title: Strays (TV series)

text: The show initially faced some criticism for the implications of the fact that Shannon, the only white character in the core cast of "Kim's Convenience", was being given her own spinoff over any of the show's Asian characters. John Doyle of "The Globe and Mail" noted the complexities of the situation, explaining that since all of the other major characters in "Kim's Convenience" were drawn from Ins Choi's original theatrical play, and Shannon was the only character who had been newly created specifically for the television series, she was the only character who was the intellectual property of the show's producers and thus the only one who could be spun off without Choi's participation.


title: Strays (TV series)

text: Doyle favourably reviewed the first episodes of the series, writing that "The sheer energy of Strays is admirable. It's gags galore and it can be fiendishly clever contrivance, often anchored in the style of that theatrical staple, the British bedroom farce. At the same time, it's a distinctly contemporary Canadian series, with a diverse cast, and if there's a tincture of subtext that subtext is tolerance. But you'd hardly notice with all the exuberance on display. Besides, there are cute animals almost everywhere."


title: School 2021

text: School 2021 () is a South Korean television series directed by Kim Min-tae and starring Kim Yo-han, Cho Yi-hyun, Choo Young-woo and Hwang Bo-reum-byeol. It is the eighth installment of KBS2's "School" franchise. The series tells the story of 18 youths, who choose a path rather than an entrance examination. It depicts their growing period of dreams, friendship, and excitement as they struggle through the undefined boundaries. It was premiered on KBS2 on November 24, 2021 and aired every Wednesday and Thursday at 21:30 (KST) till January 13, 2022.


title: School 2021

text: School friends helping each other overcome the barriers that come up while taking a less chosen path. In the course they learn valuable lessons about life, love, and friendship.


title: School 2021

text: Originally planned to be produced in 2020 under the name "School 2020" and to air in the second half of 2020, the series was delayed for completeness. The script was revised and the name was changed to "School 2021".


title: School 2021

text: In February 2020, Kim Yo-han was confirmed as the male lead. Ahn Seo-hyun was cast as female lead, but was removed from the series due to disagreement between her father (who also served as her talent manager at that time) and the producers. Kim Sae-ron was offered the female lead role later, but she declined. In April 2021, Kim Young-dae and Cho Yi-hyun joined the cast. On June 21, casting of the four main characters was confirmed. On July 15, it was reported that Kim Young-dae has dropped out of the series. On July 23, it was officially announced that Kim Young-dae withdrew. On July 27, it was reported that Choo Young-woo has been offered the role of transfer student, which originally Kim Young-dae was playing. On July 28, it was reported that Choo Young-woo officially joined. On August 5, it was announced by Kurznine Entertainment that Seo Hee-sun would debut as an idol trainee in the series. On the same day, Mystic Story announced that Kim Kang-min also joined the cast of "School 2021". On August 6, the cast lineup for teachers and families was announced. On October 13, script reading site was revealed by releasing photos.


title: School 2021

text: On November 13, one of the cast member of TV series was tested positive for COVID-19 and subsequently the main lead was also found positive, the production and presentation was suspended as per the guidelines.


title: School 2021

text: On September 24, it was reported that producers Yoon Il-sang, and artist Yoon Min-soo of Vibe, and Mamamoo's RBW Entertainment are participating in the "School 2021" album production together and working on the songs. It is progressing along with the production of the drama.


title: School 2021

text: School 2021 was originally scheduled to be released on November 17, 2021, however, Kim Yo-han caught COVID-19 and the premiere date was postponed to November 24.


title: School 2021

text: A special broadcast titled '2021, Let's Go to School!' to promote the series was aired on November 18, 2021. The production team said, "Through a special broadcast, we will present an exciting time by highlighting a fresh and refreshing story and teen romance once again."


title: Dracaena (plant)

text: Dracaena () is a genus of about 120 species of trees and succulent shrubs. The formerly accepted genera "Pleomele" and "Sansevieria" are now included in "Dracaena". In the APG IV classification system, it is placed in the family Asparagaceae, subfamily Nolinoideae (formerly the family Ruscaceae). It has also formerly been separated (sometimes with "Cordyline") into the family Dracaenaceae or placed in the Agavaceae (now Agavoideae).


title: Dracaena (plant)

text: The name "dracaena" is derived from the romanized form of the Ancient Greek – "drakaina", "female dragon".


title: Dracaena (plant)

text: The majority of the species are native to Africa, southern Asia through to northern Australia, with two species in tropical Central America.


title: Dracaena (plant)

text: Species of "Dracaena" have a secondary thickening meristem in their trunk, termed Dracaenoid thickening by some authors, which is quite different from the thickening meristem found in dicotyledonous plants. This characteristic is shared with members of the Agavoideae and Xanthorrhoeoideae among other members of the Asparagales.


title: Dracaena (plant)

text: "Dracaena" species can be classified in two growth types: treelike dracaenas ("Dracaena fragrans", "Dracaena draco", "Dracaena cinnabari"), which have aboveground stems that branch from nodes after flowering, or if the growth tip is severed, and rhizomatous dracaenas ("Dracaena trifasciata", "Dracaena angolensis"), which have underground rhizomes and leaves on the surface (ranging from straplike to cylindrical).


title: Dracaena (plant)

text: Many species of "Dracaena" are kept as houseplants due to tolerance of lower light and sparse watering.


title: Dracaena (plant)

text: Some shrubby species, such as "D. fragrans", "D. surculosa", "D. marginata", and "D. sanderiana", are popular as houseplants. Many of these are toxic to pets, though not humans, according to the ASPCA among others. Rooted stem cuttings of "D. sanderiana" are sold as "lucky bamboo", although only superficially resembling true bamboos.


title: Dracaena (plant)

text: Dracaena houseplants like humidity and moderate watering. They can tolerate periods of drought but the tips of the leaves may turn brown. Leaves at the base will naturally yellow and drop off, leaving growth at the top and a bare stem. Dracaena are vulnerable to mealybugs and scale insects.


title: Dracaena (plant)

text: A naturally occurring bright red resin, dragon's blood, is collected from "D. draco" and, in ancient times, from "D. cinnabari". Modern dragon's blood is however more likely to be from the unrelated "Daemonorops" rattan palms. It also has social functions in marking graves, sacred sites and farm plots in many African societies


title: Well

text: A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The well water is drawn up by a pump, or using containers, such as buckets or large water bags that are raised mechanically or by hand. Water can also be injected back into the aquifer through the well. Wells were first constructed at least eight thousand years ago and historically vary in construction from a simple scoop in the sediment of a dry watercourse to the qanats of Iran, and the stepwells and sakiehs of India. Placing a lining in the well shaft helps create stability, and linings of wood or wickerwork date back at least as far as the Iron Age.


title: Well

text: Wells have traditionally been sunk by hand digging, as is still the case in rural areas of the developing world. These wells are inexpensive and low-tech as they use mostly manual labour, and the structure can be lined with brick or stone as the excavation proceeds. A more modern method called caissoning uses pre-cast reinforced concrete well rings that are lowered into the hole. Driven wells can be created in unconsolidated material with a well hole structure, which consists of a hardened drive point and a screen of perforated pipe, after which a pump is installed to collect the water. Deeper wells can be excavated by hand drilling methods or machine drilling, using a bit in a borehole. Drilled wells are usually cased with a factory-made pipe composed of steel or plastic. Drilled wells can access water at much greater depths than dug wells.


title: Well

text: Two broad classes of well are shallow or unconfined wells completed within the uppermost saturated aquifer at that location, and deep or confined wells, sunk through an impermeable stratum into an aquifer beneath. A collector well can be constructed adjacent to a freshwater lake or stream with water percolating through the intervening material. The site of a well can be selected by a hydrogeologist, or groundwater surveyor. Water may be pumped or hand drawn. Impurities from the surface can easily reach shallow sources and contamination of the supply by pathogens or chemical contaminants needs to be avoided. Well water typically contains more minerals in solution than surface water and may require treatment before being potable. Soil salination can occur as the water table falls and the surrounding soil begins to dry out. Another environmental problem is the potential for methane to seep into the water.


title: Well

text: Very early neolithic wells are known from the Eastern Mediterranean: The oldest reliably dated well is from the pre-pottery neolithic (PPN) site of Kissonerga-Mylouthkia on Cyprus. At around 8400 BC a shaft (well 116) of circular diameter was driven through limestone to reach an aquifer at a depth of . Well 2070 from Kissonerga-Mylouthkia, dating to the late PPN, reaches a depth of . Other slightly younger wells are known from this site and from neighbouring Parekklisha-Shillourokambos. A first stone lined well of depth is documented from a drowned final PPN (c. 7000 BC) site at ‘Atlit-Yam off the coast near modern Haifa in Israel.


title: Well

text: Wood-lined wells are known from the early Neolithic Linear Pottery culture, for example in Ostrov, Czech Republic, dated 5265 BC, Kückhoven (an outlying centre of Erkelenz), dated 5090 BC, and Eythra in Schletz (an outlying centre of Asparn an der Zaya) in Austria, dated 5200 BC.


title: Well

text: Some of the earliest evidence of water wells is located in China. The neolithic Chinese discovered and made extensive use of deep drilled groundwater for drinking. The Chinese text "The Book of Changes", originally a divination text of the Western Zhou dynasty (1046 -771 BC), contains an entry describing how the ancient Chinese maintained their wells and protected their sources of water. A well excavated at the Hemedu excavation site was believed to have been built during the neolithic era. The well was cased by four rows of logs with a square frame attached to them at the top of the well. 60 additional tile wells southwest of Beijing are also believed to have been built around 600 BC for drinking and irrigation.


title: Well

text: In Egypt, shadoofs and sakias are used. The sakia is much more efficient, as it can bring up water from a depth of 10 metres (versus the 3 metres of the shadoof). The sakia is the Egyptian version of the noria. Some of the world's oldest known wells, located in Cyprus, date to 7000–8,500 BC. Two wells from the Neolithic period, around 6500 BC, have been discovered in Israel. One is in Atlit, on the northern coast of Israel, and the other is the Jezreel Valley.


