Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The role of mechanical forces in the planar-to-bulk transition in
  growing Escherichia coli microcolonies   Mechanical forces are obviously important in the assembly of
three-dimensional multicellular structures, but their detailed role is often
unclear. We have used growing microcolonies of the bacterium \emph{Escherichia
coli} to investigate the role of mechanical forces in the transition from
two-dimensional growth (on the interface between a hard surface and a soft
agarose pad) to three-dimensional growth (invasion of the agarose). We measure
the position within the colony where the invasion transition happens, the cell
density within the colony, and the colony size at the transition as functions
of the concentration of the agarose. We use a phenomenological theory, combined
with individual-based computer simulations, to show how mechanical forces
acting between the bacterial cells, and between the bacteria and the
surrounding matrix, lead to the complex phenomena observed in our experiments -
in particular a non-trivial dependence of the colony size at the transition on
the agarose concentration. Matching these approaches leads to a prediction for
how the friction coefficient between the bacteria and the agarose should vary
with agarose concentration. Our experimental conditions mimic numerous clinical
and environmental scenarios in which bacteria invade soft matrices, as well as
shedding more general light on the transition between two- and
three-dimensional growth in multicellular assemblies.

17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat