  The method of the nonequilibrium statistical operator developed by D. N.
Zubarev is employed to analyse and derive generalized transport and kinetic
equations. The degrees of freedom in solids can often be represented as a few
interacting subsystems (electrons, spins, phonons, nuclear spins, etc.).
Perturbation of one subsystem may produce a nonequilibrium state which is then
relaxed to an equilibrium state due to the interaction between particles or
with a thermal bath. The generalized kinetic equations were derived for a
system weakly coupled to a thermal bath to elucidate the nature of transport
and relaxation processes. It was shown that the "collision term" had the same
functional form as for the generalized kinetic equations for the system with
small interactions among particles. The applicability of the general formalism
to physically relevant situations is investigated. It is shown that some known
generalized kinetic equations (e.g. kinetic equation for magnons, Peierls
equation for phonons) naturally emerges within the NSO formalism. The
relaxation of a small dynamic subsystem in contact with a thermal bath is
considered on the basis of the derived equations. The Schrodinger-type equation
for the average amplitude describing the energy shift and damping of a particle
in a thermal bath and the coupled kinetic equation describing the dynamic and
statistical aspects of the motion are derived and analysed. The equations
derived can help in the understanding of the origin of irreversible behavior in
quantum phenomena.
