Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effects of Neutral Hydrogen on Cosmic Ray Precursors in Supernova
  Remnant Shock Waves   Many fast supernova remnant shocks show spectra dominated by Balmer lines.
The H$\alpha$ profiles have a narrow component explained by direct excitations
and a thermally Doppler broadened component due to atoms that undergo charge
exchange in the post-shock region. However, the standard model does not take
into account the cosmic-ray shock precursor, which compresses and accelerates
plasma ahead of the shock. In strong precursors with sufficiently high
densities, the processes of charge exchange, excitation and ionization will
affect the widths of both narrow and broad line components. Moreover, the
difference in velocity between the neutrals and the precursor plasma gives rise
to frictional heating due to charge exchange and ionization in the precursor.
In extreme cases, all neutrals can be ionized by the precursor.
  In this paper we compute the ion and electron heating for a wide range of
shock parameters, along with the velocity distribution of the neutrals that
reach the shock. Our calculations predict very large narrow component widths
for some shocks with efficient acceleration, along with changes in the broad-
to-narrow intensity ratio used as a diagnostic for the electron-ion temperature
ratio. Balmer lines may therefore provide a unique diagnostic of precursor
properties. We show that heating by neutrals in the precursor can account for
the observed H$\alpha$ narrow component widths, and that the acceleration
efficiency is modest in most Balmer line shocks observed thus far.

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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
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The categories of this paper are: adap-org