Browsing by Issue Date, starting with "2011-09"
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- Modellazione di una pila da ponte nell’ambito di un “Blind Prediction Contest"Publication . Biachi, Federica; Sousa, Romain; Pinho, RuiNel presente lavoro vengono descritte le strategie di modellazione impiegate per la previsione della risposta nonlineare dinamica di una pila da ponte a scala reale in cemento armato soggetta a sei accelerogrammi di crescente intensità. Il prototipo della struttura, una colonna a sezione circolare con diametro pari a 1.22 m, di altezza pari a 7.32 m misurata dal piano di fondazione e che sorregge all’estremità un blocco in cemento armato di 230 tonnellate, è stato testato sulla “NEES @ UC San Diego Large High Performance Outdoor Shake Table” in occasione del recente “Concrete Column Blind Prediction Contest 2010”. Al termine della competizione sono state messe a disposizione dei partecipanti le misurazioni sperimentali necessarie per procedere con il confronto con i risultati numerici della previsione. Da tale confronto è emerso che, grazie alle strategie adottate in fase di modellazione e grazie all’utilizzo di un appropriato software di calcolo agli elementi finiti (a plasticità diffusa, cioè con elementi a fibre), è stato possibile stimare in modo sufficientemente accurato il comportamento della struttura in esame.
- A transição do POC para o SNC: aplicação práticaPublication . Pereira, Manuel José Andrino
- Multi-feature Tracking Approach Using Dynamic Fuzzy SetsPublication . Lopes, Nuno Vieira; Couto, Pedro; Melo-Pinto, PedroIn this paper a new tracking approach based in fuzzy concepts is introduced. The aim of this methodology is to incorporate in the proposed model the uncertainty underlying any problem of feature tracking, through the use of fuzzy sets. Several dynamic fuzzy sets are constructed according both cinematic (movement model) and non cinematic properties (image gray levels) that distinguish the feature. Meanwhile cinematic related fuzzy sets model the feature movement characteristics, the non cinematic fuzzy sets model the feature visible image related properties. The tracking task is performed through the fusion of these fuzzy models by means of a fuzzy inference engine. This way feature detection and matching steps are performed exclusively using inference rules on fuzzy sets.
- O sector da cerâmica na segunda metade do século XX : análise formal e decorativa do produto cerâmicoPublication . Durão, Lina Raquel da CruzA região de Leiria é actualmente uma das mais importantes regiões do ponto de vista industrial. Aqui se situam importantes empresas dos sectores da cerâmica e vidro, plásticos e moldes. Estes sectores têm passado nos últimos anos por profundos processos de modernização e ajustamento face aos contextos internacionais. O sector da cerâmica é um dos mais significativos sectores industriais, sendo uma área onde Portugal tem ganho notoriedade fruto em parte do seu posicionamento geográfico. À semelhança dos outros sectores industriais desta região o sector da cerâmica encontra-se hoje sujeito a profundas transformações. Não obstante a tradição cerâmica em Portugal, este foi um sector que se consolidou do ponto vista industrial apenas no século XX, período também marcado por sucessivas transformações sociais, politicas e económicas em Portugal. Este trabalho de investigação aborda a indústria cerâmica (subsector da cerâmica utilitária e decorativa) na região de Leiria, em particular em Alcobaça dado o predomínio destas empresas nesta região, sendo considerado o maior centro cerâmico de louça utilitária e decorativa nacional. As transformações que marcaram a segunda metade do século XX em Portugal são analisadas de forma detalhada, e estudado o seu efeito ao nível deste subsector industrial. Através de um estudo detalhado de cinco empresas significativas deste subsector é feita uma análise da evolução tecnológica e metodológica. As transformações sociais e económicas que marcaram a adesão de Portugal à Comunidade Europeia são igualmente objecto de reflexão, analisando-se o novo paradigma industrial a que estas empresas tiveram que fazer face. Finalmente a análise efectuada permitiu a identificação de um conjunto de características fundamentais à sobrevivência das empresas deste subsector, que passam pela capacidade de gerar valor, e pela criação de produtos adaptados às novas realidades sociais e económicas. O produto deve ser gerado através de conhecimento tecnológico e criativo, cujo valor é percepcionado pelas características e conceitos diferenciados gerados pelo conhecimento e não pela existência do produto em si mesmo.
