1. Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland21218, United States
2. Department of Mechanical Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland21218, United States
3. Laboratoire de Tribologie et Dynamique des Systèmes, École Centrale de Lyon, CNRS UMR5513, 69134Ecully, France