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Alves M.A.,CEFT | Baptista A.,Rua Dr. Roberto Frias | Coelho P.M.,CEFT
Heat and Mass Transfer/Waerme- und Stoffuebertragung | Year: 2015

This work completes a previous study (Cruz et al., in J Heat Transf 134:091703, 2012) by evaluating the performance of the simplified method proposed therein for calculating the Nusselt number for laminar flow of non-Newtonian fluids in pipes with constant wall temperature. The methodology was tested using the Herschel-Bulkley, Bingham, Casson and Carreau-Yasuda generalized Newtonian models, and also the simplified form of the Phan-Thien–Tanner viscoelastic model. The error of the approximate methodology is below 3 %, except for yield stress fluids, for which the maximum error increases to 7.4 % for the cases analyzed, which cover a wide range of shear viscosity curves. An explicit expression of Nusselt number for Casson fluids is also presented. © 2015, Springer-Verlag Berlin Heidelberg. Source


Madaleno M.,University of Aveiro | Pinho C.,University of Aveiro | Ribeiro C.,Rua Dr. Roberto Frias
Lecture Notes in Energy | Year: 2014

This work anlyses the relationship between the returns for carbon, electricity and fossil fuel price (coal, oil and natural gas), focusing on the impacts of emissions trading via a Vector Error Autoregressive Correction Model (VECM) for both German and French markets. Results show that the effect of carbon depends on the energy mix of the country under analysis but that it is not the only factor. Less carbon coercion takes place in the European Energy Exchange (EEX) and innovations in carbon are not strongly reflected in electricity prices. Also, market power affects the correct transfer of prices, thus limiting cost increases. © Springer-Verlag Berlin Heidelberg 2014. Source


Khoshrou S.,INESC Porto | Cardoso J.S.,INESC Porto | Teixeira L.F.,Rua Dr. Roberto Frias
Machine Learning | Year: 2015

Nowadays, video surveillance systems are taking the first steps toward automation, in order to ease the burden on human resources as well as to avoid human error. As the underlying data distribution and the number of concepts change over time, the conventional learning algorithms fail to provide reliable solutions for this setting. In this paper, we formalize a learning concept suitable for multi-camera video surveillance and propose a learning methodology adapted to that new paradigm. The proposed framework resorts to the universal background model to robustly learn individual object models from small samples and to more effectively detect novel classes. The individual models are incrementally updated in an ensemble-based approach, with older models being progressively forgotten. The framework is designed to detect and label new concepts automatically. The system is also designed to exploit active learning strategies, in order to interact wisely with operator, requesting assistance in the most ambiguous to classify observations. The experimental results obtained both on real and synthetic data sets verify the usefulness of the proposed approach. © 2015, The Author(s). Source


Taveira-Pinto F.,Rua Dr. Roberto Frias | Santos I.,Rua Dr. Roberto Frias
Journal of Coastal Conservation | Year: 2014

The area of Cabedelo sand spit, located at the mouth of Douro River estuary (Porto, Portugal), reduced in recent decades. In order to study its evolution and also the impact of two breakwaters built to fix the river entrance, a dataset from 23 trimestral surveys using differential GPS techniques, conducted between 2001 and 2007, were considered. A time-series analysis and the estimation of relationships between Cabedelo spit area and several hydrodynamic parameters through statistical techniques were performed in order to determine which parameters have more influence in the Cabedelo spit behavior. From the time-series analysis a seasonal tendency is visible, with the lower values occurring in December and the higher values occurring in July. The estimation of a relationship between Cabedelo spit area and several independent variables reached better results when the dataset was divided in Part A (before the beginning of breakwaters construction) and Part B (during the breakwaters construction). An analysis of the morphological evolution of Cabedelo spit shoreline was also performed: (1) a simple analysis of retreat and accretion rates data with a geographical information system and (2) a more exhaustive analysis were performed using Empirical Orthogonal Functions (EOFs). The Cabedelo spit shoreline erosion occurs mostly on the West and North side, and the accretion mostly occurs in the area protected by the South breakwater. During the breakwater's construction, the Cabedelo spit shoreline presented high retreat rates, with a mean value greater than 100 m. In terms of spatial variance (EOFs analysis), when the dataset was divided in two parts, the first Principal Component (PC) represents 60.10 % and 89.86 % of the mean squared value of the data, for Part A and Part B, respectively. As proved, the breakwaters would tend to stabilize the coastline leading to a higher first PC value after breakwaters construction (Part B). © 2014 Springer Science+Business Media Dordrecht. Source


D Viegas C.M.,Rua Dr. Roberto Frias | Vasques F.,Rua Dr. Roberto Frias | Portugal P.,Rua Dr. Roberto Frias | Moraes R.,Federal University of Santa Catarina
Eurasip Journal on Wireless Communications and Networking | Year: 2014

With the widespread deployment of wireless mesh networks (WMNs) in industrial environments, real-time (RT) communication may benefit from the multi-hop relaying infrastructure provided by WMNs. However, RT communication must be able to coexist with non-RT traffic sources that will interfere with RT communication. Within this context, this paper assesses the impact of interferences caused by non-RT traffic sources upon RT traffic in IEEE 802.11s mesh networks. Through an extensive set of simulations, we assess the impact of external traffic sources upon a set of RT message streams in different communication scenarios. According to the simulation results, we infer that RT traffic in 802.11s networks may be highly affected by external interferences, and therefore, such interferences must be taken into account when setting-up 802.11s networks. By varying the network load imposed by external interferences, we provide some useful hints about utilization thresholds above which the network can no longer reliably support RT traffic. We also present insights about the setting-up of some network parameters in order to optimize the RT communication performance. © 2014, Viegas et al.; licensee Springer. Source

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