1. Department of Industrial Engineering, Tsinghua University, Beijing 100084, China;
2. Anderson Graduate School of Management, University of California, Los Angeles, Los Angeles, California 90095;
3. Department of Industrial Engineering and Operations Research, Department of Civil and Environmental Engineering, TBSI, University of California, Berkeley, Berkeley CA 94720;
4. College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China