Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The instability of gyrotactically-trapped cell layers   Several meters below the coastal ocean surface there are areas of high
ecological activity that contain thin layers of concentrated motile
phytoplankton. Gyrotactic trapping has been proposed as a potential mechanism
for layer formation of bottom-heavy swimming algae cells, especially in flows
where the vorticity varies linearly with depth (Durham, Stocker & Kessler,
Science, vol. 323, 2009, pp. 1067-1070). Using a continuum model for dilute
microswimmer suspensions, we report that an instability of a gyrotactically
trapped cell-layer can arise in a pressure-driven plane channel flow. The
linear stability analysis reveals that the equilibrium cell-layer solution is
hydrodynamically unstable due to negative microswimmer buoyancy (i.e. a
gravitational instability) over a range of biologically relevant parameter
values. The critical cell concentration for this instability is found to be
$N_c\simeq 10^4\textrm{cells}/\textrm{cm}^{3}$, a value comparable to the
typical maximum cell concentration observed in thin layers. This result
indicates that the instability may be a potential mechanism for limiting the
layer's maximum cell concentration, especially in regions where turbulence is
weak, and motivates the study of its nonlinear evolution, perhaps, in the
presence of turbulence.

31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph