The energy absorbing behavior of stainless steel 304L during the pulsed Nd:YAG laser welding is investigated in this thesis. The equivalent absorptivity is estimated from the comparison of measured and finite element method (FEM) results simulated melting pool shape parameters, e.g. pool width, pool depth, cross-section area and total volume of the pool. To simulate the actual pulsed laser beam, the energy density of heating source is performed as a Guassian distribution in the transection of a circular laser beam. For evaluating the feasibility and the accuracy of the estimated equivalent absorptivity, the multi-pulsed Nd:YAG laser welding is simulated by using the estimated absorptivities. A good agreement between this simulated and measured melting pool shapes are found in the multi-pulsed laser welding. The equivalent absorptivity can be interpolated from different parameters of the molten pool. However, absorptivity curve fitted from the cross-section area and total volume of the melting pool provide a more stable value. Results also indicate that the absorptivity and the pulse energy are in inverse proportion. The thermal-elastic-plastic FEM model is employed to simulate the fusion and solidification process of the pulsed laser welding. A complicate residual stress distribution introduced from the shrinkage in the solidification process is also calculated and presented. The distribution of post-weld-deformation near the melting pool has also been studied in this thesis. This post-weld-deformation may be a key factor in high precision laser welding, e.g. laser packaging for the optoelectronic components. The absorptivity estimated in this thesis may be helpful to simulate the laser welding process accurately.

>Magister Scientiae - MSc / Perovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity.

Gold-black has emerged as a popular absorptive coating for thermal radiation detectors in aerospace applications. The performance and accuracy of thermal radiation detectors largely depends on the surface optical properties of the absorptive coating. If the absorptivity of the layer is directional or wavelength dependent, then so will be the detector gain itself. This motivates our interest in the manufacture, physical characterization, and study of the wavelength and polarization sensitivity of the directional spectral absorptivity of gold-black. A first-principle model based on lossy antenna theory is presented to predict the polarization dependent directional spectral absorptivity of gold-black in the visible and near infrared. Results for normal spectral absorptivity are in good agreement with measurements reported in the literature. However, suitable experimental data were not available to validate the theory for directional spectral absorptivity. Therefore, an experimental campaign to fabricate and measure the directional spectral behavior of gold-black had to be undertaken to validate the first-principle model. New in-plane bidirectional reflectance distribution function (BRDF) measurements for two thicknesses (~4 μm and ~8 μm) of gold-black laid down on a gold mirror substrate are reported in the visible (532 nm) and near-infrared (800 and 850 nm) for p- and s-polarizations. The investigation is then extended to a three-layer sample, which is shown to exhibit off-specular reflectivity. Described are processes for laying down gold-black coatings and for measuring their in-plane BRDF as a function of thickness, wavelength, and polarization state. A novel method for retrieving the directional absorptivity from in-plane BRDF measurements is presented. The influence of polarization on directional absorptivity is shown to follow our earlier theory except at large incident zenith angles, where an unanticipated mirage effect is observed. / Doctor of Philosophy / Instruments called thermal radiation detectors play an important role in monitoring the global climate from space. Gold-black is often used as an absorptive coating to enhance the performance of these instruments. Users need to know how gold-black coatings influence instrument performance. In general, coating properties depend on the wavelength and direction of incident radiation, as well as on an optical phenomenon called polarization. This dissertation investigates the relationship between the creation of gold-black coatings and their performance. A physical model is postulated for predicting the optical behavior of gold-black in the visible and near infrared. The model produces results that are in good agreement with measurements reported in the literature. However, suitable directional measurements were not available to validate the theory. Therefore, an experimental campaign was mounted to fabricate gold-black coatings and measure their optical behavior in order to validate the mathematical model. We observed the optical behavior of several of our gold-black samples of various thickness and over a range of wavelengths. We also studied a three-layer sample which was found to exhibit an unexpected behavior called off-specular reflectivity. Described are processes for creating gold-black coatings and for measuring and explaining their optical performance. During the course of this investigation an unanticipated mirage effect was observed for the first time.

In part A, the effect of varying short-chain alkyl substitution on the spectroscopic properties of cyanine dyes was examined. Molar absorptivities and quantum yields were determined for groups of pentamethine and heptamethine dyes for which the substitution of the indole nitrogen was varied. For both sets of dyes, increasing alkyl chain length did not significantly change quantum yield or molar absorptivity. These results may be useful in designing new cyanine dyes. In part B, the effect of structure on the suitability of 2,4,6-trisubstituted pyridines as color pH indicators was studied by determining spectral effects of protonation, molar absorptivities, pKa values, and the structural origin of the spectral behavior. Good color indicating properties result from aniline substitution at the 4 position of pyridine and electron donating substitution at the 2 and 6 positions of pyridine, which provide a strong red shift in the spectra and greater red shifted peak absorptivity, respectively.

No description available.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Em aplicaÃÃes prÃticas de energia solar ativa e passiva, ou para outros fins construtivos, o revestimento superficial do material que absorve a radiaÃÃo solar tem um papel importante no que concerne à absorÃÃo e à emissÃo de radiaÃÃo solar e tÃrmica, influenciando diretamente na relaÃÃo custo-benefÃcio do equipamento. Revestimentos superficiais para as placas absorvedoras de radiaÃÃo solar, ou superfÃcies seletivas, alteram as relaÃÃes de ganho e perda de energia do equipamento e, por isso, o desempenho dos diferentes revestimentos disponÃveis, seus tipos e custos, alÃm de Ãreas potenciais de aplicaÃÃo devem ser conhecidos. Em geral, coletores de placa plana sem superfÃcies seletivas operam em temperaturas inferiores a 100ÂC, sendo utilizados no aquecimento de Ãgua, em processos de secagem, etc. Existem aplicaÃÃes prÃticas como fogÃes solares, sistemas de refrigeraÃÃo, dessalinizadores tÃrmicos onde sÃo necessÃrias temperaturas muito elevadas que sà sÃo alcanÃadas pelo uso de superfÃcies seletivas. Para alta eficiÃncia, os coletores solares devem possuir um mÃximo de absorbÃncia no espectro solar enquanto mantÃm um mÃnimo de emitÃncia no infravermelho. Este trabalho apresenta um estudo comparativo de superfÃcies seletivas para coletores solares utilizadas nos maiores centros que utilizam energias renovÃveis. SÃo apresentadas as mediÃÃes experimentais da temperatura em placas absorvedoras e da radiaÃÃo solar global e direta incidente sobre as placas em funÃÃo do tempo. As amostras foram testadas nas condiÃÃes ambientais de Fortaleza. Os valores experimentais foram usados na determinaÃÃo dos valores para a emissividade, apÃs a realizaÃÃo de um balanÃo de energia em regime permanente nessas amostras. As temperaturas de estagnaÃÃo nas amostras foram tambÃm calculadas mostrando o desempenho desses materiais. SÃo tambÃm apresentadas as anÃlises microscÃpicas (microscÃpico eletrÃnico de varredura) das diferentes superfÃcies. Os resultados mostram claramente o desempenho das amostras quando expostas à radiaÃÃo solar e que o procedimento desenvolvido para esse trabalho pode ser utilizado na determinaÃÃo de um valor mÃdio para a emissividade tÃrmica a partir de mediÃÃes mais simples. / Em aplicaÃÃes prÃticas de energia solar ativa e passiva, ou para outros fins construtivos, o revestimento superficial do material que absorve a radiaÃÃo solar tem um papel importante no que concerne à absorÃÃo e à emissÃo de radiaÃÃo solar e tÃrmica, influenciando diretamente na relaÃÃo custo-benefÃcio do equipamento. Revestimentos superficiais para as placas absorvedoras de radiaÃÃo solar, ou superfÃcies seletivas, alteram as relaÃÃes de ganho e perda de energia do equipamento e, por isso, o desempenho dos diferentes revestimentos disponÃveis, seus tipos e custos, alÃm de Ãreas potenciais de aplicaÃÃo devem ser conhecidos. Em geral, coletores de placa plana sem superfÃcies seletivas operam em temperaturas inferiores a 100ÂC, sendo utilizados no aquecimento de Ãgua, em processos de secagem, etc. Existem aplicaÃÃes prÃticas como fogÃes solares, sistemas de refrigeraÃÃo, dessalinizadores tÃrmicos onde sÃo necessÃrias temperaturas muito elevadas que sà sÃo alcanÃadas pelo uso de superfÃcies seletivas. Para alta eficiÃncia, os coletores solares devem possuir um mÃximo de absorbÃncia no espectro solar enquanto mantÃm um mÃnimo de emitÃncia no infravermelho. Este trabalho apresenta um estudo comparativo de superfÃcies seletivas para coletores solares utilizadas nos maiores centros que utilizam energias renovÃveis. SÃo apresentadas as mediÃÃes experimentais da temperatura em placas absorvedoras e da radiaÃÃo solar global e direta incidente sobre as placas em funÃÃo do tempo. As amostras foram testadas nas condiÃÃes ambientais de Fortaleza. Os valores experimentais foram usados na determinaÃÃo dos valores para a emissividade, apÃs a realizaÃÃo de um balanÃo de energia em regime permanente nessas amostras. As temperaturas de estagnaÃÃo nas amostras foram tambÃm calculadas mostrando o desempenho desses materiais. SÃo tambÃm apresentadas as anÃlises microscÃpicas (microscÃpico eletrÃnico de varredura) das diferentes superfÃcies. Os resultados mostram claramente o desempenho das amostras quando expostas à radiaÃÃo solar e que o procedimento desenvolvido para esse trabalho pode ser utilizado na determinaÃÃo de um valor mÃdio para a emissividade tÃrmica a partir de mediÃÃes mais simples. / In practical applications of active and passive solar energy, or other construction purposes, the coating material which absorbs solar radiation has an important role as regards the absorption and emission of thermal radiation and, directly influencing the cost benefit the product. Surface coatings for solar radiation-absorbing plate or selective surfaces, changing the relationship of gain and loss of energy of the equipment and, therefore, the performance of the various coatings available types and their costs as well as potential areas of application should be known. In general, flat plate collectors operate without selective surfaces at temperatures below 100  C, and for the heating of water in drying processes, etc.. There are practical applications such as solar cookers, refrigeration systems, thermal desalination plants where they are needed at very high temperatures that are only achieved by the use of selective surfaces. For high efficiency, solar collectors should have a maximum absorbance in the solar spectrum while maintaining a minimum infrared emittance. This paper presents a comparative study of selective surfaces for solar collectors used in the larger centers that use renewable energy. Shows the experimental measurements of the temperature and the plates absorbing solar radiation and directly incident on the plates as a function of time. Samples were tested in environmental conditions in Fortaleza. The experimental values ​​were used in determining values ​​for the emissivity, after conducting an energy balance in steady state in these samples. The stagnation temperatures in the samples was also calculated showing the performance of these materials. Are also presented microscopic analysis (scanning electron microscopy) of different surfaces. The results clearly show the performance of samples when exposed to solar radiation and the procedure developed for this work may be used in determining an average value for the thermal emissivity measurements from simpler. / In practical applications of active and passive solar energy, or other construction purposes, the coating material which absorbs solar radiation has an important role as regards the absorption and emission of thermal radiation and, directly influencing the cost benefit the product. Surface coatings for solar radiation-absorbing plate or selective surfaces, changing the relationship of gain and loss of energy of the equipment and, therefore, the performance of the various coatings available types and their costs as well as potential areas of application should be known. In general, flat plate collectors operate without selective surfaces at temperatures below 100  C, and for the heating of water in drying processes, etc.. There are practical applications such as solar cookers, refrigeration systems, thermal desalination plants where they are needed at very high temperatures that are only achieved by the use of selective surfaces. For high efficiency, solar collectors should have a maximum absorbance in the solar spectrum while maintaining a minimum infrared emittance. This paper presents a comparative study of selective surfaces for solar collectors used in the larger centers that use renewable energy. Shows the experimental measurements of the temperature and the plates absorbing solar radiation and directly incident on the plates as a function of time. Samples were tested in environmental conditions in Fortaleza. The experimental values ​​were used in determining values ​​for the emissivity, after conducting an energy balance in steady state in these samples. The stagnation temperatures in the samples was also calculated showing the performance of these materials. Are also presented microscopic analysis (scanning electron microscopy) of different surfaces. The results clearly show the performance of samples when exposed to solar radiation and the procedure developed for this work may be used in determining an average value for the thermal emissivity measurements from simpler.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O estudo de superfÃcies seletivas para coletores solares tÃrmicos, hà alguns anos, enfoca o uso de pastas e tintas para recobrir chapas de cobre ou alumÃnio, formando a placa absorvedora do coletor. Essas tintas ou pastas sÃo eletrodepositadas em placas metÃlicas, sendo este processo muitas vezes responsÃvel pelo levado custo de superfÃcies seletivas. O uso de compÃsitos obtidos a partir do Ãxido de cromo, Ãxido de ferro e Ãxido de titÃnio em um processo cerÃmico, utilizando a tÃcnica de deposiÃÃo por screen-printing pode ser uma alternativa para a obtenÃÃo de novas superfÃcies seletivas que tenham eficiÃncia prÃxima Ãs tintas e pastas jà comercializadas e com baixo custo de fabricaÃÃo. O objetivo deste trabalho à obter e caracterizar superfÃcies seletivas à base de cromo, ferro e titÃnio e comparÃ-las com outras superfÃcies jà comercializadas (Ãxidos metÃlicos), encontrar os valores da absortividade e caracterizar as mesmas por espectroscopÃa raman e infavermelho. / The study of selective coating for thermal solar collectors has been carried out with focus on the use of selective paints and coatings for copper and aluminum plates, which are used to manufacture the absorber plate. The processes, such as electrodeposition, used in these paints and coatings are expensive and they increasing the price of the final product. The use of composite obtained from chromium oxide, iron oxide, and titanium oxide in a ceramic process using the screen-printing deposition technique is an alternative to develop new selective coating with approximately the same thermal efficiency, but at a lower cost than the commercial ones. The results show that the absorptivity values measured with the new coatings are close to those presented by the manufacturers in the commercial sufaces. The objective is to obtain and characterize selective surfaces based on chromium, iron and titanium and compares them to other areas already marketed (metal oxides), find the values of absorptivity and characterize them by raman and infrared spectroscopy.

