number of Islamic prophets 125,673 = logarithmic number 127,777 = smallest natural number requiring 18 syllables in American English, 20 in British English 127,912 = Wedderburn–Etherington number 128,981 = Starts the first prime gap sequence of 2, 4, 6, 8, 10, 12, 14 129,106 = Keith number 130,321 = 194 131,071 = Mersenne prime 131,072 = 217 131,361 = Leyland number 134,340 = Pluto's minor planet designation 135,137 = Markov number 142,129 = 3772, square number, dodecagonal number 142,857 = Kaprekar number, smallest cyclic number in decimal.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
144,000 = number with religious significance 147,640 = Keith number 148,149 = Kaprekar number 152,381 = unique prime in base 20 156,146 = Keith number 160,000 = 204 161,051 = 115 161,280 = highly totient number 166,320 = highly composite number 167,400 = harmonic divisor number 167,894 = number of ways to partition {1,2,3,4,5,6,7,8} and then partition each cell (block) into subcells.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
173,600 = harmonic divisor number 174,680 = Keith number 174,763 = Wagstaff prime 177,147 = 311 177,777 = smallest natural number requiring 19 syllables in American English, 21 in British English 178,478 = Leyland number 181,440 = highly totient number 181,819 = Kaprekar number 183,186 = Keith number 183,231 = number of partially ordered set with 9 unlabeled elements 187,110 = Kaprekar number 194,481 = 214 195,025 = Pell number, Markov number 196,418 = Fibonacci number, Markov number 196,560 = the kissing number in 24 dimensions 196,883 = the dimension of the smallest nontrivial irreducible representation of the Monster group 196,884 = the coefficient of q in the Fourier series expansion of the j-invariant. The adjacency of 196883 and 196884 was important in suggesting monstrous moonshine.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
199,999 = prime number.
200,000 to 299,999 202,717 = k such that the sum of the squares of the first k primes is divisible by k.
206,098 – Large Schröder number 206,265 = rounded number of arc seconds in a radian (see also parsec), since 180 × 60 × 60/π = 206,264.806...
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
207,360 = highly totient number 208,012 = the Catalan number C12 208,335 = the largest number to be both triangular and square pyramidal 208,495 = Kaprekar number 212,159 = smallest unprimeable number ending in 1, 3, 7 or 9 221,760 = highly composite number 222,222 = repdigit 227,475 = Riordan number 234,256 = 224 237,510 = harmonic divisor number 238,591 = number of free 13-ominoes 241,920 = highly totient number 242,060 = harmonic divisor number 248,832 = 125, 100,00012, AKA a gross-great-gross (10012 great-grosses); the smallest fifth power that can be represented as the sum of only 6 fifth powers: 125 = 45 + 55 + 65 + 75 + 95 + 115 262,144 = 218; exponential factorial of 4; a superperfect number 262,468 = Leyland number 268,705 = Leyland number 274,177 = prime factor of the Fermat number F6 275,807/195,025 ≈ √2 277,200 = highly composite number 279,841 = 234 279,936 = 67 280,859 = a prime number whose square 78881777881 is tridigital 293,547 = Wedderburn–Etherington number 294,001 = smallest weakly prime number in base 10 294,685 = Markov number 298,320 = Keith number 300,000 to 399,999 310,572 = Motzkin number 317,811 = Fibonacci number 318,682 = Kaprekar number 325,878 = Fine number 326,981 = alternating factorial 329,967 = Kaprekar number 331,776 = 244 332,640 = highly composite number; harmonic divisor number 333,333 = repdigit 333,667 = sexy prime and unique prime 333,673 = sexy prime with 333,679 333,679 = sexy prime with 333,673 337,500 = 22 × 33 × 55 351,351 = only known odd abundant number that is not the sum of some of its proper, nontrivial (i.e. >1) divisors (sequence A122036 in the OEIS).
