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UART (Universal Asynchronous Receiver-Transmitter) is a controller chip that processes data coming in and going out of the modem. The 16550 is a modern example.
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Ultra violet (actinic rays) are non-visible light rays of short wave length occurring just beyond the violet end of the spectrum. Ultra violet rays are very destructive to paint and varnish films..
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Ultramarine is a blue pigment derived by grinding the semi-precious stone lapis lazuli. Ultramarine is also produced artificially from a mixture of silica, china clay, sulphur and soda ash, subjected to prolonged calcination. Ultramarine is attacked by acids, but has a good resistance to alkalis. Ultramarine has a good staining strength and opacity in water, but poor opacity and only moderate staining strength in oil.
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Ultrasonic is a term referring to sound waves higher in frequency than 15 kHz.
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Ultraviolet radiation is electromagnetic radiation of a wavelength between about 400 and 10 nm, extending between the visible (light) and X-ray regions of the electromagnetic radiation spectrum.
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Umber is a natural substance comprised of hydrated ferric and manganese oxides with variable proportions of earthy matter. It is used as a brown pigment.
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Umbra is the astrological term for the shadow cast by a planet or satellite.
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An undecagon is an eleven-sided polygon.
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Unicode is a standard of computer character sets that aims to unambiguously represent every known glyph in every human language. Unicode's native encoding is 32 bit (older versions use 16 bits).
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A universal joint is a joint which permits free motion in any direction to the parts joined by it. The term is specifically applied to a joint which can transmit the rotary power of a shaft at an angle.
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UNIX (In the authors' words, 'A weak pun on Multics') is an interactive time-sharing computer operating system originally invented in 1969 by Ken Thompson after Bell Labs left the Multics project, originally so he could play games on his scavenged PDP-7. Dennis Ritchie, the inventor of the programming language C, is considered a co-author of the system. The turning point in UNIX's history came when it was re-implemented almost entirely in C during 1972-1974, making it the first source-portable operating system. UNIX subsequently underwent mutations and expansions at the hands of many different people, resulting in a uniquely flexible and developer-friendly - though not user friendly - environment.
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In chemistry, unsaturated compounds are organic compounds containing double or triple bonds uniting the carbon atoms and are capable of forming addition products. They posess the characteristic property of combining directly with hydrogen to form saturated compounds in which the carbon atoms are joined by single valencies.
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In chemistry, an unsaturated solution is a solution containing less solute than the amount needed to make a saturated solution.
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Upthrust is the upward force exerted upon an object when that object is placed in or floating in liquid. Stone boulders immersed in water have an upthrust on them equal to about two-fifths of their weight, and this explains why boulders can be moved so easily by flood water. In 1952 a flood in Lynmouth, Devon resulted in 20 ton boulders being deposited on the streets. These same boulders, when immersed in water had an apparent weight of only 12 tons.
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Uranium is a silvery, heavy radioactive, polyvalent metallic element that is found especially in pitchblende and Uraninite and exists naturally as a mixture of three radioactive isotopes of mass number 234, 235 and 238 in the proportions of .006%, .71% and 99.28% respectively. Uranium was discovered by Klaproth in 1789, but not isolated until 1840. It has the symbol U.
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Urea is a crystalline substance, soluble in water which occurs in the urine of mammals, birds and reptiles. It was produced artificially by Friedrich Wohler in 1828 by evaporating an aqueous solution of ammonium cyanate. This was the first synthesis of an organic compound from inorganic materials.
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Urethane or ethyl carbamate is a colourless, crystalline substance. It is prepared by heating urea nitrate with alcohol in a sealed tube for several hours, and purifying the product. Urethane was formerly used in medicine as an hypnotic.
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Uric acid is a crystalline substance found normally in small quantities in urine in combination with sodium, potassium, and ammonium as urates. It is present in larger quantity in various diseases, particularly gout. Uric acid is formed from the breaking down of muscular tissue and organs, and in the process of digestion.
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Usenet (from 'Users' Network') is a distributed bulletin board system supported mainly by UNIX computers. It was originally implemented in 1979-1980 by Steve Bellovin, Jim Ellis, Tom Truscott, and Steve Daniel at Duke University, it quickly grew to become international in scope and is now probably the largest decentralized information utility in existence, with over 20000 discussion groups accessible through the Internet.
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In computing, a user interface is the system used to communicate between a computer system and the person using it. Windows is an example of a Graphical
user interface.
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Abbreviations
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