Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dusty Magnetohydrodynamics in Star Forming Regions   Star formation occurs in dark molecular regions where the number density of
hydrogen nuclei, nH, exceeds 10^4 cc and the fractional ionization is 10^-7 or
less. Dust grains with sizes ranging up to tenths of microns and perhaps down
to tens of nanometers contain just under one percent of the mass. Recombination
on grains is important for the removal of gas phase ions, which are produced by
cosmic rays penetrating the dark regions. Collisions of neutrals with charged
grains contribute significantly to the coupling of the magnetic field to the
neutral gas. Consequently, the dynamics of the grains must be included in the
magnetohydrodynamic models of large scale collapse, the evolution of waves and
the structures of shocks important in star formation.

20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph