Shoichi Toyabe1, Chun-Biu Li2, Kazushi Kinbara3. 1. Department of Applied Physics, Grad. Sch. of Engineering, Tohoku University, Aoba 6-6-05, Sendai, 980-8579, Japan. toyabe@tohoku.ac.jp. 2. Department of Mathematics, Stockholm University, 106 91, Stockholm, Sweden. 3. School of Life Science and Technology, Tokyo Institute of Technology, Nagatsuda-cho 4259 B58, Midori-ku, Yokohama, 226-8501, Japan.