1. School of Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
2. Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
3. Yamaha Motor Co., Ltd, 3078 Arai, Arai-cho, Kosai, Shizuoka 431-0302, Japan
4. Shanghai Jiao Tong University and Chiba University International Cooperative Research Center, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan