Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the nature of the resonant drag instability of dust streaming in
  protoplanetary disc   The recently discovered resonant drag instability (RDI) of dust streaming in
protoplanetary disc is considered as the mode coupling of subsonic gas-dust
mixture perturbations. This mode coupling is coalescence of two modes with
nearly equal phase velocities: inertial wave (IW) having positive energy and a
streaming dust wave (SDW) having negative energy as measured in the frame of
gas environment being at rest in vertical hydrostatic equilibrium. SDW is a
trivial mode produced by the bulk streaming of dust, which transports
perturbations of dust density. In this way, settling combined with radial drift
of the dust makes possible coupling of SDW with IW and the onset of the
instability. In accordance with the concept of the mode coupling, RDI growth
rate is proportional to the square root of the coupling term of the dispersion
equation, which itself is proportional to mass fraction of dust, $f\ll 1$. This
clarifies why RDI growth rate $\propto f^{1/2}$. When SDW has positive energy,
its resonance with IW provides an avoided crossing instead of the mode
coupling. In the high wavenumber limit RDI with unbounded growth rate $\propto
f^{1/3}$ is explained by the triple mode coupling, which is coupling of SDW
with two IW. It coexists with a new quasi-resonant instability accompanied by
bonding of two oppositely propagating low-frequency IW. The mode coupling does
not exist for dust streaming only radially in a disc. In this case RDI is
provided by the obscured mechanism associated with the inertia of solids.

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The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: stat
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The categories of this paper are: eess
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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: chem-ph
1
The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int