Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurements of the Solid-body Rotation of Anisotropic Particles in 3D
  Turbulence   We introduce a new method to measure Lagrangian vorticity and the rotational
dynamics of anisotropic particles in a turbulent fluid flow. We use 3D printing
technology to fabricate crosses (two perpendicular rods) and jacks (three
mutually perpendicular rods). Time-resolved measurements of their orientation
and solid-body rotation rate are obtained from stereoscopic video images of
their motion in a turbulent flow between oscillating grids with
$R_\lambda$=$91$. The advected particles have a largest dimension of 6 times
the Kolmogorov length, making them a good approximation to anisotropic tracer
particles. Crosses rotate like disks and jacks rotate like spheres, so these
measurements, combined with previous measurements of tracer rods, allow
experimental study of ellipsoids across the full range of aspect ratios. The
measured mean square tumbling rate, $\langle \dot{p}_i \dot{p}_i \rangle$,
confirms previous direct numerical simulations that indicate that disks tumble
much more rapidly than rods. Measurements of the alignment of crosses with the
direction of the solid-body rotation rate vector provide the first direct
observation of the alignment of anisotropic particles by the velocity gradients
of the flow.

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The categories of this paper are: astro-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: plasm-ph