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