1,121 research outputs found
Analysis of Mathieu Equation Stable Solutions in the First Zone of Stability
No full textAbstractThe paper presents the results of a homogeneous Mathieu equation studies. Mathieu equation solutions are oscillations, modulated in amplitude and frequency. In the computational experiments we found dependences of the given oscillations on the ratio of the coefficients. These dependences are shown in graphs that can be used for an approximate estimation of the Mathieu equation solutions without integration
Dissipation and nonlocality in a general expanding braneworld universe
No full text32 pages LATEX with 7 eps figuresInternational audienceWe study the evolution of both scalar and tensor cosmological perturbations in a Randall-Sundrum braneworld having an arbitrary expansion history. We adopt a four dimensional point of view where the degrees of freedom on the brane constitute an open quantum system coupled to an environment composed of the bulk gravitons. Due to the expansion of the universe, the brane degrees of freedom and the bulk degrees of freedom interact as they propagate forward in time. Brane excitations may decay through the emission of bulk gravitons which may escape to future infinity, leading to a sort of dissipation from the four dimensional point of view of an observer on the brane. Bulk gravitons may also be reflected off of the curved bulk and reabsorbed by the brane, thereby transformed into quanta on the brane, leading to a sort of nonlocality from the four dimensional point of view. The dissipation and the nonlocality are encoded into the bulk propagator. We estimate the dissipation rates of the bound state as well as of the matter degrees of freedom at different cosmological epochs and for different sources of matter on the brane
Pensar las escalas para pensar las luchas: Autor: Mathieu UHEL
No full textA través de un título sugerente, “pensar las escalas para pensar las luchas”, Mathieu Uhel entreteje la construcción teórico-crítica del concepto escala, generada por la geografía radical anglosajona de finales del siglo XX, con la necesidad/utilidad práctica de la escala para concienciar las luchas sociales. El artículo cumple un doble propósito: por un lado, delinear los elementos de lectura sobre el concepto escala; y, con ello, promover la atención de esta problemática en las luchas contemporáneas. En un primer apartado, Uhel ubica las discusiones académicas en torno a la escala, como herramienta metodológica útil para comprender la complejidad de las sociedades capitalistas; en el segundo apartado, el autor avanza la exposición en torno al contexto de la dimensión escalar del imperialismo capitalista; finalmente, el autor se centra en el rol de la actividad política a escala nacional en la tensa relación entre las imposiciones del capital y la lucha social.Por meio de um título sugestivo, “pensando escalas para pensar lutas”, Mathieu Uhel entrelaça a construção teórico-crítica do conceito de escala, gerado pela geografia radical anglo-saxônica do final do século XX, com a necessidade / utilidade prática escala para aumentar a consciência das lutas sociais. O artigo tem um duplo propósito: por um lado, delinear os elementos de leitura sobre o conceito de escala; e, com isso, promover atenção a esse problema nas lutas contemporâneas. Na primeira seção, Uhel localiza as discussões acadêmicas em torno da escala, como uma ferramenta metodológica útil para compreender a complexidade das sociedades capitalistas; na segunda seção, o autor avança a exposição em torno do contexto da dimensão escalar do imperialismo capitalista; por fim, o autor enfoca o papel da atividade política em escala nacional na tensa relação entre as imposições do capital e a luta social.Mathieu Uhel\u27s suggestive title, “Thinking about scales to think about struggles”, he interweaves the theoretical-critical construction of concept scale, generated by radical Anglo-Saxon geography in the late 20th century, with it´s practical utility to social struggles. The article serves two purposes: on the one hand, Uhel locates academic discussion around scale; and, with this, he promotes attention to this problem in contemporary struggles. In the first section, Uhel locates academic discussions around scale, as a useful methodological tool to understand the complexity of capitalist societies; in the second section, the author advances the argument around the context of the scalar dimension of capitalist imperialism; finally, the author focuses on the role of political activity on a national scale in the tense relationship between the impositions of capital and the social movement
Compton y-parameter map of thermal SZ effect from Planck PR4 data
No full text<p>This dataset hosts the results and processing data from the paper "An improved Compton parameter map of thermal Sunyaev-Zeldovich effect from Planck PR4 data", <a href="https://doi.org/10.1093/mnras/stad3156">https://doi.org/10.1093/mnras/stad3156</a>. Please cite this paper, should you use this data.</p>
<p>Contact: <a href="mailto:[email protected]">[email protected]</a></p>
<p>UPDATED FITS HEADER.</p>
Mathieu Ichou, Les Enfants d’immigrés à l’école
No full textIt is common to hear in the fields of educational and immigration sociology that on average, the children of immigrants do not perform as well in school as children of native-born parents. Mathieu Ichou offers an innovative sociological analysis on a topic that is heavily exploited by political and media discourse, and subject to much scientific controversy. The author takes distance from the homogenized vision of a “second generation” of students who have totally failed academically, and rep..
