Department of Physics and Astronomy, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Philadelphia, United States of America, Department of Physics and Astronomy, Northwestern University, Evanston, Illinois, United States of America.|Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Philadelphia, United States of America, Department of Neuroscience, School of Medicine, University of Virginia, Charlottesville, Virginia, United States of America.|Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Philadelphia, United States of America.|Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Philadelphia, United States of America.|Department of Physics and Astronomy, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Philadelphia, United States of America.