1,721,042 research outputs found
Ocean model of Protactinium, Thorium and Particles (ProThorP)
No full text<p>ProThorP [pɹoθɔrp] is a model of thorium, protactinium and particles. More specifically, at the moment, it is a conceptual model that describes, and a numerical model that prognostically simulates, thorium-231, protactinium-230 and lithogenic particles derived from deposited dust. In this instance it is used in combination with [NEMO 3.6](https://www.nemo-ocean.eu/).</p>
Development and use of Actinium 227 as a tracer of deep ocean mixing
No full textLe mélange vertical dans l'océan profond est un processus important pour le fonctionnement de la circulation thermohaline océanique et donc pour le système climatique global. L'actinium-227 (227Ac) est un isotope radioactif naturel produit par désintégration du protactinium-231 (231Pa) dans les sédiments marins profonds. Comme il est soluble, il diffuse dans les eaux de fond. Sa demi-vie courte (22 ans) en fait un traceur spécifique du mélange vertical dans l'océan profond. L'analyse de 227Ac par comptage nucléaire utilisé jusqu'à maintenant nécessite de 50 à plusieurs centaines de litres d'eau et reste malgré tout peu précises. Ceci a limité l'utilisation du 227Ac en océanographie. Au cours de cette thèse, nous avons développé un protocole commun de séparation et d'analyse de 227Ac et 231Pa par MC-ICPMS à partir de 10L d'eau de mer. En plus de ces deux isotopes, ce protocole de séparation produit différentes fractions pouvant permettre d'analyser d'autres traceurs (isotopes du Nd, Ra ou Th) sur un même échantillon d'eau.Ce protocole a été appliqué à des échantillons d'archives prélevés lors de la campagne Bonus GoodHope, dans le secteur Atlantique de l'océan Austral. Le 231Pa a été analysé en parallèle du 227Ac, dont l'analyse est primordiale pour exploiter les données de 227Ac . Ces nouvelles données de 231Pa ont conforté la théorie de sa forte affinité pour l'opale produite par les diatomées et a permis d'affiner le modèle de transport des radionucléides le long des isopycnes remontant au sud de l'ACC. Les résultats obtenus de 227Ac ont permis d'estimer des coefficients de mélange turbulent de 1 cm2/s au-dessus de la dorsale océanique, de 14 cm2/s à cause d'une turbulence accrue près de la marge africaine et de l'ordre de 30 cm2/s dans le gyre de Weddell. Une application de ces valeurs est notamment proposée pour décrire la distribution de la concentration et de la signature isotopique du Nd, à l'aide d'un modèle prenant en compte les processus près de la marge continentale.The vertical mixing in the deep ocean is an important process for the functioning of thermohaline circulation and also for the global climatic system. L'actinium-227 (227Ac) is a natural radioactive isotope product by the protactinium-231 (231Pa) decay in deep marine sediment. The short half-life of this isotope (22 years) makes it a specific tracer of vertical mixing of deep ocean. 227Ac analysis by nuclear counting used until now required from 50 to several hundred liters of water for a limited accuracy. This limited strongly the use of 227Ac in oceanography until today. During this thesis, we developed a join 231Pa-227Ac purification protocol suitable for 10L seawater sample, to perform analysis by MC-ICPMS. In addition to these two isotopes, this separation protocol provides different fractions that can be used to other tracers (Nd, Ra or Th isotopes) from the same water sample.This protocol was applied to archival samples collected during the Bonus GoodHope cruise, in the Southern Ocean. 231Pa was measured at the same time as 227Ac because its analysis is essential to exploit 227Ac data. These new 231Pa data support the previous hypothesis of a strong affinity toward the opal produced by the diatoms and allow to refine the transport of radionuclides along slopping isopycnal surfaces at the South of the ACC. Results from 227Ac data gave estimates of the vertical eddy diffusion coefficient of 1 cm2/s over the mid-ocean ridge, of 14 cm2/s near the African margin due to an enhanced turbulence and of the order of 30 cm2/s in the Weddell gyre. An application of these values is proposed to describe the concentration and isotopic signature distributions of Nd near the continental margin
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
Development of 135Cs/137Cs analysis adapted to low-level contaminated soils and sediments to identify the origin of radiocesium released into the environment
No full textPlusieurs sources de radiocésium peuvent contribuer à la contamination radioactive de l'environnement. Pour les identifier, un rapport isotopique peu exploré jusqu'à présent est proposé : 135Cs/137Cs. À ce jour, peu de données sur ce rapport sont disponibles dans l'environnement en raison de l'existence de plusieurs défis analytiques.Cette thèse comporte deux objectifs majeurs. Le premier concerne le développement et la validation du protocole permettant la mesure du rapport 135Cs/137Cs dans des échantillons de l'environnement. Le second objectif est de contribuer à la connaissance du fond radiologique en radiocésium en France par l'analyse d'échantillons d'intérêt.Les performances du protocole radiochimique développé sont très satisfaisantes pour des prises d'essai de sols ou de sédiments allant jusqu'à une centaine de grammes. Les rendements de récupération en Cs sont supérieurs à 80 % et de hautes puretés des fractions de mesure sont obtenues en seulement cinq jours.La mesure est ensuite réalisée par spectrométrie de masse (ICP-MS/MS). L'optimisation des conditions de gaz dans la cellule de réaction/collision a permis d'aboutir à une méthode sensible vis-à-vis du césium tout en éliminant les dernières traces d'interférents aux masses d'intérêt.Une fois le protocole développé, sa justesse a été vérifiée en comparant les rapports isotopiques 135Cs/137Cs mesurés dans des échantillons impactés par les retombées des accidents de Tchernobyl ou de Fukushima avec ceux publiés dans la littérature.Enfin, le protocole validé a été appliqué, pour la première fois, à vingt-et-un échantillons de sols ou de sédiments prélevés en France dans des régions essentiellement impactées par les retombées des essais atmosphériques d'armes nucléaires et/ou de l'accident de Tchernobyl. Les résultats obtenus ont permis, d'une part, de confirmer et de préciser la signature isotopique 135Cs/137Cs de chaque source de radiocésium et, d'autre part, d'estimer les contributions de chacune de ces sources dans des échantillons environnementaux.Several sources of radiocesium can contribute to the radioactive contamination of the environment. To discriminate them, the use of an isotopic ratio little explored until now is proposed: 135Cs/137Cs. To date, few data are available in the environment due to the existence of several analytical challenges.The current thesis has two main objectives. The first one is devoted to the development and the validation of the protocol allowing the 135Cs/137Cs ratio measurement of environmental samples. The second objective is to contribute to the knowledge of the radiocesium radiological background in France by analyzing samples of interest.The analytical performances of the developed protocol are very successful for soil or sediment samples of up to a hundred grams. The Cs recoveries exceed 80% and high purities of the measured fractions are obtained in only five days.The measurement is performed by mass spectrometry (ICP-MS/MS). The optimization of gas conditions in the collision/reaction cell allowed to obtain a sensitive method for cesium while eliminating the last traces of interferents.After the protocol development, its accuracy was verified by comparing the 135Cs/137Cs ratios measured in samples impacted by Chernobyl or Fukushima fallout with those reported in the literature.Finally, the validated protocol was applied, for the first time, to twenty-one soil or sediment samples collected in regions of France mainly impacted by fallout from nuclear weapons testing and/or Chernobyl accident. The acquired data allowed, first, to confirm and refine the isotopic signature of each 137Cs source and then to estimate the contributions of each of them in environmental samples
Utilisation des isotopes du thorium pour l'étude des particules marines dans l'Océan austral, la Mer de Barents et la Méditerranée
No full textTOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF
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
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