1. Hitachi Plant Engineering & Construction Co., Ltd, 537 Kami-hongo, Matsudo·shi, Chiba 271, Japan
2. Sumitomo Heavy Industries Ltd, 1, Kanda Nishiki-cho, 2-chome, Chiyoda-ku, Tokyo 101, Japan
3. The Institute of Public Health, Ministry of Health and Welfare, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108, Japan