1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. Department of Mechanical Engineering, Changwon National University, Changwon, South Korea.
3. Sloan School of Management, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.
4. Singapore-MIT Alliance for Research and Technology (SMART) Centre, 1 Create Way, Singapore 138602, Singapore.