78 research outputs found
Local Electronic Structure of a Single Magnetic Impurity in a Superconductor
The electronic structure near a single classical magnetic impurity in a
superconductor is determined using a fully self-consistent Koster-Slater
algorithm. Localized excited states are found within the energy gap which are
half electron and half hole. Within a jellium model we find the new result that
the spatial structure of the positive-frequency (electron-like) spectral weight
(or local density of states), can differ strongly from that of the negative
frequency (hole-like) spectral weight. The effect of the impurity on the
continuum states above the energy gap is calculated with good spectral
resolution for the first time. This is also the first three-dimensional
self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical
result
The Shapes of Flux Domains in the Intermediate State of Type-I Superconductors
In the intermediate state of a thin type-I superconductor magnetic flux
penetrates in a disordered set of highly branched and fingered macroscopic
domains. To understand these shapes, we study in detail a recently proposed
"current-loop" (CL) model that models the intermediate state as a collection of
tense current ribbons flowing along the superconducting-normal interfaces and
subject to the constraint of global flux conservation. The validity of this
model is tested through a detailed reanalysis of Landau's original conformal
mapping treatment of the laminar state, in which the superconductor-normal
interfaces are flared within the slab, and of a closely-related straight-lamina
model. A simplified dynamical model is described that elucidates the nature of
possible shape instabilities of flux stripes and stripe arrays, and numerical
studies of the highly nonlinear regime of those instabilities demonstrate
patterns like those seen experimentally. Of particular interest is the buckling
instability commonly seen in the intermediate state. The free-boundary approach
further allows for a calculation of the elastic properties of the laminar
state, which closely resembles that of smectic liquid crystals. We suggest
several new experiments to explore of flux domain shape instabilities,
including an Eckhaus instability induced by changing the out-of-plane magnetic
field, and an analog of the Helfrich-Hurault instability of smectics induced by
an in-plane field.Comment: 23 pages, 22 bitmapped postscript figures, RevTex 3.0, submitted to
Phys. Rev. B. Higher resolution figures may be obtained by contacting the
author
Local Electronic Structure of Defects in Superconductors
The electronic structure near defects (such as impurities) in superconductors
is explored using a new, fully self-consistent technique. This technique
exploits the short-range nature of the impurity potential and the induced
change in the superconducting order parameter to calculate features in the
electronic structure down to the atomic scale with unprecedented spectral
resolution. Magnetic and non-magnetic static impurity potentials are
considered, as well as local alterations in the pairing interaction. Extensions
to strong-coupling superconductors and superconductors with anisotropic order
parameters are formulated.Comment: RevTex source, 20 pages including 22 figures in text with eps
Comportement d'un pergélisol expérimental soumis à un réchauffement
The goal of this work was providing experimental data to better constrain the impact of global warming on permafrost. Methodology was based on physical modeling in a cold room. This allows identifying and defining the evolution processes of the experimental permafrost. Experimental permafrost was built-up based on available field data. The lithology of the material used was a mixture of fine sand and loam from the plain of Caen. Ice content is between 30 and 80%. Models are not scaled and dimensional problems are not considered. Indeed, these experiments are a preliminary work. This study on the behaviour of an experimental warming permafrost allows a better understanding of (i) the changes in topography (thaw-settlement), (ii) the changes in the active layer, (iii) the thermal evolution of an experimental permafrost (freezing and thawing fronts monitoring) and (iv) the influence of different parameters (temperature, lithology, water-content, ice-content and icelayer). This work has contributed to the development of new experimental techniques and it will enhance physical modeling databases on permafrost.Ce travail a pour but d'apporter des données expérimentales pour aider à mieux contraindre l'impact du réchauffement climatique sur les pergélisols. La méthodologie utilisée est basée sur la modélisation physique en enceinte de gel qui permet d'identifier et paramétrer les processus d'évolution d'un pergélisol expérimental. Le pergélisol expérimental est reconstitué en s'appuyant sur les données de terrain disponibles. La lithologie du matériau utilisé est un mélange de sable calibré de Nemours et de limons de la plaine de Caen aux caractéristiques physiques bien définies. Les teneurs en glace sont comprises entre 30 et 80%, comme mesuré sur le terrain. Le modèle n'est pas à l'échelle 1 et les problèmes de dimensionnement ne sont pas pris en compte. En effet, cette expérimentation est un travail préliminaire. Cette étude du comportement d'un pergélisol expérimental soumis à un réchauffement a permis de mieux connaître (i) l'évolution des morphologies de surface (tassement), (ii) l'évolution de la couche active, (iii) l'évolution thermique du pergélisol expérimental (suivi des fronts de gel et de dégel), (iv) l'influence respective des différents paramètres étudiés (température, lithologie, t eneur en eau et en glace, couche de glace). Ce travail a aussi permis la mise au point de nouvelles techniques expérimentales en conditions extrêmes. Il contribuera à la constitution de bases de données relatives à la modélisation physique des sols en contexte périglaciaire
Finding an Answer Based on the Recognition of the Question Focus
this report we describe how the QALC system (the Question-Answering program of the LIR group at LIMSI-CNRS, already involved in the QA-track evaluation at TREC9), was improved in order to better extract the very answer in selected sentences. The purpose of the main Question-Answering track in TREC10 was to find text sequences no longer than 50 characters or to produce a "no answer" response in case of a lack of answer in the TREC corpu
Use of prostaglandins at the time of parturition in the sow. Results in field conditions
Use of prostaglandins at the time of parturition in the sow. Results in field conditions
International audienc
L'adaptation locale des plantes : interactions biotiques et implications pour la restauration écologique
L'adaptation locale des plantes : interactions biotiques et implications pour la restauration écologiqu
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