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🔗 Measurement

ISO 1 is an international standard set by the International Organization for Standardization that specifies the standard reference temperature for geometrical product specification and verification. The temperature is fixed at 20 °C, which is equal to 293.15 kelvins and 68 degrees Fahrenheit.

Due to thermal expansion, precision length measurements need to be made at (or converted to) a defined temperature. ISO 1 helps in comparing measurements by defining such a reference temperature. The reference temperature of 20 °C was adopted by the CIPM on 15 April 1931, and became ISO recommendation number 1 in 1951. It soon replaced worldwide other reference temperatures for length measurements that manufacturers of precision equipment had used before, including 0 °C, 62 °F, and 25 °C. Among the reasons for choosing 20 °C was that this was a comfortable and practical workshop temperature and that it resulted in an integer value on both the Celsius and Fahrenheit scales.

🔗 Mathematics

This is a list of mathematical symbols used in all branches of mathematics to express a formula or to represent a constant.

A mathematical concept is independent of the symbol chosen to represent it. For many of the symbols below, the symbol is usually synonymous with the corresponding concept (ultimately an arbitrary choice made as a result of the cumulative history of mathematics), but in some situations, a different convention may be used. For example, depending on context, the triple bar "≡" may represent congruence or a definition. However, in mathematical logic, numerical equality is sometimes represented by "≡" instead of "=", with the latter representing equality of well-formed formulas. In short, convention dictates the meaning.

Each symbol is shown both in HTML, whose display depends on the browser's access to an appropriate font installed on the particular device, and typeset as an image using TeX.

🔗 Mathematics

The ant on a rubber rope is a mathematical puzzle with a solution that appears counterintuitive or paradoxical. It is sometimes given as a worm, or inchworm, on a rubber or elastic band, but the principles of the puzzle remain the same.

The details of the puzzle can vary, but a typical form is as follows:

An ant starts to crawl along a taut rubber rope 1 km long at a speed of 1 cm per second (relative to the rubber it is crawling on). At the same time, the rope starts to stretch uniformly at a constant rate of 1 km per second, so that after 1 second it is 2 km long, after 2 seconds it is 3 km long, etc. Will the ant ever reach the end of the rope?

At first consideration it seems that the ant will never reach the end of the rope, but in fact it does. (In the form stated above, it would take 8.9×10⁴³⁴²¹ years.) Whatever the length of the rope and the relative speeds of the ant and the stretching, provided that the ant's speed and the stretching remain steady, the ant will always be able to reach the end given sufficient time. Once the ant has begun moving, the rubber rope is stretching both in front of and behind the ant, conserving the proportion of the rope already walked by the ant and enabling the ant to make continual progress.

🔗 Finance & Investment 🔗 Economics 🔗 India 🔗 Arab world

Hawala or hewala (Arabic: حِوالة‎ ḥawāla, meaning transfer or sometimes trust), also known as havaleh in Persian, and xawala or xawilaad in Somali, is a popular and informal value transfer system based not on the movement of cash, or on telegraph or computer network wire transfers between banks, but instead on the performance and honour of a huge network of money brokers (known as hawaladars). While hawaladars are spread throughout the world, they are primarily located in the Middle East, North Africa, the Horn of Africa, and the Indian subcontinent, operating outside of, or parallel to, traditional banking, financial channels, and remittance systems. Hawala follows Islamic traditions but its use is not limited to Muslims.

🔗 Computing 🔗 Computing/Computer hardware

PLATO (Programmed Logic for Automatic Teaching Operations) was the first generalized computer-assisted instruction system. Starting in 1960, it ran on the University of Illinois' ILLIAC I computer. By the late 1970s, it supported several thousand graphics terminals distributed worldwide, running on nearly a dozen different networked mainframe computers. Many modern concepts in multi-user computing were originally developed on PLATO, including forums, message boards, online testing, e-mail, chat rooms, picture languages, instant messaging, remote screen sharing, and multiplayer video games.

