1. Senior Researcher, Research Institute of Industrial Science and Technology, POSCO Global R&D Center, 180-1 Songdo-Dong, Yeonsu-Gu, Incheon 406-840, South Korea.
2. Professor, Dept. of Architecture, Seoul National Univ., San 56-1, Shinlim-Dong, Kwanak-Gu, Seoul 151-744, South Korea (corresponding author).