School of Software, Central South University, Changsha 410075, China;
School of Computer and Communication, Hunan Institute of Engineering, Xiangtan 411104, China;
School of Software, Central South University, Changsha 410075, China;
School of Computer and Communication Engineering, Changsha University of Science and Technology, Changsha 410114, China;
Department of Computer Science, State University of New York at New Paltz, New York 12561, USA;