1. College of Science, Hebei United University, Tangshan 063009, China
2. College of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China
3. School of Civil Engineering and Architecture, Chongqing Jiaotong University, Chongqing 400074, China
4. Department of Mathematics and Statistics, University of Victoria, Victoria, BC, Canada V8W 3R4
5. Department of Mathematics and Mechanics, China University of Mining and Technology, Jiangsu, Xuzhou 221008, China