Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Viscosity of a classical gas: The rare-collision versus the
  frequent-collision regime   The shear viscosity $\eta$ for a dilute classical gas of hard-sphere
particles is calculated by solving the Boltzmann kinetic equation in terms of
the weakly absorbed plane waves. For the rare-collision regime, the viscosity
$\eta$ as a function of the equilibrium gas parameters -- temperature $T$,
particle number density $n$, particle mass $m$, and hard-core particle diameter
$d$ -- is quite different from that of the frequent-collision regime, e.g.,
from the well-known result of Chapman and Enskog. An important property of the
rare-collision regime is the dependence of $\eta$ on the external
("non-equilibrium") parameter $\omega$, frequency of the sound plane wave, that
is absent in the frequent-collision regime at leading order of the
corresponding perturbation expansion. A transition from the frequent to the
rare-collision regime takes place when the dimensionless parameter $nd^2
(T/m)^{1/2} \omega^{-1}$ goes to zero.

19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph