Dissertations / Theses on the topic 'Tensor of elasticity'

We consider two one-dimensional harmonic chains coupled along their length via linear springs. Casting the elastic wave equation for this system in a Dirac-like form reveals a directional representation. The elastic band structure, in a spectral representation, is constituted of two branches corresponding to symmetric and antisymmetric modes. In the directional representation, the antisymmetric states of the elastic waves possess a plane wave orbital part and a 4x1 spinor part. Two of the components of the spinor part of the wave function relate to the amplitude of the forward component of waves propagating in both chains. The other two components relate to the amplitude of the backward component of waves. The 4x1 spinorial state of the two coupled chains is supported by the tensor product Hilbert space of two identical subsystems composed of a non-interacting chain with linear springs coupled to a rigid substrate. The 4x1 spinor of the coupled system is shown to be in general not separable into the tensor product of the two 2x1 spinors of the uncoupled subsystems in the directional representation. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

La reconnaissance en vidéo atteint de meilleures performances ces dernières années, notamment grâce à l'amélioration des réseaux de neurones profonds sur les images. Pourtant l'explosion des taux de reconnaissance en images ne s'est pas directement répercuté sur les taux en reconnaissance vidéo. Cela est dû à cette dimension supplémentaire qu'est le temps et dont il est encore difficile d'extraire une description robuste. Les réseaux de neurones récurrents introduisent une temporalité mais ils ont une mémoire limitée dans le temps. Les méthodes de description vidéo de l'état de l'art gèrent généralement le temps comme une dimension spatiale supplémentaire et la combinaison de plusieurs méthodes de description vidéo apportent les meilleures performances actuelles. Or la dimension temporelle possède une élasticité propre, différente des dimensions spatiales. En effet, la dimension temporelle peut être déformée localement : une dilatation partielle provoquera un ralentissement visuel de la vidéo sans en changer la compréhension, à l'inverse d'une dilatation spatiale sur une image qui modifierait les proportions des objets. On peut donc espérer améliorer encore la classification de contenu vidéo par la conception d'une description invariante aux changements de vitesse. Cette thèse porte sur la problématique d'une description robuste de vidéo en considérant l'élasticité de la dimension temporelle sous trois angles différents. Dans un premier temps, nous avons décrit localement et explicitement les informations de mouvements. Des singularités sont détectées sur le flot optique, puis traquées et agrégées dans une chaîne pour décrire des portions de vidéos. Nous avons utilisé cette description sur du contenu sportif. Puis nous avons extrait des descriptions globales implicites grâce aux décompositions tensorielles. Les tenseurs permettent de considérer une vidéo comme un tableau de données multi-dimensionnelles. Les descriptions extraites sont évaluées dans une tache de classification. Pour finir, nous avons étudié les méthodes de normalisation de la dimension temporelle. Nous avons utilisé les méthodes de déformations temporelles dynamiques des séquences. Nous avons montré que cette normalisation aide à une meilleure classification
Video recognition gain in performance during the last years, especially due to the improvement in the deep learning performances on images. However the jump in recognition rate on images does not directly impact the recognition rate on videos. This limitation is certainly due to this added dimension, the time, on which a robust description is still hard to extract. The recurrent neural networks introduce temporality but they have a limited memory. State of the art methods for video description usually handle time as a spatial dimension and the combination of video description methods reach the current best accuracies. However the temporal dimension has its own elasticity, different from the spatial dimensions. Indeed, the temporal dimension of a video can be locally deformed: a partial dilatation produces a visual slow down during the video, without changing the understanding, in contrast with a spatial dilatation on an image which will modify the proportions of the shown objects. We can thus expect to improve the video content classification by creating an invariant description to these speed changes. This thesis focus on the question of a robust video description considering the elasticity of the temporal dimension under three different angles. First, we have locally and explicitly described the motion content. Singularities are detected in the optical flow, then tracked along the time axis and organized in chain to describe video part. We have used this description on sport content. Then we have extracted global and implicit description thanks to tensor decompositions. Tensor enables to consider a video as a multi-dimensional data table. The extracted description are evaluated in a classification task. Finally, we have studied speed normalization method thanks to Dynamical Time Warping methods on series. We have showed that this normalization improve the classification rates

