Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Confinement Stabilizes a Bacterial Suspension into a Spiral Vortex   Confining surfaces play crucial roles in dynamics, transport and order in
many physical systems, but their effects on active matter, a broad class of
dynamically self-organizing systems, are poorly understood. We investigate here
the influence of global confinement and surface curvature on collective motion
by studying the flow and orientational order within small droplets of a dense
bacterial suspension. The competition between radial confinement,
self-propulsion, steric interactions and hydrodynamics robustly induces an
intriguing steady single-vortex state, in which cells align in
inwardly-spiralling patterns accompanied by a thin counterrotating boundary
layer. A minimal continuum model is shown to be in good agreement with these
observations.

36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph