No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

<p> The inter/intramolecular interactions and associations between constituents determine the microstructure of food and its response to mechanical deformation and flow. The characterization of food rheology enables the design of efficient processing equipment, production of high-quality, stable end products, prediction of textural and sensorial attributes, and assurance of consumer acceptability. Foods are subjected to rapid and large deformations during processing operations and consumption. Dynamic oscillatory shear tests are carried out by subjecting food to a sinusoidal deformation (or stress) and probing the mechanical stress (or strain) and recording the response as a function of time. In the SAOS region, the mechanical response is in the form of a perfect sinusoidal curve and interpretation is straightforward as expected from a linear model. On the other hand, LAOS response requires complex mathematical relations to extract meaningful rheological parameters. In this dissertation, Fourier Transform-Chebyshev Decomposition (FTC) and Sequence of Physical Processes (SPP) methods were utilized to quantify the LAOS response of selected food materials. The objective of this study is to gain new insights into the nonlinear rheology and structural architecture of food materials. To offer insights into the microstructure–rheology relations, rheological measurements were accompanied by various techniques probing chemical interactions (FTIR), imaging (Cryo-SEM, SEM), quantitative network analysis, and molecular size (SDS-PAGE). This dissertation showed that LAOS rheology is highly correlated with the network structure of food shown by the quantitative network analysis utilizing SEM images. It is a powerful tool to detect the effect of small molecules on the nonlinear rheology of food (HMW-LMW glutenin ratio, gliadin for dough, fat content in yogurt, and amylopectin/amylose ratio of starch in a suspension). Nonlinear parameters were sensitive to structural changes occurring in dough structure during processing conditions including aging at room and elevated temperatures. Lastly, the SPP method enabling time-resolved interpretation of nonlinear rheology provided detailed transient microstructural interpretations whereas the FTC method gave static measures at specific strains in an oscillation cycle. Thus, nonlinear rheology of doughs with various gluten subfractions in MAOS and LAOS regions as well as shear thickening characteristic of starch suspensions with changing amylopectin/amylose ratio interpreted by the SPP method gave more sensitive results than the FTC method. The application of fundamental knowledge from this work can be a guide to evaluating the architecture and nonlinear rheology of food for the assurance of consumer acceptancy and the fabrication of efficient machinery by building more accurate mechanical models of complex food systems. </p>

[pt] Para avaliação de movimentos de corridas de detritos em vertentes montanhosas, é necessária uma abordagem reológica através de modalegem consitutiva da massa de solo descendente. O modelo de Bingham é amplamente empregado na literatura de corridas, sendo seus parâmetros a viscosidade plástica e tensão de escoamento. Esta análise provê o entendimento da propagação do movimento dos detritos em campo, ao fornecer uma estimativa de sua velocidade, espessura e alcance. O presente trabalho apresenta uma proposta para determinação da tensão de escoamento e viscosidade de solos, através de ensaios de abatimento de tubo cilíndrico. A tensão de escoamento e a viscosidade foram determinadas em um reômetro rotaticonal, com base nas taxas de cisalhamento definidas nos ensaio de abatimento. Foram estudados dois solos naturais do Rio de Janeiro, com diferentes granulometrias e plasticidades. Os resultados experimentais obtidos são comparados com soluções analíticas da literatura, e mostram que deve-se ter cuidado na definição destes parametros reológicos com base apenas em dados relacionados a distribuição granulométrica dos solos. Como resultado, foi estabelecida uma relação entre teor de umidade, tensão de escoamento e viscosidade. Comparando os dados obtidos com resultados disponíveis na literatura, conclui-se que a metodologia desenvolvida pode fornecer uma maneira simples de avaliar parâmetros reológicos de solos para análises de corridas. / [en] To evaluate debris flow downhill movements, it is necessary a rheological approach through constitutive modelling the descendent moving mass. Bingham s model is widely employed in the debris flow literature, its input parameters being plastic viscosity and yield stress. Such analysis provides understandings of the propagation of the debris motion in the field, once it provides an estimate of its velocity, thickness and range area. The present study presents a proposal for the assessment of soil yield stress and plastic viscosity, by laboratorial testing on a cylindrical tube slump test. Through the definition of shearing rates in the slump tests, yield stress and viscosity were determined on a plate–plate rheometer. Two natural soils from Rio de Janeiro, Brazil, with differing grain size distribution and plasticity, were used in the investigation. The experimental results obtained are compared with analytical and semi empirical solutions from the literature, and show that care must be taken in defining viscosities based only on data related to grain size. Correlations were obtained concerning to soil moisture and shear rates, defined in the slump tests, and also between plastic viscosity and yield stress, defined in the rheometer tests. As a result, good relationships between water content and both yield stress and viscosity were established. Comparing the obtained data with other results available in the literature it is concluded that the developed experimental methodology may provide a simple way to evaluate rheological parameters of soils for debris flow analyses.

