The purpose of the research was to develop a quantitative method which could be used to obtain a clearer understanding of the time-dependent fluid filteration and load-deformation behavior of soft, porous, fluid filled materials (e.g. biological tissues, soil). The focus of the study was on the development of a finite strain theory for multiphasic media and associated computer models capable of predicting the mechanical stresses and the fluid transport processes in porous structures (e.g. across the large blood vessels walls). The finite element (FE) formulation of the nonlinear governing equations of motion was the method of solution for a poroelastic (PE) media. This theory and the FE formulations included the anisotropic, nonlinear material; geometric nonlinearity; compressibility and incompressibility conditions; static and dynamic analysis; and the effect of chemical potential difference across the boundaries (known as swelling effect in biological tissues). The theory takes into account the presence and motion of free water within the biological tissue as the structure undergoes finite straining. Since it is well known that biological tissues are capable of undergoing large deformations, the linear theories are unsatisfactory in describing the mechanical response of these tissues. However, some linear analyses are done in this work to help understand the more involved nonlinear behavior. The PE view allows a quantitative prediction of the mechanical response and specifically the pore pressure fluid flow which may be related to the transport of the macromolecules and other solutes in the biological tissues. A special mechanical analysis was performed on a representative arterial walls in order to investigate the effects of nonlinearity on the fluid flow across the walls. Based on a finite strain poroelastic theory developed in this work; axisymmetric, plane strain FE models were developed to study the quasi-static behavior of large arteries. The accuracy of the FE models was verified by comparison with analytical solutions wherever is possible. These numerical models were used to evaluate variables and parameters, that are difficult or may be impossible to measure experimentally. For instance, pore pressure distribution within the tissue, relative fluid flow; deformation of the wall; and stress distribution across the wall were obtained using the poroelastic FE models. The effect of hypertension on the mechanical response of the arterial wall was studied using the nonlinear finite element models. This study demonstrated that the finite element models are powerful tools for the study of the mechanics of complicated structures such as biological tissue. It is also shown that the nonlinear multiphasic theory, developed in this thesis, is valid for describing the mechanical response of biological tissue structures under mechanical loadings.

A theory is presented which accounts for a particular aspect of nonlinearity caused by the deviation of plume "particles" from their mean trajectory in three-dimensional, statistically homogeneous but anisotropic porous media under an exponential covariance of log hydraulic conductivities. Quasilinear expressions for the time-dependent nonlocal dispersivity and spatial covariance tensors of ensemble mean concentration are derived, as a function of time, variance σᵧ² of log hydraulic conductivity, degree of anisotropy, and flow direction. One important difference between existing linear theories and the new quasilinear theory is that in the former transverse nonlocal dispersivities tend asymptotically to zero whereas in the latter they tend to nonzero Fickian asymptotes. Another important difference is that while all existing theories are nominally limited to situations where σᵧ² is less than 1, the quasilinear theory is expected to be less prone to error when this restriction is violated because it deals with the above nonlinearity without formally limiting σᵧ². The theory predicts a significant drop in dimensionless longitudinal dispersivity when σᵧ² is large as compared to the case where σᵧ² is small. As a consequence of this drop the real asymptotic longitudinal dispersivity, which varies in proportion to σᵧ² when σᵧ² is small, is predicted to vary as σᵧ when σᵧ² is large. The dimensionless transverse dispersivity also drops significantly at early dimensionless time when σᵧ² is large. At late time this dispersivity attains a maximum near σᵧ² = 1, varies asymptotically at a rate proportional to σᵧ² when σᵧ² is small, and appears inversely proportional to σᵧ when σᵧ² is large. The actual asymptotic transverse dispersivity varies in proportion to σᵧ⁴ when σᵧ² is small and appears proportional to σᵧ when σᵧ² is large. One of the most interesting findings is that when the mean seepage velocity vector μ is at an angle to the principal axes of statistical anisotropy, the orientation of longitudinal spread is generally offset from μ toward the direction of largest log hydraulic conductivity correlation scale. When local dispersion is active, a plume starts elongating parallel to μ. With time the long axis of the plume rotates toward the direction of largest correlation scale, then rotates back toward μ, and finally stabilizes asymptotically at a relatively small angle of deflection. Application of the theory to depth-averaged concentration data from the recent tracer experiment at Borden, Ontario, yields a consistent and improved fit without any need for parameter adjustment.

No description available.

This thesis addresses the issue of a potential future microelectronics technology, namely the possibility of utilising the optical properties of nanocrystalline silicon for optoelectronic circuits. The subject is subdivided into three chapters. Chapter 1 is an introduction. It formulates the oncoming problem for microelectronic development, explains the basics of Integrated Optoelectronics, introduces porous silicon as a new light-emitting material and gives a brief review of other competing light-emitting material systems currently under investigation. Examples of existing porous silicon devices are given. Chapter 2 reviews the basic physics relevant to the subject of this thesis and informs on the present situation in this field of research, including both experimental and theoretical knowledge gained up-to-date. The chapter provides the necessary background for correct interpretation of the results reported in Chapter 3 and for a realistic decision on the direction for future work. Chapter 3 describes my own experimental and computational results within the framework of the subject, obtained at De Montfort University. These include: onestep preparation of laterally structured porous silicon with photoluminescence and microscopy characterisation, Raman spectroscopy of porous silicon, a polarisation study of the photoluminescence from porous silicon, computer simulations of the conductivity of two-component media and of laser focused atomic deposition for nanostructure fabrication. Thus, this thesis makes a dual contribution to the chosen field: it summarises the present knowledge on the possibility of utilising optical properties of nanocrystalline silicon in silicon-based electronics, and it reports new results within the framework of the subject. The main conclusion is that due to its promising optoelectronic properties nanocrystalline silicon remains a prospective competitor for the cheapest and fastest microelectronics of the next century.

No description available.

The manufacturing of ductile materials generally inserts impurities into their microscopic composition. These impurities may detach from the surrounding matrix and even crack along progressive deformation. Due to the consequent incapacity of these undesirable particles of supporting any stress, these ductile materials are equivalently assumed to be porous. Porosity has been effectively shown to play a fundamental role in the mechanisms of ductile fracture. Many micromechanical models have been proposed since the 1970s with the aim of mathematically describing these mechanisms. Among them, the acclaimed Gurson model combines the averaging homogenization technique with the kinematic theorem of Limit Analysis to estimate the macroscopic yield criterion and porosity evolution law of porous ductile materials. However, the Gurson model and most of its extensions only account for isotropic ductile fracture. Thus, the purpose of the present work is to contribute to the conception of yield criteria for anisotropic porous ductile rupture. Three main contributions are hereby proposed by profiting from similar hypothesis to those of the Gurson model. The first contribution is the assessment of the influence of void morphology on overall yield criteria for those classes of materials. The second is the inclusion of an anisotropic yield criterion in the material matrix so that the macroscopic behavior presents matrix-induced anisotropy even for spherical cavities. The third and last advancement consists of generalizing the material matrix yield criterion of the Gurson model in order to include a linear transformation-based class of yield functions that has been widely used to represent specific high strength aluminum alloys. The results hereby presented highlight the consistency and robustness of the three formulations. Moreover, the role of the porosity on the modeling of yield behavior of aluminum alloys encourages further work regarding experimental parameter characterization. / A fabricação de materiais dúcteis insere impurezas em suas composições microscópicas. Essas impurezas podem se soltar da matriz circundante e até trincar durante um processo de deformação progressiva. Devido à consequente incapacidade destas partículas indesejáveis para suportar qualquer esforço, estes materiais dúcteis são equivalentemente assumidos como sendo porosos. Investigações experimentais têm extensamente mostrado que a porosidade desempenha um papel fundamental nos mecanismos de ruptura de materais dúcteis. Desde a década de 1970, vários modelos micromecânicos têm sido propostos para descrever esses mecanismos matematicamente. Entre eles, o célebre modelo de Gurson combina a técnica de homogeneização com o teorema cinemático da Análise Limite para estimar o critério de plastificação macroscópica e a lei de evolução da porosidade dos materiais dúcteis porosos. No entanto, o modelo de Gurson e a maioria de suas extensões consideram apenas situações de ruptura dúctil em meios isotrópos. O objetivo do presente trabalho é, portanto, contribuir para o desenvolvimento de critérios de plastificação para a ruptura dúctil de meios porosos anisotrópos. Três principais contribuições são propostas neste trabalho, as quais se valem de hipóteses semelhantes às do modelo de Gurson. A primeira contribuição é a avaliação da influência da morfologia do vazio nos critérios de plastificação macroscópica desta classe de materiais. A segunda é a inclusão de um critério de plastificação anisotrópico na representação da matriz do material, de modo que o comportamento macroscópico exiba anisotropia induzida por ela, mesmo para cavidades esféricas. O terceiro e último avanço é a generalização do critério de plasticidade da matriz de modo a incluir uma classe de funções de plastificação baseadas em transformações lineares. Esta classe de funcões tem sido amplamente utilizada com sucesso para modelar ligas de alumínio de alta resistência. Os resultados apresentados neste trabalho atestam a coerência e robustez das três formulações. Além disso, o papel da porosidade na modelagem da plasticidade das ligas de alumínio encoraja trabalhos futuros sobre a caracterização experimental de parâmetros de anisotropia.

