1. National Engineering Laboratory for Modern Silk, College of Textile and Engineering, Soochow University, Suzhou, P. R. China
2. School of Mathematical Science, Soochow University, Suzhou, P. R. China
3. School of Mathematics and Information Science, Henan Polytechnic University Jiaozuo, P. R. China
4. School of Science, Xi’an University of Architecture and Technology, Xi’an, P. R. China
5. Department of Mathematics, Government College University, Faisalabad, Pakistan