PLATO was designed and built by the University of Illinois and functioned for four decades, offering coursework (elementary through university) to UIUC students, local schools, and other universities. Courses were taught in a range of subjects, including Latin, chemistry, education, music, and primary mathematics. The system included a number of features useful for pedagogy, including text overlaying graphics, contextual assessment of free-text answers, depending on the inclusion of keywords, and feedback designed to respond to alternative answers.

Rights to market PLATO as a commercial product were licensed by Control Data Corporation (CDC), the manufacturer on whose mainframe computers the PLATO IV system was built. CDC President William Norris planned to make PLATO a force in the computer world, but found that marketing the system was not as easy as hoped. PLATO nevertheless built a strong following in certain markets, and the last production PLATO system did not shut down until 2006, coincidentally just a month after Norris died.

🔗 Aviation 🔗 Soviet Union 🔗 Russia 🔗 Russia/technology and engineering in Russia 🔗 Military history 🔗 Military history/Military aviation 🔗 Aviation/aircraft 🔗 Military history/Cold War 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Military history/Russian, Soviet and CIS military history 🔗 Russia/history of Russia 🔗 Aviation/Soviet aviation 🔗 Soviet Union/Russian, Soviet and CIS military history

The Tupolev Tu-144 (Russian: Tyполев Ту-144; NATO reporting name: Charger) is a retired jet airliner and commercial supersonic transport aircraft (SST). It was the world's first commercial SST (maiden flight – 31 December 1968), the second being the Anglo-French Concorde (maiden flight – 2 March 1969). The design was a product of the Tupolev design bureau, headed by Alexei Tupolev, of the Soviet Union and manufactured by the Voronezh Aircraft Production Association in Voronezh, Russia. It conducted 102 commercial flights, of which only 55 carried passengers, at an average service altitude of 16,000 metres (52,000 ft) and cruised at a speed of around 2,000 kilometres per hour (1,200 mph) (Mach 1.6).

The prototype's first flight was made on 31 December 1968, near Moscow from Zhukovsky Airport, two months before the first flight of Concorde. The Tu-144 first went supersonic on 5 June 1969 (Concorde first went supersonic on 1 October 1969), and on 26 May 1970 became the world's first commercial transport to exceed Mach 2. The aircraft used a new construction technique which resulted in large unexpected cracks, which resulted in several crashes. A Tu-144 crashed in 1973 at the Paris Air Show, delaying its further development. The aircraft was introduced into commercial service on 26 December 1975. In May 1978, another Tu-144 (an improved version, the Tu-144D) crashed on a test flight while being delivered. The aircraft remained in use as a cargo aircraft until 1983, when the Tu-144 commercial fleet was grounded. The Tu-144 was later used by the Soviet space program to train pilots of the Buran spacecraft, and by NASA for supersonic research until 1999, when the Tu-144 made its last flight (26 June 1999).

🔗 Philosophy 🔗 Philosophy/Aesthetics 🔗 Japan 🔗 Japan/Culture

In traditional Japanese aesthetics, wabi-sabi (侘寂) is a world view centered on the acceptance of transience and imperfection. The aesthetic is sometimes described as one of beauty that is "imperfect, impermanent, and incomplete". It is a concept derived from the Buddhist teaching of the three marks of existence (三法印, sanbōin), specifically impermanence (無常, mujō), suffering (苦, ku) and emptiness or absence of self-nature (空, kū).

Characteristics of the wabi-sabi aesthetic include asymmetry, roughness, simplicity, economy, austerity, modesty, intimacy, and appreciation of the ingenuous integrity of natural objects and processes.

🔗 Anthropology 🔗 Palaeontology 🔗 Extinction 🔗 Indonesia 🔗 Archaeology 🔗 Mammals 🔗 Evolutionary biology 🔗 Human Genetic History 🔗 Primates 🔗 Southeast Asia

Homo floresiensis ("Flores Man"; nicknamed "hobbit") is a pygmy archaic human which inhabited the island of Flores, Indonesia, until the arrival of modern humans about 50,000 years ago.

