1. School of Computer and Information Engineering, Hebei Finance University, Baoding, Hebei 071051, P. R. China
2. Key Laboratory of Optic-Electronic Information Materials of Hebei Province, College of Physics Science and Technology, Hebei University, Baoding, 071002, P. R. China
3. Department of Primary Education, Baoding Preschool Teachers College, Baoding, Hebei 071051, P. R. China