1. Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8563, JP, e-mail: morita@multi.k.u-tokyo.ac.jp
2. Dept. of Mechanical Engineering, National Inst. of Technology, Kurume College, 1-1-1 Komorino, Kurume, Fukuoka 830-8555, JP (Corresponding author), e-mail: harada@kurume-nct.ac.jp
3. Dept. of Mechanical Engineering, Faculty of Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka 819-0395, JP e-mail: nogu@mech.kyushu-u.ac.jp