1. Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2. Department of Mechanical Engineering, University of Chile, Beauchef 851, Santiago, Chile
3. Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125, USA
4. Department of Applied Mathematics, University of Washington, Seattle, WA 98195, USA
5. Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA