44 research outputs found
Backbone structure of the Edwards-Anderson spin-glass model
We study the ground-state spatial heterogeneities of the Edwards-Anderson
spin-glass model with both bimodal and Gaussian bond distributions. We
characterize these heterogeneities by using a general definition of bond
rigidity, which allows us to classify the bonds of the system into two sets,
the backbone and its complement, with very different properties. This
generalizes to continuous distributions of bonds the well known definition of a
backbone for discrete bond distributions. By extensive numerical simulations we
find that the topological structure of the backbone for a given lattice
dimensionality is very similar for both discrete and continuous bond
distributions. We then analyze how these heterogeneities influence the
equilibrium properties at finite temperature and we discuss the possibility
that a suitable backbone picture can be relevant to describe spin-glass
phenomena.Comment: 12 pages, 10 figure
Backbone structure of the Edwards-Anderson spin-glass model
We study the ground-state spatial heterogeneities of the Edwards-Anderson spin-glass model with both bimodal and Gaussian bond distributions. We characterize these heterogeneities by using a general definition of bond rigidity, which allows us to classify the bonds of the system into two sets, the backbone and its complement, with very different properties. This generalizes to continuous distributions of bonds the well-known definition of a backbone for discrete bond distributions. By extensive numerical simulations we find that the topologicalstructure of the backbone for a given lattice dimensionality is very similar for both discrete and continuous bond distributions. We then analyze how these heterogeneities influence the equilibrium properties at finite temperature and we discuss the possibility that a suitable backbone picture can be relevant to describe spin-glass phenomena.Fil: Romá, Federico José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - San Luis. Instituto de Física Aplicada; Argetnina;Fil: Risau-Gusman, S.. Comisión Nacional de Energía Atomica. Gerencia del Área de Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (cab). División Física Estadistica; Argentina
Influence of the Ground-State Topology on the Domain-Wall Energy in the Edwards-Anderson +/- J Spin Glass Model
We study the phase stability of the Edwards-Anderson spin-glass model by
analyzing the domain-wall energy. For the bimodal distribution of bonds, a
topological analysis of the ground state allows us to separate the system into
two regions: the backbone and its environment. We find that the distributions
of domain-wall energies are very different in these two regions for the three
dimensional (3D) case. Although the backbone turns out to have a very high
phase stability, the combined effect of these excitations and correlations
produces the low global stability displayed by the system as a whole. On the
other hand, in two dimensions (2D) we find that the surface of the excitations
avoids the backbone. Our results confirm that a narrow connection exists
between the phase stability of the system and the internal structure of the
ground-state. In addition, for both 3D and 2D we are able to obtain the fractal
dimension of the domain wall by direct means.Comment: 4 pages, 3 figures. Accepted for publication in Rapid Communications
of Phys. Rev.
Generalization properties of finite size polynomial Support Vector Machines
The learning properties of finite size polynomial Support Vector Machines are
analyzed in the case of realizable classification tasks. The normalization of
the high order features acts as a squeezing factor, introducing a strong
anisotropy in the patterns distribution in feature space. As a function of the
training set size, the corresponding generalization error presents a crossover,
more or less abrupt depending on the distribution's anisotropy and on the task
to be learned, between a fast-decreasing and a slowly decreasing regime. This
behaviour corresponds to the stepwise decrease found by Dietrich et al.[Phys.
Rev. Lett. 82 (1999) 2975-2978] in the thermodynamic limit. The theoretical
results are in excellent agreement with the numerical simulations.Comment: 12 pages, 7 figure
Fractal dimension of domain walls in the Edwards-Anderson spin glass model
We study directly the length of the domain walls (DW) obtained by comparing
the ground states of the Edwards-Anderson spin glass model subject to periodic
and antiperiodic boundary conditions. For the bimodal and Gaussian bond
distributions, we have isolated the DW and have calculated directly its fractal
dimension . Our results show that, even though in three dimensions
is the same for both distributions of bonds, this is clearly not the case for
two-dimensional (2D) systems. In addition, contrary to what happens in the case
of the 2D Edwards-Anderson spin glass with Gaussian distribution of bonds, we
find no evidence that the DW for the bimodal distribution of bonds can be
described as a Schramm-Loewner evolution processes.Comment: 6 pages, 5 figures. Accepted for publication in PR
Statistical Mechanics of Soft Margin Classifiers
We study the typical learning properties of the recently introduced Soft
Margin Classifiers (SMCs), learning realizable and unrealizable tasks, with the
tools of Statistical Mechanics. We derive analytically the behaviour of the
learning curves in the regime of very large training sets. We obtain
exponential and power laws for the decay of the generalization error towards
the asymptotic value, depending on the task and on general characteristics of
the distribution of stabilities of the patterns to be learned. The optimal
learning curves of the SMCs, which give the minimal generalization error, are
obtained by tuning the coefficient controlling the trade-off between the error
and the regularization terms in the cost function. If the task is realizable by
the SMC, the optimal performance is better than that of a hard margin Support
Vector Machine and is very close to that of a Bayesian classifier.Comment: 26 pages, 12 figures, submitted to Physical Review
Spontaneous circadian rhythms in a cold-Adapted natural isolate of Aureobasidium pullulans
Indexación: Scopus.Circadian systems enable organisms to synchronize their physiology to daily and seasonal environmental changes relying on endogenous pacemakers that oscillate with a period close to 24 h even in the absence of external timing cues. The oscillations are achieved by intracellular transcriptional/translational feedback loops thoroughly characterized for many organisms, but still little is known about the presence and characteristics of circadian clocks in fungi other than Neurospora crassa. We sought to characterize the circadian system of a natural isolate of Aureobasidium pullulans, a cold-Adapted yeast bearing great biotechnological potential. A. pullulans formed daily concentric rings that were synchronized by light/dark cycles and were also formed in constant darkness with a period of 24.5 h. Moreover, these rhythms were temperature compensated, as evidenced by experiments conducted at temperatures as low as 10 °C. Finally, the expression of clock-essential genes, frequency, white collar-1, white collar-2 and vivid was confirmed. In summary, our results indicate the existence of a functional circadian clock in A. pullulans, capable of sustaining rhythms at very low temperatures and, based on the presence of conserved clock-gene homologues, suggest a molecular and functional relationship to well-described circadian systems.https://www.nature.com/articles/s41598-017-14085-
Levy ratchets with dichotomic random flashing
Additive symmetric L\'evy noise can induce directed transport of overdamped
particles in a static asymmetric potential. We study, numerically and
analytically, the effect of an additional dichotomous random flashing in such
L\'evy ratchet system. For this purpose we analyze and solve the corresponding
fractional Fokker-Planck equations and we check the results with Langevin
simulations. We study the behavior of the current as function of the stability
index of the L\'evy noise, the noise intensity and the flashing parameters. We
find that flashing allows both to enhance and diminish in a broad range the
static L\'evy ratchet current, depending on the frequencies and asymmetry of
the multiplicative dichotomous noise, and on the additive L\'evy noise
parameters. Our results thus extend those for dichotomous flashing ratchets
with Gaussian noise to the case of broadly distributed noises.Comment: 15 pages, 6 figure