1. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada
2. Department of Mechanical Engineering, McGill University, Montreal, Quebec H3A 0C3, Canada
3. Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec H3A 0E9, Canada
4. Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA