A methodology for the geometrically nonlinear analysis of orthotropic shells using a rotation-free shell triangular element is developed. The method is based on the computation of the strain and stress fields in the principal fiber orientation of the material. Details of the definition of the fiber orientation in a mesh of triangles and of the general formulation of the orthotropic rotation-free element are given. The accuracy of the formulation is demonstrated in examples of application.

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The effect of microwave radiation on the hydrothermal synthesis of the double perovskite Sr2FeMoO6 has been studied based on a comparison of the particle size and structural characteristics of products from both methods. A temperature, pressure, and pH condition screening was performed, and the most representative results of these are herein presented and discussed. Radiation of microwaves in the hydrothermal synthesis method led to a decrease in crystallite size, which is an effect from the reaction temperature. The particle size ranged from 378 to 318 nm when pH was 4.5 and pressure was kept under 40 bars. According to X-ray diffraction (XRD) results coupled with the size-strain plot method, the product obtained by both synthesis methods (with and without microwave radiation) have similar crystal purity. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques showed that the morphology and the distribution of metal ions are uniform. The Curie temperature obtained by thermogravimetric analysis indicates that, in the presence of microwaves, the value was higher with respect to traditional synthesis from 335 K to 342.5 K. Consequently, microwave radiation enhances the diffusion and nucleation process of ionic precursors during the synthesis, which promotes a uniform heating in the reaction mixture leading to a reduction in the particle size, but keeping good crystallinity of the double perovskite. Precursor phases and the final purity of the Sr2FeMoO6 powder can be controlled via hydrothermal microwave heating on the first stages of the Sol-Gel method.

The objective of this work is to obtain estimations of the amplification factors and used for torsion design of buildings, from experiments. For this study, simple one-storey torsionally unbalanced (TU) steel models were considered. Models consisted of a deck supported on four columns with a selected arrangement of hinges at column ends. Two theoretical structural eccentricities (e = 0.05 and 0.15) were considered. Models were excited with a simple long-period pendulum consisting of a hanging platform with a forced-vibration generator on it. Eight models were tested at several excitation levels (frequencies and force magnitudes) in both ranges of behaviour: elastic and inelastic. Experiments were conducted at three frequency ratios of excitation. Registered accelerations of the pendulum platform indicate that the experimental set-up leads to excitations that resemble narrow-band seismic ground motions. Frame shear force estimations, based on accelerations recorded at both deck sides, indicate that torsion design factors ( and ) depend on eccentricity. Estimations of frame shears based on measurements indicate that for normalized eccentricities e 0.025, the amplification can be between 2 and 3; while factor resulted between 0.0 and 1.6. systems can provide a good global understanding of the structural behaviour of buildings, more recent analytical studies turned to linear and nonlinear multi-storey systems, most of them modelled as shear beams.In addition to these analytical studies, understanding of the torsion structural behaviour has also been gathered from experiments and from instrumented buildings when they are either subjected to earthquakes or excited with forced-vibration generators. For instance Maheri et al.[1] tested a series of structural models. Their experimental work was limited to the study of frequencies and mode shapes within the linear response.As for measurements in buildings, Foutch [2] used two forced-vibration generators to study the vibration characteristics of a 12-storey steel frame building. These generators were placed at the building top. Frequencies and mode shapes obtained from experiments were compared with those computed with finite-element models. His results confirmed that displacement amplifications can arise in some structural frames when the building is susceptible to twist. Important observations on building torsion were also obtained by Lu and Hall [3] who monitored two instrumented buildings during the 1987 Whittier Narrows Earthquake. They concluded that symmetric buildings are particularly sensitive to accidental torsion.The previous findings obtained from measurements of either models or buildings are also important because they support some of the results obtained from analytical studies. However, it seems that additional work is needed to support other results, which can be incorporated in building codes. For instance, some one-storey model studies [4,5] observed that the amplification factor related with the estimation of design eccentricity benefits more large-eccen...

En este artículo se revisa la importancia del estudio de la hemodinámica como factor relevanteen el diagnóstico de enfermedades vasculares. En primer lugar se presenta la forma de estudiar las arterias y la hemodinámica como un sistema físico, para lo cual se presentan las ecuaciones generales de gobierno del problema. A continuación se plantea la discretización de las ecuaciones generales para proceder a su solución mediante el método de los elementos finitos. Finalmente se presenta un método eficiente que permite hacer la interacción entre el flujo sanguíneo y las arterias. Se exponen diferentes casos estudiados utilizando las técnicas anteriormente descritas.