title: Feist (dog)

text: When hunting, feists, unlike hounds, are mostly silent on track until they tree a squirrel. They locate squirrels using their eyes, ears, and nose, then tree them barking loudly and circling the tree, in the same manner that a coonhound trees raccoons. When they have treed a squirrel, they chase the squirrel until it leaves their sight. During the chase, they wade through streams, leap over logs, and dash across roads to get to their prey. Leashing these dogs in the presence of squirrels is advisable. Although they put up a furious chase, feists rarely catch squirrels; they typically expect their owners to shoot them.


title: Feist (dog)

text: Various named varieties within the feist type have been developed, including the Mountain Feists, which includes the Baldwin Feist, Buckley Feist, DenMark Feist, Galla Creek Feist, Kemmer Feist, Lost Creek Feist, Sport-bred Feist, and Thornburg Feist. The Treeing Feists include the Atomic Feist, Barger Feist, Boggs Creek Feist, Original Cajun Squirrel Dog, Charlie Feist, Fleming Creek Squirrel Dog, Hickory Grounds Feist, Horse Creek Feist, Hurley Comb's-bred Feist, Mountain Cur, Mullins Feist, Redwood Feist, Riverun Feist, Shaderidge, and Rat Terrier.


title: Feist (dog)

text: The word "feist" is described in" Webster's Third New International Dictionary" as from the obsolete word "fysting", meaning "breaking wind, in such expressions as fysting dog or fysting hound". Feist is defined as "1. chiefly dial: a small dog of uncertain ancestry..."


title: Feist (dog)

text: The word feisty – "energetic, belligerent, esp. if small" – is derived from the dog, which is small and energetic.


title: Feist (dog)

text: The feist is not a new type of dog. Written accounts of the dogs go back centuries, with several spelling variations seen. George Washington referred to them in his diary in 1770 when describing a dog as "a small feist-looking yellow cur." Abraham Lincoln wrote about the "fice" dog in his poem, "The Bear Hunt". William Faulkner mentions the "fice dog" in "The Sound and the Fury", but uses the spelling "fyce" in the stories "Was" and "The Bear" from the collection "Go Down, Moses": "a brave fyce dog is killed by a bear". In her 1938 novel "The Yearling", author Marjorie Kinnan Rawlings uses the spelling of "feice" to refer to this dog. Claude Shumate, who wrote about the feist for "Full Cry" magazine, believed that the feist was descended from Native American dogs, mixed with small terriers from Britain, and was kept as early as the 17th century ("Full Cry", December, 1987). The breed was popularized by President Teddy Roosevelt, who frequently hunted with a feist named Skip, belonging to his son, Archie, and a Manchester Terrier named Jack, belonging to his son, Kermit.


title: Feist (dog)

text: Similar dogs are the Smooth and Wire Fox Terriers, originally developed to flush out foxes for hunters in England (but now primarily kept for conformation showing and as pets), and the Jack Russell Terrier, used for ratting. Fox Terriers and feists are often predominantly white so as to be visible to hunters. Many other variants of this type exist, such as the Russell Terrier, Parson Russell Terrier and Rat Terrier, with many locally developed purebred dog breeds. The original fox terrier type was documented in England in the 18th century.


title: Feist (dog)

text: Because of similarities in appearance, Mountain Feists are sometimes mistaken for Jack Russell Terriers, particularly in shelters and dog pounds. However, certain physical characteristics separate the two, and can be easy to identify to the trained eye. The coat of a feist is generally softer and smoother than that of a rough-coated Jack Russell. Its legs are longer and the tail of a Mountain Feist is usually shorter than that of a Jack Russell.


title: Feist (dog)

text: Despite some physical similarities, however, the behavior and temperament of a Mountain Feist and a Jack Russell are often quite different. Most feists are fairly quiet dogs, and lack the tendency toward excessive barking demonstrated by some Jack Russells and other hunting dogs. Jack Russells also tend to be more combative. Finally, while active, most Mountain Feists do not generally exhibit the frenetic energy of Jack Russells.


title: Feist (dog)

text: Some Mountain Feist bloodlines were indeed bred down from Jack Russell Terriers, crossing most likely with treeing dogs, such as Treeing Walker Hounds. Jack Russell traits often remain visible despite this crossbreeding. These descendants usually are mostly white in color with brown or black around the head and neck, with tall stand up, or button ears. These dogs usually hunt in packs in the Appalachian and Ozark Mountains. They use their eyes and ears exceptionally well.


title: Feist (dog)

text: Crossing of feist dogs has occurred since they are bred primarily for performance as hunting dogs. Despite considerable confusion, Mountain Feist or Treeing Feist dogs are their own unique breed. Where Rat Terriers are considered a specific breed within the feist type. Because the word "feist" refers to a general type of dog just as "hound" and "terrier" refer to a group of breeds, Rat Terriers are still often called "feists". The terriers brought to the US in the 1890s from England were crossed with feist dogs already here, in addition to some of the toy breeds (Toy Fox Terrier, Manchester Terrier, and Chihuahua) resulting in a smaller feist type dog with a more uniform appearance.


title: Carrier generation and recombination

text: In the solid-state physics of semiconductors, carrier generation and carrier recombination are processes by which mobile charge carriers (electrons and electron holes) are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as photodiodes, light-emitting diodes and laser diodes. They are also critical to a full analysis of p-n junction devices such as bipolar junction transistors and p-n junction diodes.


title: Carrier generation and recombination

text: The electron–hole pair is the fundamental unit of generation and recombination in inorganic semiconductors, corresponding to an electron transitioning between the valence band and the conduction band where generation of electron is a transition from the valence band to the conduction band and recombination leads to a reverse transition.


title: Carrier generation and recombination

text: Like other solids, semiconductor materials have an electronic band structure determined by the crystal properties of the material. Energy distribution among electrons is described by the Fermi level and the temperature of the electrons. At absolute zero temperature, all of the electrons have energy below the Fermi level; but at non-zero temperatures the energy levels are filled following a Fermi-Dirac distribution.


title: Carrier generation and recombination

text: In undoped semiconductors the Fermi level lies in the middle of a "forbidden band" or band gap between two "allowed bands" called the "valence band" and the "conduction band". The valence band, immediately below the forbidden band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is normally nearly completely empty. Because the valence band is so nearly full, its electrons are not mobile, and cannot flow as electric current.


title: Carrier generation and recombination

text: However, if an electron in the valence band acquires enough energy to reach the conduction band (as a result of interaction with other electrons, holes, photons, or the vibrating crystal lattice itself), it can flow freely among the nearly empty conduction band energy states. Furthermore, it will also leave behind a hole that can flow as current exactly like a physical charged particle.


title: Carrier generation and recombination

text: Carrier generation describes processes by which electrons gain energy and move from the valence band to the conduction band, producing two mobile carriers; while recombination describes processes by which a conduction band electron loses energy and re-occupies the energy state of an electron hole in the valence band.


title: Carrier generation and recombination

text: These processes must conserve both quantized energy and crystal momentum, and the vibrating lattice plays a large role in conserving momentum as, in collisions, photons can transfer very little momentum in relation to their energy.


title: Carrier generation and recombination

text: Recombination and generation are always happening in semiconductors, both optically and thermally. As predicted by thermodynamics, a material at thermal equilibrium will have generation and recombination rates that are balanced so that the net charge carrier density remains constant. The resulting probability of occupation of energy states in each energy band is given by Fermi–Dirac statistics.


title: Carrier generation and recombination

text: The product of the electron and hole densities (formula_1 and formula_2) is a constant formula_3 at equilibrium, maintained by recombination and generation occurring at equal rates. When there is a surplus of carriers (i.e., formula_4), the rate of recombination becomes greater than the rate of generation, driving the system back towards equilibrium. Likewise, when there is a deficit of carriers (i.e., formula_5), the generation rate becomes greater than the recombination rate, again driving the system back towards equilibrium. As the electron moves from one energy band to another, the energy and momentum that it has lost or gained must go to or come from the other particles involved in the process (e.g. photons, electron, or the system of vibrating lattice atoms).


title: Carrier generation and recombination

text: When light interacts with a material, it can either be absorbed (generating a pair of free carriers or an exciton) or it can "stimulate" a recombination event. The generated photon has similar properties to the one responsible for the event. Absorption is the active process in photodiodes, solar cells and other semiconductor photodetectors, while stimulated emission is the principle of operation in laser diodes.


title: Carrier generation and recombination

text: Besides light excitation, carriers in semiconductors can also be generated by an external electric field, for example in light-emitting diodes and transistors.


title: Carrier generation and recombination

text: When light with sufficient energy hits a semiconductor, it can excite electrons across the band gap. This generates additional charge carriers, temporarily lowering the electrical resistance of materials. This higher conductivity in the presence of light is known as photoconductivity. This conversion of light into electricity is widely used in photodiodes.


title: Carrier generation and recombination

text: Carrier recombination can happen through multiple relaxation channels. The main ones are band-to-band recombination, Shockley–Read–Hall (SRH) trap-assisted recombination, Auger recombination and surface recombination. These decay channels can be separated into radiative and non-radiative. The latter occurs when the excess energy is converted into heat by phonon emission after the mean lifetime formula_6, whereas in the former at least part of the energy is released by light emission or luminescence after a radiative lifetime formula_7. The carrier lifetime formula_8is then obtained from the rate of both type of events according to:


title: Carrier generation and recombination

text: "Band-to-band recombination" is the name for the process of electrons jumping down from the conduction band to the valence band in a radiative manner. During band-to-band recombination, a form of spontaneous emission, the energy absorbed by a material is released in the form of photons. Generally these photons contain the same or less energy than those initially absorbed. This effect is how LEDs create light. Because the photon carries relatively little momentum, radiative recombination is significant only in direct bandgap materials. This process is also known as "bimolecular recombination""."


