Submitted by Franciele Moreira (francielemoreyra@gmail.com) on 2017-12-13T14:36:06Z No. of bitstreams: 2 Dissertação - Ana Cláudia Barbosa Rezende - 2017.pdf: 21935269 bytes, checksum: 272d811b336e01cf2107f2eda5d68db3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-12-14T10:16:48Z (GMT) No. of bitstreams: 2 Dissertação - Ana Cláudia Barbosa Rezende - 2017.pdf: 21935269 bytes, checksum: 272d811b336e01cf2107f2eda5d68db3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-12-14T10:16:48Z (GMT). No. of bitstreams: 2 Dissertação - Ana Cláudia Barbosa Rezende - 2017.pdf: 21935269 bytes, checksum: 272d811b336e01cf2107f2eda5d68db3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-11-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Ultrasound is a powerful tool used in modern medical and industrial applications. The portability, applicability and ease of working with ultrasound, together with the fact that it is a non-destructive technique and of lower costs, contribute to its use. Modernly, thermoplastic polymer polymethylmethacrylate (acrylic) or PMMA has been used for a variety of applications, from transparent aerospace components to medical-hospital equipment. The study of PMMA’s acustoelasticity using ultrasonic methods allows the indirect inspection of certain physical characteristics of this material. It is known that acoustic waves are a ected by the characteristics of the medium, such as temperature, texture and tension. The research was divided into three stages, the first one to analyze the influence of temperature on the velocity of critically refracted longitudinal ultrasonic waves (Lcr) in PMMA. For this, the transmission method was used for three di erent frequencies. In the second, the structural anisotropy was evaluated using the acoustic birefringence using the pulse-echo method. At this stage a rectangular sample was fractured transversely and rejoined to simulate a symmetry break. The third and final step was devoted to characterizing the acoustoelastic constants L22, L21 and L23 of homogeneous samples by means of longitudinal and shear waves in the pulse-echo mode and the application of an uniaxial force. The results with the waves Lcr showed a significant influence of the temperature on the propagation velocity of the ultrasonic waves, another factor of influence was the frequency of the transducers. On the other hand, with acoustic birefringence it was possible to identify a great variation of this magnitude near the fractured zone, that is, of greater anisotropy. The acoustoelastic constants L22, L21 and L23 were characterized and an increase in the propagation time of the ultrasound wave as a function of the strain was observed for the constants L22 and L23. The constant L21 decreased the propagation time of the ultrasonic shear wave as a function of the deformation. The ultrasonic techniques employed were relevant and allowed to obtain new results not yet described in the literature. The characterization of the acoustoelastic constants also made it possible to estimate the third order elastic constants (l, m, n and A, B, C). The constants characterized in this research are important to obtain a complete understanding of the elastic properties of polymethylmethacrylate. / O ultrassom é uma poderosa ferramenta empregada modernamente tanto em aplicações médicas quanto industriais. A portabilidade, aplicabilidade e facilidade em se trabalhar com ultrassom, aliado ao fato de ser uma técnica não-destrutiva e de custos mais baixos, contribuem para sua utilização. Modernamente, o polímero termoplástico polimetilmetacrilato (acrílico) ou PMMA tem sido utilizado para diversas aplicações, desde componentes aeroespaciais transparentes a equipamentos médico-hospitalares. O estudo da acustoelasticidade do PMMA empregando métodos ultrassônicos possibilita a inspeção indireta de certas características físicas deste material. Sabe-se que as ondas acústicas são afetadas pelas características do meio, como a temperatura, textura e tensões. A pesquisa foi dividida em três etapas, a primeira dedicada a analisar a influência da temperatura sobre a velocidade das ondas ultrassônicas longitudinais criticamente refratadas (Lcr) noPMMA.Para isso, foi empregado o método de transmissão para três frequências distintas. Na segunda, foi avaliada a anisotropia estrutural empregando a birrefringência acústica por meio do método pulso-eco. Nesta fase uma amostra retangular foi fraturada transversalmente e novamente unida para simular uma quebra de simetria. A terceira e última etapa foi dedicada a caracterizar as constantes acustoelásticas L22, L21 e L23 de amostras homogêneas por meio de ondas longitudinais e cisalhantes no modo pulso-eco e a aplicação de uma força uniaxial. Os resultados com as ondas Lcr mostraram influência significativa da temperatura sobre a velocidade de propagação das ondas ultrassônicas, outro fator de influência foi a frequência dos transdutores. Por sua vez, com a birrefringência acústica foi possível identificar uma grande variação dessa grandeza próxima a zona fraturada, ou seja, de maior anisotropia. As constantes acustoelásticas L22, L21 e L23 foram caracterizadas e observou-se um crescimento do tempo de propagação da onda de ultrassom em função da deformação para as constantes L22 e L23. A constante L21 apresentou decréscimo do tempo de propagação da onda cisalhante ultrassônica em função da deformação. As técnicas ultrassônicas empregadas mostraram-se relevantes e possibilitaram a obtenção de novos resultados ainda não descritos na literatura. A caracterização das constantes acustoelásticas também possibilitou estimar as constantes elásticas de terceira ordem (l, m, n e A, B, C). As constantes caracterizadas nesta pesquisa são importantes para se obter uma completa compreensão das propriedades elásticas do polimetilmetacrilato.

