1. School of Mathematics and Physics, Jiangsu University of Technology, Changzhou, Jiangsu 213001, P. R. China
2. School of Science, Inner Mongolia University of Science & Technology, Baotou, Inner Mongolia Autonomous Region 014010, P. R. China
3. School of Physics and School of International Education Teachers, Changchun Normal University, Changchun, Jilin 130032, P. R. China