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The Probert Encyclopaedia of Science & Technology

U BOLT

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A U bolt is a bolt shaped like the letter U and having threads and a nut at each end. U bolts are used for fixing cylindrical objects to flat surfaces, such as pipes and aerial masts to walls.
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UART

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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UFO

UFO (United Functions and Objects) is a computer programming language that was developed by John Seargant at Manchester University for parallel computations. UFO has both procedural and object-oriented capabilities.
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ULTRA VIOLET

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

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

Ultrasonic is a term referring to sound waves higher in frequency than 15 kHz.
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ULTRAVIOLET

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

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

Umbra is the astrological term for the shadow cast by a planet or satellite.
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UMSDOS

Umsdos was an extended MS-DOS computer filesystem used by Linux. It added the capability for long filenames, UID/GID, POSIX permissions, and special files (devices, named pipes, and so on) under the MS-DOS filesystem, without sacrificing compatibility with DOS.
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UNDECAGON

An undecagon is an eleven-sided polygon.
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UNDER-SHOT WHEEL

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An under-shot wheel is a form of water-wheel in which the wheel is driven by the flow of water passing beneath the wheel.
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UNDERSHOT-WHEEL

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An undershot-wheel is a form of water-wheel having a number of float-boards disposed on its circumference, and turned round by the moving force of a stream of water acting on the float-boards at its lowest part. In this wheel the water acts entirely by its momentum.
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UNDULATORY THEORY

In physics, undulatory theory was the former theory prevalent around 1900 which regarded light as a mode of motion generated by molecular vibrations in the luminous source, and propagated by undulations in the subtle medium known as the ether, then presumed to pervade all space and to occupy the intervals which separate the molecules or atoms of bodies. When these undulations reached and acted on the nerves of our retina they were supposed to produce in us the sensation of light. The only other theory of light which at the time opposed this was variously called the corpuscular, emission, or material theory, and this supposed light to consist of material particles, emitted from the source, and projected in straight lines in all directions with a velocity which continued uniform at all distances, and was the same for all intensities. The undulatory theory was, however, generally adopted by physicists at the time as fact.
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UNGULA

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Ungula is the name given to a section of a cone, cylinder, or other solid of revolution cut off by a plane oblique to the base, and so named from its supposed resemblance to a horse's hoof.
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UNICODE

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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UNIT

In arithmetic, a unit is the least whole number, or one, represented by the figure 1. Every other number is an assemblage of units. This definition is applicable to fractions as well as to whole numbers. In mathematics and physics a unit is any known determinate quantity by the constant repetition of which any other quantity of the same kind is measured. It is not itself one, but is a length, or a surface, or a solid, or a weight, or a time, as the case may be, while 1 is only a numerical symbol.
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UNIVERSAL INDICATOR PAPER

Universal Indicator Paper is a special test paper used for testing the pH of a solution, very similar to litmus paper. Upon contact with a liquid, the Universal Indicator Paper changes colour, the resultant colour being compared with a chart to indicate the pH value of the liquid under test, ranging from a pH of 1 (very acid) through to 11 (very alkaline) the colour eanging from a deep marron red through orrange, pale yellow, olive green, lime green (neutral pH 7) through turqioise (slightly alkali) to a deep dark blue (pH 11 very alkali).
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UNIVERSAL JOINT

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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

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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UNSATURATED COMPOUNDS

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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UNSATURATED SOLUTION

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

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

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

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

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

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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USB

In computing, USB (Universal Serial Bus) is a hardware interface designed initially for low-speed devices such as keyboards, mice, joysticks, printers, scanners, modems etc. The original USB interface (known as USB 1 or USB 1.1) has a transfer rate of 1.5 MB per second and appeared in 1997. A faster version of USB, known as USB 2 later appeared with a data transfer rate of 60 MB per second, and around 2008 USB 3 with a transfer rate of 4.8 GB per second was introduced but was still only slowly being taken up by computer manufacturers several years later. All USB interfaces are backwards compatible, so a device with a USB 3 interface can be connected to a computer with a USB 2 or USB 1.1 socket, though the data will only be transferred at the lower speed supported by the computer's older, slower USB interface.

The USB interface also distributes power from the computer to the peripheral (if required) and as such allows many lower power peripherals to be powered direct from the USB port negating the need for a separate power supply, and allowing cell phones to be recharged by plugging them into the computer's USB port.
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USENET

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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USER INTERFACE

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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