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
351,352 = Kaprekar number 355,419 = Keith number 356,643 = Kaprekar number 360,360 = harmonic divisor number; the smallest number divisible by all of the numbers 1 through 15 362,880 = 9!, highly totient number 370,261 = first prime followed by a prime gap of over 100 371,293 = 135, palindromic in base 12 (15AA5112) 389,305 = self-descriptive number in base 7 390,313 = Kaprekar number 390,625 = 58 397,585 = Leyland number 400,000 to 499,999 409,113 = sum of the first nine factorials 422,481 = smallest number whose fourth power is the sum of three smaller fourth powers 423,393 = Leyland number 426,389 = Markov number 426,569 = cyclic number in base 12 437,760 to 440,319 = any of these numbers will cause the Apple II+ and Apple IIe computers to crash to a monitor prompt when entered at the BASIC prompt, due to a short-cut in the Applesoft code programming of the overflow test when evaluating 16-bit numbers. Entering 440000 at the prompt has been used to hack games that are protected against entering commands at the prompt after the game is loaded.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
444,444 = repdigit 456,976 = 264 461,539 = Kaprekar number 466,830 = Kaprekar number 470,832 = Pell number 483,840 = highly totient number 498,960 = highly composite number 499,393 = Markov number 499,500 = Kaprekar number 500,000 to 599,999 500,500 = Kaprekar number, sum of first 1,000 integers 509,203 = Riesel number 510,510 = the product of the first seven prime numbers, thus the seventh primorial. It is also the product of four consecutive Fibonacci numbers—13, 21, 34, 55, the highest such sequence of any length to be also a primorial. And it is a double triangular number, the sum of all even numbers from 0 to 1428.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
514,229 = Fibonacci prime, Markov prime 518,859 = little Schroeder number 524,287 = Mersenne prime 524,288 = 219 524,649 = Leyland number 525,600 = minutes in a non-leap year 527,040 = minutes in a leap year 531,441 = 312 533,169 = Leyland number 533,170 = Kaprekar number 537,824 = 145 539,400 = harmonic divisor number 548,834 = equal to the sum of the sixth powers of its digits 554,400 = highly composite number 555,555 = repdigit 599,999 = prime number.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
600,000 to 699,999 604,800 = number of seconds in a week 614,656 = 284 625,992 = Riordan number 646,018 = Markov number 664,579 = the number of primes under 10,000,000 665,280 = highly composite number 665,857/470,832 ≈ √2 666,666 = repdigit 676,157 = Wedderburn–Etherington number 678,570 = Bell number 694,280 = Keith number 695,520 = harmonic divisor number 700,000 to 799,999 700,001 = prime number.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
707,281 = 294 720,720 = superior highly composite number; colossally abundant number; the smallest number divisible by all the numbers 1 through 16 725,760 = highly totient number 726,180 = harmonic divisor number 729,000 = 903 739,397 = largest prime that is both right- and left-truncatable.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
742,900 = Catalan number 753,480 = harmonic divisor number 759,375 = 155 765,623 = emirp, Friedman prime 56 × 72 − 6 ÷ 3 777,777 = repdigit, smallest natural number requiring 20 syllables in American English, 22 in British English, largest number in English not containing the letter 'i' in its name 783,700 = initial number of third century xx00 to xx99 (after 400 and 1,400) containing seventeen prime numbers {783,701, 783,703, 783,707, 783,719, 783,721, 783,733, 783,737, 783,743, 783,749, 783,763, 783,767, 783,779, 783,781, 783,787, 783,791, 783,793, 783,799} 799,999 = prime number.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
800,000 to 899,999 810,000 = 304 823,543 = 77 825,265 = smallest Carmichael number with 5 prime factors 832,040 = Fibonacci number 853,467 = Motzkin number 857,375 = 953 873,612 = 11 + 22 + 33 + 44 + 55 + 66 + 77 888,888 = repdigit 890,625 = 1-automorphic number 900,000 to 999,999 900,001 = prime number 901,971 = number of free 14-ominoes 909,091 = unique prime in base 10 923,521 = 314 925,765 = Markov number 925,993 = Keith number 950,976 = harmonic divisor number 967,680 = highly totient number 970,299 = 993, the largest 6-digit cube 998,001 = 9992, the largest 6-digit square. The reciprocal of this number, in its expanded form, lists all three-digit numbers in order except 998.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
998,991 = highest triangular number with 6 digits and the 1,413th triangular number 999,983 = largest 6-digit prime number 999,999 = repdigit. Rational numbers with denominators 7 and 13 have 6-digit repetends when expressed in decimal form, because 999999 is the smallest number one less than a power of 10 that is divisible by 7 and by 13, and it is the largest number in English not containing the letter 'l' in its name.
