1. Department of Economics, College and Graduate School of Arts & Sciences, Boston University, Boston, USA
2. Business College, Guangzhou College of Technology and Business, Guangzhou, P. R. China
3. Department of Mathematics, Faculty of Science, Shahid Rajaee Teacher Training University, Tehran 16785-136, Iran
4. Department of Mathematics, Faculty of Science, Qom University of Technology, Qom, Iran
5. Department of Mathematical Sciences, University of South Africa, UNISA0003, South Africa
6. Department of Medical Research, China Medical University Hospital, China Medical University, Taichung 110122, Taiwan
7. School of Economics, Tianjin University of Commerce, Tianjin, P. R. China