1. Department of Industrial and Systems Engineering, National University of Singapore, Singapore 117576; and International Center of Management Science and Engineering, School of Management and Engineering, Nanjing University, 210093 Nanjing, China
2. Department of Management Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong
3. School of Management, Huazhong University of Science and Technology, 430074 Wuhan, China