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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
271

ComparaÃÃo de metodologias para determinaÃÃo da partiÃÃo geoquÃmica de metais-traÃo em sedimentos da plataforma continental do Cearà / Comparison of methodologies for determining the geochemical partitioning of trace-metals in sediment of the continental shelf of CearÃ

Josà Edvar Aguiar 04 June 2007 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A comparaÃÃo de metodologias de digestÃo total e parcial da fraÃÃo granulomÃtrica (<1mm) de sedimentos da plataforma continental do Cearà foi realizada para verificaÃÃo desses procedimentos sobre a interpretaÃÃo da partiÃÃo geoquÃmica dos metais no ambiente sedimentar. A determinaÃÃo final dos teores dos metais Al, Cu, Fe, Mn, Ni, Pb, V , Ti , Ba, Cr e Zn foi obtida por espectrofotometria de absorÃÃo atÃmica de chama. A anÃlise estatÃstica multivariada (Cluster Analysis) evidenciou dois grupos de suporte geoquÃmico determinantes das deposiÃÃes sedimentares. No primeiro grupo distinguiram-se metais de origem predominantemente continental Al, Fe, Mn, Cr, e Zn enquanto os elementos do segundo grupo foram Ãqueles associados à deposiÃÃo carbonÃtica marinha Ni, Pb, Ba, Cu e matÃria orgÃnica. Embora os valores absolutos sejam distintos entre as medidas realizadas apÃs os dois mÃtodos de digestÃo, nÃo houve distinÃÃo da caracterizaÃÃo geoquÃmica observada para os metais em sedimentos determinada a partir dos resultados obtidos pelos diferentes mÃtodos de digestÃo. Este resultado mostrou que a digestÃo parcial com Ãgua-rÃgia a 50% alÃm de diminuir o tempo de anÃlise, a descarga de efluente laboratorial perigoso, altamente reativo e Ãcido, permite igualmente à digestÃo total, a determinaÃÃo da caracterizaÃÃo geoquÃmica de metais em sedimentos marinhos predominantemente carbonÃticos. AlÃm disso a avaliaÃÃo do uso do (Al e Ti) como normalizadores das concentraÃÃes de metais em sedimentos costeiros foi avaliado em Ãrea vizinha e observado que a fonte continental e/ou antrÃpica (atividade portuÃria) foi distinguida em dois grupos. / A comparison of methods for total and partial digestion of the size fraction (<1mm) of sediments of the continental shelf of Cearà was performed to check these procedures on the interpretation of the partition geochemistry of metals in the sediment environment. The final determination of the levels of the metals Al, Cu, Fe, Mn, Ni, Pb, V, Ti, Ba, Cr and Zn was obtained by atomic absorption spectrophotometry in flame. A multivariate statistical analysis (cluster analysis) showed two groups of supporting geochemical determinants of sedimentary deposition. In the first group is distinguished predominantly continental origin of metals Al, Fe, Mn, Cr, and Zn as the elements of the second group were those associated with marine deposition carbonatic Ni, Pb, Ba, Cu and organic matter. Although the absolute values are different between measurements taken after the two methods of digestion, there was no distinction of Geochemical characterization observed for metals in sediment determined from the results obtained by different methods of digestion. This result showed that the partial digestion with aqua regia and 50% lower than the time of analysis, the discharge of effluent laboratory dangerous, highly reactive, acid, also allows for total digestion, the determination of the geochemical characterization of metals in marine sediments predominantly carbonates. In addition to evaluating the use of (Al and Ti) and standardized concentrations of metals in coastal sediments was evaluated in an area nearby and found that the continental source and / or anthropogenic (port activity) was distinguished into two groups.
272

Abordagens metodológicas que favorecem a construção da autonomia intelectual do estudante: o trabalho com simulação das Nações Unidas na escola

Godinho, Jones 28 December 2015 (has links)
Submitted by Inês Marinho (bele_ballet@hotmail.com) on 2016-06-17T14:06:05Z No. of bitstreams: 1 Dissertação - Jones Godinho.pdf: 5535166 bytes, checksum: 413eeb7d0035d0f96e7614c5fe8f8b19 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-06-23T20:38:02Z (GMT) No. of bitstreams: 1 Dissertação - Jones Godinho.pdf: 5535166 bytes, checksum: 413eeb7d0035d0f96e7614c5fe8f8b19 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-06-23T20:41:19Z (GMT) No. of bitstreams: 1 Dissertação - Jones Godinho.pdf: 5535166 bytes, checksum: 413eeb7d0035d0f96e7614c5fe8f8b19 (MD5) / Made available in DSpace on 2016-06-23T20:41:19Z (GMT). No. of bitstreams: 1 Dissertação - Jones Godinho.pdf: 5535166 bytes, checksum: 413eeb7d0035d0f96e7614c5fe8f8b19 (MD5) Previous issue date: 2015-12-28 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / "Methodological approaches that favor the construction of the student's intellectual autonomy: working with simulation of the United Nations in school" brings the analysis of an experiment on active methodologies, specifically with a United Nations simulation model (UN), developed in the context school with high school students in a private school in the city of Manaus/AM. Therefore, discusses about the teacher's role in shaping the student, the challenges of teaching, combining professional autonomy with intellectual autonomy, a move that highlights the teacher's possibilities of action with regard to planning their lessons, to bureaucratic tasks required, as well as the loss of autonomy in major decisions from the perspective of school organization and curriculum, and the implications arising therefrom to the quality of their work and, in particular, to student learning. Therefore, argues methodological approaches that favor the construction of the student's intellectual autonomy, through active methods of teaching and learning, in particular, work with educational projects guided by the problem-based learning and case study, and, as an example, the simulation UN. Besides questioning the obstacles and difficulties encountered in school about the teaching and learning process, points to what is substantive in teaching, inviting teachers not to be a mere executor function of tasks, but the architect of teaching process learning. In addition to literature review on the methodological approaches that favor the construction of autonomy of students, from a ethnomethod, it conducted a case study, involving monitoring and participant observation of the UN simulation activity, interviews with students and teachers, and the analysis of documents produced by the students. However, we identify with our work, the routinization and the consequent bureaucratisation of teaching become barriers to more effective teaching practices, and it makes hard the construction of student autonomy and teacher himself. However, despite this situation, it was noted that the use of active methods of teaching and learning in school, brought, students, more dynamism and enthusiasm, dialogue, cooperation and responsibility towards the construction of knowledge, and stimulate student to look/walk on their own, in an autonomous exercise, contributing to the understanding of the construction of autonomy, uniting intellectual training to the process of continuous appropriation of knowledge and practices. / "Abordagens metodológicas que favorecem a construção da autonomia intelectual do estudante: o trabalho com simulação das Nações Unidas na escola” traz a análise de uma experiência com metodologias ativas, mais especificamente com um modelo de simulação das Nações Unidas (ONU), desenvolvido no contexto escolar com alunos do Ensino Médio, em uma escola particular na cidade de Manaus/AM. Neste sentido, aborda sobre o papel do professor na formação do estudante, frente aos desafios da docência, articulando autonomia profissional com autonomia intelectual, num movimento que põe em relevo as possibilidades de atuação do professor no tocante ao planejamento de suas aulas, às tarefas burocráticas exigidas, bem como à perda de autonomia nas grandes decisões do ponto de vista da organização escolar e do currículo, e as implicações daí decorrentes à qualidade de seu trabalho e, de modo especial, à aprendizagem do aluno. Discute, pois, as abordagens metodológicas que favorecem a construção da autonomia intelectual do estudante, por meio de metodologias ativas de ensino-aprendizagem, em especial, o trabalho com projetos de ensino pautados na aprendizagem baseada em problemas e no estudo de caso, tendo, como exemplo, a simulação das Nações Unidas. Além de questionar os entraves e as dificuldades encontradas na escola sobre o processo de ensino e aprendizado, aponta para o que há de substantivo no trabalho docente, convidando o professor a desinstalar-se da função de mero executor de tarefas à artífice do processo ensino/aprendizagem. Além de análise bibliográfica sobre as abordagens metodológicas que favorecem a construção da autonomia dos alunos, partindo de um etnométodo, foi realizado um estudo de caso, envolvendo o acompanhamento e a observação participante da atividade de simulação da ONU, entrevistas com alunos e professores, e a análise de documentos produzidos pelos estudantes. Nesse sentido, identificamos com nosso trabalho que, a rotinização e a consequente burocratização do trabalho docente tornam-se entraves a práticas pedagógicas mais eficazes, além de dificultar a construção da autonomia do estudante e do próprio professor. No entanto, mesmo diante deste quadro, percebeu-se que a utilização de metodologias ativas de ensino-aprendizagem na escola, trouxe, aos alunos, mais dinamismo e entusiasmo, diálogo, cooperação e responsabilidade frente à construção do seu conhecimento, além de estimular o estudante a buscar/andar por conta própria, num exercício autônomo, contribuindo para a compreensão sobre a construção da autonomia, unindo formação intelectual ao processo de apropriação contínua de saberes e práticas.
273

Divisibilidade e congruências: aplicações no ensino fundamental II / Divisibility and congruences: applications in elementary education II

Franco, Tânia Regina Rodrigues 30 March 2016 (has links)
Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2016-06-02T19:33:53Z No. of bitstreams: 2 Dissertação - Tânia Regina Rodrigues Franco - 2016.pdf: 2643450 bytes, checksum: c01355ce5ba1fb2524facde3704a3d8e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-06-03T12:44:18Z (GMT) No. of bitstreams: 2 Dissertação - Tânia Regina Rodrigues Franco - 2016.pdf: 2643450 bytes, checksum: c01355ce5ba1fb2524facde3704a3d8e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-06-03T12:44:18Z (GMT). No. of bitstreams: 2 Dissertação - Tânia Regina Rodrigues Franco - 2016.pdf: 2643450 bytes, checksum: c01355ce5ba1fb2524facde3704a3d8e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2016-03-30 / This essay begins with a theoretical foundation about the positional system, divisibility, Euclidean division, maximum common divisor, prime numbers and modular congruence. Through the concepts discussed, we show some applications, for elementary school students. The main main points of the theory and bring notions of applicability of arithmetic in daily situations. We will work solving Diophantine linear equations; we will determine some criteria of divisibility; by the relationship of modular congruence and arithmetic of the rest; even with modular congruence we will propose activities with codes and other existing numbers in our country, ending solving problem on calendars. These applications will serve of tools and methodologies of contextualized form, the teachers, will motivate their students to understand a little more about the concept of Modular Arithmetic, easy, fast and simple way. / Esta dissertação, inicia-se com uma fundamentação teórica acerca do sistema posicional, divisibilidade, divisão euclidiana, máximo divisor comum, números primos e congruência modular. Através dos conceitos abordados, apresentaremos algumas aplicações, para alunos do ensino fundamental. O principal objetivo é apresentar os principais pontos da teoria e trazer noções da aplicabilidade da aritmética em situações cotidianas. Trabalharemos a resolução de Equações Diofantinas Lineares; determinaremos alguns critérios de divisibilidade, através da relação de congruência modular e aritmética dos restos; ainda com congruência modular proporemos atividades com códigos e outras numerações existentes em nosso país, nalizando com a resolução de problemas sobre calendários. Essas aplicações servirão de ferramentas e metodologias para que de forma contextualizada, o professor, motive seu aluno a entender um pouco mais sobre o conceito de Aritmética Modular, de maneira fácil, rápida e simples.
274

A avaliação da aprendizagem em uma escola de pedagogia Waldorf: singularidades e semelhanças / The evaluation of learning in a Waldorf school of pedagogy: singularities and similarities

Matos, Renata da Silva 27 October 2017 (has links)
Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-11-16T13:19:09Z No. of bitstreams: 2 Dissertação - Renata da Silva Matos - 2017.pdf: 1395951 bytes, checksum: d2db5cdb5ba16cc33d846f9143f0f13a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-11-16T13:19:43Z (GMT) No. of bitstreams: 2 Dissertação - Renata da Silva Matos - 2017.pdf: 1395951 bytes, checksum: d2db5cdb5ba16cc33d846f9143f0f13a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-11-16T13:19:43Z (GMT). No. of bitstreams: 2 Dissertação - Renata da Silva Matos - 2017.pdf: 1395951 bytes, checksum: d2db5cdb5ba16cc33d846f9143f0f13a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-10-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This research is a qualitative research, with elements of the case study, which seeks to find, in the school practices of the Waldorf pedagogy, actions related to the evaluation, in order to analyze them and discuss them according to the main theories of the evaluation of the learning. To this end, we sought to follow the work carried out at a Waldorf pedagogy school in the city of Goiânia, Goiás. As instruments used to collect data related to this research, we present the documentary analysis that deals with documents related to the pedagogical practices of the school, the direct observation of a Waldorf classroom in his daily life, and the semi-structured interview with a Waldorf teacher. In this way, we seek to emerge the necessary elements to discuss the evaluative practices of a school that relies on the Waldorf Pedagogy, regarding the didactic-methodological aspects of this proposal. / Esta pesquisa trata-se de uma pesquisa qualitativa, com elementos do estudo de caso, que busca encontrar, nas práticas escolares da pedagogia Waldorf, ações relativas à avaliação, a fim de analisá-las e discuti-las segundo as principais teorias da avaliação da aprendizagem. Para isso, buscamos acompanhar o trabalho realizado em uma escola de pedagogia Waldorf, na cidade de Goiânia, Goiás. Como instrumentos utilizados para a coleta dos dados referentes a esta pesquisa, apresentamos a análise documental que trata de documentos relativos às práticas pedagógicas da escola, a observação direta de uma sala de aula Waldorf, em seu dia a dia, e a entrevista semiestruturada realizada com uma professora Waldorf. Buscamos, desse modo, fazer emergir os elementos necessários para discutir as práticas avaliativas de uma escola que se apoia na Pedagogia Waldorf, no que diz respeito aos aspectos didáticometodológicos dessa proposta.
275

Estudo comparativo entre dois modelos geomorfológicos aplicados na Serra da Cantareira: bacia do Córrego do Bispo / Comparative study between two geomorphologic models applied in Serra da Cantareira: basin of córrego do bispo

Eric Macedo Massa 17 April 2008 (has links)
Através de uma abordagem analítica entre dois modelos geomorfológicos elaborados por ROSS (1994) e pelo INPE (CREPANI et. al, 1996), foi estabelecida uma comparação entre variáveis relacionadas a aspectos capitais de ambos - critérios utilizados para a definição das unidades de paisagem e importância da variável relevo e um aspecto relacionado à aplicabilidade a adequação aos ambientes urbanos. Por apresentar uma diversidade de usos e ocorrência de áreas urbanas e preservadas, a bacia do córrego do Bispo, localizada na zona norte do município de São Paulo, foi escolhida como área teste. Estes modelos apresentaram boa aplicabilidade em ambientes preservados, destacando-se o modelo de Ross, que é mais eficaz em termos de previsibilidade. Em relação às áreas urbanas os modelos apresentaram resultados semelhantes, na medida em que diagnosticam fragilidades ambientais para áreas de ocupação não consolidadas e apresentam limitações em relação às áreas de ocupação consolidadas. Objetivando ainda uma contribuição ao modelo de Ross em nível experimental, incorporou-se a classificação de vertentes de RUEH (1975) baseada na geometria destas, à variável relevo do primeiro. Como resultado, foram obtidas diferenças significativas para algumas áreas em relação ao modelo originalmente proposto por Ross. / An analytical approach between two geomorfphologic models elaborated by ROSS (1994) and INPE (CREPANI et. al, 1996), a comparison was estabilished between two variables related to capital aspects of both the criteria for the definition of landscape units, the importance of variable relief and its appliance to urban environments. For presenting a huge diversity of land uses and preserved urban areas, Córrego do Bispo basin located in north zone of São Paulo has been chosen as an experimental area. These models have shown a good applicability in preserved environmental, emphasizing specially Ross model, which is more useful in terms of predictability. Both models presented similar results in urban areas, while they make diagnostics of environmental fragilities to areas of non-consolidated occupation and presented restrictions about consolidated occupation areas. Also intending to contribute to Ross model in an experimental level, the slope classification of RUEH (1975) was included, based in its geometry to variable relief of Ross model. As a result, meaningful differences were obtained for some areas in relation to the model originally proposed by Ross.
276

