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🔗 Correction and Detention Facilities

This is a list of countries by incarceration rate.

🔗 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.

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🔗 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.

🔗 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.

🔗 Languages 🔗 Anthroponymy

An aptronym, aptonym or euonym is a personal name aptly or peculiarly suited to its owner.

🔗 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).