1. Department of Basic Science, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan; Department of Information System, Teikyo Heisei University, Uruido, Ichikawa, 290-0193, Japan; and Saitama Study Center, The University of the Air, 682-2 Nishiki-cho, Saitama 331-0851, Japan