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A proportional–integral–derivative (PID) controller, or three-term controller, is a feedback-based control loop mechanism commonly used to manage machines and processes that require continuous control and automatic adjustment. It is typically used in industrial control systems and various other applications where constant control through modulation is necessary without human intervention. The PID controller automatically compares the desired target value (setpoint or SP) with the actual value of the system (process variable or PV). The difference between these two values is called the error value, denoted as ${\displaystyle e(t)}$.

It then applies corrective actions automatically to bring the PV to the same value as the SP using three methods: The proportional (P) component responds to the current error value by producing an output that is directly proportional to the magnitude of the error. This provides immediate correction based on how far the system is from the desired setpoint. The integral (I) component, in turn, considers the cumulative sum of past errors to address any residual steady-state errors that persist over time, eliminating lingering discrepancies. Lastly, the derivative (D) component predicts future error by assessing the rate of change of the error, which helps to mitigate overshoot and enhance system stability, particularly when the system undergoes rapid changes. The PID output signal can directly control actuators through voltage, current, or other modulation methods, depending on the application. The PID controller reduces the likelihood of human error and improves automation.

A common example is a vehicle’s cruise control system. For instance, when a vehicle encounters a hill, its speed will decrease if the engine power output is kept constant. The PID controller adjusts the engine's power output to restore the vehicle to its desired speed, doing so efficiently with minimal delay and overshoot.

The theoretical foundation of PID controllers dates back to the early 1920s with the development of automatic steering systems for ships. This concept was later adopted for automatic process control in manufacturing, first appearing in pneumatic actuators and evolving into electronic controllers. PID controllers are widely used in numerous applications requiring accurate, stable, and optimized automatic control, such as temperature regulation, motor speed control, and industrial process management.

Operation Serenata de Amor is an artificial intelligence project to analyze public spending in Brazil. The project has been funded by a recurrent financing campaign since September 7, 2016, and came in the wake of major scandals of misappropriation of public funds in Brazil, such as the Mensalão scandal and what was revealed in the Operation Car Wash investigations.

The analysis began with data from the National Congress and then expanded to other types of budget and other instances of government, such as the Federal Senate. The project is built through collaboration on GitHub and using a public group with more than 600 participants on Telegram.

The name "Serenata de Amor," which means "serenade of love," was taken from a popular cashew cream bonbon produced by Chocolates Garoto in Brazil.

The 1808 mystery eruption was a large volcanic eruption conjectured to have taken place in late 1808, possibly in the southwest Pacific. A VEI-6 eruption, comparable to the 1883 eruption of Krakatoa, is suspected of having contributed to a period of global cooling that lasted for years, analogous to how the 1815 eruption of Mount Tambora (VEI-7) led to the Year Without a Summer in 1816.

Motion camouflage is camouflage which provides a degree of concealment for a moving object, given that motion makes objects easy to detect however well their coloration matches their background or breaks up their outlines.

The principal form of motion camouflage, and the type generally meant by the term, involves an attacker's mimicking the optic flow of the background as seen by its target. This enables the attacker to approach the target while appearing to remain stationary from the target's perspective, unlike in classical pursuit (where the attacker moves straight towards the target at all times, and often appears to the target to move sideways). The attacker chooses its flight path so as to remain on the line between the target and some landmark point. The target therefore does not see the attacker move from the landmark point. The only visible evidence that the attacker is moving is its looming, the change in size as the attacker approaches.

Camouflage is sometimes facilitated by motion, as in the leafy sea dragon and some stick insects. These animals complement their passive camouflage by swaying like plants in the wind or ocean currents, delaying their recognition by predators.

First discovered in hoverflies in 1995, motion camouflage by minimizing optic flow has been demonstrated in another insect order, dragonflies, as well as in two groups of vertebrates, falcons and echolocating bats. Since bats hunt at night, they cannot use camouflage. Instead they use an efficient homing strategy called constant absolute target direction. It has been suggested that anti-aircraft missiles could benefit from similar techniques.

Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction. The theory, based on string theory, black hole physics, and quantum information theory, describes gravity as an emergent phenomenon that springs from the quantum entanglement of small bits of spacetime information. As such, entropic gravity is said to abide by the second law of thermodynamics under which the entropy of a physical system tends to increase over time.

At its simplest, the theory holds that when gravity becomes vanishingly weak—levels seen only at interstellar distances—it diverges from its classically understood nature and its strength begins to decay linearly with distance from a mass.

Entropic gravity provides the underlying framework to explain Modified Newtonian Dynamics, or MOND, which holds that at a gravitational acceleration threshold of approximately 1.2×10⁻¹⁰ m/s², gravitational strength begins to vary inversely (linearly) with distance from a mass rather than the normal inverse-square law of the distance. This is an exceedingly low threshold, measuring only 12 trillionths gravity's strength at earth's surface; an object dropped from a height of one meter would fall for 36 hours were earth's gravity this weak. It is also 3,000 times less than exists at the point where Voyager 1 crossed our solar system's heliopause and entered interstellar space.

The theory claims to be consistent with both the macro-level observations of Newtonian gravity as well as Einstein's theory of general relativity and its gravitational distortion of spacetime. Importantly, the theory also explains (without invoking the existence of dark matter and its accompanying math featuring new free parameters that are tweaked to obtain the desired outcome) why galactic rotation curves differ from the profile expected with visible matter.

The theory of entropic gravity posits that what has been interpreted as unobserved dark matter is the product of quantum effects that can be regarded as a form of positive dark energy that lifts the vacuum energy of space from its ground state value. A central tenet of the theory is that the positive dark energy leads to a thermal-volume law contribution to entropy that overtakes the area law of anti-de Sitter space precisely at the cosmological horizon.

The theory has been controversial within the physics community but has sparked research and experiments to test its validity.

Bir Tawil (Egyptian Arabic: بير طويل, romanized: Bīr Ṭawīl, lit. 'tall water well', [biːɾ tˤɑˈwiːl]) is a 2,060 km² (795.4 sq mi) area of land along the border between Egypt and Sudan, which is uninhabited and claimed by neither country. When spoken of in association with the neighbouring Halaib Triangle, it is sometimes referred to as the Bir Tawil Triangle, despite the area's quadrilateral shape; the two "triangles" border at a quadripoint.

Its terra nulliuscode: lat promoted to code: la status results from a discrepancy between the straight political boundary between Egypt and Sudan established in 1899, and the irregular administrative boundary established in 1902. Egypt asserts the political boundary, and Sudan asserts the administrative boundary, with the result that the Hala'ib Triangle is claimed by both and Bir Tawil by neither. In 2014, author Alastair Bonnett described Bir Tawil as the only place on Earth that was habitable but was not claimed by any recognised government.

In governance, sortition (also known as selection by lot, allotment, demarchy, or Stochocracy) is the selection of political officials as a random sample from a larger pool of candidates. Filling individual posts or, more usually in its modern applications, to fill collegiate chambers. The system intends to ensure that all competent and interested parties have an equal chance of holding public office. It also minimizes factionalism, since there would be no point making promises to win over key constituencies if one was to be chosen by lot, while elections, by contrast, foster it. In ancient Athenian democracy, sortition was the traditional and primary method for appointing political officials, and its use was regarded as a principal characteristic of democracy.

Today, sortition is commonly used to select prospective jurors in common law-based legal systems and is sometimes used in forming citizen groups with political advisory power (citizens' juries or citizens' assemblies).

DRAKON is an algorithmic visual programming and modeling language developed within the Buran space project following ergonomic design principles. The language provides a uniform way to represent flowcharts of any complexity that are easy to read and understand.

The DRAKON Editor, which was released in September 2011, is an implementation of the language available in the public domain. It can be used for creating documentation, or for creating visual programs that can be converted to source code in other languages.

