1. Research Associate, Dept. of Rural Systems Engineering, Seoul National Univ., Seoul 151-921, Republic of Korea.
2. Associate Professor, Dept. of Rural Systems Engineering, Research Institute of Agriculture and Life Sciences, Institute of Green Bio Science and Technology, Seoul National Univ., Seoul 151-921, Republic of Korea (corresponding author).
3. Research Professor, Institute of Green Bio Science and Technology, Seoul National Univ., Seoul 151-921, Republic of Korea.