1. School of Mathematics and Information Science, Henan Polytechnic University, Jiaozuo, P. R. China
2. National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, 199 Ren-Ai Road, Suzhou, P. R. China
3. School of Science, Xi’an University of Architecture and Technology, Xi’an, P. R. China