Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vertex model instabilities for tissues subject to cellular activity or
  applied stresses   The vertex model is widely used to describe the dynamics of epithelial
tissues, because of its simplicity and versatility and the direct inclusion of
biophysical parameters. Here, it is shown that quite generally, when cells
modify their equilibrium perimeter due to their activity, or the tissue is
subject to external stresses, the tissue becomes unstable with deformations
that couple pure-shear or deviatoric modes, with rotation and expansion modes.
For short times, these instabilities deform cells increasing their ellipticity
while, at longer times, cells become non-convex, indicating that the vertex
model ceases to be a valid description for tissues under these conditions. The
agreement between the analytic calculations performed for a regular hexagonal
tissue and the simulations of disordered tissues is excellent due to the
homogenization of the tissue at long wavelengths.

12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex