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🔗 Computer science

In computer science, higher-order abstract syntax (abbreviated HOAS) is a technique for the representation of abstract syntax trees for languages with variable binders.

🔗 Philosophy 🔗 Philosophy/Philosophical literature 🔗 Books

Systems of Survival: A Dialogue on the Moral Foundations of Commerce and Politics is a book written by American urban activist Jane Jacobs in 1992.

It describes two fundamental and distinct ethical systems, or syndromes as she calls them: that of the Guardian and that of Commerce. She argues that these supply direction for the conduct of human life within societies, and understanding the tension between them can help us with public policy and personal choices.

🔗 Soviet Union 🔗 Russia 🔗 Law 🔗 Politics 🔗 Cities 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Russia/politics and law of Russia 🔗 Russia/human geography of Russia

A closed city or closed town is a settlement where travel or residency restrictions are applied so that specific authorization is required to visit or remain overnight. They may be sensitive military establishments or secret research installations that require much more space or freedom than is available in a conventional military base. There may also be a wider variety of permanent residents including close family members of workers or trusted traders who are not directly connected with its clandestine purposes.

Many closed cities existed in the Soviet Union until its collapse in 1991. After 1991, a number of them still existed in the CIS countries, especially Russia. In modern Russia, such places are officially known as "closed administrative-territorial formations" (закрытые административно-территориальные образования, zakrytye administrativno-territorial'nye obrazovaniya, or ЗАТО ZATO for short).

🔗 Aviation

Bitching Betty is a slang term used by some pilots and aircrew (mainly North American), when referring to the voices used by some aircraft warning systems.

The enunciating voice, in at least some aircraft systems, may be either male or female and in some cases this may be selected according to pilot preference. If the voice is female, it may be referred to as Bitching Betty; if the voice is male, it may be referred to as Barking Bob. A female voice is heard on military aircraft such as the F-16 Fighting Falcon, the Eurofighter Typhoon and the Mikoyan MiG-29. A male voice is heard on Boeing commercial airliners and is also used in the BAE Hawk.

In the United Kingdom the term Nagging Nora is sometimes used, and in New Zealand the term used for Boeing aircraft is Hank the Yank. The voice warning system used on London Underground trains, which also uses a female voice, is known to some staff as Sonya, as it "gets on ya nerves".

🔗 Business 🔗 Urban studies and planning 🔗 Cities

A company town is a place where practically all stores and housing are owned by the one company that is also the main employer. Company towns are often planned with a suite of amenities such as stores, houses of worship, schools, markets and recreation facilities. They are usually bigger than a model village ("model" in the sense of an ideal to be emulated).

Some company towns have had high ideals, but many have been regarded as controlling and/or exploitative. Others developed more or less in unplanned fashion, such as Summit Hill, Pennsylvania, United States, one of the oldest, which began as an LC&N Co. mining camp and mine site nine miles (14.5 km) from the nearest outside road.

🔗 Physics

Flux pinning is the phenomenon where a superconductor is pinned in space above a magnet. The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. The act of magnetic penetration is what makes flux pinning possible. At higher magnetic fields (above Hc1 and below Hc2) the superconductor allows magnetic flux to enter in quantized packets surrounded by a superconducting current vortex (see Quantum vortex). These sites of penetration are known as flux tubes. The number of flux tubes per unit area is proportional to the magnetic field with a constant of proportionality equal to the magnetic flux quantum. On a simple 76 millimeter diameter, 1-micrometer thick disk, next to a magnetic field of 28 kA/m, there are approximately 100 billion flux tubes that hold 70,000 times the superconductor's weight. At lower temperatures the flux tubes are pinned in place and cannot move. This pinning is what holds the superconductor in place thereby allowing it to levitate. This phenomenon is closely related to the Meissner effect, though with one crucial difference — the Meissner effect shields the superconductor from all magnetic fields causing repulsion, unlike the pinned state of the superconductor disk which pins flux, and the superconductor in place.

🔗 Physics

In quantum mechanics, the Kochen–Specker (KS) theorem, also known as the Bell–Kochen–Specker theorem, is a "no-go" theorem proved by John S. Bell in 1966 and by Simon B. Kochen and Ernst Specker in 1967. It places certain constraints on the permissible types of hidden-variable theories, which try to explain the predictions of quantum mechanics in a context-independent way. The version of the theorem proved by Kochen and Specker also gave an explicit example for this constraint in terms of a finite number of state vectors.

The theorem is a complement to Bell's theorem (to be distinguished from the (Bell–)Kochen–Specker theorem of this article). While Bell's theorem established nonlocality to be a feature of any hidden variable theory that recovers the predictions of quantum mechanics, the KS theorem established contextuality to be an inevitable feature of such theories.

The theorem proves that there is a contradiction between two basic assumptions of the hidden-variable theories intended to reproduce the results of quantum mechanics: that all hidden variables corresponding to quantum-mechanical observables have definite values at any given time, and that the values of those variables are intrinsic and independent of the device used to measure them. The contradiction is caused by the fact that quantum-mechanical observables need not be commutative. It turns out to be impossible to simultaneously embed all the commuting subalgebras of the algebra of these observables in one commutative algebra, assumed to represent the classical structure of the hidden-variables theory, if the Hilbert space dimension is at least three.

The Kochen–Specker theorem excludes hidden-variable theories that assume that elements of physical reality can all be consistently represented simultaneously by the quantum mechanical Hilbert space formalism disregarding the context of a particular framework (technically a projective decomposition of the identity operator) related to the experiment or analytical viewpoint under consideration. As succinctly worded by Isham and Butterfield, (under the assumption of a universal probabilistic sample space as in non-contextual hidden variable theories) the Kochen–Specker theorem "asserts the impossibility of assigning values to all physical quantities whilst, at the same time, preserving the functional relations between them".

🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Cold War

The Battle of Palmdale was the attempted shoot-down of a runaway drone by United States Air Force interceptors in the skies over Southern California in mid-August 1956. The drone was launched from Point Mugu Naval Air Station and soon went out of control. Interceptor aircraft took off from Oxnard Air Force Base and caught up with the drone, but were ultimately unable to bring it down, in spite of expending all of their rockets. After it ran out of fuel, the unmanned aircraft crashed in a sparsely populated tract of desert.

During the incident over 1000 acres were scorched and a substantial amount of property was damaged or destroyed.

🔗 Mathematics

In mathematics, the Bernoulli numbers B_n are a sequence of rational numbers which occur frequently in number theory. The Bernoulli numbers appear in (and can be defined by) the Taylor series expansions of the tangent and hyperbolic tangent functions, in Faulhaber's formula for the sum of m-th powers of the first n positive integers, in the Euler–Maclaurin formula, and in expressions for certain values of the Riemann zeta function.

The values of the first 20 Bernoulli numbers are given in the adjacent table. Two conventions are used in the literature, denoted here by ${\displaystyle B_{n}^{-{}}}$ and ${\displaystyle B_{n}^{+{}}}$; they differ only for n = 1, where ${\displaystyle B_{1}^{-{}}=-1/2}$ and ${\displaystyle B_{1}^{+{}}=+1/2}$. For every odd n > 1, B_n = 0. For every even n > 0, B_n is negative if n is divisible by 4 and positive otherwise. The Bernoulli numbers are special values of the Bernoulli polynomials ${\displaystyle B_{n}(x)}$, with ${\displaystyle B_{n}^{-{}}=B_{n}(0)}$ and ${\displaystyle B_{n}^{+}=B_{n}(1)}$ (Weisstein 2016).

The Bernoulli numbers were discovered around the same time by the Swiss mathematician Jacob Bernoulli, after whom they are named, and independently by Japanese mathematician Seki Kōwa. Seki's discovery was posthumously published in 1712 (Selin 1997, p. 891; Smith & Mikami 1914, p. 108) in his work Katsuyo Sampo; Bernoulli's, also posthumously, in his Ars Conjectandi of 1713. Ada Lovelace's note G on the Analytical Engine from 1842 describes an algorithm for generating Bernoulli numbers with Babbage's machine (Menabrea 1842, Note G). As a result, the Bernoulli numbers have the distinction of being the subject of the first published complex computer program.

🔗 Books 🔗 Maps

An Atlas of Fantasy, compiled by Jeremiah Benjamin Post, was originally published in 1973 by Mirage Press and revised for a 1979 edition by Ballantine Books. The 1979 edition dropped twelve maps from the first edition and added fourteen new ones. It also included an introduction by Lester del Rey.

To remain of manageable size, the Atlas excludes advertising maps, cartograms, most disproportionate maps, and alternate history ("might have been") maps, focusing instead on imaginary lands derived from literary sources. It purposefully omits "one-to-one" maps such as Thomas Hardy's Wessex (which merely renames places in southwest England), but includes Barsetshire and Yoknapatawpha County, which are evidently considered to be sufficiently fictionalized. The emphasis is on science fiction and fantasy, though Post suggests there exist enough mystery fiction maps to someday create The Detectives' Handy Pocket Atlas. Other maps were omitted due to permission costs or reproduction quality.

The maps are reproduced from many sources, and an Index of Artists is included.