1. Graduate School of Advanced Science and Engineering Hiroshima University 1‐4‐1, Kagamiyama, Higashihiroshima 739‐8527 Japan
2. TEPCO Research Institute Tokyo Electric Power Company Holdings, Inc. 4‐1, Egasaki‐cho, Tsurumi‐ku, Yokohama‐shi 230‐8510 Japan
3. TEPCO Power Grid, Incorporated 1‐1‐3, Uchisaiwai‐cho, Chiyoda‐ku, Tokyo 100‐8560 Japan