1. School of Mathematics and Statistics; Huazhong University of Science and Technology; Wuhan 430074 China
2. Center for Mathematical Sciences; Huazhong University of Science and Technology; Wuhan 430074 China
3. Department of Applied Mathematics; Illinois Institute of Technology; Chicago IL 60616 USA
4. Hubei Key Laboratory of Engineering Modeling and Scientific Computing; Huazhong University of Science and Technology; Wuhan 430074 China