Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geometry-driven collective ordering of bacterial vortices   Controlling the phases of matter is a challenge that spans from condensed
materials to biological systems. Here, by imposing a geometric boundary
condition, we study controlled collective motion of Escherichia coli bacteria.
A circular microwell isolates a rectified vortex from disordered vortices
masked in bulk. For a doublet of microwells, two vortices emerge but their
spinning directions show transition from parallel to anti-parallel. A
Vicsek-like model for confined self-propelled particles gives the point where
two spinning patterns occur in equal probability and one geometric quantity
governs the transition as seen in experiments. This mechanism shapes rich
patterns including chiral configurations in a quadruplet of microwells, thus
revealing a design principle of active vortices.

5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph