1. Institute of Industrial Science, University of Tokyo, Meguro, Tokyo 153-8505, Japan
2. Graduate School of Science and Technology, Tokyo Institute of Technology, Yokohama, Kanagawa 225-8503, Japan
3. LIMMS/CNRS-IIS (UMI 2820), Institute of Industrial Science, University of Tokyo, Meguro, Tokyo 153-8505, Japan
4. CNRS, LAAS, 7 Avenue du Colonel Roche, F-31400 Toulouse, France and University of Toulouse, LAAS, F-31400 Toulouse, France