Affiliation: | 1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2‐1 Yamadaoka, Suita, Osaka 565‐0871 (Japan), Fax: (+81)?6‐6879‐7404;2. Department of Mathematics, Kobe Pharmaceutical University, 4‐19‐1 Motoyama Kitamachi, Higashinada, Kobe, Hyogo 658‐8558 (Japan), Fax: (+81)?78‐441‐7582;3. Present address: The Institute of Scientific and Industrial Research, Osaka University, 8‐1 Mihogaoka, Ibaraki, Osaka 567‐0047 (Japan) |