Diffusion mechanism of bound Schottky defect in magnesium oxide

In simple ionic crystals, intrinsic point defects must satisfy electrical neutrality and exist as Schottky defects. In magnesium oxide (MgO), a Schottky defect is then a combination of anionic and cationic vacancies. Since vacancies are charged, the stable configuration of the Schottky defect corresponds to a bound pair of vacancies of opposite signs. In this study, we investigate the kinetics of formation and migration of such a bound pair on long timescales reaching in some cases thousands of seconds using the kinetic activation-relaxation technique, an off-lattice kinetic Monte Carlo method with an event catalog built on-the-fly during static molecular simulations. We show that the diffusion of this bound Schottky defect involves the migration of vacancies bounded to the first and third neighbor sites of the crystal structure with an apparent migration energy which cannot be inferred from the migration energies expected from isolated defects. Overall, this study gives insights and constraints on the oxygen diffusion mechanism reported experimentally in high-purity MgO samples

Livros didáticos, imagens dos trabalhadores e ensino de História na Escola Municipal Darcy Ribeiro II(Marabá - Pa)

This dissertation aims to understand the construction of representations through the analysis of images in the History textbook, realizing the appreciation of work as well as field workers as a theme of History and Teaching. Use textbook analysis and understanding as a method to understand issues and their perspectives in history teaching. By the way, in the school of study of the school Mara, the collection: Araribá Mais - in the books used by the textbooks of the 8th and 9th public school Darcy Ribeiro II in the field of education-PA, in the municipal context. Identifying the presence or absence of workers in visual documents. There was the cataloging of images in the didactic manual as a methodological tool, instigating the critical sense about the different representations: photography, painting, portrait, collection, woodcut, lithograph, lithograph and illustration. The exercise of criticism about the illustrations is also prioritized, as each one has its place in History and intentions. They are relevant sources for the writing of History, mainly for Cultural History. This historical study makes it indispensable for students to understand them in their artistic and social dimension of representation, which is the fundamental concept of research.Esta dissertação tem como objetivo compreender a construção das representações através da análise das imagens no livro didático de História, percebendo a valorização do trabalho bem como dos trabalhadores do campo como tema da História e do Ensino. Utilizando a análise do livro didático e questionário como método para entender as problemáticas das ilustrações e suas perspectivas no ensino de História. A propósito, na investigação trabalhamos a coleção: Araribá Mais História - nas oficinas são os livros utilizados pelos estudantes do 8º e 9º ano do ensino fundamental na escola municipal Darcy Ribeiro II em Marabá–PA, no contexto da educação do campo. Identificando a presença ou ausência dos trabalhadores nos documentos visuais. Houve a catalogação das imagens no manual didático como ferramenta metodológica, instigando o senso crítico acerca das diversas representações: fotografia, pintura, retrato, charge, xilografia, litografia, litogravura e ilustração. Prioriza-se, também, o exercício da crítica acerca das ilustrações, pois cada uma tem o seu lugar na História e suas intencionalidades. São fontes relevantes para a escrita da História, principalmente pela História Cultural. Por isso, esse estudo torna-se indispensável para que os estudantes possam compreendê-las na sua dimensão histórica, artística e social através da representação que é o conceito fundamental dessa investigação

Qualidade das Peças Obtidas por Torneamento CNC: Influência do CAD/CAM, Estratégias de Torneamento