L'impatto dell'attività tintoria sull'ambiente. Firenze alla fine del Medioevo
No full textThe author aims to examine and categorize the range of dyeings materials used in the Florentine wool and silk textile industries in the late Middle Ages, focusing mainly on those produced within the regional space in order to evaluate the impact of the Florentine dyeing activity on the natural environment and the productive landscape of the Tuscan countryside. In particular, the author establishes a line of demarcation between cultivated and uncultivated resources in order to verify which constitutes an indication of the level of industrial development of medieval textile production. This further focuses on how the transition from the exploitation of wild resources to the exploitation of cultivated resources could reflect a greater degree of economic integration between the countryside and the city and contribute to the formation of a regional economic space
Optimization of a pyrochimical process for strategical metals production : neodymium application
No full textCette thèse s'inscrit dans la continuité du programme européen REE4EU dont l'objectif était d'étudier la mise en œuvre d'une chaîne de recyclage du néodyme contenu dans les aimants permanents. A l'issue de ce programme, l'oxyde de néodyme (Nd2O3) obtenu est converti en Nd métallique par électrolyse à haute température d'un mélange LiF-NdF3-Nd2O3 (procédé de type Hall-Héroult). Dans ce procédé, Nd2O3 est dissout sous la forme d'un oxyfluorure NdOF54- qui est consommé lors de l'oxydation d'une anode en carbone (1), tandis que le composé NdF3 du solvant, qui se présente sous la forme NdF63-, est réduit en néodyme sous la forme de métal liquide (2). 2NdOF54- + C(s)+2F- → 2NdF63- + CO2(g)+ 4e- (1) NdF63- + 3e- → Nd(l) + 6F- (2) La réaction globale du procédé est alors la suivante : Nd2O3 + 3/2 C(s) → 2Nd(l) + 3/2 CO2(g)(3) L'objectif principal a été de développer des outils aidant à la gestion de ce procédé tout en déterminant des conditions opératoires optimales. Pour cela, trois thématiques de recherche ont été étudiés :(I) Développer une méthode de dosage de l'oxyde de néodyme qui soit rapide et in-situ pour gérer les ajouts de Nd2O3 et éviter la formation de boues denses polluant le métal produit. Dans cette étude, il a été montré que la dissolution de Nd2O3 dans LiF-NdF3 conduit à l'apparition d'ion oxyde libre O2-. Une méthode de dosage de O2- par voltammétrie à vague carrée utilisant une électrode de Pt est alors développée dans LiF-NdF3-Nd2O3. Cette méthode de dosage est finalement utilisée afin de déterminer la solubilité de Nd2O3 dans LiF-NdF3 entre 850 et 1050 °C. (II) Etudier l'influence de la teneur en Nd2O3 sur l'oxydation d'une anode en carbone dans LiF-NdF3-Nd2O3 afin d'éviter la production de CFX(g) pouvant engendrer un effet d'anode. En analysant par spectroscopie IR les gaz anodiques produits par électrolyse, il a été montré que lorsque l'apport en élément oxyde à l'électrode ne permettait pas d'assurer seule l'oxydation du carbone, du CF4(g) et du C2F6(g) étaient également produit. L'influence de la teneur en Nd2O3 sur la densité de courant limite de diffusion de l'oxyde de néodyme dissout a alors été déterminée par voltammétrie à l'état stationnaire entre 850 et 1050 °C. (III) Etudier l'influence de la densité de courant cathodique sur la production de Nd liquide pour optimiser le rendement et faciliter la récupération du métal. En utilisant la technique de la chronopotentiométrie inverse, il a été mis en avant une augmentation du rendement faradique avec la densité de courant. Dans les conditions de l'étude, le rendement faradique maximal est de 85%. Il a également été observé que la coalescence du néodyme liquide était favorisée pour des densités de courant cathodique