46,842 research outputs found
Active dynamics of tissue shear flow
We present a hydrodynamic theory to describe shear flows in developing
epithelial tissues. We introduce hydrodynamic fields corresponding to state
properties of constituent cells as well as a contribution to overall tissue
shear flow due to rearrangements in cell network topology. We then construct a
generic linear constitutive equation for the shear rate due to topological
rearrangements and we investigate a novel rheological behaviour resulting from
memory effects in the tissue. We identify two distinct active cellular
processes: generation of active stress in the tissue, and actively driven
topological rearrangements. We find that these two active processes can produce
distinct cellular and tissue shape changes, depending on boundary conditions
applied on the tissue. Our findings have consequences for the understanding of
tissue morphogenesis during development
Subdivision Shell Elements with Anisotropic Growth
A thin shell finite element approach based on Loop's subdivision surfaces is
proposed, capable of dealing with large deformations and anisotropic growth. To
this end, the Kirchhoff-Love theory of thin shells is derived and extended to
allow for arbitrary in-plane growth. The simplicity and computational
efficiency of the subdivision thin shell elements is outstanding, which is
demonstrated on a few standard loading benchmarks. With this powerful tool at
hand, we demonstrate the broad range of possible applications by numerical
solution of several growth scenarios, ranging from the uniform growth of a
sphere, to boundary instabilities induced by large anisotropic growth. Finally,
it is shown that the problem of a slowly and uniformly growing sheet confined
in a fixed hollow sphere is equivalent to the inverse process where a sheet of
fixed size is slowly crumpled in a shrinking hollow sphere in the frictionless,
quasi-static, elastic limit.Comment: 20 pages, 12 figures, 1 tabl
Curvature-induced stiffening of a fish fin
How fish modulate their fin stiffness during locomotive manoeuvres remains
unknown. We show that changing the fin's curvature modulates its stiffness.
Modelling the fin as bendable bony rays held together by a membrane, we deduce
that fin curvature is manifested as a misalignment of the principal bending
axes between neighbouring rays. An external force causes neighbouring rays to
bend and splay apart, and thus stretches the membrane. This coupling between
bending the rays and stretching the membrane underlies the increase in
stiffness. Using analysis of a 3D reconstruction of a Mackerel (Scomber
japonicus) pectoral fin, we calculate the range of stiffnesses this fin is
expected to span by changing curvature. The 3D reconstruction shows that, even
in its geometrically flat state, a functional curvature is embedded within the
fin microstructure owing to the morphology of individual rays. Since the
ability of a propulsive surface to transmit force to the surrounding fluid is
limited by its stiffness, the fin curvature controls the coupling between the
fish and its surrounding fluid. Thereby, our results provide mechanical
underpinnings and morphological predictions for the hypothesis that the spanned
range of fin stiffnesses correlates with the behaviour and the ecological niche
of the fish
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