Sound propagation relaxation processes

Lindsay, R. B. (1982). Relaxation processes in sound propagation in fluids a historical survey. In Physical acoustics XVI (ed. W. P. Mason and R. N. Thurston), pp. 1-36. Academic Press, London. [76, 77]... 

TS involves the measurement of the sound intensity emitted by a sample as a function of temperature. Sound emission originates from the release of thermal stresses in the sample, such as movement of dislocations, generation and propagation of cracks, nucleation of new phases, relaxation processes, and discontinuous changes in physical properties. For example, at a glass transition temperature, a discontinuous change in free volume generates elastic waves... 

In the case of liquid lattices, the difficulty in adequately characterizing their structures renders them unsuitable for treatment by quantum mechanics. Accordingly, liquid lattices are often treated classically by considering the effects of molecular rotations and translations, with characteristic correlation times, r, on time-dependent magnetic and electric fields that may influence relaxation processes. Accordingly, it becomes convenient to depart from the phonon description of sound and adopt a classical view of this as the sinusoidal propagation of a pressure wave through a medium. 

The frequencies (70 and / °A (jj have to be determined for equivalent symmetry sound propagation directions as well as for the same polarization. So far the application of eq. (4) has not been restricted to isotropic materials. If hypersonic relaxation processes are active, two different cases have to be taken into account ... 

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