1. School of Computer, Electronics and Information, Guangxi University, Nanning, Guangxi, P. R. China
2. Computer and Information Science, Northeastern University, Boston, USA
3. Beijing Advanced Innovation Center for Big Data and Brain Computing (BDBC), Beihang University, Beijing, P. R. China
4. Department of Computer and Information Science, Faculty of Science and Technology, University of Macau, Macau, P. R. China