O tratamento por técnicas eletroquímicas é provavelmente uma das metodologias mais prometedoras na descontaminação de sistemas particulados, sendo capaz da remoção, total ou parcial, de contaminantes como metais pesados, radionuclídeos, orgânicos e inorgânicos. Pelo uso de uma diferença de potencial elétrico em correntes baixas aplicadas através de pares de eletrodos, os contaminantes são movidos sob a ação do campo elétrico. A extração de impurezas pelo método eletrocinético é baseada na suposição que as moléculas estejam ou sejam evoluídos para a fase liquida. O ciclo completo envolve a adsorção, o transporte, a captação, e a remoção do contaminante dos meios porosos. Neste trabalho avaliou-se o emprego da técnica de eletroosmose na remoção de fenol em meios líquidos e porosos. O fenol foi escolhido por ser um composto altamente tóxico, proveniente de refinarias de óleos, industrias de tintas e principalmente pesticidas. Para a validação do processo em escala de laboratório, foi confeccionada uma célula eletroquímica para um volume de 700 cm3, com eletrodos de titânio. A concentração de fenol utilizada para este experimento foi constante de 11 mM. Água destilada, areia, pós de vidro e solo foram classificados, caracterizados e selecionados como meios porosos experimentais. As aplicações das cargas variaram de O a 120-140-240 minutos, sendo que o mapeamento do pH indicou eletromigração de espécies em todos os sistemas. Na eletroosmose temos o arraste das moléculas de fenol em direção ao catodo simultâneo à eletrólise da água, cujas concentrações relativas de contaminante foram avaliadas por espectroscopia de UV-Vis. A montagem dispõe de um reservatório para coleta de produtos de reação em cada eletrodo sendo possível a remoção do íon fenólico migrado. O processo apresentou eficiências variando de 40% a 60% na extração, dependendo das características do meio poroso. De um modo geral a técnica apresentou-se ecologicamente viável e econômica, como procedimento de remediação de solos e sistemas particulados diversos. / The use of electrochemical techniques is probably one of most promising technology for particulate system decontamination treatments. This methodology appears as able to remove heavy metals, radionucletides and organic and inorganic contaminations. By using an electric potential difference with low currents intensities through electrodes, the contaminants in the porous medium are dragged under electric field action. The contaminant removal is base on the supposition that the impurities are in solution or elute to the liquid phase. The whole cycle involves adsorption, transport, collection and removal of contaminants from the medium. In this work it was studied the use of the electroosmosis technique for removal of phenol from porous and aqueous medium. Phenol was chose because of its high toxicity and the regularly use in oil refineries, ink industries and pesticides. To validate the process, in laboratorial scale, an electrochemical cell of 700 cm3 volume, with titanium electrodes was constructed. The phenol concentration was 11 mM. Distillated water, sand, glass powder and sample of soil were classified, characterized and selected to constitute the porous media. The charge application time varied from 120 to 140 to 240 minutes and the pH mapping showed migration effect in ali of the systems. In the electroosmosis process we have the molecules of phenol dragged towards the cathode simultaneously to the water electrolysis. The relative concentrations of phenol were evaluated by UV-Vis spectroscopy. In the experimental setup a reservoir in each electrode was assembled in order to collect the reaction products. The process efficiencies are in a range from 40% to 60%, dependent of the porous medium characteristics. In a broad sense, the technique showed feasible as an economic and ecological procedure for soil and particulate system remediation.

