Estudo da Produção de Towpregs e Transformação por Pultrusão

Durante as últimas décadas, os materiais compósitos têm substituído com sucesso os materiais tradicionais em muitas aplicações de engenharia, muito devido às excelentes propriedades que se conseguem obter com a combinação de materiais diferentes. Nos compósitos reforçados com fibras longas ou contínuas tem-se verificado, ao longo dos últimos anos, um aumento do uso de matrizes termoplásticas, fruto de várias vantagens associadas, como o facto de serem bastante mais ecológicas, comparativamente às termoendurecíveis. No entanto, este aumento está muito dependente do desenvolvimento de novas tecnologias de processamento, pois a elevada viscosidade dos termoplásticos, comparativamente aos termoendurecíveis, dificulta significativamente o processo. Muitos equipamentos de produção de termoplásticos são resultado de adaptações de equipamentos de produção de termoendurecíveis, onde normalmente é necessário adicionar fornos de pré-aquecimento. Neste trabalho, pretendeu-se produzir pré-impregnados de fibras contínuas com matriz termoplástica, por deposição a seco de polímero em pó sobre fibras de reforço (denominados por towpreg) para, posteriormente, serem transformados por pultrusão e caracterizados. As matérias-primas utilizadas foram: Polipropileno (PP) como matriz termoplástica e fibra de carbono como reforço. Por forma a melhorar as propriedades finais do compósito, foram otimizadas as condições de processamento na produção dos towpregs, estudando-se a influência da variação dos parâmetros de processamento no teor de polímero presente nestes, tendo como objetivo teores mássicos de polímero superiores a 30%. A condição ótima e a influência dos parâmetros de processamento foram obtidas com o auxílio do Método de Taguchi. Os perfis produzidos por pultrusão foram sujeitos a ensaios de flexão, de forma a obter as suas propriedades quando sujeitos a esse tipo de esforço. Foram também realizados ensaios de calcinação de forma a obter as frações mássicas de fibra e polímero presentes no compósito final. Sabidas as frações mássicas, converteramse em frações volúmicas e obtiveram-se as propriedades teoricamente esperadas através da Lei das Misturas e compararam-se com as obtidas experimentalmente. As propriedades obtidas foram também comparadas com as de outros compósitos pultrudidos.

Information flow analysis using data-dependent logical propositions

Dissertação para obtenção do Grau de Mestre em Engenharia Informática

Optimization of fMRI Processing Parameters for Simutaneous Acquisition of EEG/fMRI in Focal Epilepsy

In the context of focal epilepsy, the simultaneous combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) holds a great promise as a technique by which the hemodynamic correlates of interictal spikes detected on scalp EEG can be identified. The fact that traditional EEG recordings have not been able to overcome the difficulty in correlating the ictal clinical symptoms to the onset in particular areas of the lobes, brings the need of mapping with more precision the epileptogenic cortical regions. On the other hand, fMRI suggested localizations more consistent with the ictal clinical manifestations detected. This study was developed in order to improve the knowledge about the way parameters involved in the physical and mathematical data, produced by the EEG/fMRI technique processing, would influence the final results. The evaluation of the accuracy was made by comparing the BOLD results with: the high resolution EEG maps; the malformative lesions detected in the T1 weighted MR images; and the anatomical localizations of the diagnosed symptomatology of each studied patient. The optimization of the set of parameters used, will provide an important contribution to the diagnosis of epileptogenic focuses, in patients included on an epilepsy surgery evaluation program. The results obtained allowed us to conclude that: by associating the BOLD effect with interictal spikes, the epileptogenic areas are mapped to localizations different from those obtained by the EEG maps representing the electrical potential distribution across the scalp (EEG); there is an important and solid bond between the variation of particular parameters (manipulated during the fMRI data processing) and the optimization of the final results, from which smoothing, deleted volumes, HRF (used to convolve with the activation design), and the shape of the Gamma function can be certainly emphasized.

Numerical Evaluation of Ventilation Performance in Children Day Care Centres

Modelling of ventilation is strongly dependent on the physical characteristics of the building of which precise evaluation is a complex and time consuming task. In the frame of a research project, two children day care centres (CDCC) have been selected in order to measure the envelope air permeability, the flow rate of mechanical ventilation systems and indoor and outdoor temperature. The data obtained was used as input to the computer code CONTAM for ventilation simulations. The results obtained were compared with direct measurements of ventilation flow from short term measurements with CO2 tracer gas and medium term measurements with perfluorocarbon tracer (PFT) gas decay method. After validation, in order to analyse the main parameters that affect ventilation, the model was used to predict the ventilation rates for a wide range of conditions. The purpose of this assessment was to find the best practices to improve natural ventilation. A simple analytical method to predict the ventilation flow rate of rooms is also presented. The method is based on the estimation of wind effect on the room through the evaluation of an average factor and on the assessment of relevant cross section of gaps and openings combined in series or in parallel. It is shown that it may be applied with acceptable accuracy for this type of buildings when ventilation is due essentially to wind action.

