2,455 research outputs found
Disorder induced brittle to quasi-brittle transition in fiber bundles
We investigate the fracture process of a bundle of fibers with random Young
modulus and a constant breaking strength. For two component systems we show
that the strength of the mixture is always lower than the strength of the
individual components. For continuously distributed Young modulus the tail of
the distribution proved to play a decisive role since fibers break in the
decreasing order of their stiffness. Using power law distributed stiffness
values we demonstrate that the system exhibits a disorder induced brittle to
quasi-brittle transition which occurs analogously to continuous phase
transitions. Based on computer simulations we determine the critical exponents
of the transition and construct the phase diagram of the system.Comment: 6 pages, 6 figure
Crossover transition in bag-like models
We formulate a simple model for a gas of extended hadrons at zero chemical
potential by taking inspiration from the compressible bag model. We show that a
crossover transition qualitatively similar to lattice QCD can be reproduced by
such a system by including some appropriate additional dynamics. Under certain
conditions, at high temperature, the system consist of a finite number of
infinitely extended bags, which occupy the entire space. In this situation the
system behaves as an ideal gas of quarks and gluons.Comment: Corresponds to the published version. Added few references and
changed the titl
Aging dynamics and the topology of inhomogenous networks
We study phase ordering on networks and we establish a relation between the
exponent of the aging part of the integrated autoresponse function
and the topology of the underlying structures. We show that in full generality on networks which are above the lower critical dimension
, i.e. where the corresponding statistical model has a phase transition at
finite temperature. For discrete symmetry models on finite ramified structures
with , which are at the lower critical dimension , we show that
is expected to vanish. We provide numerical results for the physically
interesting case of the percolation cluster at or above the percolation
threshold, i.e. at or above , and for other networks, showing that the
value of changes according to our hypothesis. For
models we find that the same picture holds in the large- limit and
that only depends on the spectral dimension of the network.Comment: LateX file, 4 eps figure
Discontinuous percolation transitions in real physical systems
We study discontinuous percolation transitions (PT) in the diffusion-limited
cluster aggregation model of the sol-gel transition as an example of real
physical systems, in which the number of aggregation events is regarded as the
number of bonds occupied in the system. When particles are Brownian, in which
cluster velocity depends on cluster size as with
, a larger cluster has less probability to collide with other
clusters because of its smaller mobility. Thus, the cluster is effectively more
suppressed in growth of its size. Then the giant cluster size increases
drastically by merging those suppressed clusters near the percolation
threshold, exhibiting a discontinuous PT. We also study the tricritical
behavior by controlling the parameter , and the tricritical point is
determined by introducing an asymmetric Smoluchowski equation.Comment: 5 pages, 5 figure
Revisiting the effect of external fields in Axelrod's model of social dynamics
The study of the effects of spatially uniform fields on the steady-state
properties of Axelrod's model has yielded plenty of controversial results. Here
we re-examine the impact of this type of field for a selection of parameters
such that the field-free steady state of the model is heterogeneous or
multicultural. Analyses of both one and two-dimensional versions of Axelrod's
model indicate that, contrary to previous claims in the literature, the steady
state remains heterogeneous regardless of the value of the field strength.
Turning on the field leads to a discontinuous decrease on the number of
cultural domains, which we argue is due to the instability of zero-field
heterogeneous absorbing configurations. We find, however, that spatially
nonuniform fields that implement a consensus rule among the neighborhood of the
agents enforces homogenization. Although the overall effects of the fields are
essentially the same irrespective of the dimensionality of the model, we argue
that the dimensionality has a significant impact on the stability of the
field-free homogeneous steady state
Dielectric properties measurements of brown and white adipose tissue in rats from 0.5 to 10 GHz
Brown adipose tissue (BAT) plays an important role in whole body metabolism and with appropriate stimulus could potentially mediate weight gain and insulin sensitivity. Although imaging techniques are available to detect subsurface BAT, there are currently no viable methods for continuous acquisition of BAT energy expenditure. Microwave (MW) radiometry is an emerging technology that allows the quantification of tissue temperature variations at depths of several centimeters. Such temperature differentials may be correlated with variations in metabolic rate, thus providing a quantitative approach to monitor BAT metabolism. In order to optimize MW radiometry, numerical and experimental phantoms with accurate dielectric properties are required to develop and calibrate radiometric sensors. Thus, we present for the first time, the characterization of relative permittivity and electrical conductivity of brown (BAT) and white (WAT) adipose tissues in rats across the MW range 0.5-10GHz. Measurements were carried out in situ and post mortem in six female rats of approximately 200g. A Cole-Cole model was used to fit the experimental data into a parametric model that describes the variation of dielectric properties as a function of frequency. Measurements confirm that the dielectric properties of BAT (Δr = 14.0-19.4, Ï = 0.3-3.3S/m) are significantly higher than those of WAT (Δr = 9.1-11.9, Ï = 0.1-1.9S/m), in accordance with the higher water content of BAT
Utility of Microwave Radiometry for Diagnostic and Therapeutic Applications of Non-Invasive Temperature Monitoring
This paper describes the use of microwave radiometry for several diagnostic and therapeutic applications that can benefit from accurate non-invasive measurement of volume average temperature of tissue regions extending 4cm or more into the body. Design features are summarized for an appropriate high sensitivity long term stable system with 2.5 and 7 cm diameter receive antennas and integral 1.35 GHz total power radiometer electronics. Radiometer performance is characterized with electromagnetic and thermal simulations and experimental measurements in realistic models of two typical clinical applications. Results demonstrate sufficient sensitivity to track clinically significant changes in temperature of deep tissue targets for applications like the non-invasive detection of vesicoureteral reflux and monitoring brain âcoreâ temperature during extended hypothermic surgery
Analytical approach to directed sandpile models on the Apollonian network
We investigate a set of directed sandpile models on the Apollonian network,
which are inspired on the work by Dhar and Ramaswamy (PRL \textbf{63}, 1659
(1989)) for Euclidian lattices. They are characterized by a single parameter
, that restricts the number of neighbors receiving grains from a toppling
node. Due to the geometry of the network, two and three point correlation
functions are amenable to exact treatment, leading to analytical results for
the avalanche distributions in the limit of an infinite system, for .
The exact recurrence expressions for the correlation functions are numerically
iterated to obtain results for finite size systems, when larger values of
are considered. Finally, a detailed description of the local flux properties is
provided by a multifractal scaling analysis.Comment: 7 pages in two-column format, 10 illustrations, 5 figure
Percolation on the average and spontaneous magnetization for q-states Potts model on graph
We prove that the q-states Potts model on graph is spontaneously magnetized
at finite temperature if and only if the graph presents percolation on the
average. Percolation on the average is a combinatorial problem defined by
averaging over all the sites of the graph the probability of belonging to a
cluster of a given size. In the paper we obtain an inequality between this
average probability and the average magnetization, which is a typical extensive
function describing the thermodynamic behaviour of the model
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