Browsing by Issue Date, starting with "2009-03"
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- Spherical continuous wavelet transforms arising from sections of the Lorentz groupPublication . Ferreira, MiltonWe consider the conformal group of the unit sphere Sn−1, the so-called proper Lorentz group Spin+(1,n), for the study of spherical continuous wavelet transforms. Our approach is based on the method for construction of general coherent states associated to square integrable group representations over homogeneous spaces. The underlying homogeneous space is an extension to the whole of the group Spin+(1,n) of the factorization of the gyrogroup of the unit ball by an appropriate gyro-subgroup. Sections on it are constituted by rotations of the subgroup Spin(n) and Möbius transformations of the type ϕa(x) = (x −a)(1 + ax)−1, where a belongs to a given section on a quotient space of the unit ball. This extends in a natural way the work of Antoine and Vandergheynst to anisotropic conformal dilations on the unit sphere.
- Database marketing intelligence supported by ontologiesPublication . Pinto, Filipe; Santos, Manuel Filipe; Marques, Alzira; Mota Pinto, Filipe; Marques, AlziraMarketing departments handles with a great volume of data which are normally task or marketing activity dependent. This requires the use of certain, and perhaps unique, specific knowledge background and framework. This article aims to introduce an almost unexplored research at marketing field: the ontological approach to the Database Marketing process. We propose a framework supported by ontologies and knowledge extraction from databases techniques. Therefore this paper has two purposes: to integrate the ontological approach into Database Marketing and to create a domain ontology, a knowledge base that will enhance the entire process at both levels, marketing and knowledge extraction techniques. In order to structure and systematize the marketing concepts, Action Research methodology has been applied. At the end of this research the ontologies will be used to pre-generalize the Database Marketing knowledge through a knowledge base.
- Desenvolvimento do sentido do número na multiplicação. Um estudo de caso com crianças de 7/8 anosPublication . Rocha, Maria Isabel; Rocha, Maria Isabel; Menino, Hugo Alexandre; Menino, HugoNeste artigo discute-se o desenvolvimento do sentido do número na multiplicação com base num estudo de caso, construído no âmbito do projecto “Desenvolvendo o sentido do número: perspectivas e exigências curriculares” realizado, em Portugal, com crianças com idades compreendidas entre os cinco e os doze anos. A metodologia utilizada é de natureza qualitativa e interpretativa, com o formato de estudo de caso. A análise está centrada nas estratégias utilizadas pelas crianças do segundo ano de escolaridade (7/8 anos de idade) na resolução de problemas de problemas de multiplicação incluídos numa cadeia de tarefas aplicada na aula. Os resultados mostram que os contextos das tarefas, assentes no modelo rectangular, se assumiram como facilitadores da compreensão da multiplicação, das suas propriedades e de relações numéricas multiplicativas.
- Sandy beach macrofaunal communities on the western coast of Portugal – Is there a steady structure under similar exposed conditions?Publication . Gonçalves, Sílvia C.; Anastácio, Pedro M.; Pardal, Miguel A.; Cardoso, Patrícia G.; Ferreira, Susana M.; Marques, João C.; Gonçalves, Sílvia; Ferreira, SusanaThe structure of macrofaunal communities at two similar exposed sandy beaches on the western coast of Portugal was monitored for approximately 18 months by sampling all the beach area, from the shoreline to the base of the dunes. The beaches' physical environment, as well as community density and composition, seasonal variations and the potential relationships between biological data and environmental parameters were studied. The two beaches had similar exposure to wave action, but differed in terms of sediment grain size, extent of the intertidal area, sediment moisture content and, especially, in the potential food availability in the form of allochthonous debris. Differences were observed with regard to the communities' structure, namely regarding composition and relative contribution of the dominant species. Seasonality, especially temperature variations, and the interaction between seasons and the beach zones (supralittoral vs. intertidal) also had a strong influence on communities: controlling dominant species' density and the horizontal distribution of the dominant species, and promoting a differential utilization of the beach by several resident macrofaunal animals. The present study allows the identification of key species in exposed sandy beaches of western Portugal and demonstrates that a steady community structure does not persist in the similarly exposed conditions observed, which may be mainly a response to distinct detritus subsidies, combined with differences in sediment grain size, sediment moisture content and extent of the intertidal area.