Compósitos mesoporosos de ZrO2-CeO2 estão sendo desenvolvidos devido às suas excelentes propriedades morfológicas e estruturais, necessárias para várias aplicações, que incluem sensores de gás, catálise automotiva e ânodos de células a combustível de óxido sólido. Nesse trabalho foi desenvolvido um novo método de síntese sol-gel com template cooperativo utilizando o polímero tribloco P-123 e os cloretos de Zr/Ce como precursores dos óxidos. Foram sintetizados ZrO2-x(mol)%CeO2 com x = 50, 70 e 90% de CeO2, uma vez que esses materiais apresentam melhores características para aplicações catalíticas. Dois processos de calcinação diferentes foram testados (até 540 e 400ºC). O NiO (60% m/m) foi impregnado para que o material obtenha a condutividade eletrônica necessária para aplicação em ânodos de SOFC. Os resultados de difração de raios X indicaram sistemas cuja fase cristalográfica predominante é a cúbica tipo fluorita (a fase tetragonal é minoritária). Fase única cúbica foi obtida para 90% de CeO2 após a calcinação até 400ºC. Dentre as características morfológicas dos materiais calcinados até 540ºC, os resultados de adsorção/dessorção de N2, imagens de microscopia eletrônica e espalhamento de raios X a baixos ângulos apresentaram aglomerados cristalinos de ZrO2-CeO2, formando um sistema mesoporoso bicontínuo, aleatéorio e sem forma definida, homogêneo em composição, com área superficial intermediária (30-40 m2/g), com alta dispersividade de poros/partículas. A calcinação a 400ºC apresentou menor dispersividade, menor tamanho de poros e maior área superficial (> 100 m2/g). O recobrimento da matriz de ZrO2-CeO2 pelas nanopartículas de NiO é superficial, sem obstrução ou preenchimento dos poros. A partir da redução à temperatura programada, observou-se que independentemente do conteúdo de CeO2, a porcentagem de redução do Ce4+ foi maior e ocorreu a menores temperaturas (início da redução em 300ºC) do que o padrão de CeO2 (750ºC). Esse comportamento se repete com as amostras após a incorporação com NiO, que se reduz a Ni também em baixas temperaturas (320ºC). A atividade catalítica para conversão do CH4 em oxidação total foi similar para ambas temperaturas de calcinação, para 90% de CeO2, atingindo 50% de conversão de CH4 para ~ 540ºC. Nos experimentos de absorção de raios X in-situ, na borda K do Ni e na borda LIII do Ce, foi possível observar que todos os conteúdos de CeO2 são ativos para oxidação parcial e total de CH4, assim como decomposição do CH4 e oxidação do CO, que ocorreu em torno de 600ºC. Os resultados de espectroscopia de impedância eletroquímica mostraram que, materiais com alto conteúdo de CeO2, apresentam baixa resistividade, de 0,97 cm2 a 750ºC em atmosfera de 5% CH4/3\\%H2O/N2. Portanto, o material desenvolvido neste trabalho apresenta as melhores propriedades morfológicas, estruturais, elétricas e catalíticas relatadas na literatura para aplicações como ânodo de SOFC e catalisador, comparado a materiais similares relatados na literatura. / Mesoporous ZrO2-CeO2 composites are being developed due to their excellent morphological and structural properties, which are necessary for their use in several applications, including gas sensors, three way catalysts (TWC) and solid oxide fuel cells (SOFCs). In this work a new synthesis method was developed based on a template cooperative sol-gel approach, using the tri-block polymer P-123 and Zr/Ce chlorides as the oxides\' precursors. Since high cerium oxide quantities lead to better catalytic performance, the ZrO2-x(mol)%CeO2 were synthesized with x = 50, 70 and 90. Two different calcination processes were tested (until 540 and 400 ºC). NiO was impregnated in order to obtain enough electronic conductivity for their application as SOFC anodes. X-ray diffraction results showed that these systems are biphasic and crystallized preferentially into cubic fluorite type structure together with smaller quantities of the tetragonal zirconia-ceria phase. A 100% cubic phase was retained for 90% of CeO2 after 400 ºC calcination. Textural and morphological characteristics for 540ºC calcination evaluated from N2 sorption, electronic microscopy images and small angle X-ray scattering revealed a two-density (pores/particles) random crystalline clusters of mesoporous ZrO2-CeO2, with homogeneous composition, average superficial area (30-40 m2/g), high dispersivity of pores/particle sizes. Calcination until 400 ºC presented