We construct a kinetic equation simulating the behavior of degenerate quantum Bose gases with the collision rate proportional to the molecule velocity. We obtain an analytic solution of the half--space boundary--value Smoluchowski problem of the temperature jump at the interface between the degenerate Bose gas and the condensed phase.
A solution is obtained for Kramers’ problem of isothermal slip of a quantum Bose gas along a flat solid surface. The reflection of molecules from the wall is assumed to be specular-diffuse. A model kinetic equation with a collision integral in the τ-model form and collision frequency proportional to the molecular velocity is used. The dependence of the slip velocity on the value of a parameter equal to the ratio of the chemical potential to the product of Boltzmann’s constant by the absolute temperature is analyzed.
,Moscow State Regional University, 105005, Moscow, Radio st., 10–A(Dated: January18,2010)The linearized kinetic equation modelling behaviour of thedegenerate quantumbose - gas withthe frequency of collisions depending on momentum of elementary excitations is constructed.The general case of dependence of the elementary excitations energy on momentum according toBogolyubov formula is considered. The analytical solution of the half–space boundary problemon temperature jump on border of degenerate bose - gas in the presence of a Bose — Einsteincondensateisreceived. ExpressionforKapitsaresistanceisreceived.Keywords: degenerate quantum Bose gas, collision integral, Bose — Einstein condensate,Bogolyubovexcitations,temperaturejump,Kapitsaresistance.
The relaxation kinetics of an ideal Bose gas coupled to a phonon bath at temperatures below or equal to the critical temperature Tc is given within a unique scenario. During the first transient stage, which lasts a few characteristic scattering times, the initial distribution disappears. The following nonexponential relaxation towards a quantum degenerate equilibrium state with a Bose-Einstein condensate is a slow adiabatic process. For this second kinetic stage we find an analytic generic solution of the Boltzmann equation. The generic solution is independent of the initial distribution and completely defined by the ratio Tc/Tb of the critical and bath temperatures.
Distribution of mass velocity of quantum Bose-gas in half-space is received. Far from half-space border the gradient of mass velocity is set. The mass velocity of Bose-gas directly at a wall is found also. All results are received on basis of the analytical solution of Kramer's problem. The analysis of dependence of velocity coefficients from parametre quantity is carried out. The parametre representing the relation of chemical potential to product of Boltzmann constant on absolute temperature. Graphic comparison of coefficients of velocity Bose- and Fermi-gases is resulted.
We study a quantum Boltzmann-Condensation system that describes the evolution of the interaction between a well formed Bose-Einstein condensate and the quasi-particles cloud. The kinetic model is valid for a dilute regime at which the temperature of the gas is very low compared to the Bose-Einstein condensation critical temperature. In particular, our system couples the density of the condensate from a Gross-Pitaevskii type equation to the kinetic equation through the dispersion relation in the kinetic model and the corresponding transition probability rate from pre to post collision momentum states. We rigorously show the following three properties (1) the well-posedness of the Cauchy problem for the system in the case of a radially symmetric initial configuration, (2) find qualitative properties of the solution such as instantaneous creation of exponential tails and, (3) prove the uniform condensate stability related to the initial mass ratio between condensed particles and quasi-particles. The stability result from (3) leads to global in time existence of the initial value problem for the quantum Boltzmann-Condensation system.
We derive a kinetic theory for a spin-1/2 Bose-condensed gas of two-level atoms at finite temperatures. The condensate dynamics is described by a generalized Gross-Pitaevskii equation for the two-component spinor order parameter, which includes the interaction with the uncondensed fraction. The noncondensate atoms are described by a quantum kinetic equation, which is a generalization of the spin kinetic equation for spin-polarized quantum gases to include couplings to the condensate degree of freedom. The kinetic equation is used to derive hydrodynamic equations for the noncondensate spin density. The condensate and noncondensate spins are coupled directly through the exchange mean field. Collisions between the condensate and noncondensate atoms give rise to an additional contribution to the spin diffusion relaxation rate. In addition, they give rise to mutual relaxation of the condensate and noncondensate due to lack of local equilibrium between the two components.