Browsing by Issue Date, starting with "2015-08"
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- Seismic Rehabilitation of RC Columns Under Biaxial Loading: An Experimental CharacterizationPublication . Pinheiro Rodrigues, Hugo Filipe; Arêde, António; Furtado, André; Rocha, PatrícioThe main purpose of this paper is to present an experimental campaign of different strategies for seismic repair and retrofit of RC columns previously subjected to biaxial cyclic loading actions and evaluate the benefits concerning their structural behaviour when again subjected to biaxial cyclic loading. Column rehabilitation was performed in order to improve the ductility and/or strength characteristics and it was obtained through increasing the concrete ductility conditions, with efficient jacketing, or increasing the amount of longitudinal and transversal steel. The aim is, therefore, to contribute in developing and calibrating a procedure that enables the evaluation of the efficiency of different retrofit solutions, their possibilities and fields of application. The results are presented in terms of shear-drift, stiffness degradation, ductility and energy dissipation. The retrofitted results will be compared with the results of the original one, deducting about the structural efficiency by each type of retrofit technique adopted.
- Two-dimensional antenna beamsteering using metamaterial transmitarrayPublication . Reis, J. R.; Al-Daher, Zaid Al-Daher; Copner, Nigel Copner; Caldeirinha, R. F. S.; Fernandes, T.A new two-dimensional (2D) beamsteering antenna technique using a metamaterial transmitarray structure is proposed in this paper. The proposed technique allows the steering of the main lobe of the original antenna pattern in both elevation and azimuth planes when coupled to a conventional horn antenna. This has been demonstrated on a 5 × 5 unit-cell stacked structure, in which electromagnetic simulations, performed at 5.35 GHz, allowed the evaluation of the unit-cell parameters and the behaviour of the array. A fixed steering output with range of θ = 25° and φ= 25° in spherical coordinates is achieved by means of electromagnetic simulations and validated against experimental results, clearly demonstrating the potential of using metamaterials structures for beamsteering purposes.
- Edge detection based on Krawtchouk polynomialsPublication . Rivero-Castillo, Daniel; Pijeira, Héctor; Assunção, PedroAbstract Discrete orthogonal polynomials are useful tools in digital image processing to extract visual object contours in different application contexts. This paper proposes an alternative method that extends beyond classic first-order differential operators, by using the properties of Krawtchouk orthogonal polynomials to achieve a first order differential operator. Therefore, smoothing of the image with a 2-D Gaussian filter is not necessary to regularize the ill-posed nature of differentiation. Experimentally, we provide simulation results which show that the proposed method achieves good performance in comparison with commonly used algorithms.
- A feasibility study on the extension of the point scatterer formulation to vegetation mediaPublication . Leonor, Nuno; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Sanchez, ManuelThis paper aims at the development of a novel ray-tracing based method to characterise and model the electromagnetic behaviour of trees and vegetation volumes. This model uses various point scatterers with specific radiation characteristics, distributed within a computational volume, to describe the effect of the trees present in the radiowave propagation path. Additionally, the method to extract the parameters of the point scatterers from measurements is presented. The performance of this novel formulation was assessed in a tree formation scenario against measurements results obtained in a controlled environment, inside an anechoic chamber, at both 20 and 62.4 GHz.
- Further remarks on the "Smith is Huq" conditionPublication . Martins-Ferreira, Nelson; Van der Linden, TimWe compare the Smith is Huq condition (SH) with three commutator conditions in semi-abelian categories: first an apparently weaker condition which arose in joint work with Bourn and turns out to be equivalent with (SH), then an apparently equivalent condition which takes commutation of non-normal subobjects into account and turns out to be stronger than (SH). This leads to the even stronger condition that weighted commutators in the sense of Gran, Janelidze and Ursini are independent of the chosen weight, which is known to be false for groups but turns out to be true in any two-nilpotent semi-abelian category.
- Obesogens beyond Vertebrates: Lipid Perturbation by Tributyltin in the Crustacean Daphnia magna.Publication . Jordão, Rita; Casas, Josefina; Fabrias, Gemma; Campos, Bruno; Piña, Benjamín; Lemos, Marco; Soares, Amadeu M V M; Tauler, Romà; Barata, CarlosThe analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism. Recent data from the crustacean Daphnia magna points to three signaling hormonal pathways related to the molting and reproductive cycles [retinoic X receptor (RXR), juvenile hormone (JH), and ecdysone] as putative targets for exogenous obesogens. Objective: The present study addresses the disruptive effects of the model obesogen tributyltin (TBT) on the lipid homeostasis in Daphnia during the molting and reproductive cycle, its genetic control, and health consequences of its disruption. Methods: D. magna individuals were exposed to low and high levels of TBT. Reproductive effects were assessed by Life History analysis methods. Quantitative and qualitative changes in lipid droplets during molting and the reproductive cycle were studied using Nile red staining. Lipid composition and dynamics were analyzed by ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer. Relative abundances of mRNA from different genes related to RXR, ecdysone, and JH signaling pathways were studied by qRT-PCR. Results and Conclusions: TBT disrupted the dynamics of neutral lipids, impairing the transfer of triacylglycerols to eggs and hence promoting their accumulation in adult individuals. TBT’s disruptive effects translated into a lower fitness for offspring and adults. Co-regulation of gene transcripts suggests that TBT activates the ecdysone, JH, and RXR receptor signaling pathways, presumably through the already proposed interaction with RXR. These findings indicate the presence of obesogenic effects in a nonvertebrate species. © 2015, Public Health Services, US Dept of Health and Human Services. All rights reserved.
