1,720,984 research outputs found
Study of intensity correlations in the light scattered by a gas of cold atoms
No full textCe manuscrit présente les travaux d'étude de la cohérence de la lumière réalisés durant ma thèse à l'aide d'un système expérimental basé sur la technologie des atomes froids. La spécificité de notre groupe est l'étude et la caractérisation des comportement collectifs,classiques ou quantiques, dans l'interaction lumière matière. Dans ce but, Nous illuminons un nuage d'atomes froids à l'aide d'un faisceau laser afin d'observer au même instant les fonctions de corrélations temporelles d'ordre un g(1)(τ ) et d'ordre deux g(2)(τ ) (aussi connue sous le nom de fonction de corrélation de l'intensité). Pour une lumière chaotique polarisée et cohérente spatialement, g(2)(τ ) et relié au module de g(1)(τ ) via la formule g(1)(τ ) = 1 + |g(1)(τ )|2. Cette équation est communément appelée la relation de Siegert.Nous avons dans notre groupe effectué des études à basse saturation dans les régimes de diffusion simple et multiple. Nous nous concentrons dans ce travail à l'étude de la lumière diffusée à haut paramètre de saturation, pour différentes épaisseurs optiques. La première étape étant la caractérisation de la cohérence temporelle en régime saturée en diffusion simple, ouvrant la voie vers l'étude en régime de diffusion multiple. Sont détaillés dans ce manuscrit les étalonnages expérimentaux et identification des sources d'incertitude nous permettant la validation expérimentale de la relation de Siegert en régime saturé.Cette étude a permis identifier, pour un nuage d'atome macroscopique, la transition entre un régime de diffusion où les mécanismes de perte de cohérence de la lumière sont d'origine thermique à un régime ou ceux-ci proviennent de l'émission spontanée.This manuscript presents the work on the study of the coherence of light carried out duringmy thesis using an experimental system based on cold atom technology. The specificity of our group is to study, detect and characterize cooperative behavior, either classical orquantum, in the light matter interaction. To do so, laser beams illuminate a cold atomic cloud and we collect the scattered light to study its properties. Our experiment benefits from a setup that allows us to observe at the same time the temporal first-order correlation function g(1)(τ ) and the temporal second-order correlation function g(2)(τ ) (also known asthe intensity correlation function). For spatially-coherent polarized chaotic light, g(2)(τ )is related to the modulus of g(1)(τ ) as follows: g(1)(τ ) = 1 + |g(1)(τ )|2. This equation is commonly called the Siegert relation. Research have already been done in our group forlow saturation limit in simple and multiple scattering regime that validate this relation.We are now studying strong saturation regime for clouds of different optical depths. Thefirst step is the characterization of temporal coherence in the saturated regime in single scattering, opening the way to the study in the multiple scattering regime. Detailed in this manuscript are the experimental calibrations and identifcation of the sources ofun certainty allowing us the experimental validation of the Siegert relation in saturated regime
Magnetic birefrigences measurements in helium and xenon gases, and in vacuum
No full textCette thèse présente les résultats obtenus au sein du projet BMV (Biréfringence Magnétique du Vide), dont l'objectif principal est la mesure de la biréfringence magnétique linéaire du vide. Cet effet est prédit dans le cadre de l'électrodynamique quantique mais n'a jamais été observé expérimentalement. La biréfringence attendue est de l'ordre de 10-24 pour un champ magnétique appliqué de 1 T. Sa mesure constitue donc un véritable défi expérimental. Dans un premier temps, le dispositif expérimental permettant la mesure de biréfringences magnétiques par polarimétrie est décrit. Puis les résultats concernant les mesures des biréfringences magnétiques circulaire (effet Faraday) et linéaire (effet Cotton-Mouton) de l'hélium et du xénon gazeux sont exposés. Enfin, une valeur de la biréfringence magnétique linéaire du vide est donnée.In this work, we present the results obtained by the BMV (Biréfringence Magnétique du Vide) project, whose goal is to measure the linear magnetic birefringence of vacuum. This effect is predicted in the framework of quantum electrodynamics but it has never been observed experimentally. The expected birefringence is as small as 10-24, for an applied magnetic field of 1 T. Thus its measurement is an experimental challenge. First, we describe the experimental setup which allows magnetic birefringences measurements using a polarimetry method. Then, we present the results concerning the measurements of the circular magnetic birefringence (Faraday effect) and the linear magnetic birefringence (Cotton-Mouton effect) of helium and xenon gases. Finally we give a value for the linear magnetic birefringence of vacuum
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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