1. R&D Department, Osaka Gas Co., Ltd. 6-19-9, Torishima, Konohana-ku, Osaka 554, Japan
2. Nagasaki Research & Development Center, Mitsubishi Heavy Industries, Ltd. 5-717-1, Fukahorimachi, Nagasaki 851-03, Japan
3. Institute of Advanced Material Study, Kyushu University 6-1, Kasugakoen, Kasuga-shi, Fukuoka 816, Japan