1. A. V. Shibaeva, Izy. VUZ. Fizika [Soviet Physics Journal], no. 6, 39, 1965.
2. P. T. Kozyrev, Zh. tekh. fiz.,26, no. 2, 1956.
3. L. Aliyarova, Dissertation, Azerbaijan State University, 1958.
4. H. Rabenhorst and J. Raab, Ann. Physic, 4, no. 6?8, 352?359, 1959.
5. W. Ludwig and F. Eckart, Z. f. Physik, 162, no. 2, 127?141, 1961.