1. Department of Industrial and Systems Engineering,University of Wisconsin–Madison,3255 Mechanical Engineering,1513 University Avenue,Madison, WI 53706e-mail: liu427@wisc.edu
2. Department of Industrial and Systems Engineering,University of Wisconsin–Madison,3255 Mechanical Engineering,1513 University Avenue,Madison, WI 53706e-mail: wu45@wisc.edu
3. Department of Mechanical and Aerospace Engineering,University of California,Los Angeles, 48-121G Eng IV,Los Angeles, CA 90095e-mail: xcli@seas.ucla.edu