Dependence of IVIM-DWI estimations on acquisition parameters

Dissertação para obtenção do Grau de Mestre em Engenharia Biomédica

Target-specific multiphysics modeling for thermal medicine applications

Dissertation to obtain the degree of Doctor of Philosophy in Biomedical Engineering

Rastreio combinado do 1º trimestre e doenças autoimunes : Impacto das variaveis pré-analíticas na avaliação do risco

RESUMO: Contexto: As anomalias congénitas, com particular destaque para as neuploidias , afectam aproximadamente 2% dos recém-nascidos, constituindo causas frequentes de morbilidade e mortalidade. Actualmente, a avaliação do grau de risco para as aneuploidias mais prevalentes (T21, T13, T18) é efectuada através do “Rastreio Combinado do 1º Trimestre”, devendo as grávidas com risco acrescido ser sujeitas a exames invasivos (ex.biópsia das vilosidades coriónicas,amniocentese). Quanto mais qualidade existir num rastreio, menos falsos positivos existirão e menor o número de exames diagnósticos invasivos desnecessários. As doenças autoimunes são doenças inflamatórias crónicas em cuja fisiopatologia se encontram distúrbios da imunidade humoral e celular, dependentes de factores genéticos, hormonais,psicológicos e ambientais. Atingem mais o sexo feminino e durante a idade fértil,podendo influenciar o outcome da gravidez e a saúde neonatal causando significativa morbilidade e mortalidade. O lúpus eritematoso sistémico para além de potencialmente afectado pelas alterações imunoendócrinas fisiológicas da gravidez, associa-se frequentemente a problemas de fertilidade. Recentemente, foi sugerido que as anormalidades ocorridas durante a invasão precoce do sinciciotrofoblasto, resultando em deficiente diferenciação, deficiente maturação e diminuição na produção de hCG, poderão ser o mecanismo fisiopatológico primário para as perdas fetais no primeiro trimestre, nos doentes com SLE. A ocorrência de níveis elevados de hCG total e ß-hCG livre no rastreio para despiste de síndrome de Down do segundo e do primeiro trimestre foi assinalada em grávidas portadoras de lúpus, mas a escassez de estudos comprovativos e a pequena dimensão das amostras estudadas constituiu uma limitação significativa na fidedignidade dos resultados obtidos. Objectivos: O estudo teve como objectivos i. estabelecer valores normativos Portugueses e de distribuição para as MoM’s dos parâmetros séricos do primeiro trimestre, por semana de gestação:(PAPP-A e ß-hCG livre), ii. avaliar a influência que as doenças autoimunes têm sobre as MoM’s individuais dos parâmetros bioquímicos PAPP-A e/ou ß-hCG livre, utilizados no rastreio pré-natal combinado do 1º trimestre, e iii. saber se as doenças autoimunes podem condicionar um aumento da taxa de resultados falsos positivos, com consequente aumento do número de amniocenteses. Metodologia: Estudo longitudinal prospectivo, consistindo num rastreio pré-natal combinado de 1º trimestre para pesquisa de aneuploidias, em duas amostras provenientes do Reino Unido (n= 45,854) e de Portugal (n=3122). Foram avaliados parâmetros socio-demográficos, ecográficos, laboratoriais, e calculados os indicadores de desempenho do rastreio combinado. A execução analítica dos testes bioquímicos séricos (PAPP-A e ß-hCG livre) foi realizada no autoanalisador Brahms Kryptor e no autoanalizador 6000 Delfia Xpress. Compararam-se os grupos autoimune e não autoimune das amostras. Resultados: Relativamente às características populacionais, o grupo auto imune tinha valores significativamente superiores nas variáveis idade materna e idade gestacional. Comparando os grupos com e sem doença autoimune, constatou-se a existência de uma elevação das MoM’s da ß-hCG livre nas grávidas com doença autoimune, nomeadamente nos casos de lúpus eritematoso sistémico. Conclusões: os resultado obtidos reforçam a indicação do rastreio combinado do 1º trimestre certificado pela FMF nas grávidas com doenças autoimunes, nomeadamente para as doentes com LES; no entanto, devem ser calculados e introduzidos factores de correcção no algoritmo de risco, de modo a evitar a subida no número de resultados falso-positivos, e consequentemente a sobre- utilização de métodos invasivos.------------ ABSTRACT: Context: Congenital anomalies, with particular reference to aneuploidias, affect approximately 2% of newborns, and are frequent causes of morbidity and mortality. Currently, the risk evaluation for the most prevalent aneuploidias (T21, T13, T18) is carried out through the “combined first trimester screening”, and pregnant women with increased risk are subjected to invasive tests (e.g. villus biopsy done, amniocentesis). The more quality exists in a screening, less false positives exists and fewer unnecessary invasive diagnostic exams. Autoimmune diseases are chronic inflammatory diseases in whose pathophysiology are immune humoral and cellular disorders, dependent on genetic factors, hormonal, psychological and environmental factors. The disease is more prevalent among females, during the child-bearing age, and may influence the outcome of pregnancy and neonatal health causing significant morbidity and mortality. Lupus Erythematosus in addition to potentially affected by immunoendocrine physiological changes of pregnancy, is often associated with fertility problems. Recently, it has been suggested that the abnormalities that occurred during the early invasion of the syncytiotrophoblast, resulting in insufficient differentiation, deficient maturation and decrease in production of hCG may be the primary pathophysiological mechanism for fetal losses in the first quarter, in patients with SLE. The occurrence of elevated levels of total hCG and free ß-hCG in screening for Down’s syndrome of the second and first trimester was reported in pregnant women with lupus, but the paucity of supporting studies and the small size of the samples studied constituted a significant limitation on the trustworthiness of the results obtained. Objectives: this study aims to i. establish normative values for the serum parameters MoM’s (PAPP-A and free β-hCG) and it’s distribution, in the first trimester, by week of pregnancy; ii. assess the influence that the autoimmune diseases have on the MoM’s of individual biochemical PAPP-A and/or β-hCG, used in antenatal screening combined for the first trimester, and iii. whether the autoimmune diseases may make an increased rate of false positives, with consequent increase in the number of amniocenteses.Methodology: Prospective longitudinal study, consisting of a combined first trimester antenatal screening for aneuploidies lookup in two samples from the United Kingdom (n=45.854) and Portugal (n= 3.122). Socio-demographic, echographic and laboratory parameters were evaluated, and combined screening performance indicators were calculated. The analytical run of serum biochemical tests (PAPP-A and ß-hCG) was held at the Brahms Kryptor and in Delfia Xpress 6000. Comparisons between autoimmune group and non-autoimmune group were made. Results: Relating to population characteristics, the autoimmune group had significantly diferente values in the variables maternal age and gestational age. Comparing the groups with and without autoimmune disease, it was noted that there is an elevation of the MoM’s of free ß-hCG levels in pregnant women with autoimmune disease, particularly in cases of systemic lupus erythematosus. Conclusions: The results obtained reinforce the indication of FMF certified combined screening in pregnant women with autoimmune diseases, notably to the patients with SLE; However, correction factors should be calculated and entered in the risk algorithm, in order to avoid the rise in the number of false positive results, and consequently the over-use of invasive methods.

