1. Supply Chain Planning and Optimization Unit, World Food Programme, 00148 Rome, Italy;
2. Department of Econometrics and Operations Research, Tilburg University, 5000 LE Tilburg, Netherlands;
3. Amsterdam Business School, University of Amsterdam, 1018 TV Amsterdam, Netherlands;
4. Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115;
5. Advanced Technology Group, United Parcel Service, Atlanta, Georgia 30328