Observação do comportamento dinâmico de estruturas de engenharia civil

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização de Estruturas

Benchmarking de identificação de ano: criação de um site para benchmarking de técnicas de identificação de dano

Dissertação para obtenção do grau de Mestre em Engenharia Mecânica na Área de Manutenção e Produção

A systematic procedure to enhance reproducibility of SWASV cycles in the determination of toxic metals in real samples

This work presents for the first time a systematic study on the optimization of the electrochemical cleaning time of a mercury film when it is used as a working electrode material in the analysis of toxic metals, such as Pb2+, used as model metal, in real samples by SWASV. The optimization study for the film’s cleaning time aimed at attaining a Pb2+ minimum value in the film after the re-oxidation step of the pre-concentrated metal, given the impossibility of complete removal of traces of the electroactive species from the film. This value was kept constant in each concentration range studied ensuring thus that all assays were performed in initial identical conditions. An assay performed on a synthetic sample was taken as reference. In it, given the absence of matrix effects, and after the electrochemical cleaning step, a direct proportionality was observed between the residual amounts of Pb2+ in the film (which for the cleaning time used was never completely removed) and Pb2+ concentration in the solution. This fact determined a high correlation between Pb2+ peak current and Pb2+ concentration which was not observed when real samples (tree leaves) were analyzed. This behavior may result from the presence of the interfering surfactants always present in real samples of complex matrix. Cleaning time optimization was performed for the following Pb2+ concentration ranges in the real samples of complex matrix: 0.006-0.020, 0.020-0.080, 0.060-0.200 and 0.100-0.600 ppb. As expected, in order to obtain identical levels of film’s cleaning efficiency, the need for longer cleaning times has been observed for higher concentrations. The optimized cleaning times for the concentration ranges under study were 120, 150, 180 e 300 s, respectively.

Synthesis, structure, and optical properties of an alternating calix[4]arene-based meta-linked phenylene ethynylene copolymer

Novel alternating copolymers comprising biscalix[4]arene-p-phenylene ethynylene and m-phenylene ethynylene units (CALIX-m-PPE) were synthesized using the Sonogashira-Hagihara cross-coupling polymerization. Good isolated yields (60-80%) were achieved for the polymers that show M-n ranging from 1.4 x 10(4) to 5.1 x 10(4) gmol(-1) (gel permeation chromatography analysis), depending on specific polymerization conditions. The structural analysis of CALIX-m-PPE was performed by H-1, C-13, C-13-H-1 heteronuclear single quantum correlation (HSQC), C-13-H-1 heteronuclear multiple bond correlation (HMBC), correlation spectroscopy (COSY), and nuclear overhauser effect spectroscopy (NOESY) in addition to Fourier transform-Infrared spectroscopy and microanalysis allowing its full characterization. Depending on the reaction setup, variable amounts (16-45%) of diyne units were found in polymers although their photophysical properties are essentially the same. It is demonstrated that CALIX-m-PPE does not form ground-or excited-state interchain interactions owing to the highly crowded environment of the main-chain imparted by both calix[4]arene side units which behave as insulators inhibiting main-chain pi-pi staking. It was also found that the luminescent properties of CALIX-m-PPE are markedly different from those of an all-p-linked phenylene ethynylene copolymer (CALIX-p-PPE) previously reported. The unexpected appearance of a low-energy emission band at 426 nm, in addition to the locally excited-state emission (365 nm), together with a quite low fluorescence quantum yield (Phi = 0.02) and a double-exponential decay dynamics led to the formulation of an intramolecular exciplex as the new emissive species.

Grid structure impact in sparse point representation of derivatives

In the Sparse Point Representation (SPR) method the principle is to retain the function data indicated by significant interpolatory wavelet coefficients, which are defined as interpolation errors by means of an interpolating subdivision scheme. Typically, a SPR grid is coarse in smooth regions, and refined close to irregularities. Furthermore, the computation of partial derivatives of a function from the information of its SPR content is performed in two steps. The first one is a refinement procedure to extend the SPR by the inclusion of new interpolated point values in a security zone. Then, for points in the refined grid, such derivatives are approximated by uniform finite differences, using a step size proportional to each point local scale. If required neighboring stencils are not present in the grid, the corresponding missing point values are approximated from coarser scales using the interpolating subdivision scheme. Using the cubic interpolation subdivision scheme, we demonstrate that such adaptive finite differences can be formulated in terms of a collocation scheme based on the wavelet expansion associated to the SPR. For this purpose, we prove some results concerning the local behavior of such wavelet reconstruction operators, which stand for SPR grids having appropriate structures. This statement implies that the adaptive finite difference scheme and the one using the step size of the finest level produce the same result at SPR grid points. Consequently, in addition to the refinement strategy, our analysis indicates that some care must be taken concerning the grid structure, in order to keep the truncation error under a certain accuracy limit. Illustrating results are presented for 2D Maxwell's equation numerical solutions.

Sistema de contagem de tráfego e classificação automática de veículos, em tempo real e sem fios

Esta tese tem por objectivo o desenho e avaliação de um sistema de contagem e classificação de veículos automóveis em tempo-real e sem fios. Pretende, também, ser uma alternativa aos actuais equipamentos, muito intrusivos nas vias rodoviárias. Esta tese inclui um estudo sobre as comunicações sem fios adequadas a uma rede de equipamentos sensores rodoviários, um estudo sobre a utilização do campo magnético como meio físico de detecção e contagem de veículos e um estudo sobre a autonomia energética dos equipamentos inseridos na via, com recurso, entre outros, à energia solar. O projecto realizado no âmbito desta tese incorpora, entre outros, a digitalização em tempo real da assinatura magnética deixada pela passagem de um veículo, no campo magnético da Terra, o respectivo envio para servidor via rádio e WAN, Wide Area Network, e o desenvolvimento de software tendo por base a pilha de protocolos ZigBee. Foram desenvolvidas aplicações para o equipamento sensor, para o coordenador, para o painel de controlo e para a biblioteca de Interface de um futuro servidor aplicacional. O software desenvolvido para o equipamento sensor incorpora ciclos de detecção e digitalização, com pausas de adormecimento de baixo consumo, e a activação das comunicações rádio durante a fase de envio, assegurando assim uma estratégia de poupança energética. Os resultados obtidos confirmam a viabilidade desta tecnologia para a detecção e contagem de veículos, assim como para a captura de assinatura usando magnetoresistências. Permitiram ainda verificar o alcance das comunicações sem fios com equipamento sensor embebido no asfalto e confirmar o modelo de cálculo da superfície do painel solar bem como o modelo de consumo energético do equipamento sensor.

Reforço estrutural de uma edificação pombalina: acompanhamento em obra

Este trabalho Final de Mestrado consiste na elaboração de um relatório de estágio que reportará o acompanhamento por parte do discente de um reforço estrutural de uma edificação pombalina. Desta forma são definidas as principais características construtivas destas edificações, fazendo um enquadramento histórico-cultural e urbanístico do edifício alvo deste trabalho. Uma vez estudado um tipo de construção especial, são mencionados diversos sistemas e metodologias de reforço que se adequam às características singulares destas construções, ilustrando-se procedimentos e técnicas que normalmente são utilizadas na reabilitação. Procedeu-se ao relato dos trabalhos executados na obra, desde a demolição dos elementos degradados e dissonantes com esta tipologia construtiva, a um estudo mais pormenorizado ao solo de fundação encontrado na zona da edificação e soluções de fundação adoptadas. São descritas neste trabalho quais as medidas adoptadas no reforço da estrutura da edificação, evidenciando os procedimentos e técnicas aplicadas pela empresa. No final deste trabalho, foi efectuada uma modelação do edifício da Rua do Carmo num software de análise estrutural SAP 2000, com o objectivo de modelar de forma aproximada a real geometria do edifício e, através da introdução das variadas acções actuantes na estrutura, fazer determinadas considerações do comportamento da mesma face às solicitações impostas. Pretendeu-se ainda estabelecer uma relação entres os resultados obtidos e as técnicas de reforço utilizadas na reabilitação destes edifícios.

Completion problems for real matrices, II

Thirty years ago, G.N. de Oliveira has proposed the following completion problems: Describe the possible characteristic polynomials of [C-ij], i,j is an element of {1, 2}, where C-1,C-1 and C-2,C-2 are square submatrices, when some of the blocks C-ij are fixed and the others vary. Several of these problems remain unsolved. This paper gives the solution, over the field of real numbers, of Oliveira's problem where the blocks C-1,C-1, C-2,C-2 are fixed and the others vary.

