Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Isotropic third-order statistics in turbulence with helicity: the
  2/15-law   The so-called 2/15-law for two-point, third-order velocity statistics in
isotropic turbulence with helicity is computed for the first time from a direct
numerical simulation of the Navier-Stokes equations in a 512^3 periodic domain.
This law is a statement of helicity conservation in the inertial range,
analogous to the benchmark Kolmogorov 4/5-law for energy conservation in
high-Reynolds number turbulence. The appropriately normalized parity-breaking
statistics, when measured in an arbitrary direction in the flow, disagree with
the theoretical value of 2/15 predicted for isotropic turbulence. They are
highly anisotropic and variable and remain so over a long times. We employ a
recently developed technique to average over many directions and so recover the
statistically isotropic component of the flow. The angle-averaged statistics
achieve the 2/15 factor to within about 7% instantaneously and about 5% on
average over time. The inertial- and viscous-range behavior of the
helicity-dependent statistics and consequently the helicity flux, which appear
in the 2/15-law, are shown to be more anisotropic and intermittent than the
cor- responding energy-dependent reflection-symmetric structure functions, and
the energy flux, which appear in the 4/5-law. This suggests that the Kolmogorov
assumption of local isotropy at high Reynolds numbers needs to be modified for
the helicity-dependent statistics investigated here.

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The categories of this paper are: astro-ph
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The categories of this paper are: physics
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The categories of this paper are: atom-ph
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat