[pt] O presente trabalho tem por objetivo analisar e comparar sistemas de trigeração (produção simultânea de eletricidade, aquecimento e refrigeração) de diferentes arquiteturas com base nas eficiências energética e exergética e nas emissões de CO2. Sistemas de trigeração são considerados mais eficientes na conversão de energia, se comparados a sistemas convencionais, devido ao reaproveitamento do calor de rejeito do motor térmico para outros fins (aquecimento, acionamento de chiller, ou geração de eletricidade). Quatro configurações (com chiller de compressão de vapor, com chiller de absorção, com a combinação dos ciclos anteriores, e combinado com um ciclo Rankine orgânico) foram estudadas a partir de modelos matemáticos resultantes dos balanços de energia e de exergia, e do cálculo de emissão de CO2 considerando as demandas energéticas (eletricidade, aquecimento e refrigeração) como independentes do desempenho do sistema. Todas as arquiteturas de trigeração aqui analisadas apresentaram um ponto ótimo de operação, onde o calor de rejeito recuperado para aquecimento se iguala à respectiva demanda. Neste ponto, o fator de utilização de energia (indicador de desempenho pela primeira Lei) e a eficiência exergética são máximos, e a emissão de CO2, mínima. A solução das equações resultantes mostrou também que a melhor arquitetura, do ponto de vista energético, exergético ou ambiental, dependerá da combinação das demandas energéticas. / [en] The present work aims at analyzing and comparing trigeneration systems (for the simultaneous production of electricity, heating and refrigeration) of different architectures based on energetic and exergetic efficiencies and on CO2 emissions. Trigeneration systems are regarded as more efficient in energy conversion, if compared to conventional systems, due to the recovery of waste heat from the heat engine. The waste heat is used for different purposes, including heating, chiller driving or electricity generation. Four trigeneration configurations (with vapor compression chiller, absorption chiller, with a combination of the two previous cycles, or combined with an organic Rankine cycle) were studied. Mathematical models resulting from the energy and exergy balances and from the calculation of CO2 emissions were developed taking into account that the three energy demands (electricity, heating and refrigeration) are independent from the trigeneration system performance. Solution of the resulting equations indicated an optimal point of operation, for all trigeneration architectures under study, where the waste heat recovered for heating equals the heating demand. At this point, the energy utilization factor (first Law indicator) and the exergy efficiency reach their maximum value, and the CO2 emissions, its lowest. Another important finding is that the configuration with best performance, from the energetic, exergetic, or environmental point of view, will depend on how the energy demands relate to each other.

[pt] Este estudo compara o Letramento Científico dos estudantes brasileiros e japoneses, com base nos resultados do PISA e procura responder às seguintes as questões de pesquisa: a) Há diferenças de competência cognitiva em Ciências entre os alunos brasileiros e dos outros países, sobretudo os do Japão no PISA?; b) Existem itens do PISA 2006 que apresentam comportamento diferencial, tendo o Brasil como referência?; e c) É possível, a partir dos dados do PISA e da adoção complementar de uma abordagem qualitativa, identificar diferentes ênfases curriculares e/ou práticas pedagógicas no Ensino de Ciências de Brasil e Japão que contribuam para a compreensão das diferenças de desempenho entre seus estudantes? Para responder a primeira questão, comparamos os resultados do Brasil e do Japão nas edições 2006 e 2015 do PISA, em que o foco foi Ciências. O Brasil se mostra em situação de desvantagem em relação a quase todos os países que participaram do Programa, o que é em parte explicado pela repetência. Na escala de desempenho, o Brasil permanece no nível 1 e o Japão, no nível 3 em2006, passou para o nível 4 em 2015. Para responder à segunda questão, utilizamos a análise de Differential Item Functioning (DIF) nos itens da prova de Ciências de 2006 e concluímos que há grande presença de DIF nesses itens comparativamente entre o Brasil e o Japão. Apesar de não serem capazes de comprometer o processo avaliativo privilegiando um grupo em detrimento do outro, esses itens sugerem diferentes ênfases curriculares em Ciências. Levando em conta essa hipótese e para responder à terceira questão adotamos uma abordagem qualitativa, com observação do uso do tempo das aulas; registro das ênfases curriculares e da ocorrência de atividades relacionadas à interação, investigação, experimentação e aplicação na perspectiva dos alunos, professores e da observação; e entrevistas com especialistas e gestores. Os resultados mostraram que mais de 20 por cento do tempo oficial de aula observados no Brasil são desperdiçados com questões outras que não o ensino efetivo de Ciências; 10 vezes mais que no Japão. No Brasil, há ênfase curricular mais acentuada nas Ciências Naturais e Biológicas. O currículo é distribuído mais homogeneamente no Japão e é seccionado no Brasil. Segundo os estudantes japoneses, não são freqüentes as atividades de interação, investigação, experimentação e aplicação. As atividades mais recorrentes observadas e percebidas pelos professores japoneses são as de experimentação e interação; no Brasil, as de interação e aplicação. Entrevistas realizadas com especialistas em Ensino de Ciências e gestoras do PISA, no Brasil e no Japão, mostraram que o sucesso do Japão nessa avaliação é associado à existência de um currículo nacional comum e à formação continuada de professores em serviço, bem como às reformas do sistema educacional japonês suscitadas pelos resultados do PISA. O baixo desempenho dos estudantes brasileiros no PISA estaria, por sua vez, relacionado com o despreparo dos estudantes, com a falta de familiaridade destes com o teste, com a deficiente formação dos professores e com o limitado uso das evidências produzidas pelas avaliações em larga escala. / [en] This study compares the Scientific Literacy of Brazilian and Japanese students, based on the results of PISA and seeks to answer the following research questions: a) Are there differences of cognitive competence in Science among Brazilian students and those from other countries, especially Japan, in the PISA ?; B) Are there items of PISA 2006 that present differential functioning, with Brazil as a reference ?; and c) Is it possible, based on the PISA data and the complementary adoption of a qualitative approach, to identify different curricular emphases and / or pedagogical practices in Science Education in Brazil and Japan that contribute to the understanding of differences in performance among their students? To answer the first question, we compared the results of Brazil and Japan in the 2006 and 2015 editions of PISA, where the focus was Science. Brazil is disadvantaged compared to almost all the countries that participated in the Program, which is partly explained by the repetition. In the performance scale, Brazil remains at level 1 and Japan at level 3 in 2006 has moved to level 4 in 2015. In order to answer the second question, we used the Differential Item Functioning (DIF) analysis in the 2006 test s Science items and we conclude that there is a large presence of DIF in these items comparatively between Brazil and Japan. Although they are not able to compromise the evaluation process by favoring one group over the other, these items suggest different curricular emphases in Science. Taking into account this hypothesis and to answer the third question we adopted a qualitative approach, with observation of the use of class time; record of curricular emphases and the occurrence of activities related to interaction, investigation, experimentation and application from the perspective of students, teachers and observation; and interviews with experts and PISA managers. The results showed that more than 20 percent of official classroom time observed in Brazil is wasted with questions other than effective teaching of science; 10 times more than in Japan. In Brazil, there is a more pronounced curricular emphasis in Natural and Biological Sciences. The curriculum is distributed more homogeneously in Japan and is sectioned in Brazil. According to Japanese students, activities of interaction, investigation, experimentation and application are not frequent. The most recurrent activities observed and perceived by Japanese teachers are those of experimentation and interaction; In Brazil, those of interaction and application. Interviews with experts in Science Education and PISA managers in Brazil and Japan have shown that Japan s success in this assessment is associated with the existence of a common national curriculum and the teachers ongoing in-service training as well as the educational system reforms raised by the PISA results. The low performance of Brazilian students in PISA would, in turn, be related to the lack of preparation of the students, their lack of familiarity with the test, poor teacher training and the limited use of the evidence produced by the large scale evaluations.

