Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Active crystals on a sphere   Two-dimensional crystals on curved manifolds exhibit nontrivial defect
structures. Here, we consider "active crystals" on a sphere, which are composed
of self-propelled colloidal particles. Our work is based on a new
phase-field-crystal-type model that involves a density and a polarization field
on the sphere. Depending on the strength of the self-propulsion, three
different types of crystals are found: a static crystal, a self-spinning
"vortex-vortex" crystal containing two vortical poles of the local velocity,
and a self-translating "source-sink" crystal with a source pole where
crystallization occurs and a sink pole where the active crystal melts. These
different crystalline states as well as their defects are studied theoretically
here and can in principle be confirmed in experiments.

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The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph