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Meccanica delle strutture a membrana in elasticità non lineare
No full textLe membrane elastiche trovano numerose applicazioni in vari ambiti tecnologici. Queste strutture sono tipicamente realizzate in materiali elastomerici, grazie alla loro capacità di sostenere grandi deformazioni elastiche. Un'adeguata analisi della meccanica delle membrane deve necessariamente considerare le non linearità geometriche e materiali. A causa della complessità matematica, i problemi riguardanti le membrane sono solitamente studiati con approcci numerici e assumendo semplici modelli di materiale incomprimibile. Questa tesi studia approfonditamente la meccanica delle membrane elastiche per colmare la mancanza di affidabili soluzioni analitiche e di accurati modelli materiali che considerino la comprimibilità. Innanzitutto viene proposto un modello semplificato per ottenere la risposta analitica di membrane piane circolari soggette a pressione laterale. Come ipotesi semplificativa, la configurazione deformata viene assunta sferica. La membrana è considerata come un solido omogeneo, isotropo e iperelastico descritto da un legame Mooney-Rivlin comprimibile. L'equilibrio al polo della membrana fornisce la relazione analitica tra la pressione e lo spostamento del polo stesso. Essendo approssimata, questa soluzione perde accuratezza in grandi deformazioni. Perciò viene calibrata una funzione correttiva basata sulla soluzione numerica del problema, ottenendo una formula chiusa e valida indipendentemente dalla geometria, dai valori dei parametri del materiale e dal livello di deformazione. Successivamente, la formulazione è estesa alle membrane circolari piane dotate di pre-stretch ed è validata attraverso simulazioni agli elementi finiti. Dei bulge test sono condotti su tre membrane elastomeriche, sia senza che con pre-stretch, e le formule proposte sono utilizzate per determinare i parametri dei materiali. A deformazioni molto elevate il modello di Mooney-Rivlin comprimibile riscontra importanti limiti, specialmente dovuti all'hardening del materiale e alle variazioni di volume. Perciò viene proposta un'energia di deformazione accurata per la risposta di elastomeri in grandi deformazioni. In particolare, la parte volumetrica dell'energia è calibrata sulla base di prove sperimentali e riflette la reale risposta volumetrica del materiale. Infine, la forma di energia proposta è usata per studiare l'effetto della comprimibilità in tre problemi di riferimento: una membrana circolare soggetta a pressione laterale, un tubo cilindrico a parete sottile in pressione, e una sfera a parete sottile in pressione. Vengono considerati quattro differenti materiali con grado di comprimibilità crescente. Al crescere della comprimibilità, si osservano differenze significative sia nella curva della pressione sia nelle deformate. Come ultima applicazione, la comprimibilità viene introdotta nella risposta di un attuatore ad elastomeri dielettrici. Viene mostrato come la comprimibilità influenzi l'accoppiamento elettromeccanico e apra nuovi possibili scenari applicativi. Da un lato, i modelli proposti forniscono uno strumento analitico affidabile e di immediato utilizzo per le applicazioni pratiche. Dall'altro, le soluzioni proposte per materiali comprimibili gettano le basi per applicazioni di membrane realizzate in materiali innovativi come schiume, gel e metamateriali, i quali mostrano una comprimibilità significativa anche a piccole deformazioni.Elastic membranes find numerous applications in several technological fields. These structures are typically made of elastomers, due to their capability to withstand large elastic deformations. A consistent analysis of the mechanics of membranes must necessarily consider geometrical and material nonlinearities. Due to the resulting mathematical complexity, membrane problems are usually studied with numerical approaches and simple incompressible material models. This thesis investigates deeply the mechanics of elastic membranes to fill the lack of reliable analytical solutions and refined material models involving material compressibility. Firstly, a simplified model to derive the analytical response of inflated circular flat membranes is proposed. Spherical deformed configurations are assumed as simplifying assumption. The membrane is regarded as a homogeneous, isotropic, hyperelastic solid described by a compressible Mooney-Rivlin constitutive law. The equilibrium at the pole of the membrane gives the analytical relation between the pressure and the deflection of the pole. Being approximate, this solution lacks of accuracy at very large deformations. A corrective function based on the numerical solution of the problem is calibrated, leading to a closed-form formula valid regardless of geometry, material parameters and range of deformation. Subsequently, the formulation is extended to pre-stretched circular flat membranes and it is validated by means of finite element simulations. Bulge tests are performed on three elastomeric membranes, both unstretched and pre-stretched, and the proposed formulas are used to identify the material parameters. At very large deformations the compressible Mooney-Rivlin model suffers major limitations, especially regarding material hardening and volume changes. Therefore, an accurate strain energy function (SED) for the response of elastomers at very large deformations is proposed. In particular, the volumetric part of the SED is calibrated on experimental tests reflecting the real volumetric response of the material. Finally, the proposed SED is applied to study the effect of compressibility in three benchmark membrane problems: inflation of a circular flat membrane, inflation of a thin-walled cylindrical tube, and inflation of a thin-walled spherical balloon. Four different materials with increasing degree of compressibility are considered. As compressibility increases, significant differences are observed in the pressure curve as well as in the deformed shapes. As final application, compressibility is introduced in the response of a dielectric elastomer membrane. It is shown how compressibility affects the electromechanical coupling, opening up new potential design scenarios. On one hand, the models proposed in this thesis provide a reliable and ready-to-use analytical tool for practical applications of inflated membranes. On the other hand, the proposed solutions for compressible materials lay the foundation for applications of membranes made of innovative materials as foams, gels, metamaterials, which exhibit significant compressibility even at small deformations
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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