1. Bar’yakhtar, V.G., Ivanov, B.A., and Chetkin, M.V., Usp. Fiz. Nauk, 1985, vol. 146, p. 417.
2. Chetkin, M.V., Kuz’menko, A.P., Gadetskii, S.N., et al., Pis’ma Zh. Eksp. Teor. Fiz., 1983, vol. 37, p. 223.
3. Chetkin, M.V., Shcherbakov, Yu.I., Gadetskii, S.N., and Tereshchenko, V.D., Zh. Tekhn. Fiz., 1985, vol. 55, p. 207.
4. Chetkin, M.V., Lykov, V.V., and Tereshchenko, V.D., Fiz. Tverd. Tela, 1990, vol. 32, p. 939.
5. Kim, P.D. and Khvan, D.Ch., Fiz. Tverd. Tela, 1982, vol. 24, p. 2300.