O Tungstato de Zircônio (ZrW2O8) é um material que exibe Expansão Térmica Negativa (ETN), isotrópica em um amplo intervalo de temperatura (0,3 a 1050 K). Apesar de amplamente estudado, existem controvérsias acerca dos mecanismos microscópicos responsáveis por este comportamento. A fase cúbica deste composto, denominada a-ZrW2O8, já foi motivo de estudo através de simulações computacionais utilizando Potenciais Interatômicos (PI) e Dinâmica de Rede na Aproximação Quasi-Harmônica (DRQH). Nos dois PI distintos propostos na literatura conseguiu-se reproduzir a ETN da a-ZrW2O8, mas não a dependência com a temperatura do tensor de elasticidade. É partindo desta observação que este trabalho pretende avaliar o desempenho de PI existentes e de novos PI em simulações computacionais visando a descrição da dependência com a temperatura do tensor de elasticidade da a-ZrW2O8 entre 0 e 300 K. Utilizaram-se dados experimentais, tais como posições atômicas, parâmetros de rede e o tensor de elasticidade da a-ZrW2O8 em temperaturas entre 0 e 300 K e, em outra série de cálculos, a hipersuperfície de energia ab initio no limite atérmico para obter os parâmetros dos PI. Diferentes estratégias foram empregadas na busca pelos parâmetros dos PI incluindo minimização em linha, Newton-Raphson/BFGS e Algoritmo Genético (AG). Concluiu-se que não é possível descrever as propriedades estruturais e elásticas da a-ZrW2O8 em função da temperatura com PI simples e que esta incapacidade não está relacionada a qualquer limitação da DRQH ou dos parâmetros dos PI, mas à forma analítica dos PI empregados. Isto sugere que se deve ter cautela na interpretação de resultados obtidos com estes potencias já disponíveis na literatura. Como alternativas para a solução deste problema, pode-se considerar o uso de redes neurais para a representação da hipersuperfície de energia ab initio, o uso de PI mais sofisticados que levam em consideração a vizinhança atômica (bond order potentials) e, também, cálculo ab initio a T > 0, este último a um custo computacional muito mais elevado.
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Zirconium tungstate (ZrW2O8) is a material that exhibits negative thermal expansion (NTE), over a wide temperature range (0.3 at 1050 K). Although thoroughly studied, controversies still remain concerning the microscopic mechanisms responsible for this behavior. The cubic phase of this compound, denominated a-ZrW2O8, was already the subject of study through computer simulations using interatomic potentials (IP) and lattice dynamics in quasiharmonic approximation (LDQH). In two different IPs proposed in the literature succeeded in reproducing the a-ZrW2O8 NTE, but not the dependence with temperature of the elasticity tensor. Starting from this observation, this work intends to evaluate of existent IPs and same proposed new IPs in computer simulations aiming the calculation of the tensor of elasticity for a-ZrW2O8 between 0 and 300 K. Experimental data (such as atomic positions, lattice parameters and the tensor of elasticity of a-ZrW2O8 at 0 and 300 K) and, in another series of calculations, the ab initio energy hypersurface in the athermic limit, were used to obtain the parameters of the IPs. Different strategies were used in the search for the parameters of IP, including line minimization, Newton-Raphson/BFGS and genetic algorithm (GA). At the end of an exhaustive search we were led to conclude that it is not possible to describe the structure and elastic properties of a-ZrW2O8 as a function of temperature with simple IPs and that this incapacity is not related the any limitation of LDQH or of the parameters of the IPs, but instead to the analytical form of the tested IPs. This suggests that same results obtained with IPs already available in the literature may be unreliable. As alternatives for the solution of this problem, it can be considered the use of a neural network for the representation of the ab initio energy hypersurface, the use of more sophisticated IPs than take into account the atomic neighborhood (bond order potentials) and even (with a computational cost much higher) ab initio calculations at T > 0.

Posterior tibial tendon dysfunction (PTTD) is a common degenerative condition leading to a severe impairment of gait. There is currently no effective method to determine whether a patient with advanced PTTD would benefit from several months of bracing and physical therapy or ultimately require surgery. Tendon degeneration is closely associated with irreversible degradation of its collagen structure, leading to changes to its mechanical properties. If these properties could be monitored in vivo, it could be used to quantify the severity of tendonosis and help determine the appropriate treatment. Ultrasound elasticity imaging (UEI) is a real-time, noninvasive technique to objectively measure mechanical properties in soft tissue. It consists of acquiring a sequence of ultrasound frames and applying speckle tracking to estimate displacement and strain at each pixel. The goals of my dissertation were to 1) use acoustic simulations to investigate the performance of UEI during tendon deformation with different geometries; 2) develop and validate UEI as a potentially noninvasive technique for quantifying tendon mechanical properties in human cadaver experiments; 3) design a platform for UEI to measure mechanical properties of the PTT in vivo and determine whether there are detectable and quantifiable differences between healthy and diseased tendons. First, ultrasound simulations of tendon deformation were performed using an acoustic modeling program. The effects of different tendon geometries (cylinder and curved cylinder) on the performance of UEI were investigated. Modeling results indicated that UEI accurately estimated the strain in the cylinder geometry, but underestimated in the curved cylinder. The simulation also predicted that the out-of-the-plane motion of the PTT would cause a non-uniform strain pattern within incompressible homogeneous isotropic material. However, to average within a small region of interest determined by principal component analysis (PCA) would improve the estimation. Next, UEI was performed on five human cadaver feet mounted in a materials testing system (MTS) while the PTT was attached to a force actuator. A portable ultrasound scanner collected 2D data during loading cycles. Young's modulus was calculated from the strain, loading force and cross sectional area of the PTT. Average Young's modulus for the five tendons was (0.45±0.16GPa) using UEI. This was consistent with simultaneous measurements made by the MTS across the whole tendon (0.52±0.18GPa). We also calculated the scaling factor (0.12±0.01) between the load on the PTT and the inversion force at the forefoot, a measurable quantity in vivo. This study suggests that UEI could be a reliable in vivo technique for estimating the mechanical properties of the human PTT. Finally, we built a custom ankle inversion platform for in vivo imaging of human subjects (eight healthy volunteers and nine advanced PTTD patients). We found non-linear elastic properties of the PTTD, which could be quantified by the slope between the elastic modulus (E) and the inversion force (F). This slope (ΔE/ΔF), or Non-linear Elasticity Parameter (NEP), was significantly different for the two groups: 0.16±0.20 MPa/N for healthy tendons and 0.45±0.43 MPa/N for PTTD tendons. A receiver operating characteristic (ROC) curve revealed an area under the curve (AUC) of 0.83±0.07, which indicated that the classifier system is valid. In summary, the acoustic modeling, cadaveric studies, and in vivo experiments together demonstrated that UEI accurately quantifies tendon mechanical properties. As a valuable clinical tool, UEI also has the potential to help guide treatment decisions for advanced PTTD and other tendinopathies.

The interaction of a muscle and associated tendon during dynamic activities such as locomotion is critical for both force production and economical movement. It is generally assumed that, under sub-maximal conditions, muscle activation patterns are optimised to achieve maximum efficiency of work. Here, I explore the interaction between the contractile component (CC) and the elastic tendinous tissue to understand the relationship between a muscle's power output and efficiency. In this thesis, I examine the interaction of the CE and the elastic tendinous tissue and its effect on power output and efficiency of muscle using both experimental and modelling techniques. In the first chapter, a model of muscle energetics is developed and validated against dynamic muscle contractions of different muscle types. I then used this model to explore how optimal muscle power and efficiency varies with different activation conditions, clastic properties and length change trajectories. The third and forth chapter presents experiments which explore ultrasound measurement techniques for determining the length changes and mechanical properties of the human gastrocnemius medial is (GM) muscle fibres and Achilles tendon (AT) respectively. I then used similar techniques to explore musclc-tcndon unit (MTU) interaction during gait under different gait conditions. Specifically, I explore how GM power output and efficiency vary with different speeds and inclination and explore how variation in tendinous compliance might influence muscle efficiency. The results suggest that muscles remain highly efficient due to compliant tendons allowing muscle fibres to act at highly powerful and efficient velocities. However variation in power output and particularly muscle function affects the efficiency of muscle. Finally, I determined that the optimal value of tendon stiffness for maximum GM efficiency during walking and running is close to that determined experimentally.

This degree work is about the exploration of the stretch in textile materials by using cartridge pleats as a method to create weight and thereby create tension. Through research in materials and stretch fabrics versus heavier woven textiles the work strives for expressions in movement as well as new ways of combining lightness and weight.
Program: Modedesignutbildningen

Optimal control problems for finite-strain elasticity are considered. An inner pressure or an inner fiber tension is acting as a driving force. Such internal forces are typical, for instance, for the motion of heliotropic plants, and for muscle tissue. Non-standard objective functions relevant for elasticity problems are introduced. Optimality conditions are derived on a formal basis, and a limited-memory quasi-Newton algorithm for their solution is formulated in function space. Numerical experiments confirm the expected mesh-independent performance.

O objetivo deste estudo é verificar qual é a efetiva contribuição prática que o monitoramento da tensão do elastano durante o processo produtivo de tecidos destinados à moda esportiva, terá sobre as características de gramatura e elasticidade, esta última traduzida como força de recuperação do tecido, na tentativa de tornar o processo mais eficiente no atendimento dos anseios dos clientes em ter o \"handle\" ou \"mão\" do tecido apresentando elevado \"power\" ou resistência ao alongamento, avaliação subjetiva muito utilizada nas confecções de artigos para fitness e moda esportiva em geral e que deve ser cientificamente parametrizada em termos de processo de forma a garantir que tais necessidades sejam atendidas. Para a manutenção de um único padrão de regulagem a ser estudado, e o estudo livre de outras variáveis, o L.F.A. e a tensão do fio de poliamida são mantidos constantes. Foi aplicado um monitoramento da tensão do elastano para mantê-lo na condição mais alta afim de evitar suas variações a menor, causada pelas variações da matéria prima, o que teoricamente leva ao empobrecimento desta força ou mão. Através deste monitoramento foi possível constatar por análise estatística, uma melhora no índice de capacidade do processo com maior número de peças dentro das faixas desejadas para o produto com suas médias mostrando o ganho de força sem alterações significativas da gramatura dos produtos conforme premissa inicial
The aim of this study is to determine what is the effective practical contribution to the monitoring of elastane tension during the production of knitted fabrics for the sports fashion, mainly on the characteristics of fabric weight and elasticity, the latter translated as tissue recovery strength, attempt to make the process more efficient in customer desires of service to have the \"handle\" or \"hand\" of the fabric featuring high \"power\" or resistance to stretching, subjective evaluation widely used in clothing articles for fitness and sports fashion in general and must be scientifically parameterized in terms of the process to ensure that these needs are met. In order to maintain a single standard regulation to be studied, and the free study other variables, L.F.A. and the tension of polyamide yarn is kept constant. The monitoring of the elastane tension was applied to keep it in the highest condition in order to prevent their smaller the variations caused by variations of the raw material, which theoretically leads to the impoverishment of this force or hand. Through this monitoring, it was verified by statistical analysis, an improvement in the capacity index of the process with the largest number of parts within the desired ranges for the product with their average showing strength gains without significant changes in the fabric weight of the product as initial premise

Material properties of polycrystalline aggregates should manifest the influence of crystallographic texture as defined by the orientation distribution function (ODF). A representation theorem on material tensors of weakly-textured polycrystals was established by Man and Huang (2012), by which a given material tensor can be expressed as a linear combination of an orthonormal set of irreducible basis tensors, with the components given explicitly in terms of texture coefficients and a number of undetermined material parameters. Man and Huang's theorem is based on the classical assumption in texture analysis that ODFs are defined on the rotation group SO(3), which strictly speaking makes it applicable only to polycrystals with (single) crystal symmetry defined by a proper point group. In the present study we consider ODFs defined on the orthogonal group O(3) and extend the representation theorem of Man and Huang to cover pseudotensors and polycrystals with crystal symmetry defined by any improper point group. This extension is important because many materials, including common metals such as aluminum, copper, iron, have their group of crystal symmetry being an improper point group. We present the restrictions on texture coefficients imposed by crystal symmetry for all the 21 improper point groups and we illustrate the extended representation theorem by its application to elasticity.

This thesis is concerned with the deformation and adhesion of thin elastic sheets that come into contact with an underlying substrate. The focus of this work is on the interplay between material and geometric properties of a system and how this interplay determines the equilibrium states of sheet and substrate, particularly in the regime of geometrically nonlinear deformations. We first consider the form of an elastic sheet that is partially adhered to a rigid substrate, accounting for deflections with large slope: the Sticky Elastica. Starting from the classical Euler Elastica we provide numerical results for the profiles of such blisters and present asymptotic expressions that go beyond the previously known, linear, approximations. Our theoretical predictions are confirmed by desktop experiments and suggest a new method for the measurement of material properties for systems undergoing large deformations. With the aim to gain better understanding of the initial appearance of blisters we next investigate the deformation of a thin elastic sheet floating on a liquid surface. We show that, after the appearance of initial wrinkles, the sheet delaminates from the liquid over a finite region at a critical compression, forming a delamination blister. We determine the initial blister size and the evolution of blister size with continuing compression before verifying our theoretical results with experiments at a macroscopic scale. We next study theoretically the deposition of thin sheets onto a grooved substrate, in the context of graphene adhesion. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives phys- ical insight into recent observations of ‘snap-through’ from flat to conforming states and emphasises the crucial role of substrate shape in determining the nature of this transition. We finally present a theoretical investigation of stiction in nanoscale electromechanical contact switches. Our model captures the elastic bending of the switch in response to both electrostatic and van der Waals forces and accounts for geometrically nonlinear deflections. We solve the resulting equations numerically to study how a cantilever beam adheres to a fixed bottom electrode: transitions between free, pinned and clamped states are shown to be discontinuous and to exhibit significant hysteresis. The implications for nanoscale switch design are discussed.

