1,705 research outputs found
Coupling of cytoplasm and adhesion dynamics determines cell polarization and locomotion
Observations of single epidermal cells on flat adhesive substrates have
revealed two distinct morphological and functional states, namely a
non-migrating symmetric unpolarized state and a migrating asymmetric polarized
state. These states are characterized by different spatial distributions and
dynamics of important biochemical cell components: F-actin and myosin-II form
the contractile part of the cytoskeleton, and integrin receptors in the plasma
membrane connect F-actin filaments to the substratum. In this way, focal
adhesion complexes are assembled, which determine cytoskeletal force
transduction and subsequent cell locomotion. So far, physical models have
reduced this phenomenon either to gradients in regulatory control molecules or
to different mechanics of the actin filament system in different regions of the
cell.
Here we offer an alternative and self-organizational model incorporating
polymerization, pushing and sliding of filaments, as well as formation of
adhesion sites and their force dependent kinetics. All these phenomena can be
combined into a non-linearly coupled system of hyperbolic, parabolic and
elliptic differential equations. Aim of this article is to show how relatively
simple relations for the small-scale mechanics and kinetics of participating
molecules may reproduce the emergent behavior of polarization and migration on
the large-scale cell level.Comment: v2 (updates from proof): add TOC, clarify Fig. 4, fix several typo
No strong coupling regime in the fermion-Higgs sector of the standard model
We present results for the renormalized quartic self-coupling \lm_R and the
renormalized Yukawa coupling in a fermion-Higgs model with two SU(2)
doublets, indicating that these couplings are not very strong.Comment: 4 pages, 4 postscript figures (appended), ITFA-92-32, HLRZ-92-92,
UCSD/PTH 92-43, Contribution to the Conference Lattice'9
Can the Couplings in the Fermion-Higgs Sector of the Standard Model be Strong?
We present results for the renormalized quartic self-coupling and
the Yukawa coupling in a lattice fermion-Higgs model with two SU(2)
doublets, mostly for large values of the bare couplings. One-component
(`reduced') staggered fermions are used in a numerical simulation with the
Hybrid Monte Carlo algorithm. The fermion and Higgs masses and the renormalized
scalar field expectation value are computed on lattices, where
ranges from to . In the scaling region these quantities are found to
have a dependence, which is used to determine their values in the
infinite volume limit. We then calculate the and from their
tree level definitions in terms of the masses and renormalized scalar field
expectation value, extrapolated to infinite volume. The scalar field
propagators can be described for momenta up to the cut-off by one fermion loop
renormalized perturbation theory and the results for and come
out to be close to the tree level unitarity bounds. There are no signs that are
in contradiction with the triviality of the Yukawa and quartic self-coupling.Comment: 36 pages + 12 postscript figures (appended), Amsterdam ITFA 92-23,
HLRZ Juelich 92-58, UCSD/PTH 92-3
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