From unthinned continent to ocean: The deep structure of the West Iberia passive continental margin at 38 degrees N

The crustal and lithospheric mantle structure at the south segment of the west Iberian margin was investigated along a 370 km long seismic transect. The transect goes from unthinned continental crust onshore to oceanic crust, crossing the ocean-continent transition (OCT) zone. The wide-angle data set includes recordings from 6 OBSs and 2 inland seismic stations. Kinematic and dynamic modeling provided a 2D velocity model that proved to be consistent with the modeled free-air anomaly data. The interpretation of coincident multi-channel near-vertical and wide-angle reflection data sets allowed the identification of four main crustal domains: (i) continental (east of 9.4 degrees W); (ii) continental thinning (9.4 degrees W-9.7 degrees W): (iii) transitional (9.7 degrees W-similar to 10.5 degrees W); and (iv) oceanic (west of similar to 10.5 degrees W). In the continental domain the complete crustal section of slightly thinned continental crust is present. The upper (UCC, 5.1-6.0 km/s) and the lower continental crust (LCC, 6.9-7.2 km/s) are seismically reflective and have intermediate to low P-wave velocity gradients. The middle continental crust (MCC, 6.35-6.45 km/s) is generally unreflective with low velocity gradient. The main thinning of the continental crust occurs in the thinning domain by attenuation of the UCC and the LCC. Major thinning of the MCC starts to the west of the LCC pinchout point, where it rests directly upon the mantle. In the thinning domain the Moho slope is at least 13 degrees and the continental crust thickness decreases seaward from 22 to 11 km over a similar to 35 km distance, stretched by a factor of 1.5 to 3. In the oceanic domain a two-layer high-gradient igneous crust (5.3-6.0 km/s; 6.5-7.4 km/s) was modeled. The intra-crustal interface correlates with prominent mid-basement, 10-15 km long reflections in the multi-channel seismic profile. Strong secondary reflected PmP phases require a first order discontinuity at the Moho. The sedimentary cover can be as thick as 5 km and the igneous crustal thickness varies from 4 to 11 km in the west, where the profile reaches the Madeira-Tore Rise. In the transitional domain the crust has a complex structure that varies both horizontally and vertically. Beneath the continental slope it includes exhumed continental crust (6.15-6.45 km/s). Strong diffractions were modeled to originate at the lower interface of this layer. The western segment of this transitional domain is highly reflective at all levels, probably due to dykes and sills, according to the high apparent susceptibility and density modeled at this location. Sub-Moho mantle velocity is found to be 8.0 km/s, but velocities smaller than 8.0 km/s confined to short segments are not excluded by the data. Strong P-wave wide-angle reflections are modeled to originate at depth of 20 km within the lithospheric mantle, under the eastern segment of the oceanic domain, or even deeper at the transitional domain, suggesting a layered structure for the lithospheric mantle. Both interface depths and velocities of the continental section are in good agreement to the conjugate Newfoundland margin. A similar to 40 km wide OCT having a geophysical signature distinct from the OCT to the north favors a two pulse continental breakup.

Enhanced short wavelength response in laser-scanned-photodiode image sensor using an a-SiC : H/a-Si : H tandem structure

We report in this paper the recent advances we obtained in optimizing a color image sensor based on the laser-scanned-photodiode (LSP) technique. A novel device structure based on a a-SiC:H/a-Si:H pin/pin tandem structure has been tested for a proper color separation process that takes advantage on the different filtering properties due to the different light penetration depth at different wavelengths a-SM and a-SiC:H. While the green and the red images give, in comparison with previous tested structures, a weak response, this structure shows a very good recognition of blue color under reverse bias, leaving a good margin for future device optimization in order to achieve a complete and satisfactory RGB image mapping. Experimental results about the spectral collection efficiency are presented and discussed from the point of view of the color sensor applications. The physics behind the device functioning is explained by recurring to a numerical simulation of the internal electrical configuration of the device.

Novel structure for large area image sensing

This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device.

