1. Department of Industrial Engineering, Tsinghua University, Beijing 100084, China;
2. Department of Management Science and Engineering, School of Economics and Management, Tsinghua University, Beijing 100084, China;
3. H. Milton Stewart School of Industrial and Systems Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332;
4. PBC School of Finance, Tsinghua University, Beijing 100083, China;
5. Heinz College, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213