1. Hitachi Research Laboratory, Hitachi, Ltd., 7-1-1 Omika, Hitachi, Ibaraki 319-12, Japan
2. Hitachi Works, Hitachi, Ltd., 3-1-1 Saiwai, Hitachi, Ibaraki 316, Japan
3. Department of Energy Engineering and Science, Nagoya University, Nagoya 464-01, Japan