770 research outputs found
Non-equilibrium wetting transition in a magnetic Eden model
Magnetic Eden clusters with ferromagnetic interaction between
nearest-neighbor spins are grown in a confined 2d-geometry with short range
magnetic fields acting on the surfaces. The change of the growing interface
curvature driven by the field and the temperature is identified as a
non-equilibrium wetting transition and the corresponding phase diagram is
evaluated.Comment: 11 pages, 6 figure
Far-from-equilibrium growth of thin films in a temperature gradient
The irreversible growth of thin films under far-from-equilibrium conditions
is studied in dimensional strip geometries. Across one of the
transverse directions, a temperature gradient is applied by thermal baths at
fixed temperatures between and , where and
is the critical temperature of the system in contact with
an homogeneous thermal bath. By using standard finite-size scaling methods, we
characterized a continuous order-disorder phase transition driven by the
thermal bath gradient with critical temperature and critical
exponents , , and , which belong
to a different universality class from that of films grown in an homogeneous
bath. Furthermore, the effects of the temperature gradient are analyzed by
means of a bond model that captures the growth dynamics. The interplay of
geometry and thermal bath asymmetries leads to growth bond flux asymmetries and
the onset of transverse ordering effects that explain qualitatively the shift
in the critical temperature.Comment: 4 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1207.253
Corner wetting in a far-from-equilibrium magnetic growth model
The irreversible growth of magnetic films is studied in three-dimensional
confined geometries of size , where is the growing
direction. Competing surface magnetic fields, applied to opposite corners of
the growing system, lead to the observation of a localization-delocalization
(weakly rounded) transition of the interface between domains of up and down
spins on the planes transverse to the growing direction. This effective
transition is the precursor of a true far-from-equilibrium corner wetting
transition that takes place in the thermodynamic limit. The phenomenon is
characterized quantitatively by drawing a magnetic field-temperature phase
diagram, firstly for a confined sample of finite size, and then by
extrapolating results, obtained with samples of different size, to the
thermodynamic limit. The results of this work are a nonequilibrium realization
of analogous phenomena recently investigated in equilibrium systems, such as
corner wetting transitions in the Ising model.Comment: 14 pages, 8 figures. EPJ styl
Criticality and the Onset of Ordering in the Standard Vicsek Model
Experimental observations of animal collective behavior have shown stunning
evidence for the emergence of large-scale cooperative phenomena resembling
phase transitions in physical systems. Indeed, quantitative studies have found
scale-free correlations and critical behavior consistent with the occurrence of
continuous, second-order phase transitions. The Standard Vicsek Model (SVM), a
minimal model of self-propelled particles in which their tendency to align with
each other competes with perturbations controlled by a noise term, appears to
capture the essential ingredients of critical flocking phenomena. In this
paper, we review recent finite-size scaling and dynamical studies of the SVM,
which present a full characterization of the continuous phase transition
through dynamical and critical exponents. We also present a complex network
analysis of SVM flocks and discuss the onset of ordering in connection with
XY-like spin models.Comment: 15 pages, 4 figures. To appear in Interface Focu
Complex Network Structure of Flocks in the Standard Vicsek Model
In flocking models, the collective motion of self-driven individuals leads to
the formation of complex spatiotemporal patterns. The Standard Vicsek Model
(SVM) considers individuals that tend to adopt the direction of movement of
their neighbors under the influence of noise. By performing an extensive
complex network characterization of the structure of SVM flocks, we show that
flocks are highly clustered, assortative, and non-hierarchical networks with
short-tailed degree distributions. Moreover, we also find that the SVM dynamics
leads to the formation of complex structures with an effective dimension higher
than that of the space where the actual displacements take place. Furthermore,
we show that these structures are capable of sustaining mean-field-like
orientationally ordered states when the displacements are suppressed, thus
suggesting a linkage between the onset of order and the enhanced dimensionality
of SVM flocks.Comment: 26 pages, 11 figures. To appear in J. Stat. Phy
Random Walk Access Times on Partially-Disordered Complex Networks: an Effective Medium Theory
An analytic effective medium theory is constructed to study the mean access
times for random walks on hybrid disordered structures formed by embedding
complex networks into regular lattices, considering transition rates that
are different for steps across lattice bonds from the rates across network
shortcuts. The theory is developed for structures with arbitrary shortcut
distributions and applied to a class of partially-disordered traversal enhanced
networks in which shortcuts of fixed length are distributed randomly with
finite probability. Numerical simulations are found to be in excellent
agreement with predictions of the effective medium theory on all aspects
addressed by the latter. Access times for random walks on these partially
disordered structures are compared to those on small-world networks, which on
average appear to provide the most effective means of decreasing access times
uniformly across the network.Comment: 12 pages, 8 figures; added new results and discussion; added appendix
on numerical procedures. To appear in PR
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