Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periodic and quasiperiodic motions of many particles falling in a
  viscous fluid   Dynamics of regular clusters of many non-touching particles falling under
gravity in a viscous fluid at low Reynolds number are analysed within the
point-particle model. Evolution of two families of particle configurations is
determined: 2 or 4 regular horizontal polygons (called `rings') centred above
or below each other. Two rings fall together and periodically oscillate. Four
rings usually separate from each other with chaotic scattering. For hundreds of
thousands of initial configurations, a map of the cluster lifetime is
evaluated, where the long-lasting clusters are centred around periodic
solutions for the relative motions, and surrounded by regions of the chaotic
scattering,in a similar way as it was observed by Janosi et al. (1997) for
three particles only. These findings suggest to consider the existence of
periodic orbits as a possible physical mechanism of the existence of unstable
clusters of particles falling under gravity in a viscous fluid.

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The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th