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Funchal, Portugal

The University of Madeira dɐ mɐˈdɐjɾɐ], 32°39′32″N 16°55′28″W) is a Portuguese public university, created in 1988 in Funchal. It houses the following departments and autonomous sections. The university offers first and second cycle academic degrees in a wide range of fields, in accordance with the Bologna process. It is now under the CMU/Portugal agreement with Carnegie Mellon University, having master programme of Human Computer Interaction and Entertainment Technology. Students admitted will be eligible for scholarships and have internship opportunity during the summer break. In addition, Madeira Interactive Technologies Institute, founded in January 2010, is devoted to building international partnership with other educational institutes and industry. Wikipedia.

Aleksandrova N.,University of Madeira
International Journal of Engineering Science

Continuous stress-displacement solution to thin rotating solid disk problem is obtained for elastic-perfectly plastic material. The solution follows the classical approach based on equation of motion, Hooke's law, yield criterion, and conditions of continuity of stresses and/or displacement at the elastic/plastic boundary. It is shown that both the displacement field derived from the flow rule associated with Mises yield criterion and the stress distributions are continuous at the elastic/plastic boundary in contrast with the discontinuous solution based on Tresca yield criterion and its associated flow rule. © 2011 Elsevier Ltd. All rights reserved. Source

Barros J.D.,University of Madeira | Silva J.F.,University of Lisbon
IEEE Transactions on Industrial Electronics

This paper presents an optimal predictive controller for a multilevel converter-based dynamic voltage restorer (DVR), which is able to improve the voltage quality of sensitive loads connected to the electrical power network. The optimal predictive controlled multilevel DVR can restore sags and short interruptions while reducing the total harmonic distortion (THD) of the ac line voltages to values lower than 1%. The DVR is based on a three-phase neutral point clamped converter to dynamically inject a compensation voltage vector in series with the line voltage, through series-connected transformer secondary windings. To assure high-quality voltages for sensitive loads, we devise optimal predictive control laws for the injected compensation ac voltages. A suitable quadratic weighed cost functional is used to choose the voltage vector, minimizing both the ac voltage errors through current injection and the dc side capacitor voltage unbalancing. The performance of the proposed predictive controller is compared to classical proportional integral (PI): synchronous frame and stationary frame (P $+$resonant) controllers. The line-side filter capacitor topology is compared to the regular converter-side filter capacitor. Obtained experimental results show that the ac voltages are almost sinusoidal in steady-state operation when facing balanced and unbalanced sags and short interruptions with unbalanced loads. Voltage THD is reduced to values lower than 1%; the DVR is behaving also as a series active power filter for the ac voltages. © 2006 IEEE. Source

A new class of stationary solutions in the theory of glow discharges and plasma-cathode interaction in ambient-gas arc discharges has been found over the past 15 years. These solutions exist simultaneously with the solution given in textbooks, which describes a discharge mode with a uniform or smooth distribution of current over the cathode surface, and describes modes with various configurations of cathode spots: normal spots on glow cathodes, patterns of multiple spots recently observed on cathodes of glow microdischarges and spots on arc cathodes. In particular, these solutions show that cathode spots represent a manifestation of self-organization caused by basic mechanisms of the near-cathode space-charge sheath; another illustration of the richness of the gas discharge science. As far as arc cathodes are concerned, the new solutions have proved relevant for industrial applications. This work is dedicated to reviewing the multiple solutions obtained to date, their systematization, and analysis of their properties and physical meaning. The treatment is performed in the context of general trends of self-organization in bistable nonlinear dissipative systems, which allows one to consider glow discharges or arc-cathode interaction within a single physically transparent framework without going into mathematical details and offers a possibility of systematic computation of the multiple solutions. Relevant computational aspects and experimental data are discussed. © 2014 IOP Publishing Ltd. Source

Nouri A.,University of Madeira | Wen C.,Swinburne University of Technology
Critical Reviews in Solid State and Materials Sciences

Mechanical alloying/milling technique is characterized by the repeated welding and fracturing of powder particles in a high-energy ball mill, which often results in excessive cold welding and agglomeration of ductile particles. To achieve the critical balance between cold welding and fracturing, the surface of the deforming particles is modified by introducing a suitable organic material, called surfactant or process control agent (PCA). However, the use of surfactants is self-contradictory by nature and requires further consideration of the milling variables and type/amount of surfactant. The current article provides a practical approach to the promises and challenges associated with surfactants in mechanical alloying/milling. An attempt has been made to address the most crucial aspects correlated with surfactants, including contamination, the morphology and size of powder particles, formation of alloy and microstructural evolution, and powder yield, as well as the physico-mechanical properties, such as magnetism, density, hardness, and compressive strength. An overview is also given on the adsorption mechanism of surfactants onto the surface of powder particles, with a special emphasis on type, amount, and the addition time of surfactants in the mechanical alloying process. © 2014 Copyright Taylor and Francis Group, LLC. Source

Aleksandrova N.,University of Madeira
International Journal of Mechanical Sciences

Taking into account paradoxes of elastic-perfectly plastic material model, the problem of solid rotating disk is considered from the perspective of delivering continuous stress-strain analytical solution for engineering applications. The novelty of the solution is based on the semi-analytical treatment of non-linear von Mises yield criterion with its associated flow rule applied to the solid disk geometry containing singularity at the plastic center. By the procedure proposed, both continuous stress and strain fields are obtained at the elastic-plastic interface as opposite to the more common application of the Tresca yield criterion which leads to discontinuity either in stress or in displacement fields. The results obtained are especially important in numerical codes where singularities are not admitted. © 2014 Elsevier Ltd. Source

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