1. Department of Computers and Information Science, Seikei University, Tokyo, Japan
2. Graduate School of Engineering, Fukuoka Institute of Technology (FIT), Fukuoka, Japan
3. Department of Information and Communication Engineering, Fukuoka Institute of Technology (FIT), Fukuoka, Japan
4. Department of Languages and Informatics Systems, Technical University of Catalonia, Jordi Girona 1-3, Barcelona, Spain