|
100,000
|
Selected 6-digit numbers (100,001–999,999)
|
Prime numbers Increments of 105 from zero through a million have the following prime counts: 9,592 primes between 0 and 100,000.99,991 is the largest prime number less than 100,000.8,392 primes between 100,000 and 200,000.This is a difference of 1,200 primes from the previous range.
104,729 is the 10,000th prime in this range.
199,999 is prime.8,013 primes between 200,000 and 300,000.A difference of 379 primes from the previous range.
224,737 is the 20,000th prime.7,863 primes between 300,000 and 400,000.A difference of 150 primes from the previous range.
350,377 is the 30,000th prime.7,678 primes between 400,000 and 500,000.A difference of 185 primes from the previous range.
Here, the difference increases by a count of 35.
479,909 is the 40,000th prime.7,560 primes between 500,000 and 600,000.A difference of 118 primes from the previous range.
7,560 is the twentieth highly composite number.
599,999 is prime.7,445 primes between 600,000 and 700,000.A difference of 115 primes from the previous range.
611,953 is the 50,000th prime.7,408 primes between 700,000 and 800,000.A difference of 37 primes from the previous range.
700,001 and 799,999 are both prime.
746,773 is the 60,000th prime.7,323 primes between 800,000 and 900,000.A difference of 85 primes from the previous range.
Here, the difference increases by a count of 48.
882,377 is the 70,000th prime.7,224 primes between 900,000 and 1,000,000.A difference of 99 primes from the previous range.
The difference increases again, by a count of 14.
900,001 is prime.In total, there are 68,906 prime numbers between 100,000 and 1,000,000.
|
Model risk
|
Model risk
|
In finance, model risk is the risk of loss resulting from using insufficiently accurate models to make decisions, originally and frequently in the context of valuing financial securities. However, model risk is more and more prevalent in activities other than financial securities valuation, such as assigning consumer credit scores, real-time probability prediction of fraudulent credit card transactions, and computing the probability of air flight passenger being a terrorist. Rebonato in 2002 defines model risk as "the risk of occurrence of a significant difference between the mark-to-model value of a complex and/or illiquid instrument, and the price at which the same instrument is revealed to have traded in the market".
|
Model risk
|
Types
|
Burke regards failure to use a model (instead over-relying on expert judgment) as a type of model risk. Derman describes various types of model risk that arise from using a model: Wrong model Inapplicability of model.
Incorrect model specification.
Model implementation Programming errors.
Technical errors.
Use of inaccurate numerical approximations.
Model usage Implementation risk.
Data issues.
Calibration errors.
|
Model risk
|
Sources
|
Uncertainty on volatility Volatility is the most important input in risk management models and pricing models. Uncertainty on volatility leads to model risk. Derman believes that products whose value depends on a volatility smile are most likely to suffer from model risk. He writes "I would think it's safe to say that there is no area where model risk is more of an issue than in the modeling of the volatility smile." Avellaneda & Paras (1995) proposed a systematic way of studying and mitigating model risk resulting from volatility uncertainty.
|
Model risk
|
Sources
|
Time inconsistency Buraschi and Corielli formalise the concept of 'time inconsistency' with regards to no-arbitrage models that allow for a perfect fit of the term structure of the interest rates. In these models the current yield curve is an input so that new observations on the yield curve can be used to update the model at regular frequencies. They explore the issue of time-consistent and self-financing strategies in this class of models. Model risk affects all the three main steps of risk management: specification, estimation and implementation.
|
Model risk
|
Sources
|
Correlation uncertainty Uncertainty on correlation parameters is another important source of model risk. Cont and Deguest propose a method for computing model risk exposures in multi-asset equity derivatives and show that options which depend on the worst or best performances in a basket (so called rainbow option) are more exposed to model uncertainty than index options.Gennheimer investigates the model risk present in pricing basket default derivatives. He prices these derivatives with various copulas and concludes that "... unless one is very sure about the dependence structure governing the credit basket, any investors willing to trade basket default products should imperatively compute prices under alternative copula specifications and verify the estimation errors of their simulation to know at least the model risks they run".
|
Model risk
|
Sources
|
Complexity Complexity of a model or a financial contract may be a source of model risk, leading to incorrect identification of its risk factors. This factor was cited as a major source of model risk for mortgage backed securities portfolios during the 2007 crisis.
|
Model risk
|
Sources
|
Illiquidity and model risk Model risk does not only exist for complex financial contracts. Frey (2000) presents a study of how market illiquidity is a source of model risk. He writes "Understanding the robustness of models used for hedging and risk-management purposes with respect to the assumption of perfectly liquid markets is therefore an important issue in the analysis of model risk in general."Convertible bonds, mortgage-backed securities, and high-yield bonds can often be illiquid and difficult to value. Hedge funds that trade these securities can be exposed to model risk when calculating monthly NAV for its investors.
|
Model risk
|
Sources
|
Spreadsheet Errors Many models are built using spreadsheet technology, which can be particularly prone to implementation errors.
Mitigation strategies include adding consistency checks, validating inputs, and using specialized tools.
|
Model risk
|
Quantitative approaches
|
Model averaging vs worst-case approach Rantala (2006) mentions that "In the face of model risk, rather than to base decisions on a single selected 'best' model, the modeller can base his inference on an entire set of models by using model averaging." This approach avoids the "flaw of averages".Another approach to model risk is the worst-case, or minmax approach, advocated in decision theory by Gilboa and Schmeidler.
|
Model risk
|
Quantitative approaches
|
In this approach one considers a range of models and minimizes the loss encountered in the worst-case scenario. This approach to model risk has been developed by Cont (2006).Jokhadze and Schmidt (2018) propose several model risk measures using Bayesian methodology. They introduce superposed risk measures that incorporate model risk and enables consistent market and model risk management. Further, they provide axioms of model risk measures and define several practical examples of superposed model risk measures in the context of financial risk management and contingent claim pricing.
|
Model risk
|
Quantitative approaches
|
Quantifying model risk exposure To measure the risk induced by a model, it has to be compared to an alternative model, or a set of alternative benchmark models. The problem is how to choose these benchmark models. In the context of derivative pricing Cont (2006) proposes a quantitative approach to measurement of model risk exposures in derivatives portfolios: first, a set of benchmark models is specified and calibrated to market prices of liquid instruments, then the target portfolio is priced under all benchmark models. A measure of exposure to model risk is then given by the difference between the current portfolio valuation and the worst-case valuation under the benchmark models. Such a measure may be used as a way of determining a reserve for model risk for derivatives portfolios.
|
Model risk
|
Quantitative approaches
|
Position limits and valuation reserves Jokhadze and Schmidt (2018) introduce monetary market risk measures that covers model risk losses. Their methodology enables to harmonize market and model risk management and define limits and required capitals for risk positions.
|
Model risk
|
Quantitative approaches
|
Kato and Yoshiba discuss qualitative and quantitative ways of controlling model risk. They write "From a quantitative perspective, in the case of pricing models, we can set up a reserve to allow for the difference in estimations using alternative models. In the case of risk measurement models, scenario analysis can be undertaken for various fluctuation patterns of risk factors, or position limits can be established based on information obtained from scenario analysis." Cont (2006) advocates the use of model risk exposure for computing such reserves.
|
Model risk
|
Mitigation
|
Theoretical basis Considering key assumptions.
Considering simple cases and their solutions (model boundaries).
Parsimony.
Implementation Pride of ownership.
Disseminating the model outwards in an orderly manner.
Testing Stress testing and backtesting.
Avoid letting small issues snowball into large issues later on.
Independent validation Ongoing monitoring and against market
|
Model risk
|
Examples of model risk mitigation
|
Parsimony Taleb wrote when describing why most new models that attempted to correct the inadequacies of the Black–Scholes model failed to become accepted: "Traders are not fooled by the Black–Scholes–Merton model. The existence of a 'volatility surface' is one such adaptation. But they find it preferable to fudge one parameter, namely volatility, and make it a function of time to expiry and strike price, rather than have to precisely estimate another."However, Cherubini and Della Lunga describe the disadvantages of parsimony in the context of volatility and correlation modelling. Using an excessive number of parameters may induce overfitting while choosing a severely specified model may easily induce model misspecification and a systematic failure to represent the future distribution.
|
Model risk
|
Examples of model risk mitigation
|
Model risk premium Fender and Kiff (2004) note that holding complex financial instruments, such as CDOs, "translates into heightened dependence on these assumptions and, thus, higher model risk. As this risk should be expected to be priced by the market, part of the yield pick-up obtained relative to equally rated single obligor instruments is likely to be a direct reflection of model risk."
|
Model risk
|
Case studies
|
NatWest—Interest rate options and swaptions—incorrect model specification.
Bank of Tokyo-Mitsubishi—Interest rate options and swaptions.
LTCM—lack of stress testing—Crouhy, Galai, and Mark.
Barclays de Zoete Wedd (BZW)—Mispriced currency options.
National Australia Bank $3 Billion AUD loss on Homeside interest rate model.
2007–2012 global financial crisis – Over-reliance on David X. Li's Gaussian copula model misprices the risk of collateralized debt obligations.
|
Skid-steer loader
|
Skid-steer loader
|
A skid loader, skid-steer loader, SSL, or skidsteer is any of a class of compact heavy equipment with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments.
|
Skid-steer loader
|
Skid-steer loader
|
Skid-steer loaders are typically four-wheeled or tracked vehicles with the front and back wheels on each side mechanically linked together to turn at the same speed, and where the left-side drive wheels can be driven independently of the right-side drive wheels. This is accomplished by having two separate and independent transmissions; one for the left side wheels and one for the right side wheels. Earliest versions of skid steer loaders used forward and reverse clutch drives. Virtually all modern skid steers designed and built since the mid-1970s use two separate hydrostatic transmissions (one for the left side and one for the right side).
|
Skid-steer loader
|
Skid-steer loader
|
The wheels typically have no separate steering mechanism and hold a fixed straight alignment on the body of the machine. Turning is accomplished by differential steering, in which the left and right wheel pairs are operated at different speeds, and the machine turns by skidding or dragging its fixed-orientation wheels across the ground. Skid-steer loaders are capable of zero-radius turning, by driving one set of wheels forward while simultaneously driving the opposite set of wheels in reverse. This "zero-turn" capability (the machine can turn around within its own length) makes them extremely maneuverable and valuable for applications that require a compact, powerful and agile loader or tool carrier in confined-space work areas.
|
Skid-steer loader
|
Skid-steer loader
|
The differential steering, zero-turn capabilities and lack of visibility often exacerbated by carrying loads with these machines means that their safe operation requires the operator have a good field of vision, good hand eye coordination, manual dexterity and the ability to remember and perform multiple actions at once. Before allowing anyone, including adults, to operate a skid steer, they should be assessed on their ability to safely operate the machine and trained in its safe operation. In the US, it is illegal for youth under age 18 employed in non-agricultural jobs to operate a skid steer. For youth hired to work in agriculture, it is recommended they be at least 16 years old and have an adult assess their abilities using the Agricultural Youth Work Guidelines before being allowed to operate a skid steer.
