1. School of Automation & Electronic Engineering; Qingdao University of Science & Technology; Qingdao 266042 P. R. China
2. Department of Electrical and Electronic Engineering; Yantai Nanshan University; Yantai 265713 P. R. China
3. School of Mathematics and Physics; Qingdao University of Science and Technology; Qingdao 266042 P. R. China
4. Department of Chemical and Materials Engineering; University of Alberta; Edmonton AB, T6G 2G6, Canada