Flocking at a distance in active granular matter
Abstract
The self-organized motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. Here, we recreate this phenomenon using actuated nonliving components. We report here that millimetre-sized tapered rods, rendered motile by contact with an underlying vibrated surface and interacting through a medium of spherical beads, undergo a phase transition to a state of spontaneous alignment of velocities and orientations above a threshold bead area fraction. Guided by a detailed simulation model, we construct an analytical theory of this flocking transition, with two ingredients: a moving rod drags beads; neighbouring rods reorient in the resulting flow like a weathercock in the wind. Theory and experiment agree on the structure of our phase diagram in the plane of rod and bead concentrations and power-law spatial correlations near the phase boundary. Our discovery suggests possible new mechanisms for the collective transport of particulate or cellular matter.
- Publication:
-
Nature Communications
- Pub Date:
- September 2014
- DOI:
- 10.1038/ncomms5688
- arXiv:
- arXiv:1402.4262
- Bibcode:
- 2014NatCo...5.4688K
- Keywords:
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- Condensed Matter - Soft Condensed Matter;
- Condensed Matter - Statistical Mechanics;
- Physics - Biological Physics
- E-Print:
- 32 pages, 14 figures, Supplementary Videos: http://www.tifrh.res.in/tcis/events/sriram_videos/