1. Department of Mechanical and Industrial Engineering, University of Minnesota Duluth, Duluth, MN 55812, USA
2. Department of Mathematics, Loyola Marymount University, Los Angeles, CA 90045, USA
3. Department of Mechanical, Industrial and Manufacturing Engineering, University of Toldeo, Toledo, OH 43606, USA
4. Department of Mathematics, University of California-Los Angeles, Los Angeles, CA 90095, USA