Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermal Instability and the Formation of Clumpy Gas Clouds   The radiative cooling of optically thin gaseous regions and the formation of
a two-phase medium and of cold gas clouds with a clumpy substructure is
investigated. In optically thin clouds, the growth rate of small isobaric
density perturbations is independent of their length scale. However, the growth
of a perturbation is limited by its transition from isobaric to isochoric
cooling. The temperature at which this transition occurs decreases with the
length scale of the perturbation. Consequently small scale perturbations have
the potential to reach higher amplitudes than large scale perturbations. When
the amplitude becomes nonlinear, advection overtakes the pressure gradient in
promoting the compression resulting in an accelerated growth of the
disturbance. The critical temperature for transition depends on the initial
amplitude. The fluctuations which can first reach nonlinearity before their
isobaric to isochoric transition will determine the characteristic size and
mass of the cold dense clumps which would emerge from the cooling of an
initially nearly homogeneous region of gas. Thermal conduction is in general
very efficient in erasing isobaric, small-scale fluctuations, suppressing a
cooling instability. A weak, tangled magnetic field can however reduce the
conductive heat flux enough for low-amplitude fluctuations to grow isobarically
and become non-linear if their length scales are of order 0.01 pc. Finally, we
demonstrate how a 2-phase medium, with cold clumps being pressure confined in a
diffuse hot residual background component, would be sustained if there is
adequate heating to compensate the energy loss.

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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: atom-ph