Tham khảo tài liệu 'dictionary of material science and high energy physics part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | X X 1 X 2 E x 3 E2. The factor x 2 is referred to as the second order susceptibility as it results in a term in the polarization second order in the applied field. This factor is only nonzero for materials with no inversion symmetry. For a material that is not isotropic the second order susceptibility is a tensor. second quantization Ordinary Schrodinger equation of one particle or more particles are described within a Hilbert space of a single particle or a fixed particle numbers. The single electron Schrodinger equation written by the position representation can be interpreted as the equation for the classical field of electrons we need to quantize the field. Then the field variable or in short the wave function is regarded as a set of an infinite number of operators on which commutation rules are imposed. This produces a formalism in which particles may be created and annihilated. We have to extend the Hilbert space of fixed particle numbers to that of arbitrary number particles. Seebeck effect The existence of a temperature gradient in a solid causes a current flow as carriers migrate along or against the gradient to minimize their energy. This effect is known as the Seebeck effect. The thermal gradient is thus equivalent to an electric field that causes a drift current. Using this analogy one can define an electric field caused by a thermal gradient called a thermoelectric field . This electric field is related to the thermal gradient according to E QV T where E is the electric field V T is the thermal gradient and Q is the thermopower. seiche Standing wave in a lake. For a lake of length L and depth H allowed wavelengths are given by 2L k 2n 1 where n 0 1 2 . selection rules 1 Not all possible transitions between energy levels are allowed with a given interaction. Selection rules describe which transitions are allowed typically described in terms of possible changes in various quantum numbers. Others are forbidden by that interaction but perhaps not by .
