1. Department of Mathematics & Physics, Shijiazhuang Tiedao University, Shijiazhuang, P.R. China
2. School of Management & Economics, Beijing Institute of Technology, Beijing, P.R. China
3. The 54th Research Institute of China Electronics Technology Group Corporation, Shijiazhuang, P.R. China
4. Business School, Shijiazhuang University of Economics, Shijiazhuang, P.R. China