Browsing by Issue Date, starting with "2009-06"
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- What does the ratio of injected current to electrode area tell us about current density in the brain during tDCS?Publication . Miranda, Pedro Cavaleiro; Faria, Paula; Hallett, Mark; Pascoal-Faria, PaulaObjective: To examine the relationship between the ratio of injected current to electrode area (I/A) and the current density at a fixed target point in the brain under the electrode during transcranial direct current stimulation (tDCS). Methods: Numerical methods were used to calculate the current density distribution in a standard spherical head model as well as in a homogeneous cylindrical conductor. Results: The calculations using the cylindrical model showed that, for the same I/A ratio, the current density at a fixed depth under the electrode was lower for the smaller of the two electrodes. Using the spherical model, the current density at a fixed target point in the brain under the electrode was found to be a non-linear function of the I/A ratio. For smaller electrodes, more current than predicted by the I/A ratio was required to achieve a predetermined current density in the brain. Conclusions: A non-linear relationship exists between the injected current, the electrode area and the current density at a fixed target point in the brain, which can be described in terms of a montage-specific I-A curve. Significance: I-A curves calculated using realistic head models or obtained experimentally should be used when adjusting the current for different electrode sizes or when comparing the effect of different current-electrode area combinations.
- Virtual and Physical Prototyping: EditorialPublication . Bártolo, Paulo; Chua, C.K.; Bartolo, PauloThe second half of 2009 is rich in international events in virtual and physical prototyping, a quite active and relevant research field. The Virtual and Physical Prototyping journal is associated with two of these events. The first one is the ECCOMAS Thematic Conference on Tissue Engineering designed to be a major international forum for the discussion of the current state-of-the-art in the fields of Tissue Engineering Modelling and Simulation. This Conference will focus on: . understanding the fundamentals of tissue engineering; . modelling and characterisation of scaffolds for tissue engineering; . modelling the relationship between scaffold, cell attachment, proliferation and differentiation; . design and development of scaffolds for tissue engineering; . fabrication and testing of scaffolds for tissue engineering; . cell signalling; . computational bone mechanics.
- Active stereo tracking of multiple free-moving targetsPublication . Perdigoto, Luis; Barreto, João P.; Caseiro, Rui; Araujo, Helder; Perdigoto, Luis;This article presents a general approach for the active stereo tracking of multiple moving targets. The problem is formulated on the plane, where cameras are modeled as ”line scan cameras” and targets are described as points with unconstrained motion. We propose to control the active system parameters in such a manner that the images of the targets in the two views are related by an homography. This homography is specified during the design stage and implicitly encodes the tracking behavior. It is shown that this formulation leads to an elegant geometric framework that enables to decide about the feasibility of a particular active tracking task. We apply it to prove that two cameras with rotation and zoom control, can track up to three moving targets, while assuring that the image location of each target is the same for both views. In addition, the framework is also useful for devising tracking strategies and deriving the required control equations. This feature is illustrated through a real experiment on tracking two independent targets using a binocular stereo head.
- Fracture toughness of the heat affected zone on Nd-YAG laser welded jointsPublication . Costa, J.M.; Ferreira, J.M.; Capela, C.; Capela, CarlosLaser deposit welding based on modern Nd-YAG lasers is a new mould repair process with advantages relatively to the traditional methods (Micro-plasma and TIG methods). For moulds steels there are no research studies about the laser deposit welding process effects in respect to fracture toughness, hardness and residual stresses variations in the laser-deposited layer and in the heat affected zone. These variations will have an important influence in the thermal-mechanical fatigue strength of the moulds parts. This paper is concerned on the study of the fracture toughness of transient microstructure regions in Nd-YAG laser welded joints performed in mould steels. Fracture toughness tests were performed in two hot-working tool steels: AISI H13 and AISI P20. Small welded specimens were prepared with U notches and filled with laser welding deposits. The hardness profiles were obtained at the middle cross-section of specimens against distance to the surface in order to identify the microstructures present at the crack tip region. Fracture toughness was evaluated and plotted against the Vickers hardness measured at the fatigue crack tip. Depending of the crack tip depth two very different toughness levels were observed in the H13 steel, while a lower variation of toughness was observed for the P20 steel. The values of fracture toughness observed in each specimen are consistent with the correspondent crack tip microstructure hardness.
