1. Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
2. Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
3. Faculty of Liberal Arts, National Institute of Technology (KOSEN), Kumamoto College, 2659-2 Suya, Koshi, Kumamoto 861-1102, Japan