1. Stolen, R.H., Physics and Chemistry of Glasses, 1970, vol. 11, p. 43.
2. Amorphous Solids: Low Temperature Properties, Phillips, W.A., Ed., Berlin: Springer-Verlag, 1981.
3. Karpov, V.G. et al., Zh. Eksp. Teor. Fiz., 1983, vol. 57, p. 439.
4. Duval, E. et al., J. Phys.: Condens. Matter, 1990, vol. 2, 10 227.
5. Buchenau, U. et al., Phys. Rev. B: Condens. Matter Mater. Phys., 1992, vol. 46, p. 2798.