ESTG - Artigos em revistas internacionais
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- Coupled cell networks: Hopf bifurcation and interior symmetryPublication . Antoneli, Fernando; Dias, Ana; Paiva, RuiWe consider interior symmetric coupled cell networks where a group of permutations of a subset of cells partially preserves the network structure. In this setup, the full analogue of the Equivariant Hopf Theorem for networks with symmetries was obtained by Antoneli, Dias and Paiva (Hopf bifurcation in coupled cell networks with interior symmetries, SIAM J. Appl. Dynam. Sys. 7 (2008) 220-248). In this work we present an alternative proof of this result using center manifold reduction.
- Peer-to-Peer Jini for Truly Service-Oriented WSNsPublication . Pereira, António; Costa, Nuno; Serôdio, CarlosIn the past, wireless sensor networks emerged and so did some state-of-the-art applications that ran above them. Most of those applications followed the centralized model and were mainly focused on environmental data gathering, where sensor nodes sensed data from the environment to be sent to an external data server for later processing. Further research took wireless sensor networks to new application areas and, today, this technology gained the ubiquitous status. However, the use of wireless sensor networks is still reserved to experts, mainly due to the huge gap between user applications and the network. This fact has led us to successfully develop a new software stack, capable of running in any sensor node even in the most resource-constrained ones. The new software stack offers a truly service-oriented approach to design and implement applications and follows a widely accepted programming language and programming paradigm.
- A generic post-deblocking filter for block based image compression algorithmsPublication . Francisco, Nelson C.; Rodrigues, Nuno M. M.; Silva, Eduardo A.B. da; Faria, Sérgio M.M. deIn this paper we propose a new post-processing deblocking technique that is independent of the compression method used to encode the image. The development of this filter was motivated by the use of Multidimensional Multiscale Parser (MMP) algorithm, a generic lossy and lossless compression method. Since it employs an adaptive block size, it presents some impairments when using the deblocking techniques presented in the literature. This led us to the development of a new and more generic deblocking method, based on total variation and adaptive bilateral filtering. The proposed method was evaluated not only for still images, but also for video sequences, encoded using pattern matching and transform based compression methods. For all cases, both the objective and subjective quality of the reconstructed images were improved, showing the versatility of the proposed technique.
- Study of the requirements of an autonomous system for surface water quality monitoringPublication . Barros, M.; Granchinho, P.; Ferreira, C.; Neves, P.; Magalhães, H.; Santos, L.; Lopes, B.; Marques, J.; Pinho, H.; Mourato, SandraIn recent years, there has been increasing awareness of the preservation, protection and sustainable use of natural resources. Water resources, being one of the most important natural resources, face major threats due to contamination by pollutants of various types and origins. Maintaining the quality of water resources requires more robust, reliable and more frequent monitoring than traditional techniques of data collection based on sporadic, discontinuous and manual processes. The management of large geographical areas, the insufficient spatiotemporal discretization of the values of samples collected by traditional processes and the unpredictability of natural phenomena, require a new approach to data collection procedures. This article, which is the result of ongoing research, defines the technical requirements and technologies used in a continuous and regular monitoring of surface water quality in freshwater systems, whose data acquisition system helps to identify the sources of pollution and the contaminants flow along the waterways. The design of a versatile real-time water quality monitoring system, which, due to its environmental constraints should be based on renewable energies and wireless transfer of energy, will contribute to improve the management and effective protection of water resources.
- INTER-REGIONAL TRADE FLOW ESTIMATION THROUGH NON-SURVEY MODELS: AN EMPIRICAL ASSESSMENTPublication . Sargento, Ana L. M.; Ramos, Pedro Nogueira; Hewings, Geoffrey J.D.Inter-regional trade estimation has been pointed out as a crucial problem when constructing a multiregional input–output system. Knowledge of inter-regional trade flows, at least of the pooled volume of exports and imports by commodity, is critical in accounting for important spillover and feedback effects deriving from inter-regional linkages. However, in most countries, there are no completely reliable survey-based statistics on inter-regional trade. Thus, this paper intends to evaluate the reasonability of using indirect inter-regional trade estimates, comparing different estimating methods and assessing the sensitivity of the model results. Based on our empirical comparisons we conclude that input–output models are not greatly affected by the insertion of different trade values. Thus, our results support the use of indirect estimates for inter-regional trade, whenever survey-based data are unavailable.
- Elder care architecture - A physical and social approachPublication . Marcelino, Isabel; Barroso, João; Cruz, José Bulas; Pereira, AntónioAs we observe society in our days, we can see that people live longer; this means that we have an older population, more likely to have health issues. The special needs presented by the elderly are becoming a major concern for all of us, along with the lack of time demonstrated by society as a whole and, as a consequence, the lack of time is seen when families are not able to take care of their own elders. Many solutions are being presented in order to solve this problem. Some of them are taking advantage of the new technological developments in the body sensor networks area. In this paper we propose the architecture of a system called Elder Care. The Elder Care solution has two primary goals: monitoring vital signs, sending alerts to family and to specialized help and providing a social network in order to help end the elderly's social isolation.
