06413_03 - C C A high-level general-purpose computer...

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C C A high-level general-purpose computer language developed in 1972. It is fast and can be used as an alternative to assembly language, with which it shares some fea- tures. It was superseded in the mid-1980s by an object-oriented version known as C++, which is better suited to the design of modular programs. cadmium Symbol Cd. A soft bluish metal belonging to * group 12 (formerly IIB) of the periodic table; a.n. 48; r.a.m. 112.41; r.d. 8.65; m.p. 320.9 ° C; b.p. 765 ° C. The element’s name is derived from the ancient name for calamine, zinc carbon- ate ZnCO 3 , and it is usually found associ- ated with zinc ores, such as sphalerite (ZnS), but does occur as the mineral greenockite (CdS). Cadmium is usually produced as an associate product when zinc, copper, and lead ores are reduced. Cadmium is used in low-melting-point al- loys to make solders, in Ni–Cd batteries, in bearing alloys, and in electroplating (over 50%). Cadmium compounds are used as phosphorescent coatings in TV tubes. Cadmium and its compounds are extremely toxic at low concentrations; great care is essential where solders are used or where fumes are emitted. It has similar chemical properties to zinc but shows a greater tendency towards com- plex formation. The element was discov- ered in 1817 by F. Stromeyer. cadmium cell See weston cell . cadmium sulphide A water-insoluble compound, CdS; r.d. 4.82. It occurs natu- rally as the mineral greenockite and is used as a pigment and in semiconductors and Û uorescent materials. caecum A pouch in the alimentary canal of vertebrates between the * small intestine and * colon. The caecum (and its * appendix) is large and highly developed in herbivorous animals (e.g. rabbits and cows), in which it contains a large popu- lation of bacteria essential for the break- down of cellulose. In humans the caecum is a * vestigial organ and is poorly devel- oped. caesium Symbol Cs. A soft silvery-white metallic element belonging to * group 1 (formerly IA) of the periodic table; a.n. 55; r.a.m. 132.905; r.d. 1.88; m.p. 28.4 ° C; b.p. 678 ° C. It occurs in small amounts in a number of minerals, the main source being carnallite (KCl.MgCl 2 .6H 2 O). It is ob- tained by electrolysis of molten caesium cyanide. The natural isotope is caesium– 133. There are 15 other radioactive iso- topes. Caesium–137 (half-life 33 years) is used as a gamma source. As the heaviest alkali metal, caesium has the lowest ion- ization potential of all elements, hence its use in photoelectric cells, etc. caesium clock An * atomic clock that depends on the energy difference be- tween two states of the caesium–133 nu- cleus when it is in a magnetic Ü eld. In one type, atoms of caesium–133 are irra- diated with * radio-frequency radiation, whose frequency is chosen to correspond to the energy difference between the two states. Some caesium nuclei absorb this radiation and are excited to the higher state. These atoms are de Û ected by a fur- ther magnetic Ü eld, which causes them to hit a detector. A signal from this detector is fed back to the radio-frequency oscilla- tor to prevent it drifting from the reso- nant frequency of 9 192 631 770 hertz. In
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