937 resultados para Dimensão fractal


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Anodic bonding of Pyrex glass/Al/Si is an important bonding technique in micro/nanoelectromechanical systems (MEMS/NEMS) industry. The anodic bonding of Pyrex 7740 glass/Aluminum film/Silicon is completed at the temperature from 300 degrees C to 375 degrees C with a bonding voltage between 150 V and 450 V. The fractal patterns are formed in the intermediate Al thin film. This pattern has the fractal dimension of the typical two-dimensional diffusion-limited aggregation (2D DLA) process, and the fractal dimension is around 1.7. The fractal patterns consist of Al and Si crystalline grains, and their occurrences are due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al layers. The formation of the fractal pattern is helpful to enhance the bonding strength between the Pyrex 7740 glass and the aluminum thin film coated on the crystal silicon substrates.

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An approximate model, a fractal geometry model, for the effective thermal conductivity of three-phase/unsaturated porous media is proposed based on the thermal-electrical analogy technique and on statistical self-similarity of porous media. The proposed thermal conductivity model is expressed as a function of porosity (related to stage n of Sierpinski carpet), ratio of areas, ratio of component thermal conductivities, and saturation. The recursive algorithm for the thermal conductivity by the proposed model is presented and found to be quite simple. The model predictions are compared with the existing measurements. Good agreement is found between the present model predictions and the existing experimental data. This verifies the validity of the proposed model. (C) 2004 American Institute of Physics.

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The analytical expressions of the fractal dimensions for wetting and non-wetting phases for unsaturated porous media are derived and are found to be a function of porosity, maximum and minimum pore sizes as well as saturation. There is no empirical constant in the proposed fractal dimensions. It is also found that the fractal dimensions increase with porosity of a medium and are meaningful only in a certain range of saturation S-w, i.e. S-w > S-min for wetting phase and S-w < S-max for non-wetting phase at a given porosity, based on real porous media for requirements from both fractal theory and experimental observations. The present analysis of the fractal dimensions is verified to be consistent with the existing experimental observations and it makes possible to analyze the transport properties such as permeability, thermal dispersion in unsaturated porous media by fractal theory and technique.

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Unsteady and two-dimensional numerical simulation is applied to study the transition process from steady convection to turbulence via subharmonic bifurcation in thermocapillary convection of a liquid bridge in the half-floating zone. The results of numerical tests show clearly the fractal structure of period-doubling bifurcations, and frequency-locking at f/4, f/8, f/16 with basic frequency f is observed with increasing temperature difference. The Feigenbaum universal constant is given by the present paper as delta(4) = 4.853, which can be compared with the theoretical value 4.6642016.

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Short fatigue crack behaviour in a weld metal has been further investigated. The Schmid factor and the fractal dimension of short cracks on iso-stress specimens subjected to reversed bending have been determined and then applied to account for the distribution and orientation characteristics of short fatigue cracks. The result indicates that the orientation preference of short cracks is attributed to the large values of Schmid factor at relevant grains. The Schmid factors of most slip systems, which produced short cracks, are less than or equal to 0.4. Crack length measurements reveal that short crack path, compared to that of long crack, possesses a more stable and relatively larger value of fractal dimension. This is regarded as one of the typical features of short cracks.

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A fractal approach was proposed to investigate the meso structures and size effect of metallic foams: For a series At foams of different relative densities, the information dimension method was applied to measure meso structures. The generalized sierpinski carpet was introduced to map the meso structures of the foam according to specific dimension. The results show that the fractal-based model can not only reveal the variation of yield strength with specimen size, but also bridge the meso structures and mechanical proper-ties of Al foams directly. Key words: metallic foams; fractal; size effect; meso structures

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This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e. the roughness w, the lateral correlation length xi and the roughness exponent alpha, from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with alpha = 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.

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Based on the rigorous formulation of integral equations for the propagations of light waves at the medium interface, we carry out the numerical solutions of the random light field scattered from self-affine fractal surface samples. The light intensities produced by the same surface samples are also calculated in Kirchhoff's approximation, and their comparisons with the corresponding rigorous results show directly the degree of the accuracy of the approximation. It is indicated that Kirchhoff's approximation is of good accuracy for random surfaces with small roughness value w and large roughness exponent alpha. For random surfaces with larger w and smaller alpha, the approximation results in considerable errors, and detailed calculations show that the inaccuracy comes from the simplification that the transmitted light field is proportional to the incident field and from the neglect of light field derivative at the interface.

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Este trabalho se propõe analisar a construção da obra de Alexandre Herculano como historiador, que teve início com a publicação de inúmeros artigos no jornal O Panorama e na Revista Universal Lisbonense. Nesses textos, procuramos perceber as reflexões iniciais que levaram a um projeto de maior fôlego intelectual, a História de Portugal, publicada em um momento de emergência das nacionalidades e da formação das consciências nacionais. Nesse sentido, procuramos perceber como Herculano concebeu a sua história analisando sua trajetória como historiador/político em meio às graduais transformações sociais que ocorriam em Portugal à sua época. Assim, propusemo-nos pensar o Alexandre Herculano político em constante diálogo com a conjuntura daquele período, tendo como referência a sua atuação social e a sua intervenção textual no processo então em curso.

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The objective of the work was to develop a non-invasive methodology for image acquisition, processing and nonlinear trajectory analysis of the collective fish response to a stochastic event. Object detection and motion estimation were performed by an optical flow algorithm in order to detect moving fish and simultaneously eliminate background, noise and artifacts. The Entropy and the Fractal Dimension (FD) of the trajectory followed by the centroids of the groups of fish were calculated using Shannon and permutation Entropy and the Katz, Higuchi and Katz-Castiglioni's FD algorithms respectively. The methodology was tested on three case groups of European sea bass (Dicentrarchus labrax), two of which were similar (C1 control and C2 tagged fish) and very different from the third (C3, tagged fish submerged in methylmercury contaminated water). The results indicate that Shannon entropy and Katz-Castiglioni were the most sensitive algorithms and proved to be promising tools for the non-invasive identification and quantification of differences in fish responses. In conclusion, we believe that this methodology has the potential to be embedded in online/real time architecture for contaminant monitoring programs in the aquaculture industry.

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Este estudo, resultado de uma pesquisa histórica, busca contribuir para a identificação e análise de representações relativas à mulher, à sua educação e à sua função educativa divulgadas na imprensa feminina, no contexto da sociedade brasileira dos anos 1950. O corpus documental deste trabalho, tratado como fonte e objeto de investigação, foi a revista semanal Jornal das Moças, a revista quinzenal Querida e a revista mensal Vida Doméstica. A consulta ao acervo indicado foi realizada na Biblioteca Nacional, localizada na cidade do Rio de Janeiro. Inserimo-nos no campo da história da educação e aproximamo-nos do campo da história cultural, da história do impresso e da história das mulheres para tecer esta pesquisa que pretende observar, tanto no espaço discursivo dos artigos e colunas, quanto no âmbito das propagandas, a divulgação de representações relacionadas à vida feminina e à adaptação desse público às novas formas de sociabilidade referente ao contexto moderno, assim como indicar os aspectos pertinentes a uma proposta de civilização e modelação social. Pode-se notar um cenário de massificação de discursos prescritivos, apoiados em valores e condutas socialmente estabilizados, que reforçavam uma identidade feminina comumente caracterizada como tradicional, ao lado de elementos que parecem ressaltar a constante negociação de tais mensagens e prescrições com a realidade social, marcada por aspectos de intensa mudança. Tal perspectiva sugere a necessidade de desnaturalização de práticas e representações sociais, como aquelas que vêem a identidade de gênero como fenômeno pré-existente e puramente biológico, desconsiderando sua dimensão social e histórica.

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Esta tese explora o campo da Saúde e Segurança no Trabalho - SST destacando as recentes propostas de inclusão dos aspectos psicossociais nas abordagens dos chamados "riscos ocupacionais" que tradicionalmente valorizam os aspectos objetivos (químicos, físicos, biológicos, ergonômicos e de acidentes) e as prescrições. Em busca de novas fundamentações teoricometodológicas, revisita-se conceitos/práticas envolvidos em SST à luz de observações oriundas da atuação como psicóloga em um setor de saúde de uma empresa no ramo de energia e de referenciais teóricos que tomam como pontos de partida e chegada a atividade, a defasagem entre o trabalho prescrito e o real, o diálogo sinérgico entre os saberes e a dimensão coletiva do trabalho. Dentre os referenciais utilizados destacam-se as contribuições de Georges Canguilhem, em especial sua concepção de saúde, a Psicodinâmica do Trabalho e a Ergologia. Sob uma perspectiva ergológica, aponta-se para norteadores de um redirecionamento, para que a prevenção incorpore aquilo que é da ordem do não antecipável, que advém das situações reais com suas dramáticas, encontros de encontros, escolhas e ressingularizações, para além do patrimônio acumulado na forma de normas antecedentes (sem desconsiderá-lo). Nesse sentido, uma vez ressaltada a dimensão gestionária das atividades, seus protagonistas são convocados não apenas a cumprir prescrições elaboradas por especialistas, mas também a exercer, individual e coletivamente, a coautoria na gestão de sua saúde, segurança, trabalho e vida.