title: Well

text: Wells for other purposes came along much later, historically. The first recorded salt well was dug in the Sichuan province of China around 2,250 years ago. This was the first time that ancient water well technology was applied successfully for the exploitation of salt, and marked the beginning of Sichuan's salt drilling industry. The earliest known oil wells were also drilled in China, in 347 CE. These wells had depths of up to about and were drilled using bits attached to bamboo poles. The oil was burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs. The ancient records of China and Japan are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum was known as "Burning water" in Japan in the 7th century.


title: Well

text: Until recent centuries, all artificial wells were pumpless hand-dug wells of varying degrees of sophistication, and they remain a very important source of potable water in some rural developing areas, where they are routinely dug and used today. Their indispensability has produced a number of literary references, literal and figurative, including the reference to the incident of Jesus meeting a woman at Jacob's well (John 4:6) in the Bible and the "Ding Dong Bell" nursery rhyme about a cat in a well.


title: Well

text: Hand-dug wells are excavations with diameters large enough to accommodate one or more people with shovels digging down to below the water table. The excavation is braced horizontally to avoid landslide or erosion endangering the people digging. They can be lined with stone or brick; extending this lining upwards above the ground surface to form a wall around the well serves to reduce both contamination and accidental falls into the well.


title: Well

text: A more modern method called caissoning uses reinforced concrete or plain concrete pre-cast well rings that are lowered into the hole. A well-digging team digs under a cutting ring and the well column slowly sinks into the aquifer, whilst protecting the team from collapse of the well bore.


title: Well

text: Hand-dug wells are inexpensive and low tech (compared to drilling) and they use mostly manual labour to access groundwater in rural locations of developing countries. They may be built with a high degree of community participation, or by local entrepreneurs who specialize in hand-dug wells. They have been successfully excavated to . They have low operational and maintenance costs, in part because water can be extracted by hand, without a pump. The water often comes from an aquifer or groundwater, and can be easily deepened, which may be necessary if the ground water level drops, by telescoping the lining further down into the aquifer. The yield of existing hand dug wells may be improved by deepening or introducing vertical tunnels or perforated pipes.


title: Well

text: Drawbacks to hand-dug wells are numerous. It can be impractical to hand dig wells in areas where hard rock is present, and they can be time-consuming to dig and line even in favourable areas. Because they exploit shallow aquifers, the well may be susceptible to yield fluctuations and possible contamination from surface water, including sewage. Hand dug well construction generally requires the use of a well trained construction team, and the capital investment for equipment such as concrete ring moulds, heavy lifting equipment, well shaft formwork, motorized de-watering pumps, and fuel can be large for people in developing countries. Construction of hand dug wells can be dangerous due to collapse of the well bore, falling objects and asphyxiation, including from dewatering pump exhaust fumes.


title: Well

text: The Woodingdean Water Well, hand-dug between 1858 and 1862, is the deepest hand-dug well at . The Big Well in Greensburg, Kansas is billed as the world's largest hand-dug well, at deep and in diameter. However, the "Well of Joseph" in the Cairo Citadel at deep and the Pozzo di S. Patrizio (St. Patrick's Well) built in 1527 in Orvieto, Italy, at deep by wide are both larger by volume.


title: Well

text: Driven wells may be very simply created in unconsolidated material with a "well hole structure", which consists of a hardened drive point and a screen (perforated pipe). The point is simply hammered into the ground, usually with a tripod and "driver", with pipe sections added as needed. A driver is a weighted pipe that slides over the pipe being driven and is repeatedly dropped on it. When groundwater is encountered, the well is washed of sediment and a pump installed.


title: Well

text: Drilled wells are typically created using either top-head rotary style, table rotary, or cable tool drilling machines, all of which use drilling stems that are turned to create a cutting action in the formation, hence the term "drilling".


title: Well

text: Drilled wells can be excavated by simple hand drilling methods (augering, sludging, jetting, driving, hand percussion) or machine drilling (rotary, percussion, down the hole hammer). Deeprock rotary drilling method is most common. Rotary can be used in 90% of formation types.


title: Well

text: Drilled wells can get water from a much deeper level than dug wells can—often down to several hundred metres.


title: Well

text: Drilled wells with electric pumps are used throughout the world, typically in rural or sparsely populated areas, though many urban areas are supplied partly by municipal wells. Most shallow well drilling machines are mounted on large trucks, trailers, or tracked vehicle carriages. Water wells typically range from deep, but in some areas can go deeper than .


title: Well

text: Rotary drilling machines use a segmented steel drilling string, typically made up of sections of galvanized steel tubing that are threaded together, with a bit or other drilling device at the bottom end. Some rotary drilling machines are designed to install (by driving or drilling) a steel casing into the well in conjunction with the drilling of the actual bore hole. Air and/or water is used as a circulation fluid to displace cuttings and cool bits during the drilling. Another form of rotary-style drilling, termed "mud rotary", makes use of a specially made mud, or drilling fluid, which is constantly being altered during the drill so that it can consistently create enough hydraulic pressure to hold the side walls of the bore hole open, regardless of the presence of a casing in the well. Typically, boreholes drilled into solid rock are not cased until after the drilling process is completed, regardless of the machinery used.


title: Well

text: The oldest form of drilling machinery is the cable tool, still used today. Specifically designed to raise and lower a bit into the bore hole, the "spudding" of the drill causes the bit to be raised and dropped onto the bottom of the hole, and the design of the cable causes the bit to twist at approximately revolution per drop, thereby creating a drilling action. Unlike rotary drilling, cable tool drilling requires the drilling action to be stopped so that the bore hole can be bailed or emptied of drilled cuttings.


title: Well

text: Drilled wells are usually cased with a factory-made pipe, typically steel (in air rotary or cable tool drilling) or plastic/PVC (in mud rotary wells, also present in wells drilled into solid rock). The casing is constructed by welding, either chemically or thermally, segments of casing together. If the casing is installed during the drilling, most drills will drive the casing into the ground as the bore hole advances, while some newer machines will actually allow for the casing to be rotated and drilled into the formation in a similar manner as the bit advancing just below. PVC or plastic is typically welded and then lowered into the drilled well, vertically stacked with their ends nested and either glued or splined together. The sections of casing are usually or more in length, and in diameter, depending on the intended use of the well and local groundwater conditions.


title: Well

text: Surface contamination of wells in the United States is typically controlled by the use of a "surface seal". A large hole is drilled to a predetermined depth or to a confining formation (clay or bedrock, for example), and then a smaller hole for the well is completed from that point forward. The well is typically cased from the surface down into the smaller hole with a casing that is the same diameter as that hole. The annular space between the large bore hole and the smaller casing is filled with bentonite clay, concrete, or other sealant material. This creates an impermeable seal from the surface to the next confining layer that keeps contaminants from traveling down the outer sidewalls of the casing or borehole and into the aquifer. In addition, wells are typically capped with either an engineered well cap or seal that vents air through a screen into the well, but keeps insects, small animals, and unauthorized persons from accessing the well.


title: Well

text: At the bottom of wells, based on formation, a screening device, filter pack, slotted casing, or open bore hole is left to allow the flow of water into the well. Constructed screens are typically used in unconsolidated formations (sands, gravels, etc.), allowing water and a percentage of the formation to pass through the screen. Allowing some material to pass through creates a large area filter out of the rest of the formation, as the amount of material present to pass into the well slowly decreases and is removed from the well. Rock wells are typically cased with a PVC liner/casing and screen or slotted casing at the bottom, this is mostly present just to keep rocks from entering the pump assembly. Some wells utilize a "filter pack" method, where an undersized screen or slotted casing is placed inside the well and a filter medium is packed around the screen, between the screen and the borehole or casing. This allows the water to be filtered of unwanted materials before entering the well and pumping zone.


title: Well

text: A special type of water well may be constructed adjacent to freshwater lakes or streams. Commonly called a collector well but sometimes referred to by the trade name Ranney well or Ranney collector, this type of well involves sinking a caisson vertically below the top of the aquifer and then advancing lateral collectors out of the caisson and beneath the surface water body. Pumping from within the caisson induces infiltration of water from the surface water body into the aquifer, where it is collected by the collector well laterals and conveyed into the caisson where it can be pumped to the ground surface.


title: Well

text: A well constructed for pumping groundwater can be used passively as a monitoring well and a small diameter well can be pumped, but this distinction by use is common.


title: Well

text: Before excavation, information about the geology, water table depth, seasonal fluctuations, recharge area and rate must be found. This work is typically done by a hydrogeologist, or a groundwater surveyor using a variety of tools including electro-seismic surveying, any available information from nearby wells, geologic maps, and sometimes geophysical imaging.


title: Well

text: Shallow pumping wells can often supply drinking water at a very low cost. However, impurities from the surface easily reach shallow sources, which leads to a greater risk of contamination for these wells compared to deeper wells. Contaminated wells can lead to the spread of various waterborne diseases. Dug and driven wells are relatively easy to contaminate; for instance, most dug wells are unreliable in the majority of the United States.


title: Well

text: Most of the bacteria, viruses, parasites, and fungi that contaminate well water comes from fecal material from humans and other animals, for example from on-site sanitation systems (such as pit latrines and septic tanks). Common bacterial contaminants include "E. coli", "Salmonella", "Shigella", and "Campylobacter jejuni". Common viral contaminants include "norovirus", "sapovirus", "rotavirus", enteroviruses, and hepatitis A and E. Parasites include "Giardia lamblia", "Cryptosporidium", "Cyclospora cayetanensis", and microsporidia.


title: Well

text: Chemical contamination is a common problem with groundwater. Nitrates from sewage, sewage sludge or fertilizer are a particular problem for babies and young children. Pollutant chemicals include pesticides and volatile organic compounds from gasoline, dry-cleaning, the fuel additive methyl tert-butyl ether (MTBE), and perchlorate from rocket fuel, airbag inflators, and other artificial and natural sources.


title: Well

text: Several minerals are also contaminants, including lead leached from brass fittings or old lead pipes, chromium VI from electroplating and other sources, naturally occurring arsenic, radon, and uranium—all of which can cause cancer—and naturally occurring fluoride, which is desirable in low quantities to prevent tooth decay, but can cause dental fluorosis in higher concentrations.


