1. Department of Mathematics, Tufts University, Medford, MA 02155 USA.
2. Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803 USA.
3. Radiation and Electrical Science, Sandia National Laboratories, Albuquerque, NM 87123 USA.
4. Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104 USA.