1. Department of Computer Science and Engineering, University of Aizu, Aizuwakamatsu, Japan
2. School of Electronics and Information Engineering, Nanjing University of Information Science and Technology, Nanjing, China
3. Department of Computer Science, City University of Hong Kong, Hong Kong SAR, China
4. College of Computer Science and Technology, State Key Laboratory of Public Big Data, Guizhou University, Guiyang, China
5. Department of Applied Mathematics and Computer Science, Technical University of Denmark (DTU), Denmark