|
Skid-steer loader
|
Skid-steer loader
|
Another thing to consider are beacon lights and reverse signal alarms that offer a warning to co-workers about the skid steer’s movements. These alarms are not always standard equipment on all farm or landscape skid steer machines, depending on factors like the age of the machine. Use and continued maintenance of these alarms greatly reduce the risk of incidents involving running over and/or pinning co-workers between the machine and an obstacle. Construction sites and their business contract requirements often call for landscapers to have operational skid steer reverse signal alarms and beacon lights. The extremely rigid frame and strong wheel bearings prevent the torsional forces caused by this dragging motion from damaging the machine. As with tracked vehicles, the high ground friction produced by skid steers can rip up soft or fragile road surfaces. They can be converted to low ground friction by using specially designed wheels such as the Mecanum wheel.
|
Skid-steer loader
|
Skid-steer loader
|
Skid-steer loaders are sometimes equipped with tracks instead of the wheels, and such a vehicle is known as a compact track loader.Skid steer loaders, both wheel and track models, operate most efficiently when they are imbalanced - either the front wheels or the back wheels are more heavily loaded. When equipped with an empty bucket, skid steer loaders are all heavier in the rear and the rear wheels pivot in place while the front wheels slide around. When a bucket is fully loaded, the weight distribution reverses and the front wheels become significantly heavier than the rear wheels. When making a zero-turn while loaded, the front wheels pivot and the rear wheels slide.
|
Skid-steer loader
|
Skid-steer loader
|
Imbalanced operation reduces the amount of power required to turn the machine and minimizes tire wear. Skilled operators always try to keep the machine more heavily loaded on either the front or the rear of the machine. When the weight distribution is 50/50 (or close to it) neither the front set of wheels nor the rear set of wheels wants to pivot or slide and the machine starts to "buck" due to high friction, evenly divided between front and rear axles. Tire wear increases significantly in this condition.
|
Skid-steer loader
|
Skid-steer loader
|
Unlike in a conventional front loader, the lift arms in these machines are alongside the driver with the pivot points behind the driver's shoulders. Because of the operator's proximity to moving booms, early skid loaders were not as safe as conventional front loaders, particularly due to the lack of a rollover protection structure. Modern skid loaders have cabs, open or fully enclosed which can serve as rollover protective structures (ROPS) and falling object protective structures (FOPS). The ROPS, FOPS, side screens and operator restraints make up the “zone of protection” in a skid steer, and are designed to reduce the possibility of operator injury or death. The FOPS shields the operator's cab from falling debris, and the ROPS shields the operator in the case of an overturn. The side screens prevent the operator from becoming wedged between the lift arms and the skid steer frame as well as from being struck by protrusions (such as limbs). The operator is secured in the operator seat when the seat belt or seat-bar restraint is utilized, keeping them within the zone of protection. Safety features and safe operation are important because skid steer loaders are hazardous when safety practices are not observed. Rollover incidents and being crushed by moving parts are the most common causes of serious injuries and death associated with skid steer loaders.Like other front loaders, they can push material from one location to another, carry material in the bucket, load material into a truck or trailer and perform a variety of digging and grading operations.
|
Skid-steer loader
|
History
|
The first three-wheeled, front-end loader was invented by brothers Cyril and Louis Keller in Rothsay, Minnesota, in 1957. The Kellers built the loader to help a farmer, Eddie Velo, mechanize the process of cleaning turkey manure from his barn. The light and compact machine, with its rear caster wheel, was able to turn around within its own length while performing the same tasks as a conventional front-end loader, hence its name.The Melroe brothers, of Melroe Manufacturing Company in Gwinner, North Dakota, purchased the rights to the Keller loader in 1958 and hired the Kellers to continue refining their invention. As a result of this partnership, the M-200 Melroe self-propelled loader was introduced at the end of 1958. It featured two independent front-drive wheels and a rear caster wheel, a 12.9 hp (9.6 kW) engine and a 750-pound (340 kg) lift capacity. Two years later they replaced the caster wheel with a rear axle and introduced the M-400, the first four-wheel, true skid-steer loader. The M-440 was powered by a 15.5 hp (11.6 kW) engine and had an 1,100-pound (500 kg) rated operating capacity. Skid-steer development continued into the mid-1960s with the M600 loader. Melroe adopted the well-known Bobcat trademark in 1962.
