Intrusion tolerant routing with data consensus in wireless sensor networks

Dissertação para obtenção do Grau de Mestre em Engenharia Informática

Tax policy stance over the business cycle: evidence from Europe

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Economics from the NOVA – School of Business and Economics

Business model analysis of Mobitto: How to solve the chicken and egg problem of a multi-sided platform?

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Management from the NOVA – School of Business and Economics

Credit cycle identification: A Markov-switching application

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Finance from the NOVA – School of Business and Economics

Cash conversion cycle across industries

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Management from the NOVA – School of Business and Economics

Watershed-scale runoff routing and solute transport in a spatially aggregated hydrological framework

Dissertation submitted in partial fulfillment of the requirements for the Degree of Master of Science in Geospatial Technologies

Spore differentiation in relation to the infectious cycle of the enteric pathogen Clostridium difficile

Clostridium difficile is a gram positive, spore former, anaerobic bacterium that is able to cause infection and disease, with symptoms ranging from mild diarrhea to pseudomembranous colitis, toxic megacolon, sepsis and death. In the last decade new strains have emerged that caused outbreaks of increased disease severity and higher recurrence, morbidity and mortality rates, and C. difficile is now considered both a main nosocomial pathogen associated with antibiotic therapy as well as a major concern in the community.(...)

A public transport bus assignment problem: parallel metaheuristics assessment

Combinatorial Optimization Problems occur in a wide variety of contexts and generally are NP-hard problems. At a corporate level solving this problems is of great importance since they contribute to the optimization of operational costs. In this thesis we propose to solve the Public Transport Bus Assignment problem considering an heterogeneous fleet and line exchanges, a variant of the Multi-Depot Vehicle Scheduling Problem in which additional constraints are enforced to model a real life scenario. The number of constraints involved and the large number of variables makes impracticable solving to optimality using complete search techniques. Therefore, we explore metaheuristics, that sacrifice optimality to produce solutions in feasible time. More concretely, we focus on the development of algorithms based on a sophisticated metaheuristic, Ant-Colony Optimization (ACO), which is based on a stochastic learning mechanism. For complex problems with a considerable number of constraints, sophisticated metaheuristics may fail to produce quality solutions in a reasonable amount of time. Thus, we developed parallel shared-memory (SM) synchronous ACO algorithms, however, synchronism originates the straggler problem. Therefore, we proposed three SM asynchronous algorithms that break the original algorithm semantics and differ on the degree of concurrency allowed while manipulating the learned information. Our results show that our sequential ACO algorithms produced better solutions than a Restarts metaheuristic, the ACO algorithms were able to learn and better solutions were achieved by increasing the amount of cooperation (number of search agents). Regarding parallel algorithms, our asynchronous ACO algorithms outperformed synchronous ones in terms of speedup and solution quality, achieving speedups of 17.6x. The cooperation scheme imposed by asynchronism also achieved a better learning rate than the original one.

