Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Flocking at a distance in active granular matter   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.

34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin