1. School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
2. Faculty of Bioresource Sciences, Akita Prefectural University, 241-438 Kaidobata-Nishi Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan