ESTG - Comunicações em conferências e congressos internacionais
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Browsing ESTG - Comunicações em conferências e congressos internacionais by Field of Science and Technology (FOS) "Ciências Naturais::Matemáticas"
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- An adaptive strategy for improving the performance of genetic programming-based approaches to evolutionary testingPublication . Ribeiro, José; Zenha-Rela, Mário Alberto; Vega, Francisco Fernández deThis paper proposes an adaptive strategy for enhancing Genetic Programming-based approaches to automatic test case generation. The main contribution of this study is that of proposing an adaptive Evolutionary Testing methodology for promoting the introduction of relevant instructions into the generated test cases by means of mutation; the instructions from which the algorithm can choose are ranked, with their rankings being updated every generation in accordance to the feedback obtained from the individuals evaluated in the preceding generation. The experimental studies developed show that the adaptive strategy proposed improves the algorithm's efficiency considerably, while introducing a negligible computational overhead.
- Assessing the influence of uncertainty in land cover mapping and digital elevation models on flood risk mappingPublication . Gonçalves, Luísa M.S.; Fonte, Cidália C.; Gomes, RicardoThis paper proposes an approach to assess the influence of the uncertainty present in the parameters dependent on the land cover and elevation data over the peak flow values and the subsequent delineation of flooded areas. The proposed approach was applied to produce vulnerability and risk maps that integrate uncertainty for the urban area of Leiria, Portugal. A SPOT-4 satellite image and DEMs of the region were used. The peak flow was computed using the Soil Conservation Service method and HECHMS, HEC-RAS, Matlab and ArcGIS software programs were used. The analysis of the results obtained for the presented case study enables the identification of the order of magnitude of uncertainty associated to the watershed peak flow value and the identification of the areas which are more susceptible to flood risk to be identified.
- Complexity Estimation for Load Balancing of 360-Degree Intra Versatile Video CodingPublication . Filipe, Jose N.; Monteiro Carreira, João Filipe; Tavora, Luis M. N.; Faria, Sergio; Navarro, Antonio; Assuncao, Pedro A. A.The ever increasing demand for image and video content poses new requirements to support higher resolutions and richer representation formats, creating new challenges in coding algorithms. The forthcoming Versatile Video Coding (VVC) standard aims to increase the coding efficiency of existing algorithms and it is particularly suitable for Ultra-High Definition (UHD) resolutions and 360° video. However, since coding efficiency gains are obtained at the cost of increased complexity, fast computational approaches are needed to cope with realtime requirements, such as parallel processing. Thus, this work presents a contribution towards efficient parallel encoding of 360° video, based on coding complexity estimation and nonuniform data-level splitting (slice-based) for load balancing across multiple processors. A machine learning approach is proposed to estimate the complexity of intra coding VVC, using uncorrelated features, obtained through Principal Component Analysis (PCA) and Extremely Randomised Trees (ERT). Then, a complexity-balanced slice partition is devised, taking advantage of the clustered complexity inherent to Equirectangular Projection (ERP). It is shown that coding complexity is estimated with an accuracy of 92.25%, and the encoding time is reduced by 8.50%, when compared to the case where the 360° frames are evenly split.
- Cooperative and decomposable approaches on royal road functionsPublication . Reis, Gustavo; Fernandéz, Francisco; Olague, Gustavo
- A meshfree method with domain decomposition for Helmholtz boundary value problemsPublication . Valtchev, SvilenIn the framework of meshfree methods, we address the numerical solution of boundary value problems (BVP) for the non-homogeneous modified Helmholtz partial differential equation (PDE). In particular, the unknown solution of the BVP is calculated in two steps. First, a particular solution of the PDE is approximated by superposition of plane wave functions with different wavenumbers and directions of propagation. Then, the corresponding homogeneous BVP is solved, for the homogeneous part of the solution, using the classical method of fundamental solutions (MFS). The combination of these two meshfree techniques shows excellent numerical results for non-homogeneous BVPs posed in simple geometries and when the source term of the PDE is sufficiently regular. However, for more complex domains or when the source term is piecewise defined, the MFS fails to converge. We overcome this problem by coupling the MFS with Lions non-overlapping domain decomposition method. The proposed technique is tested for the modified Helmholtz PDE with a discontinuous source term, posed in an L-shaped domain.
