1. Department of Biochemistry & Molecular Biology, Georgetown University Medical Center, Washington, DC 20007, United States
2. Optical Sciences Division, Code 5611, U.S. Naval Research Laboratory, Washington, DC 20375, United States
3. Biochemical Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
4. Defense Systems and Analysis Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States