[pt] Esta tese de doutorado se propõe a estudar a reologia de pastas de hidratos composta por água e tetrahidrofurano (C4H8O - THF) em diversas conjunturas. Os hidratos de gás natural são sólidos cristalinos, análogos ao gelo, formados pela agregação de água e de gás numa determinada estrutura organizada. Sua preocupação para a Indústria de petróleo e gás deve-se ao risco potencial relacionada a área de garantia de escoamento. Assim sendo, amplos investimentos são feitos com o propósito de prevenir e avaliar os ricos da formação de hidratos. Neste contexto, a reologia é um elemento chave, pois permite detectar a formação dos hidratos a partir de variações das propriedades reológicas, sendo as mais comuns: viscosidade, módulos viscoso e elástico. Entretanto, duas condições fundamentais para o sucesso desta abordagem são relativamente difíceis de se conseguir em laboratório, a combinação de alta pressão e baixa temperatura. Inicialmente serão estudadas pastas de hidratos formadas à pressão atmosférica, ainda a temperaturas acima de 0 graus Celsius. Em outro momento, serão estudados os efeitos da adição de álcool nas pastas de hidratos e, finalmente, serão analisadas as pastas formadas em pressões acima da pressão atmosférica. Foram realizados ensaios reológicos para diferentes composições de fluidos. Alcançam-se resultados transientes e de estado estacionário, mostrando que a reologia é fortemente afetada pela aglomeração e desagregação de cristais de hidratos que ocorrem simultaneamente à medida que os hidratos se formam e as condições de contorno que cercam os experimentos. / [en] This doctoral thesis proposes to study the rheology of water hydrate and tetrahydrofuran slurries (C4H8O - THF) at different conditions. Natural gas hydrates are crystalline solids, analogous to ice, formed by the aggregation of water and gas in a given organized structure. Their concern for the oil and gas industry is due to the potential risk related to the area of flow assurance. Thus, extensive investments are made for the purpose of preventing and evaluating the risk of hydrate formation. In this context, rheology is a significant element, since it allows to detect the formation of hydrates from variations in rheological properties, the most common being: viscosity, viscous and elastic modules. However, two fundamental conditions for the success of this approach are relatively difficult to achieve in the laboratory, the combination of high pressure and low temperature. Initially will be studied hydrate pastes formed at atmospheric pressure, still at temperatures above 0 Celsius degrees. In another moment, the effects of the addition of alcohol in the hydrate pastes will be studied and, finally, the pastes formed at pressures encountered above atmospheric pressure will be analyzed. Rheological tests were performed for different fluid compositions. Transient and steady-state results are reached, showing that rheology is strongly affected by the agglomeration and disaggregation of hydrate crystals occurring simultaneously as hydrates form and the boundary conditions surrounding the experiments.

The same fundamental questions that have driven enquiry into cytoskeletal mechanics can be asked of the considerably less-studied, yet arguably just as important, biopolymer matrix in the plant cell wall. In this case, it is well-known that polysaccharides, rather than filamentous and tubular protein assemblies, play a major role in satisfying the mechanical requirements of a successful cell wall, but developing a clear structure–function understanding has been exacerbated by the familiar issue of biological complexity. Herein, in the spirit of the mesoscopic approaches that have proved so illuminating in the study of cytoskeletal networks, the linear microrheological and strain-stiffening responses of biopolymeric networks reconstituted from pectin, a crucial cell wall polysaccharide, are examined. These are found to be well-captured by the glassy worm-like chain (GWLC) model of self-assembled semi-flexible filaments. Strikingly, the nonlinear mechanical response of these pectin networks is found