text
stringlengths 2
132k
| source
dict |
|---|---|
depends on the formulation of the bitumen emulsion but also storage conditions such as temperature and humidity. When emulsified bitumen gets into contact with aggregates, emulsifiers lose their effectiveness, the emulsion breaks down, and an adhering bitumen film is formed referred to as 'breaking'. Bitumen particles almost instantly create a continuous bitumen film by coagulating and separating from water which evaporates. Not each asphalt emulsion reacts as fast as the other when it gets into contact with aggregates. That enables a classification into Rapid-setting (R), Slow-setting (SS), and Medium-setting (MS) emulsions, but also an individual, application-specific optimization of the formulation and a wide field of application (1). For example, Slow-breaking emulsions ensure a longer processing time which is particularly advantageous for fine aggregates (1). Adhesion problems are reported for anionic emulsions in contact with quartz-rich aggregates. They are substituted by cationic emulsions achieving better adhesion. The extensive range of bitumen emulsions is covered insufficiently by standardization. DIN EN 13808 for cationic asphalt emulsions has been existing since July 2005. Here, a classification of bitumen emulsions based on letters and numbers is described, considering charges, viscosities, and the type of bitumen. The production process of bitumen emulsions is very complex. Two methods are commonly used, the "Colloid mill" method and the "High Internal Phase Ratio (HIPR)" method. In the "Colloid mill" method, a rotor moves at high speed within a stator by adding bitumen and a water-emulsifier mixture. The resulting shear forces generate bitumen particles between 5 μm and 10 μm coated with emulsifiers. The "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
phase is introduced into hot bitumen, enabling very high bitumen concentrations. T The "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous phase is introduced into hot bitumen, enabling very high bitumen concentrations (1).he "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous phase is introduced into hot bitumen, enabling very high bitumen concentrations (1). Bitumen emulsions are used in a wide variety of applications. They are used in road construction and building protection and primarily include the application in cold recycling mixtures, adhesive coating, and surface treatment (1). Due to the lower viscosity in comparison to hot bitumen, processing requires less energy and is associated with significantly less risk of fire and burns. Chipseal involves spraying the road surface with bitumen emulsion followed by a layer of crushed rock, gravel or crushed slag. Slurry seal is a mixture of bitumen emulsion and fine crushed aggregate that is spread on the surface of a road. Cold-mixed asphalt can also be made from bitumen emulsion to create pavements similar to hot-mixed asphalt, several inches in depth, and bitumen emulsions are also blended into recycled hot-mix asphalt to create low-cost pavements. Bitumen emulsion based techniques are known to be useful for all classes of roads, their use may also be possible in the following applications: 1. Asphalts for heavily trafficked roads (based on the use of polymer modified
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
emulsions) 2. Warm emulsion based mixtures, to improve both their maturation time and mechanical properties 3. Half-warm technology, in which aggregates are heated up to 100 degrees, producing mixtures with similar properties to those of hot asphalts 4. High performance surface dressing. === Synthetic crude oil === Synthetic crude oil, also known as syncrude, is the output from a bitumen upgrader facility used in connection with oil sand production in Canada. Bituminous sands are mined using enormous (100-ton capacity) power shovels and loaded into even larger (400-ton capacity) dump trucks for movement to an upgrading facility. The process used to extract the bitumen from the sand is a hot water process originally developed by Dr. Karl Clark of the University of Alberta during the 1920s. After extraction from the sand, the bitumen is fed into a bitumen upgrader which converts it into a light crude oil equivalent. This synthetic substance is fluid enough to be transferred through conventional oil pipelines and can be fed into conventional oil refineries without any further treatment. By 2015 Canadian bitumen upgraders were producing over 1 million barrels (160×10^3 m3) per day of synthetic crude oil, of which 75% was exported to oil refineries in the United States. In Alberta, five bitumen upgraders produce synthetic crude oil and a variety of other products: The Suncor Energy upgrader near Fort McMurray, Alberta produces synthetic crude oil plus diesel fuel; the Syncrude Canada, Canadian Natural Resources, and Nexen upgraders near Fort McMurray produce synthetic crude oil; and the Shell Scotford Upgrader near Edmonton produces synthetic crude oil plus an intermediate feedstock for the nearby Shell Oil Refinery. A sixth upgrader, under construction in 2015 near Redwater, Alberta, will upgrade half of its crude bitumen directly to diesel fuel, with the remainder of the output being sold as
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
feedstock to nearby oil refineries and petrochemical plants. === Non-upgraded crude bitumen === Canadian bitumen does not differ substantially from oils such as Venezuelan extra-heavy and Mexican heavy oil in chemical composition, and the real difficulty is moving the extremely viscous bitumen through oil pipelines to the refinery. Many modern oil refineries are extremely sophisticated and can process non-upgraded bitumen directly into products such as gasoline, diesel fuel, and refined asphalt without any preprocessing. This is particularly common in areas such as the US Gulf coast, where refineries were designed to process Venezuelan and Mexican oil, and in areas such as the US Midwest where refineries were rebuilt to process heavy oil as domestic light oil production declined. Given the choice, such heavy oil refineries usually prefer to buy bitumen rather than synthetic oil because the cost is lower, and in some cases because they prefer to produce more diesel fuel and less gasoline. By 2015 Canadian production and exports of non-upgraded bitumen exceeded that of synthetic crude oil at over 1.3 million barrels (210×10^3 m3) per day, of which about 65% was exported to the United States. Because of the difficulty of moving crude bitumen through pipelines, non-upgraded bitumen is usually diluted with natural-gas condensate in a form called dilbit or with synthetic crude oil, called synbit. However, to meet international competition, much non-upgraded bitumen is now sold as a blend of multiple grades of bitumen, conventional crude oil, synthetic crude oil, and condensate in a standardized benchmark product such as Western Canadian Select. This sour, heavy crude oil blend is designed to have uniform refining characteristics to compete with internationally marketed heavy oils such as Mexican Mayan or Arabian Dubai Crude. === Radioactive waste encapsulation matrix === Bitumen was used starting in the 1960s as a hydrophobic matrix
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
aiming to encapsulate radioactive waste such as medium-activity salts (mainly soluble sodium nitrate and sodium sulfate) produced by the reprocessing of spent nuclear fuels or radioactive sludges from sedimentation ponds. Bituminised radioactive waste containing highly radiotoxic alpha-emitting transuranic elements from nuclear reprocessing plants have been produced at industrial scale in France, Belgium and Japan, but this type of waste conditioning has been abandoned because operational safety issues (risks of fire, as occurred in a bituminisation plant at Tokai Works in Japan) and long-term stability problems related to their geological disposal in deep rock formations. One of the main problems is the swelling of bitumen exposed to radiation and to water. Bitumen swelling is first induced by radiation because of the presence of hydrogen gas bubbles generated by alpha and gamma radiolysis. A second mechanism is the matrix swelling when the encapsulated hygroscopic salts exposed to water or moisture start to rehydrate and to dissolve. The high concentration of salt in the pore solution inside the bituminised matrix is then responsible for osmotic effects inside the bituminised matrix. The water moves in the direction of the concentrated salts, the bitumen acting as a semi-permeable membrane. This also causes the matrix to swell. The swelling pressure due to osmotic effect under constant volume can be as high as 200 bar. If not properly managed, this high pressure can cause fractures in the near field of a disposal gallery of bituminised medium-level waste. When the bituminised matrix has been altered by swelling, encapsulated radionuclides are easily leached by the contact of ground water and released in the geosphere. The high ionic strength of the concentrated saline solution also favours the migration of radionuclides in clay host rocks. The presence of chemically reactive nitrate can also affect the redox conditions prevailing in the host
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
rock by establishing oxidizing conditions, preventing the reduction of redox-sensitive radionuclides. Under their higher valences, radionuclides of elements such as selenium, technetium, uranium, neptunium and plutonium have a higher solubility and are also often present in water as non-retarded anions. This makes the disposal of medium-level bituminised waste very challenging. Different types of bitumen have been used: blown bitumen (partly oxidized with air oxygen at high temperature after distillation, and harder) and direct distillation bitumen (softer). Blown bitumens like Mexphalte, with a high content of saturated hydrocarbons, are more easily biodegraded by microorganisms than direct distillation bitumen, with a low content of saturated hydrocarbons and a high content of aromatic hydrocarbons. Concrete encapsulation of radwaste is presently considered a safer alternative by the nuclear industry and the waste management organisations. === Other uses === Roofing shingles and roll roofing account for most of the remaining bitumen consumption. Other uses include cattle sprays, fence-post treatments, and waterproofing for fabrics. Bitumen is used to make Japan black, a lacquer known especially for its use on iron and steel, and it is also used in paint and marker inks by some exterior paint supply companies to increase the weather resistance and permanence of the paint or ink, and to make the color darker. Bitumen is also used to seal some alkaline batteries during the manufacturing process. Bitumen is also commonly used as a ground in the etching process of intaglio printmaking. == Production == About 164,000,000 tons were produced in 2019. It is obtained as the "heavy" (i.e., difficult to distill) fraction. Material with a boiling point greater than around 500 °C is considered asphalt. Vacuum distillation separates it from the other components in crude oil (such as naphtha, gasoline and diesel). The resulting material is typically further treated to extract small but
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
valuable amounts of lubricants and to adjust the properties of the material to suit applications. In a de-asphalting unit, the crude bitumen is treated with either propane or butane in a supercritical phase to extract the lighter molecules, which are then separated. Further processing is possible by "blowing" the product: namely reacting it with oxygen. This step makes the product harder and more viscous. Bitumen is typically stored and transported at temperatures around 150 °C (302 °F). Sometimes diesel oil or kerosene are mixed in before shipping to retain liquidity; upon delivery, these lighter materials are separated out of the mixture. This mixture is often called "bitumen feedstock", or BFS. Some dump trucks route the hot engine exhaust through pipes in the dump body to keep the material warm. The backs of tippers carrying asphalt, as well as some handling equipment, are also commonly sprayed with a releasing agent before filling to aid release. Diesel oil is no longer used as a release agent due to environmental concerns. === Oil sands === Naturally occurring crude bitumen impregnated in sedimentary rock is the prime feed stock for petroleum production from "oil sands", currently under development in Alberta, Canada. Canada has most of the world's supply of natural bitumen, covering 140,000 square kilometres (an area larger than England), giving it the second-largest proven oil reserves in the world. The Athabasca oil sands are the largest bitumen deposit in Canada and the only one accessible to surface mining, although recent technological breakthroughs have resulted in deeper deposits becoming producible by in situ methods. Because of oil price increases after 2003, producing bitumen became highly profitable, but as a result of the decline after 2014 it became uneconomic to build new plants again. By 2014, Canadian crude bitumen production averaged about 2.3 million barrels
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
(370,000 m3) per day and was projected to rise to 4.4 million barrels (700,000 m3) per day by 2020. The total amount of crude bitumen in Alberta that could be extracted is estimated to be about 310 billion barrels (50×10^9 m3), which at a rate of 4,400,000 barrels per day (700,000 m3/d) would last about 200 years. === Alternatives and bioasphalt === Although uncompetitive economically, bitumen can be made from nonpetroleum-based renewable resources such as sugar, molasses and rice, corn and potato starches. Bitumen can also be made from waste material by fractional distillation of used motor oil, which is sometimes otherwise disposed of by burning or dumping into landfills. Use of motor oil may cause premature cracking in colder climates, resulting in roads that need to be repaved more frequently. Nonpetroleum-based asphalt binders can be made light-colored. Lighter-colored roads absorb less heat from solar radiation, reducing their contribution to the urban heat island effect. Parking lots that use bitumen alternatives are called green parking lots. === Albanian deposits === Selenizza is a naturally occurring solid hydrocarbon bitumen found in native deposits in Selenice, in Albania, the only European asphalt mine still in use. The bitumen is found in the form of veins, filling cracks in a more or less horizontal direction. The bitumen content varies from 83% to 92% (soluble in carbon disulphide), with a penetration value near to zero and a softening point (ring and ball) around 120 °C. The insoluble matter, consisting mainly of silica ore, ranges from 8% to 17%. Albanian bitumen extraction has a long history and was practiced in an organized way by the Romans. After centuries of silence, the first mentions of Albanian bitumen appeared only in 1868, when the Frenchman Coquand published the first geological description of the deposits of Albanian bitumen.
