1. School of Computer Science and Engineering, Central South University, ChangSha, Hunan, P.R. China
2. Department of Electrical and Software Engineering, University of Calgary, Calgary, AB, Canada
3. Research Institute of Languages and Cultures and the College of Information Science and Engineering, Hunan Normal University, Changsha, Hunan, P.R. China
4. Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada