ESTiG - Artigos em Revistas Indexados à WoS/Scopus
URI permanente para esta coleção:
Navegar
Percorrer ESTiG - Artigos em Revistas Indexados à WoS/Scopus por data de Publicação
A mostrar 1 - 10 de 620
Resultados por página
Opções de ordenação
- Angular momentum transport by internal waves in the solar interiorPublication . Zahn, Jean-Paul; Talon, Suzanne; Matias, JoséThe internal gravity waves of low frequency which are emitted at the base of the solar convection zone are able to extract angular momentum from the radiative interior. We evaluate this transport with some simplifying assumptions: we ignore the Coriolis force, approximate the spectrum of turbulent convection by the Kolmogorov law, and couple this turbulence to the internal waves through their pressure fluctuations, following Press (1981) and Garc´ıa L´opez & Spruit (1991). The local frequency of an internal wave varies with depth in a differentially rotating star, and it can vanish at some location, thus leading to enhanced damping (Goldreich & Nicholson 1989). It is this dissipation mechanism only that we take into account in the exchange of momentum between waves and stellar rotation. The flux of angular momentum is then an implicit function of depth, involving the local rotation rate and an integral representing the cumulative effect of radiative dissipation. We find that the efficiency of this transport process is rather high: it operates on a timescale of 107 years, and is probably responsible for the flat rotation profile which has been detected through helioseismology.
- Combined numerical-experimental model for the identification of mechanical properties of laminated structuresPublication . Araújo, A.L.; Soares, C.M. Mota; Freitas, M.J.M.; Pedersen, P.; Herskovits, J.A combined numerical-experimental method for the identification of six elastic material modulus of generally thick composite plates is proposed in this paper. This technique can be used in composite plates made of different materials and with general stacking sequences. It makes use of experimental plate response data, corresponding numerical predictions and optimisation techniques. The plate response is a set of natural frequencies of flexural vibration. The numerical model is based on the finite element method using a higher-order displacement field. The model is applied to the identification of the elastic modulus of the plate specimen through optimisation techniques, using analytical sensitivities. The validity, efficiency and potentiality of the proposed technique is discussed through test cases.
- The use of ore microscopy data for flotation process control by means of a liberation model - a case studyPublication . Barros, Elisa; Leite, Mário; Cavalheiro, AbílioAny realistic description of ore processing dealing with a particulate system requires an adequate characterization of it properties, mainly particle size and grade,because these are the most important variables that influence the performance of a mineral processing separation, such as froth flotation. Experience has shown that an appropriate model for liberation of solid phases must always integrate all available mineralogical data by comminution. The present work aims too describe a case study for calibration of a liberation model with data obtained from semi-quantitative mineralogical analysis (ore microscopy). For the specific case of random comminution, a limit probability argument is used to justify the introduction of Euler's Beta Law as well-suited tool for describing the liberantion state of a comminuted ore, because it is able to predict the grade distribution of a given iso-size fraction of such particulate system.
- Pollutant emissions from modern incineratorsPublication . Lima, Rui A.; Bachmann, RobertPresently, emissions of dioxins are mainly from incinerators, domestic and industrial coal combustion, and traffic. However, the major public concern and research effort are associated with the emissions of organic micropollutants from waste incinerators. Therefore, this paper attempts to give a brief overview on the more recent research and development for the removal of dioxins and heavy metals from flue gas streams. Special attention is devoted to the origin and control of emissions from incinerators. From the study presented it is possible to conclude that flue gas cleaning systems in modern incinerators are very reliable in removing almost all polluting emissions from flue gas streams, however the fly ash residues generated pose a significant disposal problem. In this way, the fly ash has to be managed carefully as it is enriched with heavy metals and organic micropollutants.
- Determination of flexibility factors in curved pipes with end restraints using a semi-analytic formulationPublication . Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M dePiping systems are structural sets used in the chemical industry, conventional or nuclear power plants and fluid transport in general-purpose process equipment. They include curved elements built as parts of toroidal thin-walled structures. The mechanical behaviour of such structural assemblies is of leading importance for satisfactory performance and safety standards of the installations. This paper presents a semi-analytic formulation based on Fourier trigonometric series for solving the pure bending problem in curved pipes. A pipe element is considered as a part of a toroidal shell. A displacement formulation pipe element was developed with Fourier series. The solution of this problem is solved from a system of differential equations using mathematical software. To build-up the solution, a simple but efficient deformation model, from a semi-membrane behaviour, was followed here, given the geometry and thin shell assumption. The previous termflexibility factorsnext term are compared with the ASME code for some elbow dimensions adopted from ISO 1127. The stress field distribution was also calculated.
