1. H. Milton Stewart School of Industrial and Systems Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332;
2. Eindhoven University of Technology, 5612 AZ Eindhoven, Netherlands;
3. Nokia Bell Labs, Murray Hill, New Jersey 07974;
4. Eindhoven University of Technology, 5612 AZ Eindhoven, Netherlands
5. Tilburg University, 5037 AB Tilburg, Netherlands;
6. Macquarie University, North Ryde, New South Wales 2109, Australia