272 research outputs found
Nature of the Spin-glass State in the Three-dimensional Gauge Glass
We present results from simulations of the gauge glass model in three
dimensions using the parallel tempering Monte Carlo technique. Critical
fluctuations should not affect the data since we equilibrate down to low
temperatures, for moderate sizes. Our results are qualitatively consistent with
earlier work on the three and four dimensional Edwards-Anderson Ising spin
glass. We find that large scale excitations cost only a finite amount of energy
in the thermodynamic limit, and that those excitations have a surface whose
fractal dimension is less than the space dimension, consistent with a scenario
proposed by Krzakala and Martin, and Palassini and Young.Comment: 5 pages, 7 figure
The Eigenvalue Analysis of the Density Matrix of 4D Spin Glasses Supports Replica Symmetry Breaking
We present a general and powerful numerical method useful to study the
density matrix of spin models. We apply the method to finite dimensional spin
glasses, and we analyze in detail the four dimensional Edwards-Anderson model
with Gaussian quenched random couplings. Our results clearly support the
existence of replica symmetry breaking in the thermodynamical limit.Comment: 8 pages, 13 postscript figure
Monte Carlo simulations of the four-dimensional XY spin glass at low temperatures
We report results for simulations of the four-dimensional XY spin glass using
the parallel tempering Monte Carlo method at low temperatures for moderate
sizes. Our results are qualitatively consistent with earlier work on the
three-dimensional gauge glass as well as three- and four-dimensional
Edwards-Anderson Ising spin glass. An extrapolation of our results would
indicate that large-scale excitations cost only a finite amount of energy in
the thermodynamic limit. The surface of these excitations may be fractal,
although we cannot rule out a scenario compatible with replica symmetry
breaking in which the surface of low-energy large-scale excitations is space
filling.Comment: 6 pages, 8 figure
Remarks on the determination of the Landau gauge OPE for the Asymmetric three gluon vertex
We compute a compact OPE formula describing power corrections to the
perturbative expression for the asymmetric -renormalized
running coupling constant up to the leading logarithm. By the use of the
phenomelogical hypothesis leading to the factorization of the condensates
through a perturbative vacuum insertion, the only relevant condensate in the
game is . The validity of the OPE formula is tested by searching for a
good-quality coherent description of previous lattice evaluations of
-renormalized gluon propagator and running coupling.Comment: 12 pages, 3 figures (2 generated by the macro: axodraw.sty
Glassy Vortex State in a Two-Dimensional Disordered XY-Model
The two-dimensional XY-model with random phase-shifts on bonds is studied.
The analysis is based on a renormalization group for the replicated system. The
model is shown to have an ordered phase with quasi long-range order. This
ordered phase consists of a glass-like region at lower temperatures and of a
non-glassy region at higher temperatures. The transition from the disordered
phase into the ordered phase is not reentrant and is of a new universality
class at zero temperature. In contrast to previous approaches the disorder
strength is found to be renormalized to larger values. Several correlation
functions are calculated for the ordered phase. They allow to identify not only
the transition into the glassy phase but also an additional crossover line,
where the disconnected vortex correlation changes its behavior on large scales
non-analytically. The renormalization group approach yields the glassy features
without a breaking of replica symmetry.Comment: latex 12 pages with 3 figures, using epsf.sty and multicol.st
Seismic Vulnerability of Heritage Churches in Québec: the Néo-Roman Typology
Several seismic events have demonstrated the vulnerability of masonry churches. The long seismic history of the Italian territory has provided materials to observe and to study the structural performance of churches. Since the 1976 Friuli earthquake many studies have contributed to the definition of specific damage and vulnerability assessment methods for churches, based on the identification of macro-elements and kinematic mechanisms. In this context, the paper presents the application of a vulnerability assessment methodology developed and currently applied in Italy to a case study representative of the néo-roman church typology in Montreal, Québec. The study is part of a collaborative project between Politecnico di Milano and École de Technologie Supérieure of Montreal. The relevance of such a study derives from the moderate seismicity of Montreal associated to a high density of churches. Starting from a previous inventory of 108 churches in Montreal Island, the Néo-roman church typology was selected to be investigated. Specificities of this typology are the position of the bell tower in the middle of the façade and the interaction between the timber structure and masonry walls. This combination between the façade and bell tower macro-elements requires to reconsider the mechanisms associated to these elements in the original reference method. A detailed survey of the roof and bell tower timber structures of a néo-roman church was done, and a three-dimensional numerical model was developed for a better understanding of this type of structure. Modal analysis of a global model was then carried out and the first results of the modal shapes discussed
Ultrametricity in 3D Edwards-Anderson spin glasses
We perform an accurate test of Ultrametricity in the aging dynamics of the
three dimensional Edwards-Anderson spin glass. Our method consists in
considering the evolution in parallel of two identical systems constrained to
have fixed overlap. This turns out to be a particularly efficient way to study
the geometrical relations between configurations at distant large times. Our
findings strongly hint towards dynamical ultrametricity in spin glasses, while
this is absent in simpler aging systems with domain growth dynamics. A recently
developed theory of linear response in glassy systems allows to infer that
dynamical ultrametricity implies the same property at the level of equilibrium
states.Comment: 4 pages, 5 figure
Nonperturbative Effects from the Resummation of Perturbation Theory
Using the general argument in Borel resummation of perturbation theory that
links the divergent perturbation theory to the nonperturbative effect we argue
that the nonperturbative effect associated with the perturbation theory should
have a branch cut only along the positive real axis in the complex coupling
plane. The component in the weak coupling expansion of the nonperturbative
amplitude, which usually includes the leading term in the weak coupling
expansion, that gives rise to the branch cut can be calculated in principle
from the perturbation theory combined with some exactly calculable properties
of the nonperturbative effect. The realization of this mechanism is
demonstrated in the double well potential and the two-dimensional O(N)
nonlinear sigma model. In these models the leading term in weak coupling of the
nonperturbative effect can be obtained with good accuracy from the first terms
of the perturbation theory. Applying this mechanism to the infrared renormalon
induced nonperturbative effect in QCD, we suggest some of the QCD condensate
effects can be calculated in principle from the perturbation theory.Comment: 21 Pages, 1 Figure; To appear in Phys Rev
Seismic Damage Mechanisms for Churches and Damage Sequence: Considerations from a Case Study
Several high-intensity earthquakes have occurred in Italy in the last decades, causing considerable damage to architectural heritage and pointing out the particularly high seismic vulnerability of masonry churches. A significant research effort has been devoted to develop specific methods for the damage analysis and the seismic vulnerability assessment of these assets. An abacus of damage mechanisms recurring in the church structural components has been developed and has become an important reference in rapid assessment procedures as well as in more detailed analyses. In this perspective, the damage occurred to a church during the Pianura Padana Emiliana (Emilia) Earthquake of 2012 is analyzed here. The damage pattern reproduced, indeed, situations listed in the abacus of mechanisms. The seismic response of the church has been analyzed with different numerical approaches, with complete and with partial models that have allowed an appreciable understanding of the global behavior and of the modality of damage progressing into the mechanisms. The use of vector graphics software tools for 3D modelling that have become available in recent times has allowed to thoroughly understand the constructional complexity of the asset and, consequently, to develop simpler but structurally significant models for numerical analysis
Spin glasses without time-reversal symmetry and the absence of a genuine structural glass transition
We study the three-spin model and the Ising spin glass in a field using
Migdal-Kadanoff approximation. The flows of the couplings and fields indicate
no phase transition, but they show even for the three-spin model a slow
crossover to the asymptotic high-temperature behaviour for strong values of the
couplings. We also evaluated a quantity that is a measure of the degree of
non-self-averaging, and we found that it can become large for certain ranges of
the parameters and the system sizes. For the spin glass in a field the maximum
of non-self-averaging follows for given system size a line that resembles the
de Almeida-Thouless line. We conclude that non-self-averaging found in
Monte-Carlo simulations cannot be taken as evidence for the existence of a
low-temperature phase with replica-symmetry breaking. Models similar to the
three-spin model have been extensively discussed in order to provide a
description of structural glasses. Their theory at mean-field level resembles
the mode-coupling theory of real glasses. At that level the one-step replica
symmetry approach breaking predicts two transitions, the first transition being
dynamical and the second thermodynamical. Our results suggest that in real
finite dimensional glasses there will be no genuine transitions at all, but
that some features of mean-field theory could still provide some useful
insights.Comment: 11 pages, 11 figure
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