a narrower pore size distribution and smaller pores, with higher superficial area (> 100 m2/g). It was observed that NiO particles formed an uniform layer over the ZrO2-CeO2 without filling or blocking the zirconia-ceria pores. Temperature programmed reduction experiments showed that for all ceria contents the reduction percentage of Ce4+ species in the samples was higher and at lower temperatures (beginning of reduction at 300 ºC) than standard CeO2 (750 ºC). After NiO impregnation this behavior was similar, with NiO reducing at lower temperatures (320 ºC) as well. Catalytic activity for methane total oxidation reaction was similar for both calcination temperatures, for 90% CeO2, showing 50% of CH4 conversion around 540 ºC. Absorption X-ray in-situ experiments at Ni K-edge and Ce LIII-edge showed that all ceria contents are active for total and partial methane oxidation, CH4 decomposition and CO oxidation at 600 ºC. Electrochemical impedance spectroscopy measurements showed low resistivity for higher ceria content, 0,97 Ocm2 at 750 ºC in 5% CH4/3% H2O/N2 atmosphere. Resuming, the material developed in this work presents the best morphological, structural, electrical and catalytical properties for applications as SOFC anode and catalyst, compared to similar materials reported in the literature.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A combinação do material mesoporoso SBA-16 com o gel polimérico poli(N-isopropilacrilamida) contendo nanopartículas magnéticas pode conduzir à formação de um material híbrido interessante para aplicação em magnetohipertemia e liberação controlada de fármacos. Neste trabalho, foi explorada a estratégia de síntese de um sistema multifuncional, constituído por SBA-16/Fe3O4/P(N-iPAAm) com o objetivo de avaliar sua potencialidade de geração de calor a partir da magnetita e sua contribuição nos estudos de liberação controlada de fármacos. A caracterização dos materiais foi feita por Microscopia Eletrônica de Varredura (MEV), Microscopia Eletrônica de Transmissão (MET), Adsorção de Nitrogênio, Espalhamento de Raios X a Baixos Ângulos (SAXS), Análise Termogravimétrica (TG), Análise Elementar (CHN), Espectroscopia na Região do Infravermelho com Transformada de Fourier (FTIR), Difração de Raios X (DRX), Espectroscopia Mössbauer, Medidas Magnéticas e Espectroscopia de Fotoelétrons Excitados por Raios X (XPS). Através da análise dos resultados obtidos foi possível confirmar a formação do híbrido, e elucidar as propriedades físico-químicas, estruturais e magnéticas das amostras. Medidas das propriedades de geração de calor mostraram que o híbrido apresentou uma variação de temperatura (T) de 11 e 35C nas concentrações de 10 e de 20 mg/mL, respectivamente, no campo magnético alternado de 126 Oe; e apresentou uma variação de temperatura (T) de 32 e 39C nas concentrações de 10 e de 20 mg/mL, respectivamente, no campo magnético alternado de 168 Oe. Este resultado demonstrou que este sistema multifuncional apresenta potencial como agente de hipertermia para o tratamento do câncer. Por fim, foi feito o estudo da influência dessas nanopartículas magnéticas com a presença do gel na cinética de liberação do fármaco Doxorrubicina (DOX) sob condições in vitro. A liberação foi estudada na ausência e na presença de um campo magnético alternado de 126 Oe, que se constatou a influência do campo magnético no aumento da taxa de liberação da DOX. Este resultado demonstrou que a propriedade da magnetita de gerar calor aliada às propriedades do P(N-iPAAm) de transição de fases (contração) contribuiu para uma melhor taxa de liberação da DOX. / The combination of SBA-16 mesoporous materials with gel polymer poly (N-isopropylacrylamide) containing magnetic nanoparticles can lead to the formation of an interesting hybrid material for use in hybrid magnetic hyperthermia and controlled drug release. In this study, we explored the strategy of synthesis of a multifunctional system consisting of SBA-16/Fe3O4/P(N-iPAAm) in order to assess its potential for heat generation from magnetite and its contribution in the controlled drug release. The materials were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Nitrogen Adsorption, Small Angle X Ray Scattering (SAXS), Thermogravimetric Analysis (TG), Elemental Analysis (CHN), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), 57Fe Mössbauer spectroscopy, magnetic measures and X-Ray Photoeletron