Landscape composition and climatic parameters significant in the spread of an invasive species (Pine wood Nematode)

Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente

A logical foundation for session-based concurrent computation

Linear logic has long been heralded for its potential of providing a logical basis for concurrency. While over the years many research attempts were made in this regard, a Curry-Howard correspondence between linear logic and concurrent computation was only found recently, bridging the proof theory of linear logic and session-typed process calculus. Building upon this work, we have developed a theory of intuitionistic linear logic as a logical foundation for session-based concurrent computation, exploring several concurrency related phenomena such as value-dependent session types and polymorphic sessions within our logical framework in an arguably clean and elegant way, establishing with relative ease strong typing guarantees due to the logical basis, which ensure the fundamental properties of type preservation and global progress, entailing the absence of deadlocks in communication. We develop a general purpose concurrent programming language based on the logical interpretation, combining functional programming with a concurrent, session-based process layer through the form of a contextual monad, preserving our strong typing guarantees of type preservation and deadlock-freedom in the presence of general recursion and higher-order process communication. We introduce a notion of linear logical relations for session typed concurrent processes, developing an arguably uniform technique for reasoning about sophisticated properties of session-based concurrent computation such as termination or equivalence based on our logical approach, further supporting our goal of establishing intuitionistic linear logic as a logical foundation for sessionbased concurrency.

Improving silicon probe performance through layer-by-layer coating

Fully comprehending brain function, as the scale of neural networks, will only be possi-ble with the development of tools by micro and nanofabrication. Regarding specifically silicon microelectrodes arrays, a significant improvement in long-term performance of these implants is essential. This project aims to create a silicon microelectrode coating that provides high-quality electrical recordings, while limiting the inflammatory response of chronic implants. To this purpose, a combined chitosan and gold nanoparticles coating was produced allied with electrodes modification by electrodeposition with PEDOT/PSS in order to reduce the im-pedance at 1kHz. Using a dip-coating mechanism, the silicon probe was coated and then charac-terized both morphologically and electrochemically, with focus on the stability of post-surgery performance in anesthetized rodents. Since not only the inflammatory response analysis is vital, the electrodes recording degradation over time was also studied. The produced film presented a thickness of approximately 50 μm that led to an increase of impedance of less than 20 kΩ in average. On a 3 week chronic implant, the impedance in-crease on the coated probe was of 641 kΩ, compared with 2.4 MΩ obtained for the uncoated probe. The inflammatory response was also significantly reduced due to the biocompatible film as proved by histological tests.

