ESTG - Artigos em revistas internacionais
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- Customized crowds and active learning to improve classificationPublication . Costa, Joana; Silva, Catarina; Antunes, Mário; Ribeiro, BernardeteTraditional classification algorithms can be limited in their performance when a specific user is targeted. User preferences, e.g. in recommendation systems, constitute a challenge for learning algorithms. Additionally, in recent years user’s interaction through crowdsourcing has drawn significant interest, although its use in learning settings is still underused. In this work we focus on an active strategy that uses crowd-based non-expert information to appropriately tackle the problem of capturing the drift between user preferences in a recommendation system. The proposed method combines two main ideas: to apply active strategies for adaptation to each user; to implement crowdsourcing to avoid excessive user feedback. A similitude technique is put forward to optimize the choice of the more appropriate similitude-wise crowd, under the guidance of basic user feedback. The proposed active learning framework allows non-experts classification performed by crowds to be used to define the user profile, mitigating the labeling effort normally requested to the user. The framework is designed to be generic and suitable to be applied to different scenarios, whilst customizable for each specific user. A case study on humor classification scenario is used to demonstrate experimentally that the approach can improve baseline active results.
- Tunable square slot FSS EC modelling and optimisationPublication . Ferreira, David; Caldeirinha, Rafael Ferreira Silva; Cuiñas, Iñigo; Fernandes, Telmo RuiAn equivalent circuit model for tunable square slot frequency selective surfaces (FSS) is proposed. Tuning is achieved with the inclusion of a discrete capacitance element, at key points within the FSS unit cell. The equivalent circuit model takes into account the FSS physical attributes. The performance of the proposed equivalent circuit model was evaluated against results obtained from appropriate electromagnetic simulations. Results demonstrate the validity of the proposed equivalent circuit model, in which good estimations of the frequency response of FSS structures were obtained. A RMSE value of 190 MHz was extracted from the complete parametric simulation set. The model was further validated against measurements performed on a tunable active FSS prototype inside an anechoic chamber. Tuning of the FSS was achieved by means of bias voltage to modify the varicaps capacitance value. A relatively good agreement was verified between equivalent circuit model, electromagnetic simulations and measurements. Finally, this work is sought to be a useful contribution to the literature on this topic, by improving on the elementary models of such FSS structures and be useful as a good and fast first approach to determine approximate FSS unit cell dimensions.
- Effect of saline environment on mechanical properties of adhesive jointsPublication . Pereira, A. M.; Reis, P.N.B.; Ferreira, J.A.M.; Antunes, F.V.Literature reports very few works about the effect of corrosive environments on the mechanical properties of adhesive joints. Therefore, the present study intends to contribute for a better understanding of the effect of saline solution on the mechanical properties of single-lap adhesive joints. The specimens were manufactured using Docol 1000 high strength steel plates with 1 mm of thickness and Araldite® 420 A/B epoxy adhesive. The static shear strength of the joints was influenced by the exposure time in saline solutions only up to 120 h, and remained, after this period, nearly constant. In terms of fatigue strength, for 105 cycles, a decrease about 25% and 39% occurred in specimens immersed during 120 h in deionised water and saline solution, respectively, comparatively to the control samples.
- The role of country and industry factors during volatile timesPublication . Marcelo, José Luis Miralles; Quirós, José Luis Miralles; Martins, JoséGlobal stock market investment has highlighted the debate about whether country effects are typically more relevant than sector/industry effects in international stock returns. This paper studies the roles of country and industry effect on several major European financial markets. We find clear evidence that diversification over industries yields fundamental relevance for obtaining more efficient portfolios, and that ignoring the industrial mix leads to an important loss of diversification benefits. In addition we examine the behavior of country and industry effects during high (low) volatility periods. Alluring investors to diversify across industries requires a country to industry effect ratio to be substantially lower during high than low volatility periods. The fact that countries tend to move together during volatile periods posits that industry diversification may provide relatively more protection in crisis. For the entire time span we find that industries provide better protection in times of high volatility relative to countries. However, countries do perform better in absolute terms. Finally, we conclude that investors seeking global representation in their investment portfolios should continue to consider diversifying broadly across both countries and industries. Our findings have important implications for international portfolio diversification.
