A nonequilibrium ensemble formalism: Criterion for truncation of description

In the framework of a nonequilibrium statistical ensemble formalism, consis ting of the so-called Nonequilibrium Statistical Operator Method, we discus s the question of the choice of the space of thermohydrodynamic states. We consider in particular the relevant question of the truncation of descripti on (reduction of the dimension of the state space). A criterion for justify ing the different levels of truncation is derived. It depends on the range of wavelengths and frequencies which are the relevant ones for the characte rization, in terms of normal modes, of the thermohydrodynamic motion in a n onequilibrium open system. Applications to the cases of thermal-sensitive r esins and of n-doped polar semiconductors are done, numerical results are p resented, and experimental observation is discussed. (C) 2000 American Inst itute of Physics. [S0021-9606(00)50705-3].