Browsing by Issue Date, starting with "1996"
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- Aplicação de técnicas de identificação paramétrica ao motor de indução trifásicoPublication . Leite, VicenteCom o desenvolvimento das teorias de controlo e das tecnologias de aquisição e processamento de dados, nomeadamente, processadores digitais de sinal (DSP), o motor de indução trifísico tem vindo a substituir o tradicional motor de corrente contínua, como principal meio de accionamento nas aplicações de controlo industriais. Se associarmos a este desenvolvimento, as características mais importantes do motor de indução trifásico, como a robustez, a ausência de manutenção e o preço, compreendemos as razões pelas quais é hoje, o motor mais utilizado na indústria.
- Factory automation using OSI technologies: process automation in a transformers manufacturing plantPublication . Tovar, Eduardo; Oliveira, José Luís; Alves, Mário; Azevedo, Rui; Carvalho, Adriano; Sousa, Mário; Portugal, Paulo; Carvalho, José AugustoThis paper presents the work carried out in order to improve one of the areas of a factory plant, integrating it within the factory using different communication standards. The implementation described satisfies a set of data flow requirements and claims to be an example of different vendors and technologies integration. Distribution transformers have always been dried within ovens heated for the effect. This drying process has several drawbacks: a low efficiency dependence on the transformer volume and requiring a long time to complete. The new approach, presented in this paper, eliminates all those constraints.
- Transport of acetic acid in Zygosaccharomyces bailii: effects of ethanol and implications on the resistance of the yeast to acid environmentsPublication . Sousa, Maria João; Estevinho, Leticia M.; Côrte-Real, Manuela; Leão, CecíliaCells of Zygosaccharomyces bailii ISA 1307 grown in a medium with acetic acid, ethanol, or glycerol as the sole carbon and energy source transported acetic acid by a saturable transport system. This system accepted propionic and formic acids but not lactic, sorbic, and benzoic acids. When the carbon source was glucose or fructose, the cells displayed activity of a mediated transport system specific for acetic acid, apparently not being able to recognize other monocarboxylic acids. In both types of cells, ethanol inhibited the transport of labelled acetic acid. The inhibition was noncompetitive, and the dependence of the maximum transport rate on the ethanol concentration was found to be exponential. These results reinforced the belief that, under the referenced growth conditions, the acid entered the cells mainly through a transporter protein. The simple diffusion of the undissociated acid appeared to contribute, with a relatively low weight, to the overall acid uptake. It was concluded that in Z. bailii, ethanol plays a protective role against the possible negative effects of acetic acid by inhibiting its transport and accumulation. Thus, the intracellular concentration of the acid could be maintained at levels lower than those expected if the acid entered the cells only by simple diffusion.
- Expressão de genes que codificam a a-amilase em Sascharomyces cereviceaePublication . Choupina, Altino
- Is supplemental stocking of brown trout (Salmo trutta) worthwhile in low productive streams?Publication . Cortes, Rui M.V.; Teixeira, Amílcar; Pereira, ClaraThe effect of trout stocking was evaluated in two headstreams located in northern Portugal in order to assess the impact on wild trout (Salmo trutta L.) and to analyze the success of this operation. The results obtained exhibited the limitation of stocking: 1) the clumped character of the release fishes created a high mortality and limited the increasing of salmonid population to a few weeks; 2) because density-dependent factors seem to prevail in the regulation of salmonid populations, stocking is beneficial only if a population has became scarce, otherwise, the autochthonous fish may be strongly impacted; 3) the relative vulnerability of each age class of the native trout may vary according with the site.
- A new approach for the kinetic modelling of non-linear free-radical polymerizations and its application to poly(Vinyl-acetate) bulk and solution manufacturing processesPublication . Dias, Rolando; Costa, Mário RuiA New Approach for the Kinetic Modelling of Non-Linear Free-Radical Polymerizations and its Application to Poly(Vinyl-Acetate) Bulk and Solution Manufacturing Processes
- A mudança do espaço rural em zonas marginais: o caso da Terra Fria TransmontanaPublication . Rodrigues, OrlandoA questão da mudança do espaço rural em zonas marginais ou desfavorecidas e das actividades que nesse espaço se desenvolvem (sendo, normalmente, a agricultura a mais importante) tem vindo a ganhar grande actualidade. Pela leitura, por vezes apressada, de alguns indicadores económicos e/ou demográficos, conclui-se frequentemente que o abandono da agricultura e, consequentemente, a desertificação do espaço rural nessas zonas é uma evolução inelutável. Neste texto, propomo-nos abordar esta questão à luz das conclusões de uma investigação recente' para o caso da Terra Fria Transmontana". Como metodologia de exposição, optámos por abordar o tema em três etapas: primeiro, descreveremos o quadro geral da mudança; seguidamente, caracterizaremos a mudança dos modos de reprodução das famílias rurais; e, por fim, apoiados nas conclusões anteriores, abordaremos a mudança das práticas produtivas agrícolas e de gestão do património fundiário. Em cada uma destas etapas, apoiar-nos-emos numa descrição da sociedade rural tradicional' para ilustrar a mudança.
- Dry deposition of ozone and sulphur dioxide over low vegetation in moderate southern European weather conditions. Measurements and modelingPublication . Pio, Casimiro; Feliciano, ManuelLong-term measurements of SO2 and O3 dry deposition were carried out during one year over a grass field, located in the west coast of Portugal. An automatic system based on micrometeorological techniques provided, on a routine basis, an important data set for both gases. The results show strong daily and seasonal cycles in dry deposition velocity and surface resistance, for ozone, being also verified a seasonal trend for SO2. For both gases maximum Rc values were observed in summertime with the minimum values occurring in winter and spring. These differences match with surface conditions. In Portugal the vegetation reaches its maximum of activity in spring and becomes partially dry in the end of summer, after several months without rainfall. The stomatal intake seems to be the most important controlling factor on dry deposition, specially for ozone. A parameterization of surface resistance for ozone based on conclusions from recent dry deposition studies yields Re values in good agreement with the observed values. For SO2, Rc values are influenced by other factors besides stoma opening such as surface wetness, being, therefore, more difficult to evaluate the applicability of existent parameterization schemes.
- Mirandes cattle breed: genetic base and breed improvementPublication . Sousa, Fernando Ruivo de; Fragata, AntónioThe "mirandês cattle breed has had a herd book since 1913 and the agricultural service has implemented a programme of genetic improvemment since the 70's. However, in spite of what has been expected, positive results weren't found on that programme and the "mirandês" cattle breed has gone into a decline. This paper analyses the strategies of several cattle breeder types and the genetic demographic structure of cattle within a community in northeast of Portugal.The present organization of the breed improvement, centered on cattle breeders of pure breed and on farms whith a great number of cows, does not permit genetic improvement. The alternative to the present situation consists of expanding the selection basis, integrating a conceptual level with all farmers. implementation of a process to work within the middle of a population of many breeders in the community.
- Influence de la pierrosité superficielle sur l’érosion d’un sol franc-limoneux: résultats d’une experimentation de simulationPublication . Figueiredo, Tomás deLe rôle de la pierrosité sur la perte de sol a été object de plusieurs travaux dans les dernières années. L‘échelle d’approche à l’étude de l’influence de la pierrosité sur la perte de sol et, d’autre part, les caractéristiques des éléments grossiers, conditionnent cette influence, aspects pourtant normalement négligés dans le domaine de la modélisation de la perte de sol. Une expénmentation, à petite échelle, de simulation sous pluie naturelle a été mise-en-oeuvre, envisageant tester l’effet des caractéristiques des Cléments grossiers sur les aspects de la dynamique de l’eau et du sol concernant le processus de l’érosion (ruissellement et infiltration, érosion en nappe et le splash).. \ Quarente quatre caisses métalliques à fond perforé, contenant une épaisseur de 3,5 cm d’un sol franc-limoneux (terre fine), ont été exposées à 5 périodes de pluies naturelles, totalisant 240 mm. Pour simuler les Cléments grossiers, soit des carreaux céramiques ont été coupés régulièrement (forme rectangulaire et tailles de ,gavillons, cailloux et pierres), soit des anneaux plastiques ont été remplis de paraffine mélangée de morceaux de plomb pour assurer une densité comparable (forme circulaire et taille de gravillons et cailloux). Les onze modalités testées, avec quatre répétitions chacune, ont compris les deux formes et les trois tailles mentionnées, trois positions (reposant sur le sol et entérrés, à moitié ou complétement), et quatre pourcentages de couverture (O, 15,30 et ÏO% de la surface des caisses). En plus, une modalité supplémentaire avec du sable a été testée. Les caisses ont été soumises à une ”presque” saturation permanente, une pente de 10% étant imposée. Le ruissellement et la perte de sol à extremité inférieure des caisses, l’infiltration, et le splash capturé sur une planche métallique placé à côté des caisses, ont été mesurés au bout de chacune des cinq périodes de pluies tombées au cours de l’expérimentation. Celle-ci s’est installée à côté d’une station météorologique, à Bragança, Portugal. Les résultats obtenus montrent que la perte de sol dans ces conditions est de 420 kg ha-l (sol nu). La corrélation négative entre % de couverture et perte de sol s’affaiblie tout au long de l’experience, ce qui confirme l’effet de la crôute superficielle qui s’est dévelloppée par action des pluies, visuellement bien évidente, dont l’influence est d’autant plus marquée que la couverture par Cléments grossiers est moindre. Cette crôute réduit le détachement de particules terreuses, mécanisme qui semble controller la perte de sol. Le splash atteint les 700 kg ha-1 (sol nu) et est aussi corrélationé négativement avec le 9% de couverture. L‘infiltration est, pour toutes les modalités, assez élevée et vane positivement avec le % de couverture mais de façon très peu expressive. Le ruissellement diminue avec l’accroît de la couverture. Les effets de Ia taille des éléments grossiers et de leur forme, ont été testées pour 30% de couverture pierreuse. Ces effets ne sont significatifs que sur les mesures d’infiltration et comparant gravillons et cailloux.