1. Prof., Dept. of Appl. Mathematics, Indian School of Mines, Dhanbad-826 004, India.
2. Dept. of Earthquake Engrg., Univ. of Roorkee, Roorkee-247 667, India.
3. Dept. of Appl. Mathematics, Indian School of Mines, Dhanbad-826 004, India.
4. Dept. of Mathematics, Chas College, Bokaro, India.