Unlike UML's philosophy, DRAKON's language philosophy is based on being augmented if needed, by using a hybrid language, which can be illustrated as "incrustating code snippets from text language used into shape DRAKON requires". This way, DRAKON always remains a simple visual language that can be used as an augmentation for a programmer who is interested in making their own project code easier to support or other long-term needs for example improving the ergonomics of the coding process or to making code easier to review and understand.

The name DRAKON is the Russian acronym for "Дружелюбный Русский Алгоритмический [язык], Который Обеспечивает Наглядность", which translates to "Friendly Russian algorithmic [language] that illustrates (or provides clarity)". The word "наглядность" (pronounced approximately as "naa-glya-dno-st-th") refers to a concept or idea being easy to imagine and understand, and may be translated as "clarity".

The DRAKON language can be used both as a modelling/"markup" language (which is considered a standalone "pure DRAKON" program) and as a programming language (as part of a hybrid language).

Integration of a stricter, "academic", variant of a markup language into programming, such as provided by DRAKON, adds syntactic sugar allowing users of different programming languages to comprehend each other's contributions to the overall project and even provide commentary if needed.

The Negro Motorist Green Book (also The Negro Motorist Green-Book, The Negro Travelers' Green Book, or simply the Green Book) was an annual guidebook for African-American roadtrippers. It was originated and published by African American, New York City mailman Victor Hugo Green from 1936 to 1966, during the era of Jim Crow laws, when open and often legally prescribed discrimination against African Americans especially and other non-whites was widespread. Although pervasive racial discrimination and poverty limited black car ownership, the emerging African-American middle class bought automobiles as soon as they could, but faced a variety of dangers and inconveniences along the road, from refusal of food and lodging to arbitrary arrest. In response, Green wrote his guide to services and places relatively friendly to African-Americans, eventually expanding its coverage from the New York area to much of North America, as well as founding a travel agency.

Many black Americans took to driving, in part to avoid segregation on public transportation. As the writer George Schuyler put it in 1930, "all Negroes who can do so purchase an automobile as soon as possible in order to be free of discomfort, discrimination, segregation and insult." Black Americans employed as athletes, entertainers, and salesmen also traveled frequently for work purposes.

African-American travelers faced hardships such as white-owned businesses refusing to serve them or repair their vehicles, being refused accommodation or food by white-owned hotels, and threats of physical violence and forcible expulsion from whites-only "sundown towns". Green founded and published the Green Book to avoid such problems, compiling resources "to give the Negro traveler information that will keep him from running into difficulties, embarrassments and to make his trip more enjoyable." The maker of a 2019 documentary film about the book offered this summary: "Everyone I was interviewing talked about the community that the Green Book created: a kind of parallel universe that was created by the book and this kind of secret road map that the Green Book outlined".

From a New York-focused first edition published in 1936, Green expanded the work to cover much of North America, including most of the United States and parts of Canada, Mexico, the Caribbean, and Bermuda. The Green Book became "the bible of black travel during Jim Crow", enabling black travelers to find lodgings, businesses, and gas stations that would serve them along the road. It was little known outside the African-American community. Shortly after passage of the Civil Rights Act of 1964, which outlawed the types of racial discrimination that had made the Green Book necessary, publication ceased and it fell into obscurity. There has been a revived interest in it in the early 21st century in connection with studies of black travel during the Jim Crow era.

Four issues (1940, 1947, 1954, and 1963) have been republished in facsimile (as of December 2017), and have sold well. Twenty-three additional issues have now been digitized by the New York Public Library Digital Collections.

A sun dog (or sundog) or mock sun, formally called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° halo.

The sun dog is a member of the family of halos, caused by the refraction of sunlight by ice crystals in the atmosphere. Sun dogs typically appear as a pair of subtly colored patches of light, around 22° to the left and right of the Sun, and at the same altitude above the horizon as the Sun. They can be seen anywhere in the world during any season, but are not always obvious or bright. Sun dogs are best seen and most conspicuous when the Sun is near the horizon.