1. School of Journalism and Communication, Hunan University, Changsha, China
2. School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou, China
3. College of Computer Science and Electronic Engineering, Hunan University, Changsha, China
4. Department of Computer Science and Engineering, University of Connecticut, Storrs, Mansfield, CT, USA
5. Department of Computer Science, City University of Hong Kong, Kowloon, Hong Kong