Orientador: Auteliano Antunes dos Santos Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: O processo de medição de tensões mecânicas por ultra-som faz uso da teoria acustoelástica, que relaciona a variação na velocidade de propagação de ondas com as deformações no objeto sob análise. Ondas ultra-sônicas propagando-se em meios elásticos são fortemente influenciadas pelas condições ambientais. Além disso, os sistemas instrumentais ultra-sônicos também podem ser influenciados por características do método e do procedimento de medição. Esta dissertação tem como objetivo estudar o efeito da temperatura sobre o resultado do processo de medição de tensões por ultra-som para aços API 5L X70. Como tópico adicional, é apresentado o estudo dos efeitos da força de contato entre o conjunto de transdutores e a amostra sob análise e também da variação da freqüência dos transdutores. Neste trabalho foram utilizadas ondas longitudinais criticamente refratadas, que caminham paralelamente à superfície, logo abaixo desta. Os resultados mostraram que há uma influência significativa da temperatura sobre o resultado da medição e que esta influência pode ser quantificada. Embora a freqüência dos transdutores e a pressão de contato também influenciem, estas porém, podem ser controladas durante o processo de medição
Abstract: The measurement process of mechanical stresses by Ultrasonic waves uses the acousticelastic theory, which relates the variation of wave speed propagation with the deformations on the object under analysis. Ultrasonic waves propagating itself in elastic medium are widely influenced by environmental conditions. Besides, the ultrasonic instrumentation systems also can be influenced by the method and the measurement procedure. This research has the aim to study the temperature effects on the result of measurement process from stress by ultrasonic waves in API 5L X70. As additional topic, a study of the contact pressure effects is presented between transducer assembly and the sample under analysis and also the transducers frequency variation. Longitudinal critically refracted waves (LCR) were used in this survey, which travel parallel to the surface, just below it. The results showed a significant temperature influence on the measurement results and that influence can be quantified. Although the transducers frequency and the contact pressure were also influent in a measurement process, but both can be controlled.
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

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Embora as relações força-comprimento (F-C) e força-velocidade (F-V) de um músculo possam ser facilmente determinadas in-vitro, a determinação in-vivo é certamente mais complexa, e baseia-se frequentemente em medidas de torque e ângulo articular. Uma importante limitação dessa abordagem reside no fato de as mudanças de comprimento do fascículo muscular não se relacionarem de maneira simples às da unidade músculo-tendínea (UMT). Dessa forma, a investigação in-vivo da mecânica músculo-tendão torna-se necessária para a determinação da expressão dessas propriedades musculares no contexto do movimento humano. Neste trabalho, foi determinado, in-vivo, a relação F-C (Parte I) e a relação F-V (Parte II) nos níveis do fascículo e da UMT para contrações voluntárias do músculo vasto lateral (VL) em humanos. A relação F-C foi obtida para contrações máximas e submáximas e a relação F-V, para diferentes níveis de pré-contração do músculo. A fim de obter um melhor entendimento do fenômeno, o movimento de extensão de joelho foi analisado em diferentes amplitudes de acordo com características cinéticas e cinemáticas do mesmo. As coletas de dados envolveram medições sincronizadas de torque e ângulo de joelho, bem como arquitetura muscular e EMG do VL durante contrações isométricas (F-C) e isocinéticas (F-V) de extensores de joelho. Na Parte I, foi demonstrado que a quantidade de encurtamento dos fascículos em uma contração isométrica depende do comprimento da UMT/ ângulo articular, resultando em diferentes formatos para a relação F-C entre os níveis do fascículo e da UMT e entre contrações máximas e submáximas. As relações F-C para contrações submáximas foram determinadas a partir de níveis percentuais de força (como sugerido na literatura), mas, também, através de uma nova abordagem baseada em níveis percentuais de ativação (EMG). Com base na primeira abordagem, por definição, os picos de força para as relações F-C ocorrem em um comprimento muscular fixo, mas, devido a complacência da UMT, em comprimentos de fascículo maiores a medida que a força na UMT decresce. Contrariamente, na análise baseada em ativação, os picos de força ocorrem em um comprimento de fascículo constante, mas em comprimentos musculares menores a medida que a a força na UMT decresce. Este resultado sugere que o maior potencial de geração de força submáxima é obtido em comprimento de fascículo próximo ao definido como ótimo, ou seja, no comprimento onde a sobreposição dos miofilamentos é máxima. Na Parte II dessa tese, a análise da relação F-V evidenciou que a velocidade de encurtamento do fascículo durante a extensão isocinética de joelho pode ser menor, semelhante ou maior do que a da UMT dependendo da velocidade articular e de qual parte do movimento é analisada. A velocidade de encurtamento da UMT aumenta sistematicamente com a velocidade articular, enquanto que os fascículos podem permanecer com velocidades constantes para uma grande amplitude de velocidade articular. Os resultados apontam para a crítica natureza da interação entre ângulo articular, força/ativação muscular, elementos elásticos e mecânica dos fascículos musculares e auxiliam na superação das restrições encontradas quando se relaciona e se aplica conhecimento obtido nos diferentes níveis organizacionais dos músculos.
Although there are no major difficulties in obtaining the force-length (F-L) and force-velocity (F-V) relationships in skeletal muscles in-vitro, obtaining them in-vivo is certainly much more complex, and is often based on joint torque and angle. A primary problem is that fascicle length changes are not associated in a simple manner with changes in the length of the whole muscle-tendon unit (MTU). Therefore, investigation on whole muscle tendon mechanics in-vivo is needed in order to elucidate the link between these mechanical properties and the muscle performance in the context of human movement. In this thesis work, we determined the in-vivo F-L relationship (Part I) and F-V relationship (Part II) at the fascicle and MTU levels for voluntary contractions of the human vastus lateralis muscle (VL). F-L relationships were obtained for maximal and submaximal contractions, and F-V relationships for different pre-load conditions. In order to obtain a better understanding of the phenomena, different ranges of the knee extension movement were identified for their kinematic or kinetic properties and were analyzed separately. Data collection involved synchronized measurements of knee extensor torque, knee angle, VL EMG and muscle architecture (fascicle length and pennation angle) during isometric (F-L) and isokinetic (F-V) knee extensor contractions. In Part I, we demonstrated that fascicles undergo different amounts of shortening depending on MTU length/ joint angle, which results in different shapes of the fascicle and muscle F-L relationship, and produces different F-L shapes for maximal and submaximal levels of activation. The submaximal fascicle F-L relationships were determined based on percentages of force (as typically done in the literature), but novel to the literature, also based on percentages of activation (EMG). In the force-based analysis, the peak forces of F-L relationships, by definition, must occur at the same muscle length, but because of muscle-tendon compliance, it occurs at increasing fascicle lengths with decreasing levels of force. In contrast, in the activation-based analysis, the peak occurred at similar fascicle lengths, but because of muscle compliance, at decreasing muscle lengths with decreasing levels of force. This result suggests that, in the activation-based analysis, the greatest force generating potential always occurs close to optimal fascicle lengths; that is the length at which sarcomeres present maximum myofilament overlap. In Part II, analysis of the F-V relationship showed that fascicle shortening velocities during maximum isokinetic knee extension exercises can be slower, equal or faster than the corresponding MTU shortening velocities, depending on the knee extensor speed and depending on which part of the knee extension curve is analyzed. MTU shortening velocities increase systematically with increasing speeds of knee extension. However, this observation is not made for fascicle shortening velocities, which, depending on the range and conditions analyzed, remain about constant across a large range of knee extensor speeds. The results of this thesis point to the critical nature of the interaction between joint angle, muscle force/activation, series elastic compliance, and fascicle mechanics and help to overcome the difficulties in relating and applying knowledge obtained at the different organizational levels of muscles.

O objetivo do presente estudo foi avaliar o desenvolvimento das tensões de polimerização de um compósito resinoso restaurador ao longo das primeiras 24 horas após a fotoativação, segundo dois métodos de análise da propagação de trincas. A influência do armazenamento em água sobre a magnitude das tensões também foi avaliada. O grau de conversão (GC) e o módulo de elasticidade (E) do compósito foram determinados nos diferentes tempos de observação. As hipóteses nulas do trabalho foram: 1) tensão de polimerização, GC e E não variam de forma significativa ao longo do período de observação; 2) os dois métodos de análise de propagação de trincas fornecem resultados semelhantes; 3) os valores de tensão não são influenciados pelo meio de armazenamento. Foram confeccionados discos de vidro de soda-cal com 2 mm de espessura, diâmetro externo de 12 mm, com perfuração central de 4 mm de diâmetro. Os discos foram aleatorizados em três grupos. Em um deles, os discos foram restaurados (Charisma Diamond, Heraeus Kulzer) e, após os tempos de 10 min, 1, 2, 4, 8 ou 24 horas (n=10), os espécimes receberam quatro indentações Vickers, (9,8N por 20s) a 500m da margem da cavidade. O segundo grupo passou pelo mesmo processo, porém os discos ficaram armazenados em água antes de serem indentados. Em seguida, o comprimento das trincas e a diagonal da indentação foram mensurados em microscópio óptico. A tensão residual no vidro foi calculada de acordo com a norma 4-01 (The Society of Materials Science, JSMS, Japão). No terceiro grupo, os discos foram indentados e armazenados em dissecador por 24h antes de serem restaurados. As trincas foram medidas antes e após a restauração, nos mesmos tempos descritos acima, e a tensão calculada de acordo com a fórmula descrita por Yamamoto et al. (Dent Mater, 2009). O GC foi determinado por espectroscopia no infra-vermelho próximo (n=3). O E foi obtido através do teste de dobramento em três pontos (n=10). Os dados foram submetidos a ANOVA/Tukey (=0,05) e análise de regressão. A tensão de polimerização, assim como o GC e o E tiveram seus valores aumentados ao longo do tempo. O GC aumentou 28% entre 10 minutos e 24 horas, para o E houve um aumento de 1,7 GPa para 6,3 GPa entre 10 minutos e 24 horas. A tensão de polimerização aumentou 40% entre 10min e 24h para a norma 4-01 e 51% para o método do Yamamoto et al. O meio de armazenamento foi estatisticamente significativo até o tempo de 4 horas. Portanto, a primeira hipótese foi rejeitada. A segunda e a terceira hipótese podem ser apenas parcialmente rejeitadas.
The objective of this study was to evaluate composite resin restoration polymerization stress development over the first 24 hours after polymerization, according to two methods of analysis of crack propagation. The influence of water storage on the magnitude of the stresses was also evaluated. The degree of conversion (DC) and modulus of elasticity (E) of the composite were determined at various time points. The null hypotheses of this study were: 1) The polymerization stress, DC and E do not change significant throughout the observation period, 2) the two methods of analysis of crack propagation provide similar results, 3) the stress values are not influenced by storage medium. Disks were made of soda-lime glass with 2 mm thickness, 12 mm in outside diameter with central bore of 4 mm in diameter. The perforations were treated with hydrofluoric acid and silane. The discs were randomized into three groups. In one of them, the discs were restored (Charisma Diamond, Heraeus Kulzer), and, the times after 10 min, 1, 2, 4, 8 or 24 hours (n = 10), the specimens received four Vickers indentations (9.8 N for 20 s) at 500m cavity margin. The second group went through the same process, but the discs were stored in water prior to being indented. Then, the length diagonal of the indentation and crack was measured in an optical microscope. The residual stress in the glass was calculated according to standard 4-01 (The Society of Materials Science, JSMS, Japan). The third group of discs were treated similarly, indented and stored in a desiccator for 24 hours before being restored. The cracks were measured before and after the restoration following the same time, and the stress calculated according to the formula described by Yamamoto et al. (Dent Mater, 2009). The DC was determined by near-infrared spectroscopy (n = 3). The E was obtained through the bend test conducted at three-points. Data were subjected by ANOVA / Tukey test ( = 0.05) and regression analysis. The polymerization stress, as well as DC and E values were increased over time. GC increased 28% between 10 minutes and 24 hours, and for an increase of 1.7 GPa to 6.3 GPa between 10 minutes and 24 hours. The polymerization stress increased 40% between 10 min and 24 hours to the standard 4.1 and 51% for the method of Yamamoto et al. The storage medium was statistically significant at the time of 4 hours. Thus, the first hypothesis was rejected. The second and third hypothesis may only be partially rejected.

