Structural analysis of the masonry envelope of Ica Cathedral, Peru

Dissertação de mestrado em Structural Analysis of Monuments and Historical Constructions

Structural analysis of the timber structure of Ica Cathedral, Peru

Dissertação de mestrado em Structural Analysis of Monuments and Historical Constructions

An innovative framework for probabilistic-based structural assessment with an application to existing reinforced concrete structures

A novel framework for probabilistic-based structural assessment of existing structures, which combines model identification and reliability assessment procedures, considering in an objective way different sources of uncertainty, is presented in this paper. A short description of structural assessment applications, provided in literature, is initially given. Then, the developed model identification procedure, supported in a robust optimization algorithm, is presented. Special attention is given to both experimental and numerical errors, to be considered in this algorithm convergence criterion. An updated numerical model is obtained from this process. The reliability assessment procedure, which considers a probabilistic model for the structure in analysis, is then introduced, incorporating the results of the model identification procedure. The developed model is then updated, as new data is acquired, through a Bayesian inference algorithm, explicitly addressing statistical uncertainty. Finally, the developed framework is validated with a set of reinforced concrete beams, which were loaded up to failure in laboratory.

Eco-friendly luminescent hybrid materials based on EuIII and LiI co-doped chitosan

Biopolymer-based materials have been of particular interest as alternatives do synthetic polymers due to their low toxicity, biodegradability and biocompatibility. Among them, chitosan is one of the most studied ones and has recently been investigated for the application as solid state polymer electrolytes. Furthermore, it can serve as a host for luminescent species such as rare earth ions, giving rise to materials with increased functionality, of particular interest for electrochemical devices. In this study, we investigate chitosan based luminescent materials doped wit Eu3+ and Li+ triflate salts from the structural, photophysical and conductivity points of view. Because the host presents a broad emission band in the blue to green, while Eu3+ emits in the red, fine tuning of emission colour and/or generation of white light is possible by optimizing composition and excitation scheme. Europium lifetimes (5D0) are in the range 270 – 350 µs and quantum yields are as high as 2%. Although Li+ does not interfere with the luminescent properties, it grants ion-conducting properties to the material suggesting that a combination of both properties could be further explored in multifunctional device.

Novel auxetic structures from basalt braided composites for structural applications

Auxetic materials are a class of materials behaves unusual way compared to regular materials i.e. possess negative Poisson’s ratio. This paper reports, the development of auxetic structures based on re-entrant hexagon design from braided composite materials and testing of the mechanical properties (tensile property, auxetic property and work of rupture). The structure developed from glass and basalt braided composite rods and properties were compared between them. Later, the basic re-entrant hexagon design was modified with vertical straight rods to improve their mechanical behavior and their auxetic property was studied. Auxetic behavior of these structures was studied in a tensile testing machine taking video during testing by Digital camera, later the video converted into images to measure the strain values using simple software, ImageJ. Along with experimental work, analytical model was used to calculate the Poisson’s ratio of basic structure and results were compared

Electronic structure and optical signatures of semiconducting transition metal dichalcogenide nanosheets

