Browsing by Author "Nunes, A."
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- Estudo de argamassas de base cimentícia por microscopia electrónica de varrimentoPublication . Costa, Carla; Carvalho, P. Almeida de; Bordado, J. C.; Nunes, A.Cement-based materials possess a heterogeneous microstructure that changes over time. Scanning electron microscopy is an experimental technique that allows the observation of materials in a wide range of magnifications and can be associated with local chemical analysis. This work describes the fundamental microstructural characteristics of cementbased materials and presents experimental results of Portland cement mortars analysis by scanning electron microscopy. Keywords: Cement-based materials, Microstructure, Scanning electron microscopy. Os materiais de base cimentícia possuem uma microestrutura heterogénea e que se altera ao longo do tempo. A microscopia electrónica de varrimento é uma técnica experimental que permite a observação de materiais numa vasta gama de ampliações e à qual se pode associar análise química local. Neste trabalho descrevem-se as características fundamentais da microestrutura de materiais de base cimentícia e apresentam-se resultados experimentais da análise de argamassas de cimento Portland por microscopia electrónica de varrimento. palavras chave: Materiais de base cimentícia, Microestrutura, Microscopia electrónica de varrimento.
- Stochastic effects in a seasonally forced epidemic modelPublication . Rozhnova, G.; Nunes, A.The interplay of seasonality, the system's nonlinearities and intrinsic stochasticity, is studied for a seasonally forced susceptible-exposed-infective-recovered stochastic model. The model is explored in the parameter region that corresponds to childhood infectious diseases such as measles. The power spectrum of the stochastic fluctuations around the attractors of the deterministic system that describes the model in the thermodynamic limit is computed analytically and validated by stochastic simulations for large system sizes. Size effects are studied through additional simulations. Other effects such as switching between coexisting attractors induced by stochasticity often mentioned in the literature as playing an important role in the dynamics of childhood infectious diseases are also investigated. The main conclusion is that stochastic amplification, rather than these effects, is the key ingredient to understand the observed incidence patterns.