11,093 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
Experimental Generation and Observation of Intrinsic Localized Spin Wave Modes in an Antiferromagnet
By driving with a microwave pulse the lowest frequency antiferromagnetic
resonance of the quasi 1-D biaxial antiferromagnet (C_2 H_5 NH_3)_2 CuCl_4 into
an unstable region intrinsic localized spin waves have been generated and
detected in the spin wave gap. These findings are consistent with the
prediction that nonlinearity plus lattice discreteness can lead to localized
excitations with dimensions comparable to the lattice constant.Comment: 10 pages, 4 figures, accepted for publication in Physical Review
Letter
Linear and nonlinear time series analysis of the black hole candidate Cygnus X-1
We analyze the variability in the X-ray lightcurves of the black hole
candidate Cygnus X-1 by linear and nonlinear time series analysis methods.
While a linear model describes the over-all second order properties of the
observed data well, surrogate data analysis reveals a significant deviation
from linearity. We discuss the relation between shot noise models usually
applied to analyze these data and linear stochastic autoregressive models. We
debate statistical and interpretational issues of surrogate data testing for
the present context. Finally, we suggest a combination of tools from linear
andnonlinear time series analysis methods as a procedure to test the
predictions of astrophysical models on observed data.Comment: 15 pages, to appear in Phys. Rev.
Solitonic spin-liquid state due to the violation of the Lifshitz condition in FeTe
A combination of phenomenological analysis and M\"ossbauer spectroscopy
experiments on the tetragonal FeTe system indicates that the magnetic
ordering transition in compounds with higher Fe-excess, 0.11, is
unconventional. Experimentally, a liquid-like magnetic precursor with
quasi-static spin-order is found from significantly broadened M\"ossbauer
spectra at temperatures above the antiferromagnetic transition. The
incommensurate spin-density wave (SDW) order in FeTe is described by a
magnetic free energy that violates the weak Lifshitz condition in the Landau
theory of second-order transitions. The presence of multiple Lifshitz
invariants provides the mechanism to create multidimensional, twisted, and
modulated solitonic phases.Comment: 5 pages, 2 figure
Tycho Brahe's supernova: light from centuries past
The light curve of SN 1572 is described in the terms used nowadays to
characterize SNeIa. By assembling the records of the observations done in
1572--74 and evaluating their uncertainties, it is possible to recover the
light curve and the color evolution of this supernova. It is found that, within
the SNe Ia family, the event should have been a SNIa with a normal rate of
decline, its stretch factor being {\it s} 0.9. Visual light curve near
maximum, late--time decline and the color evolution sustain this conclusion.
After correcting for extinction, the luminosity of this supernova is found to
be M --19.58 --5 log (D/3.5 kpc) 0.42.Comment: 28 pages, 3 figures, 3 tables. submitted to ApJ (Main Journal
Classification of IIB backgrounds with 28 supersymmetries
We show that all IIB backgrounds with strictly 28 supersymmetries are locally
isometric to the plane wave solution of arXiv:hep-th/0206195. Moreover, we
demonstrate that all solutions with more than 26 supersymmetries and only
5-form flux are maximally supersymmetric. The N=28 plane wave solution is a
superposition of the maximally supersymmetric IIB plane wave with a heterotic
string solution. We investigate the propagation of strings in this background,
find the spectrum and give the string light-cone Hamiltonian.Comment: 30 pages, typos correcte
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