1,720,956 research outputs found
Application of classical Molecular Dynamics (MD) for calculating the wetting behavior during soldering or brazing processes
Get PDFEine Grundvoraussetzung für einen erfolgreichen Lötprozess ist eine gute Benetzung der Oberflächen der Fügepartner mit dem Lot. Allerdings ist die Güte der Benetzung im Allgemeinen nicht analytisch vorausberechenbar, da beim Benetzungsvorgang eine Vielzahl physikalisch-chemischer Vorgänge eine Rolle spielt. Insbesondere die Erfahrungen aus der löttechnischen Praxis zeigen, dass sich das Benetzungsverhalten schon dann extrem ändern kann, wenn die chemischen Zusammensetzungen der Lote oder der Fügepartner leicht variiert werden. Wird der Benetzungsvorgang auf atomarer Ebene betrachtet, reduziert sich die Vielzahl physikalisch-chemischer Vorgänge auf die Wechselwirkung einzelner Atome. Daher bietet es sich an, Benetzungsprozesse auf atomarer Ebene zu untersuchen, um Erkenntnisse über den Benetzungsvorgang auf makroskopischer Ebene gewinnen zu können. Eine Methode, mit der diese Untersuchungen numerisch erfolgen können, ist die Molekulardynamik (MD). MD ist ein Simulationsverfahren, welches auf dem numerischen Lösen der Bewegungsgleichungen eines N-Teilchensystems beruht, wobei die Teilchen Atome, Moleküle und/oder Ionen sind. Im Rahmen dieser Arbeit wird, soweit es aus der Literatur bekannt ist, erstmalig geprüft, ob sich MD als Simulationsmethode für die quantitative Vorausberechnung des Benetzungsverhaltens beim Löten eignet. Zu diesem Zweck werden Benetzungsvorgänge für verschiedene Lot-Grundwerkstoff-Systeme auf atomarer Ebene simuliert und die jeweiligen Benetzungskinetiken, die sich aus den Simulationsergebnissen ergeben, aus verschiedenen Gesichtspunkten heraus bewertet. Unter anderem wird die zeitliche Entwicklung verschiedener mikroskopischer Benetzungswinkel analysiert. Darüber hinaus werden die Simulationsergebnisse auch mit den Ergebnissen makroskopischer Benetzungsproben verglichen. Exemplarisch wird das Benetzen von Eisen mit Silber, von Eisen mit Kupfer und von Eisen mit dem Eutektikum Ag72Cu28 berechnet. Diese Systeme werden deshalb ausgewählt, weil Kupfer besser als Silber Eisen benetzt und sich das Benetzungsverhalten merklich verbessert, sobald dem Silber Kupfer beigemengt wird. Zudem wird mit dem Lot-Grundwerkstoff-System Ag72Cu28-Eisen ein ternäres Werkstoffsystem betrachtet, bei dem ein reaktives Benetzen stattfindet. Somit stellt dieses System für eine numerische Simulation eine zusätzliche Herausforderung dar. Als Potentiale für die atomare Wechselwirkung werden die EAM-Potentiale von Johnson gewählt (engl.: Embedded-Atom Method, EAM). Mit diesen EAM-Potentialen werden die Eigenschaften der schmelzflüssigen Phasen von Silber und Kupfer, insbesondere die Oberflächenspannungen, wiedergegeben. Wie sich zeigt, stimmen berechnete, theoretische sowie experimentelle Ergebnisse für die in dieser Arbeit betrachteten Werkstoffsysteme überein. Somit ergibt sich als Hauptergebnis der hier vorliegenden Arbeit, dass mit MD eine Berechnungsmethode zur Verfügung steht, die für eine quantitative Vorausberechnung des Benetzungsverhaltens beim Löten geeignet ist. Da Benetzungsvorgänge für alle Systeme simuliert werden können, bei denen geeignete Wechselwirkungspotentiale für die einzelnen Atome bzw. Legierungspartner bekannt sind, ist die in dieser Arbeit vorgestellte Vorgehensweise prinzipiell für beliebige Lotsysteme anwendbar.A basic requirement for successful soldering or brazing is to obtain suitable solder wettability of the surfaces to be joined. The quality of the wetting, nevertheless, cannot be calculated analytically in advance due to the many physico-chemical effects involved during the wetting process. In particular it is known from experiments that the wetting behavior can be influenced by a slight modification of the chemical composition of the solder or the joining partners. If the wetting process is regarded at an atomic level, the multiplicity of physico-chemical effects is reduced to interactions between single atoms. Thus the investigation of wetting at an atomic level allows to gain insights about macroscopic wetting processes. Such investigations can be carried out by Molecular Dynamics (MD) which is a simulation technique based on the numerical solution of the equations of motion for an N particle system where these particles may be atoms, molecules and/or ions. The main goal of this work is to investigate whether through applying MD it is possible to correctly calculate the wetting behavior of soldering or brazing processes. For this purpose wetting processes for different solder-joining partner-combinations are calculated at an atomic level and the resulting wetting kinetics are analyzed. Particularly the time evolution of microscopic wetting angles is investigated. Simulation results are compared with the corresponding macroscopic wetting experiments. Wetting of an iron substrate by either silver, copper or by the eutectic Ag72Cu28 is computed. These systems are selected because copper wets iron better than silver does and wetting behavior improves if silver is mixed with copper. The thus selected solder-joining partner-combination Ag72Cu28-Fe is a reactive ternary material system that also represents a challenge for the numerical simulation. In order to perform the numerical simulation interaction potentials are required. The Johnson's EAM potentials were selected (Embedded Atom Method, abbr.: EAM) to be used in this work. These EAM potentials describe the properties of the liquid phases of copper and silver, in particular their surface tensions. It turns out that the computed results show a good correlation with experimental measurements as well as theoretical estimations based on the molecular-kinetic theory and the hydrodynamic theory of wetting. Hence this work shows that MD simulations are suitable for calculating the wetting behavior in the area of soldering and brazing. Since wetting processes can be simulated for all systems for which appropriate interactions potentials are known the approach presented in this work is in principle applicable for other solder-joining partner-combinations
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
- …
