585 research outputs found
Irreversible Opinion Spreading on Scale-Free Networks
We study the dynamical and critical behavior of a model for irreversible
opinion spreading on Barab\'asi-Albert (BA) scale-free networks by performing
extensive Monte Carlo simulations. The opinion spreading within an
inhomogeneous society is investigated by means of the magnetic Eden model, a
nonequilibrium kinetic model for the growth of binary mixtures in contact with
a thermal bath. The deposition dynamics, which is studied as a function of the
degree of the occupied sites, shows evidence for the leading role played by
hubs in the growth process. Systems of finite size grow either ordered or
disordered, depending on the temperature. By means of standard finite-size
scaling procedures, the effective order-disorder phase transitions are found to
persist in the thermodynamic limit. This critical behavior, however, is absent
in related equilibrium spin systems such as the Ising model on BA scale-free
networks, which in the thermodynamic limit only displays a ferromagnetic phase.
The dependence of these results on the degree exponent is also discussed for
the case of uncorrelated scale-free networks.Comment: 9 pages, 10 figures; added results and discussion on uncorrelated
scale-free networks; added references. To appear in PR
Pacman percolation: a model for enzyme gel degradation
We study a model for the gel degradation by an enzyme, where the gel is
schematized as a cubic lattice, and the enzyme as a random walker, that cuts
the bonds over which it passes. The model undergoes a (reverse) percolation
transition, which for low density of enzymes falls in a universality class
different from random percolation. In particular we have measured a gel
fraction critical exponent beta=1.0+-0.1, in excellent agreement with
experiments made on the real system.Comment: 4 pages, 7 eps figure
Static and dynamic heterogeneities in irreversible gels and colloidal gelation
We compare the slow dynamics of irreversible gels, colloidal gels, glasses
and spin glasses by analyzing the behavior of the so called non-linear
dynamical susceptibility, a quantity usually introduced to quantitatively
characterize the dynamical heterogeneities. In glasses this quantity typically
grows with the time, reaches a maximum and then decreases at large time, due to
the transient nature of dynamical heterogeneities and to the absence of a
diverging static correlation length. We have recently shown that in
irreversible gels the dynamical susceptibility is instead an increasing
function of the time, as in the case of spin glasses, and tends asymptotically
to the mean cluster size. On the basis of molecular dynamics simulations, we
here show that in colloidal gelation where clusters are not permanent, at very
low temperature and volume fractions, i.e. when the lifetime of the bonds is
much larger than the structural relaxation time, the non-linear susceptibility
has a behavior similar to the one of the irreversible gel, followed, at higher
volume fractions, by a crossover towards the behavior of glass forming liquids.Comment: 9 pages, 3 figure
Static and dynamic heterogeneities in a model for irreversible gelation
We study the structure and the dynamics in the formation of irreversible gels
by means of molecular dynamics simulation of a model system where the gelation
transition is due to the random percolation of permanent bonds between
neighboring particles. We analyze the heterogeneities of the dynamics in terms
of the fluctuations of the intermediate scattering functions: In the sol phase
close to the percolation threshold, we find that this dynamical susceptibility
increases with the time until it reaches a plateau. At the gelation threshold
this plateau scales as a function of the wave vector as , with
being related to the decay of the percolation pair connectedness
function. At the lowest wave vector, approaching the gelation threshold it
diverges with the same exponent as the mean cluster size. These
findings suggest an alternative way of measuring critical exponents in a system
undergoing chemical gelation.Comment: 4 pages, 4 figure
Metastable states in the Blume-Emery-Griffiths spin glass model
We study the Blume-Emery-Griffiths spin glass model in presence of an
attractive coupling between real replicas, and evaluate the effective potential
as a function of the density overlap. We find that there is a region, above the
first order transition of the model, where metastable states with a large
density overlap exist. The line where these metastable states appear should
correspond to a purely dynamical transition, with a breaking of ergodicity.
Differently from what happens in p-spin glasses, in this model the dynamical
transition would not be the precursor of a 1-step RSB transition, but
(probably) of a full RSB transition.Comment: RevTeX, 4 pages, 2 fig
Storage capacity of phase-coded patterns in sparse neural networks
We study the storage of multiple phase-coded patterns as stable dynamical
attractors in recurrent neural networks with sparse connectivity. To determine
the synaptic strength of existent connections and store the phase-coded
patterns, we introduce a learning rule inspired to the spike-timing dependent
plasticity (STDP). We find that, after learning, the spontaneous dynamics of
the network replay one of the stored dynamical patterns, depending on the
network initialization. We study the network capacity as a function of
topology, and find that a small- world-like topology may be optimal, as a
compromise between the high wiring cost of long range connections and the
capacity increase.Comment: Accepted for publication in Europhysics Letter
Advertising and irreversible opinion spreading in complex social networks
Irreversible opinion spreading phenomena are studied on small-world and
scale-free networks by means of the magnetic Eden model, a nonequilibrium
kinetic model for the growth of binary mixtures in contact with a thermal bath.
In this model, the opinion of an individual is affected by those of their
acquaintances, but opinion changes (analogous to spin flips in an Ising-like
model) are not allowed. We focus on the influence of advertising, which is
represented by external magnetic fields. The interplay and competition between
temperature and fields lead to order-disorder transitions, which are found to
also depend on the link density and the topology of the complex network
substrate. The effects of advertising campaigns with variable duration, as well
as the best cost-effective strategies to achieve consensus within different
scenarios, are also discussed.Comment: 20 pages, 11 figures. To appear in IJMP
Columnar and lamellar phases in attractive colloidal systems
In colloidal suspensions, the competition between attractive and repulsive
interactions gives rise to a rich and complex phenomenology. Here, we study the
equilibrium phase diagram of a model system using a DLVO interaction potential
by means of molecular dynamics simulations and a thermodynamical approach. As a
result, we find tubular and lamellar phases at low volume fraction. Such
phases, extremely relevant for designing new materials, may be not easily
observed in the experiments because of the long relaxation times and the
presence of defects.Comment: 5 pages, 5 figure
Reconnaissance observations by CIGIDEN after the 2015 Illapel, Chile earthquake and tsunami
This paper describes the reconnaissance work conducted by researchers from the National Research Center for Integrated
Natural Disaster Management (CIGIDEN) between September 23rd and October 2nd in the area affected by the Mw 8.3
Illapel megathrust earthquake, which struck offshore the coast of the Coquimbo Region in central Chile on September 16th
,
2015. A first team focused on the seismic performance and effects of the tsunami on public hospitals and on reinforced
concrete (RC) buildings. A second team focused on the road network infrastructure. Field work included: (i) a survey on the
physical and functional damages of the public hospitals in the Region; (ii) a visual inspection and preliminary damage
assessment of 20 RC buildings in the largest cities of the region and an aftershock instrumentation of the Coquimbo
hospital; and (iii) the inspection of bridges, pedestrian bridges, and rockfall along overstepped cut slopes of the road
network. The overall limited impact of this megathrust earthquake may be explained in part by the long-term efforts made
by the country to prepare for such events. Learnings from the 2010 Maule earthquake were evidenced in the successful
evacuation along the coast of the country, and the overall good performance of engineered masonry structures, and of RC
buildings designed after 2010
Relation between positional specific heat and static relaxation length: Application to supercooled liquids
A general identification of the {\em positional specific heat} as the
thermodynamic response function associated with the {\em static relaxation
length} is proposed, and a phenomenological description for the thermal
dependence of the static relaxation length in supercooled liquids is presented.
Accordingly, through a phenomenological determination of positional specific
heat of supercooled liquids, we arrive at the thermal variation of the static
relaxation length , which is found to vary in accordance with in the quasi-equilibrium supercooled temperature regime, where
is the Vogel-Fulcher temperature and exponent equals unity. This
result to a certain degree agrees with that obtained from mean field theory of
random-first-order transition, which suggests a power law temperature variation
for with an apparent divergence at . However, the phenomenological
exponent , is higher than the corresponding mean field estimate
(becoming exact in infinite dimensions), and in perfect agreement with the
relaxation length exponent as obtained from the numerical simulations of the
same models of structural glass in three spatial dimensions.Comment: Revised version, 7 pages, no figures, submitted to IOP Publishin
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