- On the formability, geometrical accuracy, and surface quality of sheet metal parts produced by SPIFPublication . Alves, Maria; Silva, M. B.; Alves, L. M.; Martins, P. A. F.; Xiaoyuan He; Huimin Xie; YiLan KangConventional sheet metal forming processes are not suitable for flexible small-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles, development and production lead times. In fact, the present need for flexible sheet metal forming techniques requires the development of innovative technological solutions that are capable of reducing the fixed and capital costs of sheet metal forming to a level where small-batch production becomes economically feasible. Single point incremental forming (SPIF) is a new sheet metal forming process with a high potential economic payoff for rapid prototyping applications and for small quantity production. In general terms a typical SPIF set-up makes use of a small number of low cost active tools components; (i) a blankholder, (ii) a backing plate and (iii) a single point forming tool. The tool path is generated in a CNC machining center and during the process there is no backup die supporting the back surface of the sheet. Despite the contributions of many researchers on the development of industrial applications and better characterization of the forming limits of the process, several key topics related to the mechanics of deformation, likely mode of failure, geometric accuracy and surface quality of the formed parts remain little understood and scarcely systematized. This paper attempts to provide new contributions about the abovementioned issues by means of a comprehensive experimental investigation performed under laboratory controlled conditions.
- On the information provided by uncertainty measures in the classification of remote sensing imagesPublication . Gonçalves, Luisa; Fonte, Cidália C.; Júlio, Eduardo N.B.S.; Caetano, MarioThis paper investigates the potential information provided to the user by the uncertainty measures applied to the possibility distributions associated with the spatial units of an IKONOS satellite image, generated by two fuzzy classifiers, based, respectively, on the Nearest Neighbour Classifier and the Minimum Distance to Means Classifier. The deviation of the geographic unit characteristics from the prototype of the class to which the geographic unit is assigned is evaluated with the Un non-specificity uncertainty measures proposed by [1] and the exaggeration uncertainty measure proposed by [2]. The classifications were evaluated using accuracy and uncertainty indexes to determine their compatibility. Both classifications generated medium to high levels of uncertainty for almost all classes, and the global accuracy indexes computed were 70% for the Nearest Neighbour Classifier and 53% for the Minimum Distance to Means Classifier. The results show that similar conclusions can be obtained with accuracy and uncertainty indexes and the latter, along with the analysis of the possibility distributions, may be used as indicators of the classification performance and may therefore be very useful tools. Since the uncertainty indexes may be computed to all spatial units, the spatial distribution of the uncertainty was also analysed. It's visualization shows that regions where less reliability is expected present a great amount of detail that may be potentially useful to the user.
- Searching for the corner seismic moment in worldwide dataPublication . Felgueiras, Miguel; Santos, Rui; Oliveira Martins, João PauloIn this paper the existence of the corner frequency value for the seismic moment distribution is investigated, analysing worldwide data. Pareto based distributions, usually considered as the most suitable to this type of data, are fitted to the most recent data, available in a global earthquake catalog. Despite the undeniable finite nature of the seismic moment data, we conclude that no corner frequency can be established considering the available data set. © 2015 AIP Publishing LLC.
- Three-dimensional array-based group testing algorithms with one-stagePublication . Oliveira Martins, João Paulo; Felgueiras, Miguel; Santos, RuiThe use of three-dimensional array-based testing algorithms is more efficient and accurate in some situations than other more commonly used algorithms to protocol pooled samples testing. We evaluate the advantages of using of this complex pooling schemes with only one stage in the problem of estimation of the prevalence rate of some disease. Using simulation work, we show that it does not seem to exist any advantage in using three or even higher-dimensional arrays for this type of problem.