- Automatic generation of language-based toolsPublication . Henriques, Pedro Rangel; Pereira, Maria João; Mernik, Marjan; Lenic, Mitja; Advicausevic, Enis; Zumer, ViljemMany tools can be automatically derived from formal language definitions, such as compilers/interpreters, editors, analyzers, visualizers/animators, etc. Some examples of language-based tools generated automatically by the LISA system are described in the paper. In addition the specification of an algorithm animator and program visualizer, Alma, generated from an extended LISA input-grammar is discussed; LISA principles and code are reused in Alma implementation.
- A new proposal of a simple model for the lateral-torsional buckling of unrestrained steel I-beams in case of fire: Experimental and numerical validationPublication . Vila Real, Paulo M.M.; Piloto, P.A.G.; Franssen, J.-MarcThe behaviour of Steel I-Beams exhibiting lateral-torsional buckling at elevated temperature has been studied by means of experimental and numerical analysis. The authors in an earlier paper have presented an analytical formula for the buckling resistance moment in the fire design situation. This new proposal, different from the actual proposal of the Eurocode 3 Part 1.2 has been validated in this work by comparison with the results from a set of 120 experimental and numerical tests performed on IPE 100 beams, submitted to temperatures varying from room temperature to 600 °C. The numerical simulations have been based on the measured geometrical dimensions of the cross-sections, the longitudinal imperfections, i. e. the out of straightness of the beams, the residual stresses and the yield strength. The Eurocode simple model promotes ultimate loads that depend mainly on the non-dimensional slenderness of the beams. The analytical results provided by the Eurocode 3, for a certain range of the slenderness, appear to be unsafe when compared with the numerical and experimental results. It is shown that the new proposal is safer than the Eurocode 3 formulas.
- An effective thermal technology for the detoxification of the MSW fly ashPublication . Lima, Rui A.; Saloca, MarcosThe increasing public concern of potential health problems, due to improper waste disposal practices as well as the introduction of landfill taxes, have induced the practice of incineration. Presently, all UK incinerators have to meet very strict emission levels. In this way, the generated fly ash residues have to be managed very carefully as they are enriched with toxic organic micropollutants and heavy metals. The aim of the present work is to describe a novel thermal technology, known as the ash detoxification process, that has shown success not only in the destruction of its toxic organic components, but also in the fixation of its heavy metal content to form an unleachable material.
- On the use of prosodic labelling in corpus-based linguistic studies of spontaneous speechPublication . Braga, Daniela; Freitas, Diamantino Silva; Teixeira, João Paulo; Marques, AldinaThis paper addresses the construction of a spontaneous speech cor-pus in European Portuguese (hereafter EP), the corpus is presented and a pro-sodic labeling scheme that is here proposed is explained. The objective of this work is to provide a tool for linguistic analysis suitable to several research top-ics, which have speech and dialogue as objects. The main features considered in the database will be described and justified. Methodological problems and some observed prosodic and pragmatic related phenomena deriving from the labeling of the speech signal are also presented. A discussion is done about some applications on pragmatic studies, speech synthesis and prosodic pho-nology. Our purpose is to make this work available to scientific community, since there isn’t any other database of this kind available and informatically accessible for EP. Future perspectives of the on-going work are also pre-viewed.
- Evaluation of a segmental durations model for TTSPublication . Teixeira, João Paulo; Freitas, Diamantino SilvaIn this paper we present a condensed description of a European Portuguese segmental duration’s model for TTS purposes and concentrate on its evaluation. This model is based on artificial neural networks. The evaluation of the model quality was made by comparison with read speech. The standard deviation reached in test set is 19.5 ms and the linear correlation coefficient is 0.84. The model is perceptually evaluated with 4.12 against 4.30 for natural human read speech in a scale of 5.