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Mudanças nas características mecânicas de tecidos biológicos geralmente estão relacionadas com algum tipo de patologia. Técnicas de imagens elastográficas são métodos quantitativos de se estimar as propriedades mecânicas de tecidos. Em geral, o objetivo destas técnicas de imagem é medir o movimento do tecido provocado por uma força interna ou externa. Por meio desse movimento, parâmetros viscoelásticos do meio em análise são reconstruídos. A força de excitação pode ser tanto quasi-estática, como dinâmica. O trabalho apresentado nesta tese aborda as técnicas de elastografia dinâmica e quasi-estática. Na abordagem quasi-estática, a elasticidade não-linear é estudada através de phantoms com características que simulam as do tecido humano. Na abordagem dinâmica, o movimento dinâmico promovido por força de radicação acústica é avaliado através de técnicas ultrassônicas e magnéticas. O desenvolvimento de materiais para serem usados como phantoms para elastografia por ultrassom é descrito. O comportamento elástico não-linear desses materiais foi analisado através de resultados de ensaios mecânicos. Esses materiais foram desenvolvidos para apresentarem uma relação tensão/deformação que não dependesse do módulo de cisalhamento para pequenas deformações, e foram projetados para serem usados em phantoms em que configurações heterogêneas são empregadas (por exemplo, phantoms com inclusões esféricas). O efeito da não-linearidade elástica dos materiais sobre o contraste, a relação sinal ruído e a relação contraste ruído de imagens elastográficas de um phantom contendo inclusões esféricas, sofrendo altas deformações (até 20%) foi investigada. Foi demonstrada a viabilidade de se medir movimentos vibratórios induzidos por feixes acústicos confocais através de um ultrassom Doppler que utiliza ondas contínuas. A interferência de feixes de ultrassom com pequena diferença de frequências provoca o aparecimento de uma força dinâmica no alvo. Foi demonstrada a formação de imagens de uma esfera rígida imersa em um phantom viscoelástico, através da varredura de ambos os transdutores (confocal e Doppler) pelo plano focal do transdutor confocal. O comportamento dinâmico de uma esfera magnetizada induzido por força de radicação acústica foi investigado. A esfera foi suspensa em água em configuração de pêndulo. Forcas estática de longa (poucos segundos) e curta (poucos milisegundos) duração foram utilizadas. O movimento da esfera foi medido através de um sensor magnetoresistivo. A partir da nova posição de equilíbrio em resposta à força de radicação de longa duração, a amplitude dessa força foi estimada. Para se estimar a viscosidade da água, o movimento de relaxação da esfera após a força ter sido desligada foi ajustado a um modelo de movimento-harmônico amortecido. O movimento de uma esfera rígida imersa em um phantom feito de gelatina, deslocada por força de radicação acústica, foi avaliado por meio de ecos ultrassônicas obtidos com um sistema pulso/eco. A teoria utilizada para se estimar os parâmetros viscoelásticos do phantom, usando o movimento induzido na esfera, é uma extensão da teoria usada para se estimar a viscosidade da água. / Changes in the mechanical properties of soft tissues may be related with pathological disorders. Elasticity imaging is a quantitative method of estimating the mechanical properties of the tissue. In general, the aim of this technique is to measure tissue motion caused by external or internal forces and use it to reconstruct the viscoelastic parameters of the medium. The excitation stress used can be (quasi-) static or dynamic. Both elastographic approaches are explored in this thesis work. In the quasi-static approach, the nonlinear elasticity is studied through tissue-mimicking phantom experiments. In the dynamic approach, the dynamic motion provided through acoustic radiation force is evaluated using ultrasonic and magnetic techniques. The development of phantom materials for elasticity imaging is reported. These materials were specifically designed to provide nonlinear stress/strain relationship that can be controlled independently of the small strain shear modulus of the material, and were designed for use in phantoms where heterogeneous configurations (e.g, spherical targets in a uniform background) are employed. The effects of phantom materials nonlinearity over the strain contrast, signal-to-noise ratio and contrast-to-noise ratio of a phantom containing spherical inclusions undergoing large deformations (up to 20%) were investigated.The feasibility of measuring vibration movement, through a mono-channel continuous wave Doppler system, induced by focused confocal beams, is demonstrated. The interference of two ultrasonic beams promotes a dynamic force to the target. The ability to form images of a rigid spherical inhomogeneity embedded in viscoelastic phantom by scanning both ultrasonic transducers (confocal and Doppler) across the confocal transducer focal plane is presented. The dynamic behavior of a rigid magnetic sphere induced by an acoustic radiation force was investigated. The sphere was suspended in water in a simple pendulum configuration. Steady forces of long (few seconds) and short (few milliseconds) durations were used. The movement of the magnetic sphere was tracked using a magnetoresistive sensor. From the new equilibrium position of the sphere in response to the long-duration static radiation force, the amplitude of this force was estimated. To access the water viscosity, the relaxation movement after the acoustic force had stopped was fitted to a harmonic-motion model. The motion of a rigid sphere embedded in gelatin phantom, displaced by acoustic radiation force, was evaluated using the ultrasonic echoes from a pulse-echo system. The theory used to estimate the viscoelastic parameters of the phantom, from the oscillation of the rigid sphere is an extension of the relation used to estimate the water viscosity.

