1. School of Computer Science and Engineering, Central South University, Changsha, Hunan, People's Republic of China
2. School of Computer Science and Engineering, Hunan University of Science and Technology, Xiangtan, Hunan, People's Republic of China
3. School of Automation, Central South University, Changsha, Hunan, People's Republic of China
4. Department of Computer Science and Information Engr. (CSIE), Providence University, Taichung, Taiwan