FCT3-Livros (ou partes, com ou sem arbitragem científica)
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Livro científico ou capítulo de livro científico ou obra que resulte de investigação
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- A sensitivity study for full-field inversion of geoacoustic data with a towed array in shallow waterPublication . Jesus, S. M.This paper presents some of the preliminary work aimed at estimating the ocean bottom morphological structure in coastal waters using a towed array. In order to obtain an idea of the expected performance of the system and draw some conclusions on its operation this study presents the sensitivity of three processors to variations of: array length, source and receiver positions, sensor noise, source frequency and frequency band. Conclusions tend to demonstrate that cost function sensitivity to sound speed variations is higher on the bottom top layers and it increases with array length. An increased sensitivity is generally acompanied by a cost function non-monotonic behavior creating local minima and making it more di cult to reach the global minimum. Attenuations have in general small in uence on the acoustic eld structure and are therefore di cult to estimate. Increasing the signal frequency band by incoherent module averaging has no signi cant in uence on sensitivity. A cost function relaying on the conventional matched lter has shown low sensitivity to sensor noise and is being extended to matching directional data from bottom arrivals at several frequencies. Mismatch cases, mainly those related to array/source relative position, will be also presented.
- A sensitivity study for full-field inversion of geoacoustic data with a towed array in shallow waterPublication . Jesus, S. M.Inversion of acoustic data for estimating bottom acoustic parameters has been the subject of a considerable number of studies. Usually, signals are received on vertical arrays of sensors and transmitted from sound sources being towed away from the array location in order to form a syntethic aperture array. That configuration is greatly dependent on the knowledge of the sourcereceiver distance which is, in practice, relatively difficult to measure with the required precision. Also, since the vertical array is generally moored, or slowly drifting, the area that can be surveyed with such a method is limited to a tenth of a mile in shallow water. Changing area requires the recovery and redeployment of the whole system. This paper explores the possibility of using an horizontal array and a sound source simultaneously towed by a single ship where the source-receiver distance is constant. It has been shown that sensitivity to sound speed variations is higher on the first bottom layers and it increases with array length. Density and attenuation (both compressional and shear) have in general little influence on the acoustic field structure and are therefore difficult to estimate. Increasing the signal frequency bandwidth by incoherent module averaging has no significant influence on sensitivity. Mismatch cases, mainly those related to array/source relative position, showed that deviations of more than λ/2 in range and λ/5 in depth may give erroneous extremum location and therefore biased final estimates.
- Thinning of ‘Esbal’ clementine with 2,4-dichlorophenoxyacetic acid. Influence on yield, fruit size and fruit quality.Publication . Duarte, Amílcar; Trindade, D. T. G.; Guardiola, J. L.Esbal clementine, which originated as a bud sport from ‘Fina’, is a high parthenocarpyc early maturing cultivar with outstanding fruit quality. The expansion of this cultivar is nevertheless impaired by the small fruit size, as up to 40% of the total yield may be unmarketable due to this reason. Extensive hand thinning and auxin applications at June drop have been tried to overcome this problem with limited success. The application of a 2,4-D spray at or shortly after bloom thins effectively the number of fruits without affecting total yield, reducing the percentage of unmarketable fruit down to 13% and increasing the mean size of the marketable fruit. This thinning effect is not related to an auxin-induced ethylene synthesis, but results from the selective enhancement of the growth of some fruits by the 2,4-D application. The 2,4-D applications had no direct effect on sugar and acid content of the fruit nor in the maturity index, but the increase in fruit size resulted in an earlier maturity. This applications resulted in a reduction in juice content, but this reduction was smaller than observed when auxins were applied at june drop.
- São as Ulvales controladas pela macroepifauna?Publication . Aníbal, J.; Sprung, MartinEstudou-se a distribuição espacial e temporal das macroalgas Ulvales (Chlorophyta) e macroepifauna bentónica acompanhante, numa área situada na parte Ocidental da Ria Formosa (Sul de Portugal). Pretendeu-se também determinar possíveis factores bióticos e abióticos que podessem influenciar a distribuição acima referida.
- Teor de vitamina C, em citrinos cultivados no Algarve.Publication . Miguel, G.; Ferreira, A. S.; Monteiro, J. G; Duarte, AmílcarO crescimento, a maturação e a qualidade dos citrinos, através da determinação das características físico-químicas, têm sido amplamente estudadas em função de vários fac-tores, como sejam a variedade, o porta-enxertos e as condições edafo-climáticas e eco-lógicas em que são cultivados (Reuther et al., 1969; Rouse, 1989). O valor nutritivo dos citrinos é, em parte, devido ao elevado teor de ácido ascórbico presente no sumo. Este facto torna a determinação deste parâmetro muito importante não só nos frutos frescos como nos utilizados na indústria. Num futuro próximo, o teor de vitamina C no fruto poderá vir a ser considerado como um importante parâmetro de qualidade da fruta. O teor do ácido ascórbico depende de vários factortes, nomeadamente, orientação e insolação do pomar, maturação, porta-enxerto, solo e fertilização. Em solução aquosa,o ácido ascórbico oxida com relativa facilidade, o que conduz à oscilação dos seus teores no fruto. A conservação deste ácido no sumo depende das condições de laboração, do tempo e da temperatura de armazenamento, do conteúdo de oxigénio dissolvido, e do material de empacotamento, das caracterísicas intrínsecas do próprio sumo, da luz, presença de metais pesados, enzimas, etc. (Fernández, 1995). Neste trabalho, estudou-se o a evolução do índice de maturação e do teor de vitamina C em pomares de 'Newhall' e 'Valencia Late', com diferentes condições edafoclimáticas.
- Estimating equivalent bottom geoacoustial parameters from broadband inversionPublication . Demoulin, X.; Pelissero, L.; Stephan, Y.; Jesus, S. M.; Porter, M. B.; Coelho, E.A simple and fast approach to retrieve equivalent geoacoustic parameters is presented in this paper. The method is based upon the processing of 300-800 Hz broadband signals on a single hydrophone.Two stable characteristics of the impulse response of the shallow water waveguide are estimated: the time dispersion and the bottom reflection amplitudes. This two features are analytically linked to the compressional speed and to the attenuation coefficient of the medium. The inversion of the two latter geoacoustic parameters is straightforward since it relies on an analytical expression. The method is tested on INTIMATE96 data. The results show an excellent agreement between the reflection of the true medium and the reflection coefficient of the equivalent medium.
- Interaction between water and nutrient deficiencies in helianthus annuusPublication . Fonseca, Filomena; David, Maria Manuela; Barrote, Isabel; Ferreira, Gisela; Correia, Maria João; Martins-Loução, M. A.; Hips, S. H.The physiological response of plants to water deficits are known to vary according to the conditions of application of drought stress and the rate of development of leaf water deficits. At the whole plant level the effect of the water shess is usually perceived as a decrease in photosynthesis and growth, and is associated with alterations in C and N metabolism (McDonald and Davies, 1996). The decrease in water potential affects transpiration and hence xylem transport of nitrate or reduced N into growing regions. The response of the photo-synthetic apparatus either to water stress or rehydration seems to be dependent "on leaf age (O'Neill, 1983; Wolfe et al., 1988). Degradation of both thylakoid and stromal N-containing compounds can occur in response to water stress, recovery from which may pequire more than a week (Chaves, 1991).
- The INTIFANTE'00 sea trial: preliminary source localization and ocean tomography data analysisPublication . Jesus, S. M.; Coelho, E.; Onofre, J.; Picco, P.; Soares, C.; Lopes, C.The INTIFANTE'00 sea trial was a multidisciplinary experiment including testing of an autonomous surface vehicle, underwater communications, source localization and acoustic ocean tomography. The results shown here will concentrate on the source localization and ocean tomography data sets. The data gathered during a 24 hour run along a range independent track shows strong oceanographic features, possibly due to internal tide signature, both on the temperature data, as measured on the thermistor chain collocated with a vertical line array(VLA), and on the acoustic data. A range dependent track between 120 and 60 m water depth, shows a highly variable channel impulse response along time and range when the source was moving outwards from the VLA. In another acoustic track, the source was navigatated across a underwater canyon where the energy was rapidly distributed over a deep acoustic channel with sound trapped well below the thermocline. Good agreement between the modeled and measured channel responses represents the rst step towards matched- eld processinglike methods such as source localization and tracking and ocean tomography.
- Time-frequency approach to the study of underwater acoustic channel estimation and source reconstructionPublication . Gervaise, C.; Quinquis, A.; Martins, N.This communication presents a pre-processing scheme possibly included in the global methodology of passive tomography, in an underwater acoustic channel.
- Hands-on PID autotuning: a guide to better utilisationPublication . Leva, A.; Cox, C. J.; Ruano, AntonioPID regulators are the backbone of most industrial control systems. The problem of deter-mining their parameters, then, is of great importance in the professional control domain. To simplify this task and reduce the time required for it, many PID regulators nowadays incor-porate autotuning capabilities, i.e. they are equipped with a mechanism capable of comput-ing the ‘correct’ parameters automatically when the regulator is connected to the field. Due to the importance of the problem, a very wide variety of PID autotuners have been developed and are currently available on the market. This monograph is aimed at control professionals who want to approach the problem of choosing and applying a PID autotuner in a knowledgeable and effective way. This goal is pursued by inducing an understanding of the theory of autotuner operation rather than by presenting an exhaustive menu of techniques and commercial products. As a consequence, this volume does not lead to a mere selection guide but to a set of concepts that, once mas-tered, allows the reader to evaluate the effectiveness of a specific industrial autotuner for a particular application. A significant space is also devoted to the review of PID control prin-ciples, essentially for less experienced readers. Some industrial products are presented, to il-lustrate how the concept introduced for classifying and selecting autotuners reflect in the real world, and samples of current research are given based on the authors’ experience.