Modeling and optimization of extracellular polysaccharides production by Enterobacter A47

Polysaccharides are gaining increasing attention as potential environmental friendly and sustainable building blocks in many fields of the (bio)chemical industry. The microbial production of polysaccharides is envisioned as a promising path, since higher biomass growth rates are possible and therefore higher productivities may be achieved compared to vegetable or animal polysaccharides sources. This Ph.D. thesis focuses on the modeling and optimization of a particular microbial polysaccharide, namely the production of extracellular polysaccharides (EPS) by the bacterial strain Enterobacter A47. Enterobacter A47 was found to be a metabolically versatile organism in terms of its adaptability to complex media, notably capable of achieving high growth rates in media containing glycerol byproduct from the biodiesel industry. However, the industrial implementation of this production process is still hampered due to a largely unoptimized process. Kinetic rates from the bioreactor operation are heavily dependent on operational parameters such as temperature, pH, stirring and aeration rate. The increase of culture broth viscosity is a common feature of this culture and has a major impact on the overall performance. This fact complicates the mathematical modeling of the process, limiting the possibility to understand, control and optimize productivity. In order to tackle this difficulty, data-driven mathematical methodologies such as Artificial Neural Networks can be employed to incorporate additional process data to complement the known mathematical description of the fermentation kinetics. In this Ph.D. thesis, we have adopted such an hybrid modeling framework that enabled the incorporation of temperature, pH and viscosity effects on the fermentation kinetics in order to improve the dynamical modeling and optimization of the process. A model-based optimization method was implemented that enabled to design bioreactor optimal control strategies in the sense of EPS productivity maximization. It is also critical to understand EPS synthesis at the level of the bacterial metabolism, since the production of EPS is a tightly regulated process. Methods of pathway analysis provide a means to unravel the fundamental pathways and their controls in bioprocesses. In the present Ph.D. thesis, a novel methodology called Principal Elementary Mode Analysis (PEMA) was developed and implemented that enabled to identify which cellular fluxes are activated under different conditions of temperature and pH. It is shown that differences in these two parameters affect the chemical composition of EPS, hence they are critical for the regulation of the product synthesis. In future studies, the knowledge provided by PEMA could foster the development of metabolically meaningful control strategies that target the EPS sugar content and oder product quality parameters.

Time-dependent flexural behaviour of cracked steel fibre reinforced self-compacting concrete panels

In the present work are described and discussed the results of an extensive experimental program that aims to study the long-term behaviour of cracked steel fibre reinforced self-compacting concrete, SFRSCC, applied in laminar structures. In a first stage, the influence of the initial crack opening level (wcr = 0.3 and 0.5 mm), applied stress level, fibre orientation/dispersion and distance from the casting point, on the flexural creep behaviour of SFRSCC was investigated. Moreover, in order to evaluate the effects of the creep phenomenon on the residual flexural strength, a series of monotonic tests were also executed. It was found that wcr = 0.5 mm series showed a higher creep coefficient comparing to the series with a lower initial crack opening. Furthermore, the creep performance of the SFRSCC was influenced by the orientation of the extracted prismatic specimens regarding the direction of the concrete flow within the cast panel.

The relationship between stem vessel parameters and the development of strata in the early stages of secondary forest succession in Amazonia

In order to compare the development of strata in the early stages of secondary forest succession with vessel parameters of the tree species, a forest inventory was carried out in 4-year (Q1: 48 m2), 11-year (Q2: 400 m2) and 20-year (Q3: 400 m2) forests and vessel parameters were investigated from stem cross sections of 18 species obtained in Q2. Thirty three species (21 families), 77 species (35 families), 39 species (20 families) were found in Ql, Q2, Q3, respectively. The percentage of dead individuals, dead stems and the percentage of individuals with multiple stems increased with time after clear cutting. Also, the total D2H of Q3 was 26.1 times that of Q1, and the development of strata started in Q2 and Q3. The image analysis of vessel size, area and number of vessels revealed that species which reach the forest canopy had a large D2H value, vessel diameter and area, while species which remain near the forest floor had smaller ones. Poecilanthe effusa (Huber) Ducke is an example of the latter case, with a large number of individuals and abundant sprouting of new stems from stumps, but with high mortality.

Analysis of output properties of the Peroxiredoxin/Thioredoxin/Thioredoxin reductase system

Dissertação de mestrado em Bioinformática

Creep behaviour of cracked steel fibre reinforced self-compacting concrete laminar structures

Tese de Doutoramento - Civil Engineering