Volume 25 (1970)
The absorption and dispersion of sound due to dissipative phenomena such as diffusion, heat conduction and viscous flow have been investigated by Herzfeld, Litovitz and others. Whereas in these studies the total energy of the carrier system remains constant, we consider the case that it is changing. It turnes out that the wavelength X remains constant, while all other wave characteristics become time depend and can be connected with the usual sound velocity of the carrier system.The change in energy density takes place via the potential energy. Thus the original balance between potential and kinetic energy is disturbed. Modulation vibrations of the wave amplitudes around the time averages arise. In addition dephasing of the pressure and density components with respect to the acoustic velocity takes place. The phasevelocities are disturbed too. They differ from time dependence of c(t).These differences are running asymptotically towards zero, i. e. after a longer period of time a phase step remains of the total wave system. This phase step is negative for increasing energy of the carrier system and positive for decreasing energy. The value of the phase step is proportional to the wavelength λ, i. e. systems of this kind show dispersion.
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