The modelling of a squirrel-cage induction generator in an oscillating-water-column wave-energy converter

The research is focused on the modelling of a squirrel-cage induction generator in dynamic generation involving ocean-wave energy. The chosen application includes an oscillating water column fitted with a Wells turbine. The modelling approach is based on the evaluation of existing generator models. These include the equivalent steady-state and dynamic models which are considered from a timedomain (differential equation) perspective. Since generation is dynamic in nature, model stability is an important component of model evaluation. The evaluated models provide information regarding the electrical and mechanical operational variables of the generator. Power flow and energy loss between the mechanical and electrical subsystems are easily calculated from these variables. The wave-energy converter excluding the induction generator is not explicitly considered. The generator models are evaluated by considering typical generator inputs which are representative of the given application. These dynamics are reproduced experimentally and in simulations with a comparison of generator response allowing for a conclusion on model performance. Generator inputs include the stator voltage excitation and turbine torque with the generator response given by the stator currents and rotor velocity. Electrical and mechanical power are also considered. Dynamic generation is broken down into two modes of operation: the first mode involves generation for a constant sea state and the second mode involves generator operation for a change in sea state. The dynamics for the first mode involve a set generator speed (set voltage supply) and a sinusoidal prime-mover torque. Dynamics for the second operating mode are not well-defined owing to system variations. Since only the generator model is considered, an informative dynamic is tested providing an indication of possible model performance. The tested dynamic involves a sinusoidally-varying stator frequency and prime-mover torque. The steady-state model considered from a time-domain perspective is found to be unstable for all generating slip values and is, therefore, unsuitable for the given generation application. The dynamic model shows good agreement between experimental and simulated generator response for the two operating modes identified. In conclusion, the model is applicable for a constant sea state with a wave period of up to 0.2 s. Furthermore, it is suspected that the dynamic model is applicable in the case of a change in sea state. Cases involving magnetic saturation and parameter variation are left for future development. The dynamic-model evaluation assumes a balanced stator-voltage excitation – strange electrical transients including electrical faults are not considered. An important simulation consideration involves the quantification of state-variable initial conditions. Initial rotor currents are problematic as these are not easily measured or defined in a practical squirrel-cage rotor construction. The initial rotor currents are approximated by a phasor analysis of the steady-state circuit model at zero time. The use of an inverter-based generator excitation for the experimental work poses an analysis problem owing to the pulse-width-modulation-based voltage supply (not truly sinusoidal). This is solved by considering only the fundamental component of the stator voltage and current. Second-order low-pass filters are used to facilitate such measurements

Searching hit potential antimicrobials in natural compounds space against biofilm formation

Biofilms are communities of microorganisms that can colonize biotic and abiotic surfaces and thus play a significant role in the persistence of bacterial infection and resistance to antimicrobial. About 65% and 80% of microbial and chronic infections are associated with biofilm formation, respectively. The increase in infections by multi-resistant bacteria instigates the need for the discovery of novel natural-based drugs that act as inhibitory molecules. The inhibition of diguanylate cyclases (DGCs), the enzyme implicated in the synthesis of the second messenger, cyclic diguanylate (c-di-GMP), involved in the biofilm formation, represents a potential approach for preventing the biofilm development. It has been extensively studied using PleD protein as a model of DGC for in silico studies as virtual screening and as a model for in vitro studies in biofilms formation. This study aimed to search for natural products capable of inhibiting the Caulobacter crescentus enzyme PleD. For this purpose, 224,205 molecules from the natural products ZINC15 database, have been evaluated through molecular docking and molecular dynamic simulation. Our results suggest trans-Aconitic acid (TAA) as a possible starting point for hit-to-lead methodologies to obtain new inhibitors of the PleD protein and hence blocking the biofilm formation

Forçamento atmosférico de larga escala do clima de agitação marítima na zona económica exclusiva Portuguesa

A presente dissertação de Mestrado, intitulada “Forçamento atmosférico de larga escala do clima de agitação marítima na Zona Económica Exclusiva portuguesa”, pretende estudar a relação entre o clima de agitação marítima na Zona Económica Exclusiva portuguesa (ZEE) e a circulação atmosférica de larga escala. Com recurso aos dados de observações de agitação marítima de boias ondógrafo, disponibilizados pelo Instituto Hidrográfico da Marinha, para período de 1990 a 2012, é efetuada uma primeira análise do clima de agitação marítima junto à costa de Portugal Continental (ao largo de Leixões, Sines e Faro), e a sua relação com o forçamento atmosférico de larga escala, representado pelo índice da oscilação do Altântico Norte (North Atlantic Oscillation – NAO). Posteriormente, é estudado o clima de ondas em toda a ZEE Portuguesa, com utilização de dados de reanálise de ondas (ERA-Interim), no período de 1979 a 2010. É demonstrado que, na ZEE portuguesa, o clima de agitação marítima é influenciado pela circulação atmosférica de larga escala, e que que a NAO exerce mais influência no clima de agitação marítima nos meses de inverno do que nos meses de verão. Os resultados obtidos a partir dos dados das boias permitem concluir que os valores médios dos parâmetros mais representativos da agitação marítima (altura significativa, período médio, período de pico e direcção média de propagação) no regime NAO positivo são, de um modo geral, superiores e de setores mais de Norte relativamente aos encontrados no regime NAO negativo. No inverno, estes valores são mais elevados nos períodos de regime NAO positivo, e mais baixos nos períodos de regime NAO negativo. Por outro lado, no verão, são mais elevados nos períodos de regime NAO negativo, e mais baixos nos períodos de regime NAO positivo. Relativamente à variabilidade dos parâmetros, verifica-se que é mais elevada nos meses de Outono e Inverno, e é tanto maior quanto maior for a latitude. Os valores extremos dos parâmetros são mais elevados à medida que a latitude vai aumentando, atingindo o seu máximo nos meses de inverno. Por outro lado, quando a latitude é mais baixa, os valores extremos deixam de estar associados a regime NAO positivo, passando a estar associados a regime NAO negativo. Os dados da reanálise permitem concluir que, a NAO exerce mais influência no clima de agitação marítima no inverno do que no verão. No inverno, os valores dos parâmetros são em média superiores em períodos de regime NAO positivo, e inferiores em regime NAO negativo. Nos meses de verão, a influência da NAO não é tão perceptível.This thesis, entitled “Large scale atmospheric forcing of the wave climate at the Portuguese Exclusive Economic Zone” studies the relationship between the wave climate at the Portuguese Exclusive Economic Zone (EEZ), and the large scale atmospheric circulation. Using data from buoy observations, available at the portuguese Navy’s Hidrographic Institute, from 1990 to 2012, a first analysis of the wave climate near the continental Portuguese coast (offshore Leixões, Sines and Faro) and its relationship with the large scale atmospheric forcing, represented by the North Atlantic Oscillation (NAO) index, is carried on. Then, the wave climate is studied in the all Portuguese EEZ, with the use of wave reanalysis data (ERA-Interim), from 1979 to 2010. It is shown that, in the Portuguese EEZ, the wave climate is affected by the large scale atmospheric circulation, and that NAO is more influent in the wave climate during the winter months, rather than in the summer. The results from buoys allow us to conclude that mean values, from the most representative wave parameters (significant wave height, mean period, peak period and mean wave direction), at a positive NAO phase, are generally higher and from northern sectors, comparatively to the ones found at a negative NAO phase. In the winter, these values are higher at the positive NAO phase and lower during the negative NAO phase. In the summer, they are usually higher during the negative NAO phase and lower during positive NAO phase. In what respects to wave parameters variability, it is shown that it is greater during autumn and winter, and increases when the latitude is superior. Regarding extreme values these are higher when the latitude increases and peak in the winter. On the other hand, when at low latitude, the extreme values are no longer associated to a positive NAO phase, being associated to a negative NAO phase. The results from reanalysis data allowed us to conclude that NAO is more influent during winter months, rather than during the summer. Still, in the winter, parameters values are, on average, higher during positive NAO phase, and lower during negative NAO phase. In the summer, NAO influence is not so much perceptible

Projeto e construção de pórtico rolante para soldadura robotizada

Mestrado em Engenharia MecânicaEste trabalho descreve o processo de elaboração do projeto mecânico e construção mecânica de um pórtico para o suporte de robots destinados à soldadura de grandes estruturas metálicas. Com este equipamento, a Motofil Robotics fica dotada de soluções capazes de responder à solicitação dos seus clientes. Numa primeira fase do projeto foram abordadas as seguintes questões: definição das solicitações que atuam sobre a estrutura e anteprojeto das secções, onde são definidas as dimensões gerais das vigas que irão servir suporte aos robots. A estrutura do pórtico foi modelada em 3D com recurso ao software CATIA V5. Tirando partido das capacidades do software foi analisado o comportamento dos elementos do pórtico sob ação de cargas estáticas através do método dos elementos finitos e alterada a sua geometria de forma a atingir os apertados critérios de flexão. Na soldadura de grandes estruturas é frequente recorrer à técnica de balanceamento ou weaving dos cordões de soldadura. Esta técnica permite minimizar o número de cordões (passagens) para executar a junta soldada. O movimento de balanceamento é caracterizado por ser um movimento oscilatório que pode transmitir vibrações ao longo da estrutura e provocar o fenómeno de ressonância. Procedeu-se então a uma análise das frequências naturais de vibração e respetivos modos de deformação de forma a garantir a segurança de operação da máquina. Por fim, executou-se o cálculo dos conjuntos de potência (motor, redutor e pinhão) responsáveis pelos movimentos dos 4 eixos do pórtico.This thesis describes the design and construction of a robotic welding gantry intended to weld large steel structures in order to provide Motofil Robotics with solutions capable to respond it costumers demands. In the first phase of this thesis were discussed the following issues: definition of loads presents on the structure and definition overall dimensions of the sections that will serve to support the robots. The 3D modeling of the gantry was done using the CATIA V5 software. Taking advantage the software capabilities the behavior of the structure elements under static loads was analyzed. It served as inputs to apply geometric changes to achieve the small bending criteria. When welding large steel structures it is often necessary to apply a weaving movement to obtain weld seams with one single pass of the robot. The weaving movement is characterized as an oscillatory movement that can transmit vibrations along the structure and cause resonance phenomenon. Due to this reason the natural frequencies and the vibration modes where simulated to ensure the machine safe operation. Finally the calculations of the power units (servomotor, gear unit and pinion) responsible for the axis movements were done

José Sebastião e Silva (1914-1972)

A short biographical note about José Sebastião e Silva (1914-1972), one of the most distinguished portuguese mathematicians ever

Reabilitação de pavimentos utilizando misturas betuminosas com betumes modificados

Na reabilitação estrutural do pavimento do lanço CRIL-Loures da A8, a Auto-Estradas do Atlântico utilizou duas soluções distintas de reforço recorrendo a misturas betuminosas com betumes modificados. No sentido Norte-Sul foi utilizada uma mistura betuminosa com betume modificado com borracha reciclada de pneus usados (BMB) e no sentido Sul-Norte foi utilizada uma mistura betuminosa com um betume modificado com polímeros (SBS). O betume com polímeros foi utilizado num betão betuminoso aplicado com 5 cm de espessura e o betume modificado com borracha foi utilizado numa mistura betuminosa aberta aplicada com uma espessura de 2 cm. Após quatro anos em serviço foi realizado um estudo para determinar as características mecânicas das misturas betuminosas aplicadas de modo a avaliar a sua qualidade e obter indicações relativamente ao seu desempenho futuro. Para a realização deste trabalho foram retiradas lajes dos trechos experimentais que permitiram a avaliação laboratorial do módulo de deformabilidade, da resistência à fadiga e da resistência à deformação permanente. Este trabalho permitiu concluir que, em termos de comportamento mecânico, a mistura BMB, com apenas 2 cm de espessura apresenta uma resistência à fadiga e à deformação permanente superior à mistura SBS aplicada com 5 cm de espessura

PERFORMA'15: abstracts of the International Conference on Musical Performance

Abstracts of the International Conference on Musical Performance

Kinetics and thermodynamics of poly (9,9-dioctylfluorene) beta-phase formation in dilute solution

Poly(9,9-dioctylfluorene) (PFO) adopts a particular type of conformation in dilute solutions of the poor solvent methylcyclohexane (MCH) below 273 K, which is revealed by the appearance of a red-shifted absorption peak at 437−438 nm. The formation of this ordered conformation depends on the temperature but is independent of polymer concentration over the range studied (3−25 μg/mL). On the basis of absorption, steady-state, and time-resolved fluorescence data, the new absorption peak at 437−438 nm is assigned to a highly ordered conformation of PFO chains, analogous to the so-called β-phase first identified in PFO films. From the study of PFO solutions in MCH as a function of temperature, we conclude that these ordered segments (β-conformation) coexist with less ordered domains in the same chain. When the ordered domains are present, they act as efficient energy traps and the fluorescence from the disordered regions is quenched. The transition between the disordered and the ordered PFO conformations is adequately described by a mechanism that involves two steps:  a first, essentially intramolecular, one from a relatively disordered (α) to an ordered conformation (β), followed by aggregation of chains containing β-conformation into anisotropic ordered domains. From the temperature dependence of the 437−438 nm peak intensity, the transition temperature Tβ = 261 K, enthalpy ΔHβ = −18.0 kcal mol-1, and entropy ΔSβ = −68.4 cal K-1 mol-1 were obtained. The formation of the β-conformation domains were also followed as a function of time at 260 K. The rate constants at 260 K were determined, showing an order of magnitude around 10-3 s-1 (kα→β = 5.9 × 10-4 s-1; kβ→α = 9 × 10-4 s-1; kagg = 2.3 × 10-3 M-1 s-1; kdiss = 4.4 × 10-4 s-1). This small magnitude explains the long times required for a “complete” conversion to the β-conformation

POPs’ effect on cardiometabolic and inflammatory profile in a sample of women with obesity and hypertension

Persistent organic pollutants (POPs) are man-made compounds with metabolic disruption impact. We investigated the effect of POP exposure in the cardiometabolic and inflammatory profile in a population of women with obesity and hypertension. In 43 premenopausal women (22 treated vs. 21 nontreated) undergoing bariatric surgery, blood and adipose tissue samples (visceral (vAT) and abdominal subcutaneous (scAT)) were collected. Median concentrations of ∑HCH and ∑POPs in vAT were significantly higher in treated women. VAT ∑HCH and scAT ∑HCH and ∑POPs concentrations were positively correlated with systolic blood pressure in the non-treated group. Our findings suggest that exposure to POPs and its accumulation in vAT and circulating in plasma may be associated to a higher cardiovascular risk in women with obesity and hypertension, with or without antihypertensive treatment.This work was supported by FCT (Fundo Social Europeu, Programa Operacional Potencial Humano da EU (POPH); PEst-OE/SAU/UI0038/2011; SFRH/BD/46640/2008, SFRH/BD/64691/2009), and Projetos de Investigação na Pré-graduação 2011, Universidade do Porto.info:eu-repo/semantics/publishedVersio

Dietary Exposure to Toxic Metals (Cd, Pb and Hg) from Cereals Marketed in Madeira and the Azores

ABSTRACT: Cereals and cereal-based foods continue to be basic foods in all diets. Despite being known for their high nutritional value; they can also contain contaminants (hazards) such as toxic metals. This study assesses the Cd, Pb and Hg dietary exposure from cereals and derivatives marketed in Madeira and the Azores and characterizes the risks by evaluating the Cd and Hg intake contributions to the tolerable intakes and by estimating the Margin of Exposure (MOE) in the case of Pb. In Madeira, metals follow the descending order of Cd > Pb > Hg. Cd stands out as having the highest levels (0.307 mg Cd/kg in oats; 0.237 mg/kg in rye). High levels of Pb (0.347 mg/kg) were also detected in rye. Regarding total mercury, rice stands out (0.0013 mg/kg) followed by wheat (0.001 mg/kg). While all cereals and derivatives except maize consumed in Madeira exceed the maximum value of Cd allowed by the EU, 50.0% of the rye and 25.0% of the corn flour samples exceeded the European Pb limit. The daily consumption of 100 g of oats, rye flour and rye represent high contributions to the TWI of Cd (93.2 – 120%). The MOE values of Pb from the consumption of rye (100 g/day) are 1,294 (nephrotoxic effects) and 3,082 (cardiotoxic effects). In the Azores, corn flour (0.72 mg Pb/kg) stands out with 85.7% of the samples exceeding the maximum Pb EU limit and MOE values of 626 (nephrotoxic effects) and 1,490 (cardiotoxic effects). Regular daily consumption of corn flour makes a low (< 10%) contribution to the Cd TDI. In conclusion, the Pb exposure from the consumption of cereals and derivatives could have toxic effects such as nephrotoxicity or cardiotoxicity in adults. The results highlight the need to set up monitoring and surveillance programs for the safety of cereals and their derivatives in Madeira and the Azores in terms of lead and cadmium.info:eu-repo/semantics/publishedVersio