1. E. Fermi, Phys. Rev.,57, 485 (1940).
2. I. M. Frank and I. E. Tamm, Dokl. Akad. Nauk SSSR,14, 107 (1937).
3. V. L. Ginzburg and I. M. Frank, Zh. Eksp. Teor. Fiz.,16, No. 1, 15 (1946).
4. L. D. Landau and E. M. Lifshits, Electrodynamics of Continuous Media, Pergamon (1960).
5. M. Schonberg, Nuovo Cimento,8, 159 (1951).