1,720,960 research outputs found
Caracterização de revestimentos industriais do tipo TiAlN, TiAlN e TiAlN/TiAlN usados para maquinação da liga Ti6Al4V usada em aplicações aeronáuticas
No full textDissertação de Mestrado Conjunto Europeu em Tribologia de Superficies e Interfaces apresentada à Faculdade de Ciências e TecnologiaA investigação e desenvolvimento de ligas de titânio tem vindo a ser alvo de estudo durante as últimas décadas devido às suas superiors propriedades físicas, químicas e mecânicas quando comparado com outros ligas. No entanto, o fabrico de components em ligas de titânio é mais caro e requer mais tempo de processamento em comparação com outros metais devido à sua grande dificuldade de maquinar. Uma das principais soluções atualmente usadas para melhorar a maquinação das ligas de titânio é a aplicação de revestimentos na superficie das ferramentas de corte, que por um lado permitem aumentar a vida de ferramenta de corte e por outro melhorar a qualidade da superfície maquinada. Nesta tese, revestimentos industriais depositados em monocamada (TiAlN, TiAlCN) e em multicamada (TiAlN/TiAlCN) foram caracterizados relativamente a diferentes propriedades para determiner quais dos revestimentoa apresentam o melhor compromisso entre propriedades. Os revestimentos depositados foram caracterizados quanto à sua composição química, estrutura, morfologia, resistência à oxidação, estabilidade térmica, propriedades mecânicas e comportamento tribológico à temperatura ambiente. Como esperado os revestimentos apresentam diferentes composições químicas de Ti, Al, N e C devido à diferente composição dos alvos usados e potência aplicadas aos alvos durante a deposição. Todos os revestimentos apresentam uma estrutura fcc. A morfologia dos revestimentos em secção transversal exibem um crescimento columnar, onde o revestimento TiAlN apresenta uma morfologia mas densa do ques os outros revestimentos. O ponto de início de oxidação dos revestimentos é dependente da composição química dos revestimentos: ~900°C, ~850°C e ~800°C para os revestimentos TiAlN, TiAlCN e TiAlN/TiAlCN, respectivamente. Os testes isotérmicos realizados às amostras a 900°C durante 2 h aos revestimentos, promoveram a total oxidação dis revestimentos TiAlCN e TiAlN/TiAlCN, enquanto que o revestimento TiAlN foi apenas parcialmente oxidado. A notável resistência à oxidação do revestimento TiAlN deve-se à formação de uma camada continua e protetora de Al2O3 no topo da camada de óxido. A formação dessa fase foi identificada por difração de raios-x analyses SEM. O revestimento TiAlN/TiAlCN apresentou os maiores valores de dureza – 38 GPa e modulo de elastecidade – 363 GPa, entre os diferentes revestimentos. Após o recozimento, o revestimento TiAlN exibiu um grande aumento de dureza devido ao aumento da sua cristalinidade. Nos testes tribológicos, o coeficiente de atrito, a profundidade de desgaste e a taxa especifica de desgaste corroboram os resultados de dureza e tenacidade. As pistas de desgaste exibem um mecanismo de abrasão, caracterizadas pela presença de ranhuras e detritos. O revestiemnto TiAlN/TiAlCN apresentou o melhor desempenho tribológico devido à combinação de alta dureza e alta tenacidade à fratura em comparação coms outros revestimentos.The research and development on titanium alloys have been nourishing for quite some time due to their superior physical, chemical and mechanical properties. However, manufacturing titanium is more expensive and requires longer time compared with other metals due to its poor machinability. One of the leading solutions to address the difficulty in machining titanium is to deposit coating on the cutting tools in order lengthen the service lifetime and ensure good quality of machined surface. In this study, industrial made monolithic TiAlN, monolithic TiAlCN and multilayered TiAlN/TiAlCN coatings were thoroughly characterized to determine which coating displayed the best combination of properties. The deposited coatings were fully characterized for their chemical composition, structure and morphology, oxidation resistance, thermal stability, mechanical properties and tribological performance at room temperature. The coatings reported different chemical composition of Ti, Al, N and C due to the different targets, chemical composition and power applied to the target during deposition. All films displayed a fcc NaCl type structure. The SEM micrographs of the cross-section and surface morphology of the as-deposited coatings exhibited a columnar growth with TiAlN showing the densest structure. The onset point of oxidation was measured to be ~900°C, ~850°C and ~800°C for TiAlN, TiAlCN and TiAlN/TiAlCN, respectively. After the isothermal test at 900°C for 2 h, TiAlCN and TiAlN/TiAlCN were fully oxidized while a huge portion of the TiAlN coating still exists. The remarkable oxidation resistance of the latter coating was driven by the formation of a continuous and protective oxide scale Al2O3 on top of the oxide layer. The presence of this oxide scale was confirmed by XRD, SEM micrograph and elemental map distribution. The as-deposited TiAlN/TiAlCN reported the highest H and E values at 38 GPa and 363 GPa, respectively. Upon annealing, TiAlN exhibited a huge increase in hardness due to increase in crystallinity. In the tribological tests, the coefficient of friction, wear depth and wear rate corroborate the hardness and toughness results of the coatings. The wear track exhibit abrasion mechanism which is characterized by grooves and scratches and the presence of wear debris in fish-like form. The multilayered TiAlN/TiAlCN showed the best tribological performance due to the combination of high hardness and high fracture toughness compared to the monolithic TiAlN and TiAlCN coatings.Outro - Project MCTool21 - POCI-01-0247-FEDER-04594
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Investigating the effect of different environments on NMC811 positive electrode precursors using ESEM and TGA-DSC
No full textLithium-ion batteries have been a focal point of extensive research and development for various applications, including stationary energy storage, portable electronics, and electric vehicles. Two central challenges addressed by research are mitigating capacity losses and enhancing safety features to ensure the reliability and performance of these batteries. Over the years, numerous battery chemistries have been explored, both theoretically and in industrial settings, aiming to meet these challenges. Notably, novel chemistries, such as Lithium-iron-phosphate (LFP), Lithium-rich manganese oxide (LMO) and Lithium Nickel Manganese Cobalt Oxide (NMC) batteries, have garnered attention. Among the different NMC ratios tested, LiNi0.8Mn0.1Co0.1O2 (NMC811) has emerged as a promising candidate, celebrated for its remarkable energy density resulting from increased capacity and a wider operating voltage range. However, recent research has uncovered that the presence of oxygen and excess moisture during the production process has been found to induce non-uniform morphologies in these materials which can potentially disrupt mass transport and influence the thermal behaviour of the battery components. Furthermore, it is essential to emphasize the role of unlithiated precursors in the quality and performance of the final lithiated battery materials. These precursors significantly impact various properties, including morphology, thermal stability, energy density, capacity, and cycle life. This investigation encompasses an extensive analysis of varying moisture content, temperature conditions, and gaseous environments. Thermal stability is assessed through Thermogravimetric Analysis (TGA) coupled with Differential Scanning Calorimetry (DSC), while morphological features are examined using Environmental Scanning Electron Microscopy (ESEM). These findings pave the way for innovative precursor studies, focusing on enhanced structural design to mitigate risks associated with high nickel content. Therefore, in this context, the present thesis successfully achieves its objectives by investigating the influence of diverse environmental conditions on unlithiated NMC811 positive electrode precursors
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
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