The remains of an individual who would have stood about 1.1 m (3 ft 7 in) in height were discovered in 2003 at Liang Bua on the island of Flores in Indonesia. Partial skeletons of nine individuals have been recovered, including one complete skull, referred to as "LB1". These remains have been the subject of intense research to determine whether they represent a species distinct from modern humans; the dominant consensus is that these remains do represent a distinct species due to genetic and anatomical differences.

This hominin had originally been considered remarkable for its survival until relatively recent times, only 12,000 years ago. However, more extensive stratigraphic and chronological work has pushed the dating of the most recent evidence of its existence back to 50,000 years ago. The Homo floresiensis skeletal material is now dated from 60,000 to 100,000 years ago; stone tools recovered alongside the skeletal remains were from archaeological horizons ranging from 50,000 to 190,000 years ago.

🔗 Astronomy

Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a program which utilizes high-altitude balloon instrument package intended to measure the heating of the universe by the first stars and galaxies after the big bang and search for the signal of relic decay or annihilation. In July 2006 a strong residual radio source was found using the radiometer, approximately six times what is predicted by theory. This phenomenon is known as "space roar" and remains an unsolved problem in astrophysics.

ARCADE has been funded by the NASA's Science Mission Directorate under the Astronomy and Physics Research and Analysis Suborbital Investigation program. The program is composed of a team led by Alan Kogut of NASA's Goddard Space Flight Center. ARCADE was launched from NASA's Columbia Scientific Balloon Facility in Palestine, Texas, conducted under the auspices of the Balloon Program Office at Wallops Flight Facility. The balloon flew to an altitude of 120,000 feet (37 km), viewing about 7% of the sky during its observations.

The instrument is designed to detect radiation at centimeter wavelengths. The craft contained seven radiometers which were cooled to 2.7 K (−270.45 °C; −454.81 °F) using liquid helium, with the intent to measure temperature differences as small as 1/1000 of a degree against a background which is only 3 K (−270.15 °C; −454.27 °F). The optics in the instrument package were placed near the top of the dewar flask which cooled them in order to prevent the instruments from seeing the walls of the container, thereby simplifying the processing of the observational data. This design choice necessitated the use of superfluid pumps in order to drench the radiometers in liquid helium. The design also utilized heaters in order to create a cloud of helium gas, in place of using a (relatively warm) window, which also simplified processing of the observational data.

🔗 Russia 🔗 Literature 🔗 Russia/performing arts in Russia 🔗 Russia/language and literature of Russia

Chekhov's gun (Russian: Чеховское ружьё) is a dramatic principle that states that every element in a story must be necessary, and irrelevant elements should be removed. Elements should not appear to make "false promises" by never coming into play. The statement is recorded in letters by Anton Chekhov several times, with some variation:

• "Remove everything that has no relevance to the story. If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. If it's not going to be fired, it shouldn't be hanging there."
• "One must never place a loaded rifle on the stage if it isn't going to go off. It's wrong to make promises you don't mean to keep." Chekhov, letter to Aleksandr Semenovich Lazarev (pseudonym of A. S. Gruzinsky), 1 November 1889. Here the "gun" is a monologue that Chekhov deemed superfluous and unrelated to the rest of the play.
• "If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." From Gurlyand's Reminiscences of A. P. Chekhov, in Teatr i iskusstvo 1904, No. 28, 11 July, p. 521.

Ernest Hemingway mocked the interpretation given by English instructors to the principle. He gives in his essay "The Art of the Short Story" an example of two characters that are introduced and then never again mentioned in his short story "Fifty Grand". Hemingway valued inconsequential details, but conceded that readers will inevitably seek symbolism and significance in these inconsequential details.