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Propriedades termoelétricas de cerâmicas de CaMnO3 produzidas por diferentes rotas de síntese em atmosferas oxidante e redutora
Get PDFIn the pursuit of clean and sustainable energy, In the quest for clean and sustainable energy, thermoelectric materials have been extensively studied and improved, with calcium manganite, CaMnO3 (CMO), being one of the most relevant materials. In this context, a study was conducted on the production of CaMnO3 ceramics in different atmospheres to optimize their thermoelectric properties. CMO powders were synthesized using solid-state reaction (SSR) and the modified Pechini chemical method (QUI). Reducing and oxidizing atmospheres (air, O2, or 10% H2/N2) were used during the sample preparation stages, calcination, and sintering. The influence of the synthesis route was investigated by modifying the calcination and sintering times (3, 6, 12, and 24 hours), evaluating their effects on the formed phases as well as the properties of the produced ceramics. Differential thermal analysis conducted in different atmospheres identified 800 ºC as the crystallization temperature of the CMO phase, but it resulted in excessive undesirable secondary phases. Therefore, batches of powders were calcined at 1000 ºC for 3 or 24 hours in different atmospheres. Scanning electron microscopy (SEM/EDS) observations were carried out to evaluate the morphology, chemical microanalysis, and particle size distribution of the particles obtained in SSR and QUI syntheses. X-ray diffraction (XRD) analysis, coupled with Rietveld refinement, was used to quantify the formed phases. Measurements of the Seebeck coefficient and thermal and electrical conductivities as a function of temperature were performed to characterize the thermoelectric properties and calculate the Figure of Merit (zT) values for each studied condition. Little variation was observed between the phases and their respective amounts under O2 and air atmospheres; however, using the H2/N2 atmosphere during sintering resulted in the complete reduction of CMO, thus not forming the desired phase. Calcination at 1000 ºC (in air or O2) favored the formation of the CMO phase, especially for SSR powders, which presented mass fractions of the desired phase between 78% and 100%, while for QUI powders, the CMO phase fraction ranged between 60% and 70%. The powders calcined at 1000 ºC were relevant in forming the microstructure of the sintered ceramics, as the quantities of the CMO phase in the powders influenced the densification and grain growth processes, whereas using powders calcined at 800 ºC resulted in ceramics with the lowest relative densities (64.1%). Ceramics sintered in H2/N2 were found to be highly electrically resistive, whereas ceramics sintered in oxygen exhibited the highest electrical conductivity values (4117 S/m) and the highest zT values (0.08) among the produced samples. CMO ceramics obtained by the QUI route presented very low electrical conductivity compared to those produced by SSR, and therefore, achieved the lowest zT values, even though they exhibited the desirable low thermal conductivity values (1.42 W/mK) compared to those obtained for SSR CMO ceramics (4.02 W/mK).Na busca por energia limpa e sustentável, materiais termoelétricos vêm sendo estudados e aprimorados, sendo a manganita de cálcio, CaMnO3 (CMO), um dos materiais mais proeminentes. Neste contexto, foi realizado o estudo sobre a produção de cerâmicas de CaMnO3 em diferentes atmosferas com o intuito de otimizar suas propriedades termoelétricas. Pós de CMO foram sintetizados por meio da reação em estado sólido (RES) e da rota química, método de Pechini modificado (QUI). Atmosferas redutoras e oxidantes (ar, O2 ou 10 % H2/N2) foram usadas durante as etapas de preparação das amostras, calcinação e sinterização. Investigou-se a influência da rota de síntese, modificando os tempos de calcinação e sinterização (3, 6, 12 e 24 h), avaliando suas influências nas fases formadas, bem como nas propriedades das cerâmicas produzidas. A partir da análise térmica diferencial, realizada em diferentes atmosferas, a temperatura de 800 ºC foi identificada como a de cristalização da fase CMO, porém resultou em excessivas fases secundárias indesejáveis. Por isso, lotes de pós foram calcinados a 1000 ºC durante 3 ou 24 h, nas diferentes atmosferas. Microscopia eletrônica de varredura (MEV/EDS) foi utilizada para a avaliação da morfologia, da microanálise química e da granulometria das partículas obtidas nas sínteses RES e QUI. Análises de Difração de Raios X (DRX), associadas ao refinamento de Rietveld, foram empregadas para quantificar as fases formadas. Medições de coeficiente Seebeck e condutividades térmica e elétrica, em função da temperatura, foram realizadas para se caracterizar as propriedades termoelétricas e calcular os valores de Figura de Mérito (zT), obtidos para cada condição estudada. Observou-se pouca variação entre as fases e respectivas quantidades geradas, sob as atmosferas de O2 e ar, porém, o uso da atmosfera de H2/N2, na sinterização, resultou em completa redução do CMO, não formando, portanto, a fase de interesse. A calcinação a 1000 ºC (ao ar ou O2) favoreceu a formação da fase CMO, especialmente para os pós RES, que apresentaram frações mássicas da fase de interesse entre 78 % e 100 %, enquanto para os pós QUI, a fração de CMO formada variou entre 60 % e 70 %. Os pós calcinados a 1000 °C foram relevantes na formação da microestrutura das cerâmicas sinterizadas, pois as quantidades da fase CMO nos pós interferiram no processo de densificação e de crescimento de grãos, enquanto o uso dos pós calcinados a 800 ºC gerou cerâmicas com as menores densidades relativas (64,1%). As cerâmicas sinterizadas em H2/N2 se mostraram eletricamente muito resistivas, já as cerâmicas sinterizadas em oxigênio apresentaram os maiores valores de condutividade elétrica (4117 S/m), e maiores zT’s (0,08) dentre as amostras produzidas. As cerâmicas de CMO, obtidas pela rota QUI, apresentaram baixíssima condutividade elétrica em relação às produzidas por RES, e, portanto, obtiveram os menores zT’s, ainda que tenham apresentado os desejáveis e baixos valores de condutividade térmica (1,42 W/mK) comparativamente aos valores de obtidos para as cerâmicas de CMO RES (4,02 W/mK)
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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