23 research outputs found
Effective Edwards-Wilkinson equation for single-file diffusion
In this work, we present an effective discrete Edwards-Wilkinson equation
aimed to describe the single-file diffusion process. The key physical
properties of the system are captured defining an effective elasticity, which
is proportional to the single particle diffusion coefficient and to the inverse
squared mean separation between particles. The effective equation gives a
description of single-file diffusion using the global roughness of the system
of particles, which presents three characteristic regimes, namely normal
diffusion, subdiffusion and saturation, separated by two crossover times. We
show how these regimes scale with the parameters of the original system.
Additional repulsive interaction terms are also considered and we analyze how
the crossover times depend on the intensity of the additional terms. Finally,
we show that the roughness distribution can be well characterized by the
Edwards-Wilkinson universal form for the different single-file diffusion
processes studied here.Comment: 9 pages, 9 figure
Parameter free scaling relation for nonequilibrium growth processes
We discuss a parameter free scaling relation that yields a complete data
collapse for large classes of nonequilibrium growth processes. We illustrate
the power of this new scaling relation through various growth models, as for
example the competitive growth model RD/RDSR (random deposition/random
deposition with surface diffusion) and the RSOS (restricted solid-on-solid)
model with different nearest-neighbor height differences, as well as through a
new deposition model with temperature dependent diffusion. The new scaling
relation is compared to the familiar Family-Vicsek relation and the limitations
of the latter are highlighted.Comment: 4 pages, 4 figures, to appear in Physical Review
Wavelet transforms in a critical interface model for Barkhausen noise
We discuss the application of wavelet transforms to a critical interface
model, which is known to provide a good description of Barkhausen noise in soft
ferromagnets. The two-dimensional version of the model (one-dimensional
interface) is considered, mainly in the adiabatic limit of very slow driving.
On length scales shorter than a crossover length (which grows with the strength
of surface tension), the effective interface roughness exponent is
, close to the expected value for the universality class of the
quenched Edwards-Wilkinson model. We find that the waiting times between
avalanches are fully uncorrelated, as the wavelet transform of their
autocorrelations scales as white noise. Similarly, detrended size-size
correlations give a white-noise wavelet transform. Consideration of finite
driving rates, still deep within the intermittent regime, shows the wavelet
transform of correlations scaling as for intermediate frequencies.
This behavior is ascribed to intra-avalanche correlations.Comment: RevTeX, 10 pages, 9 .eps figures; Physical Review E, to be publishe
Coevolution of agents and networks: Opinion spreading and community disconnection
We study a stochastic model for the coevolution of a process of opinion
formation in a population of agents and the network which underlies their
interaction. Interaction links can break when agents fail to reach an opinion
agreement. The structure of the network and the distribution of opinions over
the population evolve towards a state where the population is divided into
disconnected communities whose agents share the same opinion. The statistical
properties of this final state vary considerably as the model parameters are
changed. Community sizes and their internal connectivity are the quantities
used to characterize such variations.Comment: To appear in Phys. Lett.
Dynamical Critical Phenomena and Large Scale Structure of the Universe: the Power Spectrum for Density Fluctuations
As is well known, structure formation in the Universe at times after
decoupling can be described by hydrodynamic equations. These are shown here to
be equivalent to a generalization of the stochastic Kardar--Parisi--Zhang
equation with time-- dependent viscosity in epochs of dissipation. As a
consequence of the Dynamical Critical Scaling induced by noise and
fluctuations, these equations describe the fractal behavior (with a scale
dependent fractal dimension) observed at the smaller scales for the
galaxy--to--galaxy correlation function and the Harrison--Zel'dovich
spectrum at decoupling. By a Renormalization Group calculation of the
two--point correlation function between galaxies in the presence of (i) the
expansion of the Universe and (ii) non--equilibrium, we can account, from first
principles, for the main features of the observed shape of the power spectrum.Comment: 13 pages with 2 encapsulated PostScript figures included, gzipped tar
forma
Kinetic roughening, global quantities, and fluctuation-dissipation relations
Growth processes and interface fluctuations can be studied through the
properties of global quantities. We here discuss a global quantity that not
only captures better the roughness of an interface than the widely studied
surface width, but that is also directly conjugate to an experimentally
accessible parameter, thereby allowing us to study in a consistent way the
global response of the system to a global change of external conditions.
Exploiting the full analyticity of the linear Edwards-Wilkinson and
Mullins-Herring equations, we study in detail various two-time functions
related to that quantity. This quantity fulfills the fluctuation-dissipation
theorem when considering steady-state equilibrium fluctuations.Comment: 13 pages, 5 figure
Symmetry based determination of space-time functions in nonequilibrium growth processes
We study the space-time correlation and response functions in nonequilibrium
growth processes described by linear stochastic Langevin equations. Exploiting
exclusively the existence of space and time dependent symmetries of the
noiseless part of these equations, we derive expressions for the universal
scaling functions of two-time quantities which are found to agree with the
exact expressions obtained from the stochastic equations of motion. The
usefulness of the space-time functions is illustrated through the investigation
of two atomistic growth models, the Family model and the restricted Family
model, which are shown to belong to a unique universality class in 1+1 and in
2+1 space dimensions. This corrects earlier studies which claimed that in 2+1
dimensions the two models belong to different universality classes.Comment: 18 pages, three figures included, submitted to Phys. Rev.
Non-equilibrium processes: driven lattice gases, interface dynamics, and quenched disorder effects on density profiles and currents
Properties of the one-dimensional totally asymmetric simple exclusion process
(TASEP), and their connection with the dynamical scaling of moving interfaces
described by a Kardar-Parisi-Zhang (KPZ) equation are investigated. With
periodic boundary conditions, scaling of interface widths (the latter defined
via a discrete occupation-number-to-height mapping), gives the exponents
, , . With open boundaries, results
are as follows: (i) in the maximal-current phase, the exponents are the same as
for the periodic case, and in agreement with recent Bethe ansatz results; (ii)
in the low-density phase, curve collapse can be found to a rather good extent,
with , , , which is apparently at
variance with the Bethe ansatz prediction ; (iii) on the coexistence line
between low- and high- density phases, , ,
, in relatively good agreement with the Bethe ansatz prediction
. From a mean-field continuum formulation, a characteristic relaxation
time, related to kinematic-wave propagation and having an effective exponent
, is shown to be the limiting slow process for the low density
phase, which accounts for the above-mentioned discrepancy with Bethe ansatz
results. For TASEP with quenched bond disorder, interface width scaling gives
, , . From a direct analytic approach
to steady-state properties of TASEP with quenched disorder, closed-form
expressions for the piecewise shape of averaged density profiles are given, as
well as rather restrictive bounds on currents. All these are substantiated in
numerical simulations
A systems biology approach to the evolution of plant-virus interactions
[EN] Omic approaches to the analysis of plant-virus interactions are becoming increasingly popular. These types of data, in combination with models of interaction networks, will aid in revealing not only host components that are important for the virus life cycle, but also general patterns about the way in which different viruses manipulate host regulation of gene expression for their own benefit and possible mechanisms by which viruses evade host defenses. Here, we review studies identifying host genes regulated by viruses and discuss how these genes integrate in host regulatory and interaction networks, with a particular focus on the physical properties of these networks. © 2011 Elsevier Ltd.This work was supported by grants from the Spanish MICINN (BFU2009-06993) and Generalitat Valenciana (PROMETEO2010/019). GR is supported by a fellowship from Generalitat Valenciana (BFPI2007-160) and JC by a contract from MICINN (Grant TIN2006-12860). We thank Jose-Antonio Dares and Gustavo G. Gomez for comments.Elena Fito, SF.; Carrera, J.; Rodrigo, J. (2011). A systems biology approach to the evolution of plant-virus interactions. Current Opinion in Plant Biology. 14(4):372-377. https://doi.org/10.1016/j.pbi.2011.03.013S37237714
Towards an integrated molecular model of plant-virus interactions
[EN] The application in recent years of network theory methods to the study of host-virus interactions is providing a new perspective to the way viruses manipulate the host to promote their own replication. An integrated molecular model of such pathosystems require three detailed maps describing, firstly, the interactions between viral elements, secondly, the interactions between host elements, and thirdly, the cross-interactions between viral and host elements. Here, we compile available information for Potyvirus infecting Arabidopsis thaliana. With an integrated model, it is possible to analyze the mode of virus action and how the perturbation of the virus targets propagates along the network. These studies suggest that viral pathogenicity results not only from the alteration of individual elements but it is a systemic property.This work was supported by the grant BFU2009-06993 from the Spanish Ministry of Science and Innovation to S.F.E. G.R. thanks an EMBO long-term fellowship co-funded by Marie Curie actions (ALTF-1177-2011).Elena Fito, SF.; Rodrigo Tarrega, G. (2012). Towards an integrated molecular model of plant-virus interactions. Current Opinion in Virology. 2(6):719-724. https://doi.org/10.1016/j.coviro.2012.09.004S7197242