First Author:   Nobuo Matsubayashi Keio University nobuo-m@pa2.so-net.ne.jp   Hiyoshi 3-14-1 Kohoku-ku Yokohama, 223-8522, Japan   +81-45-563-1151(Phone) +81-45-563-1151(Fax) http://www.ae.keio.ac.jp/lab/soc/matsubayashi/profile-e.htm Second Author: Tatsuya Hashimoto Keio University fr041712@a2.keio.jp