1. Guangdong Key Laboratory of Brain-Inspired Intelligent Computation, Department of Computer Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
2. Department of Computing, The Hong Kong Polytechnic University, Hong Kong.
3. Faculty of Technology, Bielefeld University, 33619 Bielefeld, Germany, and also with the Department of Computer Science, University of Surrey, Guildford GU2 7XH, U.K..