1. College of Science and Technology, Jiangxi Normal University, Gongqing City Jiujiang, Jiangxi 332020, P. R. China
2. Jiangxi Provincial Center for Applied Mathematics, Jiangxi Normal University, Nanchang, Jiangxi 330022, P. R. China
3. School of Mathematics and Statistics, Jiangxi Normal University Nanchang, Jiangxi 330022, P. R. China