1. K. L. Lowenstein,Phys. Chem. Glasses 2 (1961) 69.
2. A. Makishima andJ. D. Mackenzie,J. Non-Cryst. Solids 12 (1973) 35.
3. Idem, ibid. 17 (1975) 147.
4. C. Zwikker, ?Physical properties of Solid Materials? (Interscience, New York, 1954) p. 91.
5. O. L. Anderson, in ?Physical Acoustics IIIB? edited by W. P. Mason (Academic, New York, 1965) pp. 43, 64?75.