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
In 1875, the exploitation rights were granted to the Ottoman government and in 1912, they were transferred to the Italian company Simsa. Since 1945, the mine was exploited by the Albanian government and from 2001 to date, the management passed to a French company, which organized the mining process for the manufacture of the natural bitumen on an industrial scale. Today the mine is predominantly exploited in an open pit quarry but several of the many underground mines (deep and extending over several km) still remain viable. Selenizza is produced primarily in granular form, after melting the bitumen pieces selected in the mine. Selenizza is mainly used as an additive in the road construction sector. It is mixed with traditional bitumen to improve both the viscoelastic properties and the resistance to ageing. It may be blended with the hot bitumen in tanks, but its granular form allows it to be fed in the mixer or in the recycling ring of normal asphalt plants. Other typical applications include the production of mastic asphalts for sidewalks, bridges, car-parks and urban roads as well as drilling fluid additives for the oil and gas industry. Selenizza is available in powder or in granular material of various particle sizes and is packaged in sacks or in thermal fusible polyethylene bags. A life-cycle assessment study of the natural selenizza compared with petroleum bitumen has shown that the environmental impact of the selenizza is about half the impact of the road asphalt produced in oil refineries in terms of carbon dioxide emission. == Recycling == Bitumen is a commonly recycled material in the construction industry. The two most common recycled materials that contain bitumen are reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS). RAP is recycled at a greater rate than any other material in the
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
United States, and typically contains approximately 5–6% bitumen binder. Asphalt shingles typically contain 20–40% bitumen binder. Bitumen naturally becomes stiffer over time due to oxidation, evaporation, exudation, and physical hardening. For this reason, recycled asphalt is typically combined with virgin asphalt, softening agents, and/or rejuvenating additives to restore its physical and chemical properties. == Economics == Although bitumen typically makes up only 4 to 5 percent (by weight) of the pavement mixture, as the pavement's binder, it is also the most expensive part of the cost of the road-paving material. During bitumen's early use in modern paving, oil refiners gave it away. However, bitumen is a highly traded commodity today. Its prices increased substantially in the early 21st Century. A U.S. government report states: "In 2002, asphalt sold for approximately $160 per ton. By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton." The report indicates that an "average" 1-mile (1.6-kilometer)-long, four-lane highway would include "300 tons of asphalt," which, "in 2002 would have cost around $48,000. By 2006 this would have increased to $96,000 and by 2012 to $183,000... an increase of about $135,000 for every mile of highway in just 10 years." The Middle East is a significant exporter of bitumen, particularly to India and China. According to the Argus Bitumen Report (2024/07/12), India is the largest importer, driven by extensive infrastructure projects. The report projects a CAGR of 4.5% for India's bitumen imports over the next five years, while China's imports are expected to grow at a CAGR of 3.8%. The current export price to India is approximately $350 per metric ton, and for China, it is around $360 per metric ton. The Middle East's strategic advantage in crude oil
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
production underpins its capacity to meet these demands. == Health and safety == People can be exposed to bitumen in the workplace by breathing in fumes or skin absorption. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit of 5 mg/m3 over a 15-minute period. Bitumen is a largely inert material that must be heated or diluted to a point where it becomes workable for the production of materials for paving, roofing, and other applications. In examining the potential health hazards associated with bitumen, the International Agency for Research on Cancer (IARC) determined that it is the application parameters, predominantly temperature, that affect occupational exposure and the potential bioavailable carcinogenic hazard/risk of the bitumen emissions. In particular, temperatures greater than 199 °C (390 °F), were shown to produce a greater exposure risk than when bitumen was heated to lower temperatures, such as those typically used in asphalt pavement mix production and placement. IARC has classified paving asphalt fumes as a Class 2B possible carcinogen, indicating inadequate evidence of carcinogenicity in humans. In 2020, scientists reported that bitumen currently is a significant and largely overlooked source of air pollution in urban areas, especially during hot and sunny periods. A bitumen-like substance found in the Himalayas and known as shilajit is sometimes used as an Ayurveda medicine, but is not in fact a tar, resin or bitumen. == See also == == Notes == == References == === Sources === Barth, Edwin J. (1962). Asphalt: Science and Technology. Gordon and Breach. ISBN 0-677-00040-5. {{cite book}}: ISBN / Date incompatibility (help). Forbes, R. J. (1993) [Reprint of 1964 ed.], Studies in Ancient Technology, vol. 1, The Netherlands: E.J. Brill, ISBN 978-90-04-00621-8 Lay, Maxwell G. (1992), The Ways of the World: A History of the World's Roads and
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
of the Vehicles That Used Them, Rutgers University Press, ISBN 978-0-8135-2691-1 == External links == Redwood, Boverton (1911). "Asphalt" . Encyclopædia Britannica. Vol. 2 (11th ed.). p. 768. "Bitumen" . New International Encyclopedia. 1905. International Chemical Safety Card 0612 Pavement Interactive – Asphalt CSU Sacramento, The World Famous Asphalt Museum! Archived 29 May 2007 at the Wayback Machine National Institute for Occupational Safety and Health – Asphalt Fumes Scientific American, "Asphalt", 20 August 1881, pp. 121
|
{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
Heat exchangers are devices that transfer heat to achieve desired heating or cooling. An important design aspect of heat exchanger technology is the selection of appropriate materials to conduct and transfer heat fast and efficiently. Copper has many desirable properties for thermally efficient and durable heat exchangers. First and foremost, copper is an excellent conductor of heat. This means that copper's high thermal conductivity allows heat to pass through it quickly. Other desirable properties of copper in heat exchangers include its corrosion resistance, biofouling resistance, maximum allowable stress and internal pressure, creep rupture strength, fatigue strength, hardness, thermal expansion, specific heat, antimicrobial properties, tensile strength, yield strength, high melting point, alloy, ease of fabrication, and ease of joining. The combination of these properties enable copper to be specified for heat exchangers in industrial facilities, HVAC systems, vehicular coolers and radiators, and as heat sinks to cool computers, disk drives, televisions, computer monitors, and other electronic equipment. Copper is also incorporated into the bottoms of high-quality cookware because the metal conducts heat quickly and distributes it evenly. Non-copper heat exchangers are also available. Some alternative materials include aluminum, carbon steel, stainless steel, nickel alloys, and titanium. This article focuses on beneficial properties and common applications of copper in heat exchangers. New copper heat exchanger technologies for specific applications are also introduced. == History == Heat exchangers using copper and its alloys have evolved along with heat transfer technologies over the past several hundred years. Copper condenser tubes were first used in 1769 for steam engines. Initially, the tubes were made of unalloyed copper. By 1870, Muntz metal, a 60% Cu-40% Zn brass alloy, was used for condensers in seawater cooling. Admiralty metal, a 70% Cu-30% Zn yellow brass alloy with 1% tin added to improve corrosion resistance, was introduced in 1890
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
for seawater service. By the 1920s, a 70% Cu-30% Ni alloy was developed for naval condensers. Soon afterwards, a 2% manganese and 2% iron copper alloy was introduced for better erosion resistance. A 90% Cu-10% Ni alloy first became available in the 1950s, initially for seawater piping. This alloy is now the most widely used copper-nickel alloy in marine heat exchangers. Today, steam, evaporator, and condenser coils are made from copper and copper alloys. These heat exchangers are used in air conditioning and refrigeration systems, industrial and central heating and cooling systems, radiators, hot water tanks, and under-floor heating systems. Copper-based heat exchangers can be manufactured with copper tube/aluminum fin, cupro-nickel, or all-copper constructions. Various coatings can be applied to enhance corrosion resistance of the tubes and fins. == Beneficial properties of copper heat exchangers == === Thermal conductivity === Thermal conductivity (k, also denoted as λ or κ) is a measure of a material's ability to conduct heat. Heat transfer across materials of high thermal conductivity occurs at a higher rate than across materials of low thermal conductivity. In the International System of Units (SI), thermal conductivity is measured in watts per meter Kelvin (W/(m•K)). In the Imperial System of Measurement (British Imperial, or Imperial units), thermal conductivity is measured in Btu/(hr•ft⋅F). Copper has a thermal conductivity of 231 Btu/(hr-ft-F). This is higher than all other metals except silver, a precious metal. Copper has a 60% better thermal conductivity rating than aluminum and has almost 30 times more thermal conductivity than stainless steel. Further information about the thermal conductivity of selected metals is available. === Corrosion resistance === Corrosion resistance is essential in heat transfer applications where fluids are involved, such as in hot water tanks, radiators, etc. The only affordable material that has similar corrosion resistance to copper
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
is stainless steel. However, the thermal conductivity of stainless steel is 1/30th times than that of copper. Aluminum tubes are not suitable for potable or untreated water applications because it corrodes at pH<7.0 and so it releases hydrogen gas. Protective films can be applied to the inner surface of copper alloy tubes to increase corrosion resistance. For certain applications, the film is composed of iron. In power plant condensers, duplex tubes consisting of an inner titanium layer with outer copper-nickel alloys are employed. This enables the use of copper’s beneficial mechanical and chemical properties (e.g., stress corrosion cracking, ammonia attack) along with titanium’s excellent corrosion resistance. A duplex tube with inner aluminium brass or copper-nickel and outer stainless or mild steel can be used for cooling in the oil refining and petrochemical industries. === Biofouling resistance === Copper and copper-nickel alloys have a high natural resistance to biofouling relative to alternative materials. Other metals used in heat exchangers, such as steel, titanium and aluminum, foul readily. Protection against biofouling, particularly in marine structures, can be accomplished over long periods of time with copper metals. Copper-nickel alloys have been proven over many years in sea water pipework and other marine applications. These alloys resist biofouling in open seas where they do not allow microbial slime to build up and support macrofouling. Researchers attribute copper's resistance to biofouling, even in temperate waters, to two possible mechanisms: 1) a retarding sequence of colonization through slow release of copper ions during the corrosion process, thereby inhibiting the attachment of microbial layers to marine surfaces; and/or, 2) separating layers that contain corrosive products and the larvae of macro-encrusting organisms. The latter mechanism deters the settlement of pelagic larval stages on the metal surface, rather than killing the organisms. === Antimicrobial properties === Due to copper’s
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
strong antimicrobial properties, copper fins can inhibit bacterial, fungal and viral growths that commonly build up in air conditioning systems. Hence, the surfaces of copper-based heat exchangers are cleaner for longer periods of time than heat exchangers made from other metals. This benefit offers a greatly expanded heat exchanger service life and contributes to improved air quality. Heat exchangers fabricated separately from antimicrobial copper and aluminum in a full-scale HVAC system have been evaluated for their ability to limit microbial growth under conditions of normal flow rates using single-pass outside air. Commonly used aluminum components developed stable biofilms of bacteria and fungi within four weeks of operation. During the same time period, antimicrobial copper was able to limit bacterial loads associated with the copper heat exchanger fins by 99.99% and fungal loads by 99.74%. Copper fin air conditioners have been deployed on buses in Shanghai to rapidly and completely kill bacteria, viruses and fungi that were previously thriving on non-copper fins and permitted to circulate around the systems. The decision to replace aluminum with copper followed antimicrobial tests by the Shanghai Municipal Center for Disease Control and Prevention (SCDC) from 2010 to 2012. The study found that microbial levels on copper fin surfaces were significantly lower than on aluminum, thereby helping to protect the health of bus passengers. Further information about the benefits of antimicrobial copper in HVAC systems is available. === Ease of inner grooving === Internally grooved copper tube of smaller diameters is more thermally efficient, materially efficient, and easier to bend and flare and otherwise work with. It is generally easier to make inner grooved tubes out of copper, a very soft metal. == Common applications for copper heat exchangers == === Industrial facilities and power plants === Copper alloys are extensively used as heat exchanger tubing
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
in fossil and nuclear steam generating electric power plants, chemical and petrochemical plants, marine services, and desalination plants. The largest use of copper alloy heat exchanger tubing on a per unit basis is in utility power plants. These plants contain surface condensers, heaters, and coolers, all of which contain copper tubing. The main surface condenser that accepts turbine-steam discharges uses the most copper. Copper nickel is the group of alloys that are commonly specified in heat exchanger or condenser tubes in evaporators of desalination plants, process industry plants, air cooling zones of thermal power plants, high-pressure feed water heaters, and sea water piping in ships. The composition of the alloys can vary from 90% Cu–10% Ni to 70% Cu–30% Ni. Condenser and heat exchanger tubing of arsenical admiralty brass (Cu-Zn-Sn-As) once dominated the industrial facility market. Aluminum brass later rose in popularity because of its enhanced corrosion resistance. Today, aluminum-brass, 90%Cu-10%Ni, and other copper alloys are widely used in tubular heat exchangers and piping systems in seawater, brackish water and fresh water. Aluminum-brass, 90% Cu-10% Ni and 70% Cu-30% Ni alloys show good corrosion resistance in hot de-aerated seawater and in brines in multi-stage flash desalination plants. Fixed tube liquid-cooled heat exchangers especially suitable for marine and harsh applications can be assembled with brass shells, copper tubes, brass baffles, and forged brass integral end hubs. Copper alloy tubes can be supplied either with a bright metallic surface (CuNiO) or with a thin, firmly attached oxide layer (aluminum brass). These finish types allow for the formation of a protective layer. The protective oxide surface is best achieved when the system is operated for several weeks with clean, oxygen containing cooling water. While the protective layer forms, supportive measures can be carried out to enhance the process, such as the addition of
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
iron sulfate or intermittent tube cleaning. The protective film that forms on Cu-Ni alloys in aerated seawater becomes mature in about three months at 60 °F and becomes increasingly protective with time. The film is resistant to polluted waters, irregular velocities, and other harsh conditions. Further details are available. The biofouling resistance of Cu-Ni alloys enables heat exchange units to operate for several months between mechanical cleanings. Cleanings are nevertheless needed to restore original heat transfer capabilities. Chlorine injection can extend the mechanical cleaning intervals to a year or more without detrimental effects on the Cu-Ni alloys. Further information about copper alloy heat exchangers for industrial facilities is available. === Solar thermal water systems === Solar water heaters can be a cost-effective way to generate hot water for homes in many regions of the world. Copper heat exchangers are important in solar thermal heating and cooling systems because of copper's high thermal conductivity, resistance to atmospheric and water corrosion, sealing and joining by soldering, and mechanical strength. Copper is used both in receivers and in primary circuits (pipes and heat exchangers for water tanks) of solar thermal water systems. Various types of solar collectors for residential applications are available with either direct circulation (i.e., heats water and brings it directly to the home for use) or indirect circulation (i.e., pumps a heat transfer fluid through a heat exchanger, which then heats water that flows into the home) systems. In an evacuated tube solar hot water heater with an indirect circulation system, the evacuated tubes contain a glass outer tube and metal absorber tube attached to a fin. Solar thermal energy is absorbed within the evacuated tubes and is converted into usable concentrated heat. Evacuated glass tubes have a double layer. Inside the glass tube is the copper heat pipe. It
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
is a sealed hollow copper tube that contains a small amount of thermal transfer fluid (water or glycol mixture) which under low pressure boils at a very low temperature. The copper heat pipe transfers thermal energy from within the solar tube into a copper header. As the solution circulates through the copper header, the temperature rises. Other components in solar thermal water systems that contain copper include solar heat exchanger tanks and solar pumping stations, along with pumps and controllers. === HVAC systems === Air conditioning and heating in buildings and motor vehicles are two of the largest applications for heat exchangers. While copper tube is used in most air conditioning and refrigeration systems, typical air conditioning units currently use aluminum fins. These systems can harbor bacteria and mold and develop odors and fouling that can make them function poorly. Stringent new requirements including demands for increased operating efficiencies and the reduction or elimination of harmful emissions are enhancing copper's role in modern HVAC systems. Copper’s antimicrobial properties can enhance the performance of HVAC systems and associated indoor air quality. After extensive testing, copper became a registered material in the U.S. for protecting heating and air conditioning equipment surfaces against bacteria, mold, and mildew. Furthermore, testing funded by the U.S. Department of Defense is demonstrating that all-copper air conditioners suppress the growth of bacteria, mold and mildew that cause odors and reduce system energy efficiency. Units made with aluminum have not been demonstrating this benefit. Copper can cause a galvanic reaction in the presence of other alloys, leading to corrosion. === Gas water heaters === Water heating is the second largest energy use in the home. Gas-water heat exchangers that transfer heat from gaseous fuels to water between 3 and 300 kilowatts thermal (kWth) have widespread residential and commercial use
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