Le but de ce travail est d'étudier l'effet de la teneur en cuivre et de la valence des atomes de cuivre sur la structure et les propriétés mécanique du verre. Des verres de zinc- et plomb- cuivre borate ont été étudiés. Les changements structurels avec le remplacement de PbO ou ZnO par CuO sont observés par réflectance infrarouge et Raman. L'état d'oxydation, l'environnement du site et la liaison caractéristique d'ions de cuivre ont été étudiés par spectroscopie optique et de résonance de spin électronique. Les propriétés mécaniques ont été déterminées et corrélées à la structure du verre et à sa composition, en mettant l'accent sur les propriétés élastiques, le comportement d'indentation (dureté et micro-fissures), la ténacité et la dépendance à la température de l'élasticité. Le cuivre a une tendance à stabiliser le bore en coordinence trigonale et donne une structure de type métaborate plus homogène. L'ajout d'ions de cuivre au verre métaborate améliore les performances mécaniques (modules d'élasticité et dureté), et diminue la sensibilité à la température ainsi que le taux de ramollissement des verres au plomb. Toutefois, l'ajout d'ions de cuivre dans les verres au zinc a des effets opposés sur ces propriétés. Les changements chimiques à la surface des verres de borates de cuivre et de zinc après traitement thermique sont également étudiés. L'étude par nanoindentation et par rayage montre que la couche cristallisée améliore la résistance mécanique de la surface du verre
The aim of this work is to study the effect of copper content and copper valence on the structural and mechanical properties of glass. Zinc- and lead- copper borate glasses were studied. Their structural changes with the substitution of CuO for ZnO or PbO are followed by Raman and reflectance infrared. The oxidation state, site environment and bonding characteristic of copper ions are studied by optical and electron spin resonance spectroscopy. The mechanical properties were determined and correlated to the glass structure and composition, with a particular emphasis on the elastic properties, sharp indentation behavior (hardness and micro-cracking), toughness and temperature dependence of elasticity. Copper tends to stabilize trigonal boron and gives a more homogeneous metaborate structure. Adding copper ions to the metaborate glass clearly improves the mechanical performance (elastic moduli and hardness), in the meantime decreases the temperature sensitivity and soften rate of lead borate glasses. However, adding copper ions in zinc borate glasses has opposite effects on these properties. The chemistry changes at zinc-copper-borate glass surface after heat-treatment are also studied. Investigation of the nanoindentation and scratch behavior show that the crystallized layer improves the mechanical resistant of glass surface

La contrainte appliquee et l'orientation sont mesurees simultanement durant une traction uniaxiale de reseaux polybutadiene et de copolymeres sbr par fluorometrie. Le modele d'anneaux glissants, qui considere que les enchevetrements forment des anneaux virtuels et mobiles entre les chaines, est utilise pour interpreter les resultats. Caracterisation de la topologie du reseau par le modele thermique de flory et erman

O estudo da resistência à compressão e da deformabilidade de paredes de alvenaria de blocos de concreto é de fundamental importância para a caracterização desse material e o desenvolvimento de análises de estruturas compostas por esse tipo de painel. Este trabalho trata desse tema, objetivando prever com maior acuidade os principais parâmetros de deformação e de resistência de paredes de alvenaria de blocos de concreto, a saber: resistência à compressão e módulo de elasticidade longitudinal nas direções paralela e perpendicular à junta de assentamento. Foi desenvolvido um trabalho experimental para estimar a influência da resistência dos blocos, da resistência da argamassa e da direção de aplicação de forças no comportamento mecânico da alvenaria de blocos de concreto não-grauteada, quando submetida a esforços de compressão. Para tanto, realizaram-se ensaios de laboratório em blocos, argamassas, prismas de três blocos e paredinhas com dimensões de 80 cm x 80 cm. Por inferência estatística não foram obtidas correlações aceitáveis entre as variáveis estudadas. Porém, obtiveram-se tendências de comportamento dos corpos de prova estudados, confirmando a influência das características da argamassa e do bloco no comportamento estrutural da alvenaria quando submetida a esforços de compressão
The study of strength and the curved stress/strain relationship of blockwork masonry walls is basic for the material characterization and the development of structural analysis of blockwork walls. This work deals with that subject, aiming at the evaluation of the main elastic parameters and the strength of concrete blockwork walls: the compressive strength and modulus of elasticity for masonry in two orthogonal directions, parallel and perpendicular to bed joints. An experimental program was developed to evaluate the influence of the strength of blocks and mortar, and the load application direction on the mechanical behavior of ungrouted concrete block masonry under compression. A series of laboratory tests was carried out with blocks, mortar, prisms of three blocks and wallets (80 cm x 80 cm). It was impossible to obtain acceptable correlations of the defined variables, using statistical inference. However, tendencies of the specimens behavior were obtained, confirming the influence of mortar and block properties on the structural behavior of concrete blockwork walls under compression

