1. Institute of Biophysics and Department of Physics, Central China Normal University, Wuhan 430079, P. R. China
2. Department of Physics, Lanzhou University of Technology, Lanzhou 730050, P. R. China
3. School of Science, Chongqing University of Posts and Telecommunications, Chongqing 430065, P. R. China
4. NAAM-Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589, Saudi Arabia