1. School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, Georgia 30332, United States
2. Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
3. UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
4. Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, 1311 Cumberland Avenue, Knoxville, Tennessee 37996, United States