School of Air Transportation and Logistics, Korea Aerospace University 100 Hanggongdae-gil, Hwajeon-dong, Deogyang-Gu, Goyang-City, Gyeonggi-Do, 412-791, Republic of Korea e-mail: joanphan@gmail.com; phone: +82-2-300-0374
Shao Wei Lam
Department of Industrial and Systems Engineering, National University of Singapore 10 Kent Ridge Crescent, Singapore 119260