title: Carrier generation and recombination

text: This type of recombination depends on the density of electrons and holes in the excited state, denoted by formula_12 and formula_13 respectively. Let us represent the radiative recombination as formula_14 and the carrier generation rate as G.


title: Carrier generation and recombination

text: Total generation is the sum of thermal generation G and generation due to light shining on the semiconductor G:


title: Carrier generation and recombination

text: Here we will consider the case in which there is no illumination on the semiconductor. Therefore formula_16 and formula_17, and we can express the change in carrier density as a function of time as


title: Carrier generation and recombination

text: Because the rate of recombination is affected by both the concentration of free electrons and the concentration of holes that are available to them, we know that R should be proportional to np:


title: Carrier generation and recombination

text: If the semiconductor is in thermal equilibrium, the rate at which electrons and holes recombine must be balanced by the rate at which they are generated by the spontaneous transition of an electron from the valence band to the conduction band. The recombination rate formula_22 must be exactly balanced by the thermal generation rate formula_23.


title: Carrier generation and recombination

text: Using the mass action law formula_27，with formula_28 being the intrinsic carrier density, we can rewrite it as


title: Carrier generation and recombination

text: where p is the maximum excess hole concentration when t = 0. (It can be proved that formula_46, but here we will not discuss that).


title: Carrier generation and recombination

text: When formula_47, all of the excess holes will have disappeared. Therefore, we can define the lifetime of the excess holes in the material formula_48


title: Carrier generation and recombination

text: "Stimulated emission" is a process in which an incident photon interacts with an excited electron causing it to recombine and emit a photon with the same properties of the incident one, in terms of phase, frequency, polarization, and direction of travel. Stimulated emission together with the principle of population inversion are at the heart of operation of lasers and masers. It has been shown by Einstein at the beginning of the twentieth century that if the excited and the ground level are non degenerate then the absorption rate formula_49and the stimulated emission rate formula_50are the same. Else if level 1 and level 2 are formula_51-fold and formula_52-fold degenerate respectively, the new relation is:formula_53


title: Carrier generation and recombination

text: "Trap emission" is a multistep process wherein a carrier falls into defect-related wavestates in the middle of the bandgap. A "trap" is a defect capable of holding a carrier. The trap emission process recombines electrons with holes and emits photons to conserve energy. Due to the multistep nature of trap emission, a phonon is also often emitted. Trap emission can proceed by use of bulk defects or surface defects.


title: Carrier generation and recombination

text: Non-radiative recombination is a process in phosphors and semiconductors, whereby charge carriers recombine releasing phonons instead of photons. Non-radiative recombination in optoelectronics and phosphors is an unwanted process, lowering the light generation efficiency and increasing heat losses.


title: Carrier generation and recombination

text: Non-radiative life time is the average time before an electron in the conduction band of a semiconductor recombines with a hole. It is an important parameter in optoelectronics where radiative recombination is required to produce a photon; if the non-radiative life time is shorter than the radiative, a carrier is more likely to recombine non-radiatively. This results in low internal quantum efficiency.


title: Carrier generation and recombination

text: In "Shockley-Read-Hall recombination" ("SRH"), also called "trap-assisted recombination", the electron in transition between bands passes through a new energy state (localized state) created within the band gap by a dopant or a defect in the crystal lattice; such energy states are called "traps". Non-radiative recombination occurs primarily at such sites. The energy is exchanged in the form of lattice vibration, a phonon exchanging thermal energy with the material.


title: Carrier generation and recombination

text: Since traps can absorb differences in momentum between the carriers, SRH is the dominant recombination process in silicon and other indirect bandgap materials. However, trap-assisted recombination can also dominate in direct bandgap materials under conditions of very low carrier densities (very low level injection) or in materials with high density of traps such as perovskites. The process is named after William Shockley, William Thornton Read and Robert N. Hall, who published it in 1952.


title: Carrier generation and recombination

text: Even though all the recombination events can be described in terms of electron movements, it is common to visualize the different processes in terms of excited electron and the electron "holes" they leave behind. In this context, if trap levels are close to the conduction band, they can temporarily immobilize excited electrons or in other words, they are "electron traps". On the other hand, if their energy lies close to the valence band they become "hole traps."


title: Carrier generation and recombination

text: The distinction between shallow and deep traps is commonly made depending on how close electron traps are to the conduction band and how close hole traps are to the valence band. If the difference between trap and band is smaller than the thermal energy kT it is often said that it is a "shallow trap". Alternatively, if the difference is larger than the thermal energy, it is called a deep trap. This difference is useful because shallow traps can be emptied more easily and thus are often not as detrimental to the performance of optoelectronic devices.


title: Carrier generation and recombination

text: When carrier recombination occurs through traps, we can replace the valence density of states by that of the intragap state. The term formula_54is replaced by the density of trapped electrons/holes formula_55.


title: Carrier generation and recombination

text: Where formula_57 is the density of trap states and formula_58 is the probability of that occupied state. Considering a material containing both types of traps, we can define two trapping coefficients formula_59 and two de-trapping coefficients formula_60. In equilibrium, both trapping and de-trapping should be balanced and formula_61). Then, the four rates as a function of formula_58become:


title: Carrier generation and recombination

text: Where formula_64 and formula_65 are the electron and hole densities when the quasi Fermi level matches the trap energy.


title: Carrier generation and recombination

text: In steady-state condition, the net recombination rate of electrons should match the net recombination rate for holes, in other words: formula_66. This eliminates the occupation probability formula_58 and leads to the Shockley-Read-Hall expression for the trap-assisted recombination:


title: Carrier generation and recombination

text: In "Auger recombination" the energy is given to a third carrier which is excited to a higher energy level without moving to another energy band. After the interaction, the third carrier normally loses its excess energy to thermal vibrations. Since this process is a three-particle interaction, it is normally only significant in non-equilibrium conditions when the carrier density is very high. The Auger effect process is not easily produced, because the third particle would have to begin the process in the unstable high-energy state.


title: Carrier generation and recombination

text: In thermal equilibrium the Auger recombination formula_70 and thermal generation rate formula_23 equal each other


title: Carrier generation and recombination

text: where formula_73 are the Auger capture probabilities. The non-equilibrium Auger recombination rate formula_74 and resulting net recombination rate formula_75 under steady-state conditions are


title: Carrier generation and recombination

text: The mechanism causing LED efficiency drop was identified in 2007 as Auger recombination, which met with a mixed reaction. In 2013, an experimental study claimed to have identified Auger recombination as the cause of efficiency droop. However, it remains disputed whether the amount of Auger loss found in this study is sufficient to explain the droop. Other frequently quoted evidence against Auger as the main droop-causing mechanism is the low-temperature dependence of this mechanism, which is the opposite of that found for the drop.


title: Carrier generation and recombination

text: Trap-assisted recombination at the surface of a semiconductor is referred to as surface recombination. This occurs when traps at or near the surface or interface of the semiconductor form due to dangling bonds caused by the sudden discontinuation of the semiconductor crystal. Surface recombination is characterized by surface recombination velocity which depends on the density of surface defects. In applications such as solar cells, surface recombination may be the dominant mechanism of recombination due to the collection and extraction of free carriers at the surface. In some applications of solar cells, a layer of transparent material with a large band gap, also known as a window layer, is used to minimize surface recombination. Passivation techniques are also employed to minimize surface recombination.


title: Carrier generation and recombination

text: For free carriers in low-mobility systems, the recombination rate is often described with the Langevin recombination rate. The model is often used for disordered systems such as organic materials (and is hence relevant for organic solar cells) and other such systems. The Langevin recombination strength is defined as formula_79.


title: Fact-checking

text: Fact-checking is the process of verifying factual information, in order to promote the veracity and correctness of reporting.


title: Fact-checking

text: Fact-checking can be conducted before ("ante hoc") or after ("post hoc") the text is published or otherwise disseminated. Internal fact-checking is such checking done in-house by the publisher; when the text is analyzed by a third party, the process is called external fact-checking.


title: Fact-checking

text: The US remains the largest market for fact-checking. Research suggests that fact-checking does indeed correct perceptions among citizens, as well as discourage politicians from spreading false or misleading claims. However, corrections may decay over time or be overwhelmed by cues from elites that promote less accurate claims. Political fact-checking is sometimes criticized as being opinion journalism. A review of US politics fact-checkers shows a mixed result of whether fact-checking is an effective way to reduce misconceptions, and whether the method is reliable.


title: Fact-checking

text: Sensationalist newspapers in the 1850s and later led to a gradual need for a more factual media. Colin Dickey has described the subsequent evolution of fact-checking. Key elements were the establishment of Associated Press in the 1850s (short factual material needed), Ralph Pulitzer of the New York World (his Bureau of Accuracy and Fair Play, 1912), Henry Luce and Time magazine (original working title: Facts), and the famous fact-checking department of The New Yorker. More recently, the mainstream media has come under severe economic threat from online startups. In addition the rapid spread of misinformation and conspiracy theories via social media is slowly creeping into mainstream media. One solution is for more media staff to be assigned a fact-checking role, as for example The Washington Post. Independent fact-checking organisations have also become prominent, such as Politifact.


title: Fact-checking

text: Ante hoc" fact-checking aims to identify errors so that the text can be corrected before dissemination, or perhaps rejected. Post hoc" fact-checking is most often followed by a written report of inaccuracies, sometimes with a visual metric provided by the checking organization (e.g., Pinocchios from "The Washington Post" "Fact Checker," or "TRUTH-O-METER" ratings from PolitiFact). Several organizations are devoted to "post hoc" fact-checking: examples include FactCheck.org and PolitiFact in the US, and Full Fact in the UK.


title: Fact-checking

text: External "post hoc" fact-checking organizations first arose in the US in the early 2000s, and the concept grew in relevance and spread to various other countries during the 2010s.


title: Fact-checking

text: External "post hoc" fact-checking by independent organizations began in the United States in the early 2000s. In the 2010s, particularly following the 2016 election of Donald Trump as US President, fact-checking gained a rise in popularity and spread to multiple countries mostly in Europe and Latin America. However, the US remains the largest market for fact-checking.