title: Well

text: Some chemicals are commonly present in water wells at levels that are not toxic, but can cause other problems. Calcium and magnesium cause what is known as hard water, which can precipitate and clog pipes or burn out water heaters. Iron and manganese can appear as dark flecks that stain clothing and plumbing, and can promote the growth of iron and manganese bacteria that can form slimy black colonies that clog pipes.


title: Well

text: The quality of the well water can be significantly increased by lining the well, sealing the well head, fitting a self-priming hand pump, constructing an apron, ensuring the area is kept clean and free from stagnant water and animals, moving sources of contamination (pit latrines, garbage pits, on-site sewer systems) and carrying out hygiene education. The well should be cleaned with 1% chlorine solution after construction and periodically every 6 months.


title: Well

text: Well holes should be covered to prevent loose debris, animals, animal excrement, and wind-blown foreign matter from falling into the hole and decomposing. The cover should be able to be in place at all times, including when drawing water from the well. A suspended roof over an open hole helps to some degree, but ideally the cover should be tight fitting and fully enclosing, with only a screened air vent.


title: Well

text: Minimum distances and soil percolation requirements between sewage disposal sites and water wells need to be observed. Rules regarding the design and installation of private and municipal septic systems take all these factors into account so that nearby drinking water sources are protected.


title: Well

text: Education of the general population in society also plays an important role in protecting drinking water.


title: Well

text: Cleanup of contaminated groundwater tends to be very costly. Effective remediation of groundwater is generally very difficult. Contamination of groundwater from surface and subsurface sources can usually be dramatically reduced by correctly centering the casing during construction and filling the casing annulus with an appropriate sealing material. The sealing material (grout) should be placed from immediately above the production zone back to surface, because, in the absence of a correctly constructed casing seal, contaminated fluid can travel into the well through the casing annulus. Centering devices are important (usually one per length of casing or at maximum intervals of 9 m) to ensure that the grouted annular space is of even thickness.


title: Well

text: Upon the construction of a new test well, it is considered best practice to invest in a complete battery of chemical and biological tests on the well water in question. Point-of-use treatment is available for individual properties and treatment plants are often constructed for municipal water supplies that suffer from contamination. Most of these treatment methods involve the filtration of the contaminants of concern, and additional protection may be garnered by installing well-casing screens only at depths where contamination is not present.


title: Well

text: Wellwater for personal use is often filtered with reverse osmosis water processors; this process can remove very small particles. A simple, effective way of killing microorganisms is to bring the water to a full boil for one to three minutes, depending on location. A household well contaminated by microorganisms can initially be treated by shock chlorination using bleach, generating concentrations hundreds of times greater than found in community water systems; however, this will not fix any structural problems that led to the contamination and generally requires some expertise and testing for effective application.


title: Well

text: After the filtration process, it is common to implement an ultraviolet (UV) system to kill pathogens in the water. UV light affects the DNA of the pathogen by UV-C photons breaking through the cell wall. UV disinfection has been gaining popularity in the past decades as it is a chemical-free method of water treatment.


title: Well

text: A risk with the placement of water wells is soil salination which occurs when the water table of the soil begins to drop and salt begins to accumulate as the soil begins to dry out. Another environmental problem that is very prevalent in water well drilling is the potential for methane to seep through.


title: Well

text: The potential for soil salination is a large risk when choosing the placement of water wells. Soil salination is caused when the water table of the soil drops over time and salt begins to accumulate. In turn, the increased amount of salt begins to dry the soil out. The increased level of salt in the soil can result in the degradation of soil and can be very harmful to vegetation.


title: Well

text: Methane, an asphyxiant, is a chemical compound that is the main component of natural gas. When methane is introduced into a confined space, it displaces oxygen, reducing oxygen concentration to a level low enough to pose a threat to humans and other aerobic organisms but still high enough for a risk of spontaneous or externally caused explosion. This potential for explosion is what poses such a danger in regards to the drilling and placement of water wells.


title: Well

text: Low levels of methane in drinking water are not considered toxic. When methane seeps into a water supply, it is commonly referred to as "methane migration". This can be caused by old natural gas wells near water well systems becoming abandoned and no longer monitored.


title: Well

text: Lately, however, the described wells/pumps are no longer very efficient and can be replaced by either handpumps or treadle pumps. Another alternative is the use of self-dug wells, electrical deep-well pumps (for higher depths). Appropriate technology organizations as Practical Action are now supplying information on how to build/set-up (DIY) handpumps and treadle pumps in practice.


title: Well

text: A study concluded that of ~39 million groundwater wells 6-20% are at high risk of running dry if local groundwater levels decline by less than five meters, or – as with many areas and possibly more than half of major aquifers – continue to decline.


title: Well

text: Springs and wells have had cultural significance since prehistoric times, leading to the foundation of towns such as Wells and Bath in Somerset. Interest in health benefits led to the growth of spa towns including many with "wells" in their name, examples being Llandrindod Wells and Royal Tunbridge Wells.


title: Well

text: Eratosthenes is sometimes claimed to have used a well in his calculation of the Earth's circumference; however, this is just a simplification used in a shorter explanation of Cleomedes, since Eratosthenes had used a more elaborate and precise method.


title: Well

text: Many incidents in the Bible take place around wells, such as the finding of a wife for Isaac in Genesis and Jesus's talk with the Samaritan woman in the Gospels.


title: Well

text: For a well with impermeable walls, the water in the well is resupplied from the bottom of the well. The rate at which water flows into the well will depend on the pressure difference between the ground water at the well bottom and the well water at the well bottom. The pressure of a column of water of height "z" will be equal to the weight of the water in the column divided by the cross-sectional area of the column, so the pressure of the ground water a distance "z" below the top of the water table will be:


title: Well

text: where "ρ" is the mass density of the water and "g" is the acceleration due to gravity. When the water in the well is below the water table level, the pressure at the bottom of the well due to the water in the well will be less than "P" and water will be forced into the well. Referring to the diagram, if "z" is the distance from the bottom of the well to the well water level and "z" is the distance from the bottom of the well to the top of the water table, the pressure difference will be:


title: Well

text: Applying Darcy's Law, the volume rate ("F") at which water is forced into the well will be proportional to this pressure difference:


title: Well

text: where "R" is the resistance to the flow, which depends on the well cross section, the pressure gradient at the bottom of the well, and the characteristics of the substrate at the well bottom. (e.g., porosity). The volume flow rate into the well can be written as a function of the rate of change of the well water level:


title: Well

text: Note that if "dz/dt" for a depleted well can be measured, it will be equal to formula_8 and the time constant τ can be calculated. According to the above model, it will take an infinite amount of time for a well to fully recover, but if we consider a well that is 99% recovered to be "practically" recovered, the time for a well to practically recover from a level at "z" will be:


title: Well

text: For a well that is fully depleted ("z=0") it would take a time of about "4.6 τ" to practically recover.


title: Well

text: The above model does not take into account the depletion of the aquifer due to the pumping which lowered the well water level (See aquifer test and groundwater flow equation). Also, practical wells may have impermeable walls only up to, but not including the bedrock, which will give a larger surface area for water to enter the well.


title: Pole star

text: A pole star or polar star is a star, preferably bright, nearly aligned with the axis of a rotating astronomical body.


title: Pole star

text: Currently, Earth's pole stars are Polaris (Alpha Ursae Minoris), a bright magnitude-2 star aligned approximately with its northern axis that serves as a pre-eminent star in celestial navigation, and a much dimmer magnitude-5.5 star on its southern axis, Polaris Australis (Sigma Octantis).


title: Pole star

text: From around 1700 BC until just after 300 AD, Kochab (Beta Ursae Minoris) and Pherkad (Gamma Ursae Minoris) were twin northern pole stars, though neither was as close to the pole as Polaris is now.


title: Pole star

text: In classical antiquity, Beta Ursae Minoris (Kochab) was closer to the celestial north pole than Alpha Ursae Minoris.


title: Pole star

text: While there was no naked-eye star close to the pole, the midpoint between Alpha and Beta Ursae Minoris was reasonably close to the pole, and it appears that the entire constellation of Ursa Minor, in antiquity known as "Cynosura" (Greek Κυνόσουρα "dog's tail") was used as indicating the northern direction for the purposes of navigation by the Phoenicians. The ancient name of Ursa Minor, anglicized as "cynosure", has since itself become a term for "guiding principle" after the constellation's use in navigation.


title: Pole star

text: Alpha Ursae Minoris (Polaris) was described as ἀειφανής (transliterated as "aeiphanes") meaning "always above the horizon", "ever-shining" by Stobaeus in the 5th century, when it was still removed from the celestial pole by about 8°. It was known as "scip-steorra" ("ship-star") in 10th-century Anglo-Saxon England, reflecting its use in navigation. In the Vishnu Purana, it is personified under the name "Dhruva" ("immovable, fixed").


title: Pole star

text: The name "stella polaris" was coined in the Renaissance, even though at that time it was well recognized that it was several degrees away from the celestial pole; Gemma Frisius in the year 1547 determined this distance as 3°8'.


title: Pole star

text: An explicit identification of Mary as "stella maris" with the North Star ("Polaris") becomes evident in the title "Cynosura seu Mariana Stella Polaris" (i.e. "Cynosure, or the Marian Polar Star"), a collection of Marian poetry published by Nicolaus Lucensis (Niccolo Barsotti de Lucca) in 1655.


title: Pole star

text: In 2022 Polaris' mean declination is 89.35 degrees North; (at epoch J2000 it was 89.26 degrees N). So it appears due north in the sky to a precision better than one degree, and the angle it makes with respect to the true horizon (after correcting for refraction and other factors) is within a degree of the latitude of the observer.


title: Pole star

text: Due to the precession of the equinoxes (as well as the stars' proper motions), the role of North Star has passed (and will pass) from one star to another in the remote past (and in the remote future). In 3000 BC, the faint star Thuban in the constellation Draco was the North Star, aligning within 0.1° distance from the celestial pole, the closest of any of the visible pole stars. However, at magnitude 3.67 (fourth magnitude) it is only one-fifth as bright as Polaris, and today it is invisible in light-polluted urban skies.


title: Pole star

text: During the 1st millennium BC, Beta Ursae Minoris ("Kochab") was the bright star closest to the celestial pole, but it was never close enough to be taken as marking the pole, and the Greek navigator Pytheas in ca. 320 BC described the celestial pole as devoid of stars. In the Roman era, the celestial pole was about equally distant between Polaris and Kochab.