In the present thesis, magnetization reversal in both out-of-plane and in-plane magnetized thin lms and in devices fabricated out of those lms are explored. Pt/Co/Pt stacks with ultrathin Co layer were in-estimated initially for understanding their magnetic properties in this thesis. These perpendicular magnetized systems are good candidates for magnetic hard disc drives due to their large anisotropy, which may allow miniaturization of magnetic data storage devices. The spin Hall e ect mediated current-induced magnetization reversal in patterned Pt/Co/Pt devices were extensively investigated. Investigation of the magnetization reversal by means of a current instead of a magnetic eld is necessary to explore the possibilities of solid state magnetic memory devices. This is the primary motivation behind the investigation of current-induced magnetization reversal in Pt/Co/Pt system, in this thesis. Another important proposal for magnetic data storage is the race track memory, where the domain walls separating magnetic domains (in in-plane or out-of-plane magnetized materials) are moved by using a current. This involves a great deal of understanding of the domain wall motion in Nano-conduits under applied magnetics ends, and currents and also its interaction with engineered geometrical features. In this thesis work, magnetic led-driven domain wall pinning and deepening experiments on in-plane magnetized nanowires of perm alloy were performed to un-distend this interaction and the e act of domain wall chirality. In chapter 1, a general introduction to di errant data storage technologies and the current progress in the leg of spintronic is presented. This will highlight a perspective of this thesis work with respect to the present day research in spintronic and magnetization reversal studies. In chapter 2, a basic background of magnetism using the micromag-netic framework is illustrated. A brief introduction to magnetic domain walls is also presented. The Landau-Lifshitz-Gilbert dynamical equation is discussed and some case studies applied to a single domain particle with uniaxial anisotropy under the effect of spin-orbit torque are illu trated. The basics of spin-orbit coupling leading to spin Hall e ect is also explain In chapter 3, most of the essential experimental tools along with their basic working principles are described. Extensive e orts have been in-vested in designing and building the experimental tools. These include custom designs of a sputter deposition system, an ultra-high vacuum chamber for pulsed laser ablation, a magneto-optic Kerr e ect magne-tometer, a Kerr imaging system and a magneto-transport setup. All of these experimental setups have been automated, details of which are brie y discussed in this chapter. The Kerr imaging system was designed to measure hysteresis loops, observe domain wall motion and to measure domain wall velocity under applied magnetic elds and electric current. The magneto-transport setup was used for studying the domain wall pinning and depinning experiments in permalloy nanowires. In chapter 4, the optimization process for obtaining perpendicular mag-netic anisotropy in Pt/Co/Pt lms is described. The spin reorientation transition with varying thickness of Co (from 1.5 nm down to 0.35 nm) was studied. The magnetization easy axis direction changes from in-plane to out-of-plane as the thickness of Co is reduced. The dependence of Curie temperatures of ultrathin Co lms, with thickness as low as 0.35 nm, on the underlayer Pt thickness and its crystallinity was studied in detail. The e act of Ta but err layer on the texture of the Pt lm, and on the Curie temperature of the Pt/Co/Pt system was evaluated. To gain further insight of the role of the bottom Pt/Co and the top Co/Pt interfaces, ultrathin Cu lbs were inserted at the respective interfaces, and the anisotropy and magnetization reversal behaviour of these lbs were investigated. In chapter 5, studies on current-induced magnetization reversal in mi-corn sized wires of Pt/Co/Pt trilete is presented. The spin Hall e act assisted spin-orbit torque was used to reversibly switch the magnetization of these devices with and without the help of an external magnetic led. Since both the top and bottom layers are Pt, any contribution from Rashia e act towards spin-orbit torque could be ignored. By preparing devices with unequal top and bottom Pt thicknesses, a net spin-orbit torque could be applied to the magnetization of the Co layer. The thickness gradient/induced anisotropy in the Co layer was utilized to experimentally investigate current-induced deterministic switching. Sin-gel domain simulations with spin-orbit torque were also carried out to understand the mechanism of deterministic switching of magnetization in Pt/Co/Pt devices. This study is expected to have made sign cant contributions and to open up the possibilities of further investigation in the studies of spin-orbit torque in Pt/Co/Pt systems for solid state magnetic memory devices. In chapter 6, magnetic led-induced reversal in systems with in-plane magnetic anisotropy is presented. Here the e act of the width of a Nanos-trip on the anisotropy of a soft magnetic material like perm alloy was in-estimated. By introducing a nucleation pad to one end of the perm alloy nanowire, a single domain wall was generated at the junction with apple-cation of a proper magnetic led sequence. This domain wall could be in-jested into the nanowire by a magnetic led and pinned at a geometrical constriction inside the nanowire. The statistics of domain wall pinning and deepening processes indicated two di errant types of domain walls involved in the reversal process. With the assistance of micro magnetic simulations the domain walls were ident end as vortex walls of di errant chirality’s. Thus the interaction of domain walls with a Nano constriction and its dependence on the chirality of domain walls are understood. In chapter 7, a brief summary of the results obtained during the course of investigations is presented. An outlook presented at the end will help the readers of this thesis to understand the important research problems in this area and their potential future aspects.