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Dictionary of Material Science and High Energy Physics Part 10

Tham khảo tài liệu 'dictionary of material science and high energy physics part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | cillator is one of the most commonly occurring systems in physics either exactly or as an approximation. oscillatory effects Illustrated by two examples oscillatory effects in a magnetic field and electron density oscillations. The oscillations of the magnetic susceptibility at low temperature are due to the emptying of the Landau levels as the magnetic field is increased. The periodicity of the oscillations are the reciprocal of the magnetic field 1 B. Whenever 1 B changes by 2ne hSc where e is the electron charge S is the area of the orbit in k space and c is the speed of light the number of occupied Landau levels changes by one. Actually the diamagnetic susceptibility of the electron gas consists of a constant term which equals -1 3 the Pauli susceptibility plus an oscillatory part. The electron density oscillations known as Friedel s oscillations result from electron scattering by a surface barrier an edge dislocation or an impurity. The amplitude of the oscillation is proportional to the backward scattering amplitude at the Fermi energy and has the form cos 2kfx 0 xn where kf is the Fermi wave vector x is the distance from the scatterer 0 is a phase angle and n 3 for an impurity 3 dimensions 5 2 for a dislocation 2 dimensions and 2 for a surface barrier 1 dimension . Oseen approximation Approximation to Stoke s flow about a sphere such that the inertial advective terms are linearized rather than neglected altogether thus improving the accuracy of the solution in the far field. The resulting equation is pU -V p V 2u dx where u U u i v j w k. Oseen vortex See Lamb-Oseen vortex. osmosis The diffusion of a solvent usually water through a semi-permeable membrane from a solution of low ion concentration to one of a high ion concentration. The thermodynamic driving force for osmosis acts in the opposite direction to the ion diffusion gradient so as to equalize the concentrations in the two solutions. osmotic pressure The pressure that when applied to a solution .