title: Pole star

text: The precession of the equinoxes takes about 25,770 years to complete a cycle. Polaris' mean position (taking account of precession and proper motion) will reach a maximum declination of +89°32'23", which translates to 1657" (or 0.4603°) from the celestial north pole, in February 2102. Its maximum apparent declination (taking account of nutation and aberration) will be +89°32'50.62", which is 1629" (or 0.4526°) from the celestial north pole, on 24 March 2100.


title: Pole star

text: Precession will next point the north celestial pole at stars in the northern constellation Cepheus. The pole will drift to space equidistant between Polaris and Gamma Cephei ("Errai") by 3000 AD, with Errai reaching its closest alignment with the northern celestial pole around 4200 AD. Iota Cephei and Beta Cephei will stand on either side of the northern celestial pole some time around 5200 AD, before moving to closer alignment with the brighter star Alpha Cephei ("Alderamin") around 7500 AD.


title: Pole star

text: Precession will then point the north celestial pole at stars in the northern constellation Cygnus. Like Beta Ursae Minoris during the 1st millennium BC, the bright star closest to the celestial pole in the 10th millennium AD, first-magnitude Deneb, will be a distant 7° from the pole, never close enough to be taken as marking the pole, while third-magnitude Delta Cygni will be a more helpful pole star, at a distance of 3° from celestial north, around 11,500 AD. Precession will then point the north celestial pole nearer the constellation Lyra, where the second brightest star in the northern celestial hemisphere, Vega, will be a pole star around 13,700 AD, though at a distance of 5° from celestial north.


title: Pole star

text: Precession will eventually point the north celestial pole nearer the stars in the constellation Hercules, pointing towards Tau Herculis around 18,400 AD.


title: Pole star

text: The celestial pole will then return to the stars in constellation Draco (Thuban, mentioned above) before returning to the current constellation, Ursa Minor. When Polaris becomes the North Star again around 27,800 AD, due to its proper motion it then will be farther away from the pole than it is now, while in 23,600 BC it was closer to the pole.


title: Pole star

text: Over the course of Earth's 26,000-year axial precession cycle, a series of bright naked eye stars (an apparent magnitude up to +6; a full moon is −12.9) in the northern hemisphere will hold the transitory title of North Star. While other stars might line up with the north celestial pole during the 26,000 year cycle, they do not necessarily meet the naked eye limit needed to serve as a useful indicator of north to an Earth-based observer, resulting in periods of time during the cycle when there is no clearly defined North Star. There will also be periods during the cycle when bright stars give only an approximate guide to "north", as they may be greater than 5° of angular diameter removed from direct alignment with the north celestial pole.


title: Pole star

text: The 26,000 year cycle of North Stars, starting with the current star, with stars that will be "near-north" indicators when no North Star exists during the cycle, including each star's average brightness and closest alignment to the north celestial pole during the cycle:


title: Pole star

text: Currently, there is no South Star as useful as Polaris, the so-called "North Star". Polaris Australis (Sigma Octantis) is the closest naked-eye star to the south celestial pole, but at apparent magnitude 5.47 it is barely visible on a clear night, making it unusable for navigational purposes.


title: Pole star

text: It is a yellow giant 294 light years from Earth. Its angular separation from the pole is about 1° (). The Southern Cross constellation functions as an approximate southern pole constellation, by pointing to where a southern pole star would be.


title: Pole star

text: At the equator, it is possible to see both Polaris and the Southern Cross. The celestial south pole is moving toward the Southern Cross, which has pointed to the south pole for the last 2000 years or so. As a consequence, the constellation is no longer visible from subtropical northern latitudes, as it was in the time of the ancient Greeks.


title: Pole star

text: Around 200 BC, the star Beta Hydri was the nearest bright star to the celestial south pole. Around 2800 BC, Achernar was only 8 degrees from the south pole.


title: Pole star

text: In the next 7500 years, the south celestial pole will pass close to the stars Gamma Chamaeleontis (4200 AD), I Carinae, Omega Carinae (5800 AD), Upsilon Carinae, Iota Carinae (Aspidiske, 8100 AD) and Delta Velorum (Alsephina, 9200 AD). From the eightieth to the ninetieth centuries, the south celestial pole will travel through the False Cross. Around 14,000 AD Canopus will have a declination of –82°, meaning it will rise and set daily for latitudes between 8°S and 8°N, and will not rise to viewers north of this latter 8th parallel north.


title: Pole star

text: Precession and proper motion mean that Sirius will be a future southern pole star: at 88.4° S declination in the year 66,270 AD; and 87.7° S declination in the year 93,830 AD.


title: Pole star

text: Pole stars of other planets are defined analogously: they are stars (brighter than 6th magnitude, "i.e.", visible to the naked eye under ideal conditions) that most closely coincide with the projection of the planet's axis of rotation onto the celestial sphere. Different planets have different pole stars because their axes are oriented differently. (See Poles of astronomical bodies.)


title: Pole star

text: In the medieval period, Polaris was also known as "stella maris" "star of the sea" (from its use for navigation at sea), as in e.g. Bartholomeus Anglicus (d. 1272), in the translation of John Trevisa (1397):


title: Pole star

text: Polaris was associated with Marian veneration from an early time, Our Lady, Star of the Sea being a title of the Blessed Virgin.


title: Pole star

text: This tradition goes back to a misreading of Saint Jerome's translation of Eusebius' "Onomasticon", "De nominibus hebraicis" (written ca. 390). Jerome gave "stilla maris" "drop of the sea" as a (false) Hebrew etymology of the name "Maria". This "stilla maris" was later misread as "stella maris"; the misreading is also found in the manuscript tradition of Isidore's "Etymologiae" (7th century); it probably arises in the Carolingian era; a late 9th-century manuscript of Jerome's text still has "stilla", not "stella", but Paschasius Radbertus, also writing in the 9th century, makes an explicit reference to the "Star of the Sea" metaphor, saying that Mary is the "Star of the Sea" to be followed on the way to Christ, "lest we capsize amid the storm-tossed waves of the sea."


title: Pole star

text: In Mandaean cosmology, the Pole Star is considered to be auspicious and is associated with the World of Light ("heaven"). Mandaeans face north when praying, and temples are also oriented towards the north. On the contrary, the south is associated with the World of Darkness.


title: Pole star

text: In India (Hindu mythology), the Pole Star is referred as Dhruva, who was a devotee of Vishnu, and was transformed into the immortal star by Vishnu.


title: Bacillus anthracis

text: Bacillus anthracis is a gram-positive and rod-shaped bacterium that causes anthrax, a deadly disease to livestock and, occasionally, to humans. It is the only permanent (obligate) pathogen within the genus "Bacillus". Its infection is a type of zoonosis, as it is transmitted from animals to humans. It was discovered by a German physician Robert Koch in 1876, and became the first bacterium to be experimentally shown as a pathogen. The discovery was also the first scientific evidence for the germ theory of diseases.


title: Bacillus anthracis

text: "B. anthracis" measures about 3 to 5 μm long and 1 to 1.2 μm wide. The reference genome consists of a 5,227,419 bp circular chromosome and two extrachromosomal DNA plasmids, pXO1 and pXO2, of 181,677 and 94,830 bp respectively, which are responsible for the pathogenicity. It forms a protective layer called endospore by which it can remain inactive for many years and suddenly becomes infective under suitable environmental conditions. Because of the resilience of the endospore, the bacterium is one of the most popular biological weapons. The protein capsule (poly-D-gamma-glutamic acid) is key to evasion of the immune response. It feeds on the heme of blood protein haemoglobin using two secretory siderophore proteins, IsdX1 and IsdX2.


title: Bacillus anthracis

text: Untreated "B. anthracis" infection is usually deadly. Infection is indicated by inflammatory, black, necrotic lesions (eschars). The sores usually appear on the face, neck, arms, or hands. Fatal symptoms include a flu-like fever, chest discomfort, diaphoresis (excessive sweating), and body aches. The first animal vaccine against anthrax was developed by French chemist Louis Pasteur in 1881. Different animal and human vaccines are now available. The infection can be treated with common antibiotics such as penicillins, quinolones, and tetracyclines.


title: Bacillus anthracis

text: "B. anthracis" are rod-shaped bacteria, approximately 3 to 5 μm long and 1 to 1.2 μm wide. When grown in culture, they tend to form long chains of bacteria. On agar plates, they form large colonies several millimeters across that are generally white or cream colored. Most "B. anthracis" strains produce a capsule that gives colonies a slimy mucus-like appearance.


title: Bacillus anthracis

text: It is one of few bacteria known to synthesize a weakly immunogenic and antiphagocytic protein capsule (poly-D-gamma-glutamic acid) that disguises the vegetative bacterium from the host immune system. Most bacteria are surrounded by a polysaccharide capsule rather than poly-g-D-glutamic acid which provides an evolutionary advantage to "B. anthracis". Polysaccharides are associated with adhesion of neutrophil-secreted defensins that inactivate and degrade the bacteria. By not containing this macromolecule in the capsule, "B. anthracis" can evade a neutrophilic attack and continue to propagate infection. The difference in capsule composition is also significant because poly-g-D-glutamic acid has been hypothesized to create a negative charge which protects the vegetative phase of the bacteria from phagocytosis by macrophages. The capsule is degraded to a lower molecular mass and released from the bacterial cell surface to act as a decoy to protect the bacteria from .


title: Bacillus anthracis

text: Like "Bordetella pertussis", it forms a calmodulin-dependent adenylate cyclase exotoxin known as anthrax edema factor, along with anthrax lethal factor. It bears close genotypic and phenotypic resemblance to "Bacillus cereus" and "Bacillus thuringiensis". All three species share cellular dimensions and morphology. All form oval spores located centrally in an unswollen sporangium. "B. anthracis" endospores, in particular, are highly resilient, surviving extremes of temperature, low-nutrient environments, and harsh chemical treatment over decades or centuries.