- Partitioning carbon fluxes in a Mediterranean oak forest to disentangle changes in ecosystem sink strength during droughtPublication . Unger, Stephan; Máguas, Cristina; Pereira, João S.; M. Aires, Luis; S. David, Teresa; Werner, Christiane; Igreja Aires, Luis MiguelNet carbon flux partitioning was used to disentangle abiotic and biotic drivers of all important component fluxes influencing the overall sink strength of a Mediterranean ecosystem during a rapid spring to summer transition. Between May and June 2006 we analyzed how seasonal drought affected ecosystem assimilation and respiration fluxes in an evergreen oak woodland and attributed variations in the component fluxes (trees, understory, soil microorganisms and roots) to observations at the ecosystem scale. We observed a two thirds decrease in both ecosystem carbon assimilation and respiration (Reco) within only 15 days time. The impact of decreasing Reco on the ecosystem carbon balance was smaller than the impact of decreasing primary productivity. Flux partitioning of GPP and Reco into their component fluxes from trees, understory, soil microorganisms and roots showed that declining ecosystem sink strength was due to a large drought and temperature-induced decrease in understory carbon uptake (from 56% to 21%). Hence, the shallow-rooted annuals mainly composing the understory have a surprisingly large impact on the source/sink behavior of this open evergreen oak woodland during spring to summer transition and the timing of the onset of drought might have a large effect on the annual carbon budget. In response to seasonal drought Reco was increasingly dominated by respiration of heterotrophic soil microorganisms, while the root flux was found to be of minor importance. Soil respiration flux decreased with drought but its contribution to total daily CO2-exchange increased by 11.5%. This partitioning approach disentangled changes in respiratory and photosynthetic ecosystem fluxes that were not apparent from the eddy-covariance or the soil respiration data alone. By the novel combination of understory vs. overstory carbon flux partitioning with soil respiration data from trenched and control plots, we gained a detailed understanding of factors controlling net carbon exchange of Mediterranean ecosystems.
- LM2 hacia las enfermedades mentales Percepción del estigma de los estudiantes de Terapia Ocupacional de la Universidad de Castilla la Mancha hacia las personas con enfermedades mentalesPublication . Vidal-Barrantes, Francisco-Javier; Martínez, Beatriz MartínezLos comportamientos de discriminación en relación a las personas diagnosticadas con una enfermedad mental, estarán condicionados por una serie de conocimientos estereotipados. El presente estudio pretende mostrar los resultados de un estudio de investigación realizado en la Escuela de Terapia Ocupacional de la Universidad de Castilla la Mancha, utilizándose el “Cuestionario de Atribución AQ-27” validado para la población española, para demostrar hasta qué punto, los conocimientos teóricos en relación a la psiquiatría condicionan o no los preconceptos. En la investigación se observan con mayores puntuaciones en evitación, pero no se observan diferencias respecto a los otros estereotipos. A pesar de la repercusión que tiene el estigma sobre las personas enfermas y sus familiares, se ha observado que son muy pocos los artículos científicos o escasa la formación universitaria que se dedica a la estigmatización.
- Foreign entry strategies: strategic adaptation to various facets of the institutional environmentsPublication . Ferreira, Manuel Portugal; Li, Dan; Suk, Jang YongA comprehensive model of foreign entry strategies by multinational enterprises (MNEs) is developed in this paper, and a theory is proposed on how the entry strategy is likely to be determined in the interface between internal and external pressures for both conformity and legitimacy. In contrast to a selection rationale, an adaptation argument is developed, through which we enhance our understanding of the various facets of the institutional environment and the constraints MNEs encounter in their internationalization strategies.
- A Hybrid Differential Evolution Algorithm for Solving the Terminal Assignment ProblemPublication . Bernardino, Eugénia; Bernardino, Anabela; Sánchez-Pérez, Juan Manuel; Gómez-Pulido, Juan Antonio; Vega-Rodríguez, Miguel AngelThe field of communication networks has witnessed tremendous growth in recent years resulting in a large variety of combinatorial optimization problems in the design and in the management of communication networks. One of these problems is the terminal assignment problem. The task here is to assign a given set of terminals to a given set of concentrators. In this paper, we propose a Hybrid Differential Evolution Algorithm to solve the terminal assignment problem. We compare our results with the results obtained by the classical Genetic Algorithm and the Tabu Search Algorithm, widely used in literature.
- Ontology-supported database marketingPublication . Pinto, Filipe Mota; Marques, Alzira; Santos, Manuel Filipe; Mota Pinto, Filipe; Marques, AlziraDatabase marketing (DBM) provides in -depth analysis of marketing databases. Knowledge discovery in database techniques is one of the most prominent approaches to supporting some of the DBM process phases. However, in many cases, the benefits of these tools are not fully exploited by marketers. Complexity and amount of data constitute two major factors limiting the application of knowledge discovery techniques in marketing activities. Currently, ontologies may here play an important role in the marketing discipline. Motivated by its success in the area of artificial intelligence, we propose an ontology-supported DBM approach. The approach aims to enhance DBM with ontology by providing detailed step-phase specific information. Our research work has its foundations in a double methodological approach using the Delphi and Action Research methodologies. First, we use Delphi to structure related DBM knowledge, and then we align our work to the Action Research methodology in order to systematise the knowledge extraction process and knowledge base creation. The issues raised in this paper both respond and contribute to calls for a DBM process improvement. Our work was evaluated in the relationship marketing domain focusing on a relational marketing programme database. The findings of this study not only advance the state of DBM research, but also shed light on future research directions.
- Biofuel for the energy efficiency on a building with small CCHPPublication . Galvão, João; Leitão, S.; Malheiro, S.; Gaio, T.This document reports the development of a technical and economical study related to the use of a renewable energy source - biomass for electricity and heat production. It is a hybrid and autonomous system with solar PV panels and environment friendly process aiming the reduction of energy demand, costs and emissions. This energy model is a new sustainable standard about efficiency consumption energy (electrical and thermal demands) of a small hotel building, with the biomass gasification cogeneration technology. This system is one relevant contribute to certify the building agree to the new national legislation of building thermal behaviour.