83 research outputs found
The cumulative overlap distribution function in realistic spin glasses
We use a sample-dependent analysis, based on medians and quantiles, to
analyze the behavior of the overlap probability distribution of the
Sherrington-Kirkpatrick and 3D Edwards-Anderson models of Ising spin glasses.
We find that this approach is an effective tool to distinguish between RSB-like
and droplet-like behavior of the spin-glass phase. Our results are in agreement
with a RSB-like behavior for the 3D Edwards-Anderson model.Comment: Version accepted in PRB. 12 pages, 10 figure
Temperature chaos is a non-local effect
Temperature chaos plays a role in important effects, like for example memory
and rejuvenation, in spin glasses, colloids, polymers. We numerically
investigate temperature chaos in spin glasses, exploiting its recent
characterization as a rare-event driven phenomenon. The peculiarities of the
transformation from periodic to anti-periodic boundary conditions in spin
glasses allow us to conclude that temperature chaos is non-local: no bounded
region of the system causes it. We precise the statistical relationship between
temperature chaos and the free-energy changes upon varying boundary conditions.Comment: 15 pages, 8 figures. Version accepted for publication in JSTA
Comprehensive study of the critical behavior in the diluted antiferromagnet in a field
We study the critical behavior of the Diluted Antiferromagnet in a Field with
the Tethered Monte Carlo formalism. We compute the critical exponents
(including the elusive hyperscaling violations exponent ). Our results
provide a comprehensive description of the phase transition and clarify the
inconsistencies between previous experimental and theoretical work. To do so,
our method addresses the usual problems of numerical work (large tunneling
barriers and self-averaging violations).Comment: 4 pages, 2 figure
Phase transition in the computational complexity of the shortest common superstring and genome assembly
Genome assembly, the process of reconstructing a long genetic sequence by
aligning and merging short fragments, or reads, is known to be NP-hard, either
as a version of the shortest common superstring problem or in a
Hamiltonian-cycle formulation. That is, the computing time is believed to grow
exponentially with the the problem size in the worst case. Despite this fact,
high-throughput technologies and modern algorithms currently allow
bioinformaticians to handle datasets of billions of reads. Using methods from
statistical mechanics, we address this conundrum by demonstrating the existence
of a phase transition in the computational complexity of the problem and
showing that practical instances always fall in the 'easy' phase (solvable by
polynomial-time algorithms). In addition, we propose a Markov-chain Monte Carlo
method that outperforms common deterministic algorithms in the hard regime.Comment: 9 pages, 5 figures. Version accepted for publication in Phys. Rev.
Comment on "Evidence of Non-Mean-Field-Like Low-Temperature Behavior in the Edwards-Anderson Spin-Glass Model"
A recent interesting paper [Yucesoy et al. Phys. Rev. Lett. 109, 177204
(2012), arXiv:1206:0783] compares the low-temperature phase of the 3D
Edwards-Anderson (EA) model to its mean-field counterpart, the
Sherrington-Kirkpatrick (SK) model. The authors study the overlap distributions
P_J(q) and conclude that the two models behave differently. Here we notice that
a similar analysis using state-of-the-art, larger data sets for the EA model
(generated with the Janus computer) leads to a very clear interpretation of the
results of Yucesoy et al., showing that the EA model behaves as predicted by
the replica symmetry breaking (RSB) theory.Comment: Version accepted for publication in PRL. 1 page, 1 figur
Anatomical basis of sleep
El sueño es un estado biológico activo, periódico,
en el que se distinguen las etapas NREM y REM, que se
alternan sucesivamente durante la noche. Intervienen
los relojes biológicos en la modulación del sistema, así
como neurotransmisores específicos. Se trata de una
red neuronal compleja, en la que intervienen diversas
zonas del sistema nervioso central. Los procesos oníricos
están controlados además de forma neural.
Se resume la historia de las investigaciones sobre
el tema, desde el siglo XIX hasta nuestra época. Hay
que destacar los recientes descubrimientos de Lugaresi
y su equipo, que, al describir el insomnio familiar
grave, dieron importancia al núcleo dorsomedial del
tálamo en la instauración de la fase de sueño profundo.
Al grupo de Reinoso se debe el hallazgo de que el
“director de orquesta” en la instauración del sueño
REM es la zona ventral paramediana del núcleo reticular
pontino ora
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