1. Department of Industrial and Management Engineering, Incheon National University, 12-1 Songdo-dong, Yeonsu-gu, Incheon 406-840, Republic of Korea
2. Department of Industrial and Management Engineering, Sungkyul University, 400-10 Anyang-dong, Manan-gu, Anyang, Gyeonggi-do 430-742, Republic of Korea