1. School of Mathematics and Physics, Qingdao University of Science and Technology, P. R. China
2. The Research Institute for Mathematics and Interdisciplinary Sciences, Qingdao University of Science and Technology, China
3. Key Laboratory of Measurement and Control of Complex Systems of Engineering, Ministry of Education, P. R. China
4. College of Electromechanical Engineering, Qingdao University of Science and Technology, P. R. China