1. Graduate School of Engineering, Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657 8501, Japan
2. Department of Biomedical Engineering, National Cerebral and Cardiovascular Center Research Institute (NCVC), 6-1 Kishibe Shin-machi, Suita, Osaka564-8565, Japan