Browsing by Issue Date, starting with "2010-03"
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- A deconvolution method to remove distortion caused by antenna radiation pattern from measurementPublication . Cui, Huajian; Caldeirinha, Rafael; Richter, JuergenThe influence of vegetation on radiowave signals has become an important aspect of the design of wireless communication links. In recent years the theory of Radiative Energy Transfer has been adopted as a reliable tool to predict the radiowave propagation through and near vegetation. However one major factor influencing accuracy of the measurement is the radiation pattern of the receiver antenna. The measured pattern will be the convolution product of the antenna radiation pattern and the phase function of the vegetation medium. The measured pattern therefore needs to undergo a deconvolution process before enable to provide reliable information. This paper presents a deconvolution method developed using optimum compensation filtering to remove the distortion caused by the receiver antenna radiation pattern. A pre-filtering technique using auto/cross-correlation is utilised to improve the deconvolution results, as well as an error function is deployed to determine the optimal parameter in the iterative filter.
- On the Expeditious Modelling of BuildingsPublication . Santos, Diana; Dionísio, Márcio; Rodrigues, Nuno; Pereira, AntónioThe active creation of buildings as recently been the focus of the creation of virtual urban environments due to the countless advantages it presents in areas such as architecture, cinema and video games, and even in several commercial applications. The present paper demonstrates a quick method for the creation of 3D building models from floor plans and other data (for example, photographs) that allow the user to create complete models ready for virtual visits in a matter of minutes. These models represent buildings with great detail levels, defining exterior and interior base geometries and allowing the representation and placement of typical house features, such as furniture and material types. The presented method is reinforced with its testing and implementation in a software prototype destined for the real estate market with which the models used throughout this article were produced.
- Layer manufacturing of magnesium and its alloy structures for future applicationsPublication . Ng, C. C.; Savalani, M. M.; Man, H. C.; Gibson, I.This research aims to develop a rapid layer manufacturing technique to provide magnesium bone substitute for future applications in the medical fields. Selective laser melting (SLM), which is a laser based additive layer manufacturing technique and capable of producing required geometries directly from CAD data, is selected to build magnesium structures. Magnesium has several intrinsic properties including its excellent biocompat-ibility, biodegradable, bioresorbabiltity and proper mechanical properties which would make it suitable for orthopaedic applications. This paper will discuss the status quo of this material and its future implications. A miniature SLM system was built to achieve better control of the atmospheric conditions in which the magnesium would melt. The results revealed that the SLM is a promising technique to fabricate magnesium substitute for various orthopaedic applications.
- A study of the mechanical behaviour on fibre reinforced hollow microspheres hybrid compositesPublication . Ferreira, J. A. M.; Capela, C.; Costa, J. D.This paper presents the results of an investigation into the effects of hollow glass microsphere fillers and of the addition of short fibre reinforcements on the mechanical behaviour of epoxy binding matrix composites. Properties like flexural stiffness, compressive strength, fracture toughness and absorbed impact energy, were studied. The specimens were cut from plates produced by vacuum resin transfer moulding having a microsphere contents of up to 50% and with fibre reinforcement up to 1.2% by volume. The tests performed with unreinforced composites show that flexural and compressive stiffness, maximum compressive stresses, fracture toughness and impact absorbed energy decrease significantly with increasing filler content. However, in terms of specific values, both flexural and compressive stiffness and impact absorbed energy increase with microsphere content. The addition of glass fibre produces only a slight improvement in the flexure stiffness and fracture toughness, while increasing significantly the absorbed impact energy. In contrast, the addition of a small percentage of carbon fibres produces an important improvement in both fracture toughness and flexure stiffness, when hybrid composites with 0.9% carbon fibre are compared to unreinforced foam, but did not improved absorbed impact energy.
- Model-driven development for early aspectsPublication . Sánchez, Pablo; Moreira, Ana; Fuentes, Lidia; Araújo, João; Magno, JoséCurrently, non-functional requirements (NFRs) consume a considerable part of the software development effort. The good news is that most of them appear time and again during system development and, luckily, their solutions can be often described as a pattern independently from any specific application or domain. A proof of this are the current application servers and middleware platforms that can provide configurable prebuilt services for managing some of these crosscutting concerns, or aspects. Nevertheless, these reusable pattern solutions presents two shortcomings, among others: (1) they need to be applied manually; and (2) most of these pattern solutions do not use aspect-orientation, and, since NFRs are often crosscutting concerns, this leads to scattered and tangled representations of these concerns. Our approach aims to overcome these limitations by: (1) using model-driven techniques to reduce the development effort associated to systematically apply reusable solutions for satisfying NFRs; and (2) using aspect-orientation to improve the modularization of these crosscutting concerns. Regarding the first contribution, since the portion of a system related to NFRs is usually significant, the reduction on the development effort associated to these NFRs is also significant. Regarding the second contribution, the use aspect-orientation improves maintenance and evolution of the non-functional requirements that are managed as aspects. An additional contribution of our work is to define a mapping and transition from aspectual requirements to aspect-oriented software architectures, which, in turn, contributes to improve the general issue of systematically relating requirements to architecture. Our approach is illustrated by applying it to a Toll Gate case study.
- EditorialPublication . Bartolo, Paulo; Chua, C. K.Welcome to a brand new year of 2010! In this editorial, we bring you the latest update concerning rapid prototyping technologies,which of coursemany of you are aware, include many terminologies such as layer manufacturing and solid freeform fabrication, amongst others. The longstanding need to standardize the terminologies within the rapid prototyping andmanufacturing industry has nowbeenmetwith a new ASTMInternational standard, ASTMF2792, Terminology for Additive Manufacturing Technologies. The new document is the first approved standard under the jurisdiction of ASTM Committee F42 on Additive Manufacturing Technologies, which was formed in 2009.
- Analysis of manufacturing parameters on the shear strength of aluminium adhesive single-lap jointsPublication . Pereira, A. M.; Ferreira, J. M.; Antunes, F. V.; Bártolo, P. J.An experimental and numerical investigation into the shear strength behaviour of aluminium alloy adhesive lap joints was carried out in order to understand the effect of geometrical and manufacturing parameters on the strength of adhesive bonding joints, with the aim of optimizing shear strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high strength epoxy. Five surface treatments were studied. The surface treatments process using sodium dichromate-sulphuric acid etch (CSA) and abrasive polishing (AP) resulted in improved joint shear strength when compared to acetone cleaning (SW), caustic etch (CE), and Tucker's reagent etch (TR). The decrease in surface roughness was found to increase the shear strength of single-lap joints. An increase in adherend thickness and overlap length was found to increase shear strength which means that an increase in joint rigidity increases its strength. A numerical analysis was developed to explain the effect of the geometrical parameters on rotation angle, stress and strain fields, and failure load. An increase in adherend thickness and overlap length decreases the joint rotation angle, reducing the plastic strain peak and therefore increasing the failure load.
- Compressing depth maps using multiscale recurrent pattern image codingPublication . Graziosi, D. B.; Rodrigues, N. M. M.; Pagliari, C. L.; Faria, S. M. M. de; Silva, E. A. B. da; Carvalho, M. B. DeThe use of the multidimensional multiscale parser algorithm for depth maps coding is proposed. The compression method uses a block-based approach, where efficient prediction combined with pattern matching is applied to the encoding of greyscale images, which convey the disparity or depth information of a 3D image. Simulation results show gains of up to 10dB when compared with state-of-the-art methods, such as JPEG2000 and H.264/AVC.
- Disentangling drought-induced variation in ecosystem and soil respiration using stable carbon isotopesPublication . Unger, Stephan; Máguas, Cristina; Pereira, João S.; Aires, Luis M.; David, Teresa S.; Werner, ChristianeCombining C flux measurements with information on their isotopic composition can yield a process-based understanding of ecosystem C dynamics. We studied the variations in both respiratory fluxes and their stable C isotopic compositions (δ13C) for all major components (trees, understory, roots and soil microorganisms) in a Mediterranean oak savannah during a period with increasing drought. We found large drought-induced and diurnal dynamics in isotopic compositions of soil, root and foliage respiration (δ13Cres). Soil respiration was the largest contributor to ecosystem respiration (Reco), exhibiting a depleted isotopic signature and no marked variations with increasing drought, similar to ecosystem respired δ13CO2, providing evidence for a stable C-source and minor influence of recent photosynthate from plants. Short-term and diurnal variations in δ13Cres of foliage and roots (up to 8 and 4‰, respectively) were in agreement with: (1) recent hypotheses on post-photosynthetic fractionation processes, (2) substrate changes with decreasing assimilation rates in combination with increased respiratory demand, and (3) decreased phosphoenolpyruvate carboxylase activity in drying roots, while altered photosynthetic discrimination was not responsible for the observed changes in δ13Cres. We applied a flux-based and an isotopic flux-based mass balance, yielding good agreement at the soil scale, while the isotopic mass balance at the ecosystem scale was not conserved. This was mainly caused by uncertainties in Keeling plot intercepts at the ecosystem scale due to small CO2 gradients and large differences in δ13Cres of the different component fluxes. Overall, stable isotopes provided valuable new insights into the drought-related variations of ecosystem C dynamics, encouraging future studies but also highlighting the need of improved methodology to disentangle short-term dynamics of isotopic composition of Reco.
- Contact center: information systems designPublication . Rijo, Rui; Varajão, João; Gonçalves, RamiroThe economic sector of contact centers is growing by more than 8% a year. It is a multidisciplinary area in which information systems are decisive to organizations' success. Contact Centers' Information Systems deal with real time requisites and critical business information. A theorybuilding research shows a framework with 12 key design factors to consider, which managers might use to develop projects and researchers may adopt for further investigation in the area of Contact Center design. This work intends to provide a valuable link between the research community and practitioners in industry.