in water heating and heating boiler appliance applications. Demand is increasing for energy-efficient compact water heating systems. Tankless gas water heaters produce hot water when needed. Copper heat exchangers are the preferred material in these units because of their high thermal conductivity and ease of fabrication. To protect these units in acidic environments, durable coatings or other surface treatments are available. Acid-resistant coatings are capable of withstanding temperatures of 1000 °C. === Forced air heating and cooling === Air-source heat pumps have been used for residential and commercial heating and cooling for many years. These units rely on air-to-air heat exchange through evaporator units similar to those used for air conditioners. Finned water to air heat exchangers are most commonly used for forced air heating and cooling systems, such as with indoor and outdoor wood furnaces, boilers, and stoves. They can also be suitable for liquid cooling applications. Copper is specified in supply and return manifolds and in tube coils. === Direct Exchange (DX) Geothermal Heating/Cooling === Geothermal heat pump technology, variously known as "ground source," "earth-coupled," or "direct exchange," relies on circulating a refrigerant through buried copper tubing for heat exchange. These units, which are considerably more efficient than their air-source counterparts, rely on the constancy of ground temperatures below the frost zone for heat transfer. The most efficient ground source heat pumps use ACR, Type L or special-size copper tubing buried into the ground to transfer heat to or from the conditioned space. Flexible copper tube (typically 1/4-inch to 5/8-inch) can be buried in deep vertical holes, horizontally in a relatively shallow grid pattern, in a vertical fence-like arrangement in medium-depth trenches, or as custom configurations. Further information is available. === Electronic systems === Copper and aluminum are used as heat sinks and heat pipes in electronic cooling
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
applications. A heat sink is a passive component that cools semiconductor and optoelectronic devices by dissipating heat into the surrounding air. Heat sinks have temperatures higher than their surrounding environments so that heat can be transferred into the air by convection, radiation, and conduction. Aluminum is the most prominently used heat sink material because of its lower cost. Copper heat sinks are a necessity when higher levels of thermal conductivity are needed. An alternative to all-copper or all-aluminum heat sinks is the joining of aluminum fins to a copper base. Copper heat sinks are die-cast and bound together in plates. They spread heat quickly from the heat source to copper or aluminum fins and into the surrounding air. Heat pipes are used to move heat away from central processing units (CPUs) and graphics processing units (GPUs) and towards heat sinks, where thermal energy is dissipated into the environment. Copper and aluminum heat pipes are used extensively in modern computer systems where increased power requirements and associated heat emissions result in greater demands on cooling systems. A heat pipe typically consists of a sealed pipe or tube at both the hot and cold ends. Heat pipes utilize evaporative cooling to transfer thermal energy from one point to another by the evaporation and condensation of a working fluid or coolant. They are fundamentally better at heat conduction over larger distances than heat sinks because their effective thermal conductivity is several orders of magnitude greater than that of the equivalent solid conductor. When it is desirable to maintain junction temperatures below 125–150 °C, copper/water heat pipes are typically used. Copper/methanol heat pipes are used if the application requires heat pipe operations below 0 °C. == New technologies == === Internally Grooved === The benefits of smaller-diameter internally grooved copper tube for heat transfer
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
are well documented. Smaller diameter coils have better rates of heat transfer than conventional sized coils so that they can withstand higher pressures required by the new generation of environmentally friendlier refrigerants. Smaller diameter coils also have lower material costs because they require less refrigerant, fin, and coil materials; and they enable the design of smaller and lighter high-efficiency air conditioners and refrigerators because the evaporators and condensers coils are smaller and lighter. MicroGroove uses a grooved inner surface of the tube to increase the surface to volume ratio and increase turbulence to mix the refrigerant and homogenize temperatures across the tube. === 3D Printing === A new technology to make heat exchangers is 3D Printing. With 3D printing, you can create complex forms and inside channels. This results in high performance of heat exchangers. The heat exchanger printed is mainly for the industry. The heat exchangers can be printed in pure copper, CuCrZr, and CuNi2SiCr alloy. == References ==
|
{
"page_id": 37749393,
"source": null,
"title": "Copper in heat exchangers"
}
|
In decision tree learning, information gain ratio is a ratio of information gain to the intrinsic information. It was proposed by Ross Quinlan, to reduce a bias towards multi-valued attributes by taking the number and size of branches into account when choosing an attribute. Information gain is also known as mutual information. == Information gain calculation == Information gain is the reduction in entropy produced from partitioning a set with attributes a {\displaystyle a} and finding the optimal candidate that produces the highest value: IG ( T , a ) = H ( T ) − H ( T | a ) , {\displaystyle {\text{IG}}(T,a)=\mathrm {H} {(T)}-\mathrm {H} {(T|a)},} where T {\displaystyle T} is a random variable and H ( T | a ) {\displaystyle \mathrm {H} {(T|a)}} is the entropy of T {\displaystyle T} given the value of attribute a {\displaystyle a} . The information gain is equal to the total entropy for an attribute if for each of the attribute values a unique classification can be made for the result attribute. In this case the relative entropies subtracted from the total entropy are 0. == Split information calculation == The split information value for a test is defined as follows: SplitInformation ( X ) = − ∑ i = 1 n N ( x i ) N ( x ) ∗ log 2 N ( x i ) N ( x ) {\displaystyle {\text{SplitInformation}}(X)=-\sum _{i=1}^{n}{{\frac {\mathrm {N} (x_{i})}{\mathrm {N} (x)}}*\log {_{2}}{\frac {\mathrm {N} (x_{i})}{\mathrm {N} (x)}}}} where X {\displaystyle X} is a discrete random variable with possible values x 1 , x 2 , . . . , x i {\displaystyle {x_{1},x_{2},...,x_{i}}} and N ( x i ) {\displaystyle N(x_{i})} being the number of times that x i {\displaystyle x_{i}} occurs divided by the total count of
|
{
"page_id": 20251284,
"source": null,
"title": "Information gain ratio"
}
|
events N ( x ) {\displaystyle N(x)} where x {\displaystyle x} is the set of events. The split information value is a positive number that describes the potential worth of splitting a branch from a node. This in turn is the intrinsic value that the random variable possesses and will be used to remove the bias in the information gain ratio calculation. == Information gain ratio calculation == The information gain ratio is the ratio between the information gain and the split information value: IGR ( T , a ) = IG ( T , a ) / SplitInformation ( T ) {\displaystyle {\text{IGR}}(T,a)={\text{IG}}(T,a)/{\text{SplitInformation}}(T)} IGR ( T , a ) = − ∑ i = 1 n P ( T ) log P ( T ) − ( − ∑ i = 1 n P ( T | a ) log P ( T | a ) ) − ∑ i = 1 n N ( t i ) N ( t ) ∗ log 2 N ( t i ) N ( t ) {\displaystyle {\text{IGR}}(T,a)={\frac {-\sum _{i=1}^{n}{\mathrm {P} (T)\log \mathrm {P} (T)}-(-\sum _{i=1}^{n}{\mathrm {P} (T|a)\log \mathrm {P} (T|a)})}{-\sum _{i=1}^{n}{{\frac {\mathrm {N} (t_{i})}{\mathrm {N} (t)}}*\log {_{2}}{\frac {\mathrm {N} (t_{i})}{\mathrm {N} (t)}}}}}} == Example == Using weather data published by Fordham University, the table was created below: Using the table above, one can find the entropy, information gain, split information, and information gain ratio for each variable (outlook, temperature, humidity, and wind). These calculations are shown in the tables below: Using the above tables, one can deduce that Outlook has the highest information gain ratio. Next, one must find the statistics for the sub-groups of the Outlook variable (sunny, overcast, and rainy), for this example one will only build the sunny branch (as shown in the table
|
{
"page_id": 20251284,
"source": null,
"title": "Information gain ratio"
}
|
below): One can find the following statistics for the other variables (temperature, humidity, and wind) to see which have the greatest effect on the sunny element of the outlook variable: Humidity was found to have the highest information gain ratio. One will repeat the same steps as before and find the statistics for the events of the Humidity variable (high and normal): Since the play values are either all "No" or "Yes", the information gain ratio value will be equal to 1. Also, now that one has reached the end of the variable chain with Wind being the last variable left, they can build an entire root to leaf node branch line of a decision tree. Once finished with reaching this leaf node, one would follow the same procedure for the rest of the elements that have yet to be split in the decision tree. This set of data was relatively small, however, if a larger set was used, the advantages of using the information gain ratio as the splitting factor of a decision tree can be seen more. == Advantages == Information gain ratio biases the decision tree against considering attributes with a large number of distinct values. For example, suppose that we are building a decision tree for some data describing a business's customers. Information gain ratio is used to decide which of the attributes are the most relevant. These will be tested near the root of the tree. One of the input attributes might be the customer's telephone number. This attribute has a high information gain, because it uniquely identifies each customer. Due to its high amount of distinct values, this will not be chosen to be tested near the root. == Disadvantages == Although information gain ratio solves the key problem of information gain, it creates
|
{
"page_id": 20251284,
"source": null,
"title": "Information gain ratio"
}
|
another problem. If one is considering an amount of attributes that have a high number of distinct values, these will never be above one that has a lower number of distinct values. == Difference from information gain == Information gain's shortcoming is created by not providing a numerical difference between attributes with high distinct values from those that have less. Example: Suppose that we are building a decision tree for some data describing a business's customers. Information gain is often used to decide which of the attributes are the most relevant, so they can be tested near the root of the tree. One of the input attributes might be the customer's credit card number. This attribute has a high information gain, because it uniquely identifies each customer, but we do not want to include it in the decision tree: deciding how to treat a customer based on their credit card number is unlikely to generalize to customers we haven't seen before. Information gain ratio's strength is that it has a bias towards the attributes with the lower number of distinct values. Below is a table describing the differences of information gain and information gain ratio when put in certain scenarios. == See also == Information gain in decision trees Entropy (information theory) == References ==
|
{
"page_id": 20251284,
"source": null,
"title": "Information gain ratio"
}
|
The molecular formula C11H12O4 (molar mass: 208.21 g/mol, exact mass: 208.073559 u) may refer to: 3,4-Dimethoxycinnamic acid Ethyl caffeate, a hydroxycinnamic acid ethyl ester Macrophomic acid Sinapaldehyde 6-Methoxymellein
|
{
"page_id": 24838803,
"source": null,
"title": "C11H12O4"
}
|
Jean Henri Hassenfratz (20 December 1755 – 26 February 1827) was a French chemist, physics professor, mine inspector, and participant in the French Revolution. In 1794, Hassenfratz took part (with Monge) in the creation of the École Polytechnique (first known as École centrale des travaux publics). Hassenfratz became its first professor of physics, a position he held until 1815, when he was succeeded by Alexis Petit (a former child prodigy and Polytechnique alumni who would soon discover the Dulong–Petit law, in 1819). == External links == Hassenfratz's (1802) "Sur les Ombres colorées," Journal de l'Ecole polytechnique, ou Bulletin du travail fait à cette école, ser. 1, vol. 4, p. 272 - 283 - digital facsimile from the Linda Hall Library
|
{
"page_id": 34275986,
"source": null,
"title": "Jean Henri Hassenfratz"
}
|
High-valent iron commonly denotes compounds and intermediates in which iron is found in a formal oxidation state > +3 that show a number of bonds > 6 with a coordination number ≤ 6. The ferrate(VI) ion [FeO4]2− was the first structure in this class synthesized. The synthetic compounds discussed below contain highly oxidized iron in general, as the concepts are closely related. == Oxoiron compounds == Oxoferryl species are common examples of high-valent iron complexes. Such compounds are prepared by oxidation of ferrous complexes with iodosobenzene: (mac)FeL2 + OIPh → (mac)Fe=O(L) + IPh + L (mac = tetradentate macrocyclic ligand) === Fe(IV)O === Several syntheses of oxoiron(IV) species have been reported. The simplest are mixed-metal oxides of the form MFeO3, with M=Ba, Ca, or Sr. However, those compounds do not have discrete iron anions. Isolated oxoiron(IV) species are known with more complicated ligands. These compounds model biological complexes such as cytochrome P450, NO synthase, and isopenicillin N synthase. Two such reported compounds are thiolate-ligated oxoiron(IV) and cyclam-acetate oxoiron(IV). Thiolate-ligated oxoiron(IV) is formed by the oxidation of a precursor, [FeII(TMCS)](PF6) (TMCS = 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraza cyclotetradecane), and 3-5 equivalents of H2O2 at −60 ˚C in methanol. The iron(IV) compound is deep blue in color and shows intense absorption features at 460 nm, 570 nm, 850 nm, and 1050 nm. This species FeIV(=O)(TMCS)+ is stable at −60 ˚C, but decomposition is reported as temperature increases. Compound 2 was identified by Mössbauer spectroscopy, high resolution electrospray ionization mass spectrometry (ESI-MS), X-ray absorption spectroscopy, extended X-ray absorption fine structure (EXAFS), ultraviolet–visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FT-IR), and results were compared to density functional theory (DFT) calculations. Tetramethylcyclam oxoiron(IV) is formed by the reaction of FeII(TMC)(OTf)2, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; OTf = CF3SO3, with iodosylbenzene (PhIO) in CH3CN at −40 ˚C. A second method for formation of
|
{
"page_id": 25363094,
"source": null,
"title": "High-valent iron"
}
|
cyclam oxoiron(IV) is reported as the reaction of FeII(TMC)(OTf)2 with 3 equivalents of H2O2 for 3 hours. This species is pale green in color and has an absorption maximum at 820 nm. It is reported to be stable for at least 1 month at −40 ˚C. It has been characterized by Mössbauer spectroscopy, ESI-MS, EXAFS, UV-vis, Raman spectroscopy, and FT-IR. High-valent iron bispidine complexes can oxidize cyclohexane to cyclohexanol and cyclohexanone in 35% yield with an alcohol to ketone ratio up to 4. === Fe(V)O === FeVTAML(=O), TAML = tetra-amido macrocyclic ligand, is formed by the reaction of [FeIII(TAML)(H2O)](PPh4) with 2-5 equivalents of meta-chloroperbenzoic acid at −60 ˚C in n-butyronitrile. This deep green compound (two λmax at 445 and 630 nm respectively) is stable at 77 K. The stabilization of Fe(V) is attributed to the strong π–donor capacity of deprotonated amide nitrogens. === Fe(VI)O === Ferrate(VI) is found in the inorganic anion [FeO4]2−. It has been isolated as the potassium salt, potassium ferrate. It is a strong water-stable oxidizing agent. Its solutions are stable at high pH. == Nitridoiron and imidoiron compounds == Nitridoiron and imidoiron compounds are closely related to iron-dinitrogen chemistry. The biological significance of nitridoiron(V) porphyrins has been reviewed. A widely applicable method to generate high-valent nitridoiron species is the thermal or photochemical oxidative elimination of molecular nitrogen from an azide complex. ( L ) F e n N 3 ⟶ ( L ) F e n + 2 N + N 2 {\displaystyle \mathrm {(L)Fe^{n}N_{3}\longrightarrow (L)Fe^{n+2}N+N_{2}} } symbolic oxidative elimination of nitrogen yields a nitridoiron complex; L denotes the supporting ligand. === Fe(IV)N === Several structurally characterized nitridoiron(IV) compounds exist. === Fe(V)N === The first nitridoiron(V) compound was synthesised and characterized by Wagner and Nakamoto (1988, 1989) using photolysis and Raman spectroscopy at low temperatures. ===
|
{
"page_id": 25363094,
"source": null,
"title": "High-valent iron"
}
|
Fe(VI)N === A second FeVI species apart from the ferrate(VI) ion, [(Me3cy-ac)FeN](PF6)2, has been reported. This species, is formed by oxidation followed by photolysis to yield the Fe(VI) species. Characterization of the Fe(VI) complex was done by Mossbauer, EXAFS, IR, and DFT calculations. Unlike the ferrate(VI) ion, compound 5 is diamagnetic. === μ-Nitrido compounds and oxidation catalysis === Bridged μ-nitrido di-iron phthalocyanine compounds such as iron(II) phthalocyanine catalyze the oxidation of methane to methanol, formaldehyde, and formic acid using hydrogen peroxide as sacrificial oxidant. === Electronic structure === Nitridoiron(IV) and nitridoiron(V) species were first explored theoretically in 2002. == See also == Jacobsen's catalyst (high-valent manganese) == References == == Further reading == Solomon et al.; Angewandte Chemie International Edition Volume 47, Issue 47, pages 9071–9074, November 10, 2008; doi:10.1002/anie.200803740
|
{
"page_id": 25363094,
"source": null,
"title": "High-valent iron"
}
|
Synthetic immunology is the rational design and construction of synthetic systems that perform complex immunological functions. Functions include using specific cell markers to target cells for destruction and or interfering with immune reactions. US Food and Drug Administration (FDA)-approved immune system modulators include anti-inflammatory and immunosuppressive agents, vaccines, therapeutic antibodies and Toll-like receptor (TLR) agonists. == History == The discipline emerged after 2010 following the development of genome editing technology including TALENS and CRISPR. In 2015, one project created T cells that became active only in the presence of a specific drug, allowing them to be turned on and off in situ. Another example is a T cell that targets only cells that display two separate markers. In 2016, John Lin head of Pfizer's San Francisco biotech unit stated, “the immune system will be the most convenient vehicle for [engineered human cells], because they can move and migrate and play such important roles.” Advances in systems biology support high-dimensional quantitative analysis of immune responses. Techniques include viral gene delivery, inducible gene expression, RNA-guided genome editing, and site-specific recombinases for applications related to biotechnology and cellular immunotherapy. == Types == === Immunity-modulating organisms === Researchers are exploring the creation of 'smart' organisms such as bacteriophages and bacteria that can perform complex immunological tasks. Such strategies could produce organisms that perform multistep immune functions such as presenting antigen to and co-stimulating helper T cells in a specific manner, or providing integrated signals to B cells to induce affinity maturation and isotype switching during antibody production. Such engineered organisms have the potential be as safe and as inexpensive as probiotics but precise in carrying out targeted interventions. === Antibody-recruiting small molecules === Antibody therapeutics and other 'biologics' have proven to be effective in treating a diseases from rheumatoid arthritis to cancer. However, such
|
{
"page_id": 49545883,
"source": null,
"title": "Synthetic immunology"
}
|
agents can cause unwanted anaphylactic or inflammatory reactions, are administered by injection and are expensive. Small molecules, in contrast, are generally inexpensive to produce, orally bioavailable and are rarely allergenic. Synthetic antibody-recruiting small molecules have been created that redirect natural antibodies to pathogens for destruction. === Transdifferentiated cells === Deletion of a single transcription factor enables mature B cells to transform into T cells via dedifferentiation and redifferentiation. Technologies that can control cell fate include strategies to induce pluripotent stem cell formation and using small molecules to induce stem cells to differentiate into specific cell types. Dedifferentiation could be used to turn autoimmune cells into inactive progenitors or to suppress rejection of transplanted organs. In 2016 researchers transdifferentiated fibroblasts into induced neural stem cells. The team mixed the cells into an FDA-approved surgical glue that provided a physical support matrix. They administered the result to mice. Survival times increased from 160 to 220 percent, depending on the type of tumor. === Vaccines === Therapeutic vaccines treat and immunize patients already infected with a given disease. Provenge is an adoptive cell-transfer therapy in which a patient's antigen-presenting target autologous prostate cancer tissue. Advances in chemical biology include synthetic molecules that modulate B cell activation, structurally complex carbohydrate tumor antigen and adjuvants synthesis, immunogenic chemotherapeutic agents and chemically homogeneous, synthetic vaccines. == See also == Synthetic antibody – Affinity reagents generated entirely in vitro Synthetic biology – Interdisciplinary branch of biology and engineering == References == == External links == Cheung, Fred (May 25, 2012). "Ask the Expert - David Spiegel, Yale University... | ACS Network". communities.acs.org. Retrieved 2016-02-25. "Synthetic immunology" (PDF). Arizona State University iGem. 2013. Retrieved 2016-02-25.
