1. Department of Mechanical Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-21, Japan
2. Applied Laser Engineering Research Institute, 2085-16 Hukasawa, Nagaoka, Niigata 940-21, Japan
3. Niigata Thermal Power Station, Tohoku Electric Power Co. Inc., 2-200 Momoyama, Niigata, Niigata 950, Japan