1. P. L. Bhatnagar,Nonlinear Waves in One-Dimensional Dispersive Systems, Oxford (1979);
2. A. V. Kulakov and A. A. Rumyautsev,Introduction to the Physics of Nonlinear Processes [in Russian], Nauka, Moscow (1988).
3. S. L. McCall and E. L. Hahn,Phys. Rev.,183, 457 (1969).
4. N. S. Shiren,Phys. Rev. B,2, 2471 (1970).
5. G. T. Adamashvili,Zh. Eksp. Teor. Fiz.,92, 2202 (1987).