Flocking at a distance in active granular matter
Abstract
The self-organised motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. We recreate this phenomenon using actuated non-living 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.
Cite
@article{arxiv.1402.4262,
title = {Flocking at a distance in active granular matter},
author = {Nitin Kumar and Harsh Soni and Sriram Ramaswamy and A. K. Sood},
journal= {arXiv preprint arXiv:1402.4262},
year = {2014}
}
Comments
32 pages, 14 figures, Supplementary Videos: http://www.tifrh.res.in/tcis/events/sriram_videos/