In-situ X-ray diffraction studies during growth of Ni-Ti shape memory alloy films and their complementary ex-situ characterization

Shape Memory Alloy (SMA) Ni-Ti films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. Thus, the main challenge is not only the control of the microstructure, including stoichiometry and precipitates, but also the identification and control of the preferential orientation since it is a crucial factor in determining the shape memory behaviour. The aim of this PhD thesis is to study the optimisation of the deposition conditions of films of Ni-Ti in order to obtain the material fully crystallized at the end of the deposition, and to establish a clear relationship between the substrates and texture development. In order to achieve this objective, a two-magnetron sputter deposition chamber has been used allowing to heat and to apply a bias voltage to the substrate. It can be mounted into the six-circle diffractometer of the Rossendorf Beamline (ROBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, enabling an in-situ characterization by X-ray diffraction(XRD) of the films during their growth and annealing. The in-situ studies enable us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters on the structural characteristics of the deposited film. Besides the in-situ studies, other complementary ex-situ characterization techniques such as XRD at a laboratory source, Rutherford backscattering spectroscopy(RBS), Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (X-TEM), scanning electron microscopy (SEM), and electrical resistivity (ER) measurements during temperature cycling have been used for a fine structural characterization. In this study, mainly naturally and thermally oxidized Si(100) substrates, TiN buffer layers with different thicknesses (i.e. the TiN topmost layer crystallographic orientation is thickness dependent) and MgO(100) single crystals were used as substrates. The chosen experimental procedure led to a controlled composition and preferential orientation of the films. The type of substrate plays an important role for the texture of the sputtered Ni-Ti films and according to the ER results, the distinct crystallographic orientations of the Ni-Ti films influence their phase transformation characteristics.

Auxiliary mechanisms for telerobotics

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Electrotécnica e de Computadores

e-Business: estratégias e modelos

Dissertação apresentada como requisito parcial para obtenção do grau de Mestre em Estatística e Gestão de Informação

Utilização de ligas com memória de forma no controlo de vibrações em estruturas inteligentes de Engenharia Civil

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Civil - Estruturas e Geotecnia

Controlo de vibrações em engenharia civil

Dissertação para obtencão do Grau de Mestre em Engenharia Civil - Perfil Estruturas

Solução de controlo passivo de um passadiço pedonal pré-fabricado, submetido a acções sísmicas

Dissertação para obtenção do Grau de Mestre em Engenharia Civil - Perfil Estruturas

Evolution of Diplodocid Sauropod dinosaurs with emphasis on specimens from Howe Ranch, Wyoming (USA)

Diplodocidae are among the best known sauropod dinosaurs. Several species were described in the late 1800s or early 1900s. Since then, numerous additional specimens were recovered in the USA, Tanzania, Portugal, as well as possibly Spain, England, and Asia. To date, the clade includes about 12 to 15 different species, some of them with questionable taxonomic status (e.g. ‘Diplodocus’ hayi or Dyslocosaurus polyonychius). However, intrageneric relationships of the multi-species, iconic genera Apatosaurus and Diplodocus are still poorly known. The way to resolve this issue is a specimen-based phylogenetic analysis, which was done for Apatosaurus, but is here performed for the first time for the entire clade of Diplodocidae. New material from different localities and stratigraphic levels on the Howe Ranch (Shell,Wyoming, USA) sheds additional light on the evolution of Diplodocidae. Three new specimens are described herein, considerably increasing our knowledge of the anatomy of the group. The new specimens (SMA 0004, SMA 0011, and SMA 0087) represent two, to possibly three new diplodocid species. They preserve material from all parts of the skeleton, including two nearly complete skulls, as well as fairly complete manus and pedes, material which is generally rare in diplodocids. Thereby, they considerably increase anatomical overlap between the sometimes fragmentary holotype specimens of the earlier described diplodocid species, allowing for significant results in a specimenbased phylogenetic analysis. Furthermore, clavicles and interclavicles are identified, the latter for the first time in dinosaurs. Their presence seems restricted to early sauropods, flagellicaudatans, and early Macronaria, and might thus be a retained plesiomorphy, with the loss of these bones being synapomorphic for Titanosauriformes and possibly Rebbachisauridae. The new material allows to test previous hypotheses of diplodocid phylogeny. In order to do so, any type specimen previously proposed to belong to Diplodocidae was included in the study, as are relatively complete referred specimens, in order to increase the degree of overlapping material. For specimens subsequently suggested to be non-diplodocid sauropods, their hypothesized sister taxa were included as outgroups. The current phylogenetic analysis thus includes 76 operational taxonomic units, 45 of which belong to Diplodocidae. The specimens were scored for 477 morphological characters, representing one of the most extensive phylogenetic analyses done within sauropod dinosaurs. The resulting cladogram recovers the classical arrangement of diplodocid relationships. Basing on a newly developed numerical approach to reduce subjectivity in the decision of specific or generic separation, species that have historically been included into well-known genera like Apatosaurus or Diplodocus, were detected to be actually generically different. Thereby, the famous genus Brontosaurus is resuscitated, and evidence further suggests that also Elosaurus parvus (previously referred to Apatosaurus) or ‘Diplodocus’ hayi represent unique genera. The study increases our knowledge about individual variation, and helps to decide how to score multi-species genera. Such a specimen-based phylogenetic analysis thus proves a valuable tool to validate historic species in sauropods, and in paleontology as a whole.

Sistemas geotérmicos de baixa entalpia estudos de caracterização térmica

A crescente atenção revelada pelas sociedades nos últimos anos, no que respeita à sustentabilidade energética do planeta, tornou-se o principal impulsionador para o desenvolvimento de formas de exploração de energia que contribuem para a redução dos gases com efeito de estufa. A energia geotérmica de baixa entalpia (Shallow Geothermal Energy–SGE) é um dos tipos de energia verde utilizados para aquecimento e arrefecimento de edifícios. Nas últimas décadas, tem vindo a demonstrar uma elevada eficácia energética e aplicabilidade em diversos países em todo o mundo. Aos sistemas convencionais de exploração abertos e fechados, seguiram-se os sistemas com estruturas de fundações termoactivas. A Suíça e Áustria foram os países pioneiros onde se iniciou a exploração utilizando este tipo de estruturas, primeiro com recurso a lajes de fundo e depois, em 1984, através de estacas. A utilização generalizada de fundações de forma bi-funcional poderá resultar numa compensação sustentável dos seus custos de implementação. No entanto, é necessário conhecer de forma sólida o comportamento geotécnico dos solos face à imposição das diferentes acções térmicas provocadas pelos Sistemas Geotérmicos de Baixa Entalpia. A eficácia dos Ground Energy Systems (GES) está directamente associada à capacidade que os solos apresentam para fornecer ou dissipar calor. O desempenho dos GES e a sua eficiência está ainda por avaliar relativamente às condições existentes em Portugal. As propriedades térmicas dos solos são um desses aspectos, sendo da maior relevância na avaliação do seu desempenho. Nesta dissertação são abordados os diferentes mecanismos de transferência de calor nos solos bem como propriedades térmicas necessárias para a sua caracterização. Apresenta-se também um caso prático, para o qual foi realizada caracterização térmica e posterior modelação numérica de uma estrutura termoactiva, determinando-se os campos de temperaturas máximos e mínimos e os fluxos térmicos provocados pelo seu funcionamento.