standard time

Official local time of a region or country. Local mean solar time depends on longitude; it advances by four minutes per degree eastward. The Earth can thus be divided into 24 standard time zones, each approximately 15° in longitude. The actual boundaries of each time zone are determined by local authorities and in many places deviate considerably from 15°. The times in different zones usually differ by an integral number of hours; minutes and seconds are the same. Seealso Greenwich Mean Time.

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Level of material comfort that an individual or group aspires to or may achieve. This includes not only privately purchased goods and services but collectively consumed goods and services such as those provided by public utilities and governments. A standard of living determined for a group such as a country must be examined critically in terms of its constituent values. If the mean value increases over time, but at the same time the rich become richer and the poor poorer, the group may not be collectively better off. Various quantitative indicators can be used as measuring rods, including life expectancy, access to nutritious food and a safe water supply, and availability of medical care.

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In physics, the combination of two theories of particle physics into a single framework to describe all interactions of subatomic particles except those due to gravity (see gravitation). The two theories, the electroweak theory and the theory of quantum chromodynamics, describe the interactions between particles in terms of the exchange of intermediary particles. The model has proved highly accurate in predicting certain interactions, but it does not explain all aspects of subatomic particles. For example, it cannot say how many particles there should be or what their masses are. The search goes on for a more complete theory, and in particular a unified field theory describing the strong, weak, and electromagnetic forces.

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Monetary standard under which the basic unit of currency is defined as a stated quantity of silver. It is usually characterized by the coinage and circulation of silver, unrestricted convertibility of other money into silver, and the free import and export of silver for the settlement of international obligations. No country now operates under a silver standard. In the 1870s most European countries adopted the gold standard, and by the early 1900s only China, Mexico, and a few small countries still used the silver standard. In 1873 the U.S. Treasury stopped coining silver, which led to the Free Silver Movement, but the defeat of William Jennings Bryan ended agitation for free silver in the U.S. Seealso bimetallism.

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Monetary system in which the standard unit of currency is a fixed quantity of gold or is freely convertible into gold at a fixed price. The gold standard was first adopted in Britain in 1821. Germany, France, and the U.S. instituted it in the 1870s, prompted by North American gold strikes that increased the supply of gold. The gold standard ended with the outbreak of World War I in 1914; it was reestablished in 1928, but because of the relative scarcity of gold, most nations adopted a gold-exchange standard, supplementing their gold reserves with currencies (U.S. dollars and British pounds) convertible into gold at a stable rate of exchange. Though the gold-exchange standard collapsed during the Great Depression, the U.S. set a minimum dollar price for gold, an action that allowed for the restoration of an international gold standard after World War II. In 1971 dwindling gold reserves and an unfavourable balance of payments led the U.S. to suspend the free convertibility of dollars into gold, and the gold standard was abandoned. Seealso bimetallism; exchange rate; silver standard.

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Monetary standard or system based on the use of two metals, traditionally gold and silver, rather than one (monometallism). In the 19th century, a bimetallic system defined a nation's monetary unit by law in terms of fixed quantities of gold and silver (thus automatically establishing a rate of exchange between the two metals). The system provided a free and unlimited market for the two metals, imposed no restrictions on the use and coinage of either metal, and made all other money in circulation redeemable in either gold or silver. Because each nation independently set its own rate of exchange between the two metals, the resulting rates of exchange often differed widely from country to country. When the ratio of the official prices proved different from the ratio of prices in the open market, Gresham's law operated in such a way that coins of only one metal remained in circulation. A monometallic system using the gold standard proved more responsive to changes in supply and demand and was widely adopted after 1867. Seealso exchange rate; silver standard.

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in full American Standard Code for Information Interchange.

Data-transmission code used to represent both text (letters, numbers, punctuation marks) and noninput device commands (control characters) for electronic exchange and storage. Standard ASCII uses a string of 7 bits (binary digits) for each symbol and can thus represent 27 = 128 characters. Extended ASCII uses an 8-bit encoding system and can thus represent 28 = 256 characters. While ASCII is still found in legacy data, Unicode, with 8-, 16-, and 32-bit versions, has become standard for modern operating systems and browsers. In particular, the 32-bit version now supports all of the characters in every major language.

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Standard-definition television or SDTV refers to television systems that have a resolution that meets standards but not considered either enhanced definition or high definition. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as analog systems.

In ATSC, SDTV can be broadcast in 704 pixels × 480 lines with 16:9 aspect ratio (40:33 rectangular pixel), 704 pixels × 480 lines with 4:3 aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3 ratio (and square pixels). The refresh rate can be any of 24, 30 or 60 frames per second.

Digital SDTV in 4:3 aspect ratio has the same appearance as the regular analog TV (NTSC, PAL, PAL2, SECAM) minus the ghosting, snowy images and static noises. However, if the reception is poor, one may encounter various other artifacts such as blockiness and stuttering.

Standards that can broadcast digital SDTV include DVB, ATSC and ISDB. The last two were originally developed for HDTV, but they have proved to be more often used for their ability to deliver multiple SD video and audio streams via multiplexing, than to use the entire bitstream for one HD channel.

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution of 720 or 704 format.

Video Format (WxH) Name Pixel aspect ratio (W:H)
(Standard 4:3)
Pixel aspect ratio (W:H)
(Anamorphic 16:9)
720×576 576i 16:15 64:45 Used on D1/DV PAL
704×576 576p 12:11 16:11 Used on EDTV PAL
720×480 480i 8:9 32:27 Used on DV NTSC
720×486 480i 8:9 32:27 Used on D1 NTSC (ITU-R 601)
704×480 480p 10:11 40:33 Used on EDTV NTSC


In the USA, SDTV refers to digital television broadcast in 4:3 aspect ratio, the same aspect ratio as NTSC signals. When a television set is labeled "SDTV", this means that the set includes an ATSC tuner, but scans its picture in the same 480i pattern used in NTSC.

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