• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 13565
  • 4477
  • 1770
  • 1724
  • 1149
  • 1126
  • 342
  • 266
  • 266
  • 266
  • 266
  • 266
  • 260
  • 181
  • 172
  • Tagged with
  • 30671
  • 5954
  • 3379
  • 3147
  • 2794
  • 2584
  • 2460
  • 2419
  • 2188
  • 2180
  • 1945
  • 1813
  • 1576
  • 1574
  • 1547
  • 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.
171

Photophysics of Bio-Inspired Solar Energy Conversion

January 2014 (has links)
abstract: Increased global demand for energy has led to prolific use of fossil fuels, which produce and release greenhouse gases, such as carbon dioxide. This increase in atmospheric carbon dioxide affects the global weather system and has been cited as a cause for global warming. For humans to continue to meet demands for energy while reducing greenhouse emission, a sustainable, carbon-neutral energy source must be developed. The sun provides energy for the majority of life on earth, as well as the energy stored in the chemical bonds of fossil fuels. This dissertation investigates systems inspired by the biological mechanism of solar energy capture and storage. In natural photosynthesis, organisms use chlorophyll as a chromophore to absorb the sun's energy. Bio-inspired systems use close analogues like porphyrins and phthalocyanines. In this dissertation, a soluble, semiconducting porphyrin is reported. The polymer was synthesized via a Buchwald-Hartwig style coupling of porphyrin monomers which produced a polyaniline-like chain with porphyrins incorporated into the backbone. Spectroscopic and electrochemical studies were performed, which show evidence of excited state charge transfer and a first oxidation state of 0.58 V (vs SCE). These properties suggest that the polymer could be involved in excited state electron donation to fullerenes and other electron acceptors, which could be beneficial in organic photovoltaics, sensors, and other applications. Molecular dyads and triads capable of charge separation have been studied for decades, and the spectroscopic properties of two novel systems are reported in this dissertation. A peripherally-connected zinc-phthalocyanine-C60 dyad was studied, and showed excited state electron transfer from the phthalocyanine excited state to the C60, with a long-lived charge separated state. An axially-linked carotene-Si-pthalocyanine-C60 triad was studied, showing excited state electron transfer from the phthalocyanine to the C60, but fast recombination before hole transfer can occur to the carotene. Analogues of the electron transport mechanisms used in many biological systems use iron-sulfur clusters to shuttle electrons from donors to acceptors. In this dissertation, the spectroscopic properties of a de novo protein were studied. Nanosecond transient absorption was used to characterize the electron and energy transfer of an excited water-soluble porphyrin to the oxidized [FeS] clusters incorporated in the de novo protein. The triplet state of the porphyrin was strongly quenched with the holo-protein without a rise in porphyrin plus signal, suggesting that only Dexter-type energy transfer occurs between the sensitized porphyrin and the [FeS] clusters. / Dissertation/Thesis / Ph.D. Chemistry 2014
172

A Reforma do Setor Elétrico do Chile e as Ações da Eficiência Energética / The Power Sector Reform in Chile and the Shares of Energy Efficiency

Claudia Andrea Fernandez Elgueta 26 November 1999 (has links)
O uso eficiente de energia é reconhecido em muitos países do mundo como uma ferramenta de política energética para o desenvolvimento sustentável do setor. Este trabalho analisa a situação do uso eficiente de energia no setor elétrico chileno, cujo processo de reforma, marco legal e institucional e privatização constitui um paradigma da região. É realizada uma caracterização do setor elétrico, estuda-se o processo de reforma do setor, analisa-se o marco institucional, marco regulatório e o processo de planejamento do setor. Estudam-se a experiência, os potenciais e as principais barreiras para a eficiência energética e se propõem ações corretivas. O setor elétrico chileno apresenta potenciais de melhoramento da eficiência energética de implicação econômica, ambiental e social que não são aproveitados pela existência de diversas barreiras. A maior responsabilidade de ultrapassar estas barreiras recai no estado quem deve realizar modificações no marco institucional e propiciar a cooperação público-privada. / Efficient use of energy is recognized worldwide as an energy policy tool for a sustainable development in the sector. This work analyses the situation of energy efficiency in the Chilean electric sector, whose reform process, legal and institutional frameworks and privatization constitute a paradigm in the region. The electric sector is characterized, the reform process is studied, institutional and regulation frameworks and the planning process are analyzed. The experience, the potentials and the main barriers for energy efficiency are studied, and corrective measures are suggested. It is concluded that the Chilean electric sector presents large potential for energy efficiency improvements with economic, environmental and social impacts that are not being utilized due to the existence of several barriers. The state bears the main responsibility for overcoming these barriers by modifying the institutional framework and stimulating cooperation between the public and private sectors.
173