title: Bacillus anthracis

text: The endospore is a dehydrated cell with thick walls and additional layers that form inside the cell membrane. It can remain inactive for many years, but if it comes into a favorable environment, it begins to grow again. It initially develops inside the rod-shaped form. Features such as the location within the rod, the size and shape of the endospore, and whether or not it causes the wall of the rod to bulge out are characteristic of particular species of "Bacillus". Depending upon the species, the endospores are round, oval, or occasionally cylindrical. They are highly refractile and contain dipicolinic acid. Electron micrograph sections show they have a thin outer endospore coat, a thick spore cortex, and an inner spore membrane surrounding the endospore contents. The endospores resist heat, drying, and many disinfectants (including 95% ethanol). Because of these attributes, "B. anthracis" endospores are extraordinarily well-suited to use (in powdered and aerosol form) as biological weapons. Such weaponization has been accomplished in the past by at least five state bioweapons programs—those of the United Kingdom, Japan, the United States, Russia, and Iraq—and has been attempted by several others.


title: Bacillus anthracis

text: "B. anthracis" has a single chromosome which is a circular, 5,227,293-bp DNA molecule. It also has two circular, extrachromosomal, double-stranded DNA plasmids, pXO1 and pXO2. Both the pXO1 and pXO2 plasmids are required for full virulence and represent two distinct plasmid families.


title: Bacillus anthracis

text: The pXO1 plasmid (182 kb) contains the genes that encode for the anthrax toxin components: "pag" (protective antigen, PA), "lef" (lethal factor, LF), and "cya" (edema factor, EF). These factors are contained within a 44.8-kb pathogenicity island (PAI). The lethal toxin is a combination of PA with LF and the edema toxin is a combination of PA with EF. The PAI also contains genes which encode a transcriptional activator AtxA and the repressor PagR, both of which regulate the expression of the anthrax toxin genes.


title: Bacillus anthracis

text: pXO2 encodes a five-gene operon ("capBCADE") which synthesizes a poly-γ-D-glutamic acid (polyglutamate) capsule. This capsule allows "B. anthracis" to evade the host immune system by protecting itself from phagocytosis. Expression of the capsule operon is activated by the transcriptional regulators AcpA and AcpB, located in the pXO2 pathogenicity island (35 kb). AcpA and AcpB expression are under the control of AtxA from pXO1.


title: Bacillus anthracis

text: Whole genome sequencing has made reconstruction of the "B. anthracis" phylogeny extremely accurate. A contributing factor to the reconstruction is "B. anthracis" being monomorphic, meaning it has low genetic diversity, including the absence of any measurable lateral DNA transfer since its derivation as a species. The lack of diversity is due to a short evolutionary history that has precluded mutational saturation in single nucleotide polymorphisms.


title: Bacillus anthracis

text: A short evolutionary time does not necessarily mean a short chronological time. When DNA is replicated, mistakes occur which become genetic mutations. The buildup of these mutations over time leads to the evolution of a species. During the "B. anthracis" lifecycle, it spends a significant amount of time in the soil spore reservoir stage, in which DNA replication does not occur. These prolonged periods of dormancy have greatly reduced the evolutionary rate of the organism.


title: Bacillus anthracis

text: "B. anthracis" belongs to the "B. cereus" group consisting of the strains: "B. cereus", "B. anthracis", "B. thuringiensis", "B. mycoides", and "B. pseudomycoides". The first three strains are pathogenic or opportunistic to insects or mammals, while the last three are not considered pathogenic. The strains of this group are genetically and phenotypically heterogeneous overall, but some of the strains are more closely related and phylogenetically intermixed at the chromosome level. The "B. cereus" group generally exhibits complex genomes and most carry varying numbers of plasmids.


title: Bacillus anthracis

text: "B. cereus" is a soil-dwelling bacterium which can colonize the gut of invertebrates as a symbiont and is a frequent cause of food poisoning It produces an emetic toxin, enterotoxins, and other virulence factors. The enterotoxins and virulence factors are encoded on the chromosome, while the emetic toxin is encoded on a 270-kb plasmid, pCER270.


title: Bacillus anthracis

text: "B. thuringiensis" is an insect pathogen and is characterized by production of parasporal crystals of insecticidal toxins Cry and Cyt. The genes encoding these proteins are commonly located on plasmids which can be lost from the organism, making it indistinguishable from "B. cereus".


title: Bacillus anthracis

text: A phylogenomic analysis of the Cereus clade combined with average nucleotide identity (ANI) analysis revealed that the "B. anthracis" species also includes strains annotated as "B. cereus" and "B. thuringiensis."


title: Bacillus anthracis

text: "PlcR" is a global transcriptional regulator which controls most of the secreted virulence factors in "B. cereus" and "B. thuringiensis". It is chromosomally encoded and is ubiquitous throughout the cell. In "B. anthracis", however, the "plcR" gene contains a single base change at position 640, a nonsense mutation, which creates a dysfunctional protein. While 1% of the "B. cereus" group carries an inactivated "plcR" gene, none of them carries the specific mutation found only in "B. anthracis".


title: Bacillus anthracis

text: The "plcR" gene is part of a two-gene operon with "papR". The "papR" gene encodes a small protein which is secreted from the cell and then reimported as a processed heptapeptide forming a quorum-sensing system. The lack of PlcR in "B. anthracis" is a principle characteristic differentiating it from other members of the "B. cereus" group. While "B. cereus" and "B. thuringiensis" depend on the "plcR" gene for expression of their virulence factors, "B. anthracis" relies on the pXO1 and pXO2 plasmids for its virulence. "Bacillus cereus" biovar "anthracis", i.e. "B. cereus" with the two plasmids, is also capable of causing anthrax.


title: Bacillus anthracis

text: produces three plasmid-coded exotoxins: edema factor, a calmodulin-dependent adenylate cyclase that causes elevation of intracellular cAMP and is responsible for the severe edema usually seen in "B. anthracis" infections, lethal toxin which is responsible for causing tissue necrosis, and protective antigen, so named because of its use in producing protective anthrax vaccines, which mediates cell entry of edema factor and lethal toxin.


title: Bacillus anthracis

text: The symptoms in anthrax depend on the type of infection and can take anywhere from 1 day to more than 2 months to appear. All types of anthrax have the potential, if untreated, to spread throughout the body and cause severe illness and even death.


title: Bacillus anthracis

text: A number of anthrax vaccines have been developed for preventive use in livestock and humans. Anthrax vaccine adsorbed (AVA) may protect against cutaneous and inhalation anthrax. However, this vaccine is only used for at-risk adults before exposure to anthrax and has not been approved for use after exposure. Infections with "B. anthracis" can be treated with β-lactam antibiotics such as penicillin, and others which are active against Gram-positive bacteria. Penicillin-resistant "B. anthracis" can be treated with fluoroquinolones such as ciprofloxacin or tetracycline antibiotics such as doxycycline.


title: Bacillus anthracis

text: Components of tea, such as polyphenols, have the ability to inhibit the activity both of "B. anthracis" and its toxin considerably; spores, however, are not affected. The addition of milk to the tea completely inhibits its antibacterial activity against anthrax. Activity against the "B. anthracis" in the laboratory does not prove that drinking tea affects the course of an infection, since it is unknown how these polyphenols are absorbed and distributed within the body. "B. anthracis" can be cultured on PLET agar, a selective and differential media designed to select specifically for "B. anthracis".


title: Bacillus anthracis

text: Advances in genotyping methods have led to improved genetic analysis for variation and relatedness. These methods include multiple-locus variable-number tandem repeat analysis (MLVA) and typing systems using canonical single-nucleotide polymorphisms. The Ames ancestor chromosome was sequenced in 2003 and contributes to the identification of genes involved in the virulence of "B. anthracis". Recently, "B. anthracis" isolate H9401 was isolated from a Korean patient suffering from gastrointestinal anthrax. The goal of the Republic of Korea is to use this strain as a challenge strain to develop a recombinant vaccine against anthrax.


title: Bacillus anthracis

text: The H9401 strain isolated in the Republic of Korea was sequenced using 454 GS-FLX technology and analyzed using several bioinformatics tools to align, annotate, and compare H9401 to other "B. anthracis" strains. The sequencing coverage level suggests a molecular ratio of pXO1:pXO2:chromosome as 3:2:1 which is identical to the Ames Florida and Ames Ancestor strains. H9401 has 99.679% sequence homology with Ames Ancestor with an amino acid sequence homology of 99.870%. H9401 has a circular chromosome (5,218,947 bp with 5,480 predicted ORFs), the pXO1 plasmid (181,700 bp with 202 predicted ORFs), and the pXO2 plasmid (94,824 bp with 110 predicted ORFs). As compared to the Ames Ancestor chromosome above, the H9401 chromosome is about 8.5 kb smaller. Due to the high pathogenecity and sequence similarity to the Ames Ancestor, H9401 will be used as a reference for testing the efficacy of candidate anthrax vaccines by the Republic of Korea.


title: Bacillus anthracis

text: Since the genome of B. anthracis was sequenced, alternative ways to battle this disease are being endeavored. Bacteria have developed several strategies to evade recognition by the immune system. The predominant mechanism for avoiding detection, employed by all bacteria is molecular camouflage. Slight modifications in the outer layer that render the bacteria practically invisible to lysozymes. Three of these modifications have been identified and characterized. These include (1) N-glycosylation of N-acetyl-muramic acid, (2) O-acetylation of N-acetylmuramic acid and (3) N-deacetylation of N-acetyl-glucosamine. Research during the last few years has focused on inhibiting such modifications. As a result the enzymatic mechanism of polysaccharide de-acetylases is being investigated, that catalyze the removal of an acetyl group from N-acetyl-glucosamine and N-acetyl-muramic acid, components of the peptidoglycan layer.


title: Bacillus anthracis

text: As with most other pathogenic bacteria, "B. anthracis" must acquire iron to grow and proliferate in its host environment. The most readily available iron sources for pathogenic bacteria are the heme groups used by the host in the transport of oxygen. To scavenge heme from host hemoglobin and myoglobin, "B. anthracis" uses two secretory siderophore proteins, IsdX1 and IsdX2. These proteins can separate heme from hemoglobin, allowing surface proteins of "B. anthracis" to transport it into the cell.


title: Bacillus anthracis

text: "B. anthracis" must evade the immune system to establish a successful infection. "B. anthracis" spores are immediately phagocytosed by macrophages and dendritic cells once they enter the host.  The can control the infection through effective intracellular elimination, but the macrophages can transport the bacteria directly inside the host by crossing a thin layer of epithelial or endothelial cells to reach the circulatory system. Normally, in the phagocytosis process, the pathogen is digested upon internalization by the macrophage. However, rather than being degraded, the anthrax spores hijack the function of the macrophage to evade recognition by the host immune system. Phagocytosis of "B. anthracis" spores begins when the transmembrane receptors on the extracellular membrane of the phagocyte interacts with a molecule on the surface of the spore. CD14, an extracellular protein embedded in the host membrane, binds to rhamnose residues of BclA, a glycoprotein of the "B. anthracis" exosporium, which promotes inside-out activation of the integrin Mac-1, enhancing spore internalization by macrophages. This cascade results in phagocytic cellular activation and induction of an inflammatory response.


title: Bacillus anthracis

text: French physician Casimir Davaine (1812-1882) demonstrated the symptoms of anthrax were invariably accompanied by the microbe "B. anthracis". German physician Aloys Pollender (1799–1879) is credited for discovery. "B. anthracis" was the first bacterium conclusively demonstrated to cause disease, by Robert Koch in 1876. The species name "anthracis" is from the Greek "anthrax" (ἄνθραξ), meaning "coal" and referring to the most common form of the disease, cutaneous anthrax, in which large, black skin lesions are formed.


title: Bacillus anthracis

text: Throughout the 19th century, Anthrax was an infection that involved several very important medical developments. The first vaccine containing live organisms was Louis Pasteur's veterinary anthrax vaccine.


title: Kensho Ono

text: In February 2014, he launched a singing career with the single "Fantastic Tune". Since then, he has released four singles, two mini albums, and one full album. His fifth solo single "Five Star" was released through Lantis on June 27, 2018, after which he announced a summer tour titled 'Ono Kensho Live Tour 2018'.


title: Kensho Ono

text: Ono was previously represented by Sunaoka Office, a subsidiary of Gekidan Himawari; however, he is now represented by Amino Produce. He has also appeared in various anime and Japanese TV drama series. His 1st television Show was Fafner in the Azure: Dead Aggressor (2004).


title: Kensho Ono

text: In February 2017, Ono and Kana Hanazawa confirmed that they were dating during a live stream promoting Hanazawa's album release, after "Shūkan Bunshun" published allegations about their relationship. On July 8, 2020, they announced that they married.


title: National Review

text: National Review is an American conservative editorial magazine, focusing on news and commentary pieces on political, social, and cultural affairs. The magazine was founded by the author William F. Buckley Jr. in 1955. Its editor-in-chief is Rich Lowry, while the editor is Ramesh Ponnuru.


title: National Review

text: Since its founding, the magazine has played a significant role in the development of conservatism in the United States, helping to define its boundaries and promoting fusionism while establishing itself as a leading voice on the American right.


title: National Review

text: The online version, National Review Online, is edited by Philip Klein and includes free content and articles separate from the print edition. The free content is limited, but National


title: National Review

text: Before "National Review"s founding in 1955, the American right was a largely unorganized collection of people who shared intertwining philosophies but had little opportunity for a united public voice. They wanted to marginalize the antiwar, noninterventionistic views of the Old Right.


title: National Review

text: In 1953, moderate Republican Dwight D. Eisenhower was president, and many major magazines such as the "Saturday Evening Post", "Time", and "Reader's Digest" were strongly conservative and anticommunist, as were many newspapers including the "Chicago Tribune" and "St. Louis Globe-Democrat". A few small-circulation conservative magazines, such as "Human Events" and "The Freeman", preceded "National Review" in developing Cold War Conservatism in the 1950s.


title: National Review

text: In 1953, Russell Kirk published "The Conservative Mind", which traced an intellectual bloodline from Edmund Burke to the Old Right in the early 1950s. This challenged the notion among intellectuals that no coherent conservative tradition existed in the United States.


title: National Review

text: A young William F. Buckley Jr. was greatly influenced by Kirk's concepts. Buckley had money; his father grew rich from oil fields in Mexico. He first tried to purchase "Human Events", but was turned down. He then met Willi Schlamm, the experienced editor of "The Freeman"; they would spend the next two years raising the $300,000 necessary to start their own weekly magazine, originally to be called "National Weekly". (A magazine holding the trademark to the name prompted the change to "National Review".) The statement of intentions read:


title: National Review

text: Middle-of-the-Road, qua Middle of the Road, is politically, intellectually, and morally repugnant. We shall recommend policies for the simple reason that we consider them right (rather than “non-controversial”); and we consider them right because they are based on principles we deem right (rather than on popularity polls)... The New Deal revolution, for instance, could hardly have happened save for the cumulative impact of "The Nation" and "The New Republic", and a few other publications, on several American college generations during the twenties and thirties.


title: National Review

text: On November 19, 1955, Buckley's magazine began to take shape. Buckley assembled an eclectic group of writers: traditionalists, Catholic intellectuals, libertarians and ex-Communists. The group included: Revilo P. Oliver, Russell Kirk, James Burnham, Frank Meyer, and Willmoore Kendall, Catholics L. Brent Bozell and Garry Wills. The former "Time" editor Whittaker Chambers, who had been a Communist spy in the 1930s and was now intensely anti-Communist, became a senior editor. In the magazine's founding statement Buckley wrote:


title: National Review

text: The launching of a conservative weekly journal of opinion in a country widely assumed to be a bastion of conservatism at first glance looks like a work of supererogation, rather like publishing a royalist weekly within the walls of Buckingham Palace. It is not that of course; if "National Review" is superfluous, it is so for very different reasons: It stands athwart history, yelling Stop, at a time when no other is inclined to do so, or to have much patience with those who so urge it.


title: National Review

text: As editors and contributors, Buckley especially sought out intellectuals who were ex-Communists or had once worked on the far Left, including Whittaker Chambers, William Schlamm, John Dos Passos, Frank Meyer and James Burnham. When James Burnham became one of the original senior editors, he urged the adoption of a more pragmatic editorial position that would extend the influence of the magazine toward the political center. Smant (1991) finds that Burnham overcame sometimes heated opposition from other members of the editorial board (including Meyer, Schlamm, William Rickenbacker, and the magazine's publisher William A. Rusher), and had a significant effect on both the editorial policy of the magazine and on the thinking of Buckley himself.


title: National Review

text: "National Review" aimed to make conservative ideas respectable, in an age when the dominant view of conservative thought was, as expressed by Columbia professor Lionel Trilling:


title: National Review

text: [L]iberalism is not only the dominant but even the sole intellectual tradition. For it is the plain fact that nowadays there are no conservative or reactionary ideas in general circulation... the conservative impulse and the reactionary impulse do not... express themselves in ideas but only... in irritable mental gestures which seek to resemble ideas.


title: National Review

text: ["National Review"] stands athwart history, yelling Stop, at a time when no one is inclined to do so, or to have much patience with those who so urge it… it is out of place because, in its maturity, literate America rejected conservatism in favor of radical social experimentation…since ideas rule the world, the ideologues, having won over the intellectual class, simply walked in and started to…run just about everything. There never was an age of conformity quite like this one, or a camaraderie quite like the Liberals’.


title: National Review

text: "National Review" promoted Barry Goldwater heavily during the early 1960s. Buckley and others involved with the magazine took a major role in the "Draft Goldwater" movement in 1960 and the 1964 presidential campaign. "National Review" spread his vision of conservatism throughout the country.


title: National Review

text: The early "National Review" faced occasional defections from both left and right. Garry Wills broke with "National Review" and became a liberal commentator. Buckley's brother-in-law, L. Brent Bozell Jr. left and started the short-lived traditionalist Catholic magazine, "Triumph" in 1966.


title: National Review

text: Buckley and Meyer promoted the idea of enlarging the boundaries of conservatism through fusionism, whereby different schools of conservatives, including libertarians, would work together to combat what were seen as their common opponents.


title: National Review

text: Buckley and his editors used his magazine to define the boundaries of conservatism—and to exclude people or ideas or groups they considered unworthy of the conservative title. Therefore, they attacked the John Birch Society, George Wallace, and anti-Semites.


title: National Review

text: Buckley's goal was to increase the respectability of the conservative movement; as Rich Lowry noted: "Mr. Buckley's first great achievement was to purge the American right of its kooks. He marginalized the anti-Semites, the John Birchers, the nativists and their sort."


title: National Review

text: In 1957, "National Review" editorialized in favor of white leadership in the South, arguing that "the central question that emerges... is whether the White community in the South is entitled to take such measures as are necessary to prevail, politically and culturally, in areas where it does not predominate numerically? The sobering answer is Yes – the White community is so entitled because, for the time being, it is the advanced race." By the 1970s "National Review" advocated colorblind policies and the end of affirmative action.


title: National Review

text: In the late 1960s, the magazine denounced segregationist George Wallace, who ran in Democratic primaries in 1964 and 1972 and made an independent run for president in 1968. During the 1950s, Buckley had worked to remove anti-Semitism from the conservative movement and barred holders of those views from working for "National Review". In 1962 Buckley denounced Robert W. Welch Jr. and the John Birch Society as "far removed from common sense" and urged the Republican Party to purge itself of Welch's influence.


title: National Review

text: After Goldwater was defeated by Lyndon Johnson in 1964, Buckley and "National Review" continued to champion the idea of a conservative movement, which was increasingly embodied in Ronald Reagan. Reagan, a longtime subscriber to "National Review", first became politically prominent during Goldwater's campaign. "National Review" supported his challenge to President Gerald Ford in 1976 and his successful 1980 campaign.


title: National Review

text: During the 1980s "National Review" called for tax cuts, supply-side economics, the Strategic Defense Initiative, and support for President Reagan's foreign policy against the Soviet Union. The magazine criticized the Welfare state and would support the Welfare reform proposals of the 1990s. The magazine also regularly criticized President Bill Clinton. It first embraced, then rejected, Pat Buchanan in his political campaigns. A lengthy 1996 "National Review" editorial called for a "movement toward" drug legalization.