title: Fact-checking

text: One study finds that fact-checkers PolitiFact, FactCheck.org, and "The Washington Post's" Fact Checker overwhelmingly agree on their evaluations of claims. However, a study by Morgan Marietta, David C. Barker and Todd Bowser found "substantial differences in the questions asked and the answers offered." They concluded that this limited the "usefulness of fact-checking for citizens trying to decide which version of disputed realities to believe." A paper by Chloe Lim, PhD student at Stanford University, found little overlap in the statements that fact-checkers check. Out of 1,178 fact-checks by PolitiFact and 325 fact-checks by "The Washington Post"s Fact Checker, there were only 77 statements that both fact-checkers checked. The study found that the fact-checkers gave the same ratings for 49 and close ratings for 22 out of 77 statements, about 92% agreement. Lim concluded, "At least in some cases, the strategic ambiguity of politicians may impede the fact-checking movement's goals."


title: Fact-checking

text: The process of fact-checking is sometimes questionable, partly because the fact-checkers are just human subjects, and also because the purpose of some instances of fact-checking was unclear.


title: Fact-checking

text: Studies of "post hoc" fact-checking have made clear that such efforts often result in changes in the behavior, in general, of both the speaker (making them more careful in their pronouncements) and of the listener or reader (making them more discerning with regard to the factual accuracy of content); observations include the propensities of audiences to be completely unswayed by corrections to errors regarding the most divisive subjects, or the tendency to be more greatly persuaded by corrections of negative reporting (e.g., "attack ads"), and to see minds changed only when the individual in error was someone reasonably like-minded to begin with.


title: Fact-checking

text: Studies have shown that fact-checking can affect citizens' belief in the accuracy of claims made in political advertisement. A 2020 study by Paris School of Economics and Sciences Po economists found that falsehoods by Marine Le Pen during the 2017 French presidential election campaign (i) successfully persuaded voters, (ii) lost their persuasiveness when fact-checked, and (iii) did not reduce voters' political support for Le Pen when her claims were fact-checked. A 2017 study in the "Journal of Politics" found that "individuals consistently update political beliefs in the appropriate direction, even on facts that have clear implications for political party reputations, though they do so cautiously and with some bias... Interestingly, those who identify with one of the political parties are no more biased or cautious than pure independents in their learning, conditional on initial beliefs."


title: Fact-checking

text: A study by Yale University cognitive scientists Gordon Pennycook and David G. Rand found that Facebook tags of fake articles "did significantly reduce their perceived accuracy relative to a control without tags, but only modestly". A Dartmouth study led by Brendan Nyhan found that Facebook tags had a greater impact than the Yale study found. A "disputed" tag on a false headline reduced the number of respondents who considered the headline accurate from 29% to 19%, whereas a "rated false" tag pushed the number down to 16%. A 2019 study found that the "disputed" tag reduced Facebook users' intentions to share a fake news story. The Yale study found evidence of a backfire effect among Trump supporters younger than 26 years whereby the presence of both untagged and tagged fake articles made the untagged fake articles appear more accurate. In response to research which questioned the effectiveness of the Facebook "disputed" tags, Facebook decided to drop the tags in December 2017 and would instead put articles which fact-checked a fake news story next to the fake news story link whenever it is shared on Facebook.


title: Fact-checking

text: Based on the findings of a 2017 study in the journal "Psychological Science," the most effective ways to reduce misinformation through corrections is by:


title: Fact-checking

text: Large studies by Ethan Porter and Thomas J. Wood found that misinformation propagated by Donald Trump was more difficult to dispel with the same techniques, and generated the following recommendations:


title: Fact-checking

text: A 2019 meta-analysis of research into the effects of fact-checking on misinformation found that fact-checking has substantial positive impacts on political beliefs, but that this impact weakened when fact-checkers used "truth scales", refuted only parts of a claim and when they fact-checked campaign-related statements. Individuals' preexisting beliefs, ideology, and knowledge affected to what extent the fact-checking had an impact. A 2019 study in the "Journal of Experimental Political Science" found "strong evidence that citizens are willing to accept corrections to fake news, regardless of their ideology and the content of the fake stories."


title: Fact-checking

text: A 2018 study found that Republicans were more likely to correct their false information on voter fraud if the correction came from Breitbart News rather than a non-partisan neutral source such as PolitiFact.


title: Fact-checking

text: Studies published in 2020 and 2021 found that exposure to fact-checks had durable effects on reducing misperceptions, whereas a 2022 study did not find durable effects from COVID-19 fact-checks.


title: Fact-checking

text: A 2022 study found that individuals exposed to a fact-check of a false statement by a far-right politician were less likely to share the false statement.


title: Fact-checking

text: A 2022 study found that fact-checks were ineffective at reducing misinformation during the 2018 Brazilian Elections.


title: Fact-checking

text: Scholars have debated whether fact-checking could lead to a "backfire effect" whereby correcting false information may make partisan individuals cling more strongly to their views. One study found evidence of such a "backfire effect", but several other studies did not.


title: Fact-checking

text: A 2015 experimental study found that fact-checking can encourage politicians to not spread misinformation. The study found that it might help improve political discourse by increasing the reputational costs or risks of spreading misinformation for political elites. The researchers sent, "a series of letters about the risks to their reputation and electoral security if they were caught making questionable statements. The legislators who were sent these letters were substantially less likely to receive a negative fact-checking rating or to have their accuracy questioned publicly, suggesting that fact-checking can reduce inaccuracy when it poses a salient threat."


title: Fact-checking

text: One experimental study found that fact-checking during debates affected viewers' assessment of the candidates' debate performance and "greater willingness to vote for a candidate when the fact-check indicates that the candidate is being honest."


title: Fact-checking

text: A study of Trump supporters during the 2016 presidential campaign found that while fact-checks of false claims made by Trump reduced his supporters' belief in the false claims in question, the corrections did not alter their attitudes towards Trump.


title: Fact-checking

text: A 2019 study found that "summary fact-checking", where the fact-checker summarizes how many false statements a politician has made, has a greater impact on reducing support for a politician than fact-checking of individual statements made by the politician.


title: Fact-checking

text: Individual readers perform some types of fact-checking, such as comparing claims in one news story against claims in another.


title: Fact-checking

text: Rabbi Moshe Benovitz, has observed that: "modern students use their wireless worlds to augment skepticism and to reject dogma." He says this has positive implications for values development:


title: Fact-checking

text: According to Queen's University Belfast researcher Jennifer Rose, because fake news is created with the intention of misleading readers, online news consumers who attempt to fact-check the articles they read may incorrectly conclude that a fake news article is legitimate. Rose states, "A diligent online news consumer is likely at a pervasive risk of inferring truth from false premises", and suggests that fact-checking alone is not enough to reduce fake news consumption. Despite this, Rose asserts that fact-checking "ought to remain on educational agendas to help combat fake news".


title: Fact-checking

text: Fake news has become increasingly prevalent over the last few years, with the 2016 election revealing that online media platforms were especially susceptible to disseminating disinformation and misinformation. Fake news articles tend to come from satirical news websites or individual websites with an incentive to propagate false information, either as clickbait or to serve a purpose. Since these articles typically hope to intentionally promote biased or incorrect information, these articles are difficult to detect. When identifying a source of information, one must look at many attributes, including but not limited to the content of the email and social media engagements. The language, specifically, is typically more inflammatory in fake news than real articles, in part because the purpose is to confuse and generate clicks. Furthermore, modeling techniques such as n-gram encodings and bag of words have served as other linguistic techniques to determine the legitimacy of a news course. On top of that, researchers have determined that visual-based cues also play a factor in categorizing an article, specifically some features can be designed to assess if a picture was legitimate, and provides us more clarity on the news. There is also many social context features that can play a role, as well as the model of spreading the news. Websites such as "Snopes" try to detect this information manually, while certain universities are trying to build mathematical models to do this themselves.


title: Fact-checking

text: Some individuals and organizations publish their fact-checking efforts on the internet. These may have a special subject-matter focus, such as Snopes.com's focus on urban legends or the Reporters' Lab at Duke University's focus on providing resources to journalists.


title: Fact-checking

text: The adaptation of social media as a legitimate and commonly used platform has created extensive concerns for fake news in this domain. The spread of fake news via social media platforms such as Facebook, Twitter and Instagram presents the opportunity for extremely negative effects on society therefore new fields of research regarding fake news detection on social media is gaining momentum. However, fake news detection on social media presents challenges that renders previous data mining and detection techniques inadequate. As such, researchers are calling for more work to be done regarding fake news as characterized against psychology and social theories and adapting existing data mining algorithms to apply to social media networks. Further, multiple scientific articles have been published urging the field further to find automatic ways in which fake news can be filtered out of social media timelines.


title: Fact-checking

text: Since the 2016 United States presidential election, fake news has been a popular topic of discussion by President Trump and news outlets. The reality of fake news had become omnipresent, and a lot of research has gone into understanding, identifying, and combating fake news. Also, a number of researchers began with the usage of fake news to influence the 2016 presidential campaign. One research found evidence of pro-Trump fake news being selectively targeted on conservatives and pro-Trump supporters in 2016. The researchers found that social media sites, Facebook in particular, to be powerful platforms to spread certain fake news to targeted groups to appeal to their sentiments during the 2016 presidential race. Additionally, researchers from Stanford, NYU, and NBER found evidence to show how engagement with fake news on Facebook and Twitter was high throughout 2016.


title: Fact-checking

text: Recently, a lot of work has gone into detecting and identifying fake news through machine learning and artificial intelligence. In 2018, researchers at MIT's CSAIL (Computer Science and Artificial Intelligence Lab) created and tested a machine learning algorithm to identify false information by looking for common patterns, words, and symbols that typically appear in fake news. More so, they released an open-source data set with a large catalog of historical news sources with their veracity scores to encourage other researchers to explore and develop new methods and technologies for detecting fake news.


