Browsing by Issue Date, starting with "1999"
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- Characterization of the cyclic nucleotide phosphodiesterase subtypes involved in the regulation of the L-type Ca2+ current in rat ventricular myocytesPublication . Verde, Ignacio; Vandecasteele, Grégoire; Lezoualc'h, Frank; Fischmeister, RodolphePhosphorylation of cardiac L-type Ca2+ channels by cyclic AMP-dependent protein kinase (PKA) plays a determinant role in the hormonal regulation of myocardial contraction. PKA increases the mean open probability of individual Ca2+ channels which results in an increase in the macroscopic L-type calcium current (ICa) (McDonald et al., 1994). Activation of PKA usually results from an increased production of cyclic AMP by activation of membrane receptors positively coupled to adenylyl cyclase via stimulatory G proteins (Gs). The best documented of such a regulation is the positive inotropic effect of sympathomimetic amines, such as isoprenaline (Hartzell et al., 1991; Hove-Madsen et al., 1996). However, cardiac myocytes, as most other cell types, also possess a negative feedback mechanism to adenylyl cyclase activation which is constituted of the cyclic nucleotide phosphodiesterases (PDEs), a family of enzymes that break down cyclic AMP into 5'-AMP (Beavo, 1995). Cyclic nucleotide PDE activity, at any given location within the cell, will counterbalance the synthesis of cyclic AMP and determine the extent of PKA activation and, hence, of protein phosphorylation. In particular, at the sarcolemmal membrane, this balance between adenylyl cyclase and PDE activities will control the degree of ICa stimulation upon hormonal activation (Fischmeister & Hartzell, 1991; Hove-Madsen et al., 1996). Other factors are involved, such as cyclic AMP compartmentation (Jurevicius & Fischmeister, 1996), PKA tethering to the membrane (Gao et al., 1997), or phosphatase activity (Wiechen et al., 1995). [...]
- Analytical solution for fully developed channel and Pipe Flow of Phan-Thien/Tanner FluidsPublication . Oliveira, Paulo J.; Pinho, FernandoAnalytical expressions are derived for the velocity vector, the stress components and the viscosity function in fully developed channel and pipe flow of Phan-Thien/ Tanner (PTT) fluids; both the linearized and the exponential forms of the PTT equation are considered. The solution shows that the wall shear stress of a PTT fluid is substantially smaller than the corresponding value for a Newtonian or upperconvected Maxwell fluid, with implications for comparing predicted and measured values in a non-dimensional form.
- Structure of papers and NonwovensPublication . Pereira, Mário José Teixeira; Costa, A. P.; Salvado, Rita; Silvy, Jacques; Fiadeiro, PauloWe characterise the structure of fibrous materials: papers and nonwovens by diffraction and transmission of light. This allows the measurement of the fibres orientation distribution of the sample as a whole or for the surfaces using replicas. Applications of the methods are demonstrated in the case of paper for the control of the curl tendency and for two kinds of nonwoven materials, one used in the tailoring of surgical garments and the other used as components of the baby diapers.
- As vozes submersas: Nome, prece e canção em The Bridge, de Hart CranePublication . Mancelos, João deTanto os místicos como alguns escritores procuram atingir uma forma de visão. Em The Bridge, a obra maior do poeta modernista norte-americano Hart Crane, a palavra literária ultrapassa o âmbito estético e assume-se como um instrumento para atingir à visão. Nesta breve comunicação, examino como a palavra “bridge”, referindo-se à icónica “ponte de Brooklyn”, pode ser entendida, num contexto sagrado, como uma divindade, e o poema como a prece que lhe é dedicada. Para tanto, recorro à obra The Bridge, à opinião de especialistas em Crane e a mitólogos diversos.
- Ética e Estética em Do Natal, Dez Histórias Impopulares, de Vasco BrancoPublication . Mancelos, João deNeste texto crítico, abordo a obra Do Natal, Dez Histórias Impopulares (Aveiro: Lions Clube de Santa Joana Princesa, 1994), que compreende contos de Vasco Branco e desenhos de Júlio Resende. Examino aspetos como a intemporalidade do conto, a importância da literatura de intervenção e o aspeto didático destas histórias. Para tanto, convoco as narrativas da obra em estudo, e ainda palavras de poetas maiores, como Sophia Andresen, António Gedeão ou Jorge de Sena.
