1. A is usually greater than the resonance linewidth and is defined by the frequencies at which the resonance scattering rate equals the boundary scattering rate.
2. A more detailed description of these will be given by the author in ‘Non-Equilibrium Phonons in Non-metallic crystals’. (North -Holland, Amsterdam) W.Eisenmenger and A.A. Kaplyanskii.
3. R.Berman, J.C.F. Brock and D.J. Huntley: Phys.Lett. 3, 310 (1963).
4. B.R. Anderson and L.J. Challis: J. Phys C: Sol. State Phys.$, 1475 (1975), L. J. Challis and M.N. Wybourne: J. Phys.0: Sol. State Phys.12, L711 (1979).
5. L.J. Challis and D.L. Williams: J Phys C: Sol. State Phys. 10, L621 (1977).