ESTG - Artigos em revistas internacionais
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Percorrer ESTG - Artigos em revistas internacionais por Objetivos de Desenvolvimento Sustentável (ODS) "07:Energias Renováveis e Acessíveis"
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- A bi-criteria minimum spanning tree routing model for MPLS/overlay networksPublication . José Craveirinha; João Clímaco; Lúcia Martins; Silva, Carlos Gomes da; Nuno FerreiraThe MPLS platform enables the implementation of advanced multipath and multicast routing schemes. This work develops and analyses the performance of a new bicriteria minimum spanning tree model intended for routing broadcast messages in MPLS networks or constructing treebased overlay networks. The aim of the model is to obtain spanning trees which are compromise solutions with respect to two important traffic engineering metrics: load balancing cost and average delay bound. An exact solution to the formulated bi-criteria optimization problem is presented, which is based on an algorithm that enables the computation of the set of supported non-dominated spanning trees. An application model and a set of experiments on randomly generated Internet type topologies will also be presented. Finally a network performance analysis of the model considering three network performance metrics will be shown.
- AlineaGA - a genetic algorithm with local search optimization for multiple sequence alignmentPublication . Silva, Fernando José Mateus da; Pérez, Juan Manuel Sánchez; Pulido, Juan Antonio Gómez; Rodríguez, Miguel A. VegaThe alignment and comparison of DNA, RNA and Protein sequences is one of the most common and important tasks in Bioinformatics. However, due to the size and complexity of the search space involved, the search for the best possible alignment for a set of sequences is not trivial. Genetic Algorithms have a predisposition for optimizing general combinatorial problems and therefore are serious candidates for solving multiple sequence alignment tasks. Local search optimization can be used to refine the solutions explored by Genetic Algorithms. We have designed a Genetic Algorithm which incorporates local search for this purpose: AlineaGA. We have tested AlineaGA with representative sequence sets of the globin family. We also compare the achieved results with the results provided by T-COFFEE.
- Analysis of fatigue crack propagation in laser sintering metalPublication . Borrego, L. F. P.; Antunes, F. V.; Ferreira, J. A. M.; Costa, J. D.; Capela, C.Laser sintering metal has recently been used in the manufacture of components for different applications like aerospace or medicine. The approach to engineering design based on the cracks propagation assumption applying the concepts of linear elastic fracture mechanics (LEFM) is commonly used for aerospace engineering. However, fatigue crack propagation is linked to irreversible and non-linear mechanisms at the crack tip, therefore LEFM parameters can be successfully replaced by non-linear crack parameters, namely the plastic CTOD. A model linking da/dN with plastic CTOD is proposed here to characterize fatigue crack propagation. A comparison is made with other materials showing that for the same plastic CTOD the laser sintering material has a relatively large crack growth rate.
- Analysis of vehicle exhaust waste heat recovery potential using a Rankine cyclePublication . Domingues, António; Santos, Helder; Costa, MárioThis study evaluates the vehicle exhaust WHR (waste heat recovery) potential using a RC (Rankine cycle ). To this end, both a RC thermodynamic model and a heat exchanger model have been developed. Both models use as input, experimental data obtained from a vehicle tested on a chassis dynamometer. The thermodynamic analysis was performed for water, R123 and R245fa and revealed the advantage of using water as the working fluid in applications of thermal recovery from exhaust gases of vehicles equipped with a spark-ignition engine. Moreover, the heat exchanger effectiveness for the organic working fluids R123 and R245fa is higher than that for the water and, consequently, they can also be considered appropriate for use in vehicle WHR applications through RCs when the exhaust gas temperatures are relatively low. For an ideal heat exchanger, the simulations revealed increases in the internal combustion engine thermal and vehicle mechanical efficiencies of 1.4%-3.52% and 10.16%-15.95%, respectively, while for a shell and tube heat exchanger, the simulations showed an increase of 0.85%-1.2% in the thermal efficiency and an increase of 2.64%-6.96% in the mechanical efficiency for an evaporating pressure of 2 MPa. The results confirm the advantages of using the thermal energy contained in the vehicle exhaust gases through RCs. Furthermore, the present analysis demonstrates that improved evaporator designs and appropriate expander devices allowing for higher evaporating pressures are required to obtain the maximum WHR potential from vehicle RC systems.
- Are authentic leaders associated with more virtuous, committed and potent teams?Publication . Rego, Arménio; Vitória, Andreia; Magalhães, Ana; Ribeiro, Neuza; Pina e Cunha, MiguelThrough a team-level analysis, the study shows how authentic leadership (AL) predicts team potency both directly and through the mediating role of team virtuousness and team affective commitment. Data about AL and team virtuousness were collected two months before data collection on team affective commitment and team potency. Fifty-one teams were selected for testing the hypotheses. The main findings are the following: (a) AL predicts team affective commitment through the mediating role of team virtuousness; (b) team virtuousness predicts team potency through the mediating role of team affective commitment; (c) AL predicts team potency through the mediating role of team virtuousness and team affective commitment. By focusing on two positive constructs (AL and team virtuousness), for which interrelations have rarely been explored, the study contributes to the Positive Organizational Scholarship movement, and suggests that AL and virtuousness are good in themselves and also potential facilitators of team success.