|
{
"page_id": 49545883,
"source": null,
"title": "Synthetic immunology"
}
|
An anastomosis (, pl.: anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal (such as the foramen ovale in a fetus' heart) or abnormal (such as the patent foramen ovale in an adult's heart); it may be acquired (such as an arteriovenous fistula) or innate (such as the arteriovenous shunt of a metarteriole); and it may be natural (such as the aforementioned examples) or artificial (such as a surgical anastomosis). The reestablishment of an anastomosis that had become blocked is called a reanastomosis. Anastomoses that are abnormal, whether congenital or acquired, are often called fistulas. The term is used in medicine, biology, mycology, geology, and geography. == Etymology == Anastomosis: medical or Modern Latin, from Greek ἀναστόμωσις, anastomosis, "outlet, opening", Greek ana- "up, on, upon", stoma "mouth", "to furnish with a mouth". Thus the -stom- syllable is cognate with that of stoma in botany or stoma in medicine. == Medical anatomy == An anastomosis is the connection of two normally divergent structures. It refers to connections between blood vessels or between other tubular structures such as loops of intestine. === Circulatory === In circulatory anastomoses, many arteries naturally anastomose with each other; for example, the inferior epigastric artery and superior epigastric artery, or the anterior and/or posterior communicating arteries in the Circle of Willis in the brain. The circulatory anastomosis is further divided into arterial and venous anastomosis. Arterial anastomosis includes actual arterial anastomosis (e.g., palmar arch, plantar arch) and potential arterial anastomosis (e.g. coronary arteries and cortical branch of cerebral arteries). Anastomoses also form alternative routes around capillary beds in areas that do not need a large blood supply, thus helping regulate systemic blood
|
{
"page_id": 328352,
"source": null,
"title": "Anastomosis"
}
|
flow. === Surgical === Surgical anastomosis occurs when segments of intestine, blood vessel, or any other structure are connected together surgically (anastomosed). Examples include arterial anastomosis in bypass surgery, intestinal anastomosis after a piece of intestine has been resected, Roux-en-Y anastomosis and ureteroureterostomy. Surgical anastomosis techniques include linear stapled anastomosis, hand sewn anastomosis, end-to-end anastomosis (EEA). Anastomosis can be performed by hand or with an anastomosis assist device. Studies have been performed comparing various anastomosis approaches taking into account surgical "time and cost, postoperative anastomotic bleeding, leakage, and stricture". Anastomotic leakage in colorectal cancer surgery Failure of an intestinal anastomosis with leakage of intestinal content in to the abdominal cavity is one of the most severe complications after bowel surgery. The severity of anastomotic leakage varies ranging from mild with minimal impact on the patient to severe and potentially fatal, with negative impact on both short- and long-term outcomes. The incidence has not changed in recent decades, despite improvement in surgical techniques, prehabilitation and perioperative care. Anastomotic leakage after rectal cancer surgery is higher and documented to occur in 9-11%, after colon resection the incidence of leakage is lower and about 6%. Systemic factors contributing to anastomotic failure include sepsis, anemia, diabetes mellitus, previous irradiation, malnutrition, steroid use, smoking, heavy alcohol consumption, obesity and certain disease conditions like Chron's disease. Signs of an anastomotic leak include fever, abdominal pain or peritonitis, leukocytosis and tachycardia or new-onset arrythmias. Anastomotic leakage is usually diagnosed 5-8 days post-surgery. A CT scan with pneumoperitoneum and significant free fluid or inflammatory changes around the anastomosis are suggestive of an anastomotic failure. Depending on the magnitude of the defect and leak different treatments are indicated. A localized anastomotic leak without systemic sepsis or peritonitis can be managed with antibiotics and if possible, drainage of the abscess.
|
{
"page_id": 328352,
"source": null,
"title": "Anastomosis"
}
|
Anastomotic leaks associated with peritonitis or systemic sepsis requires an operation with either revision of the anastomosis if feasible or fecal diversion proximally or at the site of the anastomosis with a stoma. === Pathological === Pathological anastomosis results from trauma or disease and may involve veins, arteries, or intestines. These are usually referred to as fistulas. In the cases of veins or arteries, traumatic fistulas usually occur between artery and vein. Traumatic intestinal fistulas usually occur between two loops of intestine (entero-enteric fistula) or intestine and skin (enterocutaneous fistula). Portacaval anastomosis, by contrast, is an anastomosis between a vein of the portal circulation and a vein of the systemic circulation, which allows blood to bypass the liver in patients with portal hypertension, often resulting in hemorrhoids, esophageal varices, or caput medusae. == Biology == === Evolution === In evolution, anastomosis is a recombination of evolutionary lineage. Conventional accounts of evolutionary lineage present themselves as the branching out of species into novel forms. Under anastomosis, species might recombine after initial branching out, such as in the case of recent research that shows that ancestral populations along human and chimpanzee lineages may have interbred after an initial branching event. The concept of anastomosis also applies to the theory of symbiogenesis, in which new species emerge from the formation of novel symbiotic relationships. === Mycology === In mycology, anastomosis is the fusion between branches of the same or different hyphae. Hence the bifurcating fungal hyphae can form true reticulating networks. By sharing materials in the form of dissolved ions, hormones, and nucleotides, the fungus maintains bidirectional communication with itself. The fungal network might begin from several origins; several spores (i.e. by means of conidial anastomosis tubes), several points of penetration, each a spreading circumference of absorption and assimilation. Once encountering the tip
|
{
"page_id": 328352,
"source": null,
"title": "Anastomosis"
}
|
of another expanding, exploring self, the tips press against each other in pheromonal recognition or by an unknown recognition system, fusing to form a genetic singular clonal colony that can cover hectares called a genet or just microscopical areas. For fungi, anastomosis is also a component of reproduction. In some fungi, two different haploid mating types – if compatible – merge. Somatically, they form a morphologically similar mycelial wave front that continues to grow and explore. The significant difference is that each septated unit is binucleate, containing two unfused nuclei, i.e. one from each parent that eventually undergoes karyogamy and meiosis to complete the sexual cycle. Also the term "anastomosing" is used for mushroom gills which interlink and separate to form a network. === Botany === The growth of a strangler fig around a host tree, with tendrils fusing together to form a mesh, is called anastomosing. == Geosciences == === Geology === In geology, veins of quartz (or other) minerals can display anastomosis. Ductile shear zones frequently show anastomosing geometries of highly-strained rocks around lozenges of less-deformed material. Molten lava flows sometimes flow in anastomosed lava channels or lava tubes. In cave systems, anastomosis is the splitting of cave passages that later reconnect. === Geography and hydrology === Anastomosing rivers, anastomosing streams consist of multiple channels that divide and reconnect and are separated by semi-permanent banks formed of cohesive material, such that they are unlikely to migrate from one channel position to another. They can be confused with braided rivers based on their planforms alone, but braided rivers are much shallower and more dynamic than anastomosing rivers. Some definitions require that an anastomosing river be made up of interconnected channels that enclose floodbasins, again in contrast with braided rivers. Rivers with anastomosed reaches include the Magdalena River in Colombia,
|
{
"page_id": 328352,
"source": null,
"title": "Anastomosis"
}
|
the upper Columbia River in British Columbia, Canada, the Drumheller Channels of the Channeled Scablands of the state of Washington, US, and the upper Narew River in Poland. The term anabranch has been used for segments of anastomosing rivers. Braided streams show anastomosing channels around channel bars of alluvium. == References ==
|
{
"page_id": 328352,
"source": null,
"title": "Anastomosis"
}
|
In quantum mechanics, the variational method is one way of finding approximations to the lowest energy eigenstate or ground state, and some excited states. This allows calculating approximate wavefunctions such as molecular orbitals. The basis for this method is the variational principle. The method consists of choosing a "trial wavefunction" depending on one or more parameters, and finding the values of these parameters for which the expectation value of the energy is the lowest possible. The wavefunction obtained by fixing the parameters to such values is then an approximation to the ground state wavefunction, and the expectation value of the energy in that state is an upper bound to the ground state energy. The Hartree–Fock method, density matrix renormalization group, and Ritz method apply the variational method. == Description == Suppose we are given a Hilbert space and a Hermitian operator over it called the Hamiltonian H {\displaystyle H} . Ignoring complications about continuous spectra, we consider the discrete spectrum of H {\displaystyle H} and a basis of eigenvectors { | ψ λ ⟩ } {\displaystyle \{|\psi _{\lambda }\rangle \}} (see spectral theorem for Hermitian operators for the mathematical background): ⟨ ψ λ 1 | ψ λ 2 ⟩ = δ λ 1 λ 2 , {\displaystyle \left\langle \psi _{\lambda _{1}}|\psi _{\lambda _{2}}\right\rangle =\delta _{\lambda _{1}\lambda _{2}},} where δ i j {\displaystyle \delta _{ij}} is the Kronecker delta δ i j = { 0 if i ≠ j , 1 if i = j , {\displaystyle \delta _{ij}={\begin{cases}0&{\text{if }}i\neq j,\\1&{\text{if }}i=j,\end{cases}}} and the { | ψ λ ⟩ } {\displaystyle \{|\psi _{\lambda }\rangle \}} satisfy the eigenvalue equation H | ψ λ ⟩ = λ | ψ λ ⟩ . {\displaystyle H\left|\psi _{\lambda }\right\rangle =\lambda \left|\psi _{\lambda }\right\rangle .} Once again ignoring complications involved with a continuous spectrum of H
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
{\displaystyle H} , suppose the spectrum of H {\displaystyle H} is bounded from below and that its greatest lower bound is E0. The expectation value of H {\displaystyle H} in a state | ψ ⟩ {\displaystyle |\psi \rangle } is then ⟨ ψ | H | ψ ⟩ = ∑ λ 1 , λ 2 ∈ S p e c ( H ) ⟨ ψ | ψ λ 1 ⟩ ⟨ ψ λ 1 | H | ψ λ 2 ⟩ ⟨ ψ λ 2 | ψ ⟩ = ∑ λ ∈ S p e c ( H ) λ | ⟨ ψ λ | ψ ⟩ | 2 ≥ ∑ λ ∈ S p e c ( H ) E 0 | ⟨ ψ λ | ψ ⟩ | 2 = E 0 ⟨ ψ | ψ ⟩ . {\displaystyle {\begin{aligned}\left\langle \psi \right|H\left|\psi \right\rangle &=\sum _{\lambda _{1},\lambda _{2}\in \mathrm {Spec} (H)}\left\langle \psi |\psi _{\lambda _{1}}\right\rangle \left\langle \psi _{\lambda _{1}}\right|H\left|\psi _{\lambda _{2}}\right\rangle \left\langle \psi _{\lambda _{2}}|\psi \right\rangle \\&=\sum _{\lambda \in \mathrm {Spec} (H)}\lambda \left|\left\langle \psi _{\lambda }|\psi \right\rangle \right|^{2}\geq \sum _{\lambda \in \mathrm {Spec} (H)}E_{0}\left|\left\langle \psi _{\lambda }|\psi \right\rangle \right|^{2}=E_{0}\langle \psi |\psi \rangle .\end{aligned}}} If we were to vary over all possible states with norm 1 trying to minimize the expectation value of H {\displaystyle H} , the lowest value would be E 0 {\displaystyle E_{0}} and the corresponding state would be the ground state, as well as an eigenstate of H {\displaystyle H} . Varying over the entire Hilbert space is usually too complicated for physical calculations, and a subspace of the entire Hilbert space is chosen, parametrized by some (real) differentiable parameters αi (i = 1, 2, ..., N). The choice of the subspace is called the ansatz. Some choices of ansatzes lead to better approximations than others,
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
therefore the choice of ansatz is important. Let's assume there is some overlap between the ansatz and the ground state (otherwise, it's a bad ansatz). We wish to normalize the ansatz, so we have the constraints ⟨ ψ ( α ) | ψ ( α ) ⟩ = 1 {\displaystyle \left\langle \psi (\mathbf {\alpha } )|\psi (\mathbf {\alpha } )\right\rangle =1} and we wish to minimize ε ( α ) = ⟨ ψ ( α ) | H | ψ ( α ) ⟩ . {\displaystyle \varepsilon (\mathbf {\alpha } )=\left\langle \psi (\mathbf {\alpha } )\right|H\left|\psi (\mathbf {\alpha } )\right\rangle .} This, in general, is not an easy task, since we are looking for a global minimum and finding the zeroes of the partial derivatives of ε over all αi is not sufficient. If ψ(α) is expressed as a linear combination of other functions (αi being the coefficients), as in the Ritz method, there is only one minimum and the problem is straightforward. There are other, non-linear methods, however, such as the Hartree–Fock method, that are also not characterized by a multitude of minima and are therefore comfortable in calculations. There is an additional complication in the calculations described. As ε tends toward E0 in minimization calculations, there is no guarantee that the corresponding trial wavefunctions will tend to the actual wavefunction. This has been demonstrated by calculations using a modified harmonic oscillator as a model system, in which an exactly solvable system is approached using the variational method. A wavefunction different from the exact one is obtained by use of the method described above. Although usually limited to calculations of the ground state energy, this method can be applied in certain cases to calculations of excited states as well. If the ground state wavefunction is known, either by the
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
method of variation or by direct calculation, a subset of the Hilbert space can be chosen which is orthogonal to the ground state wavefunction. | ψ ⟩ = | ψ test ⟩ − ⟨ ψ g r | ψ test ⟩ | ψ gr ⟩ {\displaystyle \left|\psi \right\rangle =\left|\psi _{\text{test}}\right\rangle -\left\langle \psi _{\mathrm {gr} }|\psi _{\text{test}}\right\rangle \left|\psi _{\text{gr}}\right\rangle } The resulting minimum is usually not as accurate as for the ground state, as any difference between the true ground state and ψ gr {\displaystyle \psi _{\text{gr}}} results in a lower excited energy. This defect is worsened with each higher excited state. In another formulation: E ground ≤ ⟨ ϕ | H | ϕ ⟩ . {\displaystyle E_{\text{ground}}\leq \left\langle \phi \right|H\left|\phi \right\rangle .} This holds for any trial φ since, by definition, the ground state wavefunction has the lowest energy, and any trial wavefunction will have energy greater than or equal to it. Proof: φ can be expanded as a linear combination of the actual eigenfunctions of the Hamiltonian (which we assume to be normalized and orthogonal): ϕ = ∑ n c n ψ n . {\displaystyle \phi =\sum _{n}c_{n}\psi _{n}.} Then, to find the expectation value of the Hamiltonian: ⟨ H ⟩ = ⟨ ϕ | H | ϕ ⟩ = ⟨ ∑ n c n ψ n | H | ∑ m c m ψ m ⟩ = ∑ n ∑ m ⟨ c n ∗ ψ n | E m | c m ψ m ⟩ = ∑ n ∑ m c n ∗ c m E m ⟨ ψ n | ψ m ⟩ = ∑ n | c n | 2 E n . {\displaystyle {\begin{aligned}\left\langle H\right\rangle =\left\langle \phi \right|H\left|\phi \right\rangle ={}&\left\langle \sum _{n}c_{n}\psi _{n}\right|H\left|\sum _{m}c_{m}\psi _{m}\right\rangle \\={}&\sum _{n}\sum _{m}\left\langle c_{n}^{*}\psi _{n}\right|E_{m}\left|c_{m}\psi _{m}\right\rangle \\={}&\sum _{n}\sum _{m}c_{n}^{*}c_{m}E_{m}\left\langle
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
\psi _{n}|\psi _{m}\right\rangle \\={}&\sum _{n}|c_{n}|^{2}E_{n}.\end{aligned}}} Now, the ground state energy is the lowest energy possible, i.e., E n ≥ E ground {\displaystyle E_{n}\geq E_{\text{ground}}} . Therefore, if the guessed wave function φ is normalized: ⟨ ϕ | H | ϕ ⟩ ≥ E ground ∑ n | c n | 2 = E ground . {\displaystyle \left\langle \phi \right|H\left|\phi \right\rangle \geq E_{\text{ground}}\sum _{n}|c_{n}|^{2}=E_{\text{ground}}.} === In general === For a hamiltonian H that describes the studied system and any normalizable function Ψ with arguments appropriate for the unknown wave function of the system, we define the functional ε [ Ψ ] = ⟨ Ψ | H ^ | Ψ ⟩ ⟨ Ψ | Ψ ⟩ . {\displaystyle \varepsilon \left[\Psi \right]={\frac {\left\langle \Psi \right|{\hat {H}}\left|\Psi \right\rangle }{\left\langle \Psi |\Psi \right\rangle }}.} The variational principle states that ε ≥ E 0 {\displaystyle \varepsilon \geq E_{0}} , where E 0 {\displaystyle E_{0}} is the lowest energy eigenstate (ground state) of the hamiltonian ε = E 0 {\displaystyle \varepsilon =E_{0}} if and only if Ψ {\displaystyle \Psi } is exactly equal to the wave function of the ground state of the studied system. The variational principle formulated above is the basis of the variational method used in quantum mechanics and quantum chemistry to find approximations to the ground state. Another facet in variational principles in quantum mechanics is that since Ψ {\displaystyle \Psi } and Ψ † {\displaystyle \Psi ^{\dagger }} can be varied separately (a fact arising due to the complex nature of the wave function), the quantities can be varied in principle just one at a time. == Helium atom ground state == The helium atom consists of two electrons with mass m and electric charge −e, around an essentially fixed nucleus of mass M ≫ m and charge +2e. The Hamiltonian for
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
