1. T.
C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, United States
2. Department
of Biology, Johns Hopkins University, Baltimore, Maryland 21218, United States
3. Biophysics
Collaborative Access Team, Argonne National Laboratory, Argonne, Illinois 60439, United States
4. School
of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, United States