Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Simulation Study of Internal and Surface waves of Vertically Vibrated
  Granular Materials   Molecular dynamical (MD) simulations are performed to simulate two
dimensional vibrofluidized granular materials in this work. Statistics on
simulation results indicate that there exist shocks propagating upward in each
vibrating cycle. Under certain driving parameters surface waves similar to
Faraday instability in normal fluid coexist with internal waves. Relationship
between the two kinds of waves is explored. Moreover simulation results
indicate that periodically structured bottom can change the dispersion
relationship and amplitude of surface waves.

5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
9
The categories of this paper are: nlin