Optimization of wastewater quality in the Sines refinery

In order to address and resolve the wastewater contamination problem of the Sines refinery with the main objective of optimizing the quality of this stream and reducing the costs charged to the refinery, a dynamic mass balance was developed nd implemented for ammonia and polar oil and grease (O&G) contamination in the wastewater circuit. The inadequate routing of sour gas from the sour water stripping unit and the kerosene caustic washing unit, were identified respectively as the major source of ammonia and polar substances present in the industrial wastewater effluent. For the O&G content, a predictive model was developed for the kerosene caustic washing unit, following the Projection to Latent Structures (PLS) approach. Comparison between analytical data for ammonia and polar O&G concentrations in refinery wastewater originating from the Dissolved Air Flotation (DAF) effluent and the model predictions of the dynamic mass balance calculations are in a very good agreement and highlights the dominant impact of the identified streams for the wastewater contamination levels. The ammonia contamination problem was solved by rerouting the sour gas through an existing clogged line with ammonia salts due to a non-insulated line section, while for the O&G a dynamic mass balance was implemented as an online tool, which allows for prevision of possible contamination situations and taking the required preventive actions, and can also serve as a basis for establishing relationships between the O&G contamination in the refinery wastewater with the properties of the refined crude oils and the process operating conditions. The PLS model developed could be of great asset in both optimizing the existing and designing new refinery wastewater treatment units or reuse schemes. In order to find a possible treatment solution for the spent caustic problem, an on-site pilot plant experiments for NaOH recovery from the refinery kerosene caustic washing unit effluent using an alkaline-resistant nanofiltration (NF) polymeric membrane were performed in order to evaluate its applicability for treating these highly alkaline and contaminated streams. For a constant operating pressure and temperature and adequate operating conditions, 99.9% of oil and grease rejection and 97.7% of chemical oxygen demand (COD) rejection were observed. No noticeable membrane fouling or flux decrease were registered until a volume concentration factor of 3. These results allow for NF permeate reuse instead of fresh caustic and for significant reduction of the wastewater contamination, which can result in savings of 1.5 M€ per year at the current prices for the largest Portuguese oil refinery. The capital investments needed for implementation of the required NF membrane system are less than 10% of those associated with the traditional wet air oxidation solution of the spent caustic problem. The operating costs are very similar, but can be less than half if reusing the NF concentrate in refinery pH control applications. The payback period was estimated to be 1.1 years. Overall, the pilot plant experimental results obtained and the process economic evaluation data indicate a very competitive solution through the proposed NF treatment process, which represents a highly promising alternative to conventional and existing spent caustic treatment units.

Prevalência de obesidade em adolescentes do distrito de Viseu

RESUMO - Introdução: A prevalência de obesidade apresenta valores preocupantes em todas as idades e é reconhecida pela Organização Mundial da Saúde como um importante problema de saúde pública. Diversos estudos mostram que a sua prevalência tem aumentado significativamente nas últimas décadas, particularmente nos países industrializados. O objectivo da presente investigação foi calcular a prevalência de excesso de peso e de obesidade em adolescentes do distrito de Viseu. Métodos: Realizámos um estudo transversal onde avaliámos os alunos de vinte e seis das quarenta e oito escolas públicas do terceiro ciclo e secundário do distrito de Viseu, frequentadas por um total de 23 895 alunos, do 7.o ao 12.o ano. A recolha dos dados foi efectuada através de um questionário auto-aplicado e respondido pelos alunos em sala de aula. Dos 8768 questionários distribuídos recolhemos 7644 (87,2%). Foram excluídos da análise os questionários sem informação para o sexo e para a idade. Ficámos com uma amostra global de 7563 adolescentes, sendo 4117 (54,4%) do sexo feminino. O excesso de peso e a obesidade foram avaliados utilizando o índice de massa corporal (IMC) calculado pela razão entre o peso auto declarado em quilogramas e o quadrado da altura, em metros, também auto declarada (kg/m2). Definimos excesso de peso para valores compreendidos entre o percentil 85 e 95, obesidade para um percentil superior ou igual a 95, e excesso de peso e obesidade para um percentil superior ou igual a 85. Resultados: No total da amostra, a prevalência de excesso de peso é de 13,7%, superior no sexo masculino (16,0% vs. 11,6%). A prevalência de obesidade é de 3,4%, superior no sexo masculino (4,2% vs. 2,8%). A prevalência de excesso de peso e obesidade é de 17,1%, superior no sexo masculino (20,2% vs. 14,4%). Os concelhos situados a norte do distrito de Viseu apresentam prevalências superiores, de excesso de peso (15,9% vs. 13,0%, OR = 1,3; IC95% 1,1-1,5), de obesidade (4,5% vs. 3,6%, OR = 1,3; IC95% 1,0-1,7) e de excesso de peso e obesidade (19,1% vs. 15,7%, OR = 1,3; IC95% 1,1-1,4). A prevalência de excesso de peso e obesidade é superior entre os adolescentes com o índice de aglomeração superior a um. Conclusões: Regista-se uma elevada prevalência de excesso de peso e de obesidade, superior no sexo masculino, com diferenças geográficas significativas.