1. Ia B Zel’dovich, Sov. Phys. JETP 4, 942 (1957) V S Polikanov, Sov. Phys. JETP 25, 882 (1967) T Imbo and U Sukhatme, Am J. Phys. 52, 140 (1984)
2. S M Ikhdair and R Sever, Int. J. Mod. Phys. C18, 1571 (2007)
3. D P Dutta and S Mukherjee, J. Phys. A: Math. Gen. 15, 2368 (1982)
4. J Killingbeck, Phys. Lett. A65, 87(1978);
5. Phys. Lett. A67, 13 (1978)