Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Density Waves in the Flows of Granular Media   We study density waves in the flows of granular particles through vertical
tubes and hoppers using both analytic methods and molecular dynamics (MD)
simulations. We construct equations of motion for quasi one-dimensional
systems. The equations, combined with the Bagnold's law for friction, are used
to describe the time evolutions of the density and the velocity fields for
narrow tubes and hoppers. The solutions of the equations can have two types of
density waves, kinetic and dynamic. For tubes, we can show the existence of
kinetic waves, and obtain the condition for dynamic waves for tubes from the
equations. For hoppers, we obtain the solutions of the equations up to the
first order of the opening angle, which also show the existence of kinetic
waves. We reproduce density waves in the MD simulations for tubes. The waves
are believed to be kinetic based on a few evidences, including a well defined
flux-density curve. In MD simulations of flows in hoppers, we find density
waves, which are also believed to be kinetic.

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The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
32
The categories of this paper are: atom-ph