1. Department of Mathematics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore-641 020, India
2. Department of Mathematical Sciences, UAE University, P.O. Box 15551, Al-Ain, UAE
3. Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science and Technology, (KAUST), Thuwal 23955-6900, Saudi Arabia