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🔗 Computer science 🔗 Mathematics

In combinatory logic for computer science, a fixed-point combinator (or fixpoint combinator),^: p.26 is a higher-order function (i.e. a function which takes a function as argument) that returns some fixed point (a value that is mapped to itself) of its argument function, if one exists.

Formally, if ${\displaystyle {\textsf {fix}}}$ is a fixed-point combinator and the function ${\displaystyle f}$ has one or more fixed points, then ${\displaystyle {\textsf {fix}}\ f}$ is one of these fixed points, i.e.

${\displaystyle f\ ({\textsf {fix}}\ f)={\textsf {fix}}\ f\ .}$

Fixed-point combinators can be defined in the lambda calculus and in functional programming languages and provide a means to allow for recursive definitions.

🔗 Biography 🔗 Military history 🔗 Politics 🔗 Military history/Military biography 🔗 Biography/military biography 🔗 Military history/Cold War 🔗 Biography/politics and government 🔗 Military history/South American military history 🔗 Uruguay

José Alberto "Pepe" Mujica Cordano (Spanish: [xoˈse muˈxika]; born 20 May 1935) is a Uruguayan politician and farmer who served as the 40th President of Uruguay from 2010 to 2015. A former guerrilla with the Tupamaros, he was tortured and imprisoned for 14 years during the military dictatorship in the 1970s and 1980s. A member of the Broad Front coalition of left-wing parties, Mujica was Minister of Livestock, Agriculture, and Fisheries from 2005 to 2008 and a Senator afterwards. As the candidate of the Broad Front, he won the 2009 presidential election and took office as President on 1 March 2010.

He has been described as "the world's humblest head of state" due to his austere lifestyle and his donation of around 90 percent of his $12,000 monthly salary to charities that benefit poor people and small entrepreneurs. An outspoken critic of capitalism’s focus on stockpiling material possessions which do not contribute to human happiness, Pepe is often seen riding his 60-year-old bicycle. The Times Higher Education called him the "philosopher president" in 2015, a play on words of Plato's conception of the philosopher king.

🔗 Sociology

Elite overproduction is a concept developed by Peter Turchin, which describes the condition of a society which is producing too many potential elite-members relative to its ability to absorb them into the power structure. This, he hypothesizes, is a cause for social instability, as those left out of power feel aggrieved by their relatively low socioeconomic status.

Turchin said that this situation explained social disturbances during the late Roman empire and the French Wars of Religion, and predicted in 2010 that this situation would cause social unrest in the United States of America during the 2020s. According to Turchin and Jack Goldstone, periods of political instability have throughout human history been due to the purely self-interested behavior of the elite. When the economy faced a surge in the workforce, which exerted a downward pressure on wages, the elite generally kept much of the wealth generated to themselves, resisting taxation and income redistribution. In the face of intensifying competition, they also sought to restrict the window of opportunity, to preserve their power and status for their descendants. These actions exacerbated inequality, a key driver of sociopolitical turbulence due to the proneness of the relatively well-off to radicalism. Widespread progressive political beliefs among university graduates, for instance, can be due to widespread underemployment rather than from exposure to progressive ideas or experiences during their studies.

In the case of the United States, by the 2010s, it became clear that the cost of higher education has ballooned over the previous three to four decades—faster than inflation, in fact—thanks to growing demand. For this prediction, Turchin used current data and the structural-demographic theory, a mathematical model of how population changes affect the behavior of the state, the elite, and the commons, created by Jack Goldstone. Goldstone himself predicted using his model that in the twenty-first century, the United States would elect a national populist leader. Elite overproduction has been cited as a root cause of political tension in the U.S., as so many well-educated Millennials are either unemployed, underemployed, or otherwise not achieving the high status they expect. Even then, the nation continued to produce excess PhD holders before the COVID-19 pandemic hit, especially in the humanities and social sciences, for which employment prospects were dim. Moreover, according to projections by the U.S. Census Bureau, the share of people in their 20s continued to grow till the end of the 2010s, meaning the youth bulge would likely not fade away before the 2020s. As such the gap between the supply and demand in the labor market would likely not fall before then, and falling or stagnant wages generate sociopolitical stress.

In the United Kingdom, there was simply not enough working-class Britons disenchanted with the status quo to support the Brexit movement, which was also buoyed by many highly educated voters.

However, Turchin's model cannot foretell precisely how a crisis will unfold; it can only yield probabilities. Turchin likened this to the accumulation of deadwood in a forest over many years, paving the way for a cataclysmic forest fire later on. It is possible to predict a massive conflagration, but not what causes it.

🔗 Mathematics 🔗 Statistics

In mathematics, the theory of optimal stopping or early stopping is concerned with the problem of choosing a time to take a particular action, in order to maximise an expected reward or minimise an expected cost. Optimal stopping problems can be found in areas of statistics, economics, and mathematical finance (related to the pricing of American options). A key example of an optimal stopping problem is the secretary problem. Optimal stopping problems can often be written in the form of a Bellman equation, and are therefore often solved using dynamic programming.

🔗 Heraldry and vexillology

A broad arrow, of which a pheon is a variant, is a stylised representation of a metal arrowhead, comprising a tang and two barbs meeting at a point. It is a symbol used traditionally in heraldry, most notably in England, and later by the British government to mark government property. It became particularly associated with the Board of Ordnance, and later the War Department and the Ministry of Defence. It was exported to other parts of the British Empire, where it was used in similar official contexts.

In heraldry, the arrowhead generally points downwards, whereas in other contexts it more usually points upwards.

🔗 Medicine 🔗 Transhumanism 🔗 Neuroscience 🔗 Pharmacology 🔗 Psychoactive and Recreational Drugs

Modafinil, sold under the brand name Provigil among others, is a medication to treat sleepiness due to narcolepsy, shift work sleep disorder, or obstructive sleep apnea. While it has seen off-label use as a purported cognitive enhancer, the research on its effectiveness for this use is not conclusive. It is taken by mouth.

Common side effects include headache, anxiety, trouble sleeping, and nausea. Serious side effects may include allergic reactions such as anaphylaxis, Stevens–Johnson syndrome, misuse, and hallucinations. It is unclear if use during pregnancy is safe. The amount of medication used may need to be adjusted in those with kidney or liver problems. It is not recommended in those with an arrhythmia, significant hypertension, or left ventricular hypertrophy. How it works is not entirely clear. One possibility is that it may affect the areas of the brain involved with the sleep cycle.

Modafinil was approved for medical use in the United States in 1998. In the United States it is classified as a schedule IV controlled substance. In the United Kingdom it is a prescription only medication. It is available as a generic medication. In the United Kingdom it costs the NHS about £105.21 a month as of 2018. In the United States the wholesale cost per month is about US$34.20 as of 2018. In 2016, it was the 284th most prescribed medication in the United States, with more than a million prescriptions.

🔗 Medicine 🔗 Viruses

Original antigenic sin, also known as antigenic imprinting or the Hoskins effect, refers to the propensity of the body's immune system to preferentially utilize immunological memory based on a previous infection when a second slightly different version of that foreign pathogen (e.g. a virus or bacterium) is encountered. This leaves the immune system "trapped" by the first response it has made to each antigen, and unable to mount potentially more effective responses during subsequent infections. Antibodies or T-cells induced during infections with the first variant of the pathogen are subject to a form of original antigenic sin, termed repertoire freeze.

The phenomenon of original antigenic sin has been described in relation to influenza virus, dengue fever, human immunodeficiency virus (HIV) and to several other viruses.

This phenomenon was first described in 1960 by Thomas Francis Jr. in the article "On the Doctrine of Original Antigenic Sin". It is named by analogy to the theological concept of original sin. According to Francis as cited by Richard Krause:

"The antibody of childhood is largely a response to dominant antigen of the virus causing the first type A influenza infection of the lifetime. [...] The imprint established by the original virus infection governs the antibody response thereafter. This we have called the Doctrine of the Original Antigenic Sin."

🔗 Technology 🔗 Computing 🔗 Computing/Early computers

The Water Integrator (Russian: Гидравлический интегратор) was an early analog computer built in the Soviet Union in 1936 by Vladimir Sergeevich Lukyanov. It functioned by careful manipulation of water through a room full of interconnected pipes and pumps. The water level in various chambers (with precision to fractions of a millimeter) represented stored numbers, and the rate of flow between them represented mathematical operations. This machine was capable of solving inhomogeneous differential equations.

The first versions of Lukyanov's integrators were rather experimental, made of tin and glass tubes, and each integrator could be used to solve only one problem. In the 1930s it was the only computer in the Soviet Union for solving partial differential equations.

In 1941, Lukyanov created a hydraulic integrator of modular design, which made it possible to assemble a machine for solving various problems. Two-dimensional and three-dimensional hydraulic integrators were designed.

In 1949–1955, an integrator in the form of standard unified units was developed at the NIISCHETMASH Institute. In 1955, the Ryazan plant of calculating and analytical machines began the serial production of integrators with the factory brand name “IGL” (russian: Интегратор Гидравлический Лукьянова - integrator of the Lukyanov hydraulic system). Integrators were widely distributed, delivered to Czechoslovakia, Poland, Bulgaria and China.

A water integrator was used in the design of the Karakum Canal in the 1940s, and the construction of the Baikal–Amur Mainline in the 1970s. Water analog computers were used in the Soviet Union until the 1980s for large-scale modelling. They were used in geology, mine construction, metallurgy, rocket production and other fields.

Currently, two hydraulic integrators are kept in the Polytechnic Museum in Moscow.

🔗 Physics

The X17 particle is a hypothetical subatomic particle proposed by Attila Krasznahorkay and his colleagues to explain certain anomalous measurement results. The particle has been proposed to explain wide angles observed in the trajectory paths of particles produced during a nuclear transition of beryllium-8 atoms and in stable helium atoms. The X17 particle could be the force carrier for a postulated fifth force, possibly connected with dark matter, and has been described as a protophobic (i.e., ignoring protons) X boson with a mass near 17 MeV.

🔗 Transport 🔗 Urban studies and planning 🔗 Engineering

A manhole cover or maintenance hole cover is a removable plate forming the lid over the opening of a manhole, an opening large enough for a person to pass through that is used as an access point for an underground vault or pipe. It is designed to prevent anyone or anything from falling in, and to keep out unauthorized persons and material.

Manhole covers date back at least to the era of ancient Rome, which had sewer grates made from stone.