Surmounting Barriers: The Benefit of Hydrodynamic Interactions
  We experimentally and theoretically investigate the collective behavior of three colloidal particles that are driven by a constant force along a toroidal trap. Due to hydrodynamic interactions, a characteristic limit cycle is observed. When we additionally apply a periodic sawtooth potential, we find a novel caterpillar-like motional sequence that is dominated by hydrodynamic interactions and promotes the surmounting of potential barriers by the particles. 
Christoph Lutz (1), Michael Reichert (2), Holger Stark (2) and Clemens   Bechinger (1) ((1) Universitaet Stuttgart, (2) Univ...