it, neglecting the fine structure, is: H = − ℏ 2 2 m ( ∇ 1 2 + ∇ 2 2 ) − e 2 4 π ε 0 ( 2 r 1 + 2 r 2 − 1 | r 1 − r 2 | ) {\displaystyle H=-{\frac {\hbar ^{2}}{2m}}\left(\nabla _{1}^{2}+\nabla _{2}^{2}\right)-{\frac {e^{2}}{4\pi \varepsilon _{0}}}\left({\frac {2}{r_{1}}}+{\frac {2}{r_{2}}}-{\frac {1}{|\mathbf {r} _{1}-\mathbf {r} _{2}|}}\right)} where ħ is the reduced Planck constant, ε0 is the vacuum permittivity, ri (for i = 1, 2) is the distance of the i-th electron from the nucleus, and |r1 − r2| is the distance between the two electrons. If the term Vee = e2/(4πε0|r1 − r2|), representing the repulsion between the two electrons, were excluded, the Hamiltonian would become the sum of two hydrogen-like atom Hamiltonians with nuclear charge +2e. The ground state energy would then be 8E1 = −109 eV, where E1 is the Rydberg constant, and its ground state wavefunction would be the product of two wavefunctions for the ground state of hydrogen-like atoms:: 262 ψ ( r 1 , r 2 ) = Z 3 π a 0 3 e − Z ( r 1 + r 2 ) / a 0 . {\displaystyle \psi (\mathbf {r} _{1},\mathbf {r} _{2})={\frac {Z^{3}}{\pi a_{0}^{3}}}e^{-Z\left(r_{1}+r_{2}\right)/a_{0}}.} where a0 is the Bohr radius and Z = 2, helium's nuclear charge. The expectation value of the total Hamiltonian H (including the term Vee) in the state described by ψ0 will be an upper bound for its ground state energy. ⟨Vee⟩ is −5E1/2 = 34 eV, so ⟨H⟩ is 8E1 − 5E1/2 = −75 eV. A tighter upper bound can be found by using a better trial wavefunction with 'tunable' parameters. Each electron can be thought to see the nuclear charge partially "shielded" by the other electron, so we can
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
use a trial wavefunction equal with an "effective" nuclear charge Z < 2: The expectation value of H in this state is: ⟨ H ⟩ = [ − 2 Z 2 + 27 4 Z ] E 1 {\displaystyle \left\langle H\right\rangle =\left[-2Z^{2}+{\frac {27}{4}}Z\right]E_{1}} This is minimal for Z = 27/16 implying shielding reduces the effective charge to ~1.69. Substituting this value of Z into the expression for H yields 729E1/128 = −77.5 eV, within 2% of the experimental value, −78.975 eV. Even closer estimations of this energy have been found using more complicated trial wave functions with more parameters. This is done in physical chemistry via variational Monte Carlo. == References ==
|
{
"page_id": 37487265,
"source": null,
"title": "Variational method (quantum mechanics)"
}
|
Anatomy (from Ancient Greek ἀνατομή (anatomḗ) 'dissection') is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and physiology, which study the structure and function of organisms and their parts respectively, make a natural pair of related disciplines, and are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine, and is often studied alongside physiology. Anatomy is a complex and dynamic field that is constantly evolving as discoveries are made. In recent years, there has been a significant increase in the use of advanced imaging techniques, such as MRI and CT scans, which allow for more detailed and accurate visualizations of the body's structures. The discipline of anatomy is divided into macroscopic and microscopic parts. Macroscopic anatomy, or gross anatomy, is the examination of an animal's body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, and also in the study of cells. The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th-century medical imaging techniques, including X-ray, ultrasound, and magnetic resonance imaging. == Etymology and definition == Derived from
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
the Greek ἀνατομή anatomē "dissection" (from ἀνατέμνω anatémnō "I cut up, cut open" from ἀνά aná "up", and τέμνω témnō "I cut"), anatomy is the scientific study of the structure of organisms including their systems, organs and tissues. It includes the appearance and position of the various parts, the materials from which they are composed, and their relationships with other parts. Anatomy is quite distinct from physiology and biochemistry, which deal respectively with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, size, position, structure, blood supply and innervation of an organ such as the liver; while a physiologist is interested in the production of bile, the role of the liver in nutrition and the regulation of bodily functions. The discipline of anatomy can be subdivided into a number of branches, including gross or macroscopic anatomy and microscopic anatomy. Gross anatomy is the study of structures large enough to be seen with the naked eye, and also includes superficial anatomy or surface anatomy, the study by sight of the external body features. Microscopic anatomy is the study of structures on a microscopic scale, along with histology (the study of tissues), and embryology (the study of an organism in its immature condition). Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. In contrast, systemic anatomy is the study of the structures that make up a discrete body system—that is, a group of structures that work together to perform a unique body function, such as the digestive system. Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include dissection, in which
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
a body is opened and its organs studied, and endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels. The term "anatomy" is commonly taken to refer to human anatomy. However, substantially similar structures and tissues are found throughout the rest of the animal kingdom, and the term also includes the anatomy of other animals. The term zootomy is also sometimes used to specifically refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy. == Animal tissues == The kingdom Animalia contains multicellular organisms that are heterotrophic and motile (although some have secondarily adopted a sessile lifestyle). Most animals have bodies differentiated into separate tissues and these animals are also known as eumetazoans. They have an internal digestive chamber, with one or two openings; the gametes are produced in multicellular sex organs, and the zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells. Unlike plant cells, animal cells have neither a cell wall nor chloroplasts. Vacuoles, when present, are more in number and much smaller than those in the plant cell. The body tissues are composed of numerous types of cells, including those found in muscles, nerves and skin. Each typically has a cell membrane formed of phospholipids, cytoplasm and a nucleus. All of the different cells of an animal are derived from the embryonic germ layers. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
layers are called triploblastic. All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the ectoderm, mesoderm and endoderm. Animal tissues can be grouped into four basic types: connective, epithelial, muscle and nervous tissue. === Connective tissue === Connective tissues are fibrous and made up of cells scattered among inorganic material called the extracellular matrix. Often called fascia (from the Latin "fascia," meaning "band" or "bandage"), connective tissues give shape to organs and holds them in place. The main types are loose connective tissue, adipose tissue, fibrous connective tissue, cartilage and bone. The extracellular matrix contains proteins, the chief and most abundant of which is collagen. Collagen plays a major part in organizing and maintaining tissues. The matrix can be modified to form a skeleton to support or protect the body. An exoskeleton is a thickened, rigid cuticle which is stiffened by mineralization, as in crustaceans or by the cross-linking of its proteins as in insects. An endoskeleton is internal and present in all developed animals, as well as in many of those less developed. === Epithelium === Epithelial tissue is composed of closely packed cells, bound to each other by cell adhesion molecules, with little intercellular space. Epithelial cells can be squamous (flat), cuboidal or columnar and rest on a basal lamina, the upper layer of the basement membrane, the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells. There are many different types of epithelium, modified to suit a particular function. In the respiratory tract there is a type of ciliated epithelial lining; in the small intestine there are microvilli on the epithelial lining and in the large intestine there are intestinal villi. Skin consists of an outer
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
layer of keratinized stratified squamous epithelium that covers the exterior of the vertebrate body. Keratinocytes make up to 95% of the cells in the skin. The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a cuticle. In simple animals this may just be a coat of glycoproteins. In more advanced animals, many glands are formed of epithelial cells. === Muscle tissue === Muscle cells (myocytes) form the active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle, skeletal muscle and cardiac muscle. Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths. It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the uterus, bladder, intestines, stomach, oesophagus, respiratory airways, and blood vessels. Cardiac muscle is found only in the heart, allowing it to contract and pump blood round the body. === Nervous tissue === Nervous tissue is composed of many nerve cells known as neurons which transmit information. In some slow-moving radially symmetrical marine animals such as ctenophores and cnidarians (including sea anemones
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
and jellyfish), the nerves form a nerve net, but in most animals they are organized longitudinally into bundles. In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as chemoreceptors and photoreceptors are found in groups and send messages along neural networks to other parts of the organism. Neurons can be connected together in ganglia. In higher animals, specialized receptors are the basis of sense organs and there is a central nervous system (brain and spinal cord) and a peripheral nervous system. The latter consists of sensory nerves that transmit information from sense organs and motor nerves that influence target organs. The peripheral nervous system is divided into the somatic nervous system which conveys sensation and controls voluntary muscle, and the autonomic nervous system which involuntarily controls smooth muscle, certain glands and internal organs, including the stomach. == Vertebrate anatomy == All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics: a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal arches; and a tail posterior to the anus. The spinal cord is protected by the vertebral column and is above the notochord, and the gastrointestinal tract is below it. Nervous tissue is derived from the ectoderm, connective tissues are derived from mesoderm, and gut is derived from the endoderm. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut. The mouth is found at the anterior end of the animal, and the anus at the base of the tail. The defining characteristic of a vertebrate is the vertebral column, formed in the development of the segmented
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
series of vertebrae. In most vertebrates the notochord becomes the nucleus pulposus of the intervertebral discs. However, a few vertebrates, such as the sturgeon and the coelacanth, retain the notochord into adulthood. Jawed vertebrates are typified by paired appendages, fins or legs, which may be secondarily lost. The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor. This is one of the arguments put forward by Charles Darwin to support his theory of evolution. === Fish anatomy === The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in cartilaginous fish, or bone in bony fish. The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays, which with the exception of the caudal fins, have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and on round the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or middle ear. Low frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large, yolky eggs. Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases. The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column. === Amphibian anatomy === Amphibians are a class of animals comprising frogs, salamanders and caecilians. They are tetrapods, but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size. Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have articular processes. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, but contains many mucous glands and
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
in some species, poison glands. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Amphibians breathe by means of buccal pumping, a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin which needs to be kept moist. In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs. The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing. Frogs have large eyes and no tail. Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail. Caecilians superficially resemble earthworms and are limbless. They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side. === Reptile anatomy === Reptiles are a class of animals comprising turtles, tuataras, lizards, snakes and crocodiles. They are tetrapods, but the snakes and a few species of lizard either have no limbs or their limbs are much reduced in size. Their bones are better ossified and their skeletons stronger than those of amphibians. The teeth are conical and mostly uniform in size. The surface cells of the epidermis are modified into horny scales which create a waterproof layer. Reptiles are unable to use their skin for respiration as do amphibians and have a more efficient respiratory system drawing air into their lungs by expanding their chest walls.
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
The heart resembles that of the amphibian but there is a septum which more completely separates the oxygenated and deoxygenated bloodstreams. The reproductive system has evolved for internal fertilization, with a copulatory organ present in most species. The eggs are surrounded by amniotic membranes which prevents them from drying out and are laid on land, or develop internally in some species. The bladder is small as nitrogenous waste is excreted as uric acid. Turtles are notable for their protective shells. They have an inflexible trunk encased in a horny carapace above and a plastron below. These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine. The neck is long and flexible and the head and the legs can be drawn back inside the shell. Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates. In aquatic species, the front legs are modified into flippers. Tuataras superficially resemble lizards but the lineages diverged in the Triassic period. There is one living species, Sphenodon punctatus. The skull has two openings (fenestrae) on either side and the jaw is rigidly attached to the skull. There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews. The teeth are merely projections of bony material from the jaw and eventually wear down. The brain and heart are more primitive than those of other reptiles, and the lungs have a single chamber and lack bronchi. The tuatara has a well-developed parietal eye on its forehead. Lizards have skulls with only one fenestra on each side, the lower bar of bone below the second fenestra having been lost. This results in the jaws
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
being less rigidly attached which allows the mouth to open wider. Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes. Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye. Snakes are closely related to lizards, having branched off from a common ancestral lineage during the Cretaceous period, and they share many of the same features. The skeleton consists of a skull, a hyoid bone, spine and ribs though a few species retain a vestige of the pelvis and rear limbs in the form of pelvic spurs. The bar under the second fenestra has also been lost and the jaws have extreme flexibility allowing the snake to swallow its prey whole. Snakes lack moveable eyelids, the eyes being covered by transparent "spectacle" scales. They do not have eardrums but can detect ground vibrations through the bones of their skull. Their forked tongues are used as organs of taste and smell and some species have sensory pits on their heads enabling them to locate warm-blooded prey. Crocodilians are large, low-slung aquatic reptiles with long snouts and large numbers of teeth. The head and trunk are dorso-ventrally flattened and the tail is laterally compressed. It undulates from side to side to force the animal through the water when swimming. The tough keratinized scales provide body armour and some are fused to the skull. The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating. Valves seal the nostrils and ears when it is submerged. Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood. === Bird
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
anatomy === Birds are tetrapods but though their hind limbs are used for walking or hopping, their front limbs are wings covered with feathers and adapted for flight. Birds are endothermic, have a high metabolic rate, a light skeletal system and powerful muscles. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. There are no teeth and the narrow jaws are adapted into a horn-covered beak. The eyes are relatively large, particularly in nocturnal species such as owls. They face forwards in predators and sideways in ducks. The feathers are outgrowths of the epidermis and are found in localized bands from where they fan out over the skin. Large flight feathers are found on the wings and tail, contour feathers cover the bird's surface and fine down occurs on young birds and under the contour feathers of water birds. The only cutaneous gland is the single uropygial gland near the base of the tail. This produces an oily secretion that waterproofs the feathers when the bird preens. There are scales on the legs, feet and claws on the tips of the toes. === Mammal anatomy === Mammals are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight. They mostly have four limbs, but some aquatic mammals have no limbs or limbs modified into fins, and the forelimbs of bats are modified into wings. The legs of most mammals are situated below the trunk, which is held well clear of the ground. The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of prismatic enamel.
