1. School of Natural and Applied Sciences, Northwestern Polytechnical University, Xi’an 710129, P. R. China
2. College of Science, Zhongyuan University of Technology, Zhengzhou 450007, P. R. China
3. MIIT Key Laboratory of Dynamics and Control of Complex Systems, Xi’an 710072, P. R. China
4. School of Natural and Applied Sciences, School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710129, P. R. China