O presente trabalho relaciona-se à modelagem viscoelástica estrutural, objetivando-se a simulação numérica, com ênfase às estruturas de concreto. Faz-se, inicialmente, uma revisão dos modelos reológicos básicos unidimensionais para facilitar o entendimento das características intrínsecas da resposta viscoelástica das estruturas, tais como o fenômeno de fluência. Dentre as teorias que permitem levar em conta a idade do concreto no instante da aplicação do carregamento, são apresentadas a da hereditariedade e a do envelhecimento. Apresentam-se, em seguida, as funções de fluência e relaxação em notação apropriada à implementação numérica, combinada com o Método dos Elementos Finitos. Alguns aspectos da integração numérica das relações constitutivas ao longo do tempo são discutidos, com a apresentação, em particular, de um esquema de solução explícito fundamentado na Técnica dos \'Núcleos Degenerados\'. Finalmente, exemplos constituídos da análise de treliças planas ilustram a aplicabilidade dos modelos e procedimentos numéricos comentados. / The present work is related to structural viscoelastic modeling aiming numerical simulation, with emphasis on concrete structures. First of all, a revision of unidimentional basic reologic models is given, in order to enhance the inherent features of structural viscoelastic response, such as creep phenomenon. Among the theories able to consider the concrete age at the instant of loading, the hereditary and the aging theories are here presented. After that, the creep and relaxation functions are given in appropriate notation for numerical implementation, combined with the Finite Element Method. Some aspects of time numerical integration of constitutiva relations are discussed, mainly an explicit solution scheme based on the so called Degenerate Kernel Technic. Finally, examples consisting of plane trusses analysis illustrate the applicability of the models and numerical procedures commented.

CHARLES UNIVERSITY Faculty of Pharmacy in Hradec Kralove Department of Pharmaceutical technology Name: Klára Tenorová Title of diploma thesis: Thixotropy test of semisolid preparations Supervisor: PharmDr. Eva Snejdrova, Ph.D. This thesis deals with the study of thixotropic properties of selected semi-solid preparations such as Vaselinum album, Adep lanae, Adeps lanae cum aqua, Alcoholis cetylici unguentum and Alcoholis cetylici cremor. The theoretical part deals with characterization of semi-solid preparations and ointment bases, rheology, rheometry and description of the tests used in the measurement. The experimental part deals with the description of viscosity curves and with the measurement of time dependency of flow behaviour by thixotropic test. Model semi-solid samples show only partial recovery, i.e. false thixotropy. The highest recovery of the structure was shown by Adeps lanae, 83 % at 25 řC and 79 % at 32 řC. The flow behaviour are changed by incorporation of the water depending on the character of the semisolid preparation. At 25 ř C, the viscosity recovery rate was lower than at 32 ř C for all samples except Adeps lanae. After the emulsification of 25% water to Adeps lanae, the recovery rate at both temperatures was significantly reduced, which means that lanolin is slower to recover...

[pt] Uma nova equação constitutiva para o tensor das tensões é proposta. Esta equação permite o ajuste de dados experimentais de funções materiais de regime permanente em escoamentos de cisalhamento e extensão devido a um desacoplamento total destas funções. Através de um classificador cinemático local. O modelo é capaz de captar as influencias de movimentos de corpo rígido, escoamento de cisalhamento puro e extensional puro em regiões de características cinemáticas intermediárias em relação a estes casos limites, facilitando a análise de escoamentos complexos. A aplicação do modelo em uma contração abrupta 4 por 1 acarretou resultados coerentes com a literatura tais como o crescimento do vértice com o aumento do exponente power law da viscosidade extensional e a inibição de alguns efeitos extensionais causada pela presença de propriedades elásticas. A variação de uma propriedade de origem puramente elástica foi um teste sem precedentes na literatura, na medida em que os modelos típicos não possuem um desacoplamento total deste efeito. / [en] A new constitutive equation for the stress tensor is proposed. This equation allows fitting os stationary shear and elongational material functions experimental data due to the total discoupling of these functions. A local kinematic criteria of classifying flows is used in order to capture the influence of rigid body motion, pure shear flows and shear free flows to intermediate regions where the kinematics characteristics are in between these limit cases, making easy the analysis of complex flows. The model was tested in a 4 for 1 abrupt contraction and some results were in good agreement with literature, like the vortex growth with increasing extensional power law index and the countrary effects of elastic and extensional propertys. The effects of changing a purely elastic property was studied for the first time, because tipical models cant isolate this effect.