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
The teeth are shed once (milk teeth) during the animal's lifetime or not at all, as is the case in cetaceans. Mammals have three bones in the middle ear and a cochlea in the inner ear. They are clothed in hair and their skin contains glands which secrete sweat. Some of these glands are specialized as mammary glands, producing milk to feed the young. Mammals breathe with lungs and have a muscular diaphragm separating the thorax from the abdomen which helps them draw air into the lungs. The mammalian heart has four chambers, and oxygenated and deoxygenated blood are kept entirely separate. Nitrogenous waste is excreted primarily as urea. Mammals are amniotes, and most are viviparous, giving birth to live young. Exceptions to this are the egg-laying monotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a teat and completes its development. ==== Human anatomy ==== Humans have the overall body plan of a mammal. Humans have a head, neck, trunk (which includes the thorax and abdomen), two arms and hands, and two legs and feet. Generally, students of certain biological sciences, paramedics, prosthetists and orthotists, physiotherapists, occupational therapists, nurses, podiatrists, and medical students learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials and in addition, medical students generally also learn gross anatomy through practical experience of dissection and inspection of cadavers. The study of microscopic anatomy (or histology) can be aided by practical experience examining histological preparations (or slides) under a microscope. Human anatomy, physiology and biochemistry are complementary basic medical sciences,
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
which are generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems. The major anatomy textbook, Gray's Anatomy, has been reorganized from a systems format to a regional format, in line with modern teaching methods. A thorough working knowledge of anatomy is required by physicians, especially surgeons and doctors working in some diagnostic specialties, such as histopathology and radiology. Academic anatomists are usually employed by universities, medical schools or teaching hospitals. They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells. == Invertebrate anatomy == Invertebrates constitute a vast array of living organisms ranging from the simplest unicellular eukaryotes such as Paramecium to such complex multicellular animals as the octopus, lobster and dragonfly. They constitute about 95% of the animal species. By definition, none of these creatures has a backbone. The cells of single-cell protozoans have the same basic structure as those of multicellular animals but some parts are specialized into the equivalent of tissues and organs. Locomotion is often provided by cilia or flagella or may proceed via the advance of pseudopodia, food may be gathered by phagocytosis, energy needs may be supplied by photosynthesis and the cell may be supported by an endoskeleton or an exoskeleton. Some protozoans can form multicellular colonies. Metazoans are a multicellular organism, with different groups of cells serving different functions. The most basic types of metazoan tissues are epithelium and connective tissue, both of which are present in nearly all invertebrates. The outer surface of the epidermis is normally formed of epithelial cells and secretes an extracellular matrix which provides support
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
to the organism. An endoskeleton derived from the mesoderm is present in echinoderms, sponges and some cephalopods. Exoskeletons are derived from the epidermis and is composed of chitin in arthropods (insects, spiders, ticks, shrimps, crabs, lobsters). Calcium carbonate constitutes the shells of molluscs, brachiopods and some tube-building polychaete worms and silica forms the exoskeleton of the microscopic diatoms and radiolaria. Other invertebrates may have no rigid structures but the epidermis may secrete a variety of surface coatings such as the pinacoderm of sponges, the gelatinous cuticle of cnidarians (polyps, sea anemones, jellyfish) and the collagenous cuticle of annelids. The outer epithelial layer may include cells of several types including sensory cells, gland cells and stinging cells. There may also be protrusions such as microvilli, cilia, bristles, spines and tubercles. Marcello Malpighi, the father of microscopical anatomy, discovered that plants had tubules similar to those he saw in insects like the silk worm. He observed that when a ring-like portion of bark was removed on a trunk a swelling occurred in the tissues above the ring, and he unmistakably interpreted this as growth stimulated by food coming down from the leaves, and being captured above the ring. === Arthropod anatomy === Arthropods comprise the largest phylum of invertebrates in the animal kingdom with over a million known species. Insects possess segmented bodies supported by a hard-jointed outer covering, the exoskeleton, made mostly of chitin. The segments of the body are organized into three distinct parts, a head, a thorax and an abdomen. The head typically bears a pair of sensory antennae, a pair of compound eyes, one to three simple eyes (ocelli) and three sets of modified appendages that form the mouthparts. The thorax has three pairs of segmented legs, one pair each for the three segments that compose the thorax
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
and one or two pairs of wings. The abdomen is composed of eleven segments, some of which may be fused and houses the digestive, respiratory, excretory and reproductive systems. There is considerable variation between species and many adaptations to the body parts, especially wings, legs, antennae and mouthparts. Spiders a class of arachnids have four pairs of legs; a body of two segments—a cephalothorax and an abdomen. Spiders have no wings and no antennae. They have mouthparts called chelicerae which are often connected to venom glands as most spiders are venomous. They have a second pair of appendages called pedipalps attached to the cephalothorax. These have similar segmentation to the legs and function as taste and smell organs. At the end of each male pedipalp is a spoon-shaped cymbium that acts to support the copulatory organ. == Other branches of anatomy == Surface anatomy is important as the study of anatomical landmarks that can be readily seen from the exterior contours of the body. It enables medics and veterinarians to gauge the position and anatomy of the associated deeper structures. Superficial is a directional term that indicates that structures are located relatively close to the surface of the body. Comparative anatomy relates to the comparison of anatomical structures (both gross and microscopic) in different animals. Artistic anatomy relates to anatomic studies of body proportions for artistic reasons. == History == === Ancient === In 1600 BCE, the Edwin Smith Papyrus, an Ancient Egyptian medical text, described the heart and its vessels, as well as the brain and its meninges and cerebrospinal fluid, and the liver, spleen, kidneys, uterus and bladder. It showed the blood vessels diverging from the heart. The Ebers Papyrus (c. 1550 BCE) features a "treatise on the heart", with vessels carrying all the body's fluids to or
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
from every member of the body. Ancient Greek anatomy and physiology underwent great changes and advances throughout the early medieval world. Over time, this medical practice expanded due to a continually developing understanding of the functions of organs and structures in the body. Phenomenal anatomical observations of the human body were made, which contributed to the understanding of the brain, eye, liver, reproductive organs, and nervous system. The Hellenistic Egyptian city of Alexandria was the stepping-stone for Greek anatomy and physiology. Alexandria not only housed the biggest library for medical records and books of the liberal arts in the world during the time of the Greeks but was also home to many medical practitioners and philosophers. Great patronage of the arts and sciences from the Ptolemaic dynasty of Egypt helped raise Alexandria up, further rivalling other Greek states' cultural and scientific achievements. Some of the most striking advances in early anatomy and physiology took place in Hellenistic Alexandria. Two of the most famous anatomists and physiologists of the third century were Herophilus and Erasistratus. These two physicians helped pioneer human dissection for medical research, using the cadavers of condemned criminals, which was considered taboo until the Renaissance—Herophilus was recognized as the first person to perform systematic dissections. Herophilus became known for his anatomical works, making impressive contributions to many branches of anatomy and many other aspects of medicine. Some of the works included classifying the system of the pulse, the discovery that human arteries had thicker walls than veins, and that the atria were parts of the heart. Herophilus's knowledge of the human body has provided vital input towards understanding the brain, eye, liver, reproductive organs, and nervous system and characterizing the course of the disease. Erasistratus accurately described the structure of the brain, including the cavities and membranes, and
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
made a distinction between its cerebrum and cerebellum During his study in Alexandria, Erasistratus was particularly concerned with studies of the circulatory and nervous systems. He could distinguish the human body's sensory and motor nerves and believed air entered the lungs and heart, which was then carried throughout the body. His distinction between the arteries and veins—the arteries carrying the air through the body, while the veins carry the blood from the heart was a great anatomical discovery. Erasistratus was also responsible for naming and describing the function of the epiglottis and the heart's valves, including the tricuspid. During the third century, Greek physicians were able to differentiate nerves from blood vessels and tendons and to realize that the nerves convey neural impulses. It was Herophilus who made the point that damage to motor nerves induced paralysis. Herophilus named the meninges and ventricles in the brain, appreciated the division between cerebellum and cerebrum and recognized that the brain was the "seat of intellect" and not a "cooling chamber" as propounded by Aristotle Herophilus is also credited with describing the optic, oculomotor, motor division of the trigeminal, facial, vestibulocochlear and hypoglossal nerves. Incredible feats were made during the third century BCE in both the digestive and reproductive systems. Herophilus discovered and described not only the salivary glands but also the small intestine and liver. He showed that the uterus is a hollow organ and described the ovaries and uterine tubes. He recognized that spermatozoa were produced by the testes and was the first to identify the prostate gland. The anatomy of the muscles and skeleton is described in the Hippocratic Corpus, an Ancient Greek medical work written by unknown authors. Aristotle described vertebrate anatomy based on animal dissection. Praxagoras identified the difference between arteries and veins. Also in the 4th century
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
BCE, Herophilos and Erasistratus produced more accurate anatomical descriptions based on vivisection of criminals in Alexandria during the Ptolemaic period. In the 2nd century, Galen of Pergamum, an anatomist, clinician, writer, and philosopher, wrote the final and highly influential anatomy treatise of ancient times. He compiled existing knowledge and studied anatomy through the dissection of animals. He was one of the first experimental physiologists through his vivisection experiments on animals. Galen's drawings, based mostly on dog anatomy, became effectively the only anatomical textbook for the next thousand years. His work was known to Renaissance doctors only through Islamic Golden Age medicine until it was translated from Greek sometime in the 15th century. === Medieval to early modern === Anatomy developed little from classical times until the sixteenth century; as the historian Marie Boas writes, "Progress in anatomy before the sixteenth century is as mysteriously slow as its development after 1500 is startlingly rapid".: 120–121 Between 1275 and 1326, the anatomists Mondino de Luzzi, Alessandro Achillini and Antonio Benivieni at Bologna carried out the first systematic human dissections since ancient times. Mondino's Anatomy of 1316 was the first textbook in the medieval rediscovery of human anatomy. It describes the body in the order followed in Mondino's dissections, starting with the abdomen, thorax, head, and limbs. It was the standard anatomy textbook for the next century. Leonardo da Vinci (1452–1519) was trained in anatomy by Andrea del Verrocchio. He made use of his anatomical knowledge in his artwork, making many sketches of skeletal structures, muscles and organs of humans and other vertebrates that he dissected. Andreas Vesalius (1514–1564), professor of anatomy at the University of Padua, is considered the founder of modern human anatomy. Originally from Brabant, Vesalius published the influential book De humani corporis fabrica ("the structure of the human body"),
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
a large format book in seven volumes, in 1543. The accurate and intricately detailed illustrations, often in allegorical poses against Italianate landscapes, are thought to have been made by the artist Jan van Calcar, a pupil of Titian. In England, anatomy was the subject of the first public lectures given in any science; these were provided by the Company of Barbers and Surgeons in the 16th century, joined in 1583 by the Lumleian lectures in surgery at the Royal College of Physicians. === Late modern === Medical schools began to be set up in the United States towards the end of the 18th century. Classes in anatomy needed a continual stream of cadavers for dissection, and these were difficult to obtain. Philadelphia, Baltimore, and New York were all renowned for body snatching activity as criminals raided graveyards at night, removing newly buried corpses from their coffins. A similar problem existed in Britain where demand for bodies became so great that grave-raiding and even anatomy murder were practised to obtain cadavers. Some graveyards were, in consequence, protected with watchtowers. The practice was halted in Britain by the Anatomy Act of 1832, while in the United States, similar legislation was enacted after the physician William S. Forbes of Jefferson Medical College was found guilty in 1882 of "complicity with resurrectionists in the despoliation of graves in Lebanon Cemetery". The teaching of anatomy in Britain was transformed by Sir John Struthers, Regius Professor of Anatomy at the University of Aberdeen from 1863 to 1889. He was responsible for setting up the system of three years of "pre-clinical" academic teaching in the sciences underlying medicine, including especially anatomy. This system lasted until the reform of medical training in 1993 and 2003. As well as teaching, he collected many vertebrate skeletons for his museum of
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
comparative anatomy, published over 70 research papers, and became famous for his public dissection of the Tay Whale. From 1822 the Royal College of Surgeons regulated the teaching of anatomy in medical schools. Medical museums provided examples in comparative anatomy, and were often used in teaching. Ignaz Semmelweis investigated puerperal fever and he discovered how it was caused. He noticed that the frequently fatal fever occurred more often in mothers examined by medical students than by midwives. The students went from the dissecting room to the hospital ward and examined women in childbirth. Semmelweis showed that when the trainees washed their hands in chlorinated lime before each clinical examination, the incidence of puerperal fever among the mothers could be reduced dramatically. Before the modern medical era, the primary means for studying the internal structures of the body were dissection of the dead and inspection, palpation, and auscultation of the living. The advent of microscopy opened up an understanding of the building blocks that constituted living tissues. Technical advances in the development of achromatic lenses increased the resolving power of the microscope, and around 1839, Matthias Jakob Schleiden and Theodor Schwann identified that cells were the fundamental unit of organization of all living things. The study of small structures involved passing light through them, and the microtome was invented to provide sufficiently thin slices of tissue to examine. Staining techniques using artificial dyes were established to help distinguish between different tissue types. Advances in the fields of histology and cytology began in the late 19th century along with advances in surgical techniques allowing for the painless and safe removal of biopsy specimens. The invention of the electron microscope brought a significant advance in resolution power and allowed research into the ultrastructure of cells and the organelles and other structures within them.
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
About the same time, in the 1950s, the use of X-ray diffraction for studying the crystal structures of proteins, nucleic acids, and other biological molecules gave rise to a new field of molecular anatomy. Equally important advances have occurred in non-invasive techniques for examining the body's interior structures. X-rays can be passed through the body and used in medical radiography and fluoroscopy to differentiate interior structures that have varying degrees of opaqueness. Magnetic resonance imaging, computed tomography, and ultrasound imaging have all enabled the examination of internal structures in unprecedented detail to a degree far beyond the imagination of earlier generations. == See also == Anatomical model Bibliography of biology § Anatomy Outline of human anatomy Plastination Evelyn tables Anatomy portal == References == == External links == Anatomy, In Our Time. BBC Radio 4. Melvyn Bragg with guests Ruth Richardson, Andrew Cunningham and Harold Ellis. "Anatomy of the Human Body". 20th edition. 1918. Henry Gray Parsons, Frederick Gymer (1911). "Anatomy" . Encyclopædia Britannica. Vol. 1 (11th ed.). pp. 920–943. Anatomia Collection: anatomical plates 1522 to 1867 (digitized books and images) Lyman, Henry Munson. The Book of Health (1898). Science History Institute Digital Collections Archived 2 February 2019 at the Wayback Machine. Gunther von Hagens True Anatomy for New Ways of Teaching. == Sources == This article incorporates text from a free content work. Licensed under CC BY 4.0. Text taken from Openstax Anatomy and Physiology, J. Gordon Betts et al, Openstax.
|
{
"page_id": 674,
"source": null,
"title": "Anatomy"
}
|
The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (np) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons. For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number Z and the neutron number N gives the atom's atomic mass number A. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the "relative isotopic mass"), is within 1% of the whole number A. Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth determines the element's standard atomic weight. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century. The conventional symbol Z comes from the German word Zahl 'number', which, before the modern synthesis of ideas from chemistry and physics, merely denoted an element's numerical place in the periodic table, whose order was then approximately, but not completely,
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge and a physical characteristic of atoms, did the word Atomzahl (and its English equivalent atomic number) come into common use in this context. The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons. == Notation == The atomic number is used in AZE notation, (with A as the mass number, Z the atomic number, and E for element) to denote an isotope. When a chemical symbol is used, e.g. "C" for carbon, standard notation uses a superscript at the upper left of the chemical symbol for the mass number and indicates the atomic number with a subscript at the lower left (e.g. 32He, 42He, 126C, 146C, 23592U, and 23992U). Because the atomic number is given by the element symbol, it is common to state only the mass number in the superscript and leave out the atomic number subscript (e.g. 3He, 4He, 12C, 14C, 235U, and 239U). The common pronunciation of the AZE notation is different from how it is written: 42He is commonly pronounced as helium-four instead of four-two-helium, and 23592U as uranium two-thirty-five (American English) or uranium-two-three-five (British) instead of 235-92-uranium. Various notations appear in older sources were used, such as Ne(22) in 1934,: 226 Ne22 for neon-22 (1935) or Pb210 for lead-210 (1933): 7 == History == In the 19th century, the term "atomic number" typically meant the number of atoms in a given volume. Modern chemists prefer to use the concept of molar concentration. In 1913, Antonius van den Broek proposed that the electric charge of an atomic nucleus, expressed as a multiplier of the elementary charge, was equal
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
to the element's sequential position on the periodic table. Ernest Rutherford, in various articles in which he discussed van den Broek's idea, used the term "atomic number" to refer to an element's position on the periodic table. No writer before Rutherford is known to have used the term "atomic number" in this way, so it was probably he who established this definition. After Rutherford deduced the existence of the proton in 1920, "atomic number" customarily referred to the proton number of an atom. In 1921, the German Atomic Weight Commission based its new periodic table on the nuclear charge number and in 1923 the International Committee on Chemical Elements followed suit. === The periodic table and a natural number for each element === The periodic table of elements creates an ordering of the elements, and so they can be numbered in order.: 222 Dmitri Mendeleev arranged his first periodic tables (first published on March 6, 1869) in order of atomic weight ("Atomgewicht"). However, in consideration of the elements' observed chemical properties, he changed the order slightly and placed tellurium (atomic weight 127.6) ahead of iodine (atomic weight 126.9). This placement is consistent with the modern practice of ordering the elements by proton number, Z, but that number was not known or suspected at the time. A simple numbering based on atomic weight position was never entirely satisfactory. In addition to the case of iodine and tellurium, several other pairs of elements (such as argon and potassium, cobalt and nickel) were later shown to have nearly identical or reversed atomic weights, thus requiring their placement in the periodic table to be determined by their chemical properties.: 222 However the gradual identification of more and more chemically similar lanthanide elements, whose atomic number was not obvious, led to inconsistency and uncertainty in
