1. School of Electrical and Information Engineering, Xihua University, Chengdu, P.R. China
2. Key Laboratory of Fluid and Power Machinery, Ministry of Education, Xihua University, Chengdu, P.R. China
3. School of Applied Mathematics, University of Electronic Science and Technology of China, Chengdu, P.R. China
4. School of Science, Hubei University for Nationalities, Enshi, P.R. China