Avaliação das propriedades mecânicas da madeira in situ por ensaios em mesoprovetes

Uma das principais dificuldades da avaliação do estado de segurança de estruturas de madeira existentes é a determinação das propriedades mecânicas a utilizar para efeitos de cálculo. Os procedimentos habituais de estabelecimento das propriedades mecânicas com base no estabelecimento de classes de resistência por avaliação visual validada com ensaios não-destrutivos conduzem a resultados muito conservativos. No presente trabalho será apresentado um método semi-destrutivo que avalia a resistência à tracção da madeira através de amostras recolhidas do elemento estrutural, sendo estabelecidas relações entre resultados análogos de mesoprovetes e provetes normalizados para peças de pinho bravo (Pinus pinaster Ait.) e castanho nacional (Castanea sativa Mill.)

Selected research and case studies in ancient portuguese structures

The present paper presents some of the recent activity of University of Minho, regarding case studies for Portuguese timber structures in four ancient buildings, including the Cathedral of Porto, a Church in Coimbra and a Church in Braga. NDT is combined with analysis methods aiming at non-invasive strengthening solutions or replacement of the timber structure (only as a last resort). Research studies carried out in UM and currently running on LNEC and UM are also presented, being showed the relevance of this research studies for the assessment and analysis of historical timber structures

A semi-destructive tension method for evaluating the strength and stiffness of clear wood zones of structural timber elements in-service

The paper presents a new semi destructive method for obtaining a prediction of the tension parallel to the grain properties of clear wood of structural timber members. This method is less intrusive than other existing methods and consists in extracting four small specimens along the length of the timber members. The tension strength and stiffness obtained is intended to be used as input data for the assessment of timber members in situ. Since the method only provides information regarding clear wood, it will have to be used together with other non or semidestructive methods that could accommodate the effect of defects on the loss of clear wood properties. The validation of the method was carried out by a comparison with results obtained from a standard method used for determination of clear wood properties. The results show a good agreement between stiffness values but a medium agreement in the case of tension strength.The authors acknowledge the support given by the Fundacao para a Ciencia e a Tecnologia (FCT) for the PhD Grant SFRH/BD/27353/2006, as well as for the research Project "Safety evaluation of timber structures by means of non-destructive tests and stochastic analysis" (FCT PTDC/ECM/66527/2006)

A neural system for deforestation monitoring on Landsat images of the Amazon Region

AbstractWe deal with the problem of automating the interpretation of satellite images of the Amazon region for deforestation monitoring. Our approach is based on a combination of image segmentation and classification techniques, the latter emplying a neural-network architecture that works on a fuzzy model of classification. The architecture implements a relaxation mechanism on top of a feedforward neural network, in order to take advantage of the interrelations among neighboring image segments. Our fuzzy, segment-based approach has numerous advantages over more traditional, pixel-based approaches employing statistical techniques. These advantages range from the possibility of treating transition and interference phenomena in the images to the ease with which complex information related to a region's geometry, texture, and contextual setting can be used. We report on a great variety of experiments on representative portions of the Amazon region, employing neural networks trained by the back-propagation algorithm. The results indicate very good overall performance, and allow us to draw some conclusions regarding the effectiveness of the various sources of information available as input to the system. In particular, it appears that simple spectral information, together with textural information on a region's entropy and correlation and simple contextual information, are effective in the classification for deforestation monitoring. It also appears that the effective incorporation of geometric information would require further investigation on possible enhancements to the system

Avaliação da segurança de cobertura tradicional de madeira sujeita a degradação biológica

O presente trabalho propõe-se apresentar a modelação probabilística de uma estrutura-tipo de uma cobertura tradicional de madeira, sendo tomadas como variáveis aleatórias as dimensões geométricas das secções transversais, as propriedades mecânicas da madeira e as acções aplicadas à estrutura, dando especial ênfase ao vento e neve. Depois de estabelecido o índice de fiabilidade β para uma situação de não degradação, será avaliada a sua variação em função da evolução da degradação biológica provocada por fungos, modelada probabilisticamente como uma variação de secção transversal

EEG-Based Epileptic Seizure Prediction Using Temporal Multi-Channel Transformers

Epilepsy is one of the most common neurological diseases, characterized by transient and unprovoked events called epileptic seizures. Electroencephalogram (EEG) is an auxiliary method used to perform both the diagnosis and the monitoring of epilepsy. Given the unexpected nature of an epileptic seizure, its prediction would improve patient care, optimizing the quality of life and the treatment of epilepsy. Predicting an epileptic seizure implies the identification of two distinct states of EEG in a patient with epilepsy: the preictal and the interictal. In this paper, we developed two deep learning models called Temporal Multi-Channel Transformer (TMC-T) and Vision Transformer (TMC-ViT), adaptations of Transformer-based architectures for multi-channel temporal signals. Moreover, we accessed the impact of choosing different preictal duration, since its length is not a consensus among experts, and also evaluated how the sample size benefits each model. Our models are compared with fully connected, convolutional, and recurrent networks. The algorithms were patient-specific trained and evaluated on raw EEG signals from the CHB-MIT database. Experimental results and statistical validation demonstrated that our TMC-ViT model surpassed the CNN architecture, state-of-the-art in seizure prediction.Comment: 15 pages, 10 figure

Gatewaying IEEE 1149.1 and IEEE 1149.7 test access ports

In this paper, we present a description of ourdeveloped adapter, which takes acts as a gateway between IEEE1149.1 and IEEE 1149.7 test infrastructures. The referredadapter reduces the pins of the TAP from 4 to 2 and implementsadvanced capabilities, such as Parking State of a TAPC and theReset and Selection Unit (RSU)

IEEE Std 1149.7: What, Why, Where?

The IEEE Std 1149.7 holds the promise of greatimprovements for testing electronic circuits, when used alongwith other IEEE standards (particularly those that use the IEEEStd 1149.1 for test access and control). In this paper we describewhat is the IEEE Std 1149.7, the reasons why we mayconsider to use it instead of IEEE Std 1149.1, and we highlightthe application spectrum where this new standard can beuseful

Reliability analysis of a timber truss system subjected to decay

Assessing the safety of existing timber structures is of paramount importance for taking reliable decisions on repair actions and their extent. The results obtained through semi-probabilistic methods are unrealistic, as the partial safety factors present in codes are calibrated considering the uncertainty exhibited by new structures. In order to overcome these limitations, and also to include the e ects of decay in the safety analysis, probabilistic methods, based on Monte-Carlo simulation are applied here to assess the safety of existing timber structures. In particular, the impact of decay on structural safety is analyzed and discussed using a simple structural model, similar to that used for current semi-probabilistic analysis.Fundação para a Ciência e a Tecnologia (FCT