- On-road performance comparison of two identical cars consuming petrodiesel and biodieselPublication . Serrano, L.; Carreira, V.; Câmara, R.; Gameiro da Silva, M.The present work studies the impact on vehicle performance and fuel consumption when using 100% diesel with petroleum origin (fossil diesel), compared to a mixture of 20% biodiesel in 80% of fossil diesel fuel (B20). For the accomplishment of this work an assessment was made using some primary tests on a chassis dynamometer, measuring vehicle performance and consumption. Subsequently a methodology was developed to conduct road tests. These considered the simultaneous circulation of two identical vehicles, fed with the two different fuels, but running on the same traffic and road conditions. Both vehicles were equippedwith geo-referencing systems (GPS) and datameasured by the Electronic Control Unit (ECU) were acquired. A precision balance was used in fuel consumption measurements of an auxiliary reservoir. The results demonstrate that the use of biodiesel has a penalizing effect on themass fuel consumption and on vehicle's performance, but this is largely dependent on the type of circuit used. One can also conclude that the methodology implemented on the study of fuel alternatives is extremely important. It is noticeable that for different route needs, different energetic solutions are more suitable than others, which can only be properly assessed by conducting road tests.
- Additive manufacturing as an enabling technology for digital construction: A perspective on Construction 4.0Publication . Duarte, José Pinto; Bartolo, Paulo Jorge; Craveiro, Flávio; Bartolo, HelenaThe construction sector plays a key role in any country's economy.According to a report published by the World Economic Forum, the construction industry currently accounts for about 6% of the world GDP [1] and is expected to reach around 14.7% in 2030 [2]. Construction is a strategically important sector for the European economy involving a wide range of stakeholders and companies, providing 18 million jobs[209]. According to the World Economic Forum, a 1% rise in productivity worldwide could save $100 billion a year in construction costs [3], with the potential to contribute for a country's competitiveness and sustainable development [4–6]. The construction industry consumes a very significant proportion of the raw materials produced around the world, using for instance 50% ofthe global steel production, and is responsible for 30% of the world greenhouse gas emissions. Nonetheless, it provides the fabric of the built environment on which society depends [1,3]. The population living in urban areas is rapidly increasing, which impacts the need for affordable houses, public transportation and utility infrastructure. Yet the perceived image of the construction sector is predominantly low-tech, still relying on craft-based methods, characterized by a poorperformance and quality image [7–10]. The 2016 survey ‘Sustainability in the Supply Chain’ carried out bythe Scape Group [11] concluded that 58% of all construction supplier And contractor respondents identified skilled workforce shortages as anobstacle for a future modernized construction sector
- Explaining the seismic moment of large earthquakes by heavy and extremely heavy tailed modelsPublication . Felgueiras, Miguel MartinsThe search of physical laws that explain the energy released by the great magnitude earthquakes is a relevant question, since as a rule they cause heavy losses. Several statistical distributions have been considered in this process, namely heavy tailed laws, like the Pareto distribution with shape parameter α ≈ 0. 6667. Yet, for the usually considered Californian region (where earthquakes with moment magnitude, MW, greater than 7. 9 were never registered) the Pareto distribution with index near the above mentioned seems to have a "too heavy" tail for explaining the bigger earthquakes seismic moments. Usually an exponential tapper is applied to the distribution right tail (above the so called corner seismic moment), or another distribution is considered to explain these high seismic moment data (like another Pareto with different shape parameter). The situation is different for other regions where seisms of larger magnitudes do occur, leading to data sets for which heavy or even extremely heavy tailed models are appropriated. The purpose of this paper is to reduce the seismic moment, M0, of the very large earthquakes to particular heavy and extremely heavy tailed distributions. Using world seismic moment information, we apply Pareto, Log-Pareto and extended slash Pareto distributions to the data, truncated for M0 ≥ 1021 Nm and for M0 ≥ 1021. 25 Nm. For these great seisms we conclude that extended slash Pareto is a promising alternative to the more traditional Pareto and Log-Pareto distributions as a candidate to the real model underlying the data.
- A maximum independent set approach for collusion detection in voting poolsPublication . Araujo, Filipe; Farinha, Jorge; Domingues, Patrício; Silaghi, Gheorghe Cosmin; Kondo, DerrickFrom agreement problems to replicated software execution, we frequently find scenarios with voting pools. Unfortunately, Byzantine adversaries can join and collude to distort the results of an election. We address the problem of detecting these colluders, in scenarios where they repeatedly participate in voting decisions. We investigate different malicious strategies, such as naïve or colluding attacks, with fixed identifiers or in whitewashing attacks. Using a graph-theoretic approach, we frame collusion detection as a problem of identifying maximum independent sets. We then propose several new graph-based methods and show, via analysis and simulations, their effectiveness and practical applicability for collusion detection.