élevées (> 3 A.cm-2) facilitant alors sa récupération. A l'issue de ce travail, l'influence d'un changement d'échelle sur le rendement de production de Nd a été étudié en réalisant une électrolyse visant à produire environ 100 g de métal, avec les paramètres opératoires optimisés (densités de courant anodique et cathodique). Un impact significatif du changement d'échelle sur le procédé a ainsi pu être observé avec la dispersion et la dissolution de particules de Nd métal dans le sel. Les résultats obtenus ont permis de proposer des pistes d'étude pour poursuivre l'optimisation du procédé.This thesis follows previous works realized in the REE4EU European program, dedicated to the deployment of neodymium permanent magnets recycling chain. At the end of this program, neodymium oxide (Nd2O3) is obtained then and converted into Nd metal by electrolysis of a LiF-NdF3-Nd2O3 mixture at high temperature (analog to Hall-Heroult process). In this process, Nd2O3 is solubilized into an oxyfluoride complexe NdOF54- that is consumed by anodic reaction to produce CO2(g) (1), meanwhile NdF3 compound (complexed as NdF63-) is reduced into liquid metal (2). 2NdOF54- + C(s)+2F- → 2NdF63- + CO2(g)+ 4e- (1) NdF63- + 3e- → Nd(l) + 6F- (2) The global reaction of the process is: Nd2O3 + 3/2 C(s) → 2Nd(l) + 3/2 CO2(g)(3) The main objectives were to develop tools and methods that help to operate the process and determine optimized parameters. This works was divided into three problematics: (I) Develop a fast and in-situ Nd2O3 titration method in order to manage Nd2O3 feeding and prevent sludge formation that pollutes the produced metal. In this study, it was observed that Nd2O3 dissolution leads to O2- formation. A titration method of O2- using square wave voltammetry on Pt electrode was then developed in LiF-NdF3-Nd2O3. This method was also used to determine Nd2O3 solubility in LiF-NdF3 in the 850 - 1050 °C temperature range. (II) Investigate the influence of Nd2O3 content on the oxidation of carbon anode in LiF-NdF3-Nd2O3 in order to prevent CFX(g) formation that could lead to an anode effect. IR spectroscopic analysis of anodic gas shows that oxide depletion leads to CF4(g) and C2F6(g) production instead of CO2(g). The influence of Nd2O3 content on the critical current density, above which one CFX(g) are produced, was determined by steady state voltammetry in the 850 - 1050 °C temperature range. (III) Investigate the influence of cathodic current density on neodymium production in order to optimize current efficiency and facilitate metal recovering. The chronopotentiometry with current reversal method allowed to observe a current efficiency increase with current density. In our experiment conditions, maximum that could be obtained is 85%. Moreover, a better liquid neodymium coalescence (and then recovery) was observed for high current density (above 3 A.cm-2). Finally, an electrolysis able to produce 100 g of Nd metal was realized in order to study the scale up influence on Nd production with optimized cathodic current density. Dispersed neodymium particles and neodymium dissolution were observed and impacted the neodymium production. The results permit then to propose new research thematic to improve neodymium process
Mathieu de Fossey: su visión del mundo indígena mexicano
No full textThroughout these pages the author shows how Mathieu de Fossey perceived that it was not easy to make indigenous communities fit within the mould of the nation-state which, being based on the liberal and egualitarian ideology, was against the recognition of special regimes, such as those that created a peculiar status for the native population of the American territory during the period of Spanish colonial domination
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