|
Skid-steer loader
|
History
|
By the late 1960s, competing heavy equipment manufacturers were selling machines of this form factor.
|
Skid-steer loader
|
Attachments
|
The conventional bucket of many skid loaders can be replaced with a variety of specialized buckets or attachments, many powered by the loader's hydraulic system. The list of attachments available is virtually endless. Some examples include backhoe, hydraulic breaker, pallet forks, angle broom, sweeper, auger, mower, snow blower, stump grinder, tree spade, trencher, dumping hopper, pavement miller, ripper, tillers, grapple, tilt, roller, snow blade, wheel saw, cement mixer, and wood chipper machine.
|
Skid-steer loader
|
Attachments
|
Some models of skid steer now also have an automatic attachment changer mechanism. This allows a driver to change between a variety of terrain handling, shaping, and leveling tools without having to leave the machine, by using a hydraulic control mechanism to latch onto the attachments. Traditionally hydraulic supply lines to powered attachments may be routed so that the couplings are located near the cab, and the driver does not need to leave the machine to connect or disconnect those supply lines. Recently, manufacturers have also created automatic hydraulic connection systems that allow changing attachments without having to manually disconnect/connect hydraulic lines
|
Skid-steer loader
|
Loader-arm design
|
Radial lift The original skid-steer loader arms were designed using a hinge near the top of the loader frame towers at the rear of the machine. When the loader arms were raised the mechanism would pivot the loader arm up into the air in an arc that would swing up over the top of the operator. This is known as a radial lift loader. This design is simple to manufacture and lower cost. Radial lift loaders start with the bucket close to the machine when the arms are fully down and start moving up and forward away from the machine as the arms are raised. This provides greater forward reach at mid-point in the lift for dumping at around four to five feet, but less stability at the middle of their lift arc (because the bucket is so much further forward). As the loader arms continue to raise past mid-height the bucket begins to move back closer to the machine and becomes more stable at full lift height, but also has far less forward reach at full height.
|
Skid-steer loader
|
Loader-arm design
|
Radial lift machines are lower cost and tend to be preferred for users who do a lot of work at lower height of lift arms, such as digging and spreading materials at low heights. Radial lift designs have very good lift capacity/stability when the loader arms are all the way down and become less stable (lower lift capacity) as the arms reach mid-point and the bucket is furthest forward. Static stability increases as the arms continue to rise, but raised loads are inherently less stable and safe for all machine types. One downside of radial lift design is that when fully-raised the bucket is back closer to the machine, so it has relatively poor reach when trying to load trucks or hoppers or spreaders. In addition, the bucket is almost over the operator's head and spillage over the back of the bucket can end up on top of the machine or in the operator's lap. Another downside of radial lift machines is that the large frame towers to which the loader arms are attached tend to restrict an operator's visibility to the rear and back corners of the machine. The radial arm is still the most common design and preferred by many users, but almost all manufacturers that started with radial lift designs began also producing "vertical lift" designs as well.
|
Skid-steer loader
|
Loader-arm design
|
Vertical lift "Vertical lift" designs use additional links and hinges on the loader arm, with the main pivot points towards the center or front of the machine. This allows the loader arm to have greater operating height and reach while retaining a compact design. There are no truly "vertical lift" designs in production. All loaders use multiple links (that all move in radial arcs) which aim to straighten the lift path of the bucket as it is raised. This allows close to vertical movement at points of the lift range, to keep the bucket forward of the operator's cab, allowing safe dumping into tall containers or vehicles. Some designs have more arc in the lowest part of the lift arc while other designs have more arc near the top of the lift arc.