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
the periodic numbering of elements at least from lutetium (element 71) onward (hafnium was not known at this time). === The Rutherford-Bohr model and van den Broek === In 1911, Ernest Rutherford gave a model of the atom in which a central nucleus held most of the atom's mass and a positive charge which, in units of the electron's charge, was to be approximately equal to half of the atom's atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% different from the atomic number of gold (Z = 79, A = 197), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford's estimation that gold had a central charge of about 100 (but was element Z = 79 on the periodic table), a month after Rutherford's paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electrons in an atom were exactly equal to its place in the periodic table (also known as element number, atomic number, and symbolized Z). This eventually proved to be the case. === Moseley's 1913 experiment === The experimental position improved dramatically after research by Henry Moseley in 1913. Moseley, after discussions with Bohr who was at the same lab (and who had used Van den Broek's hypothesis in his Bohr model of the atom), decided to test Van den Broek's and Bohr's hypothesis directly, by seeing if spectral lines emitted from excited atoms fitted the Bohr theory's postulation that the frequency of the spectral lines be proportional to the square of Z. To do this, Moseley measured the wavelengths of the innermost photon transitions (K and L lines) produced by the elements from aluminium (Z = 13) to gold
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
(Z = 79) used as a series of movable anodic targets inside an x-ray tube. The square root of the frequency of these photons (x-rays) increased from one target to the next in an arithmetic progression. This led to the conclusion (Moseley's law) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley's work) to the calculated electric charge of the nucleus, i.e. the element number Z. Among other things, Moseley demonstrated that the lanthanide series (from lanthanum to lutetium inclusive) must have 15 members—no fewer and no more—which was far from obvious from known chemistry at that time. === Missing elements === After Moseley's death in 1915, the atomic numbers of all known elements from hydrogen to uranium (Z = 92) were examined by his method. There were seven elements (with Z < 92) which were not found and therefore identified as still undiscovered, corresponding to atomic numbers 43, 61, 72, 75, 85, 87 and 91. From 1918 to 1947, all seven of these missing elements were discovered. By this time, the first four transuranium elements had also been discovered, so that the periodic table was complete with no gaps as far as curium (Z = 96). === The proton and the idea of nuclear electrons === In 1915, the reason for nuclear charge being quantized in units of Z, which were now recognized to be the same as the element number, was not understood. An old idea called Prout's hypothesis had postulated that the elements were all made of residues (or "protyles") of the lightest element hydrogen, which in the Bohr-Rutherford model had a single electron and a nuclear charge of one. However, as early as 1907, Rutherford and Thomas Royds had shown that alpha particles, which had a charge of
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
+2, were the nuclei of helium atoms, which had a mass four times that of hydrogen, not two times. If Prout's hypothesis were true, something had to be neutralizing some of the charge of the hydrogen nuclei present in the nuclei of heavier atoms. In 1917, Rutherford succeeded in generating hydrogen nuclei from a nuclear reaction between alpha particles and nitrogen gas, and believed he had proven Prout's law. He called the new heavy nuclear particles protons in 1920 (alternate names being proutons and protyles). It had been immediately apparent from the work of Moseley that the nuclei of heavy atoms have more than twice as much mass as would be expected from their being made of hydrogen nuclei, and thus there was required a hypothesis for the neutralization of the extra protons presumed present in all heavy nuclei. A helium nucleus was presumed to have four protons plus two "nuclear electrons" (electrons bound inside the nucleus) to cancel two charges. At the other end of the periodic table, a nucleus of gold with a mass 197 times that of hydrogen was thought to contain 118 nuclear electrons in the nucleus to give it a residual charge of +79, consistent with its atomic number. === Discovery of the neutron makes Z the proton number === All consideration of nuclear electrons ended with James Chadwick's discovery of the neutron in 1932. An atom of gold now was seen as containing 118 neutrons rather than 118 nuclear electrons, and its positive nuclear charge now was realized to come entirely from a content of 79 protons. Since Moseley had previously shown that the atomic number Z of an element equals this positive charge, it was now clear that Z is identical to the number of protons of its nuclei. == Chemical properties ==
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
Each element has a specific set of chemical properties as a consequence of the number of electrons present in the neutral atom, which is Z (the atomic number). The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element's electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. Hence, it is the atomic number alone that determines the chemical properties of an element; and it is for this reason that an element can be defined as consisting of any mixture of atoms with a given atomic number. == New elements == The quest for new elements is usually described using atomic numbers. As of 2025, all elements with atomic numbers 1 to 118 have been observed. The most recent element discovered was number 117 (tennessine) in 2009. Synthesis of new elements is accomplished by bombarding target atoms of heavy elements with ions, such that the sum of the atomic numbers of the target and ion elements equals the atomic number of the element being created. In general, the half-life of a nuclide becomes shorter as atomic number increases, though undiscovered nuclides with certain "magic" numbers of protons and neutrons may have relatively longer half-lives and comprise an island of stability. A hypothetical element composed only of neutrons, neutronium, has also been proposed and would have atomic number 0, but has never been observed. == See also == Atomic theory Chemical element – Chemical substance not composed of simpler ones Effective nuclear charge – Measurement in atomic physics Effective atomic number (compounds and mixtures) – Approximate atomic number calculated for materials with many elements Even and odd atomic nuclei – Nuclear physics classification method History of the periodic table – Development of the table of
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
chemical elements List of chemical elements Mass number – Number of heavy particles in the atomic nucleus Neutron number – The number of neutrons in a nuclide Neutron–proton ratio – Ratio of neutrons to protons in an atomic nucleus Prout's hypothesis – Early model of the atom that did not account for mass defect == References ==
|
{
"page_id": 673,
"source": null,
"title": "Atomic number"
}
|
The wet leakage current test is an electrical withstanding test carried out on electrical appliances to test the electrical isolation of the housing. The test is carried out by submersing the appliance into water with one lead attached to the electrical leads of the appliance, and the other lead connected to the water. It is often carried out on photovoltaic modules in order to qualify them for IEC61646 or IEC61625 certification. == External links == http://www.harrexco.com http://www.hipot-test.com
|
{
"page_id": 25494178,
"source": null,
"title": "Wet leakage current test"
}
|
S-adenosyl-L-methionine:(3-phospho-D-glycerate-carboxy-lyase (dimerizing))-lysine 6-N-methyltransferase may refer to: (Ribulose-bisphosphate carboxylase)-lysine N-methyltransferase, an enzyme (Fructose-bisphosphate aldolase)-lysine N-methyltransferase, an enzyme
|
{
"page_id": 38601381,
"source": null,
"title": "S-adenosyl-L-methionine:(3-phospho-D-glycerate-carboxy-lyase (dimerizing))-lysine 6-N-methyltransferase"
}
|
The Biological Institute (Portuguese: Instituto Biológico) is an applied research center established in 1924 in São Paulo, Brazil. It is a governmental organisation concerned with the prevention of zoonoses and foodborne animal pathogens such as rabies and tuberculosis, sanitary advertisement campaigns, alternatives to the chemical control of diseases such as organic farming and biological control. Among its main achievements are the biological control of the coffee borer beetle in the 1920s in Brazil, the discovery of bradykinin, and the production of vaccines that combat the Newcastle disease, foot-and-mouth disease and the black plague in pigs. == History == Brazil used to be an important world coffee supplier in the international commodities markets in the beginning of the 20th century. Especially in the state of São Paulo, coffee became a major source of income from exports, and newly-rich coffee barons were sprouting all over the state. In the early 1920s, coffee farmers in the state of São Paulo were having a hard time in controlling the coffee borer beetle (Hypothenemus hampei), a bug that destroys coffee berries by perforating them (perforated coffee berries have no value in the commodities market). Gabriel Ribeiro dos Santos, the Secretary of Agriculture of the state of São Paulo at that time, has organised a commission of scientists in May 1924 to identify the coffee borer beetle and prevent further losses in the coffee fields. A report was delivered to the Secretary of Agriculture, and the actual research started in the same year with Arthur Neiva, Adalberto Queiros Teles and Edmundo Navarro, who worked in two chemistry and entomology laboratories. The goal of the Commission was to find out more information about the parasite, and hence discover effective ways of preventing its growth. The academic studies in process were widely advertised among more than 1,300 coffee
|
{
"page_id": 11928230,
"source": null,
"title": "Biological Institute (São Paulo)"
}
|
farms, or about 50 million farmers overall, in order to apply the results of the ongoing research. Arthur Neiva then ended the research at the end of the year, and the results from such a massive scientific and technical experiment soon arrived, and the damages caused by the beetle were finally under biological control. By importing the ectoparasitoid Prorops nasuta from Uganda and using it against the coffee borer beetle, the Commission was able to mitigate the losses in the coffee farms. The catastrophic uprising of the coffee borer beetle, which caught both farmers and the government short and unprepared, and the subsequent fast control of the bug founded on scientific research have shown politicians that it was impossible to protect agriculture from parasites and diseases without a permanent fitosanitary organisation, based on active research and specialised technicians and scientists. On 26 December 1927, a law enacted the creation of the Instituto Biológico de Defesa Agrícola e Animal (Biological Institute of Agricultural and Veterinary Defence); its current name, Instituto Biológico (Biological Institute), was applied in 1937. == The Institute == In 1928, an area of 239,000 square metres near Ibirapuera Park, known as "Campo do Barreto", was donated to the Institute for the construction of its research centre. The construction works took 17 years to be completed, and the building was finally inaugurated on 25 January 1945. Some of the construction materials were donated by private firms and wealthy individuals from the farming elites at that time. The institute also has a symbolic plantation of coffee in the middle of the greatest megalopolis of South America. == References == == External links == (in Portuguese) Biological Institute
|
{
"page_id": 11928230,
"source": null,
"title": "Biological Institute (São Paulo)"
}
|
Carl Theodor Liebermann (23 February 1842 – 28 December 1914) was a German chemist and student of Adolf von Baeyer. == Life == Liebermann first studied at the University of Heidelberg where Robert Wilhelm Bunsen was teaching. He then joined the group of Adolf von Baeyer at the University of Berlin where he received his PhD in 1865. Together with Carl Gräbe, Liebermann synthesised the orange-red dye alizarin in 1868. After his habilitation in 1870 he became professor at the University of Berlin after Adolf von Baeyer left for the University of Strasbourg. Shortly after Liebermann retired, in 1914, he died. == Work == In 1826, the French chemist Pierre Jean Robiquet had isolated from the root of a plant, madder, and defined the structure of, alizarin, a remarkable red dye. Liebermann's 1868 discovery that alizarin can be reduced to form anthracene, which is an abundant component in coal tar, opened the road for synthetic alizarin. The patent of Liebermann and Carl Gräbe for the synthesis of alizarin from anthracene was filed one day before the patent of William Henry Perkin. The synthesis is a chlorination or bromination of anthracene with a subsequent oxidation forming the alizarin. == See also == Pierre Jean Robiquet Carl Gräbe William Henry Perkin == References ==
|
{
"page_id": 14484134,
"source": null,
"title": "Carl Theodor Liebermann"
}
|
Wehrlite is an ultramafic and ultrabasic rock that is a mixture of olivine and clinopyroxene. It is a subdivision of the peridotites. The nomenclature allows up to a few percent of orthopyroxene. Accessory minerals include ilmenite, chromite, magnetite and an aluminium-bearing mineral (plagioclase, spinel or garnet). Wehrlites occur as mantle xenoliths and in ophiolites. Another occurrence is as cumulate in gabbro and norite layered intrusions. Some meteorites can also be classified as wehrlites (e.g. NWA 4797). Wehrlite is named after Alois Wehrle. He was born 1791 in Kroměříž, Czech Republic (then Kremsier in Mähren) and was a professor at the "Ungarische Bergakademie" (Hungarian Mining School) in Banská Štiavnica, Slovakia (then Schemnitz, Kingdom of Hungary). == References ==
|
{
"page_id": 38208167,
"source": null,
"title": "Wehrlite"
}
|
A blank value in analytical chemistry is a measurement of a blank. The reading does not originate from a sample, but the matrix effects, reagents and other residues. These contribute to the sample value in the analytical measurement and therefore have to be subtracted. The limit of blank is defined by the Clinical And Laboratory Standards Institute as the highest apparent analyte concentration expected to be found when replicates of a sample containing no analyte are tested. == See also == Blank (solution) == References ==
|
{
"page_id": 70189737,
"source": null,
"title": "Blank value"
}
|
Defence Nuclear Material within the UK is defined as: Nuclear weapons (warheads) Special Nuclear Materials (SNM), including new and used reactor fuel from Royal Navy submarines. == References ==
|
{
"page_id": 6816424,
"source": null,
"title": "Defence Nuclear Material"
}
|
Bi-scalar tensor vector gravity theory (BSTV) is an extension of the tensor–vector–scalar gravity theory (TeVeS). TeVeS is a relativistic generalization of Mordehai Milgrom's Modified Newtonian Dynamics MOND paradigm proposed by Jacob Bekenstein. BSTV was proposed by R.H.Sanders. BSTV makes TeVeS more flexible by making a non-dynamical scalar field in TeVeS into a dynamical one. == References ==
|
{
"page_id": 28005582,
"source": null,
"title": "Bi-scalar tensor vector gravity"
}
|
Protein moonlighting is a phenomenon by which a protein can perform more than one function. It is an excellent example of gene sharing. Ancestral moonlighting proteins originally possessed a single function but, through evolution, acquired additional functions. Many proteins that moonlight are enzymes; others are receptors, ion channels or chaperones. The most common primary function of moonlighting proteins is enzymatic catalysis, but these enzymes have acquired secondary non-enzymatic roles. Some examples of functions of moonlighting proteins secondary to catalysis include signal transduction, transcriptional regulation, apoptosis, motility, and structural. Protein moonlighting occurs widely in nature. Protein moonlighting through gene sharing differs from the use of a single gene to generate different proteins by alternative RNA splicing, DNA rearrangement, or post-translational processing. It is also different from the multifunctionality of the protein, in which the protein has multiple domains, each serving a different function. Protein moonlighting by gene sharing means that a gene may acquire and maintain a second function without gene duplication and without loss of the primary function. Such genes are under two or more entirely different selective constraints. Various techniques have been used to reveal moonlighting functions in proteins. The detection of a protein in unexpected locations within cells, cell types, or tissues may suggest that a protein has a moonlighting function. Furthermore, the sequence or structure homology of a protein may be used to infer both primary functions as well as secondary moonlighting functions of a protein. The most well-studied examples of gene sharing are crystallins. These proteins, when expressed at low levels in many tissues function as enzymes, but when expressed at high levels in eye tissue, become densely packed and thus form lenses. While the recognition of gene sharing is relatively recent—the term was coined in 1988, after crystallins in chickens and ducks were found to
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
be identical to separately identified enzymes—recent studies have found many examples throughout the living world. Joram Piatigorsky has suggested that many or all proteins exhibit gene sharing to some extent, and that gene sharing is a key aspect of molecular evolution.: 1–7 The genes encoding crystallins must maintain sequences for catalytic function and transparency maintenance function. Inappropriate moonlighting is a contributing factor in some genetic diseases, and moonlighting provides a possible mechanism by which bacteria may become resistant to antibiotics. == Discovery == The first observation of a moonlighting protein was made in the late 1980s by Joram Piatigorsky and Graeme Wistow during their research on crystallin enzymes. Piatigorsky determined that lens crystallin conservation and variance are due to other moonlighting functions outside of the lens. Originally Piatigorsky called these proteins "gene sharing" proteins, but the colloquial description moonlighting was subsequently applied to proteins by Constance Jeffery in 1999 to draw a similarity between multitasking proteins and people who work two jobs. The phrase "gene sharing" is ambiguous since it is also used to describe horizontal gene transfer, hence the phrase "protein moonlighting" has become the preferred description for proteins with more than one function. == Evolution == It is believed that moonlighting proteins came about by means of evolution through which uni-functional proteins gained the ability to perform multiple functions. With alterations, much of the protein's unused space can provide new functions. Many moonlighting proteins are the result of the gene fusion of two single function genes. Alternatively a single gene can acquire a second function since the active site of the encoded protein typically is small compared to the overall size of the protein leaving considerable room to accommodate a second functional site. In yet a third alternative, the same active site can acquire a second function through
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
mutations of the active site. The development of moonlighting proteins may be evolutionarily favorable to the organism since a single protein can do the job of multiple proteins conserving amino acids and energy required to synthesize these proteins. However, there is no universally agreed upon theory that explains why proteins with multiple roles evolved. While using one protein to perform multiple roles seems advantageous because it keeps the genome small, we can conclude that this is probably not the reason for moonlighting because of the large amount of noncoding DNA. == Functions == Many proteins catalyze a chemical reaction. Other proteins fulfill structural, transport, or signaling roles. Furthermore, numerous proteins have the ability to aggregate into supramolecular assemblies. For example, a ribosome is made up of 90 proteins and RNA. A number of the currently known moonlighting proteins are evolutionarily derived from highly conserved enzymes, also called ancient enzymes. These enzymes are frequently speculated to have evolved moonlighting functions. Since highly conserved proteins are present in many different organisms, this increases the chance that they would develop secondary moonlighting functions. A high fraction of enzymes involved in glycolysis, an ancient universal metabolic pathway, exhibit moonlighting behavior. Furthermore, it has been suggested that as many as 7 out of 10 proteins in glycolysis and 7 out of 8 enzymes of the tricarboxylic acid cycle exhibit moonlighting behavior. An example of a moonlighting enzyme is pyruvate carboxylase. This enzyme catalyzes the carboxylation of pyruvate into oxaloacetate, thereby replenishing the tricarboxylic acid cycle. Surprisingly, in yeast species such as H. polymorpha and P. pastoris, pyruvate carboylase is also essential for the proper targeting and assembly of the peroxisomal protein alcohol oxidase (AO). AO, the first enzyme of methanol metabolism, is a homo-octameric flavoenzyme. In wild type cells, this enzyme is present as enzymatically
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
