Gas tungsten arc welding of NiTi shape memory alloy

Shape memory alloys are characterized by the ability of recovering their initial shape after being deformed and by superelasticity. Since the discovery of these alloys, a new field of interest emerged not only for the scientific community but also to many industries. However, these alloys present poor machinability which constitute a constrain in the design of complex components for new applications. Thus, the demand for joining techniques able to join these alloys without compromising their properties became of great importance to enlarge the complexity of existing applications. Literature shows that these alloys are joined mainly using laser welding. In the present study, similar NiTi butt joints, were produced using TIG welding. The welds were performed in 1.5 mm thick plates across the rolling direction. A special fixture and gas assist device was designed and manufactured. Also a robot arm was adapted to accommodate the welding torch to assure the repeatability of the welding parameters. Welds were successfully achieved without macroscopic defects, such as pores and distortions. Very superficial oxidation was seen on the top surface due to insufficient shielding gas flow on the weld face. The welded joints were mechanically tested and structurally characterized. Testing methods were used to evaluate macro and microstructure, as well as the phase transformation temperatures, the mechanical single and cyclic behaviour and the shape recovery ability. Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), microhardness measurements were techniques also used to evaluate the welded joints. A depletion in Ni in the fusion zone was seen, as well as a shift in Ms temperature. For strain values of 4% the accumulated irrecoverable strain was of about 30% and increased with the strain imposed during cycling. Nevertheless, a complete recovery of initial shape was observed when testing the shape memory effect on a dedicated device that introduces a deformation of 6.7%. That is, the welding procedure does not remove the ability of the specimens to recover their initial shape.

Exposição a ozono em cabinas de avião

RESUMO - O ozono é o principal componente da poluição fotoquímica do ar. Como agente irritante do aparelho respiratório, os seus efeitos sobre a saúde caracterizam-se, essencialmente, por tosse, dispneia, desconforto torácico e alterações da função pulmonar, encontrando-se também associadas à exposição ambiental a O3 tanto uma maior frequência e gravidade de crises de asma como a ocorrência de quadros clínicos de irritação conjuntival. É sobretudo a partir dos anos 50, com a descoberta de concentrações elevadas de ozono em ambientes de trabalho respeitantes à actividade de soldadura «a arco», que aquele gás passa a ser encarado como factor profissional de risco. No início dos anos 60 surgem os primeiros estudos de exposição a O3 em cabinas de avião, suscitados pela ocorrência, em tripulantes e passageiros, de queixas clínicas de irritação do tracto respiratório. Esta sintomatologia era, até então, atribuída à acção de outros factores, designadamente o sistema de ventilação e o baixo teor de humidade do ar. Posteriormente, alguns estudos revelaram que, em voos comerciais subsónicos, os teores elevados de O3 observados no interior das cabinas poderiam ser provocados pela sua insuficiente destruição nos sistemas de entrada de ar.O presente estudo, efectuado em voos de longo curso realizados em aeronaves Airbus A340-300 numa única rota comercial, teve por objectivo avaliar a exposição a ozono no ar interior em cabina de avião. Os teores médios de concentração de ozono observados foram inferiores aos valores susceptíveis de provocarem efeitos adversos sobre o aparelho respiratório. Como valor máximo instantâneo, foi atingida a concentração de 152 ppb. Adicionalmente, foi constatada a influência das estações do ano nos teores de O3. O conjunto dos resultados obtidos permite concluir que as concentrações de ozono no ar interior nas cabinas de avião estudadas são inferiores às correspondentes concentrações máximas admissíveis, tendo, em todos os voos, sido observado o cumprimento da norma da FAA respeitante à protecção da exposição ao ozono em cabinas de aeronaves de aviação comercial.

Laser welding of shape memory alloys

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

Magnetic pulse welding

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Mecânica

Metabolic flux analysis of neural cell metabolism in primary cultures

Dissertation presented to obtain the Ph.D degree in Biochemistry, Neuroscience

Estudo dosimétrico para implementação da técnica radioterapêutica volumetric modulated arc therapy (VMAT)

Dissertação para obtenção do Grau de Mestre em Engenharia Biomédica

Production of aluminium based composites reinforced with embedded NiTi by friction stir welding

Dissertação para a obtenção do grau de Mestre em Engenharia Mecânica

Flexural strengthening by means of a arc overlay in the tension zone

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

Analysis of metabolic flux distributions in relation to the extracellular environment in Avian cells

Continuous cell lines that proliferate in chemically defined and simple media have been highly regarded as suitable alternatives for vaccine production. One such cell line is the AG1.CR.pIX avian cell line developed by PROBIOGEN. This cell line can be cultivated in a fully scalable suspension culture and adapted to grow in chemically defined, calf serum free, medium [1]–[5]. The medium composition and cultivation strategy are important factors for reaching high virus titers. In this project, a series of computational methods was used to simulate the cell’s response to different environments. The study is based on the metabolic model of the central metabolism proposed in [1]. In a first step, Metabolic Flux Analysis (MFA) was used along with measured uptake and secretion fluxes to estimate intracellular flux values. The network and data were found to be consistent. In a second step, Flux Balance Analysis (FBA) was performed to access the cell’s biological objective. The objective that resulted in the best predicted results fit to the experimental data was the minimization of oxidative phosphorylation. Employing this objective, in the next step Flux Variability Analysis (FVA) was used to characterize the flux solution space. Furthermore, various scenarios, where a reaction deletion (elimination of the compound from the media) was simulated, were performed and the flux solution space for each scenario was calculated. Growth restrictions caused by essential and non-essential amino acids were accurately predicted. Fluxes related to the essential amino acids uptake and catabolism, the lipid synthesis and ATP production via TCA were found to be essential to exponential growth. Finally, the data gathered during the previous steps were analyzed using principal component analysis (PCA), in order to assess potential changes in the physiological state of the cell. Three metabolic states were found, which correspond to zero, partial and maximum biomass growth rate. Elimination of non-essential amino acids or pyruvate from the media showed no impact on the cell’s assumed normal metabolic state.