Análise Comparativa das Crises Energéticas na Califórnia e no Brasil / Comparison of the Energy Crisis in California and Brazil

Riolando Longo 02 May 2003 (has links)
Os anos 1990 foram marcados pela teoria econômica que preconiza a atuação das forças de mercado, com a capacidade de atender, com qualidade e quantidade, a oferta dos serviços do setor elétrico. Entretanto, ao término dessa década e início do novo século os acontecimentos demonstraram que a teoria tem se revelado inconsistente naquilo que prometia, isto é, a crescente expansão do sistema; a inovação da tecnologia, e não promovendo a redução de custos das tarifas de energia elétrica. Os resultados alcançados no recente processo de reestruturação do setor elétrico, inspirados no livre mercado, comprovaram a inconsistência da teoria liberal, conforme constatado no desenvolvimento do presente trabalho. / The 1990s were marked by the economical theory that commended the performance of market forces with the capacity to assist, with quality and quantity, the offer of electrical energy services. However, at the end of the 1990s and beginning of the new century the data of reality demonstrated that the theory has revealed itself inconsistent in what it had promised, i.e., the system expansion; the innovation of technology, and it didn´t promote the cost reduction of electric power tariffs. The results reached in the recent process of restructuring of the electrical energy industry, inspired in the free market, prove the inconsistency of the liberal theory, as verified in the development of this thesis.
174

Energia e Antecipação Tecnologica na Obra de Jules Verne / Energy and Technological Advance in the Work of Jules Verne

Berenice Cabral de Moura Coutinho 16 November 1994 (has links)
não há resumo. / There is no abstract.
175

Alternativas de usos finais da eletricidade deslocada da cocção elétrica na Colômbia / Alternative end uses of electricity displaced in Colombia\'s electric cooking

Juan Guillermo Alvarez Giraldo 12 September 1994 (has links)
Esta dissertação analisa, do ponto de vista técnico, econômico e social, diferentes altemativas de usos finais para a eletricidade deslocada da cocção elétrica no setor residencial da Colômbia. Neste trabalho mostra-se que o cozimento e preparo de alimentos por meio da eletricidade, tem um custo social elevado. Discute-se, portanto, o papel de diversos energéticos substitutos da eletricidade nesse uso final. Analisaram-se projetos de eletrificação no setor de transportes. Os resultados mostram que, a curto prazo, existem opções interessantes do ponto de vista técnico. econômico e ambiental de eletricação de transporte de massa nas grandes cidades (Santafé de Bogotá e Medellín). Contudo, determinou-se que provavelmente as reduções de demanda de eletricidade pelo setor residencial na Colômbia redundarão no adiamento do aumento de oferta e não na conquista de novos e importantes mercados para a eletricidade. / This dissertation analyses, various end-use alternatives for the electricity saved from electric cooking in Colombia; technical, economic and social issues were studied. This document shows that preparation of food, using electricity has a high social cost. Therefore, discussion about the role of several types of energy that could substitute electricity in that end-use was made. There were also analyzed some projects of electrification in the transport sector. The results show that in a short range period of time there are interesting options of massive transport electrication in the largest cities of Colombia (Santafe de Bogota and Medellin) taking into consideration, technical, economic and environmental aspects. However, it was determined that reductions on electricity demand of the residential sector will be more likely reflected in a delay of increasing supply than of new and large electricity market formation.
176

Avaliação de distúrbios em sistemas de distribuição de energia elétrica devido às distorções harmônicas / Evaluation of disturbances in distribution systems of electric power due to harmonic distortion

