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HandWiki is the world's largest wiki-style encyclopedia dedicated to science, technology and computing. It allows you to create and edit articles as long as you have external citations and login account. In addition, this is a content management environment that can be used for collaborative editing of original scholarly content, such as books, manuals, monographs and tutorials.

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Timeline of Plague
This is a timeline of plague, describing major epidemics and key medical developments.
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Topic Review
Ischemia
Ischemia or ischaemia is a restriction in blood supply to any tissues, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue i.e. hypoxia and microvascular dysfunction. It also means local hypoxia in a given part of a body sometimes resulting from constriction (such as vasoconstriction, thrombosis or embolism). Ischemia comprises not only insufficiency of oxygen, but also reduced availability of nutrients and inadequate removal of metabolic wastes. Ischemia can be partial (poor perfusion) or total blockage. The inadequate delivery of oxygenated blood to the organs must be resolved either by treating the cause of the inadequate delivery or reducing the oxygen demand of the system that needs it. For example, patients with myocardial ischemia have a decreased blood flow to the heart and are prescribed with medications that reduce chronotrophy and ionotrophy to meet the new level of blood delivery supplied by the stenosed so that it is adequate.
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Topic Review
List of DCS Modules
The below list includes all standalone products (commonly known as "modules") in Digital Combat Simulator, an air combat video game developed by Russian developer Eagle Dynamics. Fighter aircraft, helicopters and trainer aircraft modules can be flown by human players and artificial intelligence. Aircraft carriers, tanker aircraft and airborne early warning and control aircraft cannot be operated by human players.
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Topic Review
Prion
Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It is not known what causes a normal protein to misfold, but the resulting abnormal three-dimensional structure confers infectious properties by collapsing nearby protein molecules into the same shape. The word prion is derived from the term, "proteinaceous infectious particle". In comparison to all other known infectious agents such as viroids, viruses, bacteria, fungi, and parasites, all of which contain nucleic acids (DNA, RNA, or both), the hypothesized role of a protein as an infectious agent stands in contrast. Prion isoforms of the prion protein (PrP), whose specific function is uncertain, are hypothesized as the cause of transmissible spongiform encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease (CWD) in deer, bovine spongiform encephalopathy (BSE) in cattle (commonly known as "mad cow disease") and Creutzfeldt–Jakob disease (CJD) in humans. All known prion diseases in mammals affect the structure of the brain or other neural tissue; all are progressive, have no known effective treatment, and are always fatal. Until 2015, all known mammalian prion diseases were caused by the prion protein (PrP); however, in 2015 it was hypothesized that multiple system atrophy (MSA) was caused by a prion form of alpha-synuclein. Prions are a type of intrinsically disordered protein, which change their conformation unless they are bound to a specific partner such as another protein. With a prion, two protein chains are stabilized if one binds to another in the same conformation. The probability of this happening is low, but once it does the combination of the two is very stable. Then more units can get added, making a sort of "fibril". Prions form abnormal aggregates of proteins called amyloids, which accumulate in infected tissue and are associated with tissue damage and cell death. Amyloids are also responsible for several other neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. A prion disease is a type of proteopathy, or disease of structurally abnormal proteins. In humans, prions are believed to be the cause of Creutzfeldt–Jakob disease (CJD), its variant (vCJD), Gerstmann–Sträussler–Scheinker syndrome (GSS), fatal familial insomnia (FFI), and kuru. There is also evidence suggesting prions may play a part in the process of Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS); these have been termed prion-like diseases. Several yeast proteins have also been identified as having prionogenic properties, as well as a protein involved in modification of synapses during the formation of memories (see Eric Kandel § Molecular changes during learning). Prion replication is subject to epimutation and natural selection just as for other forms of replication, and their structure varies slightly between species. Prion aggregates are stable, and this structural stability means that prions are resistant to denaturation by chemical and physical agents: they cannot be destroyed by ordinary disinfection or cooking. This makes disposal and containment of these particles difficult.
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Topic Review
Radio Frequency Welding
Radio frequency welding, also known as dielectric welding and high frequency welding, is a plastics joining process that utilizes high-frequency radio waves to heat plastic parts to the point they form a melt layer. After the development of the melt layer, the parts are pressed together and then allowed to cool causing fusion. This process is capable of producing high quality joints in a range of plastics. Advantages of this process are fast cycle times, easily automated, repeatable, and good weld appearance. While this process has some great advantages, there are some limitations. Only plastics which have dipoles can be heated using radio waves and therefore not all plastics are able to be welded using this process. Also, this process is not well suited for thick or overly complex joints. The most common use of this process is lap joints or seals on thin plastic sheets or parts.
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Topic Review
Science, Technology, Engineering, and Mathematics
Science, technology, engineering, and mathematics (STEM) is a broad term used to group together these academic disciplines. This term is typically used to address an education policy or curriculum choices in schools. It has implications for workforce development, national security concerns (as a shortage of STEM-educated citizens can reduce effectiveness in this area) and immigration policy. There is no universal agreement on which disciplines are included in STEM; in particular whether or not the science in STEM includes social sciences, such as psychology, sociology, economics, and political science. In the United States, these are typically included by organizations such as the National Science Foundation (NSF). The National Science Foundation deals with all matters concerning science and new discoveries in science as it affects development, research, and innovations, the Department of Labor's O*Net online database for job seekers, and the Department of Homeland Security. In the United Kingdom, the social sciences are categorized separately and are instead grouped together with humanities and arts to form another counterpart acronym HASS (Humanities, Arts, and Social Sciences), rebranded in 2020 as SHAPE (Social Sciences, Humanities and the Arts for People and the Economy).
