ESTG - Artigos em revistas internacionais
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- Distributed Coding/Decoding Complexity in Video Sensor NetworksPublication . Cordeiro, Paulo J.; Assunção, PedroVideo Sensor Networks (VSNs) are recent communication infrastructures used to capture and transmit dense visual information from an application context. In such large scale environments which include video coding, transmission and display/storage, there are several open problems to overcome in practical implementations. This paper addresses the most relevant challenges posed by VSNs, namely stringent bandwidth usage and processing time/power constraints. In particular, the paper proposes a novel VSN architecture where large sets of visual sensors with embedded processors are used for compression and transmission of coded streams to gateways, which in turn transrate the incoming streams and adapt them to the variable complexity requirements of both the sensor encoders and end-user decoder terminals. Such gateways provide real-time transcoding functionalities for bandwidth adaptation and coding/decoding complexity distribution by transferring the most complex video encoding/decoding tasks to the transcoding gateway at the expense of a limited increase in bit rate. Then, a method to reduce the decoding complexity, suitable for system-on-chip implementation, is proposed to operate at the transcoding gateway whenever decoders with constrained resources are targeted. The results show that the proposed method achieves good performance and its inclusion into the VSN infrastructure provides an additional level of complexity control functionality.
- From guidelines to decision-making: using mobile applications and semantic web in the practical case of guides to support patientsPublication . Lima, Vinicius Costa; Rijo, Rui Pedro Charters Lopes; Pellison, Felipe Carvalho; Lima, Ricardo Roberto de; Correia, Ricardo João Cruz; Giuriati, Henrique Tresmonde; Alves, DomingosThe use of guidelines, procedures and recommendations is very common and also a simple way to structure, organize and retrieve relevant information that, in turn, may impact on patient care. However, it is necessary to expedite the retrieval of stored information. By simplifying the access to the desired data, it is possible to make the process practical, fast and intuitive for the health professional. The main goal of this article is to present a development approach for a project that proposes decision-making tools, based on guidelines, to assist health professionals in the care process of patients with specific diseases (or a combination of them). These tools will be developed for use on mobile devices and as a web-based system, which will transform a passive and declarative manual into an interactive tool that will provide not only data and information, but also knowledge through semantic web paradigm. Further, we will show an example of usability and feasibility of the proposed application through a functional prototype developed for Android platform.
- Development and proposal of a reference tool for semi-structured interviews for the characterization of the management in mental health networksPublication . Vinci, André Luiz Teixeira; Rijo, Rui Pedro Charters Lopes; Marques, João Mazzoncini de Azevedo; Alves, DomingosIn 2011, Brazil’s mental health care networks were instituted; nevertheless, standardized arrangements or indicators for network evaluation and management were not established. Hence, a proposed model to evaluate municipal and regional management of such networks was elaborated. One of its steps consists of semi-structured interviews aiming the network management knowledge. Therefore, this paper aimed the development and validation of a reference tool for conducting interviews focusing on assessment of mental health care network management. Methods comprised definition of interest topics, questions elaboration for each topic, preliminary script preparation, script validation, script adequacy and definition of final script. Thus, the developed script consisted of 29 questions and 8 follow-up questions divided over 8 topics (interviewee characterization, legislation, decision-making processes, network structure, management participants, information systems, indicators, and knowledge of external experiences). The script also added individualized field reports and interview planning and execution guidelines. After validation, it was concluded that chosen topics were relevant and appropriate, despite minor modifications; and estimated average interview time remained close to prior established. Therefore, the developed tool can assist collecting information to help managers evaluate the network and improving population health. Moreover, the tool could be used in other localities or adapted for other networks.
- Effects of Channel Estimation on Multiuser Virtual MIMO-OFDMA Relay-Based NetworksPublication . Jiménez, Víctor P. Gil; Ribeiro, Carlos; Gameiro, Atilio; Armada, Ana GarcíaA practical multiuser cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for multiple-input multiple-output-orthogonal frequency division multiple access (MIMO-OFDMA) relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm and using low-density parity-check (LDPC) codes. It is shown that this scheme is robust against channel estimation errors. It offers diversity and array gain, keeping the complexity low with a multiuser and multiantenna channel estimation algorithm that is simple and efficient. In addition, the combination with LDPC codes provides improved gains; diversity gains larger than 6dB can be easily obtained with a reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays.
- Assessment of the fatigue life on functional hybrid laser sintering steel componentsPublication . Ferreira, J.A.M.; Santos, L.M.S.; Silva, J. da; Costa, J.M.; Capela, C.The construction of hybrid parts: comprised of two different materials or obtained by two distinct technological processes is one of the main advantages of laser sintering metal. Various important aspects strongly affect the mechanical properties of sintering metal components: porosity, surface roughness, scan speed, layer thickness, and residual stresses. A major drawback is the occurrence of pores originating from initial powder contaminations, evaporation or local voids after powder-layer deposition, once these pores can act as stress concentrators leading to failure, especially under fatigue loading. The purpose of present work was to study the effect scan speed on the porosity and mechanical properties. Also the performance of two different material parts was studied. The sintering laser parts were manufactured in maraging steel AISI 18Ni300, while the substrates of hybrid specimens were produced alternatively in two materials: the steel for hot work tools AISI H13 and the stainless steel AISI 420. The results showed that a very high scan speed (400 or 600 mm/s) causes the appearance of high porosity percentages and consequent drastic reduction of tensile strength and stiffness. Tensile properties of sintered specimens and two different material parts was similar. However, the fatigue strength of two different material parts tends to decrease, for long lives, when compared with single sintered specimens. © 2015 The Authors.
- The Importance of the Numerical Resolution of the Laplace Equation in the optimization of a Neuronal Stimulation TechniquePublication . Faria, PaulaFor the past few years, the potential of transcranial direct current stimulation (tDCS) for the treatment of several pathologies has been investigated. Knowledge of the current density distribution is an important factor in optimizing such applications of tDCS. For this goal, we used the finite element method to solve the Laplace equation in a spherical head model in order to investigate the three dimensional distribution of the current density and the variation of its intensity with depth using different electrodes montages: the traditional one with two sponge electrodes and new electrode montages: with sponge and EEG electrodes and with EEG electrodes varying the numbers of electrodes. The simulation results confirm the effectiveness of the mixed system which may allow the use of tDCS and EEG recording concomitantly and may help to optimize this neuronal stimulation technique. The numerical results were used in a promising application of tDCS in epilepsy.
- Formulations for the Weight-Constrained Minimum Spanning Tree ProblemPublication . Requejo, Cristina; Agra, Agostinho; Cerveira, Adelaide; Santos, EuláliaWe consider the Weight-constrained Minimum Spanning Tree problem (WMST). The WMST aims at finding a minimum spanning tree such that the overall tree weight does not exceed a specified limit on a graph with costs and weights associated with each edge. We present and compare, from the computational point of view, several formulations for the WMST. From preliminary computational results we propose a model that combines a formulation similar to the well known Miller-Tucker-Zemlin formulation with the cut-set inequalities.
- Radio Frequency Numerical Simulation Techniques Based on Multirate Runge‐Kutta SchemesPublication . Oliveira, Jorge F.; Pedro, José C.; Oluwole D. MakindeElectronic circuit simulation, especially for radio frequency (RF) and microwave telecommunications, is being challenged by increasingly complex applications presenting signals of very different nature and evolving on widely separated time scales. In this paper, we will briefly review some recently developed ways to address these challenges, by describing some advanced numerical simulation techniques based on multirate Runge‐Kutta schemes, which operate in the one‐dimensional time and also within multidimensional frameworks.
- Experimental study of thermal and vibrational behaviour of an induction motorPublication . García, D.; Oliveira, F.T.; Peláez, G.; Donsión, M.P.Induction machines are the most common option to generate rotary motor in industry, and at present the use of variable speed drives with these machines is spreading in an unprecedented way. This has mostly to do with the advantages provided by these devices, such as added versatility and, in most cases, improved overall efficiency. Because variable speed drives provide a modified wave form, non-sinusoidal, several power quality issues and some effects can be observed. This paper focus particularly on the thermal and vibrational effects, and forms part of a broader study on the effects of the power supply on the behaviour of dynamic rotary loads.
- Weakly Mal’tsev Categories and Strong RelationsPublication . Janelidze, Zurab; Martins-Ferreira, NelsonWe define a strong relation in a category C to be a span which is “orthogonal” to the class of jointly epimorphic pairs of morphisms. Under the presence of finite limits, a strong relation is simply a strong monomorphism R → X × Y . We show that a category C with pullbacks and equalizers is a weakly Mal’tsev category if and only if every reflexive strong relation in C is an equivalence relation. In fact, we obtain a more general result which includes, as its another particular instance, a similar well-known characterization of Mal’tsev categories.