This diploma thesis deals with microrheology measured via the fluorescence correlation spectroscopy. As microrheological probes, fluorescently marked nanoparticles of 5 sizes in the range of 10-100 nm, were used. The particles had been immersed in a variety of concentrated glycerol solutions and agarose gels of different concentrations, and the FCS measurement revealed a diffusion coefficient of individual particles in each environment. Based on the coefficient, the viscosity of the glycerol needed to stop the particles could be determined. Particles of 10 nm size were not stopped even by the 100 wt% glycerol. In the case of the agarose gels, a combination of higher agarose concentration and larger particles resulted in an increase in the diffusion coefficient to an unlikely high value. This was caused probably by an agarose autofluorescence and the value indicates stopping of the particles in the given agarose gel. Later, the data acquired by the FCS measurement were converted to MSD curves using MATLAB software. The thesis discusses the influence of the experimental parameters on the shape of the MSD curve. The results showed that the number of particles and autocorrelation function have the most significant effect.

Materials such as asphalt, polymers or the Earth's crust tend to behave in a way that can be described neither with a model of viscous fluid, nor a model from solid mechanics. There are indeed models capable of capturing these so called viscoelastic phenomena far better, but they are based on the presumption of constant temperature. In many cases, e.g. in the glass industry or in geophysics, the properties of a viscoelastic material strongly depend on temperature. That is why it is precisely these changes that need to be described. There are viscoelastic models used in practice that take into account the material parameters' dependence on temperature, however, they do not consider the viscoelastic nature of the material when describing the temperature evolution. The objective of this thesis is to derive thermodynamically consistent viscoelastic models with temperature dependent parameters and the appropriate evolution equation for temperature, implementation of the models and computing simple test simulations. Powered by TCPDF (www.tcpdf.org)

Current mathematical models, developed on straight asphalt binders, are inadequate to characterize the frequency dependence of response of polymer-modified asphalt binders. In an earlier study at Virginia Tech, mathematical models were developed to predict the storage and loss shear moduli of polymer-modified binders. However the model developed for the loss shear moduli is limited at high frequency (G" less than or equal to 10^7.5 Pa). This thesis presents a statistical modeling of loss shear modulus of polymer (random copolymers and thermoplastic block copolymers) modified binder. Data from dynamic mechanical analysis on modified binders, at temperatures between 5 and 75°C and frequencies ranging from 0.06 to 0188.5 rad/s, were reduced to dynamic master curves of moduli, and used to develop the model. Twenty-one polymer-binder blends prepared and tested earlier at Virginia Tech where included in the study. Realistic characterization of loss shear moduli values was obtained using the Gompertz statistical model. The model was validated by using mean square error of prediction (MSEP) in which a second set of frequency data was input in the model to obtain the moduli values, which were compared to the measured data of the second set. Although this model was successfully tested for shear loss modulus prediction of polymer-modified binders, caution should be exercised when it is applied, as such a model should be able to predict the storage modulus for a known phase angle. / Master of Science

Energy dissipation during penetration is an important consideration in materials selection for lightweight armoring to protect against hypervelocity impacts (HVIs). Impact-induced glass transition in polymeric materials has been observed to increase energy dissipation during penetration. Incorporating unconventional armor materials like polymers could improve performance in these types of applications. A series of HVIs was performed, with impact velocities over the range of 2-7 km/s, on samples of ultra-high molecular weight polyethylene and poly(methyl methacrylate). A relationship between back face debris cloud velocity and impact velocity was developed for each material. Damage zone sizes were compared, offering insights into the effects of molecular architecture on stress delocalization and energy dissipation during hypervelocity perforation. Thermal analysis of the two material systems provides quasi-static glass transition temperatures, as well as melting and crystallization temperatures. The apparent failure mechanisms, in conjunction with thermal analysis, were used to explain the relative performance of each material.

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