Theoretical study of electronic transport through a small quantum dot with a magnetic impurity

We model a small quantum dot with a magnetic impurity by the Anderson Hamiltonian with a supplementary exchange interaction term. The transport calculations are performed by means of the Green functions within the equation of motion scheme, in which two decoupling procedures are proposed, for high and low temperatures, respectively. The paper focuses on the charge fluctuations for such a system, aspect not addressed before, as well as on the Kondo resonance. We show a specific role of the excited state, which can be observed in transport and in spin-spin correlations. Our studies show on a new many-body feature of the phase shift of transmitted electrons, which is manifested in a specific dip. In the Kondo regime, our calculations complement existing theoretical results. The system shows three Kondo peaks in the density of states: one at the Fermi energy and two side peaks, at a distance corresponding to the singlet-triplet level spacing. The existence of the central peak is conditioned by a degenerate state (the triplet) below the Fermi energy.Comment: 12 pages, 4 figure

Kinetic Energy Density Study of Some Representative Semilocal Kinetic Energy Functionals

There is a number of explicit kinetic energy density functionals for non-interacting electron systems that are obtained in terms of the electron density and its derivatives. These semilocal functionals have been widely used in the literature. In this work we present a comparative study of the kinetic energy density of these semilocal functionals, stressing the importance of the local behavior to assess the quality of the functionals. We propose a quality factor that measures the local differences between the usual orbital-based kinetic energy density distributions and the approximated ones, allowing to ensure if the good results obtained for the total kinetic energies with these semilocal functionals are due to their correct local performance or to error cancellations. We have also included contributions coming from the laplacian of the electron density to work with an infinite set of kinetic energy densities. For all the functionals but one we have found that their success in the evaluation of the total kinetic energy are due to global error cancellations, whereas the local behavior of their kinetic energy density becomes worse than that corresponding to the Thomas-Fermi functional.Comment: 12 pages, 3 figure

Local Behavior of the First-Order Gradient Correction to the Thomas-Fermi Kinetic Energy Functional

The first order gradient correction to the Thomas-Fermi functional, proposed by Haq, Chattaraj and Deb (Chem. Phys. Lett. vol. 81, 8031, 1984) has been studied by evaluating both the total kinetic energy and the local kinetic energy density. For testing the kinetic energy density we evaluate its deviation from an exact result through a quality factor, a parameter that reflects the quality of the functionals in a better way than their relative errors. The study is performed on two different systems: light atoms (up to Z=18) and a noninteracting model of fermions confined in a Coulombic-type potential. It is found than this approximation gives very low relative errors and a better local behavior than any of the usual generalized gradient approximation semilocal kinetic density functionals.Comment: 7 pages, 2 tables, 4 figure

Cooperative thalamocortical circuit mechanism for sensory prediction errors

The brain functions as a prediction machine, utilizing an internal model of the world to anticipate sensations and the outcomes of our actions. Discrepancies between expected and actual events, referred to as prediction errors, are leveraged to update the internal model and guide our attention towards unexpected events1-10. Despite the importance of prediction-error signals for various neural computations across the brain, surprisingly little is known about the neural circuit mechanisms responsible for their implementation. Here we describe a thalamocortical disinhibitory circuit that is required for generating sensory prediction-error signals in mouse primary visual cortex (V1). We show that violating animals' predictions by an unexpected visual stimulus preferentially boosts responses of the layer 2/3 V1 neurons that are most selective for that stimulus. Prediction errors specifically amplify the unexpected visual input, rather than representing non-specific surprise or difference signals about how the visual input deviates from the animal's predictions. This selective amplification is implemented by a cooperative mechanism requiring thalamic input from the pulvinar and cortical vasoactive-intestinal-peptide-expressing (VIP) inhibitory interneurons. In response to prediction errors, VIP neurons inhibit a specific subpopulation of somatostatin-expressing inhibitory interneurons that gate excitatory pulvinar input to V1, resulting in specific pulvinar-driven response amplification of the most stimulus-selective neurons in V1. Therefore, the brain prioritizes unpredicted sensory information by selectively increasing the salience of unpredicted sensory features through the synergistic interaction of thalamic input and neocortical disinhibitory circuits

Ultrafast manipulation of electron spins in a double quantum dot device: A real-time view

We consider a double quantum dot system with two embedded and non-aligned spin impurities to manipulate the magnitude and polarization of the electron spin density. The device is attached to semi-infinite one-dimensional leads which are treated exactly. We provide a real-time description of the electron spin dynamics when a sequence of ultrafast voltage pulses acts on the device. The numerical simulations are carried out using a spin generalized and modified version of a recently proposed algorithm for the time propagation of open systems [Phys. Rev. B {\bf 72}, 035308 (2005)]. Time-dependent spin accumulations and spin currents are calculated during the entire operating regime which includes spin injection and read-out processes. The full knowledge of the electron dynamics allows us to engineer the transient responses and improve the device performance. An approximate rate equation for the electron spin is also derived and used to discuss the numerical results.Comment: 13 pages, 13 eps figure

A subpath kernel for learning hierarchical image representations

International audienceTree kernels have demonstrated their ability to deal with hierarchical data, as the intrinsic tree structure often plays a discrimi-native role. While such kernels have been successfully applied to various domains such as nature language processing and bioinformatics, they mostly concentrate on ordered trees and whose nodes are described by symbolic data. Meanwhile, hierarchical representations have gained increasing interest to describe image content. This is particularly true in remote sensing, where such representations allow for revealing different objects of interest at various scales through a tree structure. However, the induced trees are unordered and the nodes are equipped with numerical features. In this paper, we propose a new structured kernel for hierarchical image representations which is built on the concept of subpath kernel. Experimental results on both artificial and remote sensing datasets show that the proposed kernel manages to deal with the hierarchical nature of the data, leading to better classification rates

La calidad de vida en la tercera edad. Estudio de una muestra de la población en Zaragoza.

En las personas, la calidad de vida se establece a partir de un conjunto de factores muy variados, entre los cuales encontramos caracteres culturales, físicos, económicos, entre otros. Es por ello que determinar una única definición para el concepto de calidad de vida sea complicado. El concepto de calidad de vida es un concepto bastante reciente. Si bien es cierto que la preocupación y el interés por la calidad de vida ha existido desde la antigüedad, no es hasta la década de los años 60 cuando comienza a popularizarse, hasta llegar a nuestros días, donde el concepto aparece en una gran cantidad de ámbitos. En la actualidad, seguimos teniendo una falta de acuerdo sobre la definición de calidad de vida. La siguiente tabla agrupa algunas definiciones del concepto

Factors influencing completion of multi-dose vaccine schedules in adolescents: a systematic review.

BACKGROUND: Completion of multiple dose vaccine schedules is crucial to ensure a protective immune response, and maximise vaccine cost-effectiveness. While barriers and facilitators to vaccine uptake have recently been reviewed, there is no comprehensive review of factors influencing subsequent adherence or completion, which is key to achieving vaccine effectiveness. This study identifies and summarises the literature on factors affecting completion of multi-dose vaccine schedules by adolescents. METHODS: Ten online databases and four websites were searched (February 2014). Studies with analysis of factors predicting completion of multi-dose vaccines were included. Study participants within 9-19 years of age were included in the review. The defined outcome was completion of the vaccine series within 1 year among those who received the first dose. RESULTS: Overall, 6159 abstracts were screened, and 502 full texts were reviewed. Sixty one studies were eligible for this review. All except two were set in high-income countries. Included studies evaluated human papillomavirus vaccine, hepatitis A, hepatitis B, and varicella vaccines. Reported vaccine completion rates, among those who initiated vaccination, ranged from 27% to over 90%. Minority racial or ethnic groups and inadequate health insurance coverage were risk factors for low completion, irrespective of initiation rates. Parental healthcare seeking behaviour was positively associated with completion. Vaccine delivery in schools was associated with higher completion than delivery in the community or health facilities. Gender, prior healthcare use and socio-economic status rarely remained significant risks or protective factors in multivariate analysis. CONCLUSIONS: Almost all studies investigating factors affecting completion have been carried out in developed countries and investigate a limited range of variables. Increased understanding of barriers to completion in adolescents will be invaluable to future new vaccine introductions and the further development of an adolescent health platform. PROSPERO reg# CRD42014006765