1. School of Electrical and Information Engineering, Hunan University of Technology, Zhuzhou 412007, China
2. School of Computer Science, Hunan University of Technology, Zhuzhou 412007, China
3. College of Railway Transportation, Hunan University of Technology, Zhuzhou 412007, China
4. School of Computer Science, South China Normal University, Guangzhou 510631, China
5. School of Computer Science, University of Glasgow, Glasgow G12 8QQ, UK