Browsing by Issue Date, starting with "2007-05"
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- Long distance real-time echo cancellationPublication . J. Ferreira, Artur; Marques, Paulo; Carvalho, HélderThis paper describes an implementation of a long distance echo canceller, operating on full-duplex with handsfree and in real-time with a single Digital Signal Processor (DSP). The proposed solution is based on short length adaptive filters centered on the positions of the most significant echoes, tracked by time delay estimators. To deal with double talking situations a speech detector is employed. The floating-point DSP TMS320C6713 from Texas Instruments is used with software written on the C++ programming language using some compiler optimizations to reduce execution time. The resulting algorithm enables long distance echo cancellation with low computational requirements. It reaches greater echo return, loss enhancement and shows faster convergence speed than the conventional solu tion. Our experimental results also approach the CCITT G.165 recommendation for echo cancellers.
- Grupo profissional dos professores: proposta de mapeamento da produção científica produzida em PortugalPublication . Campos, JoanaA investigação produzida acerca do grupo profissional dos professores não é recente em Portugal e para o seu desenvolvimento têm contribuido investigadores de diversos domínios científicos.
- Reactividade infantil e a qualidade da interacção mãe-filhoPublication . Faria, Anabela; Fuertes, MarinaNo quadro dos estudos sobre o relacionamento mãe-filho, procurámos averiguar a relação entre a reactividade infantil observada em condições de stress e a qualidade do comportamento interactivo infantil e materno em jogo livre. Para o efeito, seleccionámos uma amostrade 40 díades mãe-filho cujos bebés tinham cerca de 3 meses e não apresentavam nenhuma condição declarada de risco. A qualidade da interacção mãe-filho foi avaliada em jogo livre através da escala CARE-Index. Para testar a reactividade infantil submetemos os bebés à situação experimental Still-Face. Os resultados mostram que a reactividade infantil expressa naquela situação laboratorial não é independente do comportamento dos bebés em jogo livre. Com efeito, os bebés com maior dificuldade em conformar-se com a ausência de resposta materna apresentam um comportamento menos cooperativo e difícil em jogo livre. Em sentido inverso, os bebés que em jogo livre são menos participativos apresentam menores índices de reactividade negativa quando a mãe mantém a cara inexpressiva. Em termos diádicos, verificamos que existe uma forte correlação entre o comportamento cooperativo do bebé e a sensibilidade materna em jogo livre. Os resultados são discutidos no quadro do desenvolvimento dos processos de interacção mãe e filho.
- Integração profissional do deficiente visualPublication . Lança, Carla; Cunha, Ana; Gonçalves, SandraCada vez mais se privilegia a visão em detrimento dos outros sentidos, sendo constantes os apelos à imagem. A visão representa 80% dos estímulos visuais recebidos. A perda ou diminuição da visão coloca o indivíduo deficiente visual numa posição de desvantagem social. Objectivos do estudo: quantos deficientes visuais existem no mundo e em Portugal? Estão empregados? Quantos e em que sector de actividade? Como funciona o processo de integração profissional?