Spectroscopy (XPS). Through the analysis of the results it was possible to confirm the formation of the hybrid system, and elucidate the physicochemical, structural and magnetic properties of the samples. Measurements of the properties of heat generation showed that the hybrid presents a temperature variation (T) of 11 and 35C in concentrations of 10 and 20 mg/mL, respectively, in the alternating magnetic field of 126 Oe, and presents a temperature variation (T) 32 and 39C at concentrations of 10 and 20 mg/mL, respectively, in alternating magnetic field of 168 Oe. This result indicates that the multifunctional system shows great potential as a hyperthermia agent for cancer treatment. Finally, the study of the influence of these magnetic particles in the kinetics of release of the doxorubicin (DOX) was made in the presence of gel under in vitro conditions. The release was studied in the absence and in the presence of an alternating magnetic field of 126 Oe; it was found that the presence of magnetic field increased the release rate of DOX. This result demonstrated that the property of heat generate from magnetite combined with phase transition (contraction) properties of P(N-iPAAm) contributed to a better control of release of DOX from hybrid system.

Made available in DSpace on 2015-03-04T18:51:12Z (GMT). No. of bitstreams: 1 TeseRosaLuz.pdf: 2324271 bytes, checksum: 38301fe0e11f9cf83a774f763dbb7ec0 (MD5) Previous issue date: 2009-01-01 / Conselho Nacional de Desenvolvimento Cientifico e Tecnologico / In the context of the stochastic perturbations theories we analyze the accuracy of two linear poroelastic models applied to highly heterogeneous porous media subject to uncertainties in the permeability and the elastic constants. The poroelastic models completely and weakly coupled analized arise characterized by the degree of intensity coupling between the hydrodinamics, governor of the percolation of the fluid and poromechanics which governs the deformation of the porous matrix. New equations for the moments of effective solutions using techniques of asymptotic expansion. In light of the perturbation theory are set simplifying assumptions that clarify clearly the domain of validity of weakly coupled model, widely used in simulation of oil reservoirs in the presence of heterogeneities and correlation in poroelastic coefficients. Computational simulations of the primary extraction of oil process are carried out using Monte Carlo techniques in conjunction with finite element methods. Results obtained clearly confirm the conjecture established by the perturbation theorie related with the inaccuracy of the weakly coupled model in the presence of variability in the elastic constants. The methodology used allows to quantify the distance between the two poroelastics models and therefore propose the appropriate model for different conditions of loading and variability of the geological formation. / No contexto das teorias de perturbação estocástica, analisamos a acurácia de dois modelos poroelásticos lineares aplicados a meios porosos altamente heterogêneos sujeitos as incertezas na permeabilidade e nas constantes elásticas. Os modelos poroelásticos completamente e fracamente acoplados analisados surgem caracterizados pelo grau de intensidade de acoplamento entre a hidrodinámica governante da percolação o do fluido e a poromecânica que rege as deformações da matriz porosa. Novas equações efetivas para os momentos das soluções são obtidas fazendo uso de técnicas de expansão assintótica. À luz da teoria de perturbação, são estabelecidas hipóteses simplificadoras que elucidam o domínio de validade do modelo fracamente acoplado, amplamente utilizado nos simuladores de Reservatórios de Petróleo, na presença de heterogeneidades e correlação nos coeficientes poroelásticos. Simulações computacionais do processo de extração primária de petróleo são realizadas utilizando técnicas de Monte Carlo em conjunção com métodos de elementos finitos. Resultados numéricos obtidos confirmam claramente a conjectura estabelecida pela teoria de perturbação relacionada com a inacurácia do modelo fracamente acoplado na presença de variabilidade nas constantes elásticas. A metodologia empregada permite quantificar a distância entre os dois modelos poroelásticos, e consequentemente, propor a escolha do modelo apropriado para diferentes condições de carregamento e variabilidade da formação geológica.