Análise da fragilidade ambiental relevo-solo com aplicação de três modelos alternativos nas altas aacias do Rio Jaguari-Mirim, Ribeirão do Quartel e Ribeirão da Prata. / Environmental fragility analysis using three methodological models at the high basins of rivers Jaguari-Mirim, do Quartel and da Prata.

Christiane Spörl 14 August 2001 (has links)
Este trabalho apresenta uma comparação de três modelos metodológicos aplicados aos estudos da Fragilidade Ambiental. A aplicação destes modelos resultou na confecção de três mapeamentos diferenciados de Fragilidade, os quais foram analisados e comparados entre si. Dos três modelos metodológicos aplicados, dois foram propostos por ROSS (1994), um com apoio nos Índices de Dissecação do Relevo, e o outro nas Classes de Declividade. O terceiro modelo foi proposto por CREPANI et ali (1996) baseado nas Unidades Territoriais Básicas - UTB's. Os três modelos de análise da Fragilidade ambiental propostos partem do mesmo princípio: as Unidades Ecodinâmicas preconizadas por TRICART (1977) para delimitar áreas no contexto dos diagnósticos ambientais. As áreas são caracterizadas por diversos atributos: rochas, relevo, solo, cobertura vegetal/ uso da terra e pluviosidade. No entanto, estes modelos apresentam diferenças na operacionalização dos métodos, e também, nas variáveis analisadas. Destas divergências resultam três mapeamentos diferenciados. Apesar dos diferentes resultados apresentados pelos três modelos de análise da Fragilidade, seus objetivos são os mesmos, servir como subsídio ao planejamento estratégico ambiental. Os mapeamentos das Fragilidades Ambientais identificam e analisam os ambientes em função de seus diferentes níveis de fragilidade. Através destes documentos torna-se possível apontar as áreas onde os graus de fragilidade são mais baixos favorecendo, então, determinados tipos de inserção; e áreas mais frágeis onde são necessárias ações tecnicamente mais adequadas a essas condições. / This work presents a comparison between three methodological models which were applied to Environmental Fragility studies. The application of these models resulted in three different Environmental Fragility maps, which were analyzed e compared with each other. Of the three methodological methods used, two were proposed by ROSS (1994), one of them based on the Relief’s Dissection Index and the other on the Slope Classes. The third model was proposed by the INPE (1996), based on the Basic Territorial Units – BTU's. The three models come from the same principle: The Ecodynamics Units, defended by TRICART (1977) to classify areas regard to its environmental diagnosis. The areas characterized by several information: rocks, topography, soil, vegetation/ use of the soil and pluviosity. However, these models present differences in the operationalization of the methods, and also in the variables analyzed. These divergences results three different mappings. Although the different results presented by the three models, its purposes are the same: to gather information to the Environmental Strategic Planning. The environmental Fragility mappings identify and analyze the areas according to its different fragility levels. Through these documents it´s possible to point out the lowest fragility rated areas, favoring then certain types of insertion; and the most fragile areas, where more adequate technical actions are required.
277

Adopting Free/Libre/Open Source Software Practices, Techniques and Methods for Industrial Use

