1. Department of Mechanical Engineering, Virginia Tech 1 , Blacksburg, Virginia 24061, USA
2. Department of Mathematics, University of Utah 2 , Salt Lake City, Utah 84112, USA
3. Department of Mechanical Engineering, McGill University 3 , Montréal, Quebec H3A 0C3, Canada
4. Department of Mechanical Engineering, University of Utah 4 , Salt Lake City, Utah 84112, USA