Jose Gil Oliveira 30 June 1995 (has links)
As redes de Distribuição de Energia Elétrica podem ser submetidas a perturbações, causadas pela proliferação de cargas não-lineares, provocando distúrbios nos alimentadores das sub-estações e afetando cargas sensíveis, obrigando as empresas de energia elétrica e aos consumidores a adotarem medidas preventivas e corretivas. Esses distúrbios quando afetam a forma de onda da tensão ou da corrente, provocando o aparecimento de freqüências múltiplas as da fundamental, é um fenômeno conhecido como distorção harmônica. Para avalia-la, foi desenvolvido um equipamento eletrônico controlado por microprocessadores, possibilitando medições em campo da tensão e corrente harmônica, assim como o módulo e fase de cada harmônico, múltiplo de 60 Hz, até o 40° harmônico. Com base nos dados coletados pelo equipamento, foram avaliados os distúrbios provocados pelas cargas não-lineares num consumidor gerador de harmônicos. Foram realizadas comparações entre os registros de consumo medidos pelo equipamento e o registrado pela concessionária. Foi comparada também a distorção harmônica, na corrente e na tensão, com as normas nacionais e internacionais. Os resultados indicaram, mesmo em se considerando uma série histórica pouco expressiva, coerência com o estado do conhecimento sobre o fenômeno. / The distribution lines can be affected by disturbances, caused by the increase of non- linear loads, provoking disturbances in substation feeders. These disturbances can affect sensitive loads, demanding therefore from the Utilities preventive and remedial actions. When they affect the voltage waveforms, current and voltage, causing the occurrence of multiply frequency at the fundamental frequency, it is a phenomena known as harmonic distortion. An electronic equipment controlled by microprocessors was developed to the disturbance assessment and to make measurements in site possible, sampling the waveform and calculating the rst 40 harmonics of the 60 Hz, fundamental, for both voltage and current waveform. The data bases were collected by the equipment and the disturbances caused by non-linear loads were veried, at a certain consumer who generates harmonics. Two comparisons were performed: the data consumption measured by equipment versus the Utility\'s data consumption and the harmonic distortion current and voltage, versus international and local standards. Results have shown coherence with the state of knowledge. In spite of the presented data being of a short period duration.
177

Gerenciamento da Demanda de Energia usada para Iluminação e Cocção no Setor Residencial da Região da CNFL da Costa Rica / Demand Management Energy used for lighting and cooking in the Residential Sector of the Region of Costa Rica CNFL

Luis Renan Chen Apuy Chacon 26 September 1997 (has links)
não há resumo / there is no abstract
178

Estudo do Metabolismo Energético do Sistemas de Transporte: Caso de Curitiba / Study of energy metabolism of the transport system: Case of Curitiba

Renata Marson Teixeira de Andrade 23 July 1998 (has links)
O meio ambiente urbano vem sofrendo drásticas transformações ao longo destas últimas décadas. E um dos principais problemas é o aumento significativo da poluição atmosférica devido ao metabolismo realizado pela frota de veículos motorizados e indústrias instaladas nos centros urbanos. Neste trabalho, a cidade é compreendida como um sistema aberto e vista como um organismo vivo, que se alimenta de recursos naturais, realiza seu próprio metabolismo, produz resíduos, como subprodutos resultantes deste metabolismo, sob a forma de emissão gasosa, liquida e sólida que agridem e desequilibram o meio biogeofísico e afetam a comunidade al residente, bem como de regiões circunvizinhas e até bem distantes. Uma cidade ou um de seus sistemas podem ser considerados como possuidor de um metabolismo eficiente, quando consomem menos energia ou recurso natural para realizar as mesmas funções de manutenção, de geração de serviços, de crescimento urbano e de desenvolvimento sócio-econômico, produzindo menores quantidades de emissões, diminuindo os impactos negativos sobre o meio biogeofísico. Por meio de uma abordagem sistêmica e multidisciplinar, utilizado o modelo do metabolismo de uma cidade, focaliza-se no metabolismo energético do sistema de transportes. Como estudo de caso a cidade de Curitiba, estudando o metabolismo energético de seu sistema de circulação, em especial da Rede integrada de Transportes RIT, criada a partir de 1971. / In the less developed countries, the urban environment has been suffering drastic transformations in the last decades. One of the main problems from the city growth is the signicant increase of the atmospheric pollution due to emissions resulted from the metabolism of the Circulatory System, caused by traffic stream. In this work, the city is understood as an open system and seen as an alive organism that accomplishes its own metabolism: it consumes energy and material and produces residues, as resulting by-products from its metabolism. The waste disposal is in the form of gaseous, liquid and solid emissions that change the environment and affect the inhabitants of the urban areas. The city or one of its systems can accomplish an efficient metabolism, when they consume less energy or any resource to maintain its functions (generation of services, urban growth and social-economical development), producing smaller amounts of emissions and nally decreasing the negative impacts on the environment. By a systemic and multidisciplinary approach, the indicators of the metabolism of a city are used to study the energy metabolism of the transport system. The case of this study is the city of Curitiba, looking at the energy metabolism of its system of circulation, specially of RlTS - Public Transport integrated Net.
179

