517 research outputs found
Persistence distributions for non gaussian markovian processes
We propose a systematic method to derive the asymptotic behaviour of the
persistence distribution, for a large class of stochastic processes described
by a general Fokker-Planck equation in one dimension. Theoretical predictions
are compared to simple solvable systems and to numerical calculations. The very
good agreement attests the validity of this approach.Comment: 7 pages, 1 figure, to be published in Europhysics Letter
Random pinning limits the size of membrane adhesion domains
Theoretical models describing specific adhesion of membranes predict (for
certain parameters) a macroscopic phase separation of bonds into adhesion
domains. We show that this behavior is fundamentally altered if the membrane is
pinned randomly due to, e.g., proteins that anchor the membrane to the
cytoskeleton. Perturbations which locally restrict membrane height fluctuations
induce quenched disorder of the random-field type. This rigorously prevents the
formation of macroscopic adhesion domains following the Imry-Ma argument [Y.
Imry and S. K. Ma, Phys. Rev. Lett. 35, 1399 (1975)]. Our prediction of
random-field disorder follows from analytical calculations, and is strikingly
confirmed in large-scale Monte Carlo simulations. These simulations are based
on an efficient composite Monte Carlo move, whereby membrane height and bond
degrees of freedom are updated simultaneously in a single move. The application
of this move should prove rewarding for other systems also.Comment: revised and extended versio
Lipid Bilayers and Membrane Dynamics: Insight into Thickness Fluctuations
Thickness fluctuations have long been predicted in biological membranes but never directly observed experimentally. Here, we utilize neutron spin echo spectroscopy to experimentally reveal such fluctuations in a pure, fully saturated, phosphocholine lipid bilayer system. These fluctuations appear as an excess in the dynamics of undulation fluctuations. Like the bending rigidity, the thickness fluctuations change dramatically as the lipid transition temperature is crossed, appearing to be completely suppressed below the transition. Above the transition, the relaxation rate is on the order of 100 ns and is independent of temperature. The amplitude of the thickness fluctuations is , which agrees well with theoretical calculations and molecular dynamics simulations. The dependence of the fluctuations on lipid tail lengths is also investigated and determined to be minimal in the range of 14 to 18 carbon tails
Pseudo-boundaries in discontinuous 2-dimensional maps
It is known that Kolmogorov-Arnold-Moser boundaries appear in sufficiently
smooth 2-dimensional area-preserving maps. When such boundaries are destroyed,
they become pseudo-boundaries. We show that pseudo-boundaries can also be found
in discontinuous maps. The origin of these pseudo-boundaries are groups of
chains of islands which separate parts of the phase space and need to be
crossed in order to move between the different sub-spaces. Trajectories,
however, do not easily cross these chains, but tend to propagate along them.
This type of behavior is demonstrated using a ``generalized'' Fermi map.Comment: 4 pages, 4 figures, Revtex, epsf, submitted to Physical Review E (as
a brief report
BRCT domains: A little more than kin, and less than kind
AbstractBRCT domains are versatile protein modular domains found as single units or as multiple copies in more than 20 different proteins in the human genome. Interestingly, most BRCT-containing proteins function in the same biological process, the DNA damage response network, but show specificity in their molecular interactions. BRCT domains have been found to bind a wide array of ligands from proteins, phosphorylated linear motifs, and DNA. Here we discuss the biology of BRCT domains and how a domain-centric analysis can aid in the understanding of signal transduction events in the DNA damage response network
Current large deviations in a driven dissipative model
We consider lattice gas diffusive dynamics with creation-annihilation in the
bulk and maintained out of equilibrium by two reservoirs at the boundaries.
This stochastic particle system can be viewed as a toy model for granular gases
where the energy is injected at the boundary and dissipated in the bulk. The
large deviation functional for the particle currents flowing through the system
is computed and some physical consequences are discussed: the mechanism for
local current fluctuations, dynamical phase transitions, the
fluctuation-relation
Molecular observation of contour-length fluctuations limiting topological confinement in polymer melts
In order to study the mechanisms limiting the topological chain confinement in polymer melts, we have performed neutron-spin-echo investigations of the single-chain dynamic-structure factor from polyethylene melts over a large range of chain lengths. While at high molecular weight the reptation model is corroborated, a systematic loosening of the confinement with decreasing chain length is found. The dynamic-structure factors are quantitatively described by the effect of contour-length fluctuations on the confining tube, establishing this mechanism on a molecular level in space and time
Kustaanheimo-Stiefel Regularization and the Quadrupolar Conjugacy
In this note, we present the Kustaanheimo-Stiefel regularization in a
symplectic and quaternionic fashion. The bilinear relation is associated with
the moment map of the - action of the Kustaanheimo-Stiefel
transformation, which yields a concise proof of the symplecticity of the
Kustaanheimo-Stiefel transformation symplectically reduced by this circle
action. The relation between the Kustaanheimo-Stiefel regularization and the
Levi-Civita regularization is established via the investigation of the
Levi-Civita planes. A set of Darboux coordinates (which we call
Chenciner-F\'ejoz coordinates) is generalized from the planar case to the
spatial case. Finally, we obtain a conjugacy relation between the integrable
approximating dynamics of the lunar spatial three-body problem and its
regularized counterpart, similar to the conjugacy relation between the extended
averaged system and the averaged regularized system in the planar case.Comment: 19 pages, corrected versio
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