Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Long-Time Behavior of Velocity Autocorrelation Function for Interacting
  Particles in a Two-Dimensional Disordered System   The long-time behavior of the velocity autocorrelation function (VACF) is
investigated by the molecular dynamics simulation of a two-dimensional system
which has both a many-body interaction and a random potential. With
strengthening the random potential by increasing the density of impurities, a
crossover behavior of the VACF is observed from a positive tail, which is
proportional to t^{-1}, to a negative tail, proportional to -t^{-2}. The latter
tail exists even when the density of particles is the same order as the density
of impurities. The behavior of the VACF in a nonequilibrium steady state is
also studied. In the linear response regime the behavior is similar to that in
the equilibrium state, whereas it changes drastically in the nonlinear response
regime.

12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph