1. C. Cattaneo, C. R. Acad. Sci. Paris 247 (1958) 431.
2. P. Vemotte, C. R. Acad. Sci. Paris 246 (1958) 3154.
3. C. C. Ackerman and R. A. Guyer, Ann. Phys. (NY) 50 (1986) 128.
4. S. J. Roger, Phys. Rev. B 3 (1971) 1440
5. S. J. Roger, R. J. von Gutfeld in Physical Acoustics (W. P. Mason, ed.) vol. V, Academic Press, London, 1968.