Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: MRI-active inner regions of protoplanetary discs. II. Dependence on
  dust, disc and stellar parameters   Close-in super-Earths are the most abundant exoplanets known. It has been
hypothesized that they form in the inner regions of protoplanetary discs, out
of the dust that may accumulate at the boundary between the inner region
susceptible to the magneto-rotational instability (MRI) and an MRI-dead zone
further out. In Paper I we presented a model for the viscous inner disc which
includes heating due to both irradiation and MRI-driven accretion; thermal and
non-thermal ionization; dust opacities; and dust effects on ionization. Here we
examine how the inner disc structure varies with stellar, disc and dust
parameters. For high accretion rates and small dust grains, we find that: (1)
the main sources of ionization are thermal ionization and thermionic and ion
emission; (2) the disc features a hot, high-viscosity inner region, and a local
gas pressure maximum at the outer edge of this region (in line with previous
studies); and (3) an increase in the dust-to-gas ratio pushes the pressure
maximum outwards. Consequently, dust can accumulate in such inner discs without
suppressing the MRI, with the amount of accumulation depending on the viscosity
in the MRI-dead regions. Conversely, for low accretion rates and large dust
grains, there appears to be an additional steady-state solution in which: (1)
stellar X-rays become the main source of ionization; (2) MRI-viscosity is high
throughout the disc; and (3) the pressure maximum ceases to exist. Hence, if
planets form in the inner disc, larger accretion rates (and thus younger disks)
are favoured.

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The categories of this paper are: hep-th
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The categories of this paper are: hep-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: cs
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The categories of this paper are: adap-org
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The categories of this paper are: eess