Departamento de Física
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- 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.
- 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.
- 3-D Characterisation of Nonwoven Fabrics by means of an optical systemPublication . Pereira, Mário José Teixeira; Salvado, Rita; Fiadeiro, Paulo; Silvy, JacquesThe characterisation of fabric structure by means of quantified parameters is essential for the control of the fabrication processes and the resulting properties of the nonwoven materials. Important parameters of the structure are the porosity, the mean pore size and the pore size distribution, the specific area of the texture, the fibres orientation the last one needing to be characterised in the three dimension of the fabric web. In this research work we intend to evaluate the porous fibres orientation in geotextiles nonwovens using a procedure based on the fibres light conducting and their associated scattering. The interpretation of the phenomena is made through a modelisation concept of the pore fibre interfaces
- The Double Monochromator Geometric Theory and Compensatlon of AberratlonSPublication . Sokolova, Elena; Mogo, SandraThe light path function for the double monochromator is constructed, and the formulas of account of the members of its expanding in ascending power series adequate for the defocusing and the first order astigmatism aberrations are found. On the basis of results of the minimisation of obtained expressions the opportunity of construction of a double monochromator so that the second monochromator fractionally compensates aberrations of the first one is analysed. It is also noticed, that in the scheme of the double monochromator under certain conditions compensation of an astigmatism of the second order is automatically carried out. It allows to use a deviation angle of the scheme for more complete compensation of other aberrations and to develop double monochromators with the improved performances.
- Paper surface diffraction to characterise the fibre orientation distributionPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo; Silvy, JacquesMany paper mills use ultrasonic techniques to measure the Tensile Stiffness Index, TSI, of the paper sheet. They then assume that the TSI value is the same as the fibre orientation anisotropy. This is true if the paper is allowed to dry without any internal tension or elongation, but does not apply to paper manufactured in a paper machine. The paper machine introduces tension and elongation as soon as the fibre is placed on the forming fabric. These factors increase through the press section and are accentuated in the drying section. In order to uniquely measure the fibre orientation anisotropy on the surfaces, the proposed method uses replicas of both paper surfaces to produce a laser diffraction pattern. The obtained pattern reveals an elliptical shape, which is related to the fibre orientation anisotropy of the paper surface. By measuring the ellipticity of the diffraction pattern and the deviation with respect to the machine direction, one can quantify the fibre orientation distribution. Different papers from the bench market have been successfully tested with the developed system. This article describes the new developed optical system and its innovative capabilities in the field to produce maps of the fibre orientation of a complete paper sheet surface. A selection of the obtained results to prove its feasibility is also presented.
- de Broglie–Bohm FRW universes in quantum string cosmologyPublication . Marto, João; Moniz, PauloThe purpose of this paper is to establish possible implications of the de Broglie–Bohm interpretation of quantum mechanics towards superstring cosmological dynamics. In this context, we investigate spatially flat FRW models retrieved from scalar-tensor theories of gravity with a cosmological constant present in the gravitational sector. These models are further characterized by the presence of different types of de Broglie– Bohm quantum potential terms. These are constructed from various classes of wave packets formed by superpositions of Bessel functions of different imaginary orders. As far as pre-big-bang scenarios are concerned, we find that quantum potentials yield varied types of an amplified influence of the singular classical boundary into the FRW early dynamics. Some consequences of the de Broglie–Bohm program towards pre-big-bang inflation and the graceful exit problem are then discussed. Other cosmological scenarios are also studied by means of modulation effects extracted from additional wave packets. We subsequently obtain a broader set of new solutions. Among the new solutions we find that they could still be related by duality properties, although a separation into pre- and post-big-bang classes is less clear. Some solutions show a cyclical behavior. Inflationary solutions can be identified and some of their dynamical features are subsequently analyzed. In particular, we discuss some of the differences between string inspired inflationary cosmologies with quantum potentials. The results suggest that de Broglie–Bohm quantum gravitational terms slow down inflation, constituting an effect similar to others previously described in the literature.
- Reconhecimento do Padrão Óptico da Estrutura da Folha de PapelPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo TorrãoDevido ao processo de fabrico o papel apresenta uma estrutura anisotrópica da orientação da distribuição das fibras de celulose. A maior parte dessa anisotropia resulta da orientação da distribuição das fibras na superfície da folha de papel. A resistência mecânica dos produtos papeleiros depende fortemente dessa distribuição de orientação das fibras. Variações na orientação das fibras na folha de papel contribuem para a instabilidade dimensional para diferenças na porosidade e rugosidade e para a diminuição das suas propriedades mecânicas. Devido à importância da distribuição de orientação das fibras no papel métodos quantitativos para medir o grau e o ângulo de orientação das fibras são fundamentais para a indústria papeleira. Tendo em atenção este facto o método proposto e desenvolvido nesta tese pretende ser uma contribuição importante para um melhor conhecimento das estruturas fibrosas. O método está baseado na análise de padrões de difracção produzidos por réplicas transparentes das superfícies da folha de papel. Os padrões de difracção obtidos com as réplicas das superfícies da folha de papel apresentam uma forma elíptica característica da estrutura da rede de fibras com uma elipticidade e orientação específicas relativamente ao eixo maior da elipse o qual é perpendicular à orientação principal da distribuição das fibras. Com o método implementado para a produção de réplicas é possível produzir simultaneamente e portanto nas mesmas condições réplicas de ambas as superfícies da folha de papel. Através das imagens obtidas por microscopia óptica e por microscopia electrónica de varrimento é possível avaliar a qualidade das réplicas obtidas e concluir-se que são cópias fiéis embora negativas das superfícies da folha de papel. O método aqui proposto mostra a existência de boas correlações com os resultados obtidos por outros métodos para a quantificação da orientação da distribuição de fibras. Este método foi ainda aplicado com sucesso na quantificação da anisotropia e ângulo de orientação em folhas clivadas em materiais não-tecidos e na detecção de anomalias na distribuição de orientação das fibras à superfície do papel.
- Can Non-Local Interferometry Experiments Reveal A Local Model of Matter?Publication . Marto, João; Croca, J. R.In the following we consider the possibility of interpretating non-local interferometric experiments according to the De Broglie causal model. With the help of a simplified mathematical model based on wavelet analysis it is indeed possible to explain it in a causal way. Furthermore we show the distinction between the two formalisms and discuss some experimental conditions that may make these differences evident.
- Non-local interferometry: a causal explanation by means of local wavelet analysisPublication . Marto, João; Croca, J. R.In the following we consider the possibility of interpretating recent non-local interferometric experiments according to the De Broglie causal model. With the help of a simplified mathematical model based on wavelet analysis it is indeed possible to explain it in a causal way. Furthermore we show the distinctions between the two formalisms and discuss some experimental conditions that may make these differences evident.
- The Surface Measurement of Fibre Orientation Anisotropy and Misalignment Angle by Laser DiffractionPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo; Jesus, M. E. P.; Silvy, JacquesThe dimensional stability in fibre webs mainly depends of the fibre anisotropy and its orientation on the surfaces. These parameters are influenced during the manufacturing process, where the length and type of the fibres is determinant. The web quality control, in general, is performed based on the measurement of these parameters in the bulk of the fibre webs. This paper presents an optical laser diffraction method to measure the fibre anisotropy and the fibre orientation distribution only at the paper surfaces. The developed system has been successfully used with a set of well-characterised paper sheets. The results shown a high correlation and accurate precision when compared with the results obtained by other techniques. This method has also been used successfully in non-woven fabrics.