SUMMARYThe return mapping algorithm is one of the most e cient procedures to solve elasto-plastic problems. However, a criticism that may be lodged against this method is the di culty of the practical computation of the consistent tangent matrix when the return is non-radial. Much research has been done to handle this matrix. In this paper, a uniÿed approach is presented in such a way that a simple closed-form expression gives the consistent tangent matrix for the classical constitutive relations (von Mises, Tresca, Mohr-Coulomb, Drucker-Prager). The basic ideas are in the properties of eikonal equations appearing in several ÿelds as image treatment, short time computation in elastic waves and others. The same kinds of ideas can be extended to non-classical models.

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The detection and characterisation of hepatic lesions is fundamental in clinical practice, from the diagnosis stages to the evolution of the therapeutic response. Hepatic magnetic resonance is a usual practice in the localization and quantification of lesions. Automatic segmentation of the liver is illustrated in Ti weighted images. This task is necessary for detecting the lesions. The proposed liver segmentation is based on 3D anisotropic diffusion processing without any control parameter. Combinations of edge detection techniques, histogram analysis, morphological post-processing and evolution of an active contour have been applied to the liver segmentation. The active contour evolution is based on the minimization of variances in luminance between the liver and its closest neighbourhood.

Abstract-The effect caused by ground fault current in a complex system of interacting electrodes is theoretically studied. The calculation applies to a specific case in which a set of interconnected electrodes, which are part of a grounding facility network, are activated by a ground fault current. Transferred potentials to adjacent passive electrodes are calculated and the most relevant parameters of the electrode system are evaluated. Finally, the convenience of connecting the grounding electrodes is discussed.Index Terms-Transferred potentials, grounding analysis, thin wire structures, earth fault, Method of Moments. I. INTRODUCTIONhe grounding systems (GS) are an essential part of the distribution networks of electrical power. Proper design of these systems prevents the occurrence of anomalous potential that can be dangerous to people and damage sensitive equipment and other neighboring facilities. The situations in which such a GS is indicated ranges from fault currents in electrical systems due to a malfunction, to an eventual lightning stroke. In any situation, the main target of a GS is to ensure that their electrical resistance is low enough to guarantee that fault currents dissipate mainly through the grounding grid into the earth, while maximum potential differences between close points on the earth's surface must be kept under certain tolerances (step, touch, and meshIn real GSs, we should take into account not only the conductors directly involved in the installation to be protected, but also any other conductor, connected to it or not, that can interact with the whole GS in case of activation [3]. The transfer of potentials between the grounding area and outer points by buried conductors, such as communication or signal circuits, neutral wires, pipes, rails, or metallic fences, may produce serious safety problems [4], [5]. It is also important to take into account the metal structures of the neighboring buildings of the protected area because there may appear transferred contact potentials out of the tolerance range [6], [7]. The ground potential rise (GPR) due to electrical current dissipation to the ground is a well known and studied phenomenon from the equations of electromagnetism [8]. However, in practical situations, many difficulties may appear which greatly complicate obtaining a solution. The shape of the electrodes and their spatial arrangement together with the possible interconnection of some of them, establish multiple boundary conditions added to the problem which can greatly complicate reaching an acceptable solution, which is obtained in most cases by applying numerical methods [9]-[12].In this paper, we consider a section of the electric power network of an urban area, where several Secondary Substations (SS) can be found together with their corresponding GS. In the case of study, the GSs of all the SS considered, are interconnected via the underground cable shield that transmits power to the SS. Besides ensuring an equal electric potential of all the interconnected GS electrodes, ...

Abstract:The influence of the irregular surface of a multi-layered soil on the estimation of the ground resistance of a complex electrode is studied. The electrode is placed in the first layer while the irregular surface is treated as the interface of an inhomogeneous volume filled with air and embedded in the first layer. A wide sample of irregular soils is generated and the variation of the electrode grounding resistance, as a function of a parameter that measures the surface unevenness, is evaluated. A stochastic model of the grounding resistance is proposed for which the variation of the electrode grounding resistance with its horizontal position relative to the surface is studied. The model features allow us to explain the variability found, as we are able to estimate the part of the uncertainty about the electrode grounding resistance measurements due to the non-planar soil surface.