title: National Review

text: In 1985, "National Review" and Buckley were represented by attorney J. Daniel Mahoney during the magazine's $16 million libel suit against "The Spotlight".


title: National Review

text: Victor Davis Hanson, a regular contributor since 2001, sees a broad spectrum of conservative and anti-liberal contributors:


title: National Review

text: In 2015, the magazine published an editorial entitled "Against Trump," calling him a "philosophically unmoored political opportunist" and announcing its opposition to his candidacy for the Republican nomination for president. Since Trump's election to the presidency, the "National Review" editorial board has continued to criticize him.


title: National Review

text: However, contributors to "National Review" and "National Review Online" take a variety of positions on Trump. Lowry and Hanson support him, while "National Review" contributors such as Ramesh Ponnuru and Jonah Goldberg have remained critical of Trump. In a "Washington Post" feature on conservative magazines, T.A. Frank noted: "From the perspective of a reader, these tensions make National Review as lively as it has been in a long time."


title: National Review

text: A popular feature of "National Review" is the web version of the magazine, "National Review Online" ("N.R.O."), which includes a digital version of the magazine, with articles updated daily by "National Review" writers, and conservative blogs. The on-line version is called "N.R.O." to distinguish it from the paper magazine. It also features free articles, though these deviate in content from its print magazine. The site's editor is Charles C. W. Cooke.


title: National Review

text: Each day, the site posts new content consisting of conservative, libertarian, and neoconservative opinion articles, including some syndicated columns, and news features.


title: National Review

text: Markos Moulitsas, who runs the liberal "Daily Kos" web-site, told reporters in August 2007 that he does not read conservative blogs, with the exception of those on N.R.O.: "I do like the blogs at the "National Review"—I do think their writers are the best in the [conservative] blogosphere," he said.


title: National Review

text: The N.R.I. works in policy development and helping establish new advocates in the conservative movement. National Review Institute was founded by William F. Buckley Jr. in 1991 to engage in policy development, public education, and advocacy that would advance the conservative principles he championed.


title: National Review

text: In 2019, the Whittaker Chambers family had NRI stop an award in Chambers' name following award to people whom the family found objectionable.


title: National Review

text: As with most political opinion magazines in the United States, "National Review" carries little corporate advertising. The magazine stays afloat from subscription fees, donations, and black-tie fundraisers around the country. The magazine also sponsors cruises featuring "National Review" editors and contributors as lecturers.


title: National Review

text: "National Review" sometimes endorses a candidate during the primary election season. Editors at "National Review" have said, "Our guiding principle has always been to select the most conservative viable candidate." This statement echoes what has come to be called "The Buckley Rule". In a 1967 interview, in which he was asked about the choice of presidential candidate, Buckley said, "The wisest choice would be the one who would win... I'd be for the most right, viable candidate who could win."


title: National Review

text: The magazine's current editor-in-chief is Rich Lowry. Many of the magazine's commentators are affiliated with think-tanks such as The Heritage Foundation and American Enterprise Institute. Prominent guest authors have included Newt Gingrich, Mitt Romney, Peter Thiel, and Ted Cruz in the on-line and paper edition.


title: National Review

text: Current and past contributors to "National Review" ("N.R.") magazine, "National Review Online" ("N.R.O."), or both:


title: National Review

text: In June 2008, six days after Hillary Clinton conceded to Barack Obama in the Democratic primary, "National Review" correspondent Jim Geraghty published an article encouraging the Obama campaign to release the candidate's birth certificate in order "to squash all the conspiracy theories once and for all." Geraghty's column notes that it was unlikely that Obama was born in Kenya. Attorney Loren Collins, who has tracked the origins of birther movement for years, says that Geraghty may have "unwittingly shined a national spotlight on a fringe internet theory." Geraghty's article "became fodder for cable television." In a 2009 editorial, the "National Review" editorial board called conspiracies about Obama's citizenship "untrue," writing: "Like Bruce Springsteen, he has a lot of bad political ideas; but he was born in the U.S.A."


title: National Review

text: One "National Review" article said that Obama's parents could be communists because “for a white woman to marry a black man in 1958, or ’60, there was almost inevitably a connection to explicit Communist politics”.


title: National Review

text: As of 2018, Dinesh D'Souza was on the "National Review" masthead, despite stirring controversy for a number of years making inflammatory remarks and promoting conspiracy theories. D'Souza was no longer on the magazine's masthead in 2020. In comments that earned rebukes from "National Review" colleagues, D'Souza said that billionaire George Soros was a "collection boy for Hitler and the Nazis," attacked Roy Moore accuser Beverly Young Nelson, said that accusations against Roy Moore were “most likely fabricated,” and described Rosa Parks as an "overrated Democrat".


title: National Review

text: According to Philip Bump of "The Washington Post", "National Review" "has regularly criticized and rejected the scientific consensus on climate change". In 2015, the magazine published an intentionally deceptive graph that suggested that there was no climate change. The graph set the lower and upper bounds of the chart at -10 and 110 degree Fahrenheit and zoomed out so as to obscure warming trends.


title: National Review

text: In 2017, "National Review" published an article alleging that a top NOAA scientist claimed that the National Oceanic and Atmospheric Administration engaged in data manipulation and rushed a study based on faulty data in order to influence the Paris climate negotiations. The article largely repeated allegations made in the "Daily Mail" without independent verification. The scientist in question later rejected the claims made by "National Review", noting that he did not accuse NOAA of data manipulation but instead raised concerns about "the way data was handled, documented and stored, raising issues of transparency and availability".


title: National Review

text: In 2014, climate scientist Michael E. Mann sued the "National Review" after columnist Mark Steyn accused Mann of fraud and referenced a quote from Competitive Enterprise Institute writer Rand Simberg that called Mann "the Jerry Sandusky of climate science, except that instead of molesting children, he has molested and tortured data." Civil liberties organizations such as the ACLU and the Electronic Frontier Foundation and several publications such as "The Washington Post" expressed support for "National Review" in the lawsuit, filing amicus briefs in their defense.


title: National Review

text: Two days after the 9/11 attacks, "National Review" published a column by Ann Coulter in which she wrote of Muslims, "This is no time to be precious about locating the exact individuals directly involved in this particular terrorist attack. We should invade their countries, kill their leaders and convert them to Christianity. We weren't punctilious about locating and punishing only Hitler and his top officers. We carpet-bombed German cities; we killed civilians. That's war. And this is war." "National Review" later called the column a "mistake" and fired Coulter as a contributing editor.


title: National Review

text: In 2019, "The New York Times" reported that "National Review" was one of three news outlets (along with "Forbes" and "HuffPost") that had published stories written by Jeffrey Epstein's publicists. The "National Review" article was written by Christina Galbraith, Epstein's publicist at the time the article was published in 2013. The "National Review" bio for Galbraith described her as a science writer. The "National Review" retracted the article in July 2019 with apologies and spoke of new methods being used to better filter freelance content.


title: Insulated-gate bipolar transistor

text: An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch, which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating layers (P–N–P–N) that are controlled by a metal–oxide–semiconductor (MOS) gate structure.


title: Insulated-gate bipolar transistor

text: Although the structure of the IGBT is topologically the same as a thyristor with a "MOS" gate (MOS-gate thyristor), the thyristor action is completely suppressed, and only the transistor action is permitted in the entire device operation range. It is used in switching power supplies in high-power applications: variable-frequency drives (VFDs), electric cars, trains, variable-speed refrigerators, lamp ballasts, arc-welding machines, induction hobs, and air conditioners.


title: Insulated-gate bipolar transistor

text: Since it is designed to turn on and off rapidly, the IGBT can synthesize complex waveforms with pulse-width modulation and low-pass filters, so it is also used in switching amplifiers in sound systems and industrial control systems. In switching applications modern devices feature pulse repetition rates well into the ultrasonic-range frequencies, which are at least ten times higher than audio frequencies handled by the device when used as an analog audio amplifier. , the IGBT was the second most widely used power transistor, after the power MOSFET.


title: Insulated-gate bipolar transistor

text: An IGBT cell is constructed similarly to an n-channel vertical-construction power MOSFET, except the n+ drain is replaced with a p+ collector layer, thus forming a vertical PNP bipolar junction transistor.


title: Insulated-gate bipolar transistor

text: This additional p+ region creates a cascade connection of a PNP bipolar junction transistor with the surface n-channel MOSFET.


title: Insulated-gate bipolar transistor

text: The metal–oxide–semiconductor field-effect transistor (MOSFET) was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. The basic IGBT mode of operation, where a pnp transistor is driven by a MOSFET, was first proposed by K. Yamagami and Y. Akagiri of Mitsubishi Electric in the Japanese patent S47-21739, which was filed in 1968.


title: Insulated-gate bipolar transistor

text: Following the commercialization of power MOSFETs in the 1970s, B. Jayant Baliga submitted a patent disclosure at General Electric (GE) in 1977 describing a power semiconductor device with the IGBT mode of operation, including the MOS gating of thyristors, a four-layer VMOS (V-groove MOSFET) structure, and the use of MOS-gated structures to control a four-layer semiconductor device. He began fabricating the IGBT device with the assistance of Margaret Lazeri at GE in 1978 and successfully completed the project in 1979. The results of the experiments were reported in 1979. The device structure was referred to as a "V-groove MOSFET device with the drain region replaced by a p-type anode region" in this paper and subsequently as "the insulated-gate rectifier" (IGR), the insulated-gate transistor (IGT), the conductivity-modulated field-effect transistor (COMFET) and "bipolar-mode MOSFET".


title: Insulated-gate bipolar transistor

text: An MOS-controlled triac device was reported by B. W. Scharf and J. D. Plummer with their lateral four-layer device (SCR) in 1978. Plummer filed a patent application for this mode of operation in the four-layer device (SCR) in 1978. USP No. 4199774 was issued in 1980, and B1 Re33209 was reissued in 1996. The IGBT mode of operation in the four-layer device (SCR) switched to thyristor operation if the collector current exceeded the latch-up current, which is known as "holding current" in the well known theory of the thyristor.


title: Insulated-gate bipolar transistor

text: The development of IGBT was characterized by the efforts to completely suppress the thyristor operation or the latch-up in the four-layer device because the latch-up caused the fatal device failure. IGBTs had, thus, been established when the complete suppression of the latch-up of the parasitic thyristor was achieved as described in the following.