- Knowledge Representation of Crime-Related Events: a Preliminary ApproachPublication . Carnaz, Gonçalo; Nogueira, Vítor Beires; Antunes, MárioThe crime is spread in every daily newspaper, and particularly on criminal investigation reports produced by several Police departments, creating an amount of data to be processed by Humans. Other research studies related to relation extraction (a branch of information retrieval) in Portuguese arisen along the years, but with few extracted relations and several computer methods approaches, that could be improved by recent features, to achieve better performance results. This paper aims to present the ongoing work related to SEM (Simple Event Model) ontology population with instances retrieved from crime-related documents, supported by an SVO (Subject, Verb, Object) algorithm using hand-crafted rules to extract events, achieving a performance measure of 0.86 (F-Measure).
- District Metered Areas Design Under Different Decision Makers’ Options: Cost AnalysisPublication . Gomes, Ricardo; Marques, Alfeu S. A.; Sousa, JoaquimWater loss is a big challenge for water supply companies worldwide, and the Water Network Partitioning (WNP) is an excellent tool for water loss management–particularly in the current difficult economic and financial conditions. WNP is a recent research line and consists in dividing the water distribution network into smaller zones called District Metered Areas (DMAs) with one (or more, in exceptional cases) supply point, to reduce the network complexity and/or allow pressure management. Since there are several possible future scenarios, such as the water demand and/or the infrastructure degradation forecasts, which may have different impacts on the hydraulic behaviour, in this paper a computational application, based on an optimization model, is proposed to achieve a compromise between robustness required for the DMAs design (using a baseline scenario) and different decision makers’ options (using other scenarios with a lower “probability” of occurrence), to reduce the total cost. The objective function reflects the minimization of the squared deviations between the total cost of the DMAs design and the minimum cost for each scenario forecasted for the project plan, multiplied by the weight or “probability” of occurrence for each of the scenarios. The performance of the computational application is illustrated with a case study, and the results are encouraging.
- Principal Schottky bundles over Riemann surfacesPublication . Casimiro, A. C.; Ferreira, Susana; Florentino, C.We introduce and study (strict) Schottky G-bundles over a compact Riemann surface X, where G is a connected reductive algebraic group. Strict Schottky representations are shown to be related to branes in the moduli space of G-Higgs bundles over X, and we prove that all Schottky G-bundles have trivial topological type. Generalizing the Schottky moduli map introduced in Florentino (Manuscr Math 105:69–83, 2001) to the setting of principal bundles, we prove its local surjectivity at the good and unitary locus. Finally, we prove that the Schottky map is surjective onto the space of flat bundles for two special classes: when G is an abelian group over an arbitrary X, and the case of a general G-bundle over an elliptic curve.
- Global spatial risk assessment of sharks under the footprint of fisheriesPublication . Queiroz, Nuno; Humphries, Nicolas E.; Couto, Ana; Vedor, Marisa; Costa, Ivo da; Sequeira, Ana M. M.; Mucientes, Gonzalo; Santos, António M.; Abascal, Francisco J.; Abercrombie, Debra L.; Abrantes, Katya; Acuña-Marrero, David; Afonso, André; Afonso, Pedro; Anders, Darrell; Araujo, Gonzalo; Arauz, Randall; Bach, Pascal; Barnett, Adam; Bernal, Diego; Berumen, Michael L.; Bessudo Lion, Sandra; Bezerra, Natalia P. A.; Blaison, Antonin V.; Block, Barbara A.; Bond, Mark E.; Bonfil, Ramón; Bradford, Russell W.; Braun, Camrin D.; Brooks, Edward J.; Brooks, Annabelle; Brown, Judith; Bruce, Barry D.; Byrne, Michael E.; Campana, Steven E.; Carlisle, Aaron B.; Chapman, Demian D.; Chapple, Taylor K.; Chisholm, John; Clarke, Christopher R.; Clua, Eric G.; Cochran, Jesse E. M.; Crochelet, Estelle C.; Dagorn, Laurent; Daly, Ryan; Devia Cortés, Daniel; Doyle, Thomas K.; Drew, Michael; Duffy, Clinton A. J.; Erikson, Thor; Espinoza, Eduardo; Ferreira, Luciana C.; Ferretti, Francesco; Filmalter, John D.; Fischer, G. Chris; Fitzpatrick, Richard; Fontes, Jorge; Forget, Fabien; Fowler, Mark; Francis, Malcolm P.; Gallagher, Austin J.; Gennari, Enrico; Goldsworthy, Simon D.; Gollock, Matthew J.; Green, Jonathan R.; Gustafson, Johan A.; Guttridge, Tristan L.; Guzman, Hector M.; Hammerschlag, Neil; Harman, Luke; Hazin, Fábio H. V.; Heard, Matthew; Hearn, Alex R.; Holdsworth, John C.; Holmes, Bonnie J.; Howey, Lucy A.; Hoyos, Mauricio; Hueter, Robert E.; Hussey, Nigel E.; Huveneers, Charlie; Irion, Dylan T.; Jacoby, David M. P.; Jewell, Oliver J. D.; Johnson, Ryan; Jordan, Lance K. B.; Jorgensen, Salvador J.; Joyce, Warren; Daly, Clare A. Keating; Ketchum, James T.; Klimley, A. Peter; Kock, Alison A.; Koen, Pieter; Ladino, Felipe; Lana, Fernanda O.; Lea, James S. E.; Llewellyn, Fiona; Lyon, Warrick S.; MacDonnell, Anna; Macena, Bruno C. L.; Marshall, Heather; McAllister, Jaime D.; McAuley, Rory; Meÿer, Michael A.; Morris, John J.; Nelson, Emily R.; Papastamatiou, Yannis P.; Patterson, Toby A.; Peñaherrera-Palma, Cesar; Pepperell, Julian G.; Pierce, Simon J.; Poisson, Francois; Quintero, Lina Maria; Richardson, Andrew J.; Rogers, Paul J.; Rohner, Christoph A.; Rowat, David R. L.; Samoilys, Melita; Semmens, Jayson M.; Sheaves, Marcus; Shillinger, George; Shivji, Mahmood; Singh, Sarika; Skomal, Gregory B.; Smale, Malcolm J.; Snyders, Laurenne B.; Soler, German; Soria, Marc; Stehfest, Kilian M.; Stevens, John D.; Thorrold, Simon R.; Tolotti, Mariana T.; Towner, Alison; Travassos, Paulo; Tyminski, John P.; Vandeperre, Frederic; Vaudo, Jeremy J.; Watanabe, Yuuki Y.; Weber, Sam B.; Wetherbee, Bradley M.; White, Timothy D.; Williams, Sean; Zárate, Patricia M.; Harcourt, Robert; Hays, Graeme C.; Meekan, Mark G.; Thums, Michele; Irigoien, Xabier; Eguiluz, Victor M.; Duarte, Carlos M.; Sousa, Lara L.; Simpson, Samantha J.; Southall, Emily J.; Sims, David W.Effective ocean management and the conservation of highly migratory species depend on resolving the overlap between animal movements and distributions, and fishing effort. However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions (the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real-time, dynamic management.
- 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.
- Intensive Agriculture Production in Low Consumption Energy EnvironmentPublication . Galvão, J.; Nabais, A.; Correia, H.; Amaro, P.; Negrão, A.; Ribeiro, V.This work involves the study and dissemination of energy management practices for greater energy efficiency in a context of renewable energies, intensive production of flowers in greenhouses and the integration of data sensors, which enables the system to connect and exchange information from these systems to end users in a communication network. These several variavles can be monitored in real time with the support of the Internet of Things (IoT). It is intended to conceive a software and hardware prototype, in one new environment consumption, with the change for renewable energy sources, for better control of the variables involved in plant growth and more sustainability, in this intensive agricultural production sector.