1. School of Mathematics and Statistics, Northeastern University at Qinhuangdao, Qinhuangdao 066004, China
2. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
3. Eighth Geological Brigade of Hebei Bureau of Geology and Mineral Resources Exploration, Qinhuangdao 066000, China
4. Department of Mathematics, Harbin Institute of Technology at Weihai, Weihai 264209, China