Garrigós, Janina, Minoves, Pau January 2009 (has links)
Today’s software companies face the challenges of highly distributed development projects and constant changing requirements. To be competitive, the software time to market has to be reduced as much as possible while keeping the expected quality. Development methodologies try to address this challenges by introducing new practices, techniques and methods for communication, requirements management, quality assurance, etc. This thesis proposes the adoption of relevant Free/Libre/Open Source Software practices to improve industrial developments. Many FLOSS projects have proven very successful, producing high quality products with steady frequent releases. The selection of the FLOSS best practices that would benefit industrial developments, and its adaptation for a corporate environment is the aim of this study. To achieve this goal, a framework to compare FLOSS and industrial development methodologies has been created and executed. Three successful FLOSS projects where selected as study targets, as well as two Ericsson’s projects. The framework served to identify FLOSS methodology strengths and compare them with the Ericsson projects. Analysing the significant differences resulting from this comparison, FLOSS best practices were tailored to fit industrial development environments. The final results of the thesis are six adoption opportunities that aim to improve software quality and overall development productivity while increasing practitioners’ motivation and commitment.
278

The Process of Metathinking in the Area of Information Systems Design

Nero, Eva January 2000 (has links)
In the area of information systems design it is important to select an appropriate methodology in order to get an information system that functions as expected. The perspective behind the methodology is seldom stated explicitly. The epistemology that a methodology is based on has impacts on the design of the system. Therefore, the process of selecting an appropriate methodology is important. The aim of this work is to study how the process of metamodelling or metathinking is considered in the area of information systems design. Interviews and a study of the literature have been performed in order to investigate the awareness of metamodelling thinking in the area of information systems design.In the literature we found that only a small part dealt with the process of metamodelling. The method engineering (ME) approach was found as a way of thinking that seems to consider metamodelling thinking. We have evaluated ME according to a synthesis of the works by van Gigch, Churchman, and Flood and Carson. The evaluation has shown that ME deals with metamodelling thinking. In order to improve the metamodelling thinking in ME, it is important to explicitly define how ME considers the aspect of participation of motivated actors and the iterative process. The interviews have shown that information systems designers use some kind of metamodelling thinking, but they do not seem to be aware of the process. In an information system design process, it is important to shift perspectives from reality to modelling, and to the metamodelling level, in order to apply metamodelling thinking. Further work should be performed with the purpose of making the information systems designers aware of the importance of applying metamodelling thinking.
279

Oppression, Manifesting from a Government Mission of Positive Social Change

Ramstad, David P. 01 January 2016 (has links)
Government social interventions hold considerable power over what choices and opportunities impoverished households have available to escape the oppressive socioeconomic trappings of poverty. The U.S. Internal Revenue Service's Low Income Housing Tax Credit (LIHTC) is one such program. While there are many positive mission statements of social governance, this study focused on the regressive potential for oppressive institutional policies and practices. Theoretical frameworks guiding the study were Pierce's 1979 model of oppression and Crenshaw's 1989 intersectionality theory. The quantitative design's hypothesis and research question focused on whether significant relationships exist between LIHTC project placement and highest concentrations of six commonly recognized socioeconomically oppressive conditions, each separately defined by U.S. Census demographics and American Housing Survey (AHS) structured-interview data. Mann-Whitney U tests showed non-significant differences between the two source dataset's separate identification of socioeconomically oppressive conditions across Minnesota's Twin City metropolitan area. Spearman's rho and Cohen's standard show similarly significant results from both pairings of AHS and Census data with the LIHTC project database. Results support conclusions that LIHTC project placement most often maintains external socioeconomic oppressors in the lives of program residents. Implications for positive social change hinge on the realization that social interventions may not be entirely anti-oppressive. In such cases, these conclusions should lead policymakers to change or replace programs so that interventions are not an accessory to the subjugation of service users to oppressive circumstances.
280

Desenvolvimento computacional de um teste mecânico para caracterização do material através de análise inversa / Computational design of a technological mechanical test for material characterization by inverse analysis / Conception d’un essai mécanique pour la caractérisation du comportement d’un matériau par analyse inverse

