Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Columnar structure formation of a dilute suspension of settling
  spherical particles in a quiescent fluid   The settling of heavy spherical particles in a column of quiescent fluid is
investigated. The performed experiments cover a range of Galileo numbers ($110
\leq \text{Ga} \leq 310$) for a fixed density ratio of $\Gamma = \rho_p/\rho_f
= 2.5$. In this regime the particles are known (M. Jenny, J. Du\v{s}ek and G.
Bouchet, Journal of Fluid Mechanics 508, 201 (2004).) to show a variety of
motions. It is known that the wake undergoes several transitions for increasing
$\text{Ga}$ resulting in particle motions that are successively: vertical,
oblique, oblique oscillating, and finally chaotic. Not only does this change
the trajectory of single, isolated, settling particles, but it also changes the
dynamics of a swarm of particles as collective effects become important even
for dilute suspensions, with volume fraction up to $\Phi_V =
\mathcal{O}\left(10^{-3}\right)$, which are investigated in this work.
Multi-camera recordings of settling particles are recorded and tracked over
time in 3 dimensions. A variety of analysis are performed and show a strong
clustering behavior. The distribution of the cell areas of the Vorono\"i
tessellation in the horizontal plane are compared to that of a random
distribution of particles and shows clear clustering. Moreover, a negative
correlation was found between the Vorono\"i area and the particle velocity;
clustered particles fall faster. In addition, the angle between two adjacent
particles and the vertical is calculated and compared to a homogeneous
distribution of particles, clear evidence of vertical alignment of particles is
found. The experimental findings are compared to simulations.

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The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org