title: Fact-checking

text: The concept for International Fact-Checking Day was introduced at a conference for journalists and fact-checkers at the London School of Economics in June 2014. The holiday was officially created in 2016 and first celebrated on April 2, 2017. The idea for International Fact-Checking day rose out of the many misinformation campaigns found on the internet, particularly social media sites. It rose in importance after the 2016 elections, which brought fake news, as well as accusations of it, to the forefront of media issues.


title: Fact-checking

text: Activities for International Fact-Checking Day consist of various media organizations contributing to fact-checking resources, articles, and lessons for students and the general public to learn more about how to identify fake news and stop the spread of misinformation.


title: Fact-checking

text: 2020's International Fact-Checking Day focused specifically on how to accurately identify information about COVID-19.


title: Fact-checking

text: Political fact-checking is increasingly criticized as being opinion journalism.<ref name="Reason – Robby Soave – 7/29/2022"></ref> Criticism has included that fact-checking organizations in themselves are biased or that it is impossible to apply absolute terms such as "true" or "false" to inherently debatable claims. In September 2016, a Rasmussen Reports national telephone and online survey found that "just 29% of all Likely U.S. Voters trust media fact-checking of candidates' comments. Sixty-two percent (62%) believe instead that news organizations skew the facts to help candidates they support."


title: Fact-checking

text: A paper by Andrew Guess (of Princeton University), Brendan Nyhan (Dartmouth College) and Jason Reifler (University of Exeter) found that consumers of fake news tended to have less favorable views of fact-checking, in particular Trump supporters. The paper found that fake news consumers rarely encountered fact-checks: "only about half of the Americans who visited a fake news website during the study period also saw any fact-check from one of the dedicated fact-checking website (14.0%)."


title: Fact-checking

text: Deceptive websites that pose as fact-checkers have also been used to promote disinformation; this tactic has been used by both Russia and Turkey.


title: Fact-checking

text: During the COVID-19 pandemic, Facebook announced it would "remove false or debunked claims about the novel coronavirus which created a global pandemic", based on its fact-checking partners, collectively known as the International Fact-Checking Network. In 2021, Facebook reversed its ban on posts speculating the COVID-19 disease originated from Chinese labs, following developments in the investigations into the origin of COVID-19, including claims by the Biden administration, and a letter by eighteen scientists in the journal Science, saying a new investigation is needed because 'theories of accidental release from a lab and zoonotic spillover both remain viable." The policy led to an article by "The New York Post" that suggested a lab leak would be plausible to be initially labeled as "false information" on the platform. This reignited debates into the notion of scientific consensus. In an article published by the medical journal The BMJ, journalist Laurie Clarke said "The contentious nature of these decisions is partly down to how social media platforms define the slippery concepts of misinformation versus disinformation. This decision relies on the idea of a scientific consensus. But some scientists say that this smothers heterogeneous opinions, problematically reinforcing a misconception that science is a monolith." David Spiegelhalter, the Winton Professor of the Public Understanding of Risk at Cambridge University, argued that "behind closed doors, scientists spend the whole time arguing and deeply disagreeing on some fairly fundamental things". Clarke further argued that "The binary idea that scientific assertions are either correct or incorrect has fed into the divisiveness that has characterised the pandemic."


title: Fact-checking

text: Among the benefits of printing only checked copy is that it averts serious, sometimes costly, problems. These problems can include lawsuits for mistakes that damage people or businesses, but even small mistakes can cause a loss of reputation for the publication. The loss of reputation is often the more significant motivating factor for journalists.


title: Fact-checking

text: Fact checkers verify that the names, dates, and facts in an article or book are correct. For example, they may contact a person who is quoted in a proposed news article and ask the person whether this quotation is correct, or how to spell the person's name. Fact-checkers are primarily useful in catching accidental mistakes; they are not guaranteed safeguards against those who wish to commit journalistic frauds.


title: Fact-checking

text: Professional fact checkers have generally been hired by newspapers, magazines, and book publishers, probably starting in the early 1920s with the creation of "Time" magazine in the United States, though they were not originally called "fact-checkers". Fact checkers may be aspiring writers, future editors, or freelancers engaged other projects; others are career professionals.


title: Fact-checking

text: Historically, the field was considered women's work, and from the time of the first professional American fact checker through at least the 1970s, the fact checkers at a media company might be entirely female or primarily so.


title: Fact-checking

text: The number of people employed in fact-checking varies by publication. Some organizations have substantial fact-checking departments. For example, "The New Yorker" magazine had 16 fact checkers in 2003 and the fact checking department of the German weekly magazine "Der Spiegel" counted 70 staff in 2017. Others may hire freelancers per piece, or may combine fact-checking with other duties. Magazines are more likely to use fact checkers than newspapers. Television and radio programs rarely employ dedicated fact checkers, and instead expect others, including senior staff, to engage in fact-checking in addition to their other duties.


title: Fact-checking

text: Stephen Glass began his journalism career as a fact-checker. He went on to invent fictitious stories, which he submitted as reportage, and which fact-checkers at "The New Republic" (and other weeklies for which he worked) never flagged. Michael Kelly, who edited some of Glass's concocted stories, blamed himself, rather than the fact-checkers, saying: "Any fact-checking system is built on trust ... If a reporter is willing to fake notes, it defeats the system. Anyway, the real vetting system is not fact-checking but the editor."


title: Fact-checking

text: With the circulation of fake news on the internet, many organizations have dedicated time to create guidelines to help read to verify the information they are consuming. Many universities across America provide university students resources and tools to help them verify their sources. Universities provide access to research guides that help students conduct thorough research with reputable sources within academia. Organizations like FactCheck.org, OntheMedia.org, and PolitiFact.com provide procedural guidelines that help individuals navigate the process to fact-check a source.


title: Fact-checking

text: MIT and Stanford began an online MOOC course in the fall of 2020 called Sorting Truth From Fiction: Civic Online Reasoning. This course is for educators that want to teach students how to do basic fact-checking.


title: Fact-checking

text: The following is a list of individuals for whom it has been reported, reliably, that they have played such a fact-checking role at some point in their careers, often as a stepping point to other journalistic endeavors, or to an independent writing career:


title: Gelignite

text: Gelignite (), also known as blasting gelatin or simply "jelly", is an explosive material consisting of collodion-cotton (a type of nitrocellulose or guncotton) dissolved in either nitroglycerine or nitroglycol and mixed with wood pulp and saltpetre (sodium nitrate or potassium nitrate).


title: Gelignite

text: It was invented in 1875, by Swedish chemist Alfred Nobel, who also invented dynamite. It is more stable than dynamite, but can still suffer from "sweating" or leaching out nitroglycerine. Its composition makes it easily moldable and safe to handle without protection, as long as it is not near anything capable of detonating it.


title: Gelignite

text: One of the cheapest explosives, it burns slowly and cannot explode without a detonator, so it can be stored safely.


title: Gelignite

text: In the United Kingdom, an explosives certificate, issued by the local Chief Officer of Police, is required for possession of gelignite. Due to its widespread civilian use in quarries and mining, it has historically been used by terrorist groups such as the Provisional Irish Republican Army and the Ulster Volunteer Force who often used gelignite as a booster.


title: Gelignite

text: The 1970s saw Irish Industrial Explosives Limited producing annually 6,000 tonnes of Frangex, a commercial gelignite intended for use in mines and quarries. It was produced at Ireland's largest explosives factory in Enfield, County Meath. The Gardaí and the Irish Army patrolled the area, preventing the IRA from gaining direct access.


title: Gelignite

text: However, indirectly, the Provisional Irish Republican Army (PIRA) acquired amounts of the material. At the time of his arrest was found in the possession of Patrick Magee and discovered in a hijacked road tanker in January 1976.


title: Gelignite

text: PIRA volunteer, later informer, Sean O'Callaghan estimated that planting of Frangex would kill everyone within an radius. The Real IRA (RIRA) also acquired Frangex, and, in December 2000, eighty sticks were discovered on a farm in Kilmacow, County Kilkenny, near Waterford.


title: Gelignite

text: In early 1982 the Irish National Liberation Army stole of Frangex commercial explosives from the Tara mines in County Tipperary, enabling the organisation to intensify its bombing campaign. The INLA carried out its deadliest attack in December 1982 with the bombing of the Droppin' Well disco in Ballykelly, County Londonderry, which catered to British military personnel, in which 11 soldiers on leave and 6 civilians were killed. A bomb, estimated to be of Frangex explosive, small enough to fit into a handbag, was left beside a support pillar and brought down the roof when it exploded .


title: Barbara Colby

text: Barbara Colby (July 2, 1939 – July 24, 1975) was an American actress. She appeared in episodes of numerous television series before a 1974 appearance on "The Mary Tyler Moore Show" led to a main cast role on the new series "Phyllis"; after filming three episodes, she and a colleague were murdered outside an acting class, in an unsolved shooting.


title: Barbara Colby

text: Born in New York City on July 2, 1939, Colby was predominantly raised in New Orleans, where she had interest in acting while attending high school. After graduating, she received a scholarship to Bard College in Annandale-On-Hudson, New York, followed by a semester at the Paris-Sorbonne University in France.


title: Barbara Colby

text: Colby started her acting career in the theater. Following a performance in "Six Characters in Search of an Author" in 1964, she moved to Broadway with a debut in "The Devils" the following year. Throughout the rest of the decade, she appeared in such plays as "Under Milk Wood", "Murder in the Cathedral", "Dear Liar" and "A Doll's House" and garnered fine reviews for her Portia in "Julius Caesar" in 1966.


title: Barbara Colby

text: Colby's first important television role was in the first season of "Columbo" in an episode titled "Murder by the Book" in 1971. She played many support/guest roles on such established shows as "The Odd Couple", "McMillan & Wife", "The F.B.I.", "Medical Center", "Kung Fu" and "Gunsmoke".


title: Barbara Colby

text: Colby was a leading actor in the American Conservatory Theater in San Francisco for two years. She appeared in 1970s plays such as "Aubrey Beardsley the Neophyte", "House of Blue Leaves", "Afternoon Tea" and "The Hot l Baltimore". She returned to the classics with an off-Broadway role as Elizabeth in "Richard III" and was back on Broadway with the plays "Murderous Angels" in 1971 and a revival of "A Doll's House" in 1975.


title: Barbara Colby

text: In 1974, Colby appeared in two films, "California Split" and "Memory of Us". In 1975, she co-starred in "Rafferty and the Gold Dust Twins".


title: Barbara Colby

text: A role as a streetwise prostitute opposite Mary Tyler Moore in an episode of "The Mary Tyler Moore Show" led to an appearance in a subsequent episode. In 1975, Colby appeared as a new regular player on the "Mary Tyler Moore Show" spin-off "Phyllis", starring Cloris Leachman. Colby, who had appeared with Leachman in the TV movie "A Brand New Life" in 1973, was cast as Leachman's boss, Julie Erskine, the owner of a commercial photography studio.


title: Barbara Colby

text: On July 24, 1975, Colby and acting colleague James Kiernan were walking to their car following an acting class in Palms, Los Angeles, California, when they were shot inside a parking area. The murders occurred sometime after the first three episodes of the upcoming TV series "Phyllis" had been filmed. Colby was killed instantly, but Kiernan was able to describe the shooting to police before he died of his wounds. Kiernan said that he did not recognize the two men who shot them and that the shooting had occurred without warning or provocation. It was normal for Colby and classmates to congregate in the parking lot after acting class and talk. They were approached by two black men in a light-colored van and were each shot once. Police said there was no attempt to rob the pair and concluded that it was a random drive-by shooting or a targeted killing. The killers were never identified and the case remained an open cold case.


title: Barbara Colby

text: At the time of her death, Colby was separated from her husband, Bob Levitt, son of Ethel Merman. While the first three episodes of the first season of "Phyllis" were her final works, all released in the September 1975, her final appearance to be released was in the TV movie "The Ashes of Mrs. Reasoner", aired in January 1976.


title: Lal Shahbaz Qalandar

text: Hazrat Sayyid Usman Marwandi, (1177 - 19 February 1274) popularly known as Lal Shahbaz Qalandar (), was a Sufi saint and poet of present-day Pakistan and Afghanistan.


title: Lal Shahbaz Qalandar

text: Lal Shahbaz Qalandar was born in Marwand, Sistan to a family from Baghdad. He eventually settled in Sindh and helped many people in converting to Islam and was revered by the local Sindhi population. Lal Shahbaz Qalandar had also been reputed for performing many miracles and was seen as a very holy figure in Sindh.


title: Lal Shahbaz Qalandar

text: The 19th century spiritual Sufi Manqabat "Dama Dam Mast Qalandar" is dedicated to Lal Shahbaz Qalandar and is widely popular in the sub-continent.


title: Lal Shahbaz Qalandar

text: He is called "Lal" ("ruby-coloured") because of the ruby-like glow on his face/forehead and "Shahbaz" to denote a noble and divine spirit and "Qalandar" as he was a wandering spiritual man.


title: Lal Shahbaz Qalandar

text: Lal Shahbaz Qalandar is sometimes called "Jhulelal" (Sindhi/Urdu: ). The term Jhulelal means "red bridegroom". According to the Garland Encyclopedia, Lal Shahbaz Qalandar was referred to as Jhulelal (red bridegroom) because he was promised marriage to a daughter of his friend, but the friend died and later his friend's son refused to allow the agreed upon marriage, which caused Lal Shahbaz Qalandar grief.


title: Lal Shahbaz Qalandar

text: Lal Shahbaz Qalandar, son of Syed Kabeeruddin, was born in Marwand to parents from Baghdad, Iraq. He later settled in Sehwan, Sindh under the reign of the Ghaznavid and Ghurids (today's Punjab, Pakistan).


title: Lal Shahbaz Qalandar

text: A contemporary of Rumi, he travelled around the Muslim world and settled in Sehwan, Sindh where he was eventually buried. There is evidence of his presence in Sindh in 1196 when he met Pir Haji Ismail Panhwar of Paat and he is believed to have arrived in Sehwan around 1251. There he established a meeting house ("khanqah"), taught in the Fuqhai Islam Madarrsah and wrote his treatises "Mizan-us-Surf", "Kism-e-Doyum", "Aqd" and "Zubdah". Lal Shahbaz lived a celibate life.


title: Lal Shahbaz Qalandar

text: In Multan, he met Baha-ud-din Zakariya of the Suhrawardiyya order, Baba Fariduddin Ganjshakar of the Chishtiyya and Syed Jalaluddin Bukhari. The friendship of these four became legendary. They were known as the Chahar Yar (In Persian "the four friends"). According to some historians, the four friends visited various parts of Sindh and Punjab (in present-day Pakistan).


title: Lal Shahbaz Qalandar

text: The shrine of Lal Shahbaz Qalandar was built by Feroz Shah Tughlaq in 1356, expanded by Mirza Jani Beg and his son Mirza Ghazi Beg of Tarkhan Dynasty, but was not completed until 1639, when Nawab Dindar Khan paved the courtyard with glazed tiles. The silver work on the gate, the balustrade around the tomb and the top of the dome was gifted by Mir Karam Ali Talpur of Talpur Dynasty. Later on the shrine was decorated with Sindhi 'kashi-tiles', mirror-work and a gold-plated door was installed by the late Prime Minister of Pakistan, Zulfikar Ali Bhutto. The inner sanctum is about 100 square yards with a silver-canopied grave in the middle, according to Nadeem Wagan, Cutharo silver donated by Sardar Mahboob Ali Khan Wagan (Chief Sardar of Wagan Tribe) on one side of the marble floor is a row of about folding wooden stands, on which there is a set of copies of the Quran for devotees to read. On the other side, beside a bundle of incense, are rows of oil-lamps lighted by devotees. Thousands of devotees visit the tomb particularly every Thursday. The shrine is considered being the chief shrine for "malangs" and "qalandars" - adherents of a distinct Sufi order inspired by the teachings of Lal Shahbaz Qalandar.


title: Lal Shahbaz Qalandar

text: Lal Shahbaz's annual "Urs" (death anniversary), held on the 18 Sha'aban – the eighth month of the Muslim lunar calendar, brings more than two million pilgrims from all over Pakistan and parts of India, Bangladesh. Essentially, it is a south Asian affair.


title: Lal Shahbaz Qalandar

text: On 16 February 2017, a group claimed responsibility for a suicide attack on the shrine, which resulted in the deaths of 88 people. The following morning, the shrine's caretaker continued the daily tradition of ringing the shrine's bell at 3:30 A.M. and defiantly vowed that he would not be intimidated by the terrorists. Pakistani government and security forces have also launched a nationwide security crackdown and have recently killed 37 terrorists. The shrine's "dhamaal", or meditative dancing ceremony, was resumed the very next evening following the attack.


title: Gary Graham

text: Gary Graham (born June 6, 1950) is an American actor, musician, and author. He may be best known for his starring role as Detective Matthew Sikes in the television series "Alien Nation" (1989–1990) and five subsequent "Alien Nation" television films (1994–1997).


title: Gary Graham

text: Graham was born in Long Beach, California. One of his earliest roles was in the 1980 CBS mini series "Scruples" based on the Judith Krantz novel starring Lindsay Wagner. He was cast as a "hitman" on the television show "Moonlighting" co-starring opposite Bruce Willis.


title: Gary Graham

text: As well as Alien Nation and Star Trek, Graham starred in a 2008 TV pilot styled after "Sin City" called "Dead End City".


title: Gary Graham

text: December 18, 1984 episode of Remington Steele, "Let's Steele A Plot" (Season 3,episode 11), as Butch Beemis.


title: Gary Graham

text: As well as starring as Detective Matthew Sikes in the television series "Alien Nation" (1989–1990), he resumed this role in the TV movies "" (1994), "" (1995), "" (1996), "" (1996), and "" (1997). He was also in Monk (2004) where he posed a huge threat to Adrian and Alison Marie.


title: Gary Graham

text: Graham guest-starred on "" as the recurring character Ambassador Soval, a Vulcan ambassador to Earth. He also guest-starred on "" (1995) once, playing Ocampan community leader Tanis in the season 2 episode "". He plays Ragnar in the fan production "" and continued this role in "".


title: Gary Graham

text: His films include "Hardcore", "The Hollywood Knights", "All the Right Moves", "The Arrogant", "The Last Warrior", "Robot Jox", "Running Woman", "Siren". Gary's most recent films are "InAlienable", "Action Hero" and "Dreams Awake". Graham made his directorial debut in the spring of 2008 with the film "Interviews" which he also wrote.


title: Gary Graham

text: Graham also made appearances as the "Smoking Jacket Guy" in the introduction and other scenes in the Internet gaming show "The Jace Hall Show".


title: Gary Graham

text: Graham played Dr. David Macavoy in the web series Universal Dead. In late June, 2010 it was announced that Universal Dead will be made into a feature film.


