Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetohydronamic Evolution of HII Regions in Molecular Clouds:
  Simulation Methodology, Tests, and Uniform Media   We present a method for simulating the evolution of HII regions driven by
point sources of ionizing radiation in magnetohydrodynamic media, implemented
in the three-dimensional Athena MHD code. We compare simulations using our
algorithm to analytic solutions and show that the method passes rigorous tests
of accuracy and convergence. The tests reveal several conditions that an
ionizing radiation-hydrodynamic code must satisfy to reproduce analytic
solutions. As a demonstration of our new method, we present the first
three-dimensional, global simulation of an HII region expanding into a
magnetized gas. The simulation shows that magnetic fields suppress sweeping up
of gas perpendicular to magnetic field lines, leading to small density
contrasts and extremely weak shocks at the leading edge of the HII region's
expanding shell.

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The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: q-alg
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The categories of this paper are: econ
2
The categories of this paper are: math
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The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
1
The categories of this paper are: cs