3,621 research outputs found
Ising model on the Apollonian network with node dependent interactions
This work considers an Ising model on the Apollonian network, where the
exchange constant between two neighboring spins
is a function of the degree of both spins. Using the exact
geometrical construction rule for the network, the thermodynamical and magnetic
properties are evaluated by iterating a system of discrete maps that allows for
very precise results in the thermodynamic limit. The results can be compared to
the predictions of a general framework for spins models on scale-free networks,
where the node distribution , with node dependent
interacting constants. We observe that, by increasing , the critical
behavior of the model changes, from a phase transition at for a
uniform system , to a T=0 phase transition when : in the
thermodynamic limit, the system shows no exactly critical behavior at a finite
temperature. The magnetization and magnetic susceptibility are found to present
non-critical scaling properties.Comment: 6 figures, 12 figure file
Targeted Recovery as an Effective Strategy against Epidemic Spreading
We propose a targeted intervention protocol where recovery is restricted to
individuals that have the least number of infected neighbours. Our recovery
strategy is highly efficient on any kind of network, since epidemic outbreaks
are minimal when compared to the baseline scenario of spontaneous recovery. In
the case of spatially embedded networks, we find that an epidemic stays
strongly spatially confined with a characteristic length scale undergoing a
random walk. We demonstrate numerically and analytically that this dynamics
leads to an epidemic spot with a flat surface structure and a radius that grows
linearly with the spreading rate.Comment: 6 pages, 5 figure
A micromechanical model of collapsing quicksand
The discrete element method constitutes a general class of modeling
techniques to simulate the microscopic behavior (i.e. at the particle scale) of
granular/soil materials. We present a contact dynamics method, accounting for
the cohesive nature of fine powders and soils. A modification of the model
adjusted to capture the essential physical processes underlying the dynamics of
generation and collapse of loose systems is able to simulate "quicksand"
behavior of a collapsing soil material, in particular of a specific type, which
we call "living quicksand". We investigate the penetration behavior of an
object for varying density of the material. We also investigate the dynamics of
the penetration process, by measuring the relation between the driving force
and the resulting velocity of the intruder, leading to a "power law" behavior
with exponent 1/2, i.e. a quadratic velocity dependence of the drag force on
the intruder.Comment: 5 pages, 4 figures, accepted for granular matte
Large cities are less green
We study how urban quality evolves as a result of carbon dioxide emissions as
urban agglomerations grow. We employ a bottom-up approach combining two
unprecedented microscopic data on population and carbon dioxide emissions in
the continental US. We first aggregate settlements that are close to each other
into cities using the City Clustering Algorithm (CCA) defining cities beyond
the administrative boundaries. Then, we use data on emissions at a
fine geographic scale to determine the total emissions of each city. We find a
superlinear scaling behavior, expressed by a power-law, between
emissions and city population with average allometric exponent
across all cities in the US. This result suggests that the high productivity of
large cities is done at the expense of a proportionally larger amount of
emissions compared to small cities. Furthermore, our results are substantially
different from those obtained by the standard administrative definition of
cities, i.e. Metropolitan Statistical Area (MSA). Specifically, MSAs display
isometric scaling emissions and we argue that this discrepancy is due to the
overestimation of MSA areas. The results suggest that allometric studies based
on administrative boundaries to define cities may suffer from endogeneity bias
Computer simulation of fatigue under diametrical compression
We study the fatigue fracture of disordered materials by means of computer
simulations of a discrete element model. We extend a two-dimensional fracture
model to capture the microscopic mechanisms relevant for fatigue, and we
simulate the diametric compression of a disc shape specimen under a constant
external force. The model allows to follow the development of the fracture
process on the macro- and micro-level varying the relative influence of the
mechanisms of damage accumulation over the load history and healing of
microcracks. As a specific example we consider recent experimental results on
the fatigue fracture of asphalt. Our numerical simulations show that for
intermediate applied loads the lifetime of the specimen presents a power law
behavior. Under the effect of healing, more prominent for small loads compared
to the tensile strength of the material, the lifetime of the sample increases
and a fatigue limit emerges below which no macroscopic failure occurs. The
numerical results are in a good qualitative agreement with the experimental
findings.Comment: 7 pages, 8 figures, RevTex forma
Fracturing the optimal paths
Optimal paths play a fundamental role in numerous physical applications
ranging from random polymers to brittle fracture, from the flow through porous
media to information propagation. Here for the first time we explore the path
that is activated once this optimal path fails and what happens when this new
path also fails and so on, until the system is completely disconnected. In fact
numerous applications can be found for this novel fracture problem. In the
limit of strong disorder, our results show that all the cracks are located on a
single self-similar connected line of fractal dimension .
For weak disorder, the number of cracks spreads all over the entire network
before global connectivity is lost. Strikingly, the disconnecting path
(backbone) is, however, completely independent on the disorder.Comment: 4 pages,4 figure
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