[1] Johns Hopkins Univ, Dept Chem & Biomol Engn, Baltimore, MD 21218 USA
[2] Univ Minnesota, Sch Math, Minneapolis, MN 55455 USA
[3] Brown Univ, Dept Comp Sci, Providence, RI 02912 USA
[4] Univ Massachusetts, Dept Math & Stat, Amherst, MA 01003 USA
[5] Brown Univ, Div Appl Math, Providence, RI 02906 USA
[6] Johns Hopkins Univ, Dept Chem, Baltimore, MD 21218 USA