Resonant interaction of acoustic waves in nonequilibrium gases

Nonlinear equations are derived, which describe the evolution of two-dimensional acoustic disturbances in a thermodynamically nonequilibrium gas. The characteristic features of parametric interaction of wave packets in acoustically active media are analyzed. The transmission band under conditions of critical and noncritical matching and the threshold of parametric amplification are determined. Conditions are obtained, under which a giant parametric pulse may form in an acoustically active medium, with the amplitude of this pulse exceeding that of a pumping wave.