- Plane contraction flows of upper convected Maxwell and phan-ThienTanner fluids as predicted by a finite-volume methodPublication . Oliveira, Paulo J.; Pinho, FernandoA finite-volume (FV) procedure is applied to the prediction of two-dimensional (2-D) laminar flow through a 4 : 1 planar contraction of upper convected Maxwell (UCM) and simplified Phan-Thien±Tanner (SPTT) fluids. The method incorporates general coordinates, indirect addressing for easy mapping of complex domains, and is based on the collocated mesh arrangement. Calculations with the UCM model at a Reynolds number of 0.01 were carried out with three consecutively refined meshes which enabled the estimation of the accuracy of the predictions of the main vortex characteristics through Richardson's extrapolation. Converged solutions with the first-order upwind differencing scheme for the convective terms were obtained up to at least De à 8 in the finest mesh, but were limited to De 1, De 3 and De 5 for the fine, medium and coarse meshes, respectively, when using the second-order linear upwind scheme. The predicted flow patterns for increasing Deborah numbers with the UCM model resemble the well known lip vortex enhancement mechanism reported in the literature for constant-viscosity fluids in axisymmetric contractions and shear-thinning fluids in planar contraction, but very fine meshes were required in order to capture the described vortex activity. Predictions with the SPTT model also compared well with the behaviour reported in the literature.
- Review of: Monika Schlicher, Portugal in Ost-Timor, Eine kritische Untersuchung zur portugiesischen Kolonialgeschichte in Ost-Timor 1850 bis 1912.Publication . Schouten, Maria Johanna ChristinaReview of book on history of eastern Timor in the period of implementation of the Portuguese colonial regime. With attention for the political history of Portugal in that period.
- Escrita teleguiada: guiões para audiovisuaisPublication . Lopes, Frederico Nuno VicenteO objecto deste estudo é a escrita que precede o aparecimento dos artefactos a que chamamos audiovisuais e com eles mantém uma relação especial. À prática dessa escrita chamarei guionismo e o estudo que lhe dedico pretende pôr em evidência a natureza daquela relação, bem como o processo comunicacional nela implícito. As questões da autoria e da recepção, por exemplo, servem para ilustrar esta pretensão, mas trata-se apenas de um exemplo que não esgota a rede das inter-relações possíveis, muito menos esgotará, ainda, todos os possíveis ângulos de abordagem do objecto a que chamamos guião. Tematizar a natureza daquela escrita não é apenas esboçar uma resposta para uma questão ontológica do tipo: o que é um guião? Relacionando escrita e imagem, autoria e recepção da obra, é como rasgar sulcos nas camadas históricas e sociológicas de práticas culturais, para, na estratigrafia assim desenhada, tentar pôr a descoberto as particularidades dum objecto a partir das quais se possa avançar, com alguma segurança, na elaboração de conceitos indispensáveis para a formulação duma teoria do guião. [...]
- New method for the measurement of fibres orientation on the paper faces applied to the analysis of hygro-instability in paper sheetsPublication . Pereira, Mário José Teixeira; Costa, A. P.; Trindade, A. C.; Fiadeiro, Paulo; Silvy, Jacques; Tosio, J. M. SerraFor a given change in the humidity of a paper the hygro-instability of the sheet depends of two main factors: the sheet structural parameters which reflects its structure: the sheet porosity, the fibres orientation distribution mainly in the sheet plane and the variations of these parameters across the paper sheet thickness. the water reactivity of the components of the paper sheet which depends mainly of the sheet composition: the cellulosic and the fillers content, the nature of the fibres, softwood or hardwood, their degree of delignification, the beating degree of the pulp, the fines content, the conditions of the sheet drying with a more or less conditions of restraint. In this research initiated at the University of Beira Interior (UBI) with the collaboration of the Ecole Française de Papeterie (EFPG), we have tried to identify these main parameters of the paper hygro-instability. For this purpose we characterise the sheet structural parameters by optical methods developed at the Optical Centre of UBI.
- Numerical procedure for the computation of fluid flow with arbitrary stress-strain relationshipsPublication . Oliveira, Paulo J.; Pinho, FernandoA finite-volume method is presented that allows for general stress-strain constitutive equations to be incorporated into a standard momentum± pressure-correction procedure. The method is sequential and segregated in nature, the various equations for mass and momentum conservation and for the evolution of the stress tensor are solved following a predefined order, and one of its features is the use of nonstaggered, and generally nonorthogonal, computational meshes. Two types of constitutive equations are used to test the method: the standard explicit and algebraic Newtonian model, and one of the simplest implicit differential equations, the upper-convected Maxwell model. In spite of its apparent simplicity, this latter model is known to pose the most severe numerical difficulties. However, the results in this article show the method to be effective in solving the equations for the flow of Newtonian and viscoelastic fluids through abrupt planar contractions with an area reduction of 4 to 1, one typical benchmark problem. The results are compared with available data and with solutions from a standard and validated code, and good agreement and consistency is found. A new formulation to evaluate stresses at cell faces is presented and shown to lead to improved results.