1. School of Electronic Engineering, Guangxi Normal University, Guilin 541004, P. R. China
2. Business School, University of Edinburgh, Edinburgh, EH8 9JS, UK
3. School of Computing, Engineering and Intelligent Systems, Ulster University, BT48 7JL, UK
4. College of Mathematics and Informatics, Fujian Normal University, Fuzhou 350108, P. R. China