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Percorrer CDRsp - Artigos em revistas internacionais por Domínios Científicos e Tecnológicos (FOS) "Ciências Naturais::Ciências Físicas"
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- High-pressure range shock wave data for syntactic foamsPublication . Ribeiro, J.; Mendes, R.; Plaksin, I.; Campos, J.; Capela, Carlos; Elert, Mark; Furnish, Michael D.; Anderson, William W.; Proud, William G.; Butler, William T.Syntactic foams [SF] are a porous composite material resulting from the mixture of Hollow Glass Micro Spheres [HGMS] with a polymeric binder. Beyond a set of technological advantages over the polymer considered alone, SF present as an essential feature the possibility to control in wide limits the amount, the shape and the size of the pores and for that reason are being used for benchmarking in the area of shock wave [SW] behavior of porous materials. In this paper, SW loading experiments of SF samples were performed in order to assess the high-pressure range Hugoniot equation of state as a function of the SF initial density. Hugoniot data were assessed coupling the SW velocity within the SF samples with the SW velocity in a reference material or with manganin gauge results. The results obtained present a significant variation with the initial specific mass and can be described with appreciable precision by the Thouvenin/Hofmann Plate Gap model, while the concordance between the experimental results and the Gruüneisen model seems to be very dependent on the Gruüneisen coefficient values.
- The Importance of the Numerical Resolution of the Laplace Equation in the optimization of a Neuronal Stimulation TechniquePublication . Faria, PaulaFor the past few years, the potential of transcranial direct current stimulation (tDCS) for the treatment of several pathologies has been investigated. Knowledge of the current density distribution is an important factor in optimizing such applications of tDCS. For this goal, we used the finite element method to solve the Laplace equation in a spherical head model in order to investigate the three dimensional distribution of the current density and the variation of its intensity with depth using different electrodes montages: the traditional one with two sponge electrodes and new electrode montages: with sponge and EEG electrodes and with EEG electrodes varying the numbers of electrodes. The simulation results confirm the effectiveness of the mixed system which may allow the use of tDCS and EEG recording concomitantly and may help to optimize this neuronal stimulation technique. The numerical results were used in a promising application of tDCS in epilepsy.
- Strain sequence effect on fatigue life and fracture surface topography of 7075-T651 aluminium alloyPublication . Macek, Wojciech; Branco, Ricardo; Costa, José Domingos; Pereira, CândidaThe paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface topographies in 7075-T651 aluminum alloy specimens. Fatigue tests were performed in two ways: (i) constant-amplitude loading and (ii) two series of variable amplitude loading with non-zero mean strain values. The topography of the fatigue fractures was measured over their entire surfaces with the help of an optical confocal measurement system. The results of fatigue tests in the form of equivalent strains, εaeq, such as the weighted mean of strain components, εa1, εa2, and fatigue life, Nf, were used as the sum of the partial number of cycles N1, and N2. This study indicates, inter alia, that the values of the fracture surface parameter core height Sk, found in the two-step loading program, are linearly dependent on the equivalent strain, and logarithmically dependent on the fatigue life.