1. School of Mathematics and Statistics, Hubei Normal University, Huangshi 435002, P. R. China
2. Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
3. Jiangsu Key Laboratory for NSLSCS, School of Mathematical Sciences, Nanjing Normal University, Nanjing 210023, P. R. China
4. Department of Mathematics, Faculty of Science and Arts, Düzce University, Düzce, Turkey
5. Department of Mathematics, Huzhou University, Huzhou 313000, P. R. China