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🔗 Mathematics 🔗 Physics

Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic fields, but was first applied to electrostatic fields.

Earnshaw's theorem applies to classical inverse-square law forces (electric and gravitational) and also to the magnetic forces of permanent magnets, if the magnets are hard (the magnets do not vary in strength with external fields). Earnshaw's theorem forbids magnetic levitation in many common situations.

If the materials are not hard, Braunbeck's extension shows that materials with relative magnetic permeability greater than one (paramagnetism) are further destabilising, but materials with a permeability less than one (diamagnetic materials) permit stable configurations.

🔗 United States 🔗 Biography 🔗 Virginia 🔗 Montana 🔗 United States/Wyoming

John Colter (c.1770–1775 – May 7, 1812 or November 22, 1813) was a member of the Lewis and Clark Expedition (1804–1806). Though party to one of the more famous expeditions in history, Colter is best remembered for explorations he made during the winter of 1807–1808, when he became the first known person of European descent to enter the region which later became Yellowstone National Park and to see the Teton Mountain Range. Colter spent months alone in the wilderness and is widely considered to be the first known mountain man.

🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Architecture 🔗 England 🔗 Military history/Fortifications 🔗 Military history/Napoleonic era 🔗 Ireland 🔗 Kent 🔗 Military history/European military history 🔗 Military history/British military history 🔗 Irish Maritime

Martello towers, sometimes known simply as Martellos, are small defensive forts that were built across the British Empire during the 19th century, from the time of the French Revolutionary Wars onwards. Most were coastal forts.

They stand up to 40 feet (12 m) high (with two floors) and typically had a garrison of one officer and 15–25 men. Their round structure and thick walls of solid masonry made them resistant to cannon fire, while their height made them an ideal platform for a single heavy artillery piece, mounted on the flat roof and able to traverse, and hence fire, over a complete 360° circle. A few towers had moats or other batteries and works attached for extra defence.

The Martello towers were used during the first half of the 19th century, but became obsolete with the introduction of powerful rifled artillery. Many have survived to the present day, often preserved as historic monuments.

🔗 Telecommunications

Signaling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also performs number translation, local number portability, prepaid billing, Short Message Service (SMS), and other services.

In North America SS7 is often referred to as Common Channel Signaling System 7 (CCSS7). In the United Kingdom, it is called C7 (CCITT number 7), number 7 and Common Channel Interoffice Signaling 7 (CCIS7). In Germany, it is often called Zentraler Zeichengabekanal Nummer 7 (ZZK-7).

The SS7 protocol is defined for international use by the Q.700-series recommendations of 1988 by the ITU-T. Of the many national variants of the SS7 protocols, most are based on variants standardized by the American National Standards Institute (ANSI) and the European Telecommunications Standards Institute (ETSI). National variants with striking characteristics are the Chinese and Japanese Telecommunication Technology Committee (TTC) national variants.

The Internet Engineering Task Force (IETF) has defined the SIGTRAN protocol suite that implements levels 2, 3, and 4 protocols compatible with SS7. Sometimes also called Pseudo SS7, it is layered on the Stream Control Transmission Protocol (SCTP) transport mechanism for use on Internet Protocol networks, such as the Internet.

🔗 Game theory

Game theory studies strategic interaction between individuals in situations called games. Classes of these games have been given names. This is a list of the most commonly studied games

🔗 Mathematics

In mathematics, 0.999... (also written as 0.9, among other ways) denotes the repeating decimal consisting of infinitely many 9s after the decimal point (and one 0 before it). This repeating decimal represents the smallest number no less than every decimal number in the sequence (0.9, 0.99, 0.999, ...). This number is equal to 1. In other words, "0.999..." and "1" represent the same number. There are many ways of showing this equality, from intuitive arguments to mathematically rigorous proofs. The technique used depends on the target audience, background assumptions, historical context, and preferred development of the real numbers, the system within which 0.999... is commonly defined. (In other systems, 0.999... can have the same meaning, a different definition, or be undefined.)

More generally, every nonzero terminating decimal has two equal representations (for example, 8.32 and 8.31999...), which is a property of all base representations. The utilitarian preference for the terminating decimal representation contributes to the misconception that it is the only representation. For this and other reasons—such as rigorous proofs relying on non-elementary techniques, properties, or disciplines—some people can find the equality sufficiently counterintuitive that they question or reject it. This has been the subject of several studies in mathematics education.

🔗 History of Science

A knowledge production mode is a term from the sociology of science which refers to the way (scientific) knowledge is produced. So far, three modes have been conceptualized. Mode 1 production of knowledge is knowledge production motivated by scientific knowledge alone (basic research) which is not primarily concerned by the applicability of its findings. Mode 1 is founded on a conceptualization of science as separated into discrete disciplines (e.g., a biologist does not bother about chemistry). Mode 2 was coined in 1994 in juxtaposition to Mode 1 by Michael Gibbons, Camille Limoges, Helga Nowotny, Simon Schwartzman, Peter Scott and Martin Trow. In Mode 2, multidisciplinary teams are brought together for short periods of time to work on specific problems in the real world for knowledge production (applied research) in the knowledge society. Mode 2 can be explained by the way research funds are distributed among scientists and how scientists focus on obtaining these funds in terms of five basic features: 1) knowledge produced in the context of application; (2) transdisciplinarity; (3) heterogeneity and organizational diversity; (4) social accountability and reflexivity; (5) and quality control. Subsequently, Carayannis and Campbell described a Mode 3 knowledge in 2006.

🔗 Aviation 🔗 Disaster management 🔗 Aviation/Aviation accident 🔗 Canada 🔗 Aviation/aircraft 🔗 Aviation/gliding 🔗 Canada/History of Canada 🔗 Canada/Manitoba

Air Canada Flight 143 was a Canadian scheduled domestic passenger flight between Montreal and Edmonton that ran out of fuel on July 23, 1983, at an altitude of 41,000 feet (12,000 m), midway through the flight. The crew was able to glide the Boeing 767 aircraft safely to an emergency landing at a former Royal Canadian Air Force base in Gimli, Manitoba, that had been turned into a motor racing track. This unusual aviation incident earned the aircraft the nickname "Gimli Glider".

The subsequent investigation revealed that a combination of company failures, human errors and confusion over unit measures had led to the aircraft being refuelled with insufficient fuel for the planned flight.

🔗 Computing

Logic Theorist is a computer program written in 1956 by Allen Newell, Herbert A. Simon and Cliff Shaw. It was the first program deliberately engineered to perform automated reasoning and is called "the first artificial intelligence program". It would eventually prove 38 of the first 52 theorems in Whitehead and Russell's Principia Mathematica, and find new and more elegant proofs for some.

🔗 Electronics 🔗 Electrical engineering

The trancitor as the combined word of a "transfer-capacitor" is to be considered as another active-device category besides the transistor as a "transfer-resistor". As observed in the table shown, four kinds of active devices are theoretically deduced. Among them, trancitors are missing to be the third and fourth kinds, whereas transistors, such as bipolar junction transistor (BJT) and field-effect transistor (FET), were already invented as the first and second kinds, respectively. Unlike the transistor switching the current at its output (i.e., current source), the trancitor transfers its input to the voltage output (i.e., voltage source), so an inverse relationship with each other.