Rendimento de painéis solar térmicos poliméricos unglazed e glazed

Mestrado em Engenharia Físicaas energias renováveis representam uma solução limpa para a diminuição da dependência da nossa sociedade nos combustíveis fósseis. Recentemente verificou-se um aumento na procura de combustíveis fósseis em todo mundo, levando a um acentuado aumento no seu preço. Considerando que uma fracção considerável do nosso consumo energético é usado para aquecimento de água, a conversão solar térmica torna-se um tema de elevado interesse. Actualmente, existem vários sistemas solares térmicos para aquecimento de água com eficiências e tempos de recuperação de investimento razoáveis. Aqueles que usam absorsores poliméricos, apresentam ser uma solução economicamente eficiente para aplicações de aquecimento de água a baixa temperatura. Neste trabalho apresentam-se os resultados da análise do desempenho de um painel comercial solar térmico polimérico sem cobertura, unglazed, usado primariamente para o aquecimento de piscinas, que usa como absorsor tiras de epdm (ethylene propylene diene monomer). Este polímero tem boas propriedades mecânicas e boa resistência aos UV. O objectivo principal deste trabalho é comparar a eficiência e as alterações físicas no colector quando é introduzida uma cobertura transparente e estruturada de PC (policarbonato), transformando-o num painel solar térmico glazed. ABSTRACT: renewable energies represent a clean solution to decrease the dependence of our societies on fossil fuels. In recent times we have witnessed an increase in the demand for fossil fuels worldwide, leading to ever increasing prices. Considering that a considerable fraction of our energy consumption goes to water heating applications, solar thermal conversion becomes a relevant approach. Presently, several solar water heating systems with reasonable efficiencies and with acceptable payback times are available. Those using polymeric solar absorbers can be an economical and efficient solution for low temperature water heating applications. This work presents the results of the performance analysis of an unglazed commercial polymeric solar thermal collector, primarily used for swimming pool heating, made from epdm (ethylene propylene diene monomer). This polymer shows good mechanical properties and good UV resistance. The main goal of this work is to compare the efficiency and the changes on material physical properties when this unglazed collector is covered with a transparent PC (polycarbonate) structured sheet, transforming it into a glazed solar thermal collector

Implementing Inflation Targeting in Brazil

Brazil has put in place an inflation-targeting framework for monetary policy in mid-1999, less than six months after moving to a floating exchange rate system. This paper presents the macroeconomic background that has led to the shift in monetary policy regime, and describes the general institutional arrangements and operational framework that has been adopted. The paper also discusses the basic modeling approach that has aided the decision-making process in the initial phase of inflation targeting in Brazil. We describe the family of small-scale macroeconomic models that has been used for informing and disciplining discussions about monetary policy within the Central Bank. These models contain few equations and few variables, but carry a considerable theoretical content and provide a stylized representation of the monetary policy transmission mechanism. They are easily understood, and especially suitable for simulation of a wide range of issues. We conclude with the main lessons that may be drawn from the initial Brazilian experience with inflation targeting.

Can ultrastrong coupling change ground state chemical reactions?

Recent advancements on the fabrication of organic micro- and nanostructures have permitted the strong collective light-matter coupling regime to be reached with molecular materials. Pioneering works in this direction have shown the effects of this regime in the excited state reactivity of molecular systems and at the same time has opened up the question of whether it is possible to introduce any modifications in the electronic ground energy landscape which could affect chemical thermodynamics and/or kinetics. In this work, we use a model system of many molecules coupled to a surface-plasmon field to gain insight on the key parameters which govern the modifications of the ground-state Potential Energy Surface (PES). Our findings confirm that the energetic changes per molecule are determined by single-molecule-light couplings which are essentially local, in contrast with those of the electronically excited states, for which energetic corrections are of a collective nature. Still, we reveal some intriguing quantum-coherent effects associated with pathways of concerted reactions, where two or more molecules undergo reactions simultaneously, and which can be of relevance in low-barrier reactions. Finally, we also explore modifications to nonadiabatic dynamics and conclude that, for this particular model, the presence of a large number of dark states yields negligible changes. Our study reveals new possibilities as well as limitations for the emerging field of polariton chemistry

Theory for Nonlinear Spectroscopy of Vibrational Polaritons

Molecular polaritons have gained considerable attention due to their potential to control nanoscale molecular processes by harnessing electromagnetic coherence. Although recent experiments with liquid-phase vibrational polaritons have shown great promise for exploiting these effects, significant challenges remain in interpreting their spectroscopic signatures. In this letter, we develop a quantum-mechanical theory of pump-probe spectroscopy for this class of polaritons based on the quantum Langevin equations and the input-output theory. Comparison with recent experimental data shows good agreement upon consideration of the various vibrational anharmonicities that modulate the signals. Finally, a simple and intuitive interpretation of the data based on an effective mode-coupling theory is provided. Our work provides a solid theoretical framework to elucidate nonlinear optical properties of molecular polaritons as well as to analyze further multidimensional spectroscopy experiments on these systems

