Gain-lever lasers in optical subcarrier transmission systems

This thesis is concerned with the gain-lever effect in quantum well semiconductor lasers with a view to their application in subcarrier multiplexed fibre optical systems. The increased modulation efficiency and reduced noise figure of the gain-lever laser makes it very attractive for microwave optical transmission. However, their possible application to subcarrier multiplexed systems requires a full assessment of the effects of their intrinsic nonlinearity. With this in view, the first part of the study is dedicated to the modelling of the modulation and noise characteristics of the gain-lever laser based on the single-mode rate equations. These equations also provide an adequate basis for the analysis of the laser intrinsic dynamic nonlinearity. The Volterra series method of nonlinear system theory is then applied to develop analytical models that describe the nonlinear distortion. Both intensity and frequency modulation are useful in gain-lever laser transmitters. Therefore analytical models were developed that account for distortion effects of both the intensity and frequency components of the laser light as well as of a nonlinear optical discriminator. The Volterra theory enables the calculation of both the harmonic and intermodulation distortion power. This measure is used to compare different gain-lever laser transmitters to the conventional DFB laser. Finally, the analytic model is used to investigate both dynamic range constraints and the performance of a gain-lever laser transmitter in a fibre radio subcarrier multiplexed system

Computational modelling of the selective laser sintering process

Dissertação de mestrado integrado em Engenharia de PolímerosA Manufatura Aditiva (AM do inglês Additive Manufacturing) tem ganho popularidade em várias indústrias importantes e exigentes devido à sua capacidade de produzir peças com geometrias complexas e pouco desperdício. Como uma das suas mais populares técnicas, a Sinterização Seletiva a Laser (SLS do inglês Selective Laser Sintering) é muito procurada por diversas indústrias que pretendem substituir processos convencionais mais dispendiosos. No entanto, o processo de SLS é intrinsecamente complexo devido aos vários fenómenos multi-fisícos e são necessários mais estudos para obter uma melhor perceção dos mesmos. Isto tem originado um elevado interesse académico em otimizar o processo para que este cumpra os requisitos industriais. Grande parte destas otimizações são feitas através de métodos experimentais que são demorados, dispendiosos e nem sempre resultam nas configurações ótimas. Este enquadramento tem motivado investigadores a recorrer à modelação computacional com o objetivo de entender melhor o processo, de modo a antecipar e corrigir defeitos. O objetivo principal do presente trabalho foi desenvolver um modelo capaz de simular o processo de SLS para aplicações poliméricas, em código de distribuição livre, à escala do tamanho da partícula. Como são necessárias abordagens distintas para simular com precisão cada etapa do processo, diferentes métodos numéricos foram aplicados para desenvolver uma ferramenta capaz de estudar o impacto, numa secção representativa da cama de pó, dos parâmetros físicos que podem ser ajustados no processo. O trabalho desenvolvido integrou diversas etapas, começando por um estudo extenso dos aspetos teóricos do processo de SLS que visou a familiarização com os fenómenos envolvidos, o desenrolar do processo, os seus parâmetros e respetivas influências, assim como a avaliação das limitações e desafios existentes. Este estudo foi seguido por uma análise detalhada dos modelos mais populares empregues para representar os principais fenómenos associados ao processo e do nível de precisão das abordagens, com base nas simplificações consideradas. Um conjunto de ferramentas computacionais foi posteriormente apresentado e os seus respetivos modelos selecionados, quando possível, de acordo com a revisão bibliográfica efetuada. Por último, vários testes foram executados, visando uma validação experimental qualitativa dos códigos utilzados, para garantir que o modelo em uso era adequado para simular o processo, permitindo o estudo e observação da influência dos principais parâmetros do processo e a evolução da sinterização. Os desenvolvimentos obtidos representam um avanço significativo para a simulação do processo de SLS. Com o uso de software open-source (LIGGGHTS e OpenFOAM), vários estudos foram feitos numa geometria realista e, apesar da ausência de dados experimentais suficientes e mais detalhados, os resultados da simulação mostraram-se bem correlacionados com os usados para comparação. Em suma, o trabalho efetuado permitiu concluir que a ferramenta desenvolvida apresenta um elevado potencial para estudar, com detalhe, o processo de SLS e a influência dos seus parâmetros e, deste modo, contribuir para a sua otimização.Additive Manufacturing (AM) has increased in popularity in numerous important and demanding industries due to the capability of manufacturing parts with complex geometries with little wastage. As one of its most popular techniques, Selective Laser Sintering (SLS) is sought after by several industries that aim to replace conventional and more expensive processes. However, the SLS process is intrinsically complex due to the various underlying multi-physics phenomena and more studies are needed to obtain more insights about it. These has resulted in many academical interests to optimize the process and allow it to achieve industrial standards. Most of these optimization attempts are performed through experimental methods that are time consuming, expensive and do not always provide the optimal configurations. This has lead researchers to resort to computational modelling, aiming at better understanding the process to anticipate and fix the defects. The main objective of the present work was to develop a model capable of simulating the SLS process for polymeric applications, within an open-source framework, at particle length scale. Since distinct approaches are required for accurately simulating each step of the SLS process, different numerical methods were employed to develop a tool capable of studying the impact, in a representative section of the powder bed, of the physical parameters that can be adjusted in the process. The developed work comprised several steps, starting with an extensive study of the theoretical aspects of the SLS process that aimed at the acquaintance with the involved phenomena, process unwind, its parameters and their influence, as well as evaluating the existing limitations and challenges. This study was then followed by a detailed analysis of the most common employed models to represent the major phenomena and of the accuracy level of the approaches, based on the employed simplifications. A set of computational tools was then exhibited and their built in models were selected, when possible, according to the precedent literature review. Lastly, various tests were carried to obtain an experimental qualitative validation of the used code, to assure that the used model was adequate to simulate the process, allowing the study and observation of the principal parameter influence and sintering progression. The achieved developments represent a significant advance towards the SLS process simulation. With the use of open-source software (LIGGGHTS e OpenFOAM), several studies were performed on a realistic geometry and, despite the absence of enough and more detailed experimental data, the simulation results are in agreement with the ones used for comparison. Overall, the accomplished work allowed to conclude that the developed tool constitutes a great potential to study, in detail, the SLS process and its parameters influence and, therefore, contribute to its optimization.Financially, I acknowledge the support of National Funds through FCT - Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2019 and UIDB/04436/2020, and project SIFA - Sistema Inteligente de Fabricação Aditiva (POCI 01-0247-FEDER-047108). I also acknowledge the computing facilities support by Search-ON2: Revitalization of HPC Infrastructure of UMinho (project no. NORTE-07-0162-FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2 -- O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF)

