1,721,014 research outputs found
Optimizing Porosity and Acidity of Faujasite Zeolites For Sugar Transformation
No full textLe 5-HMF, produit à partir de la transformation des sucres issus de la biomasse, est l'une des molécules plateformes potentiellement à la base de produits chimiques biosourcés et forte valeur ajoutée. Les zéolithes faujasite acides de Brønsted sont parmi les catalyseurs les plus prometteurs pour la valorisation de la biomasse grâce à sa porosité et son acidité modulables. Dans cette thèse, nous ciblons la déshydratation du fructose en 5-HMF catalysée par des zéolites de type faujasite, et nous examinons les relations entre leurs propriétés et leur activité catalytique. Tout d’abord, nous étudions d’un point de vue mécanistique la réaction de déshydratation catalytique du fructose en 5-HMF dans le dimethylsulfoxyde. Une combinaison techniques analytiques (HPLC, RMN 1H et 13C et GC) permet d'identifier les intermédiaires et sous-produits et de classer de nombreux dérivés du fructose identifiés selon leurs comportements cinétiques. Grâce à ces techniques, nous proposons un modèle cinétique cohérent avec les données expérimentales. Nous évaluons ensuite l'activité catalytique d’une série de zéolites faujasite commerciales et mettons en avant sur cette série que le volume mésoporeux semble être le critère déterminant, probablement en raison de problèmes de limitations diffusionelles et d’accessibilité des sites acides sur certains échantillons. Nous nous concentrons alors sur la post-modification de ces matéiraux afin d’améliorer l’accessibilité. Nos méthodes sont basées sur la desilication et la désalumination, introduisant de la mésoporosité et altèrant l'acidité. Nous utilisons les zéolithes CBV712 (Si/Al= 6), CBV720 (15) et CBV760 (30) comme matériaux de base pour examiner l’effet du rapport Si/Al sur la modification. Nous utilisons de l'hydroxyde de tétraalkylammonium en variant la longueur de la chaîne alkyle de C1 à C4, et de l'acide oxalique pour la désiliciation et la désalumination, respectivement. Étant donné que non seulement les propriétés texturales et l’acidité, mais également d'autres propriétés liées, sont modifiées, nous caractérisons intégralement les zéolites modifiées par physisorption de N2, DRX, XRF, ICP, 27Al MAS RMN, MEB, MET et FTIR. Nous examinons également l'accessibilité des sites actifs par la 2,4,6-tri-tert-butylpyridine (TTBPy) qui est encombrée stériquement. Enfin, nous développons une méthode optimale pour la fabrication d’une zéolite hiérarchique avec des volume de mésopores larges sans perte en cristallinité. Dans un dernier temps, nous évaluons l'activité catalytique des catalyseurs modifiés en relation avec leurs propriétés. Une approche chimiométrique des résultats obtenus fournit non seulement des informations complémentaires sur la relation entre les propriétés de la zéolite et les performances catalytiques, mais cette approche statistique et mathématique offre également une vue globale inédite. Grâce aux analyses, nous avons découvert les propriétés les plus importantes de la zéolite dans la déshydratation du fructose en 5-HMF, et sommes en mesure de proposer des guides pour la préparation optimisée de catalyseurs.5-HydroxyMethylFurfural (5-HMF), produced from the transformation of biomass-based sugar, is one of the most important platform chemicals. It can lead to various high added-value chemicals as potential alternatives to petroleum-based chemicals. Brønsted acid faujasite zeolite is one of the most competitive and compatible catalysts for the valorization of biomass owing to its tunable porosity and acidity. In this thesis, we target the dehydration of fructose to 5-HMF catalyzed by faujasite zeolite, and we question the properties-activity relationships in such catalysts. First, we investigate the reaction mechanism at stake in the catalytic dehydration of fructose to 5-HMF over faujasite zeolite in dimethylsulfoxide. A combination of analytic techniques (HPLC, 1H and 13C NMR, and GC) allows us to identify the intermediates and byproducts, and we classify the different derivatives according to their kinetic behaviors. Thanks to these techniques, we propose a kinetic model, consistent with experimental values, taking into account the various families of compounds. We then evaluate the catalytic activity of a set of commercial faujasite zeolites, and we determine that over this series, improving the mesoporous volume seems the most important parameter, likely as diffusion limitations may limit the accessibility to the active sites in some of the samples. Next, we focus on the post-modification of faujasite zeolite with the aim to further improve the mesoporous volume and active site accessibility. Our methods are based on desilication and dealumination which introduce mesoporosity and alter acidity. We use CBV712 (Si/Al= 6), CBV720 (15), and CBV760 (28) as starting materials to see the impact of the Si/Al ratio on the modification. We use tetraalkylammonium hydroxide varying its alkyl chain from C1 to C4, and oxalic acid for desilication and dealumination, respectively. Because not only the textural and acidic properties but also other linked properties are modified, we fully characterize the modified zeolites by N2 physisorption, XRD, XRF, ICP, 27Al MAS NMR, SEM, TEM, and FTIR. We also examine the accessibility of active sites by sterically hindered 2,4,6-tri-tert-butylpyridine (TTBPy). Finally, we develop an optimal method to make a hierarchical zeolite with large mesopore volumes without losing crystallinity. Lastly, we evaluate the catalytic activity of modified compounds in relation with the properties of the modified catalysts. The chemometric approach provides not only additional information about interrelation between zeolite properties and catalytic performance, but also this statistical and mathematical approach offers an unbiased comprehensive view. Thanks to the analyses, we figure out the most important properties of zeolite in fructose dehydration to 5-HMF and provide guidelines for optimizing the catalytic activity of the materials
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
- …