- Assessing the relevance of load profiling information in electrical load forecasting based on neural network modelsPublication . Sousa, J.C.; Neves, L.P.; H.M. JorgeThe article is focused on evaluating the relevance of load profiling information in electrical load forecasting, using neural networks as the forecasting methodology. Different models, with and without load profiling information, were tested and compared, and, the importance of the different inputs was investigated, using the concept of partial derivatives to understand the relevance of including this type of data in the input space. The paper presents a model for the day ahead load profile prediction for an area with many consumers. The results were analyzed with a simulated load diagram (to illustrate a distribution feeder) and also with a specific output of a 60/15 kV real distribution substation that feeds a small town. The adopted methodology was successfully implemented and resulted in reducing the mean absolute percentage error between 0.5% and 16%, depending on the nature of the concurrent methodology used and the forecasted day, with a major benefit regarding the treatment of special days (holidays). The results illustrate an interesting potential for the use of the load profiling information in forecasting.
- Asymptotic Analysis of the Method of Fundamental Solutions for Acoustic Wave PropagationPublication . Valtchev, Svilen S.The asymptotic behavior of the Method of Fundamental Solutions (MFS) is analyzed, for the numerical solution of acoustic wave propagation problems in 2D and 3D bounded domains. As a consequence, a meshfree method, based on superposition of plane acoustic waves, referred to as the Plane Waves Method (PWM), is developed. Numerical examples are included in order to illustrate the relation between the two methods and the accuracy of the PWM.
- Autonomous Wireless Sensor with a Low Cost TEG for Application in Automobile VehiclesPublication . Costa, A.; Costa, D.; Morgado, J.; Santos, Helder; Ferreira, Carlos Daniel HenriquesThe present work consists in the development of an autonomous, low cost, reliable, energy scavenger sensor for automotive applications. Thermoelectric generators typically exhibit low efficiency but high reliability, making them suitable for autonomous, low average energy consumption, applications. A prototype sensor was developed for mounting in the engine exhaust pipe using a step-up voltage converter, a microcontroller, temperature and pressure sensing elements, conditioning electronics and a wireless transceiver, all powered by a low cost TEG (Peltier module TEC1-12706), through the scavenging of exhaust gases thermal energy. During the tests the prototype was able to sustain a regular signal transmission throughout the engine operation. The sensor was installed directly at the measuring point eliminating wired cables to hot and vibrating parts, thus, simplifying the installation of components and improving the reliability of the vehicle systems.
- Bases of the space of solutions of some fourth-order linear difference equations: applications in rational approximationPublication . Marcellán, Francisco; Mendes, Ana; Pijeira, HéctorIt is very well known that a sequence of polynomials {Qn(x)}∞n=0 orthogonal with respect to a Sobolev discrete inner product 〈f,g〉s = ∫Ifg dμ+λf′(0)g′(0), λ ∈ ℝ+ where μ is a finite Borel measure and I is an interval of the real line, satisfies a five-term recurrence relation. In this contribution we study other three families of polynomials which are linearly independent solutions of such a five-term linear difference equation and, as a consequence, we obtain a polynomial basis of such a linear space. They constitute the analogue of the associated polynomials in the standard case. Their of {Qn(x)}∞n=0 explicit expression in terms of using an integral representation is given. Finally, an application of these polynomials in rational approximation is shown.
- Bond strength of textured micropiles grouted to concrete footingsPublication . Veludo, J.; Dias-da-Costa, D.; Júlio, E.N.B.S.; Pinto, P.L.In a previous research study the authors performed push-out tests with smooth micropile inserts grouted under varying confinement conditions. It was shown that: (i) failure always occurs at the steel-to-grout interface; and (ii) the connection capacity increases with the passive confinement. To increase the connection capacity, it is a common practice to weld steel rings on the surface of the micropile and execute grooves in the predrilled hole. Therefore, a new study is herein presented aiming to widen the conclusions already drawn by analysing the influence of most important parameters in the bond strength of textured micropiles grouted to concrete footings. Laboratory tests were specifically designed for assessing the effect on the connection capacity of the: (i) diameter of the predrilled hole; (ii) insert’s embedment length; (iii) active confinement of the footing; and (iv) treatment of the hole surface. Eighteen textured micropile inserts grouted in RC footings were submitted to monotonic push-out tests until failure. In brief, it can be stated that the capacity of the micropile-to-footing connection increases by increasing the insert’s embedment length and by decreasing the hole diameter. Moreover, an adequate active confinement must be provided to achieve the required capacity.