Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Diffusion Approximation in Turbulent Two-Particle Dispersion   We solve an inverse problem for fluid particle pair-statistics: we show that
a time sequence of probability density functions (PDF's) of separations can be
exactly reproduced by solving the diffusion equation with a suitable
time-dependent diffusivity. The diffusivity tensor is given by a time-integral
of a conditional Lagrangian velocity structure-function, weighted by a ratio of
PDF's. Physical hypotheses for hydrodynamic turbulence (sweeping, short memory,
mean-field) yield simpler integral formulas, including one of Kraichnan and
Lundgren. We evaluate the latter using a spacetime database from a numerical
Navier-Stokes solution for driven turbulence. This diffusion theory reproduces
PDF's well at rms separations, but growth rate of mean-square dispersion is
overpredicted due to neglect of memory effects. More general applications of
our approach are sketched.

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The categories of this paper are: hep-th
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: ao-sci