1. R. A. Uritam, Phys. Rev.,D6, 3233, 1972.
2. P. Nuthakki and R. A. Uritam, Phys. Rev.,D8, 3196, 1973.
3. G. K. Greenhut and G. W. Intemann, Phys. Rev.,D14, 764, 1976.
4. R. Purushottamudu and P. Nuthakki, Z. Phys.,C14, 257, 1982.
5. P. Nuthakki and R. Purushottamudu, Phys. Rev.D27, 650, 1983.