Browsing by Issue Date, starting with "1991"
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- A memória do RomanceiroPublication . Ferré, PereMuitos autores se têm confrontado, quando tratam da lírica ou da narrativa ditas populares, com a chamada contradição que encerra a expressão "literatura oral".
- Detection symmetry and asymmetry.Publication . du Buf, J. M. H.Experiments were performed on the detection symmetry and asymmetry of incremental and decremental disks, as a function of both disk diameter and duration. It was found that, for a background luminance of 300 cd.m-2, thresholds of dynamic (briefly presented) foveal disks are symmetrical for all diameters, and that thresholds of quasi-statically presented disks are symmetrical for large diameters only. Threshold curves of quasi-static incremental and decremental disks are mutually shifted along the log area axis. In order to obtain a better insight into the underlying detection mechanism, additional experiments were performed with halfwave-rectified concentric cosine gratings, i.e. with either incremental or decremental phases. Threshold curves of these gratings proved to be identical, that is independent of polarity, and of the same shape as those obtained with fullwave cosine gratings, though 0.3 log unit shifted in amplitude. The discrepancy between threshold curves of quasi-static disks (asymmetry) and halfwave-rectified gratings (symmetry) is discussed in terms of a multiple-channel theory.
- Spatial and temporal variation of bacterioplankton abundance and biomass in a coastal lagoon (Ria Formosa, SE Portugal)Publication . Barbosa, Ana B.Water samples were collected at bimonthly intervals (April – October 1988) from three stations located in the Ria Formosa coastal lagoon (SE Portugal). Abundance and biovolume of heterotrophic bacterioplankton ranged between 1.2 – 18 x 106 cells.ml-1 and 0.10 - 0.21 μm3.cell-1, respectively. Lowest values were detected at the station close to the ocean and highest values at the station impacted by a domestic effluent. Total bacterial counts showed slight temporal fluctuations while saprophyte numbers (Colony Forming Units) presented a much stronger variation, with maxima during summer. Biovolume exhibited minimal values during summer. Reasons for different patterns of spatial and temporal variability of the bacterial population are discussed.
- A new formulation of the learning problem for a neural network controllerPublication . Ruano, Antonio; Jones, D. I.; Fleming, P. J.In this paper we consider the learning problem for a class of multilayer perceptrons which is practically relevant in control systems applications. By reformulating this problem, a new criterion is developed, which reduces the number of iterations required for the learning phase.
- Algumas notas sobre a dramaticidade do Romanceiro Tradicional PortuguêsPublication . Ferré, PereHá alguns anos já, a caminho do Aeroporto de Lisboa, disse-me Luciana Stegagno: «O que me interessa, especialmente, no Romanceiro é a sua dramaticidade.» Retive esta afirmação e pouco depois, sob a orientação de Diego Catalán, alterei a minha tese de doutoramento, que, uma vez finalizada, se passou a chamar "Estratégias Dramatizadoras do Romanceiro Tradicional Português". Aqui fica o agradecimento público, aqui fica consignada a minha homenagem à sábia amiga cujas palavras são sempre uma lição.
- Reactions of azoalkenes derived from hydrazones of ethyl bromopyruvate with electron rich alkenes and heterocyclesPublication . Clarke, S; Gilchrist, Thomas L.; Lemos, A.; Roberts, Tony G.Three hydrazones of ethyl bromopyruvate, the dinitrophenylhydrazone 2a, the toluene-4-sulphonylhydrazone 2b and the t-butoxycarbonylhydrazone 2c, have been reacted with a series of nucleophilic alkenes and heterocycles in the presence of sodium carbonate. Azoalkenes 3 are presumed as intermediates and adducts have been isolated. The azoalkenes derived from hydrazones 2a and 2c are found to be useful electrophiles and electrophilic dienes.
- A neural network controllerPublication . Ruano, Antonio; Jones, D. I.; Fleming, P. J.Proportional, Integral and Derivative (PID) regulators are standard building blocks for industrial automation. The popularity of these regulators comes from their rebust performance in a wide range of operating conditions, and also from their functional simplicity, which makes them suitable for manual tuning.
- A connectionist approach to PID autotuningPublication . Ruano, Antonio; Fleming, P. J.; Jones, D. I.Proportional, Integral and Derivative (PID) regulators are standard building blocks for industrial automation. The popularity of these regulators comes from their rebust performance in a wide range of operating conditions, and also from their functional simplicity, which makes them suitable for manual tuning.
- Metallothionein induction inMytilus edulis exposed to cadmiumPublication . Bebianno, Maria João; Langston, W. J.The exposure of mussels,Mytilus edulis, collected from Whitsand Bay, southwest England, in August 1988, to sublethal concentrations of cadmium (400µg l−1) for 65 d resulted in the induction of metallothionein (MT) synthesis in the soft tissues. In cadmium-exposed mussels, metallothionein concentrations, measured by differential pulse polarography, increased by a factor of three, from 2 to 3 mg g−1 to a maximum of 9 mg g−1 after 30 d. No significant changes could be detected in controls. Cadmium accumulated in the soft tissues of mussels correlated significantly with metallothionein concentrations and can be described by the relationship: MT (mg g−1)=0.045 Cd (µg g−1)+3.03 (r=0.803,P<0.001). Gel chromatography of heat-treated cytosolic extracts showed that the accumulated cadmium is bound principally to the newly formed metallothioneins. Copper and zinc were also analysed in the whole soft-tissues and in subcellular fractions of cadmium-exposed mussels. Although copper concentrations were not affected by cadmium-exposure, zinc levels were significantly reduced. The results demonstrate that the induction of metallothioneins inM. edulis is a quantifiable biological response to sublethal levels of cadmium exposure.
- Texture features based on Gabor phasePublication . du Buf, J. M. H.; Heitkämper, P.Local phase information obtained by Gabor filtering may be used for texture discrimination and image segmentation purposes. Explored are the densities of isolated zero points, discontinuities and zero contours. The phase gradient and local demodulation methods are studied as well. It is shown that most of these methods can render useful boundary and region information if simple test images are considered. However, the quality of this information degrades if the textures are disturbed by a small amount of jitter or by band-limited additive noise. © 1991.