1. Assistant Professor Department of Mathematics, COMSATS Institute of Information Technology, Kamra Road, 43600 Attock, Pakistan e-mail:
2. Rtd. Professor Department of Mathematics, University of Dhaka, 1000 Dhaka, Bangladesh e-mail:
3. Postdoctoral Research Fellow School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia e-mail: ;