Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The effect of ambipolar resistivity on the formation of dense cores   We aim to understand the formation of dense cores by magnetosonic waves in
regions where the thermal to magnetic pressure ratio is small. Because of the
low-ionisation fraction in molecular clouds, neutral and charged particles are
weakly coupled. Ambipolar diffusion then plays an important role in the
formation process. A quiescent, uniform plasma is perturbed by a fast-mode
wave. Using 2D numerical simulations, we follow the evolution of the fast-mode
wave. The simulations are done with a multifluid, adaptive mesh refinement MHD
code. Initial perturbations with wavelengths that are 2 orders of magnitude
larger than the dissipation length are strongly affected by the ion-neutral
drift. Only in situations where there are large variations in the magnetic
field corresponding to a highly turbulent gas can fast-mode waves generate
dense cores. This means that, in most cores, no substructure can be produced.
However, Core D of TMC-1 is an exception to this case. Due to its atypically
high ionisation fraction, waves with wavelengths up to 3 orders of magnitude
greater than the dissipation length can be present. Such waves are only weakly
affected by ambipolar diffusion and can produce dense substructure without
large wave-amplitudes. Our results also explain the observed transition from
Alfvenic turbulent motion at large scales to subsonic motions at the level of
dense cores.

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The categories of this paper are: math
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org