Validation et application d'une technique d'etude de la corrosion sous contraintes: l'essai de traction lente. Definition d'une procedure experimentale pour la preparation des eprouvettes et choix de conditions experimentales optimales. Confirmation par l'essai de traction lente des resultats obtenus dans le cas de deux aciers 10cd9-10 et z10cdnbv0-2 lors d'essais statiques. Application de la methode de traction lente a la recherche des conditions de fissuration a 95**(o)c de deux aciers utilises dans les turbines francaises (20cnd8 et 26ncdv14-7)

Eshelby-type inclusion problems of an infinite or a finite homogeneous isotropic elastic body containing an arbitrary-shape inclusion prescribed with an eigenstrain and an eigenstrain gradient are analytically solved. The solutions are based on a simplified strain gradient elasticity theory (SSGET) that includes one material length scale parameter in addition to two classical elastic constants. For the infinite-domain inclusion problem, the Eshelby tensor is derived in a general form by using the Green’s function in the SSGET. This Eshelby tensor captures the inclusion size effect and recovers the classical Eshelby tensor when the strain gradient effect is ignored. By applying the general form, the explicit expressions of the Eshelby tensor for the special cases of a spherical inclusion, a cylindrical inclusion of infinite length and an ellipsoidal inclusion are obtained. Also, the volume average of the new Eshelby tensor over the inclusion in each case is analytically derived. It is quantitatively shown that the new Eshelby tensor and its average can explain the inclusion size effect, unlike its counterpart based on classical elasticity. To solve the finite-domain inclusion problem, an extended Betti’s reciprocal theorem and an extended Somigliana’s identity based on the SSGET are proposed and utilized. The solution for the disturbed displacement field incorporates the boundary effect and recovers that for the infinite-domain inclusion problem. The problem of a spherical inclusion embedded concentrically in a finite spherical body is analytically solved by applying the general solution, with the Eshelby tensor and its volume average obtained in closed forms. It is demonstrated through numerical results that the newly obtained Eshelby tensor can capture the inclusion size and boundary effects, unlike existing ones. Finally, a homogenization method is developed to predict the effective elastic properties of a heterogeneous material using the SSGET. An effective elastic stiffness tensor is analytically derived for the heterogeneous material by applying the Mori-Tanaka and Eshelby’s equivalent inclusion methods. This tensor depends on the inhomogeneity size, unlike what is predicted by existing homogenization methods based on classical elasticity. Numerical results for a two-phase composite reveal that the composite becomes stiffer when the inhomogeneities get smaller.

The Eshelby-type problems of an arbitrary-shape polygonal or polyhedral inclusion embedded in an infinite homogeneous isotropic elastic material are analytically solved using a simplified strain gradient elasticity theory (SSGET) that contains a material length scale parameter. The Eshelby tensors for a plane strain inclusion with an arbitrary polygonal cross section and for an arbitrary-shape polyhedral inclusion are analytically derived in general forms in terms of three potential functions. These potential functions, as area integrals over the polygonal cross section and volume integrals over the polyhedral inclusion, are evaluated. For the polygonal inclusion problem, the three area integrals are first transformed to three line integrals using the Green's theorem, which are then evaluated analytically by direct integration. In the polyhedral inclusion case, each of the three volume integrals is first transformed to a surface integral by applying the divergence theorem, which is then transformed to a contour (line) integral based on Stokes' theorem and using an inverse approach. In addition, the Eshelby tensor for an anti-plane strain inclusion with an arbitrary polygonal cross section embedded in an infinite homogeneous isotropic elastic material is analytically solved. Each of the newly derived Eshelby tensors is separated into a classical part and a gradient part. The latter includes the material length scale parameter additionally, thereby enabling the interpretation of the inclusion size effect. For homogenization applications, the area or volume average of each newly derived Eshelby tensor over the polygonal cross section or the polyhedral inclusion domain is also provided in a general form. To illustrate the newly obtained Eshelby tensors and their area or volume averages, different types of polygonal and polyhedral inclusions are quantitatively studied by directly using the general formulas derived. The numerical results show that the components of the each SSGET-based Eshelby tensor for all inclusion shapes considered vary with both the position and the inclusion size. It is also observed that the components of each averaged Eshelby tensor based on the SSGET change with the inclusion size.

碩士
國立臺灣大學
電機工程學系研究所
86
The primary function of tendon is to propagate muscle tension and to store energy in an elastic form. In order to maintain its function, sufficient strength and stiffness are required. The strength and stiffness of tendon, however, tend to degrade with injury or inflammation. It is the purpose of rehabilitation to restore its mechanical properties such that tendon can return to its normal function. Recently, ultrasonic elasticity imaging has become popular as a non-invasive way to investigate the mechanical properties of biological tissue. Different from conventional B-mode imaging, contrast of elasticity imaging is resulted from differences of the elastic modulus between tissues. In theory, ultrasonic elasticity imaging has the potential to provide significant improvement in tissue characterization against conventional B-mode sonogram. In this thesis, protocols for measuring the elasticity difference between the normal tendon and the ischemic tendon at early inflammation stage by ultrasound were established. In addition, the change of composition inside the inflammatory tendon was evaluated by measuring elasticity distribution. Dissected normal and ischemic Achilles tendon of rabbit were prepared in the agar hydro-gel-based phantom, and a 5MHz ultrasonic transducer was used to measure the deformation of tendon thickness under external pressure. The elasticity of rabbit's tendon on the transverse plane and the internal elasticity distribution were obtained by analyzing the A-scan data using a correlation-based algorithm. Results showed that the differences of elasticity measured by ultrasound between the normal and the ischemic tendon were significant. In addition, assuming noise is sufficiently low, the composition change of the ischemic tendon can be effectively monitored by measuring the elasticity distribution using a speckle-tracking algorithm. Therefore, it is believed that reconstruction of the internal elasticity distribution of tendon has the potential of being an effective tool for rehabilitation treatment follow-up in clinics.

