Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Simple pairs potential-density for flat rings   Pairs potential-density in terms of elementary functions that represents flat
rings structures are presented. We study structures representing one or several
concentric flat rings. Also disks surrounded by concentric flat rings are
exhibited. The stability of concentrically circular orbits of particles moving
on a flat ring structure is analyzed for radial perturbations.

25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio