1. College of Mathematics and System Sciences, Xinjiang University, Ürümqi 830046, P. R. China
2. Department of Mathematics, Huzhou University, Zhejiang, Huzhou 313000, P. R. China
3. Department of Mathematics, Shanghai Normal University, Shanghai 200234, P. R. China
4. Institute of Applied System Analysis, Jiangsu University, Jiangsu, Zhenjiang 212013, P. R. China
5. Department of Mathematics, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada
6. School of Mathematical Science, Hebei Normal (Teachers) University, Shijiazhuang, Hebei 050016, P. R. China