Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The first $R_{cr}$ as a possible measure of the entrainment length in a
  2D steady wake   At a fixed distance from the body which creates the wake, entrainment is only
seen to increase with the Reynolds number ($R$) up to a distance of almost 20
body scales. This increase levels up to a Reynolds number close to the critical
value for the onset of the first instability. The entrainment is observed to be
almost extinguished at a distance which is nearly the same for all the steady
wakes within the $R$ range here considered, i.e. [20-100], which indicates that
supercritical steady wakes have the same entrainment length as the subcritical
ones. It is observed that this distance is equal to a number of body lengths
that is equal to the value of the critical Reynolds number ($\sim 47$), as
indicated by a large compilation of experimental results. {\it A fortiori} of
these findings, we propose to interpret the unsteady bifurcation as a process
that allows a smooth increase-redistribution of the entrainment along the wake
according to the weight of the convection over the diffusion. The entrainment
variation along the steady wake has been determined using a matched asymptotic
expansion of the Navier-Stokes velocity field [Tordella and Belan, {\it Physics
of Fluids}, 15(2003)] built on criteria that include the matching of the
transversal velocity produced by the entrainment process.

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The categories of this paper are: adap-org
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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: cond-mat
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The categories of this paper are: eess
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: math
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: econ