1. Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
2. Center for Exploratory Research, Research and Development Group, Hitachi, Ltd., 1-280, Higashi-koigakubo, Kokubunji, Tokyo 185-8601, Japan
3. Research Institute of Nuclear Engineering, University of Fukui, 1-3-33 Kanawa-cho, Tsuruga, Fukui 914-0055, Japan
4. JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan