06413_01 - A aa See lava AAS See atomic absorption spectroscopy ab A prex attached to the name of a practical electrical unit to provide a name for

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A aa See lava . AAS See atomic absorption spec- troscopy . ab- A pre Ü x attached to the name of a practical electrical unit to provide a name for a unit in the electromagnetic system of units ( see electromagnetic units ), e.g. abampere, abcoulomb, abvolt. The pre Ü x is an abbreviation of the word ‘absolute’ as this system is also known as the abso- lute system . Compare stat- . In modern practice both absolute and electrostatic units have been replaced by * SI units. abdomen The posterior region of the body trunk of animals. In vertebrates it contains the stomach and intestines and the organs of excretion and reproduction. It is particularly well de Ü ned in mam- mals, being separated from the * thorax by the * diaphragm. In many arthropods, such as insects and spiders, it may be seg- mented. Abelian group See group . aberration 1. (in optics) A defect in the image formed by a lens or curved mirror. In chromatic aberration the image formed by a lens (but not a mirror) has coloured fringes as a result of the different extent to which light of different colours is re- fracted by glass. It is corrected by using an * achromatic lens. In spherical aberra- tion , the rays from the object come to a focus in slightly different positions as a result of the curvature of the lens or mir- ror. For a mirror receiving light strictly parallel with its axis, this can be cor- rected by using a parabolic surface rather than a spherical surface. Spherical aberra- tion in lenses is minimized by making both surfaces contribute equally to the ray deviations, and can (though with re- duced image brightness) be reduced by the use of diaphragms to let light pass only through the centre part of the lens. See also astigmatism ; coma . 2. (in astron- omy) The apparent displacement in the position of a star as a result of the earth’s motion round the sun. Light appears to come from a point that is slightly dis- placed in the direction of the earth’s mo- tion. The angular displacement α = v / c , where v is the earth’s orbital velocity and c is the speed of light. abiogenesis The origin of living from nonliving matter, as by * biopoiesis. See also spontaneous generation . abiotic factor Any of the nonliving fac- tors that make up the abiotic environ- ment in which living organisms occur. They include all the aspects of climate, geology, and atmosphere that may affect the biotic environment. Compare biotic factor . abomasum The fourth and Ü nal cham- ber of the stomach of ruminants. It leads from the * omasum and empties into the small intestine. The abomasum is re- ferred to as the ‘true stomach’ as it is in this chamber that protein digestion oc- curs, in acidic conditions. See ruminantia . ABO system One of the most impor- tant human * blood group systems. The system is based on the presence or ab- sence of * antigens A and B on the surface of red blood cells and of * antibodies against these in blood serum. A person whose blood contains either or both these antibodies cannot receive a transfu- sion of blood containing the correspond-
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This note was uploaded on 05/29/2009 for the course CIVIL ENG 12345 taught by Professor Xhfxfh during the Spring '09 term at Amirkabir University of Technology.

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06413_01 - A aa See lava AAS See atomic absorption spectroscopy ab A prex attached to the name of a practical electrical unit to provide a name for

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