Fluorescent proteins (FPs) are the workhorses of biological molecular imaging. Important imaging modalities (such as polarization microscopy or FRET imaging) exploit anisotropic optical properties of fluorescent proteins. In this thesis, we present the results of our polarization microscopy and X-ray diffraction experiments on FP crystals, as well as mathematical interpretation of these results, yielding information on the directionality of one- and two-photon absorption within the investigated fluorescent protein molecules. For the anisotropy of one-photon absorption, we determine the transition dipole moment (TDM) orientations in three representative fluorescent proteins. Validation with available quantum mechanical predictions values and an experimentally determined TDM orientation of the GFP gives confidence to the results obtained. For the two-photon absorption, we first test our hypothesis that two-photon absorptivity tensors of representative FPs exhibit vector-like behaviour and then examine the applicability of this simplification as a basis for the interpretation of our two-photon polarization microscopy data.

This master thesis deals with a durability of concrete, which has become the centre of the interests of international scientific insitutes during the last years. The resistence of reinforced concrete depends on the covercrete which the aggresive liquids and gases penetrate through from the environment to reinforcement. According to the ability of the covercrete to penetrate degradative species is possible to tell the durability of concrete constructions. In experimental part we look for the actual state of covercrete, ordinary and high strength, by combination of various experiments. We can find here the test´s results of water and gas permeability and absorbability and sorption of concrete which complete the permeability tests. In final part the impact of different concrete types on durability of reinforced concrete is discussed.

Detta examensarbete har utförts med begäran från Trafikförvaltningen. Arbetets huvudmål är att undersöka om det är möjligt att använda värmestrålning direkt mot ytan av strömskenan för att hindra isbildning på en kortare tid då absorptiviteten är som bäst. / This dissertation has been written with the request from Trafikvörvaltningen. The study's main goal is to investigate whether it is possible to use heat radiation against the surface of the third rail to prevent ice creation during the best efficient of absorptivity.