title: Insulated-gate bipolar transistor

text: Hans W. Becke and Carl F. Wheatley developed a similar device, for which they filed a patent application in 1980, and which they referred to as "power MOSFET with an anode region". The patent claimed that "no thyristor action occurs under any device operating conditions". The device had an overall similar structure to Baliga's earlier IGBT device reported in 1979, as well as a similar title.


title: Insulated-gate bipolar transistor

text: A. Nakagawa et al. invented the device design concept of non-latch-up IGBTs in 1984. The invention is characterized by the device design setting the device saturation current below the latch-up current, which triggers the parasitic thyristor. This invention realized complete suppression of the parasitic thyristor action, for the first time, because the maximal collector current was limited by the saturation current and never exceeded the latch-up current. After the invention of the device design concept of non-latch-up IGBTs, IGBTs evolved rapidly, and the design of non-latch-up IGBTs became a de facto standard and the patent of non-latch-up IGBTs became the basic IGBT patent of actual devices.


title: Insulated-gate bipolar transistor

text: In the early development stage of IGBT, all the researchers tried to increase the latch-up current itself in order to suppress the latch-up of the parasitic thyristor. However, all these efforts failed because IGBT could conduct enormously large current. Successful suppression of the latch-up was made possible by limiting the maximal collector current, which IGBT could conduct, below the latch-up current by controlling/reducing the saturation current of the inherent MOSFET. This was the concept of non-latch-up IGBT. “Becke’s device” was made possible by the non-latch-up IGBT.


title: Insulated-gate bipolar transistor

text: The IGBT is characterized by its ability to simultaneously handle a high voltage and a large current. The product of the voltage and the current density that the IGBT can handle reached more than 5 W/cm, which far exceeded the value, 2 W/cm, of existing power devices such as bipolar transistors and power MOSFETs. This is a consequence of the large safe operating area of the IGBT. The IGBT is the most rugged and the strongest power device yet developed, affording ease of use and so displacing bipolar transistors and even GTOs.


title: Insulated-gate bipolar transistor

text: This excellent feature of the IGBT had suddenly emerged when the non-latch-up IGBT was established in 1984 by solving the problem of so-called “latch-up,” which is the main cause of device destruction or device failure. Before that, the developed devices were very weak and were easy to be destroyed because of “latch-up.”


title: Insulated-gate bipolar transistor

text: Practical devices capable of operating over an extended current range were first reported by B. Jayant Baliga et al. in 1982. The first experimental demonstration of a practical discrete vertical IGBT device was reported by Baliga at the IEEE International Electron Devices Meeting (IEDM) that year. General Electric commercialized Baliga's IGBT device the same year. Baliga was inducted into the National Inventors Hall of Fame for the invention of the IGBT.


title: Insulated-gate bipolar transistor

text: A similar paper was also submitted by J. P. Russel et al. to IEEE Electron Device Letter in 1982. The applications for the device were initially regarded by the power electronics community to be severely restricted by its slow switching speed and latch-up of the parasitic thyristor structure inherent within the device. However, it was demonstrated by Baliga and also by A. M. Goodman et al. in 1983 that the switching speed could be adjusted over a broad range by using electron irradiation. This was followed by demonstration of operation of the device at elevated temperatures by Baliga in 1985. Successful efforts to suppress the latch-up of the parasitic thyristor and the scaling of the voltage rating of the devices at GE allowed the introduction of commercial devices in 1983, which could be utilized for a wide variety of applications. The electrical characteristics of GE's device, IGT D94FQ/FR4, were reported in detail by Marvin W. Smith in the proceedings of PCI April 1984. Marvin W. Smith showed in Fig.12 of the proceedings that turn-off above 10 amperes for gate resistance of 5kOhm and above 5 amperes for gate resistance of 1kOhm was limited by switching safe operating area although IGT D94FQ/FR4 was able to conduct 40 amperes of collector current. Marvin W. Smith also stated that the switching safe operating area was limited by the latch-up of the parasitic thyristor.


title: Insulated-gate bipolar transistor

text: Complete suppression of the parasitic thyristor action and the resultant non-latch-up IGBT operation for the entire device operation range was achieved by A. Nakagawa et al. in 1984. The non-latch-up design concept was filed for US patents. To test the lack of latch-up, the prototype 1200 V IGBTs were directly connected without any loads across a 600 V constant voltage source and were switched on for 25 microseconds. The entire 600 V was dropped across the device and a large short circuit current flowed. The devices successfully withstood this severe condition. This was the first demonstration of so-called "short-circuit-withstanding-capability" in IGBTs. Non-latch-up IGBT operation was ensured, for the first time, for the entire device operation range. In this sense, the non-latch-up IGBT proposed by Hans W. Becke and Carl F. Wheatley was realized by A. Nakagawa et al. in 1984. Products of non-latch-up IGBTs were first commercialized by Toshiba in 1985. This was the real birth of the present IGBT.


title: Insulated-gate bipolar transistor

text: Once the non-latch-up capability was achieved in IGBTs, it was found that IGBTs exhibited very rugged and a very large safe operating area. It was demonstrated that the product of the operating current density and the collector voltage exceeded the theoretical limit of bipolar transistors, 2 W/cm, and reached 5 W/cm.


title: Insulated-gate bipolar transistor

text: The insulating material is typically made of solid polymers which have issues with degradation. There are developments that use an ion gel to improve manufacturing and reduce the voltage required.


title: Insulated-gate bipolar transistor

text: The first-generation IGBTs of the 1980s and early 1990s were prone to failure through effects such as latchup (in which the device will not turn off as long as current is flowing) and secondary breakdown (in which a localized hotspot in the device goes into thermal runaway and burns the device out at high currents). Second-generation devices were much improved. The current third-generation IGBTs are even better, with speed rivaling power MOSFETs, and excellent ruggedness and tolerance of overloads. Extremely high pulse ratings of second and third-generation devices also make them useful for generating large power pulses in areas including particle and plasma physics, where they are starting to supersede older devices such as thyratrons and triggered spark gaps. High pulse ratings and low prices on the surplus market also make them attractive to the high-voltage hobbyists for controlling large amounts of power to drive devices such as solid-state Tesla coils and coilguns.


title: Insulated-gate bipolar transistor

text: The device proposed by J. D. Plummer in 1978 (US Patent Re.33209) is the same structure as a thyristor with a MOS gate. Plummer discovered and proposed that the device can be used as a transistor although the device operates as a thyristor in higher current density level. The device proposed by J. D. Plummer is referred here as “Plummer’s device.” On the other hand, Hans W. Becke proposed, in 1980, another device in which the thyristor action is eliminated under any device operating conditions although the basic device structure is the same as that proposed by J. D. Plummer. The device developed by Hans W. Becke is referred here as “Becke’s device” and is described in US Patent 4364073. The difference between “Plummer’s device” and “Becke’s device” is that “Plummer’s device” has the mode of thyristor action in its operation range and “Becke’s device” never has the mode of thyristor action in its entire operation range. This is a critical point, because the thyristor action is the same as so-called “latch-up.” “Latch-up” is the main cause of fatal device failure. Thus, theoretically, “Plummer’s device” never realizes a rugged or strong power device which has a large safe operating area. The large safe operating area can be achieved only after “latch-up” is completely suppressed and eliminated in the entire device operation range. However, the Becke's patent (US Patent 4364073) did not disclose any measures to realize actual devices.


title: Insulated-gate bipolar transistor

text: Despite Becke's patent describing a similar structure to Baliga's earlier IGBT device, several IGBT manufacturers paid the license fee of Becke's patent. Toshiba commercialized “non-latch-up IGBT” in 1985. Stanford University insisted in 1991 that Toshiba's device infringed US Patent RE33209 of “Plummer’s device.” Toshiba answered that “non-latch-up IGBTs” never latched up in the entire device operation range and thus did not infringe US Patent RE33209 of “Plummer’s patent.” Stanford University never responded after Nov. 1992. Toshiba purchased the license of “Becke’s patent” but never paid any license fee for “Plummer’s device.” Other IGBT manufacturers also paid the license fee for Becke's patent.


title: Insulated-gate bipolar transistor

text: , the IGBT is the second most widely used power transistor, after the power MOSFET. The IGBT accounts for 27% of the power transistor market, second only to the power MOSFET (53%), and ahead of the RF amplifier (11%) and bipolar junction transistor (9%). The IGBT is widely used in consumer electronics, industrial technology, the energy sector, aerospace electronic devices, and transportation.


title: Insulated-gate bipolar transistor

text: The IGBT combines the simple gate-drive characteristics of power MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors. The IGBT combines an isolated-gate FET for the control input and a bipolar power transistor as a switch in a single device. The IGBT is used in medium to high-power applications like switched-mode power supplies, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high current-handling capabilities in the order of hundreds of amperes with blocking voltages of . These IGBTs can control loads of hundreds of kilowatts.


title: Insulated-gate bipolar transistor

text: An IGBT features a significantly lower forward voltage drop compared to a conventional MOSFET in higher blocking voltage rated devices, although MOSFETS exhibit much lower forward voltage at lower current densities due to the absence of a diode Vf in the IGBT's output BJT. As the blocking voltage rating of both MOSFET and IGBT devices increases, the depth of the n- drift region must increase and the doping must decrease, resulting in roughly square relationship decrease in forward conduction versus blocking voltage capability of the device. By injecting minority carriers (holes) from the collector p+ region into the n- drift region during forward conduction, the resistance of the n- drift region is considerably reduced. However, this resultant reduction in on-state forward voltage comes with several penalties:


title: Insulated-gate bipolar transistor

text: In general, high voltage, high current and low switching frequencies favor the IGBT while low voltage, medium current and high switching frequencies are the domain of the MOSFET.


title: Insulated-gate bipolar transistor

text: Circuits with IGBTs can be developed and modeled with various circuit simulating computer programs such as SPICE, Saber, and other programs. To simulate an IGBT circuit, the device (and other devices in the circuit) must have a model which predicts or simulates the device's response to various voltages and currents on their electrical terminals. For more precise simulations the effect of temperature on various parts of the IGBT may be included with the simulation.