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Topic Review
Perl Compatible Regular Expressions
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. PCRE's syntax is much more powerful and flexible than either of the POSIX regular expression flavors (BRE, ERE) and than that of many other regular-expression libraries. While PCRE originally aimed at feature-equivalence with Perl, the two implementations are not fully equivalent. During the PCRE 7.x and Perl 5.9.x phase, the two projects have coordinated development, with features being ported between them in both directions. In 2015 a fork of PCRE was released with a revised programming interface (API). The original software, now called PCRE1 (the 1.xx–8.xx series), has had bugs mended, but no further development. (As of 2020), it is considered obsolete, and the current 8.45 release is likely to be the last. The new PCRE2 code (the 10.xx series) has had a number of extensions and coding improvements and is where development takes place. A number of prominent open-source programs, such as the Apache and Nginx HTTP servers, and the PHP and R scripting languages, incorporate the PCRE library; proprietary software can do likewise, as the library is BSD-licensed. As of Perl 5.10, PCRE is also available as a replacement for Perl's default regular-expression engine through the "re::engine::PCRE" module. The library can be built on Unix, Windows, and several other environments. PCRE2 is distributed with a POSIX C wrapper, several test programs, and the utility program "pcre2grep" built in tandem with the library.
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Topic Review
Working Animal
A working animal is an animal, usually domesticated, that is kept by humans and trained to perform tasks instead of being slaughtered to harvest animal products. Some are beasts of burden (draught animals) that provide transportation (e.g. riding horses and camels) and aid in physical labor (e.g. oxens and elephants), while others are service animals trained to execute certain specialized tasks (e.g. hunting and guide dogs, messenger pigeons and fishing cormorants). They may also be used for milking or herding. Some, at the end of their working lives, may also be used for meat or other products such as leather. The history of working animals may predate agriculture, with dogs used by our hunter-gatherer ancestors. Around the world, millions of animals work in relationship with their owners. Domesticated species are often bred for different uses and conditions, especially horses and working dogs. Working animals are usually raised on farms, though some are still captured from the wild, such as dolphins and some Asian elephants. People have found uses for a wide variety of abilities in animals, and even industrialised societies use many animals for work. People use the strength of horses, elephants, and oxen to pull carts and move loads. Police forces use dogs for finding illegal substances and assisting in apprehending wanted persons, others use dogs to find game or search for missing or trapped people. People use various animals — camels, donkeys, horses, dogs, etc.—for transport, either for riding or to pull wagons and sleds. Other animals, including dogs and monkeys, help disabled people. On rare occasions, wild animals are not only tamed, but trained to perform work—though often solely for novelty or entertainment, as such animals tend to lack the trustworthiness and mild temper of true domesticated working animals. Conversely, not all domesticated animals are working animals. For example, while cats may catch mice, it is an instinctive behaviour, not one that can be trained by human intervention. Other domesticated animals, such as sheep or rabbits, may have agricultural uses for meat, hides and wool, but are not suitable for work. Finally, small domestic pets, such as most small birds (other than certain types of pigeon) are generally incapable of performing work other than providing companionship.
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Topic Review
Symbol
In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised. Earlier symbols for chemical elements stem from classical Latin and Greek vocabulary. For some elements, this is because the material was known in ancient times, while for others, the name is a more recent invention. For example, Pb is the symbol for lead (plumbum in Latin); Hg is the symbol for mercury (hydrargyrum in Greek); and He is the symbol for helium (a new Latin name) because helium was not known in ancient Roman times. Some symbols come from other sources, like W for tungsten (Wolfram in German) which was not known in Roman times. A 3-letter temporary symbol may be assigned to a newly synthesized (or not-yet synthesized) element. For example, "Uno" was the temporary symbol for hassium (element 108) which had the temporary name of unniloctium, based on its atomic number being 8 greater than 100. There are also some historical symbols that are no longer officially used. In addition to the letters for the element itself, additional details may be added to the symbol as superscripts or subscripts a particular isotope, ionization, or oxidation state, or other atomic detail. A few isotopes have their own specific symbols rather than just an isotopic detail added to their element symbol. Attached subscripts or superscripts specifying a nuclide or molecule have the following meanings and positions: In Chinese, each chemical element has a dedicated character, usually created for the purpose (see Chemical elements in East Asian languages). However, Latin symbols are also used, especially in formulas. Many functional groups also have their own chemical symbol, e.g. Ph for the phenyl group, and Me for the methyl group. A list of current, dated, as well as proposed and historical signs and symbols is included here with its signification. Also given is each element's atomic number, atomic weight, or the atomic mass of the most stable isotope, group and period numbers on the periodic table, and etymology of the symbol. Hazard pictographs are another type of symbols used in chemistry.
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Topic Review
Peruvian Havana Embassy Crisis of 1980
On April 1, 1980, six Cuban citizens made their way into the Peruvian embassy in Havana, Cuba, instigating an international crisis over the diplomatic status of around 10,000 asylum-seeking Cubans who joined them over the following days. The Peruvian ambassador, Ernesto Pinto Bazurco Rittler, spearheaded the effort to protect Cubans, most of whom were disapproved of by Fidel Castro’s regime and were seeking protection at the embassy. This episode marked the start of the Cuban refugee crisis, which was followed by a series of diplomatic initiatives between various countries in both North and South America that tried to organize the fleeing of people from the island of Cuba to the United States and elsewhere. The embassy crisis culminated with the substantial exodus of 125,266 Cuban asylum-seekers during the Mariel Boatlift.
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