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Regras de ocupação e influência de dopantes trivalentes em matrizes cerâmicas transparentes de PLZT 9/65/35
Get PDFIn this work, were investigated the occupancy of rare-earth ions in lattice site of the ferroelectric system (Pb,La)(Zr,Ti)O3, or PLZT. The influence on the structural, microestructural, dielectric, ferroelectric, optical and electro-optical properties, due to the aliovalent occupancy were also investigated. The rare-earth oxides (Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3) were added, at 1.0 weight %, to the ceramic powders of PLZT (with La/Zr/Ti=9/65/35), synthesized by the conventional oxide mixing process, and then were re-calcined. The ceramic bodies, conformed from the milled powders, were densified by uniaxial hot pressing method. The properties of the ceramics were comparatively analyzed as a function of the rare-earth doping ions. The structural characterization, at room temperature, was made using the Rietveld refinement of the XRD patterns. In this way, for each composition, the effective stoichiometry, the lattice parameter and the crystalline symmetry were identified. The occupancy of the rare-earth ions were confirmed in the both, A and B, sites of the PLZT s perovskite structure (ABO3). The ionic occupancy is ruled by its atomic radii, pre-determined by Pauling rules for the structural stability. The effects of the aliovalent ionic occupancy were investigated using a novel parameter, the ―effective radius‖, defined as an average of the radius and the atomic concentration for each coordination number, i.e., a parameter which the geometric characteristic of the ion (ionic radius) and its molar content in each site are considered. In this way, it was observed that dopants with effective radius > 1.2 Å, as the Nd+3, preferentially occupy the A sites of the PLZT s perovskite structure. In this specific case, at room temperature, a cubic crystalline symmetry (paraelectric) was stabilized; a typical quadratic electro-optic effect and a slimloop polarization hysteresis were found. Up to 1.0 weight % of Nd2O3, ~1.9 mol % of Nd+3, were found no formation of segregated phase, that shows the ion stability in the crystalline lattice. The preferential occupancy of the A sites, as also in the case of the Ho+3, have the formation of lattice vacancies in the A sites, as consequence. The effects of these vacancies are the decrease of the polarization values and an increase of the diffusiveness of the phase transition. By the way, for doping ions with effective radius 1,2 Å, como no caso do Nd+3, têm ocupação preferencial nos sítios A da matriz PLZT. Neste caso, a temperatura ambiente, se estabiliza uma simetria cristalina do tipo cúbica (paraelétrica), o que resulta em um material com efeito eletro-ótico predominantemente quadrático e curvas de polarização versus campo elétrico do tipo slim-loop. Observou-se até o limite de 1,0% em peso de Nd2O3 adicionado, o que equivale a ~1,9% em mol do íon Nd+3, não há a formação de fases segregadas, o que indica sua estabilidade na rede cristalina. A ocupação aliovalente preferencial nos sítios A, neste caso como também no caso do Ho+3, resulta na formação de vacâncias nesse mesmo sítio, VA, assim, os efeitos dessas vacâncias, como a redução dos valores da polarização e o aumento da difusividade da transição de fase podem ser observados. Já para o caso de dopantes com raio efetivo <1 Å, caso de Tm+3 e Yb+3, observou-se que sua ocupação preferencial ocorre nos sítios B da estrutura perovskita do PLZT. Neste caso a formação de vacâncias, por ser também uma ocupação aliovalente, ocorre nos sítios do oxigênio, Vo. As conseqüências dessas vacâncias, como o aumento da polarizabilidade, o processo de fadiga ferroelétrica e o efeito eletro-ótico linear, foram observadas para essas cerâmicas. Para a concentração de 1,0% em peso desses óxidos adicionado à matriz de PLZT já se observa a formação de fases segregadas, o que resulta na redução dos valores da transmissão ótica. Dopantes com raios efetivos intermediários, como é o caso do Er+3 possuem ocupação dividida entre os sítios A e os sítios B, tal que as influências dessa incorporação são mistas para os dois casos. Desse modo, baseado nesses resultados, propõe-se a existência de um limite de concentração de dopantes trivalentes nos sítios A (ou B) da estrutura perovskita do PLZT 9/65/35, tal que os efeitos de sua ocupação podem ser vistos com diferentes tendências em relação à matriz sem dopante
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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