- Seismic behaviour of vernacular architecturePublication . Varum, H.; Pinheiro Rodrigues, Hugo Filipe; Lourenço, Paulo B.; Vasconcelos, GraçaVernacular buildings are in several seismic prone regions a relevant part of the building stock. They represent an important part of the of the cultural legacy, and of the technological and heritage context of the society. The present paper presents a revision of the effect of recent earthquake disasters in old buildings, and discusses the influence of the main structural elements in the vulnerability of these buildings, as well as the more common failure mechanisms. Finally, it is presented a review on the elements that more contribute to the seismic behaviour and performance of vernacular buildings.
- Knowledge of the Portuguese population on Basic Life Support and availability to attend trainingPublication . Dixe, Maria dos Anjos Coelho Rodrigues; Gomes, José Carlos RodriguesObjective: To evaluate the level of knowledge and the availability of the Portuguese population to attend training in Basic Life Support (BLS) and identify factors related to their level of knowledge about BLS. Method: Observational study including 1,700 people who responded to a questionnaire containing data on demography, profession, training, interest in training and knowledge about BLS. Results: Among 754 men and 943 women, only 17.8% (303) attended a course on BLS, but 95.6% expressed willingness to carry out the training. On average, they did not show good levels of knowledge on basic life support (correct answers in 25.9 ± 11.5 of the 64 indicators). Male, older respondents who had the training and those who performed BLS gave more correct answers, on average (p<0.01). Conclusion: The skill levels of the Portuguese population are low, but people are available for training, hence it is important to develop training courses and practice to improve their knowledge.
- Mecanismos de formação, redução e simulação da lesão cervical, resultantes de acidentes rodoviários com impacto lateralPublication . Baptista, Paulo António Roldão; Martinho, Pedro Miguel Gonçalves; Santos, Sérgio Pereira dosContexto: os acidentes rodoviários, com veículos ligeiros de passageiros, constituem um domínio que desafia a sociedade na procura continuada de soluções que mitiguem os seus impactos. Dados da Comissão Europeia revelam que, em 2011 e apenas no território dos países pertences à União Europeia, mais de 1,5 milhões de pessoas sofreram algum tipo de lesão em consequência de acidentes rodoviários, das quais, cerca de 250 mil terão sofrido lesões classificadas como graves. Esta dissertação visa a formulação de hipóteses para a redução da lesão cervical, em ocupantes de veículos sujeitos a colisão lateral e a validação de diretrizes para a conceção e o desenvolvimento, no âmbito da engenharia e do design, de uma solução de segurança passiva. Metodologia: recorrendo à literatura publicada, é analisada a anatomia, a fisiologia e a biomecânica da região cervical, bem como o controlo neuromuscular. São também revistos aspetos relevantes dos mecanismos de formação da lesão cervical, da sua classificação, das propriedades mecânicas dos tecidos e da ferramenta principal deste estudo que é a simulação e os modelos numéricos antropomórficos, de elementos finitos (FE). É apresentado o estado da arte do seu desenvolvimento para a simulação da biomecânica cervical e a compreensão dos mecanismos que conduzem à lesão e, posteriormente, à sua redução. Finalmente, são testados um conjunto de hipóteses para a redução do risco de lesão, no modelo ES-2re. Conclusões: a variação do módulo de elasticidade dos elementos viscoelásticos da região cervical do modelo ES-2re, revelou que o aumento global da rigidez cervical provoca um aumento dos valores máximos de deslocação, aceleração e velociade do CG da cabeça. Não é possível, no entanto, comparar o aumento da rigidez cervical avaliado nesta investigação com os testes onde essa rigidez acontece em resultado da ativação muscular. Por falta de correspondência, não é possível verificar a validade das hipóteses apresentadas em 4.4.
- Estudo de materiais estruturais de base polimérica para reforço de estruturas em betãoPublication . Costa, Pedro Filipe Carvalho; Martinho, Pedro Miguel Gonçalves; Barreiros, Fátima Maria CarvalhinhasVivemos na era das cidades de betão e cada vez mais a nível mundial se aplica este tipo de material. Na construção civil o betão é o material predominante produzido através de uma mistura de diversas matérias-primas, sejam naturais ou sintéticas, permitindo várias formas estruturais, desde as regulares às mais excêntricas, e é com enorme facilidade que o betão preenche os moldes ou cofragens. O ser humano, valendo-se da ambição e necessidade de superar novos desafios muitas vezes impostos por novas ideias, por questões levantadas pela arquitetura e pela engenharia, procurou desenvolver novos tipos de betão capazes de dar resposta a estas exigências e ser também cada vez mais uma matéria nobre da construção. Como tal, e sabendo que o betão também apresenta características que podem limitar a sua aplicação, tais como: baixa resistência à tração, diminuta ductilidade, elevada densidade dos elementos estruturais (significativamente superior ao das estruturas de aço com a mesma capacidade de carga) e vulnerabilidade à penetração de substâncias nocivas que aceleram o processo de corrosão das armaduras, ainda há margem para progressos no estudo do betão e possibilidade de desenvolver as suas propriedades mecânicas. Assim, ao longo do presente trabalho estudou-se e compreendeu-se as potencialidades do betão e as mais-valias e valências do betão reforçado com polímero, aliado aos reais benefícios na aplicabilidade deste material na construção.