06413_17 - Q QCD See quantum chromodynamics. QED See...

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Q QCD See quantum chromodynamics . QED See quantum electrodynamics . QFD Quantum Û avourdynamics. See electroweak theory . QSG See quasars . QSO See quasars . QSS See quasars . quadrat An ecological sampling unit consisting of a small square area of ground within which all species of inter- est are noted or measurements taken. Quadrats may be spaced over a larger area to form an overall view when a total survey would be impracticable, or they may be used to sample along a * transect. quadrate A paired bone in the upper jaw of bony Ü shes, amphibians, reptiles, and birds that articulates with the lower jawbone. It is absent in mammals, being reduced to a small bone (the incus) in the middle ear ( see ear ossicles ). quadratic equation An equation of the second degree having the form ax 2 + bx + c = 0. Its roots are: x = [– b ±√ ( b 2 – 4 ac )]/2 a . quadrature The position of the moon or an outer planet when the line joining it to the earth makes a right angle with a line joining the earth to the sun. quadrivalent Having a valency of four. qualitative analysis See analysis . qualitative variation See discontinu- ous variation . quality of sound (timbre) The quality a musical note has as a result of the pres- ence of * harmonics. A pure note consists only of the fundamental; however, a note from a musical instrument will have sev- eral harmonics present, depending on the type of instrument and the way in which it is played. For example, a plucked string (as in a guitar) produces a series of har- monics of diminishing intensity, whereas a struck string (as in a piano) produces a series of harmonics of more nearly equal intensity. quantitative analysis See analysis . quantitative inheritance See poly- genic inheritance . quantitative variation See continu- ous variation . quantization The process of construct- ing a quantum theory for a system, using the original classical theory as a basis. The starting point for such a process is to write the * Lagrangian or * Hamiltonian of the classical system. The formulation of the quantum theory for the system can be performed using a formalism such as * matrix mechanics, or * wave mechanics. The application of these methods leads to the conclusion that energy levels in sys- tems, such as atoms, are discrete ( quan- tized ) rather than continuous. Before the discovery of quantum mechanics in the mid 1920s, quantization involved a series of ad hoc postulates for atomic systems, such as the * Bohr theory and its exten- sions. quantum ( pl. quanta ) The minimum amount by which certain properties, such as energy or angular momentum, of a sys- tem can change. Such properties do not, therefore, vary continuously, but in inte- gral multiples of the relevant quantum, and are described as quantized . This con- cept forms the basis of the * quantum theory. In waves and Ü elds the quantum can be regarded as an excitation, giving a particle-like interpretation to the wave or Ü eld. Thus, the quantum of the electro-
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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_17 - Q QCD See quantum chromodynamics. QED See...

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