1. School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA.
2. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA.
3. Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
4. Department of Structural Biology, Jacobs School of Medicine and Biological Sciences, University at Buffalo, Buffalo, NY 14203, USA.