This chart displays the United States Air Force officer rank insignia. The ranks are divided into three sections: company grade, field grade, and general officers. Company grade officers are those officers of grades O-1 to O-3. Field grade officers are those of grades O-4 to O-6. General officers are those of O-7 and above.


title: United States Air Force officer rank insignia

text: Currently, promotion from Second Lieutenant to First Lieutenant is virtually guaranteed after two years of satisfactory service. Promotion to Captain is virtually guaranteed after another two years of satisfactory service. Previously there was a Promotion Board to Captain, but that was discontinued in 2013. An officer's record is reviewed by a selection board at the Air Force Personnel Center at Randolph Air Force Base in San Antonio, Texas. This process occurs approximately between the nine- and eleven-year mark, where a certain percentage of Captains will be selected for Major. This process will repeat at the 13-16 year mark for promotion to Lieutenant Colonel and then around the twenty-year mark for promotion to Colonel.


text: The five-star grade General of the Air Force has only been held by General of the Air Force Henry H. Arnold. Federal law currently contains no provisions to promote an officer to five-star grade.


text: On the Air Force Mess Dress uniform, officer rank insignia are embroidered in silver or gold thread on detachable shoulder boards which are attached to the mess dress jacket. No rank insignia are worn on the mess dress shirt.


text: On the service dress uniform, metal rank insignia pins are worn on the epaulets of the Air Force Blue service dress jacket. Rank insignia are also worn on epaulets which slide onto the epaulet loops on the light blue shirt; the rank insignia is embroidered in silver or gold thread on an Air Force blue field. The slide-on epaulet for field-grade officers' shirts has a single line of silver piping toward the outer edge of the epaulet. The slide-on epaulet for general officers' shirts has silver piping on both the inner and outer edges of the epaulets. These slide-on epaulets are also worn on the cardigan and pull-over uniform sweaters. Unlike the Army, Navy, and Marine Corps, metal rank insignia for general officers consists of separate rather than conjoined stars.


text: The Flight Duty Uniform (FDU) features subdued cloth rank insignia sewn onto the shoulders. The Air Force flight cap is worn with the FDU and service dress uniforms (the service cap may also be worn with the service uniform). The flight cap is solid Air Force Blue for enlisted personnel, but features a solid silver edge braid for general officers, and an edge braid in a silver and blue diamond pattern for other officers. Officers wear a bright metal rank insignia toward the front edge of the (wearer's) left side of the flight cap.


text: On the Operational Camouflage Pattern (OCP) uniform rank is worn as a velcro patch on the center of the chest. Subdued cloth rank is worn on the front of the OCP patrol cap, above the bill. Air Force officers authorized to wear berets (Security Forces Officers, Special Tactics Officers, Combat Rescue Officers, and Combat Weather Officers) wear a bright metal rank insignia on the beret's flash.


text: Subdued rank insignia, as worn on the OCP and FDU, are designed to reduce visibility of the wearer under field conditions. The subdued versions of silver insignia are embroidered in dark blue thread on an olive-drab backing. The subdued versions of gold insignia are embroidered in brown thread on an olive-drab backing. On Desert FDUs and OCP uniforms, OCP patterned backing (or tan for the FDU) replaces the olive-drab backing (with black thread in place of dark blue thread). Subdued metal insignia are black and brown in place of silver and gold, respectively. General officers wear black stars as subdued rank.


text: Agents of the Air Force Office of Special Investigations normally do not wear uniforms while on duty, but even when in uniform they often do not wear rank insignia. However, when attending Professional Military Education courses, they do wear rank insignia.


text: The current Air Force officer rank names and insignia were taken from the Army upon the establishment of the Air Force as a separate service in 1947. The insignia have been essentially unchanged since then, except for a brief period during the 1990s, when then-Air Force Chief of Staff General Merrill A. McPeak redesigned the service dress uniform.


text: His redesign replaced the metal rank insignia for officers with silver braid on the sleeves, similar to the officer rank insignia now used by the US Navy and Coast Guard. This was similar to the rank insignia of the British Royal Air Force, the Canadian Armed Forces and other Commonwealth air forces. The uniform reforms also introduced for the first time in the USAF slip-on shoulder marks on the other uniforms, using the traditional rank insignia. The "McPeak uniform" was very unpopular, drawing comparisons to the jackets worn by airline pilots, and the traditional rank insignia were reinstated within a week of General McPeak's retirement in 1994 on the shoulder boards, while the slip-on insignia stayed.


text: Senior members are members who joined CAP for the first time past the age of 18, or who are former cadets who transferred to the senior member program, which must happen by the cadet's 21st birthday. Senior members who have not yet turned 21 years are eligible for flight officer grades, which include flight officer, technical flight officer, and senior flight officer. There is no mandatory retirement age for CAP members, and there are no physical requirements for joining. Members may enter retired status after twenty years of service. The only physical requirements senior members must follow are the weight and grooming standards required in order to wear the United States Air Force-style uniforms. Senior members who do not meet the weight and grooming standards of the United States Air Force may wear alternative uniforms known as CAP Corporate uniforms.


text: Officer grades up to lieutenant colonel reflect progression in training and organizational seniority, rather than command authority. Because of this, it is not uncommon for senior members commanding groups and squadrons to have members of superior grades serving under them. Current, retired and former members of the United States Armed Forces may be promoted directly to the CAP grade equivalent to their military grade, although some choose to follow the same standards as non-prior-service members. Except for a few exceptional cases, senior members are only promoted to the grade of CAP colonel upon appointment as a Region Commander, responsible for overseeing multiple states, or Wing Commander, responsible for the administration of CAP units across an entire state.


title: Why We Sleep

text: Why We Sleep: The New Science of Sleep and Dreams (or simply known as Why We Sleep) is a 2017 popular science book about sleep written by Matthew Walker, an English scientist and the director of the Center for Human Sleep Science at the University of California, Berkeley, who specializes in neuroscience and psychology. In the book, Walker discusses about the importance of sleeping, the side effects of failing to do so and its impact on society.


title: Why We Sleep

text: Walker spent four years writing the book, in which he asserts that sleep deprivation is linked to numerous fatal diseases, including dementia.


title: Why We Sleep

text: "Why We Sleep" has gone on to become a bestseller under "The New York Times" and "The Sunday Times" that questions its namesake from the viewpoint of neuroscience. The book has received generally positive reviews from critics, who praised Walker's research and views on the science of sleep, while criticizing the book for its certain claims regarding sleep.


title: Why We Sleep

text: According to Walker, who had never written a book at the time, he was motivated to write the book after an encounter with a woman who peeked at his work related to sleep and its benefits for health, with the woman stating, "When that comes out, I want to read it". Walker described this encounter as a sincere "independent ratification" that made him write the book. The book took Walker roughly four and a half years to write. Walker and his team spent roughly 20 years studying the rejuvenating ability sleep has, to much avail. Walker's communication style, in which he makes use of "metaphors and analogies effectively," allowed him to explain ideas related to sleep in detail.


title: Why We Sleep

text: At 18 years of age, Walker, who was a medical student at the time, became an "accidental sleep researcher" and moved over to studying neuroscience because of his habit of asking many questions. It was during his PhD at London's Medical Research Council when Walker learned about how little information there was on sleep. A scientific paper helped Walker with his research after his failure to determine the differences of brainwave activity between various dementia found in people, with the paper's contents describing the areas of the brain each variant of dementia attacks. It was then Walker realized that in order to measure his patients' brainwave patterns properly, they need to be asleep. Walker spent six months teaching himself how to set up his sleep laboratory, which allowed him to voice his findings on sleep differences amongst his patients.


title: Why We Sleep

text: Walker noted that many people misinterpret the amount of sleep they actually receive, likely caused by deep thought during the light sleep phases. Following the release of the book, Walker went on to describe his book has having the potential to make readers sleep and jokingly admitted to being concerned to hear if his book kept people awake at night.


title: Why We Sleep

text: The book is written from a neuroscientific view and is mainly devoted to discussing about the impact sleep has on the functions of the human brain. The book is divided into four parts, each section focusing on how sleep works, its benefits, the reason why dreams occur and sleep issues surrounding society. The book is written in a way so that it does not need to be read sequentially. In the book, Walker discusses about the effects of the widespread effect of sleep-loss, in which the goal in mind being that readers will endeavour in achieving eight hours of sleep once they learn about the connection sleep loss has to other health issues, such as Alzheimer's disease. Other details about lack of sleep explained by Walker include adults who sleep for less than 6 hours at the age of 40 and above have a higher chance of suffering a cardiac arrest or a stroke during their lifetime.


title: Why We Sleep

text: "Sleep pressure and circadian rhythms", the driving forces and the framework of sleep, are brought up by Walker in the book. Other sleep behaviors, such as non-rapid eye movement sleep and rapid eye movement sleep, and the impact sleep has on "synaptic pruning" and the creation of memories during a human's lifespan are also covered. NREM and REM are further explained by Walker to be the two sleeping basics, with 5 cycles present in a person's good night sleep. The book mentions about "morning types" and "evening types" of people, with Walker writing about how spending fewer amounts of time sleeping benefited earlier human predecessors who slept in groups of people due to their time period being safer than now.


title: Why We Sleep

text: The book emphasises on the significance of having a good night's sleep without the feeling of uneasiness or guilt of laziness. Walker, in his book, defines insomnia as a disorder that usually related to an overwrought commiserating nervous system that's usually caused by anxiousness. He goes on to addresses the P.T.S.D victims' nightmares, stating that their dreams' ability to heal them by reducing the emotions connected to a distressing memory is affected by an unusual quantity of noradrenaline being created. Walker also believed that dreams carry information regarding fundamental emotions while admitting that they can be quite apparent to people, resulting in no explanations required to describe them.


title: Why We Sleep

text: The values of sleep and the consequences of sleep deprivation are also brought up in the book. One particular research conducted in the past, where people volunteered themselves to sleep for only six hours in a span of 10 nights, is brought up by Walker. This resulted in the volunteers being "cognitively impaired" along with their brains being heavily damaged, regardless of the three week eight-hour sleep schedule they received later. Actions carried out by sleep-deprived people, such as answering emails at every hour of a day, are brought to question in the book. Walker wrote that research proves that sleeping after studying allows for "memory, integration and retention benefits" to occur. He further wrote that sleeping has the ability to retain memories and amend the abilities of human learning. Many organizations, who make creativeness, productiveness and resilient workers valued, give themselves a "sleep bonus", with the amount of extra sleep received being determined through electronic monitoring. Walker further noted that companies are changing their workplaces by allowing more "flexible working" and comfort zones for people to rest.


title: Why We Sleep

text: Walker's research on what impacts sleep is brought up in the book, with temperature influencing sleep being one of them. A five-step guideline is written in the book, with Walker explaining how to prevent "self-euthanasia" from missing sleep. The guideline also brings up "individual-level transformation" and a reformation of society. The book teaches about the basics behind how sleep works neurologically and biologically. The impact of caffeine on sleep is written in the book, with Walker noting its effects on the adenosine that allows people to fall asleep. It is further explained that caffeine will take more time to exit the body as it ages, with younger people having the ability to break caffeine down at a fast pace.


title: Why We Sleep

text: Walker wrote the book in a "reader-friendly" in areas such as discussing about neuroscientific techniques and how they were created. The book ends with Walker's advice for better sleep through 12 tips, with one of the tips written in the book being to have an eight-to-nine-hour period of sleep.


title: Why We Sleep

text: Why We Sleep has garnered a generally positive reception from critics, with Walker admitting to not knowing his book would be a hit amongst readers. The book would go on to make Walker famous in his field of expertise. The book became an international bestseller, including a #1 on the Sunday Times Bestseller in the UK, and a #8 on the New York Times Bestseller. It received numerous other reviews, including the Guardian, BBC, NPR, Financial Times, UC Berkeley and Kirkus Reviews. Critics praised the book for Walker's convincing studies on the importance of sleep and its impact on society.


title: Why We Sleep

text: Seithikurippu R. Pandi-Perumal praised Walker's structuring of the book, calling it informative, organised and intelligibly written while noting its informative yet reader-friendly nature. In a review from Bill Gates, he noted that the book teaches about the importance of sleeping, despite some points in the book not being convincing. He also noted that the book aided him in sleeping better, pointing out that it took a longer time to finish the book as he followed Walker's word on putting the book down to go to sleep. Kylie O'Brien's review described the book as "beautifully written" and filled with scientific facts that clarifies the question its title asks.


title: Why We Sleep

text: A review by Christopher Torrens in The Physiological Society described the book as informative and helpful, noting the book's evidence related to the consequences of having little to no sleep. He praised the book's style and formatting of being able to be read "from cover to cover or by cherry-picking chapters in whatever order you choose". A review by Joy Richards described the book as "tremendously terrifying" and unforgettable. Ruth Armstrong wrote that the book was loaded with recent research towards sleep, noting the change in his sleeping patterns.


title: Why We Sleep

text: Criticism surrounding the book involved the book telling stories about sleep instead of explaining facts about it. A review from Alexey Guzey, an independent researcher, criticized the book in an essay entitled "Matthew Walker's "Why We Sleep" Is Riddled with Scientific and Factual Errors". The criticism was discussed on the BBC series "More and Less". Guzey's criticism was also discussed by Andrew Gelman, a statistician at Columbia University. In a later post on Columbia's statistics blog, Gelman indicated that Walker's purported removal of a bar from a graph could be a "smoking gun," commenting that it entered "research misconduct" territory.


title: Why We Sleep

text: The book's failure to answer its own title 'Why We Sleep' has been criticised, with renowned sleep researcher William Dement commenting that people only need sleep due to the sleepiness accumulated. Anu Valtonen found fault in the book naming neuroscience as "the science that provides the knowledge of sleep and dreams" and its overlooking of other disciplinary areas related to sleep. She also criticised the book for lacking certain information on sleep, such as the "social aspects" of sleep or "socio-historical" route of sleep hygiene. Rosa Breed criticised Walker's lack of references when writing the book, noting that there was no proof in certain statements made by him, such as Walker's suggestion of sleeping for eight hours as a necessity. Jonathan Hawken felt that some of the book's contents were rather selective, criticising the book's lack of in-depth analysis towards the effect of sleep apnea.


title: Why We Sleep

text: The book has spawned controversy related to Walker's belief that the amount of sleep received worldwide has decreased. A researcher on sleep, Jim Horne, disagreed with the idea regarding how people are weighed down by a lack of sleep and that everybody was required to sleep for at least eight hours. Bill Gates wrote that he disagreed with Walker's claim that sleep and Alzheimer's disease have a strong connection to each other. Anu Valtonen voiced her concern regarding the speculation the book makes when taking a neuroscientific stance on the main insights into how sleep and dreams function.


title: Why We Sleep

text: Some critics felt that Walker's way of writing made the book feel similar to a horror story. Rosa Breed felt that some ideas brought up by Walker in the book were thought to be disturbing, noting Walker's suggestion for having people's sleeping behaviours be measured by "health insurance companies" to be prying. Some of Walker's claims were based on laboratory studies without supporting real-world evidence, making them questionable to critics.


title: David Morrell

text: David Morrell (born April 24, 1943) is a Canadian-American novelist whose debut 1972 novel "First Blood", later adapted as the 1982 film of the same name, went on to spawn the successful "Rambo" franchise starring Sylvester Stallone. He has written 28 novels, and his work has been translated into 30 languages. He also wrote the 2007–2008 "Captain America" comic book miniseries "The Chosen".


title: David Morrell

text: Morrell was born on April 24, 1943, in Kitchener, Ontario, Canada, the son of Beatrice, an upholsterer, and George Morrell, a Royal Navy flier. He decided to become a writer at the age of 17, after being inspired by the writing in the classic television series "Route 66". In 1966, Morrell received his B.A. in English from St. Jerome's University (affiliated with the University of Waterloo) and moved to the United States to study with Hemingway scholar Philip Young at Pennsylvania State University, where he would eventually receive his M.A. and Ph.D. in American literature.


title: David Morrell

text: During his time at Penn State he met science fiction writer Philip Klass, better known by the pseudonym William Tenn, who taught the basics of writing fiction. Morrell began work as an English professor at the University of Iowa in 1970. In 1972, his novel "First Blood" was published; it would eventually be made into the 1982 film of the same name starring Sylvester Stallone as Vietnam veteran John Rambo. Morrell continued to write many other novels, including "The Brotherhood of the Rose", the first in a trilogy of novels, which was adapted into a 1989 NBC miniseries starring Robert Mitchum. He gave up his tenure at the university in 1986 in order to write full-time. In 1988 he received the Horror Writers Association award for best novella; "Orange Is for Anguish, Blue for Insanity".


title: David Morrell

text: Morrell's teenaged son Matthew died of Ewing's sarcoma, a rare form of bone cancer, in 1987. In 2009 his granddaughter died of the same form of cancer. The trauma of his loss influenced Morrell's work, in particular in his creative fiction memoir about Matthew, "Fireflies". The protagonist of Morrell's novel "Desperate Measures" also experiences the loss of a son.


title: David Morrell

text: Morrell is a graduate of the National Outdoor Leadership School for wilderness survival as well as the G. Gordon Liddy Academy of Corporate Security. He is also an honorary lifetime member of the Special Operations Association and the Association of Former Intelligence Officers.


title: David Morrell

text: According to his website, he has been trained to handle firearms, crisis negotiation, assuming identities, executive protection, and defensive driving, among numerous other action skills that he describes in his novels. He earned an FAA licence to pilot his own small plane as part of research for his 2009 novel, "The Shimmer".


title: Photovoltaic power station

text: A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building-mounted and other decentralised solar power because they supply power at the utility level, rather than to a local user or users. The generic expression utility-scale solar is sometimes used to describe this type of project.


title: Photovoltaic power station

text: The solar power source is solar panels that convert light directly to electricity. However, this differs from and should not be confused with concentrated solar power, the other major large-scale solar generation technology, which uses heat to drive a variety of conventional generator systems. Both approaches have their own advantages and disadvantages, but to date, for a variety of reasons, photovoltaic technology has seen much wider use. , about 97% of utility-scale solar power capacity was PV.


title: Photovoltaic power station

text: In some countries, the nameplate capacity of photovoltaic power stations is rated in megawatt-peak (MW), which refers to the solar array's theoretical maximum DC power output. In other countries, the manufacturer states the surface and the efficiency. However, Canada, Japan, Spain, and the United States often specify using the converted lower nominal power output in MW, a measure more directly comparable to other forms of power generation. Most solar parks are developed at a scale of at least 1 MW. As of 2018, the world's largest operating photovoltaic power stations surpassed 1 gigawatt. At the end of 2019, about 9,000 solar farms were larger than 4 MW (utility scale), with a combined capacity of over 220 GW.


title: Photovoltaic power station

text: Most of the existing large-scale photovoltaic power stations are owned and operated by independent power producers, but the involvement of community and utility-owned projects is increasing. Previously, almost all were supported at least in part by regulatory incentives such as feed-in tariffs or tax credits, but as levelized costs fell significantly in the 2010s and grid parity has been reached in most markets, external incentives are usually not needed.


title: Photovoltaic power station

text: The first 1 MW solar park was built by Arco Solar at Lugo near Hesperia, California, at the end of 1982, followed in 1984 by a 5.2 MW installation in Carrizo Plain. Both have since been decommissioned (although a new plant, Topaz Solar Farm, was commissioned in Carrizo Plain in 2015). The next stage followed the 2004 revisions to the feed-in tariffs in Germany, when a substantial volume of solar parks were constructed.


title: Photovoltaic power station

text: Several hundred installations over 1 MW have since been installed in Germany, of which more than 50 are over 10 MW. With its introduction of feed-in tariffs in 2008, Spain briefly became the largest market with some 60 solar parks over 10 MW, but these incentives have since been withdrawn. The USA, China, India, France, Canada, Australia, and Italy, among others, have also become major markets as shown on the list of photovoltaic power stations.


title: Photovoltaic power station

text: The land area required for a desired power output varies depending on the location, the efficiency of the solar panels, the slope of the site, and the type of mounting used. Fixed tilt solar arrays using typical panels of about 15% efficiency on horizontal sites, need about /MW in the tropics and this figure rises to over in northern Europe.


title: Photovoltaic power station

text: Because of the longer shadow the array casts when tilted at a steeper angle, this area is typically about 10% higher for an adjustable tilt array or a single axis tracker, and 20% higher for a 2-axis tracker, though these figures will vary depending on the latitude and topography.


title: Photovoltaic power station

text: The best locations for solar parks in terms of land use are held to be brown field sites, or where there is no other valuable land use. Even in cultivated areas, a significant proportion of the site of a solar farm can also be devoted to other productive uses, such as crop growing or biodiversity. The change in albedo affects local temperature. One study claims a temperature rise due to the heat island effect, and another study claims that surroundings in arid ecosystems become cooler.


title: Photovoltaic power station

text: Agrivoltaics is using the same area of land for both solar photovoltaic power and agriculture. A recent study found that the value of solar generated electricity coupled to shade-tolerant crop production created an over 30% increase in economic value from farms deploying agrivoltaic systems instead of conventional agriculture.


title: Photovoltaic power station

text: In some cases, several different solar power stations with separate owners and contractors are developed on adjacent sites. This can offer the advantage of the projects sharing the cost and risks of project infrastructure such as grid connections and planning approval. Solar farms can also be co-located with wind farms.


title: Photovoltaic power station

text: Sometimes 'solar park' is used to describe a set of individual solar power stations, which share sites or infrastructure, and 'cluster' is used where several plants are located nearby without any shared resources. Some examples of solar parks are the Charanka Solar Park, where there are 17 different generation projects; Neuhardenberg, with eleven plants, and the Golmud solar park with total reported capacity over 500MW. An extreme example would be calling all of the solar farms in the Gujarat state of India a single solar park, the Gujarat Solar Park.


title: Photovoltaic power station

text: To avoid land use altogether, in 2022, a 5 MW floating solar park was installed in the Alqueva Dam reservoir, Portugal, enabling solar power and hydroelectric energy to be combined. Separately, a German engineering firm committed to integrating an offshore floating solar farm with an offshore wind farm to use ocean space more efficiently. The projects involve "hybridization", in which different renewable energy technologies are combined in one site.


title: Photovoltaic power station

text: Most solar parks are ground mounted PV systems, also known as free-field solar power plants. They can either be fixed tilt or use a single axis or dual axis solar tracker. While tracking improves the overall performance, it also increases the system's installation and maintenance cost. A solar inverter converts the array's power output from DC to AC, and connection to the utility grid is made through a high voltage, three phase step up transformer of typically 10 kV and above.


title: Photovoltaic power station

text: The solar arrays are the subsystems which convert incoming light into electrical energy. They comprise a multitude of solar panels, mounted on support structures and interconnected to deliver a power output to electronic power conditioning subsystems. The majority are free-field systems using ground-mounted structures, usually of one of the following types:


title: Photovoltaic power station

text: Many projects use mounting structures where the solar panels are mounted at a fixed inclination calculated to provide the optimum annual output profile. The panels are normally oriented towards the Equator, at a tilt angle slightly less than the latitude of the site. In some cases, depending on local climatic, topographical or electricity pricing regimes, different tilt angles can be used, or the arrays might be offset from the normal east–west axis to favour morning or evening output.


title: Photovoltaic power station

text: A variant on this design is the use of arrays, whose tilt angle can be adjusted twice or four times annually to optimise seasonal output. They also require more land area to reduce internal shading at the steeper winter tilt angle. Because the increased output is typically only a few percent, it seldom justifies the increased cost and complexity of this design.


title: Photovoltaic power station

text: To maximise the intensity of incoming direct radiation, solar panels should be orientated normal to the sun's rays. To achieve this, arrays can be designed using two-axis trackers, capable of tracking the sun in its daily movement across the sky, and as its elevation changes throughout the year.


title: Photovoltaic power station

text: These arrays need to be spaced out to reduce inter-shading as the sun moves and the array orientations change, so need more land area. They also require more complex mechanisms to maintain the array surface at the required angle. The increased output can be of the order of 30% in locations with high levels of direct radiation, but the increase is lower in temperate climates or those with more significant diffuse radiation, due to overcast conditions. So dual axis trackers are most commonly used in subtropical regions, and were first deployed at utility scale at the Lugo plant.


title: Photovoltaic power station

text: A third approach achieves some of the output benefits of tracking, with a lesser penalty in terms of land area, capital and operating cost. This involves tracking the sun in one dimension – in its daily journey across the sky – but not adjusting for the seasons. The angle of the axis is normally horizontal, though some, such as the solar park at Nellis Air Force Base, which has a 20° tilt, incline the axis towards the equator in a north–south orientation – effectively a hybrid between tracking and fixed tilt.


title: Photovoltaic power station

text: Single axis tracking systems are aligned along axes roughly north–south. Some use linkages between rows so that the same actuator can adjust the angle of several rows at once.


title: Photovoltaic power station

text: Solar panels produce direct current (DC) electricity, so solar parks need conversion equipment to convert this to alternating current (AC), which is the form transmitted by the electricity grid. This conversion is done by inverters. To maximise their efficiency, solar power plants also vary the electrical load, either within the inverters or as separate units. These devices keep each solar array string close to its peak power point.


title: Photovoltaic power station

text: There are two primary alternatives for configuring this conversion equipment; centralized and string inverters, although in some cases individual, or micro-inverters are used. Single inverters allows optimizing the output of each panel, and multiple inverters increases the reliability by limiting the loss of output when an inverter fails.


title: Photovoltaic power station

text: These units have relatively high capacity, typically of the order between 1 MW up to 7 MW for newer units (2020), so they condition the output of a substantial block of solar arrays, up to perhaps in area. Solar parks using centralized inverters are often configured in discrete rectangular blocks, with the related inverter in one corner, or the centre of the block.


title: Photovoltaic power station

text: String inverters are substantially lower in capacity than central inverters, of the order of 10 kW up to 250 KW for newer models (2020), and condition the output of a single array string. This is normally a whole, or part of, a row of solar arrays within the overall plant. String inverters can enhance the efficiency of solar parks, where different parts of the array are experiencing different levels of insolation, for example where arranged at different orientations, or closely packed to minimise site area.


title: Photovoltaic power station

text: The system inverters typically provide power output at voltages of the order of 480 V up to 800 V. Electricity grids operate at much higher voltages of the order of tens or hundreds of thousands of volts, so transformers are incorporated to deliver the required output to the grid. Due to the long lead time, the Long Island Solar Farm chose to keep a spare transformer onsite, as transformer failure would have kept the solar farm offline for a long period. Transformers typically have a life of 25 to 75 years, and normally do not require replacement during the life of a photovoltaic power station.


title: Photovoltaic power station

text: The performance of a solar park depends on the climatic conditions, the equipment used and the system configuration. The primary energy input is the global light irradiance in the plane of the solar arrays, and this in turn is a combination of the direct and the diffuse radiation. In some regions soiling, the accumulation of dust or organic material on the solar panels that blocks incident light, is a significant loss factor.


title: Photovoltaic power station

text: A key determinant of the output of the system is the conversion efficiency of the solar panels, which depends in particular on the type of solar cell used.


title: Photovoltaic power station

text: There will be losses between the DC output of the solar panels and the AC power delivered to the grid, due to a wide range of factors such as light absorption losses, mismatch, cable voltage drop, conversion efficiencies, and other parasitic losses. A parameter called the 'performance ratio' has been developed to evaluate the total value of these losses. The performance ratio gives a measure of the output AC power delivered as a proportion of the total DC power which the solar panels should be able to deliver under the ambient climatic conditions. In modern solar parks the performance ratio should typically be in excess of 80%.


title: Photovoltaic power station

text: Early photovoltaic systems output decreased as much as 10%/year, but as of 2010 the median degradation rate was 0.5%/year, with panels made after 2000 having a significantly lower degradation rate, so that a system would lose only 12% of its output performance in 25 years. A system using panels which degrade 4%/year will lose 64% of its output during the same period. Many panel makers offer a performance guarantee, typically 90% in ten years and 80% over 25 years. The output of all panels is typically warranted at plus or minus 3% during the first year of operation.


title: Photovoltaic power station

text: Solar power plants are developed to deliver merchant electricity into the grid as an alternative to other renewable, fossil or nuclear generating stations.


title: Photovoltaic power station

text: The plant owner is an electricity generator. Most solar power plants today are owned by independent power producers (IPP's), though some are held by investor- or community-owned utilities.


title: Photovoltaic power station

text: Some of these power producers develop their own portfolio of power plants, but most solar parks are initially designed and constructed by specialist project developers. Typically the developer will plan the project, obtain planning and connection consents, and arrange financing for the capital required. The actual construction work is normally contracted to one or more engineering, procurement, and construction (EPC) contractors.


title: Photovoltaic power station

text: Major milestones in the development of a new photovoltaic power plant are planning consent, grid connection approval, financial close, construction, connection and commissioning. At each stage in the process, the developer will be able to update estimates of the anticipated performance and costs of the plant and the financial returns it should be able to deliver.


title: Photovoltaic power station

text: Photovoltaic power stations occupy at least one hectare for each megawatt of rated output, so require a substantial land area; which is subject to planning approval. The chances of obtaining consent, and the related time, cost and conditions, vary by jurisdiction and location. Many planning approvals will also apply conditions on the treatment of the site after the station has been decommissioned in the future. A professional health, safety and environment assessment is usually undertaken during the design of a PV power station in order to ensure the facility is designed and planned in accordance with all HSE regulations.


title: Photovoltaic power station

text: The availability, locality and capacity of the connection to the grid is a major consideration in planning a new solar park, and can be a significant contributor to the cost.


title: Photovoltaic power station

text: Most stations are sited within a few kilometres of a suitable grid connection point. This network needs to be capable of absorbing the output of the solar park when operating at its maximum capacity. The project developer will normally have to absorb the cost of providing power lines to this point and making the connection; in addition often to any costs associated with upgrading the grid, so it can accommodate the output from the plant. Therefore, solar power stations are sometimes built at sites of former coal-fired power stations to reuse existing infrastructure.