16,967 research outputs found
Spin-selective localization due to intrinsic spin-orbit coupling
We study spin-dependent diffusive transport in the presence of a tunable
spin-orbit (SO) interaction in a two-dimensional electron system. The spin
precession of an electron in the SO coupling field is expressed in terms of a
covariant curvature, affecting the quantum interference between different
electronic trajectories. Controlling this curvature field by modulating the SO
coupling strength and its gradients by, e.g., electric or elastic means, opens
intriguing possibilities for exploring spin-selective localization physics. In
particular, applying a weak magnetic field allows the control of the electron
localization independently for two spin directions, with the spin-quantization
axis that could be "engineered" by appropriate SO interaction gradients.Comment: 7 pages, 1 figur
Fluctuation theorem for entropy production during effusion of a relativistic ideal gas
The probability distribution of the entropy production for the effusion of a
relativistic ideal gas is calculated explicitly. This result is then extended
to include particle and anti-particle pair production and annihilation. In both
cases, the fluctuation theorem is verified.Comment: 6 pages, no figure
Thermodynamics of the L\'evy spin glass
We investigate the L\'evy glass, a mean-field spin glass model with power-law
distributed couplings characterized by a divergent second moment. By combining
extensively many small couplings with a spare random backbone of strong bonds
the model is intermediate between the Sherrington-Kirkpatrick and the
Viana-Bray model. A truncated version where couplings smaller than some
threshold \eps are neglected can be studied within the cavity method
developed for spin glasses on locally tree-like random graphs. By performing
the limit \eps\to 0 in a well-defined way we calculate the thermodynamic
functions within replica symmetry and determine the de Almeida-Thouless line in
the presence of an external magnetic field. Contrary to previous findings we
show that there is no replica-symmetric spin glass phase. Moreover we determine
the leading corrections to the ground-state energy within one-step replica
symmetry breaking. The effects due to the breaking of replica symmetry appear
to be small in accordance with the intuitive picture that a few strong bonds
per spin reduce the degree of frustration in the system
Superconductivity-Related Insulating Behavior
We present the results of an experimental study of superconducting,
disordered, thin-films of amorphous Indium Oxide. These films can be driven
from the superconducting phase to a reentrant insulating state by the
application of a perpendicular magnetic field (). We find that the high-
insulator exhibits activated transport with a characteristic temperature,
. has a maximum value () that is close to the
superconducting transition temperature () at = 0, suggesting a
possible relation between the conduction mechanisms in the superconducting and
insulating phases. and display opposite dependences on the
disorder strength.Comment: Tex file and 5 figures; Revised version; To appear in Phys. Rev.
Lett. (2004
Post-training load-related changes of auditory working memory: An EEG study
Working memory (WM) refers to the temporary retention and manipulation of information, and its capacity is highly susceptible to training. Yet, the neural mechanisms that allow for increased performance under demanding conditions are not fully understood. We expected that post-training efficiency in WM performance modulates neural processing during high load tasks. We tested this hypothesis, using electroencephalography (EEG) (N = 39), by comparing source space spectral power of healthy adults performing low and high load auditory WM tasks. Prior to the assessment, participants either underwent a modality-specific auditory WM training, or a modality-irrelevant tactile WM training, or were not trained (active control). After a modality-specific training participants showed higher behavioral performance, compared to the control. EEG data analysis revealed general effects of WM load, across all training groups, in the theta-, alpha-, and beta-frequency bands. With increased load theta-band power increased over frontal, and decreased over parietal areas. Centro-parietal alpha-band power and central beta-band power decreased with load. Interestingly, in the high load condition a tendency toward reduced beta-band power in the right medial temporal lobe was observed in the modality-specific WM training group compared to the modality-irrelevant and active control groups. Our finding that WM processing during the high load condition changed after modality-specific WM training, showing reduced beta-band activity in voice-selective regions, possibly indicates a more efficient maintenance of task-relevant stimuli. The general load effects suggest that WM performance at high load demands involves complementary mechanisms, combining a strengthening of task-relevant and a suppression of task-irrelevant processing
Influence of diffractive interactions on cosmic ray air showers
A comparative study of commonly used hadronic collision simulation packages
is presented. The characteristics of the products of hadron-nucleus collisions
are analyzed from a general perspective, but focusing on their correlation with
diffractive processes. One of the purposes of our work is to give quantitative
estimations of the impact that different characteristics of the hadronic models
have on air shower observables. Several sets of shower simulations using
different settings for the parameters controlling the diffractive processes are
used to analyze the correlations between diffractivity and shower observables.
We find that the relative probability of diffractive processes during the
shower development have a non negligible influence over the longitudinal
profile as well as the distribution of muons at ground level. The implications
on experimental data analysis are discussed
Storage capacity of correlated perceptrons
We consider an ensemble of single-layer perceptrons exposed to random
inputs and investigate the conditions under which the couplings of these
perceptrons can be chosen such that prescribed correlations between the outputs
occur. A general formalism is introduced using a multi-perceptron costfunction
that allows to determine the maximal number of random inputs as a function of
the desired values of the correlations. Replica-symmetric results for and
are compared with properties of two-layer networks of tree-structure and
fixed Boolean function between hidden units and output. The results show which
correlations in the hidden layer of multi-layer neural networks are crucial for
the value of the storage capacity.Comment: 16 pages, Latex2
Correlations between hidden units in multilayer neural networks and replica symmetry breaking
We consider feed-forward neural networks with one hidden layer, tree
architecture and a fixed hidden-to-output Boolean function. Focusing on the
saturation limit of the storage problem the influence of replica symmetry
breaking on the distribution of local fields at the hidden units is
investigated. These field distributions determine the probability for finding a
specific activation pattern of the hidden units as well as the corresponding
correlation coefficients and therefore quantify the division of labor among the
hidden units. We find that although modifying the storage capacity and the
distribution of local fields markedly replica symmetry breaking has only a
minor effect on the correlation coefficients. Detailed numerical results are
provided for the PARITY, COMMITTEE and AND machines with K=3 hidden units and
nonoverlapping receptive fields.Comment: 9 pages, 3 figures, RevTex, accepted for publication in Phys. Rev.
Inference for threshold models with variance components from the generalized linear mixed model perspective
International audienc
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