- Effect of a sardine supplement on C-reactive protein in patients receiving hemodialysisPublication . Moreira, Ana Catarina; Gaspar, Augusta; Serra, Maria Adelaide; Simões, Jacinto; Cruz, José Lopes da; Amaral, Teresa Freitas doObjective - The study evaluated the effect of a canned sardine supplement in C-reactive protein (CRP) in patients on hemodialysis (HD) and the compliance and adherence to this supplement. Design - This was a quasi-experimental study: Participants with a serum CRP of 5 mg/dL or less volunteered to consume a sardine supplement or were maintained on the usual cheese/ham sandwich supplement. Setting - The study took place in two outpatient dialysis units in Lisbon, Portugal. Patients - The study comprised 63 patients receiving maintenance HD three times per week for at least 6 months and an initial CRP concentration of 5 mg/dL or less. Exclusion criteria included the presence of graft vascular access or history of cancer. Intervention - After a 4-week washout period, the nutritional intervention included a canned sardine sandwich for the case group (n = 31) and a cheese or ham sandwich for the control group (n = 32), to be ingested during each routine HD session, 3 times per week, for 8 weeks. Main outcome measure - Serum levels of high-sensitivity CRP were the outcome measure. Results - Only 65 patients from the invited 186 patients met the inclusion criteria and agreed to eat the sardine sandwich supplement three times per week and were involved in the study. A significant proportion of 48% (n = 31, case group) consumed the sardine sandwich supplement three times per week for 8 weeks, fulfilling the requirements and completing the study. The present investigation showed that a sardine sandwich supplement had no effect on CRP levels among patients on HD. However, when participants were stratified according to tertiles of CRP distribution values at baseline, a reduction in CRP levels was found for those in the higher tertile, being higher for the case group (P = .047). Although diabetic patients were excluded from the analysis (eight in the sardine supplementation group and seven in the control group) a significant CRP reduction was found (P = .034). Conclusion - Although a supplement of low-dose n-3 long-chain polyunsaturated fatty acids had no effect on the plasma high-sensitivity CRP of the supplemented group, a reduction in CRP levels was found when patients were stratified for tertiles of CRP (for the upper tertile) and diabetic status (for nondiabetic patients). These findings need to be further confirmed. This canned sardine supplement was accepted by an important proportion of patients, enhancing diet variety and contributing for a greater n-3 long-chain polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid intake.
- Perífrases aspectuais : estar a / andar a + infinitivoPublication . Sousa, OtíliaA reflexão apresentada inside sobre duas formas perífrásticas do Português europeu que são particularmente pertinentes na construção da categoria aspecto.
- Mechanical behaviour of concrete made with fine recycled concrete aggregatesPublication . Evangelista, Luís; Brito, Jorge deThis paper concerns the use of fine recycled concrete aggregates to partially or globally replace natural fine aggregates (sand) in the production of structural concrete. To evaluate the viability of this process, an experimental campaign was implemented in order to monitor the mechanical behaviour of such concrete. The results of the following tests are reported: compressive strength, split tensile strength, modulus of elasticity and abrasion resistance. From these results, it is reasonable to assume that the use of fine recycled concrete aggregates does not jeopardize the mechanical properties of concrete, for replacement ratios up to 30%.
- Blind hyperspectral unmixingPublication . Nascimento, Jose; Bioucas-Dias, José M.This paper introduces a new hyperspectral unmixing method called Dependent Component Analysis (DECA). This method decomposes a hyperspectral image into a collection of reflectance (or radiance) spectra of the materials present in the scene (endmember signatures) and the corresponding abundance fractions at each pixel. DECA models the abundance fractions as mixtures of Dirichlet densities, thus enforcing the constraints on abundance fractions imposed by the acquisition process, namely non-negativity and constant sum. The mixing matrix is inferred by a generalized expectation-maximization (GEM) type algorithm. This method overcomes the limitations of unmixing methods based on Independent Component Analysis (ICA) and on geometrical based approaches. DECA performance is illustrated using simulated and real data.
- Boosting of (very) weak learnersPublication . J. Ferreira, Artur; Figueiredo, MárioIn this paper we apply boosting to weak (binary) learners. The main idea is to combine the output of several simple learners in order to obtain a better classifier. As weak learners we consider generative classifiers and radial basis function classifiers.Our tests on synthetic data show that the proposed algorithm has good convergence properties. On benchmark data, boosting of these weak learners attains results close to the well-known Real AdaBoost algorithm (with decision trees) and support vector machines, constituting a low complexity competitive choice.
- The shape of soap films and Plateau bordersPublication . Fortes, M. A.; Teixeira, Paulo; Deus, A. M.We have calculated the shapes of flat liquid films, and of the transition region to the associated Plateau borders (PBs), by integrating the Laplace equation with a position-dependent surface tension γ(x), where 2x is the local film thickness. We discuss films in either zero or non-zero gravity, using standard γ(x) potentials for the interaction between the two bounding surfaces. We have investigated the effects of the film flatness, liquid underpressure, and gravity on the shape of films and their PBs. Films may exhibit 'humps' and/or 'dips' associated with inflection points and minima of the film thickness. Finally, we propose an asymptotic analytical solution for the film width profile.