12,542 research outputs found
Stochastic dynamics of adhesion clusters under shared constant force and with rebinding
Single receptor-ligand bonds have finite lifetimes, so that biological
systems can dynamically react to changes in their environment. In cell
adhesion, adhesion bonds usually act cooperatively in adhesion clusters.
Outside the cellular context, adhesion clusters can be probed quantitatively by
attaching receptors and ligands to opposing surfaces. Here we present a
detailed theoretical analysis of the stochastic dynamics of a cluster of
parallel bonds under shared constant loading and with rebinding. Analytical
solutions for the appropriate one-step master equation are presented for
special cases, while the general case is treated with exact stochastic
simulations. If the completely dissociated state is modeled as an absorbing
boundary, mean cluster lifetime is finite and can be calculated exactly. We
also present a detailed analysis of fluctuation effects and discuss various
approximations to the full stochastic description.Comment: Revtex, 29 pages, 23 postscript figures included (some with reduced
image quality
Bistability of cell-matrix adhesions resulting from non-linear receptor-ligand dynamics
Bistability is a major mechanism for cellular decision making and usually
results from positive feedback in biochemical control systems. Here we show
theoretically that bistability between unbound and bound states of adhesion
clusters results from positive feedback mediated by structural rather than
biochemical processes, namely by receptor-ligand dissociation and association
dynamics which depend non-linearly on mechanical force and receptor-ligand
separation. For small cell-matrix adhesions, we find rapid switching between
unbound and bound states, which in the initial stages of adhesion allows the
cell to explore its environment through many transient adhesions.Comment: Revtex, 3 pages, 3 postscript figures included, to appear in
Biophysical Journal as Biophysical Lette
Phase Separation Dynamics Induced by an Interaction Quench of a Correlated Fermi-Fermi Mixture in a Double Well
We explore the interspecies interaction quench dynamics of ultracold
spin-polarized few-body mass balanced Fermi-Fermi mixtures confined in a
double-well with an emphasis on the beyond Hartree-Fock correlation effects. It
is shown that the ground state of particle imbalanced mixtures exhibits a
symmetry breaking of the single-particle density for strong interactions in the
Hartree-Fock limit, which is altered within the many-body approach. Quenching
the interspecies repulsion towards the strongly interacting regime the two
species phase separate within the Hartree-Fock approximation while remaining
miscible in the many-body treatment. Despite their miscible character on the
one-body level the two species are found to be strongly correlated and exhibit
a phase separation on the two-body level that suggests the anti-ferromagnetic
like behavior of the few-body mixture. For particle balanced mixtures we show
that an intrawell fragmentation (filamentation) of the density occurs both for
the ground state as well as upon quenching from weak to strong interactions, a
result that is exclusively caused by the presence of strong correlations.
Inspecting the two-body correlations a phase separation of the two species is
unveiled being a precursor towards an anti-ferromagnetic state. Finally, we
simulate in-situ single-shot measurements and showcase how our findings can be
retrieved by averaging over a sample of single-shot images.Comment: 15 pages, 9 figure
Focal adhesions as mechanosensors: the two-spring model
Adhesion-dependent cells actively sense the mechanical properties of their
environment through mechanotransductory processes at focal adhesions, which are
integrin-based contacts connecting the extracellular matrix to the
cytoskeleton. Here we present first steps towards a quantitative understanding
of focal adhesions as mechanosensors. It has been shown experimentally that
high levels of force are related to growth of and signaling at focal adhesions.
In particular, activation of the small GTPase Rho through focal adhesions leads
to the formation of stress fibers. Here we discuss one way in which force might
regulate the internal state of focal adhesions, namely by modulating the
internal rupture dynamics of focal adhesions. A simple two-spring model shows
that the stiffer the environment, the more efficient cellular force is built up
at focal adhesions by molecular motors interacting with the actin filaments.Comment: Latex, 17 pages, 5 postscript figures include
Focal adhesions as mechanosensors: the two-spring model
Adhesion-dependent cells actively sense the mechanical properties of their
environment through mechanotransductory processes at focal adhesions, which are
integrin-based contacts connecting the extracellular matrix to the
cytoskeleton. Here we present first steps towards a quantitative understanding
of focal adhesions as mechanosensors. It has been shown experimentally that
high levels of force are related to growth of and signaling at focal adhesions.
In particular, activation of the small GTPase Rho through focal adhesions leads
to the formation of stress fibers. Here we discuss one way in which force might
regulate the internal state of focal adhesions, namely by modulating the
internal rupture dynamics of focal adhesions. A simple two-spring model shows
that the stiffer the environment, the more efficient cellular force is built up
at focal adhesions by molecular motors interacting with the actin filaments.Comment: Latex, 17 pages, 5 postscript figures include
Noise-Induced Transition from Translational to Rotational Motion of Swarms
We consider a model of active Brownian agents interacting via a harmonic
attractive potential in a two-dimensional system in the presence of noise. By
numerical simulations, we show that this model possesses a noise-induced
transition characterized by the breakdown of translational motion and the onset
of swarm rotation as the noise intensity is increased. Statistical properties
of swarm dynamics in the weak noise limit are further analytically
investigated.Comment: 7 pages, 7 figure
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