Equations of state of a dilute gas under a heat flux

Thermal and caloric equations of state for a dilute gas under a heat flux are used to provide a possible microscopic interpretation of temperature in nonequilibrium states. Two possible experiments in which this nonequilibrium temperature could be shown are discussed. They include the study of the Doppler broadening of spectral lines, and of the velocity of long sound waves, both in a nonequilibrium situation characterized by a steady heat flux. © 1995 The American Physical Society.