Ce mémoire s’est attaché à comprendre les dimensions émergentes de la constitution de l’image d’une organisation. A l’issue de l’étude de la littérature de recherche existante, nous nous sommes intéressée à l’image réfractée, qui est l’image d’une organisation construite par une catégorie de publics nommés arbitres externes. Ce sont les organisations mandatées qui diffusent de l’information au grand public. En adoptant l’approche qualitative, nous avons réalisé une étude du processus de travail des journalistes travaillant pour des journaux différents et des membres des organismes environnementaux dans le cas de la mise en œuvre du projet de loi C-38 du gouvernement fédéral canadien. L’étude empirique nous a permis de proposer un modèle conceptuel du phénomène de la construction de l’image réfractée. Nous avons pu ainsi suggérer d’observer ce phénomène à travers les pratiques de travail des acteurs pour appréhender les dynamiques d’émergence de l’image. Aussi, nous avons insisté sur la pertinence de considérer des paramètres qui constituent le cadre dans lequel se déroule le processus de travail des acteurs appartenant à des communautés de publics différentes. Car ce sont ces paramètres qui engendrent des dynamiques régulant la construction de l’image organisationnelle au sein de chaque communauté de public. / Our research aimed to understand the emergent dimensions of an organization’s image construction. Following the review of existing research literature, we are interested in the refracted image, which is the image of an organization built by a specific public named external arbiters. These external arbiters are mandated organizations that disseminate information to the general public. By adopting a qualitative approach, we conducted a study about the case of the implementation of Bill C-38 by the Canadian Federal Government. Specifically, we examined the working process of two arbiters communities : journalists working for different newspapers, and environmental organizations’ members. The empirical study has allowed us to propose a conceptual model of the construction of the refracted image phenomenon. We thus suggested to observe this phenomenon through the actors’ working practices to understand the emergence of the image dynamics. Also, we emphasized the relevance to consider factors that constitute the framework within which the working process of the actors belonging to different public communities takes place. For it is these parameters that generate the various dynamics regulating the organizational image’s construction by each public community.

Two optimisation problems were considered, in which market exposure is indirectly controlled. The first one models the capital of a company and an independent portfolio of new businesses, each one represented by a Cram\'r-Lundberg process. The company can choose the proportion of new business it wants to take on and can alter this proportion over time. Here the objective is to find a strategy that maximises the survival probability. We use a point processes framework to deal with the impact of an adapted strategy in the intensity of the new business. We prove that when Cram\'{e}r-Lundberg processes with exponentially distributed claims, it is optimal to choose a threshold type strategy, where the company switches between owning all new businesses or none depending on the capital level. For this type of processes that change both drift and jump measure when crossing the constant threshold, we solve the one and two-sided exit problems. This optimisation problem is also solved when the capital of the company and the new business are modelled by spectrally positive L\'vy processes of bounded variation. Here the one-sided exit problem is solved and we prove optimality of the same type of threshold strategy for any jump distribution. The second problem is a stochastic variation of the work done by Taylor about underwriting in a competitive market. Taylor maximised discounted future cash flows over a finite time horizon in a discrete time setting when the change of exposure from one period to the next has a multiplicative form involving the company's premium and the market average premium. The control is the company's premium strategy over a the mentioned finite time horizon. Taylor's work opened a rich line of research, and we discuss some of it. In contrast with Taylor's model, we consider the market average premium to be a Markov chain instead of a deterministic vector. This allows to model uncertainty in future conditions of the market. We also consider an infinite time horizon instead of finite. This solves the time dependency in Taylor's optimal strategies that were giving unrealistic results. Our main result is a formula to calculate explicitly the value function of a specific class of pricing strategies. Further we explore concrete examples numerically. We find a mix of optimal strategies where in some examples the company should follow the market while in other cases should go against it.

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