A vantagem competitiva de uma empresa baseia-se em equipamentos sofisticados com tecnologia de ponta, que proporcione aos clientes produtos de alta qualidade no prazo estabelecido, com redução substancial dos recursos utilizados e desperdícios. Com o desenvolvimento das tecnologias CNC, a linha de produção veio a ser enriquecida e aprimorada e este naturalmente reflete-se na qualidade e produtividade do produto acabado. Com finalidade de contribuir para o enriquecimento da informação nesta área e complementar minha formação foi efetuado o presente trabalho. Neste, são abordados os principais conceitos e definições do corte por arranque de apara, particularmente incluídas no tornamento CNC. Foram revistas os conceitos relativos aos parâmetros de corte e do comando SSV no torneamento com intuito de investigar as influências no acabamento das peças, medidas através da rugosidade que daí resulta. O procedimento do trabalho constituiu, em primeiro lugar, em avaliar os parâmetros de corte no torneamento e das respetivas medições das rugosidades, em cada experiência. Seguiu-se a comparação de quais apresentam melhores resultados para se obter um bom acabamento superficial das peças. Um caso especial do estudo foi o da aplicação do comando SSV nas amostras. Numa primeira análise, verificou-se que, de modo convencional, não se iriam obter grandes conclusões, uma vez que o acabamento depende em simultâneo, de várias variáveis. Então optou-se pela análise estatística, recorrendo-se à análise de variância, ANOVA, e ao teste de Tukey. Os estudos efetuados foram conclusivos relativamente a velocidade de corte, ao avanço, à ferramenta e o uso do SSV no acabamento das peças. O estudo complementar de torneamento baseado no CAD/CAM, inicialmente proposto, foi efetuado relativamente a uma peça simples. Foram efetuadas simulações para avaliar a influência das estratégias de tornamento, disponíveis no software Mastercam, no acabamento e na produtividade.ABSTRACT: The competitive advantage of a company is based on sophisticated equipment with state-of the-art technology, which provides customers with high quality products on time, with a substantial reduction in resources used and waste. With the development of CNC technologies, the production line has been enriched and improved and this naturally reflects on the quality and productivity of the finished product. In order to contribute to the enrichment of information in this area and complement my instruction, the present work was carried out. In this one, the main concepts and definitions of the chip start cutting are discussed, particularly included in CNC turning. The concepts related to the cutting parameters and the SSV command in turning were reviewed in order to investigate the influences on the finishing of the parts, measured through the resulting roughness. The work procedure consisted, in the first place, in evaluating the cutting parameters in the turning and the respective measurements of the roughness, in each experiment. It was followed by the comparison of which ones present better results to obtain a good surface finish of the parts. A special case of the study was the application of the SSV command in the samples. In a first analysis, it was verified that, in a conventional way, great conclusions would not be obtained, since the finish depends simultaneously on several variables. Then we opted for statistical analysis, using analysis of variance, ANOVA, and Tukey's test. The studies carried out were conclusive regarding the cutting speed, the feed, the tool and the use of SSV in the finishing of the parts. The complementary study of turning based on CAD/CAM, initially proposed, was carried out in relation to a single part. Simulations were carried out to evaluate the influence of turning strategies, available in the Mastercam software, on finishing and productivity

Financeirização e seus impactos para o crescimento do Brasil: 1980 - 2009

Explora a questão da financeirização no Brasil, e seus impactos para a dinâmica de crescimento no país. Observou-se uma significativa redução da taxa de crescimento do PIB brasileiro, a partir de 1980, ao mesmo tempo em que o setor financeiro crescia e ganhava importância na economia. A financeirização começa a se disseminar no país na forma de títulos da dívida pública, para posteriormente, com a estabilização da moeda, se diversificar e assumir novas formas. Enquanto isso, a acumulação de capital torna-se mais lenta e deixa de acompanhar a evolução das taxas de lucro, o que aparenta ser um rompimento com o padrão operava antes de 1980. São assim, explorados, nesse trabalho, argumentos e evidências empíricas e históricas que demonstrem a relação entre o crescimento e desenvolvimento do setor financeiro, e a redução na acumulação de capital e crescimento econômico

Atravessando o oceano: a expressão do sujeito pronominal de referência definida no português europeu insular

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Microcapillary film reactor outperforms single-bore mesocapillary reactors in continuous flow chemical reactions

Meso- and micro-flow reactors are routinely used in continuous flow chemistry, however the role of capillary diameter, D, on conversion and reaction rates is often overlooked during scale-up. Volume, pressured drop and diffusion distances/times must be delicately balanced to fully realize the hydrodynamic capabilities of continuous chemical flow reactors. We carried out a comprehensive Computational Fluid Dynamics analysis experimentally validated with detailed fluid tracing, residence time distributions and continuous chemical reactions (neutralization and 4th Bourne reaction) to fully elucidate the role of D and molecular diffusion in reagents dispersion and chemical conversion. To our understanding, we captured and reported both numerically and experimentally for the first time the transition from convective, segregated flow to plug flow and dispersed flow, which we propose is linked to a dimensionless ratio between the time scales of diffusion to convection, tdiff/tconv. We tested three tubular systems: a small-bore (i.d. ~1100 µm) and large-bore (i.d. ~2400 µm) capillary reactor and a novel multiplexed (10-bore) Microcapillary Film Reactor (MFR) with mean i.d. 363 ± 32.2 µm. In the MFR's narrow microcapillaries we observed excellent radial diffusion linked to the small diffusion distance, with low dimensionless axial dispersion coefficient values (Dax/uL) ranging from 0.0015 ± 0.0005 to 0.0033 ± 0.0006 (for flow rates 0.5–5.0 mL/min), exhibiting all the desired features of a high-performance ‘plug’ flow system. Dax/uL remained mostly independent of the Reynolds number, whereas for the single, large bore capillary the Dax/uL values (0.032–0.057) increased linearly with the Reynolds numbers (19.4–48.5), shifting towards very dispersive flow. We propose splitting flow through multiple parallel microcapillaries as in the MFR is a superior strategy for scaling-up continuous flow reactions compared to increasing D, which neglects diffusive effects.</p

