485 research outputs found
Injected Power Fluctuations in 1D Dissipative Systems
Using fermionic techniques, we compute exactly the large deviation function
(ldf) of the time-integrated injected power in several one-dimensional
dissipative systems of classical spins. The dynamics are T=0 Glauber dynamics
supplemented by an injection mechanism, which is taken as a Poissonian flipping
of one particular spin. We discuss the physical content of the results,
specifically the influence of the rate of the Poisson process on the properties
of the ldf.Comment: 18 pages, 8 figure
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
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
Globular Structures of a Helix-Coil Copolymer: Self-Consistent Treatment
A self-consistent field theory was developed in the grand-canonical ensemble
formulation to study transitions in a helix-coil multiblock globule. Helical
and coil parts are treated as stiff rods and self-avoiding walks of variable
lengths correspondingly. The resulting field-theory takes, in addition to the
conventional Zimm-Bragg (B.H. Zimm, I.K. Bragg, J. Chem. Phys. 31, 526 (1959))
parameters, also three-dimensional interaction terms into account. The
appropriate differential equations which determine the self-consistent fields
were solved numerically with finite element method. Three different phase
states are found: open chain, amorphous globule and nematic liquid-crystalline
(LC) globule. The LC-globule formation is driven by the interplay between the
hydrophobic helical segments attraction and the anisotropic globule surface
energy of an entropic nature. The full phase diagram of the helix-coil
copolymer was calculated and thoroughly discussed. The suggested theory shows a
clear interplay between secondary and tertiary structures in globular
homopolypeptides.Comment: 26 pages, 30 figures, corrected some typo
Solving advection equations by applying the crank-nicolson scheme combined with the richardson extrapolation
Advection equations appear often in large-scale mathematical models arising in many fields of science and engineering. The Crank-Nicolson scheme can successfully be used in the numerical treatment of such equations. The accuracy of the numerical solution can sometimes be increased substantially by applying the Richardson Extrapolation. Two theorems related to the accuracy of the calculations will be formulated and proved in this paper. The usefulness of the combination consisting of the Crank-Nicolson scheme and the Richardson Extrapolation will be illustrated by numerical examples. Copyright Zahari Zlatev et al
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
Algebraic Correlation Function and Anomalous Diffusion in the HMF model
In the quasi-stationary states of the Hamiltonian Mean-Field model, we
numerically compute correlation functions of momenta and diffusion of angles
with homogeneous initial conditions. This is an example, in a N-body
Hamiltonian system, of anomalous transport properties characterized by non
exponential relaxations and long-range temporal correlations. Kinetic theory
predicts a striking transition between weak anomalous diffusion and strong
anomalous diffusion. The numerical results are in excellent agreement with the
quantitative predictions of the anomalous transport exponents. Noteworthy, also
at statistical equilibrium, the system exhibits long-range temporal
correlations: the correlation function is inversely proportional to time with a
logarithmic correction instead of the usually expected exponential decay,
leading to weak anomalous transport properties
Different faces of the phantom
The SNe type Ia data admit that the Universe today may be dominated by some
exotic matter with negative pressure violating all energy conditions. Such
exotic matter is called {\it phantom matter} due to the anomalies connected
with violation of the energy conditions. If a phantom matter dominates the
matter content of the universe, it can develop a singularity in a finite future
proper time. Here we show that, under certain conditions, the evolution of
perturbations of this matter may lead to avoidance of this future singularity
(the Big Rip). At the same time, we show that local concentrations of a phantom
field may form, among other regular configurations, black holes with
asymptotically flat static regions, separated by an event horizon from an
expanding, singularity-free, asymptotically de Sitter universe.Comment: 6 pages, presented at IRGAC 2006, Barcelona, 11-15 July 200
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