From a simple EHR to the market lead: what technologies to add

Electronic health records (EHRs) can store, capture, and present patient data in an organized way that improves physicians’ workflow and patient care. This makes EHRs key to addressing many of today’s health care challenges. An interdisciplinary review and qualitative study of artificial intelligence, machine learning, natural language processing, and real-time location services in health care was conducted. The results show that in an industry where digitization is key, several recommendations can be made to leverage these technologies in ways that can improve current systems and help EHR vendors become the market lead

From the Solitude of the Metropole to a Horizon of Possibilities

UIDB/04666/2020 UIDP/04666/2020 BPD/107783/2015The purpose of this book is to study the relation between Portuguese colonial art, especially painting, and political power in the contemporary context. The subtlety of suggestions and the complexity of relations that stem from the power of art and the art of power mean that the history of colonial art’s journey is not a univocal narrative but a series of heterogeneous and inter-relational products that emerged in multifarious ways from the metropole and also the overseas possessions. Hence Pintura Colonial Contemporânea [Contemporary Colonial Painting] sets out Da Solidão da Metrópole a um Horizonte de Possibilidades [From the Solitude of the Metropole to a Horizon of Possibilities] in the context of the colonial coming-and-going within a hybrid genealogy formed and developed in antonymic mirrors in which art and travel each needed the other in order to define themselves.publishersversionpublishe

Plasma Sanitizers on Flexible Substrates

Technologies related to low-temperature plasma have gained tremendous importance in recent years due to the numerous advantages they present. These types of treatments allow modifying surfaces without changing their volume properties, in a durable way and according to affordable processes. The mixture of reactive species that cold plasma produces also makes it possible to disinfect surfaces and treat biological tissues. However, the existing cold plasma production techniques are expensive, polluting, and use rigid components that cannot conform to irregular surfaces. To overcome those limitations, this dissertation's objective consists of production, optimization, and testing plasma generators that take advantage of the principle of dielectric barrier discharge (DBD). The generators developed were produced by two methods, a laser made shadow mask and inkjet printing process, and consist of a structure with one or two electrodes. Three different types of paper were used as the DBD dielectric layer: two commercial papers used for printed electronics, Felix Schoeller smart type 3 and Powercoat ™ XD 125, and a third one mostly used for drawing purposes, Canson vegetal paper. It has been proven that generators patterned by a laser made shadow mask and by inkjet printing can generate plasma in a vacuum chamber, in a pressure range of 0.55 to 10.5 Torr (23 to 1400 Pa) and with a power range from 2 to 16W. It is shown that generators with two electrodes can confine plasma better than the ones using a single electrode. Also, it was observed that the gas atmosphere, patterning method, and structure of the paper influences the lifetime of the paper-based generators. Moreover, it was noticed that the generators made with vegetal paper and powercoat XD paper withstand for a longer period of time. The use of plasma generators for surface modification was tested on different surfaces. The wettability of cork, vegetal paper, and spinach leaf surfaces was assessed for different plasma times.As tecnologias relacionadas com o plasma de baixa temperatura ganharam muita importância nos últimos anos devido às inúmeras vantagens que apresentam. Estes tipos de tratamentos permitem modificar superfícies sem alterar suas propriedades em volume, de forma duradoura e de acordo com processos acessíveis. A mistura de espécies reativas que o plasma frio produz também permite desinfetar superfícies e tratar tecidos biológicos. No entanto, as técnicas de produção existentes são caras, poluentes e utilizam componentes rígidos incapazes de se conformar sob as mais diversas irregularidades. Com o intuito de responder às limitações apresentadas, o objetivo da presente dissertação consiste na produção, otimização e teste de geradores de plasma que tiram partido do princípio da descarga de barreira dielétrica (DBD). Os geradores desenvolvidos foram produzidos por gravação de padrões a laser e por impressão a jato de tinta, e são compostos por uma estrutura com um ou dois elétrodos. Três tipos de papeis diferentes foram utilizados como camada dielétrica do DBD, dois papéis comerciais usados para eletrónica impressa, Felix Schoeller smart type 3 e Powercoat ™ XD 125, e um terceiro usado principalmente para desenho (papel vegetal Canson). Foi provado que os geradores padronizados por uma máscara feita a laser e por impressão a jato de tinta podem gerar plasma numa câmara de vácuo segundo uma gama de pressão de 0.55 a 10.5 Torr (23 a 1400 Pa) e com uma gama de potência de 2 a 16W. Comprovou-se também que os geradores com dois elétrodos conseguem confinar melhor o plasma do que os geradores com um único elétrodo. Foi ainda observado que o tipo de gás, o método de padronização e a estrutura do papel influenciam o tempo de vida útil dos geradores. Para além disso, observou-se que os geradores produzidos com papel vegetal e papel powercoat XD conseguem suportar maiores períodos de tempo a gerar plasma. O uso de geradores de plasma para modificação de superfície foi testado em diferentes superfícies. A molhabilidade das superfícies da cortiça, do papel vegetal e das folhas de espinafre foi avaliada para diferentes tempos de plasma

Association of radio polar cap brightening with bright patches and coronal holes

Radio-bright regions near the solar poles are frequently observed in Nobeyama Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal holes. However, the origin of these polar brightening has not been established yet. We propose that small magnetic loops are the source of these bright patches, and present modeling results that reproduce the main observational characteristics of the polar brightening within coronal holes at 17 GHz. The simulations were carried out by calculating the radio emission of the small loops, with several temperature and density profiles, within a 2D coronal hole atmospheric model. If located at high latitudes, the size of the simulated bright patches are much smaller than the beam size and they present the instrument beam size when observed. The larger bright patches can be generated by a great number of small magnetic loops unresolved by the NoRH beam. Loop models that reproduce bright patches contain denser and hotter plasma near the upper chromosphere and lower corona. On the other hand, loops with increased plasma density and temperature only in the corona do not contribute to the emission at 17 GHz. This could explain the absence of a one-to-one association between the 17 GHz bright patches and those observed in extreme ultraviolet. Moreover, the emission arising from small magnetic loops located close to the limb may merge with the usual limb brightening profile, increasing its brightness temperature and width.Comment: 8 pages, 6 figures, 1 table. Accepted for publication in The Astrophysical Journa

Computational modelling and digital materialization of Alberti’s column system: a reflection on results obtained

We hereby focus the study of the Albertian column system, as part of the Digital Alberti project, a research initiative that aims to shed some light on the influence of Alberti on Portuguese architecture. Starting from Alberti’s treatise on architecture, De Re Aedificatoria, and its translation into Portuguese, Da Arte Edificatória, a generative computational model was developed that encodes Alberti’s prescriptions about the elements of the column system, as well as their proportions and shapes. This research complements the elaboration of the corresponding shape grammar on Alberti’s column system. This project is a paradigmatic example of the use of digital technology for understanding architectural tradition. The development of the referred models implied deepening the understanding of Alberti’s rules about the column elements. This in-depth analysis revealed a very coherent hierarchical structure ruling the relationships among the several elements. It also revealed that information was insufficient to inform a formal model of all them, especially the ones showing more complex geometry, such as the corinthian and composite capitals. Therefore, it can be considered that the application of digital technologies allowed to more accurately understand and reproduce Alberti’s guidelines for the art of building

Análise comparativa para geração de energia heliotérmica em diferentes regiões brasileiras

Monografia (graduação)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2016.O presente trabalho apresenta uma avaliação técnica da tecnologia solar concentrada disponível e em desenvolvimento, além de conceitos sobre radiação solar, aspectos econômicos e o potencial brasileiro. Também é ilustrado o cenário mundial e nacional das plantas heliotérmicas. Com auxílio do software específico SAM, System AdvisorModel, o conceito de simulações de plantas heliotérmicas é introduzido como forma de prever o funcionamento técnico e a viabilidade econômica, bem como a comparação entre diferentes tecnologias e localidades de implantação. __________________________________________________________________________ ABSTRACTThis paper presents a technical evaluation of available concentrated solar power technology and its development, as well as concepts of solar radiation and the Brazilians potential. It is also illustrated the national and world perspective for Heliothermal plants.With the aid of the specific software SAM, System Advisor Model, is introduced the concept of heliothermal plants simulations in order to predict the technical operation and economic viability, as well the comparison between different technologies and deployment locations