Metales traza (Cu, Zn, Cd y Pb) en peces juveniles de las guarderías estuáricas a lo largo de la costa portuguesa

Organic and inorganic pollution can impact organisms directly and affect condition, growth and survival of juvenile fish which use estuaries as nurseries, and thereby affect marine adult populations quantitatively and qualitatively. Trace element contamination (Cu, Zn, Cd, Pb) in juveniles of commercial fish Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax collected in putative nurseries of the main Portuguese estuaries (with diverse intensities and sources of anthropogenic pressures) was determined via atomic absorption spectrometry. Contamination was significantly different among species. Similar levels of contamination were found among estuaries, except for D. vulgaris. Cu and Zn concentrations ranged from 1.0 to 2.1 and 14 to 59 μg g-1 muscle dry weight respectively; while Cd and Pb concentrations were very low. The results indicate that juvenile migration to off-shore habitats is associated with low export of contamination, and no particular estuary increases the potential contamination of adult stocks. This knowledge is of the utmost importance in view of the ecological and economical value of these species and their use of estuarine areas as nurseries.La contaminación orgánica e inorgánica puede afectar a los organismos, a saber al estado fisiológico, crecimiento y supervivencia de los peces juveniles los cuales utilizan los estuarios como guarderías; afectando de forma cuantitativa y cualitativa a la poblaciones marinas adultas. La contaminación de elementos traza (Cu, Zn, Cd, Pb) en las formas juveniles de los peces comerciales Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris y Dicentrarchus labrax recolectados en guarderías putativas de los principales estuarios portugueses (con diversos tipos e intensidades de presiones antropogénicas) fueron determinados por espectrometría de absorción atómica. La contaminación era significativamente diferente entre especies. Sobre todo se encontraron niveles similares de contaminación entre estuarios, excepto para D. vulgaris. Las concentraciones de Cu y Zn oscilaban desde 1.0 a 2.1 y desde 14 a 59 μg g-1 peso seco muscular, respectivamente, mientras que las concentraciones de Cd y Pb eran muy bajas. Los resultados indican que la migración de los juveniles a mar abierto está asociada a la baja exportación de la contaminación y que los estuarios no amplifican particularmente el potencial de contaminación de los adultos. En vista del valor ecológico y económico de estas especies y del uso de las zonas estuáricas como guarderías, este conocimiento es de vital importancia

Trace metals (Cu, Zn, Cd and Pb) in juvenile fish from estuarine nurseries along the Portuguese coast

Organic and inorganic pollution can impact organisms directly and affect condition, growth and survival of juvenile fish which use estuaries as nurseries, and thereby affect marine adult populations quantitatively and qualitatively. Trace element contamination (Cu, Zn, Cd, Pb) in juveniles of commercial fish Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax collected in putative nurseries of the main Portuguese estuaries (with diverse intensities and sources of anthropogenic pressures) was determined via atomic absorption spectrometry. Contamination was significantly different among species. Similar levels of contamination were found among estuaries, except for D. vulgaris. Cu and Zn concentrations ranged from 1.0 to 2.1 and 14 to 59 μg g-1 muscle dry weight respectively; while Cd and Pb concentrations were very low. The results indicate that juvenile migration to off-shore habitats is associated with low export of contamination, and no particular estuary increases the potential contamination of adult stocks. This knowledge is of the utmost importance in view of the ecological and economical value of these species and their use of estuarine areas as nurseries