|
Skid-steer loader
|
Loader-arm design
|
One downside of vertical lift designs is somewhat higher cost and complexity of manufacturing. Some vertical lift designs may also have reduced rear or side visibility when the arms are down low, but superior visibility as the arms are raised (especially if the design does not require a large rear frame tower). Most Vertical lift machines provide more constant stability as the arms are raised from fully-lowered to fully-raised position since the bucket (load) has a similar distance from the machine from bottom to top of the lift path. As a side benefit to constant stability, most vertical lift machines have larger bucket capacities and longer, flatter low-profile buckets that can carry more material per cycle and tend to provide smoother excavating and grading than short-lip buckets. Vertical lift designs have grown rapidly in popularity in the past thirty years and now make up a significant proportion of new skid loader sales.
|
Skid-steer loader
|
Loader-arm design
|
One note of caution regarding loader arms : when controls are activated, the loader or lift arm attachments can move and crush individuals who are within the range of the machinery. To prevent injuries, it is strongly advised to never start or operate controls from outside of the cab. When in the operator’s seat always fasten the seatbelt and lower the safety bar to stay securely in the cab and avoid being crushed. Also be sure that any helpers or bystanders are clear of the machine before starting it.
|
Skid-steer loader
|
Applications
|
A skid-steer loader can sometimes be used in place of a large excavator by digging a hole from the inside. This is especially true for digging swimming pools in a back yard where a large excavator cannot fit. The skid loader first digs a ramp leading to the edge of the desired excavation. It then uses the ramp to carry material out of the hole. The skid loader reshapes the ramp making it steeper and longer as the excavation deepens. This method is also useful for digging under a structure where overhead clearance does not allow for the boom of a large excavator, such as digging a basement under an existing house. Several companies make backhoe attachments for skid-steers. These are more effective for digging in a small area than the method above and can work in the same environments.
|
Skid-steer loader
|
Applications
|
Other applications may consist of transporting raw material around a job site, either in buckets or using pallet forks. Rough terrain forklifts have very poor maneuverability; and smaller "material handling" forklifts have good maneuverability but poor traction. Skid steer loaders have very good maneuverability and traction but typically lower lift capacity than forklifts.
Skid steer loaders excel at snow removal, especially in smaller parking lots where maneuverability around existing cars, light poles, and curbs is an issue with larger snow plows. Skid steers also have the ability to actually remove the snow rather than just plowing it and pushing snow into a pile.
|
Quine (computing)
|
Quine (computing)
|
A quine is a computer program which takes no input and produces a copy of its own source code as its only output. The standard terms for these programs in the computability theory and computer science literature are "self-replicating programs", "self-reproducing programs", and "self-copying programs".
A quine is a fixed point of an execution environment, when that environment is viewed as a function transforming programs into their outputs. Quines are possible in any Turing-complete programming language, as a direct consequence of Kleene's recursion theorem. For amusement, programmers sometimes attempt to develop the shortest possible quine in any given programming language.
The name "quine" was coined by Douglas Hofstadter, in his popular science book Gödel, Escher, Bach, in honor of philosopher Willard Van Orman Quine (1908–2000), who made an extensive study of indirect self-reference, and in particular for the following paradox-producing expression, known as Quine's paradox: "Yields falsehood when preceded by its quotation" yields falsehood when preceded by its quotation.
|
Quine (computing)
|
History
|
The idea of self-reproducing automata came from the dawn of computing, if not before. John von Neumann theorized about them in the 1940s. Later, Paul Bratley and Jean Millo's article "Computer Recreations: Self-Reproducing Automata" discussed them in 1972.
Bratley first became interested in self-reproducing programs after seeing the first known such program written in Atlas Autocode at Edinburgh in the 1960s by the University of Edinburgh lecturer and researcher Hamish Dewar.
The "download source" requirement of the Affero General Public License is based on the idea of a quine.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.