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Modélisation de l'allumage d'un carburant hypergolique pour la propulsion de fusées hybrides
Get PDFRÉSUMÉ: Le borazane (AB pour 'ammonia borane' en anglais) a rapidement attiré l'attention de par sa capacité à pouvoir stocker le dihydrogène, car l'AB est composé à 19.6% en masse de H2. Avec l'acide nitrique, l'AB peut former un mélange hypergolique, c'est à dire permettant un allumage spontané sans dispositif particulier. Un carburant hybride, dont l'ergol solide est composé d'AB comme additif dans une matrice de paraffine et l'ergol liquide composé d'acide nitrique concentré (WFNA pour 'White Fuming Nitric Acid' en anglais) permettrait de ne plus utiliser les mélanges hypergoliques classiques contenant souvent de l'hydrazine et ses dérivés, des substances très toxiques. Afin que ce carburant hybride soit viable, son délai d'allumage (ID, de l'anglais 'Ignition Delay'), le temps au bout duquel le mélange hypergolique s'enflamme, doit être inférieur à 10 ms. Certains travaux montrent qu'il est possible de contrôler la valeur du délai d'allumage en ajoutant un polymère, l'alpha-oléfine, dans la paraffine, dont un des effets principaux semble être d'augmenter la viscosité de la paraffine fondue. Dans les travaux présentés ici, une simulation 1D multiphysique en différences finies a été implémentée afin de modéliser les réactions chimiques, transferts thermiques et transports de matière entre les trois phases en jeu : la phase solide composée d'AB dans une matrice de paraffine, la phase liquide composée de WFNA et de la paraffine fondue, et la phase gazeuse. Le manque de données dans la littérature a nécessité la réalisation d'expériences simples pour fournir de l'information sur la cinétique et la thermodynamique de la réaction initiale entre l'AB solide et le WFNA. Cela a permis de regrouper toutes les valeurs d'entrée pour la réalisation d'une première simulation numérique permettant le calcul des valeurs de délai d'allumage. Ces résultats de simulation ont ensuite été confrontés aux valeurs expérimentales obtenues par l'équipe de Elzein et al [1], dont les mesures ont aussi été prises à Polytechnique Montréal. Tout comme dans les tests expérimentaux, les résultats numériques montrent que le délai d'allumage semble décroître avec la viscosité de la paraffine fondue, liée à la concentration en alpha-oléfine. Cependant, la décroissance est beaucoup moins marquée pour les résultats numériques, qui varient de quelques millisecondes contrairement aux résultats expérimentaux pouvant varier de plusieurs dizaines de millisecondes. En revanche, la taille des grains d'AB a un impact beaucoup plus prononcé sur les résultats numériques. Plus les grains sont gros, plus l'ID diminue et moins celui-ci dépend de la viscosité de la paraffine, alors que cela n'est pas observé dans les résultats expérimentaux. ABSTRACT: The storage of hydrogen is one of the main obstacles to the use of this energy carrier in different kinds of space propulsion, or even in the car industry. The Ammonia Borane (AB) quickly drew attention due to its ability to store hydrogen in solid state, as AB is composed of 19.6 wt.% of hydrogen. With nitric acid, AB forms a hypergolic mixture, allowing spontaneous ignition without ignition device. A hybrid fuel, with the solid propellant composed of AB as an additive in a matrix of paraffin, and the liquid propellant composed of White Fuming Nitric Acid (WFNA) would make it possible to get rid of classic toxic hypergolic mixture, usually containing hydrazine and its derivatives. To make this hybrid fuel viable, its Ignition Delay (ID), the time take by the mixture to spontaneously ignite, should be less than 10ms. Studies show that it's possible to control the value of the ID by adding a polymere additive in the paraffin, here the alpha-olefin (AO), to increase the viscosity of the molten paraffin. In this work, a 1D finite difference multiphysics has been implemented in order to model the chemical reactions, and physical phenomenona between the three phases involved: solid phase composed of AB in paraffin, liquid phase composed of WFNA and molten paraffin, and the gas phase, where the ignition occurs. Simple experiments were needed to provide data on the kinetic of the initial reaction between solid AB and WFNA, that was missing in the litterature. This allowed to regroup all the inputs for the realisation of a first numerical simulation allowing the calculation of numerical values of the ID. The results of the simulation were then compared with the experimental values obtained by Elzein and al., whose experiments were performed at Polytechnique Montreal. Just like the experimental data, the results from the numerical simulation shows that the value of ID seems to decrease with the viscosity of the molten paraffin, thus with the concen- tration of AO. However, this decrease is less important in the simulation, where there is only few milliseconds of variation of the value of the ID, whereas this variation is about tens of milliseconds in the experiments. In contrast, the effect of the size of the grains of AB seem to be overestimated in this numerical model. The bigger the grains of AB are, the lower the ID is, and the weaker is the dependance of the ID with respect to the viscosity, which is not seen in the experimental values
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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