Projecto de estabilidade da Escola Superior de Enfermagem Artur Ravara

O presente trabalho, refere-se ao projecto de estabilidade, em betão armado e pré-esforçado, da Escola Superior de Enfermagem Artur Ravara, situada na zona da EXPO em Lisboa. O edifício apresenta-se com uma implantação em “L”, tendo como dimensões máximas 38,50m x 54,80m e desenvolve-se em altura por quatro pisos, dos quais, dois são enterrados. A estrutura do edifício em causa, apresenta duas juntas de dilatação, por forma a tornar desprezáveis os efeitos devidos à retracção e diminuição de temperatura, dividindo o edifício em três blocos. As suas fundações são indirectas, constituídas por estacas moldadas no terreno e respectivos maciços de encabeçamento. As lajes são fungiformes aligeiradas de moldes perdidos, de modo a permitir vencer maiores vãos, que variam entre os 6,60m e os 10,00m, e permitindo também maior rapidez de execução e maior economia. As consolas de 3,50m de vão, em laje maciça, são suportadas por vigas pré-esforçadas de secção variável. Para o cálculo automático da estrutura e da obtenção dos respectivos desenhos das armaduras, foi utilizado o programa de cálculo automático, Tricalc 7.1. O conteúdo do projecto em questão, sendo de carácter académico, não corresponde à versão real, à qual não se teve acesso. O dimensionamento das fundações, devido à fraca resistência dos solos e o dimensionamento da estrutura, devido à geometria e dimensões do edifício, permitiram enfrentar desafios interessantes. Tais desafios, deram possibilidade de enriquecer bastante os conhecimentos sobre a engenharia de estruturas.

Intervenções em estruturas antigas

O presente relatório de estágio, definido como Trabalho Final de Mestrado, surge como resultado de um estágio profissional realizado no âmbito do Mestrado em Engenharia Civil do Instituto Superior de Engenharia de Lisboa, e tem como objectivos primordiais, expor as actividades realizadas e reflectir os conhecimentos adquiridos durante o período de estágio. Após uma formação académica maioritariamente vocacionada para os aspectos teóricos e de natureza científica, tornou-se fundamental ao estagiário garantir um contacto real com a profissão de Engenheiro Civil antes do ingresso no mercado de trabalho. Foi com base nesse pressuposto que a opção do Trabalho Final de Mestrado incidiu sobre a realização de um estágio curricular em detrimento das restantes possibilidades. O período de estágio iniciou-se a 14 de Março de 2011 e incidiu sobre a área de Conservação, Restauro e Reabilitação de edifícios com valor patrimonial, sendo feito referência no capítulo 2 aos princípios importantes da intervenção neste tipo de edifícios. O capítulo 3 faz uma abordagem geral do que são as coberturas servindo de complemento ao capítulo 4, onde são abordados e analisados os processos e métodos construtivos envolvidos, contemplando a evolução construtiva da cobertura do Cruzeiro, no Convento de Cristo em Tomar. Nos restantes capítulos, 5 e 6, é feita a caracterização e constituição da estrutura de um edifício da segunda metade do século XVIII, e a análise estrutural feita ao edifício no Antigo Convento do Santíssimo Sacramento, em Lisboa, respectivamente. O capítulo 4 é complementado pelo Anexo A, sendo utilizado como referência ao esquema da estrutura artesanal encontrada na cobertura do Cruzeiro.

Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders

Oxide based diluted magnetic semiconductor (DMS) materials have been a subject of increasing interest due to reports of room temperature ferromagnetism in several systems and their potential use in the development of spintronic devices. However, concerns on the stability of the magnetic properties of different DMS systems have been raised. Their magnetic moment is often unstable, vanishing with a characteristic decay time of weeks or months, which precludes the development of real applications. This paper reports on the ferromagnetic properties of two-year-aged Ti1-xCoxO2-δ reduced anatase nanopowders with different Co contents (0.03≤x≤0.10). Aged samples retain rather high values of magnetization, remanence and coercivity which provide strong evidence for a quite preserved long-range ferromagnetic order. In what concern Co segregation, some degree of metastability of the diluted Co doped anatase structure could be inferred in the case of the sample with the higher Co content.

Influence of growth temperature and carrier flux on the structure and transport properties of highly oriented CrO2 on Al2O3 (0001)

In this work we report on the structure and magnetic and electrical transport properties of CrO2 films deposited onto (0001) sapphire by atmospheric pressure (AP)CVD from a CrO3 precursor. Films are grown within a broad range of deposition temperatures, from 320 to 410 degrees C, and oxygen carrier gas flow rates of 50-500 seem, showing that it is viable to grow highly oriented a-axis CrO2 films at temperatures as low as 330 degrees C i.e., 60-70 degrees C lower than is reported in published data for the same chemical system. Depending on the experimental conditions, growth kinetic regimes dominated either by surface reaction or by mass-transport mechanisms are identified. The growth of a Cr2O3 interfacial layer as an intrinsic feature of the deposition process is studied and discussed. Films synthesized at 330 degrees C keep the same high quality magnetic and transport properties as those deposited at higher temperatures.