1. School of Mathematical and Statistical Sciences, University of Galway, University Road, H91 TK33 Galway, Ireland
2. School of Mathematics, Iran University of Science and Technology, Narmak, Tehran 13114-16846, Iran
3. Department of Mathematics, Science Faculty, Firat University, Elazig 23119, Turkey
4. Department of Medical Research, China Medical University, Taichung 40402, Taiwan