1. School of Information, Hunan University of Humanities, Science and Technology, Loudi, China
2. School of Information Technology, Carleton University, Ottawa, ON, Canada
3. School of Computer Science and Engineering, Central South University, Changsha, China
4. College of Information Science and Engineering, Hunan Normal University, Changsha, Hunan, China
5. Department of Computer Science and Technology, Tsinghua University, Beijing, China