1. Department of Mathematics, University of Pune, Pune 411007, India
2. Department of Mathematics, Shivaji University, Kolhapur 416004, India
3. Department of Mathematics and Computer Science, Faculty of Arts and Sciences, Cankaya University, 06530 Ankara, Turkey
4. Institute of Space Sciences, P.O. Box, MG-23, R 76900, Magurele-Bucharest, Romania
5. Department of Bioengineering, University of Illinois, 851 S. Morgan St., Chicago 60607, USA