1. V. V. Afrosimov, Yu. S. Gordeev, A. N. Zinov’ev, et al., JETP Lett. 24, 28 (1976).
2. V. V. Afrosimov, G. G. Meskhi, N. N. Tsarev, and A. P. Shergin, Sov. Phys. JETP 57, 263 (1983).
3. A. Z. Devdariani, V. N. Ostrovskii, and Yu. N. Sebyakin, Sov. Phys. JETP 46, 215 (1977).
4. J. Eichler, U. Wille, B. Fastrup, et al., Phys. Rev. A 14, 707 (1976).
5. V. K. Nikulin and N. A. Guschina, J. Phys. B 11, 3553 (1978).