Dimensionamento de lajes aligeiradas betonadas "in situ"

A conjuntura económica da construção não se encontra numa fase de prosperidade, existindo a necessidade de criar soluções construtivas que permitam a redução de custos dos materiais a nível de obra. As lajes de betão armado, devido à sua grande área de implantação, possuem uma parcela importante no orçamento final de qualquer obra de edifícios correntes. Sabendo das possibilidades de aligeiramento de lajes, torna-se necessária a realização de um estudo pormenorizado e comparativo entre soluções de aligeiramento. O desenvolvimento deste relatório reflete todo o trabalho efetuado durante a realização de um estágio curricular desenvolvido na empresa FercaNorte – Estruturas, Lajes e Cofragens, Lda. e foca-se num dimensionamento e estudo comparativo de soluções de lajes fungiformes aligeiradas, aplicadas a dois casos de estudo e também num dimensionamento e estudo comparativo de soluções de lajes aligeiradas unidirecionais mas apenas aplicadas a um caso de estudo. No primeiro caso de estudo, laje fungiforme com um vão de 6 metros nas duas direções, são dimensionadas e comparadas quatro soluções: laje fungiforme maciça; laje fungiforme aligeirada com blocos elipsoides perdidos dispostos de forma ortogonal e envolvidos totalmente por betão; laje fungiforme aligeirada com blocos elipsoides perdidos dispostos em formato de favo de mel e envolvidos totalmente por betão; e laje fungiforme nervurada com moldes recuperáveis. No segundo caso de estudo, laje fungiforme com um vão de 7,04 metros nas duas direções, são dimensionadas e comparadas cinco soluções: laje fungiforme maciça, laje fungiforme aligeirada com blocos cúbicos perdidos dispostos de forma ortogonal e envolvidos totalmente por betão; laje fungiforme aligeirada, com blocos elipsoides perdidos dispostos de forma ortogonal e envolvidos totalmente por betão; laje fungiforme aligeirada com blocos elipsoides perdidos dispostos em formato de favo de mel e envolvidos totalmente por betão; e laje fungiforme nervurada com moldes recuperáveis. No terceiro caso de estudo, laje unidirecional com um vão de 8 metros apoiada em vigas com vão de 5 metros, são dimensionadas e comparadas três soluções: laje maciça; laje aligeirada com perfis tubulares com secção transversal reta oval; e laje nervurada com moldes recuperáveis. No final é apresentada uma estimativa orçamental para cada solução analisada nos três casos de estudo abordados.The economic environment of the building is not in a phase of prosperity, there is a need to create constructive solutions to the reduction of material costs in terms of work. The slabs of reinforced concrete, because of its large deployment area have an important part in the final budget of any work of current buildings. Knowing the possibilities of removing concrete in slabs, it is necessary to carry out a detailed and comparative study between the possible solutions. The development of this report reflects all the work done during the course of a traineeship developed in “FercaNorte – Estruturas, Lajes e Cofragens, Lda.” and focuses on a design and comparative study of voided flat slabs solutions, applied to two cases of study and also a dimensioning and comparative study of one-way hollow slab solutions but only applied to a case study. In the first case study, flat slab with a span equal in both directions of six meters, are sized and compared four solutions: Solid flat slab; voided flat slab with lost ellipsoids blocks arranged in orthogonal way and fully involved in concrete; voided flat slab with lost ellipsoids blocks arranged in a honeycomb shape and fully involved in concrete; and waffle slab with recoverable molds. In the second case study, flat slab with a span equal in both directions of 7.04 meters, are sized and compared five solutions: Solid flat slab, voided flat slab with lost cubic blocks arranged in orthogonal way and fully involved in concrete; voided flat slab, with lost ellipsoids blocks arranged in orthogonal way and fully involved in concrete; voided flat slab with lost ellipsoids blocks arranged in a honeycomb shape and fully involved in concrete; and waffle slab with recoverable molds. In the third case study, one-way slab with a span of 8 meters supported with beams ranging from 5 meters, are sized and compared three solutions: slab; one-way hollow slab with straight oval cross-section; and one-way ribbed slab with recoverable molds. A budget estimate for each solution analyzed all three are addressed at the end of study is presented