Souto, Nelson 09 October 2015 (has links)
Grâce au développement des méthodes de mesure de champs, de nouvelles stratégies d’identification de paramètres matériau de lois de comportement mécanique sont proposées, fondées sur l’utilisation d’essais mécaniques hétérogènes. Les champs de déformation hétérogènes développés au cours de ces essais permettent une meilleure caractérisation du comportement mécanique des tôles métalliques et, par conséquent, de réduire considérablement le nombre d’essais nécessaires pour identifier les paramètres matériau de modèles phénoménologiques complexes. Mais comment concevoir ces essais? Dans ce travail, une méthodologie d’optimisation pour le développement d’essais mécaniques hétérogènes est présentée. L’objectif principal est la conception, par analyse inverse et en proposant un indicateur représentatif des états de déformation, d’un essai capable de caractériser le comportement mécanique des tôles métalliques pour plusieurs états de contrainte et déformation. Pour cela, cette étude a été réalisée en considérant un matériau virtuel (acier doux sous forme de tôle mince), obtenu à partir de données expérimentales. En outre, un indicateur qui caractérise les essais mécaniques a été proposé pour être utilisé dans la méthodologie d’optimisation. D’un côté, le comportement mécanique de l’acier doux a été représenté avec un modèle phénoménologique complexe composé du critère anisotrope de plasticité Yld2004-18p, combiné à une loi d’écrouissage mixte et un critère macroscopique de rupture. Pour cette loi de comportement, un procédé d’identification des paramètres du matériau a été développé et le jeu de paramètres identifiés a été validé en comparant des résultats expérimentaux et numériques de l’emboutissage d’un godet cylindrique. D’un autre côté, un indicateur quantitatif pour évaluer l’information du champ de déformation des essais mécaniques a été formulé et sa pertinence a été évaluée à travers l’analyse numérique d’essais classiques et hétérogènes de la littérature. Concernant la méthodologie d’optimisation, deux approches différentes ont été considérées pour la conception de l’essai mécanique hétérogène. La première approche est fondée sur une procédure en une seule étape, où l’optimisation de la forme de l’éprouvette et des conditions aux limites, imposées par un outil, a été effectuée. La seconde approche est fondée sur une technique incrémentale en plusieurs étapes, en optimisant la forme de l’éprouvette et le chemin de déformation, par l’application des déplacements locaux. Les résultats obtenus sont comparés et un essai est retenu pour identifier les paramètres matériau, en utilisant le matériau virtuel comme référence, afin d’illustrer la pertinence de la démarche / With the development of full-field measurements methods, recent material parameters identification strategies call upon the use of heterogeneous tests. The inhomogeneous strain fields developed during these tests lead to a more complete mechanical characterization of the sheet metals, allowing the substantial reduction of the number of tests in the experimental database needed for material parameters identification purposes. In the present work, an innovative design optimization process for the development of heterogeneous tests is presented. The main goal is the design of a mechanical test able to characterize the material behavior of thin metallic sheets under several stress and strain paths and amplitudes. To achieve this aim, the study was carried out with a virtual material, though derived from experimental data. An indicator of the mechanical interest of the test was proposed, and was used in an optimization procedure to design both the boundary conditions and the sample shape. On the one hand, the virtual behavior of a mild steel was characterized using a complex phenomenological model composed by the Yld2004-18p anisotropic yield criterion combined with a mixed isotropic-kinematic hardening law and a macroscopic rupture criterion. An efficient material parameters identification process based on finite element model updating type was implemented and the identified parameters set was validated by performing a deep drawing test leading either to full drawing or rupture of the blank. On the other hand, an indicator which rates the strain field of the experiment by quantifying the mechanical information of the test was formulated. The relevance of the indicator was stressed out by the numerical analysis of already known classical as well as heterogeneous tests and the results obtained were validated by a material parameter sensitivity study. Two different optimization approaches were used for designing the heterogeneous test, namely (i) a one-step procedure designing both specimen shape and loading path by using a tool and (ii) a sequential incremental technique designing the specimen shape and the loading path of the specimen considering local displacements. The results obtained revealed that the optimization approach proposed was very promising for designing a single experiment able to fully characterize the several strain paths and amplitudes encountered in sheet metal forming processes.

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