Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Heat and Dust in Active Layers of Protostellar Disks   Requirements for magnetic coupling and accretion in the active layer of a
protostellar disk are re-examined, and some implications for thermal emission
from the layer are discussed. The ionization and electrical conductivity are
calculated following the general scheme of Ilgner and Nelson but with an
updated UMIST database of chemical reactions and some improvements in the grain
physics, and for the minimum-mass solar nebula rather than an alpha disk. The
new limits on grain abundance are slightly more severe than theirs. Even for
optimally sized grains, the layer should be at least marginally optically thin
to its own thermal radiation, so that narrow, highly saturated emission lines
of water and other molecular species would be expected if accretion is driven
by turbulence and standard rates of ionization prevail. If the grain size
distribution extends broadly from well below a micron to a millimeter or more,
as suggested by observations, then the layer may be so optically thin that its
cooling is dominated by molecular emission. Even under such conditions, it is
difficult to have active layers of more than 10g/cm^2 near 1AU unless dust is
entirely eliminated or greatly enhanced ionization rates are assumed.
Equipartition-strength magnetic fields are then required in these regions of
the disk if observed accretion rates are driven by magnetorotational
turbulence. Wind-driven accretion might allow weaker fields and less massive
active layers but would not heat the layer as much as turbulence and therefore
might not produce emission lines.

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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con