1. College of Science, Hebei United University, Tangshan, China
2. College of Mechanical Engineering, Yanshan University, Qinhuangdao, China
3. Department of Mathematics, University of Salerno, Via Ponte don Melillo, Fisciano, 84084 Salerno, Italy
4. School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China
5. School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi, China
6. Department of Mathematics and Mechanics, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China