active AO octamers in the peroxisomal matrix. However, in cells lacking pyruvate carboxylase, AO monomers accumulate in the cytosol, indicating that pyruvate carboxylase has a second fully unrelated function in assembly and import. The function in AO import/assembly is fully independent of the enzyme activity of pyruvate carboxylase, because amino acid substitutions can be introduced that fully inactivate the enzyme activity of pyruvate carboxylase, without affecting its function in AO assembly and import. Conversely, mutations are known that block the function of this enzyme in the import and assembly of AO, but have no effect on the enzymatic activity of the protein. The E. coli anti-oxidant thioredoxin protein is another example of a moonlighting protein. Upon infection with the bacteriophage T7, E. coli thioredoxin forms a complex with T7 DNA polymerase, which results in enhanced T7 DNA replication, a crucial step for successful T7 infection. Thioredoxin binds to a loop in T7 DNA polymerase to bind more strongly to the DNA. The anti-oxidant function of thioredoxin is fully autonomous and fully independent of T7 DNA replication, in which the protein most likely fulfills the functional role. ADT2 and ADT5 are other examples of moonlighting proteins found in plants. Both of these proteins have roles in phenylalanine biosynthesis like all other ADTs. However ADT2, together with FtsZ is necessary in chloroplast division and ADT5 is transported by stromules into the nucleus. == Examples == == Mechanisms == In many cases, the functionality of a protein not only depends on its structure, but also its location. For example, a single protein may have one function when found in the cytoplasm of a cell, a different function when interacting with a membrane, and yet a third function if excreted from the cell. This property of moonlighting proteins is known as "differential localization". For
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
example, in higher temperatures DegP (HtrA) will function as a protease by the directed degradation of proteins and in lower temperatures as a chaperone by assisting the non-covalent folding or unfolding and the assembly or disassembly of other macromolecular structures. Furthermore, moonlighting proteins may exhibit different behaviors not only as a result of its location within a cell, but also the type of cell that the protein is expressed in. Multifunctionality could also be as a consequence of differential post translational modifications (PTMs). In the case of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) alterations in the PTMs have been shown to be associated with higher order multi functionality. Other methods through which proteins may moonlight are by changing their oligomeric state, altering concentrations of the protein's ligand or substrate, use of alternative binding sites, or finally through phosphorylation. An example of a protein that displays different function in different oligomeric states is pyruvate kinase which exhibits metabolic activity as a tetramer and thyroid hormone–binding activity as a monomer. Changes in the concentrations of ligands or substrates may cause a switch in a protein's function. For example, in the presence of high iron concentrations, aconitase functions as an enzyme while at low iron concentration, aconitase functions as an iron-responsive element-binding protein (IREBP) to increase iron uptake. Proteins may also perform separate functions through the use of alternative binding sites that perform different tasks. An example of this is ceruloplasmin, a protein that functions as an oxidase in copper metabolism and moonlights as a copper-independent glutathione peroxidase. Lastly, phosphorylation may sometimes cause a switch in the function of a moonlighting protein. For example, phosphorylation of phosphoglucose isomerase (PGI) at Ser-185 by protein kinase CK2 causes it to stop functioning as an enzyme, while retaining its function as an autocrine motility factor. Hence
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
when a mutation takes place that inactivates a function of a moonlighting proteins, the other function(s) are not necessarily affected. The crystal structures of several moonlighting proteins, such as I-AniI homing endonuclease / maturase and the PutA proline dehydrogenase / transcription factor, have been determined. An analysis of these crystal structures has demonstrated that moonlighting proteins can either perform both functions at the same time, or through conformational changes, alternate between two states, each of which is able to perform a separate function. For example, the protein DegP plays a role in proteolysis with higher temperatures and is involved in refolding functions at lower temperatures. Lastly, these crystal structures have shown that the second function may negatively affect the first function in some moonlighting proteins. As seen in ƞ-crystallin, the second function of a protein can alter the structure, decreasing the flexibility, which in turn can impair enzymatic activity somewhat. == Identification methods == Moonlighting proteins have usually been identified by chance because there is no clear procedure to identify secondary moonlighting functions. Despite such difficulties, the number of moonlighting proteins that have been discovered is rapidly increasing. Furthermore, moonlighting proteins appear to be abundant in all kingdoms of life. Various methods have been employed to determine a protein's function including secondary moonlighting functions. For example, the tissue, cellular, or subcellular distribution of a protein may provide hints as to the function. Real-time PCR is used to quantify mRNA and hence infer the presence or absence of a particular protein which is encoded by the mRNA within different cell types. Alternatively immunohistochemistry or mass spectrometry can be used to directly detect the presence of proteins and determine in which subcellular locations, cell types, and tissues a particular protein is expressed. Mass spectrometry may be used to detect proteins based on
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
their mass-to-charge ratio. Because of alternative splicing and posttranslational modification, identification of proteins based on the mass of the parent ion alone is very difficult. However tandem mass spectrometry in which each of the parent peaks is in turn fragmented can be used to unambiguously identify proteins. Hence tandem mass spectrometry is one of the tools used in proteomics to identify the presence of proteins in different cell types or subcellular locations. While the presence of a moonlighting protein in an unexpected location may complicate routine analyses, at the same time, the detection of a protein in unexpected multiprotein complexes or locations suggests that protein may have a moonlighting function. Furthermore, mass spectrometry may be used to determine if a protein has high expression levels that do not correlate to the enzyme's measured metabolic activity. These expression levels may signify that the protein is performing a different function than previously known. The structure of a protein can also help determine its functions. Protein structure in turn may be elucidated with various techniques including X-ray crystallography or NMR. Dual-polarization interferometry may be used to measure changes in protein structure which may also give hints to the protein's function. Finally, application of systems biology approaches such as interactomics give clues to a proteins function based on what it interacts with. == Higher order multifunctionality == In the case of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in addition to the large number of alternate functions it has also been observed that it can be involved in the same function by multiple means (multifunctionality within multifunctionality). For example, in its role in maintenance of cellular iron homeostasis GAPDH can function to import or extrude iron from cells. Moreover, in case of its iron import activities it can traffic into cells holo-transferrin as well as
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
the related molecule lactoferrin by multiple pathways. == Crystallins == In the case of crystallins, the genes must maintain sequences for catalytic function and transparency maintenance function. The abundant lens crystallins have been generally viewed as static proteins serving a strictly structural role in transparency and cataract. However, recent studies have shown that the lens crystallins are much more diverse than previously recognized and that many are related or identical to metabolic enzymes and stress proteins found in numerous tissues. Unlike other proteins performing highly specialized tasks, such as globin or rhodopsin, the crystallins are very diverse and show numerous species differences. Essentially all vertebrate lenses contain representatives of the α and β/γ crystallins, the "ubiquitous crystallins", which are themselves heterogeneous, and only few species or selected taxonomic groups use entirely different proteins as lens crystallins. This paradox of crystallins being highly conserved in sequence while extremely diverse in number and distribution shows that many crystallins have vital functions outside the lens and cornea, and this multi-functionality of the crystallins is achieved by moonlightining. === Gene regulation === Crystallin recruitment may occur by changes in gene regulation that leads to high lens expression. One such example is gluthathione S-transferase/S11-crystallin that was specialized for lens expression by change in gene regulation and gene duplication. The fact that similar transcriptional factors such as Pax-6, and retinoic acid receptors, regulate different crystalline genes, suggests that lens-specific expression have played a crucial role for recruiting multifunctional protein as crystallins. Crystallin recruitment has occurred both with and without gene duplication, and tandem gene duplication has taken place among some of the crystallins with one of the duplicates specializing for lens expression. Ubiquitous α –crystallins and bird δ –crystallins are two examples. === Alpha crystallins === The α-crystallins, which contributed to the discovery of crystallins as
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
borrowed proteins, have continually supported the theory of gene sharing, and helped delineating the mechanisms used for gene sharing as well. There are two α-crystallin genes (αA and αB), which are about 55% identical in amino acid sequence. Expression studies in non-lens cells showed that the αB-crystallin, other than being a functional lens protein, is a functional small heat shock protein. αB-crystallin is induced by heat and other physiological stresses, and it can protect the cells from elevated temperatures and hypertonic stress. αB-crystallin is also overexpressed in many pathologies, including neurodegenerative diseases, fibroblasts of patients with Werner syndrome showing premature senescence, and growth abnormalities. In addition to being overexpressed under abnormal conditions, αB-crystallin is constitutively expressed in heart, skeletal muscle, kidney, lung and many other tissues. In contrast to αB-crystallin, except for low-level expression in the thymus, spleen and retina, αA-crystallin is highly specialized for expression in the lens and is not stress-inducible. However, like αB-crystallin, it can also function as molecular chaperone and protect against thermal stress. === Beta/gamma-crystallins === β/γ-crystallins are different from α-crystallins in that they are a large multigene family. Other proteins like bacterial spore coat, a slime mold cyst protein, and epidermis differentiation-specific protein, contain the same Greek key motifs and are placed under β/γ crystallin superfamily. This relationship supports the idea that β/γ- crystallins have been recruited by a gene-sharing mechanism. However, except for few reports, non-refractive function of the β/γ-crystallin is yet to be found. === Corneal crystallins === Similar to lens, cornea is a transparent, avascular tissue derived from the ectoderm that is responsible for focusing light onto the retina. However, unlike lens, cornea depends on the air-cell interface and its curvature for refraction. Early immunology studies have shown that BCP 54 comprises 20–40% of the total soluble protein in bovine cornea.
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
Subsequent studies have indicated that BCP 54 is ALDH3, a tumor and xenobiotic-inducible cytosolic enzyme, found in human, rat, and other mammals. === Non refractive roles of crystallins in lens and cornea === While it is evident that gene sharing resulted in many of lens crystallins being multifunctional proteins, it is still uncertain to what extent the crystallins use their non-refractive properties in the lens, or on what basis they were selected. The α-crystallins provide a convincing case for a lens crystallin using its non-refractive ability within the lens to prevent protein aggregation under a variety of environmental stresses and to protect against enzyme inactivation by post-translational modifications such as glycation. The α-crystallins may also play a functional role in the stability and remodeling of the cytoskeleton during fiber cell differentiation in the lens. In cornea, ALDH3 is also suggested to be responsible for absorbing UV-B light. === Co-evolution of lens and cornea through gene sharing === Based on the similarities between lens and cornea, such as abundant water-soluble enzymes, and being derived from ectoderm, the lens and cornea are thought to be co-evolved as a "refraction unit." Gene sharing would maximize light transmission and refraction to the retina by this refraction unit. Studies have shown that many water-soluble enzymes/proteins expressed by cornea are identical to taxon-specific lens crystallins, such as ALDH1A1/ η-crystallin, α-enolase/τ-crystallin, and lactic dehydrogenase/ -crystallin. Also, the anuran corneal epithelium, which can transdifferentiate to regenerate the lens, abundantly expresses ubiquitous lens crystallins, α, β and γ, in addition to the taxon-specific crystallin α-enolase/τ-crystallin. Overall, the similarity in expression of these proteins in the cornea and lens, both in abundance and taxon-specificity, supports the idea of co-evolution of lens and cornea through gene sharing. == Relationship to similar concepts == Gene sharing is related to, but distinct from,
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
several concepts in genetics, evolution, and molecular biology. Gene sharing entails multiple effects from the same gene, but unlike pleiotropy, it necessarily involves separate functions at the molecular level. A gene could exhibit pleiotropy when single enzyme function affects multiple phenotypic traits; mutations of a shared gene could potentially affect only a single trait. Gene duplication followed by differential mutation is another phenomenon thought to be a key element in the evolution of protein function, but in gene sharing, there is no divergence of gene sequence when proteins take on new functions; the single polypeptide takes on new roles while retaining old ones. Alternative splicing can result in the production of multiple polypeptides (with multiple functions) from a single gene, but by definition, gene sharing involves multiple functions of a single polypeptide.: 8–14 == Clinical significance == The multiple roles of moonlighting proteins complicates the determination of phenotype from genotype, hampering the study of inherited metabolic disorders. The complex phenotypes of several disorders are suspected to be caused by the involvement of moonlighting proteins. The protein GAPDH has at least 11 documented functions, one of which includes apoptosis. Excessive apoptosis is involved in many neurodegenerative diseases, such as Huntington's, Alzheimer's, and Parkinson's as well as in brain ischemia. In one case, GAPDH was found in the degenerated neurons of individuals who had Alzheimer's disease. Although there is insufficient evidence for definite conclusions, there are well documented examples of moonlighting proteins that play a role in disease. One such disease is tuberculosis. One moonlighting protein in M. tuberculosis has a function which counteracts the effects of antibiotics. Specifically, the bacterium gains antibiotic resistance against ciprofloxacin from overexpression of glutamate racemase in vivo. GAPDH localized to the surface of pathogenic mycobacteriea has been shown to capture and traffic the mammalian iron carrier
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
protein transferrin into cells resulting in iron acquisition by the pathogen. == See also == Enzyme promiscuity Pseudoenzymes == External links == Media related to Moonlighting proteins at Wikimedia Commons moonlightingproteins.org database == References ==
|
{
"page_id": 30999216,
"source": null,
"title": "Protein moonlighting"
}
|
Cadalene or cadalin (4-isopropyl-1,6-dimethylnaphthalene) is a polycyclic aromatic hydrocarbon with a chemical formula C15H18 and a cadinane skeleton. It is derived from generic sesquiterpenes, and ubiquitous in essential oils of many higher plants. Cadalene, together with retene, simonellite and ip-iHMN, is a biomarker of higher plants, which makes it useful for paleobotanic analysis of rock sediments. The ratio of retene to cadalene in sediments can reveal the ratio of the genus Pinaceae in the biosphere. == References ==
|
{
"page_id": 7013043,
"source": null,
"title": "Cadalene"
}
|
The Lydersen method is a group contribution method for the estimation of critical properties temperature (Tc), pressure (Pc) and volume (Vc). The method is named after Aksel Lydersen who published it in 1955. The Lydersen method is the prototype for and ancestor of many new models like Joback, Klincewicz, Ambrose, Gani-Constantinou and others. The Lydersen method is based in case of the critical temperature on the Guldberg rule which establishes a relation between the normal boiling point and the critical temperature. == Equations == === Critical temperature === T c = T b 0.567 + ∑ G i − ( ∑ G i ) 2 {\displaystyle T_{c}={\frac {T_{b}}{0.567+\sum G_{i}-\left(\sum G_{i}\right)^{2}}}} Guldberg has found that a rough estimate of the normal boiling point Tb, when expressed in kelvins (i.e., as an absolute temperature), is approximately two-thirds of the critical temperature Tc. Lydersen uses this basic idea but calculates more accurate values. === Critical pressure === P c = M ( 0.34 + ∑ G i ) 2 {\displaystyle P_{c}={\frac {M}{\left(0.34+\sum G_{i}\right)^{2}}}} === Critical volume === V c = 40 + ∑ G i {\displaystyle V_{c}\,=\,40+\sum G_{i}} M is the molar mass and Gi are the group contributions (different for all three properties) for functional groups of a molecule. == Group contributions == == Example calculation == Acetone is fragmented in two different groups, one carbonyl group and two methyl groups. For the critical volume the following calculation results: Vc = 40 + 60.0 + 2 * 55.0 = 210 cm3 In the literature (such as in the Dortmund Data Bank) the values 215.90 cm3, 230.5 cm3 and 209.0 cm3 are published. == References ==
|
{
"page_id": 21693114,
"source": null,
"title": "Lydersen method"
}
|
The Markó–Lam deoxygenation is an organic chemistry reaction where the hydroxy functional group in an organic compound is replaced by a hydrogen atom to give an alkyl group. The Markó-Lam reaction is a variant of the Bouveault–Blanc reduction and an alternative to the classical Barton–McCombie deoxygenation. It is named for the Belgian chemists István Markó and Kevin Lam. The main features of the reaction are: short reaction time (5 seconds to 5 minutes). the use of a stable toluate derivative. the use of SmI2/HMPA system or electrolysis instead of the classical and difficult to remove tributyltin hydride. == Mechanism == A hydroxyl group is first derivitised into a stable and very often crystalline toluate derivative. The aromatic ester is submitted to a monoelectronical reduction, by the use of SmI2/HMPA or by electrolysis, to yield the a radical-anion which decomposes into the corresponding carboxylate and into the radical of the alkyl fragment. This radical could be used for further chemical reactions or can abstract a hydrogen atom to form the deoxygenated product. == Variations == In presence of methanol or isopropanol, the reduction lead to the selective deprotection of the aromatic esters. In presence of ketones, allylic derivatives lead to the coupling product when treated in Barbier's conditions with samarium diiodide. == Scope == The Markó-Lam reaction was used as a final step in the total synthesis of Trifarienol B: == References ==
|
{
"page_id": 25625276,
"source": null,
"title": "Markó–Lam deoxygenation"
}
|
Astroecology concerns the interactions of biota with space environments. It studies resources for life on planets, asteroids and comets, around various stars, in galaxies, and in the universe. The results allow estimating the future prospects for life, from planetary to galactic and cosmological scales. Available energy, and microgravity, radiation, pressure and temperature are physical factors that affect astroecology. The ways by which life can reach space environments, including natural panspermia and directed panspermia are also considered. Further, for human expansion in space and directed panspermia, motivation by life-centered biotic ethics, panbiotic ethics and planetary bioethics are also relevant. == Overview == The term "astroecology" was first applied in the context of performing studies in actual meteorites to evaluate their potential resources favorable to sustaining life. Early results showed that meteorite/asteroid materials can support microorganisms, algae and plant cultures under Earth's atmosphere and supplemented with water. Several observations suggest that diverse planetary materials, similar to meteorites collected on Earth, could be used as agricultural soils, as they provide nutrients to support microscopic life when supplemented with water and an atmosphere. Experimental astroecology has been proposed to rate planetary materials as targets for astrobiology exploration and as potential biological in-situ resources. The biological fertilities of planetary materials can be assessed by measuring water-extractable electrolyte nutrients. The results suggest that carbonaceous asteroids and Martian basalts can serve as potential future resources for substantial biological populations in the Solar System. Analysis of the essential nutrients (C, N, P, K) in meteorites yielded information for calculating the amount of biomass that can be constructed from asteroid resources. For example, carbonaceous asteroids are estimated to contain about 1022 kg potential resource materials, and laboratory results suggest that they could yield a biomass on the order of 6·1020 kg, about 100,000 times more than biological matter presently
|
{
"page_id": 21168829,
"source": null,
"title": "Astroecology"
}
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.