CONSPECTUS: Two-dimensional (2D) crystals derived from transition metal dichalcogenides (TMDs) are intriguing materials that offer a unique platform to study fundamental physical phenomena as well as to explore development of novel devices. Semiconducting group 6 TMDs such as MoS2 and WSe2 are known for their large optical absorption coefficient and their potential for high efficiency photovoltaics and photodetectors. Monolayer sheets of these compounds are flexible, stretchable, and soft semiconductors with a direct band gap in contrast to their well-known bulk crystals that are rigid and hard indirect gap semiconductors. Recent intense research has been motivated by the distinct electrical, optical, and mechanical properties of these TMD crystals in the ultimate thickness regime. As a semiconductor with a band gap in the visible to near-IR frequencies, these 2D MX2 materials (M = Mo, W; X = S, Se) exhibit distinct excitonic absorption and emission features. In this Account, we discuss how optical spectroscopy of these materials allows investigation of their electronic properties and the relaxation dynamics of excitons. We first discuss the basic electronic structure of 2D TMDs highlighting the key features of the dispersion relation. With the help of theoretical calculations, we further discuss how photoluminescence energy of direct and indirect excitons provide a guide to understanding the evolution of the electronic structure as a function of the number of layers. We also highlight the behavior of the two competing conduction valleys and their role in the optical processes. Intercalation of group 6 TMDs by alkali metals results in the structural phase transformation with corresponding semiconductor-to-metal transition. Monolayer TMDs obtained by intercalation-assisted exfoliation retains the metastable metallic phase. Mild annealing, however, destabilizes the metastable phase and gradually restores the original semiconducting phase. Interestingly, the semiconducting 2H phase, metallic 1T phase, and a charge-density-wave-like 1T' phase can coexist within a single crystalline monolayer sheet. We further discuss the electronic properties of the restacked films of chemically exfoliated MoS2. Finally, we focus on the strong optical absorption and related exciton relaxation in monolayer and bilayer MX2. Monolayer MX2 absorbs as much as 30% of incident photons in the blue region of the visible light despite being atomically thin. This giant absorption is attributed to nesting of the conduction and valence bands, which leads to diversion of optical conductivity. We describe how the relaxation pathway of excitons depends strongly on the excitation energy. Excitation at the band nesting region is of unique significance because it leads to relaxation of electrons and holes with opposite momentum and spontaneous formation of indirect excitons.

Fluorescence-based approaches towards the assessment of structural and functional alterations in lysosomes and vacuoles induced by lactoferrin and acetic acid

Dissertação de mestrado em Biofísica e Bionanossistemas

Structure dependent resistivity and dielectric characteristics of tantalum oxynitride thin films produced by magnetron sputtering

tThe main purpose of this work is to present and to interpret the change of electrical properties of TaxNyOzthin films, produced by DC reactive magnetron sputtering. Some parameters were varied during deposi-tion: the flow of the reactive gases mixture (N2and O2, with a constant concentration ratio of 17:3); thesubstrate voltage bias (grounded, −50 V or −100 V) and the substrate (glass, (1 0 0) Si or high speed steel).The obtained films exhibit significant differences. The variation of the deposition parameters inducesvariations of the composition, microstructure and morphology. These differences cause variation of theelectrical resistivity essentially correlated with the composition and structural changes. The gradualdecrease of the Ta concentration in the films induces amorphization and causes a raise of the resistivity.The dielectric characteristics of some of the high resistance TaxNyOzfilms were obtained in the sampleswith a capacitor-like design (deposited onto high speed steel, with gold pads deposited on the dielectricTaxNyOzfilms). Some of these films exhibited dielectric constant values higher than those reported forother tantalum based dielectric films.

Composition and structure variation for magnetron sputtered tantalum oxynitride thin films, as function of deposition parameters

Tantalum oxynitride thin films were produced by magnetron sputtering. The films were deposited usinga pure Ta target and a working atmosphere with a constant N2/O2ratio. The choice of this constant ratiolimits the study concerning the influence of each reactive gas, but allows a deeper understanding of theaspects related to the affinity of Ta to the non-metallic elements and it is economically advantageous.This work begins by analysing the data obtained directly from the film deposition stage, followed bythe analysis of the morphology, composition and structure. For a better understanding regarding theinfluence of the deposition parameters, the analyses are presented by using the following criterion: thefilms were divided into two sets, one of them produced with grounded substrate holder and the otherwith a polarization of −50 V. Each one of these sets was produced with different partial pressure of thereactive gases P(N2+ O2). All the films exhibited a O/N ratio higher than the N/O ratio in the depositionchamber atmosphere. In the case of the films produced with grounded substrate holder, a strong increaseof the O content is observed, associated to the strong decrease of the N content, when P(N2+ O2) is higherthan 0.13 Pa. The higher Ta affinity for O strongly influences the structural evolution of the films. Grazingincidence X-ray diffraction showed that the lower partial pressure films were crystalline, while X-rayreflectivity studies found out that the density of the films depended on the deposition conditions: thehigher the gas pressure, the lower the density. Firstly, a dominant -Ta structure is observed, for lowP(N2+ O2); secondly a fcc-Ta(N,O) structure, for intermediate P(N2+ O2); thirdly, the films are amorphousfor the highest partial pressures. The comparison of the characteristics of both sets of produced TaNxOyfilms are explained, with detail, in the text.

Optical properties of zirconium oxynitride films: the effect of composition, electronic and crystalline structures

tThis work is devoted to the investigation of zirconium oxynitride (ZrOxNy) films with varied opticalresponses prompted by the variations in their compositional and structural properties. The films wereprepared by dc reactive magnetron sputtering of Zr, using Ar and a reactive gas mixture of N2+ O2(17:3).The colour of the films changed from metallic-like, very bright yellow-pale and golden yellow, for low gasflows to red-brownish for intermediate gas flows. Associated to this colour change there was a significantdecrease of brightness. With further increase of the reactive gas flow, the colour of the samples changedfrom red-brownish to dark blue or even to interference colourations. The variations in composition dis-closed the existence of four different zones, which were found to be closely related with the variationsin the crystalline structure. XRD analysis revealed the change from a B1 NaCl face-centred cubic zirco-nium nitride-type phase for films prepared with low reactive gas flows, towards a poorly crystallizedover-stoichiometric nitride phase, which may be similar to that of Zr3N4with some probable oxygeninclusions within nitrogen positions, for films prepared with intermediate reactive gas flows. For highreactive gas flows, the films developed an oxynitride-type phase, similar to that of -Zr2ON2with someoxygen atoms occupying some of the nitrogen positions, evolving to a ZrO2monoclinic type structurewithin the zone where films were prepared with relatively high reactive gas flows. The analysis carriedout by reflected electron energy loss spectroscopy (REELS) revealed a continuous depopulation of thed-band and an opening of an energy gap between the valence band (2p) and the Fermi level close to 5 eV.The ZrN-based coatings (zone I and II) presented intrinsic colourations, with a decrease in brightness anda colour change from bright yellow to golden yellow, red brownish and dark blue. Associated to thesechanges, there was also a shift of the reflectivity minimum to lower energies, with the increase of thenon-metallic content. The samples lying in the two last zones (zone III, oxynitride and zone IV, oxide films)revealed a typical semi-transparent-optical behaviour showing interference-like colourations only dueto the complete depopulation of the d band at the Fermi level. The samples lying in these zones presentedalso an increase of the optical bandgap from 2 to 3.6 eV.

Thin films composed of Ag nanoclusters dispersed in TiO2: Influence of composition and thermal annealing on the microstructure and physical responses

Noble metal powders containing gold and silver have been used for many centuries, providing different colours in the windows of the medieval cathedrals and in ancient Roman glasses. Nowadays, the interest in nanocomposite materials containing noble nanoparticles embedded in dielectric matrices is related with their potential use for a wide range of advanced technological applications. They have been proposed for environmental and biological sensing, tailoring colour of functional coatings, or for surface enhanced Raman spectroscopy. Most of these applications rely on the so-called localised surface plasmon resonance absorption, which is governed by the type of the noble metal nanoparticles, their distribution, size and shape and as well as of the dielectric characteristics of the host matrix. The aim of this work is to study the influence of the composition and thermal annealing on the morphological and structural changes of thin films composed of Ag metal clusters embedded in a dielectric TiO2 matrix. Since changes in size, shape and distribution of the clusters are fundamental parameters for tailoring the properties of plasmonic materials, a set of films with different Ag concentrations was prepared. The optical properties and the thermal behaviour of the films were correlated with the structural and morphological changes promoted by annealing. The films were deposited by DC magnetron sputtering and in order to promote the clustering of the Ag nanoparticles the as-deposited samples were subjected to an in-air annealing protocol. It was demonstrated that the clustering of metallic Ag affects the optical response spectrum and the thermal behaviour of the films.

Evolution of the functional properties of titanium–silver thin films for biomedical applications: Influence of in-vacuum annealing

In this work, the thermal stability of TiAgx thin films, deposited by magnetron sputtering, was evaluated, envisaging their application in biomedical devices, namely as electrodes for biosignal acquisition. Based on the composition and microstructural characterization, a set of four representative TiAgx thin films was selected in order to infer whether they are thermally stable in terms of functional properties. In order to achieve this purpose, the structural and morphological evolution of the films with annealing temperature was correlated with their electrical, mechanical and thermal properties. Two distinct zones were identified and two samples from each zone were extensively analysed. In the first zone (zone I), Ti was the main component (Ti-rich zone) while in the second, zone II, the Ag content was more significant. The selected samples were annealed in vacuum at four different temperatures up to 500 oC. For the samples produced within zone I, small microstructural changes were observed due to the recrystallization of the Ti structure and grain size increment. Also, no significant changes were observed with annealing temperature regarding the f l ’ functional properties, being thermally stable up to 500 oC. For higher Ag contents (zone II) the energy supplied by thermal treatments was sufficient to activate the crystallization of Ti-Ag intermetallic phases. A strong increase of the grain size of these phases was also reported. The structural and morphological organization proved to be determinant for the physical responses of the TiAgx system. The hardness and Y g’s modulus were significantly improved with the formation of the intermetallic phases. The silver addition and annealing treatments also played an important role in the electrical conductivity of the films, which was once again improved by the formation of Ti-Ag phases. The thermal diffusivity of the films was practically unchanged with the heat-treatment. This set of results shows that this intermetallic-like thin film system has good thermal stability up to high temperatures (as high as 500 oC), which in case of the highest Ag content zone is particularly evident for electrical and mechanical properties, showing an important improvement. Hardness increases about three times, while resistivity values become half of those from the lowest Ag contents zone. These set of characteristics are consistent with the targeted applications, namely in terms of biomedical sensing devices.

A gestão de recursos humanos nas pequenas e médias empresas em Portugal: Definição de um modelo de atuação

Tese de Doutoramento em Ciências Empresariais

A estimulação cognitiva através da aprendizagem mediada: uma proposta de promoção das habilidades cognitivas em crianças de meio social desfavorecido

Partindo de dois referenciais teóricos da inteligência, psicométrico e cognitivo, esta tese centra-se no conceito de modificabilidade cognitiva e nos programas de estimulação (treino) cognitiva. Em particular é feita uma descrição detalhada do Programa de Enriquecimento Instrumental-PEI (Feuerstein et al., 1980), nomeadamente alguns conceitos centrais à sua fundamentação e implementação, por exemplo a experiência de aprendizagem mediada, o mapa cognitivo e a modificação cognitiva estrutural, pois que foi o programa considerado no nosso estudo empírico. Em termos empíricos procedemos à aplicação do PEI (tarefa de organização de pontos) junto de um grupo de crianças de 10 a 13 anos, do 4º ano do ensino fundamental, provenientes de um meio sociocultural desfavorecido. Este grupo representava a globalidade de uma turma da escola escolhida (25 crianças), havendo uma outra turma similar da mesma escola que serviu de grupo de comparação (26 crianças). O plano experimental inclui uma avaliação de pré-teste e pósteste com provas cognitivas e de leitura. Igualmente foi considerado o rendimento escolar das crianças, acrescentando-se no grupo experimental uma avaliação mais qualitativa assente nas funções cognitivas, atitudes e comportamentos das crianças ao longo da realização das atividades propostas no programa de estimulação cognitiva. Os resultados obtidos apontam para um efeito benéfico do programa quando comparamos as crianças do grupo experimental e de controlo no pós-teste em termos das habilidades cognitivas e numa das provas de leitura. Igualmente se observam melhorias nas suas funções cognitivas, atitudes e comportamentos de implicação na realização das tarefas ao longo do programa, registando-se uma melhoria do pré-teste para o pós-teste no rendimento académico, contudo esta melhoria ocorre igualmente no grupo de controlo. Estes resultados são discutidos à luz da investigação sobre os programas de treino cognitivo, e em particular do PEI, retirando-se ilações para a prática educativa e para a continuidade da investigação nesta área.

A integração de técnicas BIM (Building Information Modeling) no projeto e na construção de estruturas de madeira

Dissertação de mestrado integrado em Engenharia Civil