1. Graduate School of System and Information Engineering, University of Tsukuba, 1-1-1, Tennoudai, Tsukuba 305-8573, Japan
2. Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Umezono, Tsukuba 305-8568, Japan
3. Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan