1. Department of Computational Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2. Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
4. Singapore-MIT Alliance for Research and Technology (SMART) Centre, Singapore 138602
5. Department of Applied Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA