1,721,065 research outputs found
Deposition of SiOx layer by plasma-enhanced chemical vapor deposition for the protection of silver (Ag) surfaces
No full textSilver surfaces have been treated with plasma-enhanced chemical vapor deposition to produce SiO2-like coatings for possible applications in the jewelry industry. Different experimental conditions have been tested in order to optimize the protective effectiveness of the deposited layers. Samples were analyzed with optical and scanning electron microscopy and energy-dispersive spectrometry
Laser ablation and induced nano-particle synthesis
Get PDFLaser pulses are largely used for processing and analysis of materials and in particular for nano-particle synthesis. This paper addresses fundamentals of the generation of nano-materials following specific thermodynamic paths of the irradiated material. Computer simulations using the hydro code MULTI and the SESAME equation of state have been performed to follow the dynamics of a target initially heated by a short laser pulse over a distance comparable to the metal skin depth
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
Diagnostic par rayons X et imagerie par rayons X de plasmas produits par laser
No full textCe travail s'est axé sur le développement et l'optimisation des diagnostics par rayons X pour l'étude des plasmas produits par laser. En particulier l'imagerie par contraste de phase à rayons X résolue en temps (XPCI) est étudiée comme alternative à l'utilisation de la radiographie par rayons X pour sonder les phénomènes dynamiques dans les plasmas à haute densité. L'XPCI a été spécifiquement appliquée pour étudier la dynamique des chocs générés par laser dans des cibles en plastique. Les résultats expérimentaux obtenus ont été complétés par des simulations hydrodynamiques 1D et 2D. Il a été possible de réaliser l'XPCI dans diverses installations laser à haute énergie, avec des conditions d’irradiation laser tres différentes.De plus, les travaux ont également porté sur la caractérisation des spectres de bremsstrahlung générés lors d'interactions laser-plasma de haute intensité à l'échelle de la femtoseconde, en vue de leur utilisation comme source de "backlighter" dans l'XPCI. Ces émissions de rayons X sont également intéressantes en tant que diagnostic de plasma car elles permettent de caractériser les électrons chauds qui sont responsables de l'émission de bremsstrahlung. Un module semi-analytique a été développé permettant une estimation rapide de la température de la population d'électrons chauds à partir des spectres mesurés.Ces sujets traités sont d'importance pour la physique de la haute densité d'énergie (HED) et pour la fusion par confinement inertiel.This work was focused on the development and optimization of X-ray diagnostics for the study of laser produced plasmas and in particular time-resolved x-ray contrast imaging (XPCI) as an alternative to the use of X-ray radiography in probing dynamical phenomena in high density plasmas. XPCI was specifically applied to study the dynamics of laser-generated shocks in plastic targets. The obtained experimental results were completed by 1D and 2D hydrodynamic simulations. It was possible to realize XPCI in various high-energy laser facilities, for variable nanosecond laser drive conditions.In addition, the work also focused on the characterization of bremsstrahlung spectra generated in high-intensity femtosecond-scale laser-plasma interactions, for their use as a backlighter source in XPCI. These X-ray emissions are also interesting as a plasma diagnostic because they allow us to characterize the hot electrons which are responsible for the bremsstrahlung emission. A semi-analytical module was developed allowing for a fast estimation of the hot electron population temperature from the measured spectra.These developed topics are of importance for high energy density (HED) physics and for inertial confinement fusion
Study of the physics of shock ignition
No full textUne décennie d'expériences au "National Ignition Facility" a démontré que la fusion par confinement inertiel constitue une approche crédible pour la production d'énergie, avec des résultats allant au-delà du régime d'allumage. Cependant, l'approche par attaque indirecte se révèle inadéquate pour les implosions à gain élevé et une production d'énergie fiable. L'option d'allumage par attaque directe est privilégiée en raison de ses conceptions de cible plus simples et de son meilleur couplage énergétique. Actuellement, aucune installation laser à l'échelle d'allumage n'est configurée selon l'approche directe standard, posant ainsi un défi à relever. Les expériences intégrées d'allumage par attaque directe se sont principalement concentrées sur la compréhension de la physique à des échelles réduites, dans le but ultime de démontrer la nécessité et la faisabilité de construire une installation laser internationale dédiée à l'attaque directe.Ce manuscrit de thèse présente une étude approfondie sur la validation de codes d'hydrodynamique radiative 3D à l'état de l'art, ainsi que sur la compréhension des bas modes d'éclairement laser et du couplage laser-cible, jouant un rôle crucial dans la fusion par confinement inertiel. L'examen attentif des modèles de CBET revêt une importance capitale dans ce contexte, assurant la précision des simulations et contribuant à la conception des futures installations à attaque directe. De plus, l'investigation de l'homogénéité du laser sur la cible est impérative pour appréhender son impact global sur le système.A decade of experiments at the National Ignition Facility has proven that inertial confinement fusion is a credible approach to energy production, with experiments having exceeded the ignition regime. However, the indirect-drive approach is not suited for high gain implosions and reliable energy production. The direct-drive ignition approach is favoured for energy production as it features simpler target designs and couples more energy to them. There are currently no ignition-scale laser facilities configured for the standard direct-drive approach. Integrated direct-drive experiments have mostly been focused on understanding the physics at reduced scales, with the ultimate goal of demonstration of necessity and feasibility of construction of an international direct-drive laser facility.This thesis manuscript presents a study on the validation of state-of-the-art 3D radiative hydrodynamics codes and the understanding of low modes and laser coupling which play crucial roles in the study of inertial fusion energy. Careful examination of CBET models is of paramount importance in this context, ensuring the accuracy of simulations and contributing to the design of future direct-drive facilities. In addition, the investigation of laser homogeneity on target is imperative to understand its overall impact on the system
Alternative Approaches to Fast Ignition Laser Driven Fusion
No full textExperimental and theoretical studies of laser fusion topicsExperimental and theoretical studies of laser fusion topicskatedra fyzikální elektronik
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
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