Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonlinear plasma waves in an electron gas   The nature of traveling wave solutions to equations of hydrodynamics of a
generic three-dimensional electron gas with parabolic dispersion law depends on
whether the motion is subsonic or supersonic. Solitons representing localized
depressions of the electrostatic potential and electron density are predicted
to exist in the subsonic regime: at rest the solitons are dark while in motion
they are grey. Two types of periodic waves are found in the supersonic regime:
(i) smooth waves whose small amplitude limit is described by harmonic theory,
and (ii) waves with sharp troughs and smooth crests of the potential with the
electrons accumulating in the troughs.

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The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga