Tham khảo tài liệu 'dictionary of material science and high energy physics part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ference of n 2 with the aid of a quarter-wave plate. The doubly refracting transparent plates transmit light with different propagation velocities in two perpendicular directions. quasi-Boltzmann distribution of fluctuations Any variable x of a thermodynamic system that is unconstrained will fluctuate about its mean value. The distribution of these fluctuations may under certain conditions reduce to an expression in terms of the free energy or other such thermodynamic potentials of the thermodynamic system. For example the fluctuations in x of an isolated system held at constant temperature are given by the expression f x e-F x kT where f x is the fluctuation distribution and F x is the free energy both as a function of the system variable x. Under these conditions the fluctuation distribution is said to follow a quasi-Boltzmann distribution. quasi-classical distribution Representations of the density operator for the electromagnetic field in terms of coherent rather than photon number states. Two such distributions are given by the Wigner function W a and the Q-function Q a . The Q-function is defined by Q a n a p a where a is a coherent state. The Wigner function W p q is characterized by the position q and momentum p of the electromagnetic oscillator and is defined by 1 W p q 2n dye iypp q - y p q y J x W p q is quasi-classical owing to the lack of positive definiteness for such distributions. quasi-continuum Used to describe quantum mechanical states which do not form a continuous band but are very closely spaced in energy. quasi-geostrophic flow Nearly geostrophic flow in which the time-dependent forces are much smaller than the pressure and Coriolis forces in the horizontal plane. quasi-linear approximation A weakly non-linear theory of plasma oscillations which uses perturbation theory and the random phase approximation to find the time-evolution of the plasma state. quasi-neutrality The condition that the electron density is almost exactly equal to the sum