Uso Eficiente de Energia Elétrica no Setor de Iluminação Pública (IP) do Equador / Efficient Use of Electricity Sector in Public Lighting (IP) of Ecuador

Jorge Patricio Muñoz Vizhñay 02 February 1996 (has links)
O setor de iluminação Pública (IP) do Equador representa um consumo de energia de 7% do Setor Elétrico. Uma quantidade aproximada de 450.000 luminárias existem instaladas cuja potência corresponde a 90 MW e consomem 394 GWh/ano de energia das quais 72% usam tecnologia de mercúrio, 26% tecnologia de sódio e o restante tecnologias de luz mista, incandescente e fluorescente. O potencial passível de conservação considerando as tecnologias de mercúrio e luz mista é de 66.1 MW; o maior potencial encontra-se nas luminárias HG-l75 W com 35,1 MW (53%), depois as luminárias HG- I25 W com I8,7 MW (28%). O estudo de caso propõe a substituição de luminárias de vapor de mercúrio e luz mista por vapor de sódio de alta pressão nas seguintes potências: HG-l25 W por NA-70 W; HG- 175 W por NA-I00 W; HG-250 W por NA-150 W; HG-400 W por NA-250 W; e, MS- 160 W por NA-50 W. Trocando todas as luminárias convencionais pelas respectivas eficientes (no ano atual), a potência do sistema de IP diminui para 64 MW (potência conservada de 26 MW) e, a energia diminui para 281 GWh/ano (energia conservada de 113 GWh/ano), ou seja a diminuição é 29% tanto em potência quanto em energia (diminuição de 2% do sistema elétrico). O investimento para comprar 370.000 luminárias de vapor de mercúrio e luz mista o substituir por suas equivalentes eficientes é US$ 47,7 milhões (valor anualizado de US$ 8,4 milhões/ano). Por outro lado, o valor CDVA das luminárias com potencial de conservação de energia (luminárias de vapor de mercúrio o luz mista) é de US$ 32,6 milhões/ano, com a implantação dos programas de uso eficiente de energia baixará para US$ 24,7 milhões/ano, que resulta em vantagem do ponto de vista econômico para o Equador. Além disso, o investimento inicial produz resultados satisfatórios nas figuras de mérito tais como no CEC para o elenco de substituições que situa-se em 13,2 US$/MWh, valor inferior do que o custo marginal médio de energia 83 US$/MWh. De maneira similar, o CPC situa-se em 328 US$/kW, valor inferior que qualquer alternativa de oferta de energia. Além disso, se recomenda substituir o elenco de luminárias de vapor de mercúrio e luz mista por vapor de sódio no período de três anos e obter a maior vantagem da TIR que situa-se em 46,7%. Os programas de uso eciente de energia produzem deslocamentos doa investimentos nas áreas de geração, transmissão o distribuição num valor equivalente a US$ 6,1 milhões/ano (o valor presente desta quantidade atinge US$ 33,9 milhões e é igual ao deslocamento nas instalações para produzir e transmitir energia com um custo unitário igual ao marginal de potência). A poupança pela diminuição de potência e do consumo de energia atinge US$ 9,4 milhões/ano (US$ 6,1 milhões por potência e US$ 3,3 milhões por energia). No entanto, os custos operacionais aumentam em US$ 1,5 milhões/ano. Portanto, o balanço abrangente de perdas e ganhos proporciona um saldo positivo de US$ 7.9 milhões/ano (o valor presente é US$ 44,6 milhões). / Equador´s Public illumination (PI) is responsible for 7% of the total electric energy consumption of the Electric Sector: There are nearly 450,000 lamps installed, with an electric power demand of 90 MW and a consumption of 394 GWh/year of energy. Mercury lamps represent 72% of the consumption, sodium lamps represent 26% and the remaining is used by mix, incandescent and uorescent lamps. The expected saving of capacity with the retrotting of mercury and mix lamps is 66.1 MW. The greater saving is for the lamps HG-l 75W with 35.1 MW (53%) and the lamps HG-l25W with l8.7 MW (28%). This thesis propose to replace mercury vapor and mix lights by high pressure sodium lamps with the following power: HG-125W by NA-70W; HG-I75W by NA-100W; HG-250W by NA- 150W; HG-400W by NA-250W and MS-160W by NA-50W. If conventional technology is replaced by the efficient one (at this moment), dernand capacity of the PI system decrease to 64 MW (power conservation, 26 MW), energy consumption to 281 GWh/year (saved energy of 113 (GWh/year), that is a decrease of 29% for the power and electric systems requirements (electric system decrease in 2%). To change 370,000 mercury and mix lamps by the eicient lights needs US$ 47.7 millions (annualized US$ 8.4 millions/year). The Annualized Life-cycle Cost of the potential conservation of energy (mercury vapor lamps and mix lights) is US$ 32.6 millions/year. This replacement decrease by US$ 24.7 millions/year the electricity bill of the sector showing that Equador has economic gain. Besides that, the initial investment shows advantage on merit figures as the Cost Saved Energy for the alternatives of substitution of 13.2 US$/MWh, that is lower than the energy marginal cost of 83 US$/MWh. Identically the Cost Saved Power is 328 US$/kW that is lower than any other supply option. The recommendation is to distribute the replacement during three years carrying out the substitution of the conventional lamps as they extinguished obtaining a best advantage in the Internal Rate of Return of 46.7%. The substitution program (energy efficient use) produces a displacement of investments in the generation, transmission and distribution areas with a value of US$ 6.1 millions/year (this amount is similar to the displacement of installation of more system electric power at an initial cost US $ 33.9 millions). Saved power and energy represents an amount US$ 9.4 rnillions/year (US$ 6.1 millions by power and US$ 3.3 millions by energy). However the operation cost increases by US$ 1.5 millions/year, therefore the balance including costs and gains has a net positive balance of US$ 7.9 millions/year (present value represents US$ 44.6 millions).
180

The fabrication and analysis of the magnetic and crystallographic properties of Fe-rich (Fe x Ga 1-x) Galfenol alloys

Quinn, C. J. January 2012 (has links)
Understanding the fundamental physics and properties of smart materials is a very important area of research for nano and micro mechanical systems especially in the applications of sensing and actuation, such as SONAR. This thesis is focused on the investigations of Galfenol solid solutions and the associated magnetic properties, crystal structures and the influence that additional Ga has upon a Fe-rich Galfenol system. This has been achieved by using a variety of compositions of Fe1-xGax melt-spun alloy ribbons and then characterised using a number of measurement techniques including; x-ray diffraction, neutron diffraction, Mössbauer interaction, differential scanning calorimetry, vibrating sample magnetometry and electron microscopy. By identifying the various crystallographic phases and their relevant magnetic properties a clearer picture has been established to enable further research to build upon the results published in this thesis. After fabrication several standard measurements were taken to evaluate the crystalline phases within and the proposed site occupancy of the atomic structure. Compositional analysis was performed in order to clarify the specific atomic weight percentages produced. Magnetic and thermal magnetic measurements were then undertaken to measure magnetic saturation values and relevant Curie temperatures. Further thermal measurements were taken in order to explain some of the anomalous thermo-magnetic results in the two most dilute compositions. These results were directly compared to ascertain both the structural and magnetic changes that were instigated by the thermal treatment of the alloys. Finally, some rapid annealing and quenching and also a slow cooling treatment was applied to the most dilute composition in order to capture the structural transformation caused by the thermal treatment and these resulting phases identified and the results discussed.

Page generated in 0.0762 seconds