60 research outputs found
Spin accumulation probed in multiterminal lateral all-metallic devices
We study spin accumulation in an aluminium island, in which the injection of
a spin current and the detection of the spin accumulation are done by means of
four cobalt electrodes that connect to the island through transparent tunnel
barriers. Although the four electrodes are designed as two electrode pairs of
the same shape, they nonetheless all exhibit distinct switching fields. As a
result the device can have several different magnetic configurations. From the
measurements of the amplitude of the spin accumulation, we can identify these
configurations, and using the diffusion equation for the spin imbalance, we
extract the spin relaxation length ~nm and an
interface spin current polarization at low temperature and
~nm, at room temperature
Transmission phase of a singly occupied quantum dot in the Kondo regime
We report on the phase measurements on a quantum dot containing a single
electron in the Kondo regime. Transport takes place through a single orbital
state. Although the conductance is far from the unitary limit, we measure for
the first time, a transmission phase as theoretically predicted of \pi/2. As
the dot's coupling to the leads is decreased, with the dot entering the Coulomb
blockade regime, the phase reaches a value of \pi. Temperature shows little
effect on the phase behaviour in the range 30--600 mK, even though both the
two-terminal conductance and amplitude of the Aharonov-Bohm oscillations are
strongly affected. These results confirm that previous phase measurements
involved transport through more than a single level.Comment: 4 pages, 5 figure
Spin-Flip Noise in a Multi-Terminal Spin-Valve
We study shot noise and cross correlations in a four terminal spin-valve
geometry using a Boltzmann-Langevin approach. The Fano factor (shot noise to
current ratio) depends on the magnetic configuration of the leads and the
spin-flip processes in the normal metal. In a four-terminal geometry, spin-flip
processes are particular prominent in the cross correlations between terminals
with opposite magnetization.Comment: 4 pages, 3 figure
Spin dependent quantum interference in non-local graphene spin valves
Spin dependent electron transport measurements on graphene are of high
importance to explore possible spintronic applications. Up to date all spin
transport experiments on graphene were done in a semi-classical regime,
disregarding quantum transport properties such as phase coherence and
interference. Here we show that in a quantum coherent graphene nanostructure
the non-local voltage is strongly modulated. Using non-local measurements, we
separate the signal in spin dependent and spin independent contributions. We
show that the spin dependent contribution is about two orders of magnitude
larger than the spin independent one, when corrected for the finite
polarization of the electrodes. The non-local spin signal is not only strongly
modulated but also changes polarity as a function of the applied gate voltage.
By locally tuning the carrier density in the constriction we show that the
constriction plays a major role in this effect and indicates that it can act as
a spin filter device. Our results show the potential of quantum coherent
graphene nanostructures for the use in future spintronic devices
Extremely long quasiparticle spin lifetimes in superconducting aluminium using MgO tunnel spin injectors
There has been an intense search in recent years for long-lived
spin-polarized carriers for spintronic and quantum-computing devices. Here we
report that spin polarized quasi-particles in superconducting aluminum layers
have surprisingly long spin-lifetimes, nearly a million times longer than in
their normal state. The lifetime is determined from the suppression of the
aluminum's superconductivity resulting from the accumulation of spin polarized
carriers in the aluminum layer using tunnel spin injectors. A Hanle effect,
observed in the presence of small in-plane orthogonal fields, is shown to be
quantitatively consistent with the presence of long-lived spin polarized
quasi-particles. Our experiments show that the superconducting state can be
significantly modified by small electric currents, much smaller than the
critical current, which is potentially useful for devices involving
superconducting qubits
Clinical Risk Score to Predict Pathogenic Genotypes in Patients With Dilated Cardiomyopathy
Background: Although genotyping allows family screening and influences risk-stratification in patients with nonischemic dilated cardiomyopathy (DCM) or isolated left ventricular systolic dysfunction (LVSD), its result is negative in a significant number of patients, limiting its widespread adoption.
Objectives: This study sought to develop and externally validate a score that predicts the probability for a positive genetic test result (G+) in DCM/LVSD.
Methods: Clinical, electrocardiogram, and echocardiographic variables were collected in 1,015 genotyped patients from Spain with DCM/LVSD. Multivariable logistic regression analysis was used to identify variables independently predicting G+, which were summed to create the Madrid Genotype Score. The external validation sample comprised 1,097 genotyped patients from the Maastricht and Trieste registries.
Results: A G+ result was found in 377 (37%) and 289 (26%) patients from the derivation and validation cohorts, respectively. Independent predictors of a G+ result in the derivation cohort were: family history of DCM (OR: 2.29; 95% CI: 1.73-3.04; P < 0.001), low electrocardiogram voltage in peripheral leads (OR: 3.61; 95% CI: 2.38-5.49; P < 0.001), skeletal myopathy (OR: 3.42; 95% CI: 1.60-7.31; P = 0.001), absence of hypertension (OR: 2.28; 95% CI: 1.67-3.13; P < 0.001), and absence of left bundle branch block (OR: 3.58; 95% CI: 2.57-5.01; P < 0.001). A score containing these factors predicted a G+ result, ranging from 3% when all predictors were absent to 79% when ≥4 predictors were present. Internal validation provided a C-statistic of 0.74 (95% CI: 0.71-0.77) and a calibration slope of 0.94 (95% CI: 0.80-1.10). The C-statistic in the external validation cohort was 0.74 (95% CI: 0.71-0.78).
Conclusions: The Madrid Genotype Score is an accurate tool to predict a G+ result in DCM/LVSD
On the complexity of solving polytree-shaped limited memory influence diagrams with binary variables
A Fully Polynomial Time Approximation Scheme for Updating Credal Networks of Bounded Treewidth and Number of Variable States
Credal networks lift the precise probability assumption of Bayesian networks, enabling a richer representation of uncertainty in the form of closed convex sets of probability measures. The increase in expressiveness comes at the expense of higher computational costs. In this paper we present a new algorithm which is an extension of the wellknown variable elimination algorithm for computing posterior inferences in extensively specified credal networks. The algorithm efficiency is empirically shown to outperform a state-of-the-art algorithm. We then provide the first fully polynomial time approximation scheme for inference in credal networks with bounded treewidth and number of states per variable
The Complexity of Approximately Solving Influence Diagrams
Influence diagrams allow for intuitive and yet precise description of complex situations involving decision making under uncertainty. Unfortunately, most of the problems described by influence diagrams are hard to solve. In this paper we discuss the complexity of approximately solving influence diagrams. We do not assume no-forgetting or regularity, which makes the class of problems we address very broad. Remarkably, we show that when both the treewidth and the cardinality of the variables are bounded the problem admits a fully polynomial-time approximation scheme.
Risk stratification in cardiomyopathy
Prognostic stratification of cardiomyopathies represents a cornerstone for the appropriate management of patients and is focused mainly on arrhythmic events and heart failure. Cardiopulmonary exercise testing provides additional prognostic information, particularly in the setting of heart failure. Cardiopulmonary exercise testing data, integrated in scores such as the Metabolism Exercise Cardiac Kidney Index score have been shown to improve the risk stratification of these patients. Cardiopulmonary exercise testing has been analysed as a potential supplier of prognostic parameters in the context of hypertrophic cardiomyopathy, for which it has been shown that a reduced oxygen consumption peak, an increased ventilation/carbon dioxide production slope and chronotropic incompetence correlate with a worse prognosis. To a lesser extent, in dilated cardiomyopathy, it has been shown that the percentage of oxygen consumption peak, not the pure value, and the ventilation/carbon dioxide production slope are associated with a greater cardiovascular risk. Few data are available about other cardiomyopathies (arrhythmogenic and restrictive). Cardiomyopathy patients should be early and routinely referred to heart failure advanced centres in order to perform a comprehensive risk stratification which should include a cardiopulmonary exercise test, with variables and cut-offs shown to improve their risk stratification
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