Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Biased swimming cells do not disperse in pipes as tracers: a population
  model based on microscale behaviour   There is much current interest in modelling suspensions of algae and other
micro-organisms for biotechnological exploitation, and many bioreactors are of
tubular design. Using generalized Taylor dispersion theory, we develop a
population-level swimming-advection-diffusion model for suspensions of
micro-organisms in a vertical pipe flow. In particular, a combination of
gravitational and viscous torques acting on individual cells can affect their
swimming behaviour, which is termed gyrotaxis. This typically leads to local
cell drift and diffusion in a suspension of cells. In a flow in a pipe, small
amounts of radial drift across streamlines can have a major impact on the
effective axial drift and diffusion of the cells. We present a Galerkin method
to calculate the local mean swimming velocity and diffusion tensor based on
local shear for arbitrary flow rates. This method is validated with asymptotic
results obtained in the limits of weak and strong shear. We solve the resultant
swimming-advection-diffusion equation using numerical methods for the case of
imposed Poiseuille flow and investigate how the flow modifies the dispersion of
active swimmers from that of passive scalars. We establish that generalized
Taylor dispersion theory predicts an enhancement of gyrotactic focussing in
pipe flow with increasing shear strength, in contrast to earlier models. We
also show that biased swimming cells may behave very differently to passive
tracers, drifting axially at up to twice the rate and diffusing much less.

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The categories of this paper are: funct-an
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The categories of this paper are: econ
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
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The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-alg