Percorrer por autor "Almeida, Luis Pedro"
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- Beach erosion and recovery during consecutive storms at a steep-sloping, meso-tidal beachPublication . Vousdoukas, Michalis; Almeida, Luis Pedro; Ferreira, ÓscarThis study analyses beach morphological change during six consecutive storms acting on the meso-tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep-sloping beaches, since sub-aerial beach volume reductions up to 30m3/m were followed by intertidal area recovery (–2
- Correlating wave hindcast and buoy data with artificial neural networksPublication . Almeida, Luis Pedro; Vousdoukas, Michalis; Ferreira, P. M.; Ruano, AntonioThis work presents results from the use of Artificial Neural Networks (ANN) to improve wave models hindcasting capacity off the South coast of Portugal. Comparison of the original model results with field measurements showed significant non linear deviations. To compensate for such deviations, a three-layer Multilayer Perceptron (MLP – a type of an ANN) was trained, using the Levenberg-Marquardt method, to improve the fit between the hindcast (generated by WW3) and Faro buoy data in an effort to reconstruct missing data from the wave buoy time series. The results obtained so far are very positive; with the training with annual datasets showing better results than the training with the entire dataset, while both improved significantly the fitting of the raw model results. Further improvements are expected by trying different ANN types, by searching for optimised ANN input-output structure, and by performing sub-set selection on the data sets.
- Geoprocessing tool to model the storm impact over sandy beachesPublication . Almeida, Luis Pedro; Ferreira, Óscar; Taborda, RuiO presente trabalho descreve o desenvolvimento de uma ferramenta de geoprocessamento para modelação da erosão de praias provocada por tempestades, denominada de GEOSTORM (geoprocessing tool to model beach erosion due to storms). Esta ferramenta possui um interface gráfico principal, desenvolvido através da linguagem de programação Visual Basic for Applications (VBA), que pode ser chamado dentro do ambiente ArcMap (ArcGis v. 9.3 - ESRI) e é composto por dois módulos (Módulo 1 e 2). O Módulo 1 permite ao utilizador definir um conjunto de parâmetros (e.g. distancia lateral e orientação dos transeptos) necessários para a criação de um conjunto de transeptos relativos a uma linha de base (baseline – linha paralela à linha de costa traçada do lado continental adjacente à praia em estudo) fornecida pelo utilizador no formato de Tema do tipo linha. Através dos transeptos criados o Módulo 1 permite também a extracção de perfis transversais de praia sobre um modelo digital de elevação (MDT) fornecido pelo utilizador. Este Módulo (1) é constituído por um conjunto de scripts escritos em linguagem de programação Python (v. 2.6), recorrendo a bibliotecas gratuitas para manipulação e processamento de dados espaciais do tipo matricial (e.g. rasters) e vectorial (e.g. Temas), como as bibliotecas GDAL, OGR e GMT. Os dados de saída do Módulo 1 estão ligados directamente com o Módulo 2, onde o utilizador acede a um novo interface gráfico (escrito com a linguagem de programação Matlab) o qual permite a utilização do modelo de erosão de praias de Kriebel e Dean (1993). Dentro deste novo interface gráfico o utilizador pode utilizar o um conjunto de ferramentas que permitem de forma intuitiva e simples a utilização do modelo de Kriebel e Dean (1993) para a determinação da distância de recuo (Rmax) e volume erodido (Vmax) em cada um dos perfis transversais de praia obtidos no Módulo 1. Ainda dentro do Módulo 2, e após a obtenção dos resultados da modelação, é feita a conversão dos resultados para o formato Tema, do tipo linha, e estes são exportados para a tabela de conteúdos do ArcMap. O modelo de Kriebel e Dean (1993) foi validado para a área de estudo, Praia de Faro no Sul de Portugal, através da comparação dos resultados das simulações com medições efectuadas no campo para um conjunto de 4 tempestades. As medições no campo consistiram na aquisição de perfis topográficos transversais em situação de pré e pós-temporal entre 2002 e 2009. Os resultados das comparações entre Rmax e Vmax simulados pelo modelo e verificados no campo permitiram verificar que o modelo de Kriebel e Dean (1993) apresenta em geral uma boa concordância com as medições no campo, com diferencias máximas na ordem de 1,9 m para o caso do Rmax e de 36 % para o caso do parâmetro Vmax. Posteriormente ao processo de validação do modelo de Kriebel e Dean (1993), a ferramenta GEOSTORM foi utilizada para a simulação de um cenário de uma tempestade severa, com um período de retorno de 25 anos, sobre a praia de Faro. Para esta simulação foram utilizados dados provenientes de um levantamento topográfico LIDAR efectuado sobre toda a área de estudo em Novembro de 2009, assim como as condições hidrodinâmicas determinadas para uma tempestade com um período de retorno de 25 anos. Os resultados desta aplicação indicam recuos médios na ordem dos 8 m e volume médio de erosão de aproximadamente 37 m3/m. A sobreposição dos resultados sobre um ortofotomapa de 2009 da área de estudo permitiu identificar que em várias zonas da Praia de Faro o recuo previsto pelo modelo para esta tempestade se sobrepõe a algumas das infra-estruturas humanas existentes no local (ex. parque de estacionamento, estradas, muros e casas). O desenvolvimento de ferramentas como a GEOSTORM é de extrema importância para uma largo leque de entidades responsáveis pela gestão e ordenamento das zonas costeiras. O conceito de uma ferramenta simples de utilizar mas capaz de prever indicadores simples, mas importantes, como a distância de recuo ou o volume de erosão, são de extrema utilidade para um variado conjunto de possíveis aplicações, como por exemplo: (1) previsão da resposta da praia a uma tempestade que se prevê chegar em breve; (2) apoio na produção de cartografia de vulnerabilidade ou risco a tempestades para determinada zona costeira; (3) apoio na elaboração de estudos multidisciplinares como, por exemplo, estudos do impacto ambiental; e (4) apoio a estudos ou projectos de realimentações de praias.
- Network analysis reveals humans as top predators and the key role of cuttlefish in the food web structure of a marine protected area (Arrábida Natural Park)Publication . Vinagre, Catarina; Almeida, Luis Pedro; Ronquillo, Pilar; Alegria Mendonça, Vanessa Sofia; Frade, Duarte Gonçalves; Gonçalves, Emanuel J.; Erzini, Karim; Serrao, Ester A.The marine protected area (MPA) of the Arrábida Natural Park is a mid-latitude hotspot for biodiversity. To understand its trophic structure, a highly defined food web network was assembled for this ecosystem, consisting of 884 taxa. Network analysis showed that humans are the top predators, as well as various seabirds, dolphins and sharks. This web is dominated by intermediate species, and its general organization follows previously reported patterns for other marine and coastal ecosystems. Two swimming crabs, Polybius navigator and Polybius henslowii, assume important roles as mid-trophic level consumers and prey, due to their high connectivity in the network. The cuttlefish, Sepia officinalis, a cephalopod of high commercial value, assumes the most pivotal role in the network, as it is the species with the highest number of prey and is among the top 10 most highly connected species (with more links to other species). Additionally, the cuttlefish is among the species with shortest path length, that is the lowest number of links connecting it to any other species. Since, this cephalopod is highly mobile and extends its territory outside the MPA, into the Sado estuary, where it is the main target of local fisheries, and is exposed to various pollution sources, close monitoring the local population of cuttlefish is of the utmost importance, not only in the Arrabida ´ MPA but also in the adjacent Sado estuary.
- Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South PortugalPublication . Vousdoukas, Michalis; Ferreira, P. M.; Almeida, Luis Pedro; Dodet, Guillaume; Psaros, Fotis; Andriolo, Umberto; Taborda, Rui; Silva, Ana Nobre; Ruano, Antonio; Ferreira, ÓscarThis study discusses site-specific system optimization efforts related to the capability of a coastal video station to monitor intertidal topography. The system consists of two video cameras connected to a PC, and is operating at the meso-tidal, reflective Faro Beach (Algarve coast, S. Portugal). Measurements from the period February 4, 2009 to May 30, 2010 are discussed in this study. Shoreline detection was based on the processing of variance images, considering pixel intensity thresholds for feature extraction, provided by a specially trained artificial neural network (ANN). The obtained shoreline data return rate was 83%, with an average horizontal cross-shore root mean square error (RMSE) of 1.06 m. Several empirical parameterizations and ANN models were tested to estimate the elevations of shoreline contours, using wave and tidal data. Using a manually validated shoreline set, the lowest RMSE (0.18 m) for the vertical elevation was obtained using an ANN while empirical parameterizations based on the tidal elevation and wave run-up height resulted in an RMSE of 0.26 m. These errors were reduced to 0.22 m after applying 3-D data filtering and interpolation of the topographic information generated for each tidal cycle. Average beach-face slope tan(β) RMSE were around 0.02. Tests for a 5-month period of fully automated operation applying the ANN model resulted in an optimal, average, vertical elevation RMSE of 0.22 m, obtained using a one tidal cycle time window and a time-varying beach-face slope. The findings indicate that the use of an ANN in such systems has considerable potential, especially for sites where long-term field data allow efficient training.
- Stress granules, RNA-binding proteins and polyglutamine diseases: too much aggregation?Publication . Marcelo, Adriana; Koppenol, Rebekah; Almeida, Luis Pedro; Matos, Carlos A; Nóbrega, ClévioStress granules (SGs) are membraneless cell compartments formed in response to different stress stimuli, wherein translation factors, mRNAs, RNA-binding proteins (RBPs) and other proteins coalesce together. SGs assembly is crucial for cell survival, since SGs are implicated in the regulation of translation, mRNA storage and stabilization and cell signalling, during stress. One defining feature of SGs is their dynamism, as they are quickly assembled upon stress and then rapidly dispersed after the stress source is no longer present. Recently, SGs dynamics, their components and their functions have begun to be studied in the context of human diseases. Interestingly, the regulated protein self-assembly that mediates SG formation contrasts with the pathological protein aggregation that is a feature of several neurodegenerative diseases. In particular, aberrant protein coalescence is a key feature of polyglutamine (PolyQ) diseases, a group of nine disorders that are caused by an abnormal expansion of PolyQ tract-bearing proteins, which increases the propensity of those proteins to aggregate. Available data concerning the abnormal properties of the mutant PolyQ disease-causing proteins and their involvement in stress response dysregulation strongly suggests an important role for SGs in the pathogenesis of PolyQ disorders. This review aims at discussing the evidence supporting the existence of a link between SGs functionality and PolyQ disorders, by focusing on the biology of SGs and on the way it can be altered in a PolyQ disease context.