- Analysis Issues on Seismic Assessment of Existing StructuresPublication . Sousa, Romain; Biachi, Federica; Nascimbene, Roberto; Pinho, RuiMany existing RC structures worldwide were designed for gravity loads only, with inadequate lateral load resistance, lateral stiffness and poor detailing of the reinforcement. Moreover, the concept of regularity both in plan and elevation that characterise a good conceptual design was, in most cases, not taken into account. The introduction in Europe of the regulations for seismic assessment of existing structures imposed stricter performance requirements for building structures. In order to take into account the poor seismic behaviour of such buildings, recent seismic codes – namely EC8 and NTC08, introduce a number of prescriptions regarding issues such as analysis type, load distribution, accidental eccentricity, etc. At the same time, these codes give room for engineering judgment to be used with reference to the definition of structural and non-structural elements such as slabs or infill walls, and obviously leave it up to the analyst decisions regarding Finite Elements typology, meshing, mass modelling, etc. The main goal of this work is thus to provide an extensive and wide evaluation on the influence of each of the abovementioned parameter on the seismic assessment of structures. For this purpose, nonlinear static analysis, as well as nonlinear dynamic analysis are performed on a real building that has also been experimentally tested in the past. The results will hopefully provide indications on the relative importance of each modelling parameter or decision.
- Um olhar sobre a intenção das jovens em amamentarPublication . Henriques, Carolina; Dixe, Maria dos Anjos; Catarino, Helena
- A Pilot-Data Based Channel Estimation Method for OFDM Relay-Assisted SystemsPublication . Neves, D.; Ribeiro, C.; Silva, A.; Gameiro, A.In this work we propose and evaluate a pilot and data-based channel estimation scheme for SFBC OFDM-based cooperative scenario. We consider that both the base station and the relay node are equipped with double antenna arrays whereas the user terminal is a single antenna device. The relay protocol considered is equalise-andforward. In this paper we propose a channel estimation method that iteratively uses the information carried by the pilots and data to improve the estimate of the equivalent channels for the path Base Station – Relay Node – User Terminal. The MMSE criterion is used in the design of the estimator for both the pilot-based and data-aided iterations. The proposed method is evaluated in terms of the channel estimation MSE and the results show that the proposed scheme allows, with a single data iteration, a reduction of the number of pilots by a factor of approximately two when compared with non-data-aided schemes.
- Adaptive least squares prediction for stereo image codingPublication . Lucas, Luis F. R.; M. M. Rodrigues, Nuno; Silva, Eduardo A. B. da; Faria, SergioState-of-the art approaches towards stereo image coding exploit inter-view redundancy by employing block-matching methods for disparity estimation and compensation. However, the efficiency of these methods is affected by mismatched areas, due to occlusions, brightness variations, or perspective distortion between objects of the two views. In this paper we present a new prediction scheme for stereo image coding, that combines an implicit disparity estimation method, with an adaptive least squares (LS)-based filtering. The Multidimensional Multiscale Parser image coding algorithm was used to evaluate the efficiency of the proposed scheme. Experimental results demonstrate the advantage of LS prediction in stereo image coding. Furthermore, the rate-distortion performance of the MMP based stereo encoder is well above that of the state-of-the-art H.264/AVC Stereo Profile, especially at medium and high bit rates.
- Error recovery of image-based depth maps using Bézier curve fittingPublication . Marcelino, S.; Assunção, Pedro; Faria, Sergio; Soares, S.This paper proposes a method to recover lost regions in image-based depth maps used in video plus depth 3D format. This method performs depth maps reconstruction taking into account depth contours within the lost regions. This is achieved by extracting the contours and recovering their lost segments based on Bézier curve fitting, followed by spatial interpolation. The proposed method maintains contour smoothness and uses them as the boundary limits of homogeneous depth regions, which are then filled through weighted pixel interpolation. The experimental results show that the proposed method yields better synthesized images than classic spatial concealment methods, uniquely based on pixel interpolation techniques. The method presented in this paper is able to outperform the reference method, in terms of PSNR by up to 1.91dB. The subjective quality is also shown as being significantly better.
- Compression of touchless multiview fingerprintsPublication . Francisco, Nelson C.; Zaghetto, Alexandre; Macchiavello, Bruno; Silva, Eduardo A. B. da; Lima-Marques, Mamede; Rodrigues, Nuno M. M.; Faria, SergioRecently, touchless multiview fingerprinting technology has been proposed as an alternative to overcome the intrinsic problems of traditional contact-based systems. Nevertheless, compression of this kind of signal has not been fully evaluated and standardized. This paper investigates the comparative performance of several encoders for this data, namely WSQ, JPEG2000, H.264/AVC and MMP. Experimental results show that WSQ encoder, which is the current compression standard for contact-based fingerprints, is objectively outperformed by all others. In particular, MMP, which achieved the best results, outperforms WSQ by up to 4 dB.