- Study on the fatigue strength of AA 6082-T6 adhesive lap jointsPublication . Pereira, António; Ferreira, J.M.; Antunes, F.V.; Bartolo, PauloA research study on the fatigue behaviour of aluminium alloy adhesive lap joints was carried out to understand the effect of surface pre-treatment and adherends thickness on the fatigue strength of adhesive joints. The adherend material used for the experimental tests was an aluminium alloy 6082-T6 in the form of thin sheets, and the adhesive used was a high strength epoxy (Araldite 420 A/B). The surface preparation included an abrasive preparation (AP joints) and sodium dichromate-sulphuric acid etch (CSA joints). A maximum fatigue strength was obtained for the CSA surface treatment with a 1.0 mm adherends' thickness. The fastest fatigue damage was related with a high surface roughness and a high stress perpendicular to adhesive surface, which helps to promote the adhesive failure. A numerical analysis was also performed to understand the effect of the adherends thickness on the stress level. Results showed an increase of the out-of-plane peak stresses with the increase of adherends thickness.
- Use of available phasor measurements for system observability: A case studyPublication . Vide, Paula Sofia Pita da Silva e Castro; Barbosa, F. P. Maciel; Ferreira, Isabel M.This paper proposes the use of available PMU measurements for establishing network observability. State estimation is an important EMS application for providing real time, reliable and qualitative information on the system state. The observability analysis is the necessary function of the whole network state estimation.This paper addresses the incorporation of PMU measurements with the purpose of full network observability. The methodology is validated by the results on IEEE 14, 30 and 57 bus test system.
- Anything goes? Uma discussão ética sobre arte extremaPublication . Santos, David Rodrigues dosO ponto de ignição deste texto recai, quase na sua totalidade, na crescente necessidade de uma discussão sobre um tema que, pela sua natureza litigiosa, requer um debate capaz de identificar aspectos passíveis de contestação. A história da arte habituou-nos a inúmeros movimentos de ruptura, a paradoxos e a outras contendas ao longo dos anos. Contudo, começam agora a surgir, e cada vez com maior intensidade, debates, conferências, ensaios e análises mais cuidadas que tentam iluminar um caminho de investigação sobre estas novas contendas que, parte da produção artística, tem reclamado como sua. Ora, referimo-nos, especificamente a produções que foram historicamente denominadas das mais diversas formas. Nascendo sob a égide de Body Art (titulo que ganhou outras conotações ligadas a outros campos que não apenas o da produção artística), desembocou em outras acções que foram sendo nomeadas de Carnal Art, de Bioart, de Disturbing Art e, daquela que adoptamos para este texto, baptizada por Francesca Migleti – a Arte Extrema. Estas práticas ganharam o seu nome pelas suas características síncronas, de perturbação e de libertação através do uso do obsceno, da nudez, do sangue, de excrementos, mutilações, dor, perigo e, da possibilidade iminente da morte.
- Short-term load forecasting using information obtained from low voltage load profilesPublication . Sousa, João; Pires Neves, Luís; Humberto M.M. JorgeRecent researches in load forecasting are quite often based on the use of neural networks in order to predict a specific variable (maximum demand, active electric power or hourly consumption) using past values of the same variable and other exogenous factors proved to influence the value being predicted. This work aims to explore different input patterns in neural networks incorporating information derived from load profiles of different consumers' classes.
- Network reconfiguration using a genetic approach for loss and reliability optimization in distribution systemsPublication . Vitorino, Romeu; Jorge, Humberto M. M.; Pires Neves, LuísThis paper presents a new method to improve reliability and also minimize losses in radial distribution systems (RDS), trough a process of network reconfiguration, using a genetic algorithm approach. The methodology adopted to enhance reliability, uses the Monte Carlo simulation and an historical data of the network such as the level of reliability and the severity of potential contingencies in each branch. The method analyses the RDS in two perspectives. A first perspective of optimization considering no investment, therefore using only the switches presented in the network, and a second perspective of optimization where is given the possibility to place a limited number of tie-switches and thus get better results. Here, the number of tie-switches and the branches that can receive them are defined by a decision agent. The effectiveness of the proposed method is demonstrated through the analysis of a 69 bus RDS.
- Supply current polar chart analysis of SRM drives under normal and faulty operating conditionsPublication . S. Gameiro, Natália; A. J. Marques CardosoA polar chart of the power converter supply current, comprising phase currents and rotor mechanical position information, is presented, in order to characterize the dynamic operation of a SRM drive. Power converter supply current can be used as additional information of extreme importance when a sensor error or failure occurs. Its analysis is then important and permits to develop appropriate fault tolerant control strategies to solve failures or errors on phase current measurements. Time-domain waveforms of the phase currents and power converter supply current are presented and discussed. Two different speed operating conditions examples are presented, in order to understand the differences on SRM dynamic behavior in the all speed range. For both situations, the normal and the faulty operation due to the absence of one motor phase are analyzed. The adopted SRM control strategy, based on the electromagnetic torque regulation, is clearly explained for the all SRM speed range.