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Paramagnetism study of actinides in solution
No full textLes propriétés physicochimiques des actinides (An) en solution restent difficiles à interpréter et plus particulièrement la différence de comportement entre An(III) et Ln(III). L'étude du comportement paramagnétique des cations actinide peut constituer une méthode « simple » et particulièrement intéressante qui permet de sonder les propriétés électroniques de ces éléments et obtenir des informations sur la nature de l'interaction ligand-actinide. L'objectif de ce travail de thèse est d'appréhender les propriétés paramagnétiques de ces éléments par des mesures de susceptibilité magnétique d'une part et l'étude des déplacements chimiques d'autre part.L'apport d'informations sur les propriétés électroniques des ions actinide pour une variété de degrés d'oxydation (+III, +IV, +V et +VI) a été réalisé par des mesures de susceptibilité magnétique en solution selon la méthode d'Evans. Contrairement aux éléments Ln(III), il n'existe aucun modèle spécifique décrivant clairement les propriétés magnétiques de ces ions en solution. L'acquisition de données de bonnes qualités étant nécessaires, l'influence des dispositifs expérimentaux et de la radioactivité de ces éléments a été analysée. Afin de décrire la structure des états électroniques de faible énergie pour ces cations, les résultats expérimentaux ont été confrontés à des calculs de chimie quantique à partir desquels l'influence du champ des ligands a été étudiée. Ces interprétations ont ensuite été appliquées à la variation des propriétés magnétiques des cations actinide lors de la complexation avec les anions chlorure et nitrate. Les informations sur les liaisons ligand-actinide peuvent être déduites de l'étude directe par RMN des déplacements chimiques de complexes d'actinide. En effet, la présence d'un ion paramagnétique au sein d'un complexe induit des modifications spectrales pouvant être séparées en deux composantes. L'une reliée au degré de covalence des liaisons de coordination et l'autre à la structure tridimensionnelle des complexes en solution. Le problème majeur de ce type d'étude réside dans la difficulté de distinguer les deux contributions. Afin de réaliser une telle étude, nous avons choisi de travailler avec les complexes d'actinide de l'acide dipicolinique (DPA). Dans un premier temps, une étude structurale (par DRX monocristal puis EXAFS) a été menée sur ces complexes formés avec les cations actinide aux degrés d'oxydation +III, +IV, +V et +VI pour caractériser avec précision leurs paramètres structuraux. Ensuite, les différentes méthodes de séparation des deux contributions mettant en jeu la spectroscopie RMN et éprouvées lors de l'étude des complexes de lanthanide (III) ont ensuite été appliquées aux éléments actinide. L'étude des déplacements paramagnétiques associée aux calculs de chimie quantique a permis de caractériser les propriétés magnétiques de ces cations. Contrairement aux études réalisées sur les ions Ln(III), une contribution de contact importante participe au déplacement paramagnétique des complexes d'An(III) et d'An(IV). A l'inverse, pour les cations actinyle, le déplacement paramagnétique des signaux RMN 1H est caractérisé par l'absence de contribution de contact. Cette particularité associée à la géométrie de ces ions a permis de caractériser précisément leurs propriétés magnétiques. Une application de ces résultats à l'étude de complexes formés avec le ligand TEDGA a pu être réalisée. Il apparait de cette étude que les informations obtenues par la description du comportement magnétique des actinides apportent une meilleure compréhension des propriétés physicochimiques de ces ions en solution.The physiochemical properties of actinide (An) solutions are still difficult to explain, particularly the behavioral differences between An(III) and Ln(III). The study of actinide paramagnetic behavior may be a “simple” method to analyze the electronic properties of actinide elements and to obtain information on the ligand-actinide interaction. The objective of this PhD thesis is to understand the paramagnetic properties of these elements by magnetic susceptibility measurements and chemical shift studies.Studies on actinide electronic properties at various oxidation states in solution were carried out by magnetic susceptibility measurements in solution according to the Evans method. Unlike Ln(III) elements, there is no specific theory describing the magnetic properties of these ions in solution. To obtain accurate data, the influence of experimental measurement technique and radioactivity of these elements was analyzed. Then, to describe the electronic structure of their low-energy states, the experimental results were complemented with quantum chemical calculations from which the influence of the ligand field was studied. Finally, these interpretations were applied to better understand the variations in the magnetic properties of actinide cations in chloride and nitrate media.Information about ligand-actinide interactions may be determined from an NMR chemical shift study of actinide complexes. Indeed, modifications induced by a paramagnetic complex can be separated into two components. The first component, a Fermi contact contribution (δc) is related to the degree of covalency in coordination bonds with the actinide ions and the second, a dipolar contribution (δpc) is related to the structure of the complex. The paramagnetic induced shift can be used only if we can isolate these two terms. To achieve this study on actinide elements, we chose to work with the complexes of dipicolinic acid (DPA).Firstly, to characterize the geometrical parameters, a structural study (by monocrystal XRD and EXAFS) was performed on these complexes with the actinide cations at various oxidation states +III, +IV, +V et +VI. Secondly, various methods for separating the two contributions involving NMR spectroscopy were checked with Ln(III) complexes and applied to actinide elements. The paramagnetic induced shift associated with quantum chemical calculations allowed us to characterize the magnetic properties of these cations. Unlike studies on Ln(III) ions, the An(III) and An(IV) paramagnetic induced shifts suggest a major Fermi contact contribution (δc). On the contrary, for actinyle cations, the paramagnetic induced shifts on 1H NMR signals show no Fermi contact contribution (δc). This characteristic, related to the geometry of these ions, allowed for their magnetic properties to be accurately described. An application of these results to the study of complexes with the TEDGA ligand has been performed.It is apparent from this study that the additional information gained on the description of actinide paramagnetic behavior has led to an improved understanding of the physiochemical properties of these ions in solution
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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