1. School of Science, Xi’an University of Architecture and Technology, Xi’an, 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 Mathematical Science, Soochow University, Suzhou, P. R. China
4. School of Civil Engineering, Xi’an University of Architecture & Technology, Xi’an 710055, China