1. School of Applied Life Sciences, Keck Graduate Institute, Claremont, CA 91711, USA
2. Mathematics Department, Claremont Graduate University, Claremont, CA 91711, USA
3. Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4. Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA