1. School of Information Management, Jiangxi University of Finance and Economics, Nanchang 330013, China
2. College of Computer Science and Electronic Engineering, Hunan University, Changsha 410082, China
3. Chongqing Research Institute, Hunan University, Chongqing 401120, China
4. School of Engineering and Computer Science, University of Hertfordshire, Hatfield AL10 9AB, UK