Title: Viscousand elastic properties of soft tissue"in situ" Goals and methods: The aim of this thesis is to measure the viscoelastic properties of human soleus muscle and Achilles tendonin vivo and post mortem in situ. It is a pilot study that uses myotonometry as the method of measurement. Based on the response of connective tissues on deformation made by tip of myotonometer, resp. its viscoelastic properties, curves in graphsare created. Three main described parameters of thecurveare steepness, deflection and its surface area. Main goal of the experiment is to compare properties of different types of tissue and their potential differences while denervated or innervated. Results of this study may help with better understanding of the soft tissues behavior in response to manual therapeutic contact. The study also describes the differences between in vivo and post mortem tissue properties that may be help further studies which use post mortem tissues to predict in vivo behavior. Results: Soft tissues in vivo have higher viscosity. In comparison, post mortem tissues have significantly higher stiffness and energy dissipation than in vivo. Elasticproperties of denervated soft tissue manifest with approx. 7 secondsdelay. Viscoelastic properties of muscle tissueshow changes depending on deeper...

Cette thèse a porté sur l'étude d'une classe de matériaux cellulaires, les micro nids d'abeille, destinés à combiner des propriétés mécaniques et acoustiques afin d'être employés comme absorbants acoustiques dans les tuyères des turbomachines. Les bonnes qualités d'absorption acoustique prédites par les modèles théoriques ont tout d'abord été vérifiées expérimentalement. Le travail s'est ensuite porté sur la modélisation des propriétés élastiques de ces structures. Pour ce faire une approche par milieu équivalent a été retenue et, de manière à tenir compte des effets d'échelle présents dans la structure, un milieu de substitution du type " élasticité du second gradient " a été choisi. Pour cela une méthode de construction par homogénéisation des opérateurs de cette loi de comportement a était introduite. Devant l'absence de résultats concernant les classes d'anisotropie des opérateurs d'élasticité du
second ordre, une étude détaillée de ce point a conduit à l'identification des matrices à implémenter dans un code éléments finis. Les opérateurs du second ordre construits par homogénéisation ont pu ensuite être comparés à leurs formes théoriques. Ceci nous a permis de montrer que vis-à-vis du comportement de matériaux nida les effets du second ordre sont, dans certain cas, d'un ordre de grandeur comparable à ceux de l'élasticité classique. Les méthodes mises en place pour l'étude théorique des symétries des opérateurs d'élasticité sont généralisables à toutes lois de comportement linéaire.

Myosin 1c (Myo1c) is a molecular motor involved in regulation of tension-gated ion channels, exocytosis, endocytosis, motility and other membrane-related events. Moreover, it acts as a dynamic linker between the cell membrane and cortical actin network, contributing to the maintenance of plasma membrane tension. In contrast, nuclear myosin 1 (NM1), an isoform of Myo1c, has been described only in the nucleus where it participates in various nuclear processes, including transcription or chromatin remodeling. However, although traditionally regarded as exclusively cytoplasmic or nuclear, all myosin 1c isoforms participate in nuclear functions and they are present in the cytoplasm as well. The main focus of this study was to characterize the functional significance of NM1 in the cytoplasm. We have found that NM1 localizes to plasma membrane and shows a uniform punctuated distribution with a high concentration at the cell periphery. Moreover, atomic force microscopy measurements of mouse NM1 KO fibroblasts revealed a significant increase in an overall plasma membrane elasticity in comparison to WT cells, indicating a disruption in the regulation of plasma membrane tension caused by the loss of NM1. Since a higher membrane elasticity and deformability is a characteristic marker of cancer cells,...

Mestrado em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia
Although the Portuguese oak wood (Quercus faginea L.) has been used in shipbuilding in the past, nowadays it has hardly any use and the knowledge about it is scarce, which requires the characterization and study of its potential for noble use. In this study physical and mechanical properties of Portuguese oak were determined, and the resistance to attack by subterranean termites evaluated, using standard methodologies. Ten trees were used from two regions in Trás-os-Montes. The results showed that this wood is heavy (870 kg/m3), has a heartwood with a very high hardness (101 N/mm2), with low bending strength (99 N/mm2), medium compression strength (47 N/mm2) and is moderately durable regarding termite attack. To evaluate its behavior in composite products, 30 oak wood pieces with three thicknesses were produced and glued on spruce wood (Picea abies H. Karsten). The results showed that hardness of the composites was not very affected for the tested oak wood dimensions.------------------------------Apesar de a madeira de carvalho português (Quercus faginea L.) ter sido aplicada no passado na construção naval, hoje pouco se utiliza e pouco se conhece, o que requer a sua caracterização e o estudo do seu potencial para uso nobre. Neste trabalho determinaram-se propriedades físico-mecânicas da madeira de carvalho português e avaliou-se a sua resistência ao ataque de térmitas subterrâneas, utilizando metodologias normalizadas. Foram utilizadas dez árvores provenientes de duas regiões de Trás-os-Montes. Os resultados mostraram que a madeira é pesada (870 kg/m3), tem dureza muito alta no cerne (101 N/mm2) e apresenta resistência fraca quanto à tensão de ruptura à flexão estática (99 N/mm2) e média quanto à compressão (47 N/mm2). Face ao ataque de térmitas subterrâneas, esta madeira é classificada como moderadamente durável. Para avaliar o comportamento em produtos compósitos, produziram-se 30 peças com três espessuras de madeira de carvalho português, coladas a madeira de espruce (Picea abies H. Karsten). Os resultados demonstram que a qualidade dos produtos compósitos quanto à sua dureza não é fortemente afectada para as dimensões estudadas.