Cette thèse aborde l'étude du vieillissement thermique du système Fe-Cr. Nous avons étudié le mécanisme de diffusion de la lacune dans le cadre de la théorie de la fonctionnelle de la densité (Density Functional Theory - DFT) et examiné la capacité d'un potentiel empirique de la classe EAM (Embedded Atom Method) à reproduire les résultats DFT. Nous avons montré que l'énergie de migration de la lacune dépend fortement de l'environnement atomique du point de col où les interactions chrome-chrome et chrome-lacune déterminent en partie l’énergie de point de col. Nous avons proposé trois approches pour la paramétrisation d'un modèle Monte Carlo Cinétique (MCC) atomique : l’une entièrement basée sur le potentiel EAM, les autres partiellement basées sur nos calculs DFT. Les simulations par MCC du vieillissement thermique des alliages Fe-20% at. Cr et Fe-25% at. Cr à 773 K montrent la formation de précipités riches en chrome dont la croissance avec le temps suit une loi de puissance avec un exposant 1/3, en accord avec la théorie de Lifshitz-Slyozov-Wagner. La paramétrisation des simulations par MCC entièrement basée sur le potentiel EAM prédit une taille moyenne des précipités supérieure à celle observée expérimentalement, alors que cette dernière est sous-estimée par les paramétrisations partiellement basées sur nos calculs DFT. Ce désaccord semble avoir une origine cinétique plutôt que thermodynamique. La composition de la phase riche en chrome varie au cours de la séparation de phase, indiquant ainsi que la démixtion se produit par nucléation non-classique ou par décomposition spinodale. Des précipités interconnectés sont plus susceptibles de se former dans le système Fe-25% at. Cr plutôt que dans l’alliage Fe-20% at. Cr suggérant ainsi que, lorsque la concentration en soluté augmente, le mécanisme de démixtion se rapproche de la décomposition spinodale. / In this thesis, we address the study of the microstrucutre evolution of the Fe-Cr system under thermal ageing. The vacancy diffusion mechanism was investigated in the framework of the density functional theory (DFT) and the capability of a recently developed embedded atom method (EAM) empirical cohesive model to reproduce the DFT results was examined. We have shown that the vacancy migration energy strongly depends on the saddle point atomic environment where the chromium-chromium and the chromium-vacancy interactions partially determine the saddle point energy. We proposed three approaches for the parameterisation of an atomistic kinetic Monte Carlo (AKMC) model: one fully based on the EAM potential, the others partially based on our DFT calculations. The AKMC simulations of the thermal ageing of the Fe-20 at.%Cr and Fe-25 at.%Cr alloys at 773 K show the formation of chromium-rich precipitates whose growth with time follows a power law with exponent 1/3. This is consistent with the Lifshitz-Slyozov-Wagner theory of coarsening. The AKMC parameterisation fully based on the EAM potential predicts a mean precipitate size higher than the experimentally observed one, whereas the parameterisations partially based on our DFT calculations underestimate it. This disagreement seems to have a kinetic rather than thermodynamic origin. The composition of the precipitating phase varies during the phase separation thus indicating that the unmixing is driven by either a non-classical nucleation or a spinodal decomposition. Interconnected precipitates are more likely to form in the Fe-25 at.%Cr alloy than in the Fe-20 at.%Cr thus suggesting that, as the solute concentration increases, the spinodal decomposition is more likely to occur.

Since the burst of the internet bubble there is a great deal of interest in the way investment bank prices and allocates initial public offerings (IPOs). The additional scrutiny and spotlight is also because of the dominance of bookbuilding mechanism, which gives complete discretion in terms of allocation and pricing to underwriters, and the huge amount of money left on the table by the issuers, especially during the internet bubble period. Numerous press stories and law suit by investors and issuers alleged conflicts of interest by investment banks at the expense of issuers and investors. On the basis of scoping study we identified five areas to examine conflicts of interest: laddering, spinning, relationship banking, profit sharing allocation and allocation to affiliated funds. The findings of the systematic review show that very limited research has been done on the areas identified. Moreover, there is almost no evidence available to examine the behaviour of investment banks post internet bubble burst. Likewise, very limited evidence is available from countries other than United States. From whatever limited research has been done in these areas there does seem to be enough evidence to suggest that investment banks have been involved in activities that is in conflict with their responsibilities and duties. There is clear evidence of wrong doing by investment banks in US during the internet bubble period by being involved in spinning, laddering and profit sharing allocations. There is not much evidence available at the moment to charge the underwriters of exploiting issuers and investors through the use of affiliated banks, venture capitalists and mutual funds. There is a great need to examine the behaviour of investment banks not only for the sake of the stability of the financial markets but also for the financial intermediaries themselves as unnecessary regulations undermine the efficient operations of financial markets.

Magister Scientiae - MSc / This thesis is concerned with singularly perturbed two-parameter problems. We study a tted nite difference method as applied on two different meshes namely a piecewise mesh (of Shishkin type) and a graded mesh (of Bakhvalov type) as well as a tted operator nite di erence method. We notice that results on Bakhvalov mesh are better than those on Shishkin mesh. However, piecewise uniform meshes provide a simpler platform for analysis and computations. Fitted operator methods are even simpler in these regards due to the ease of operating on uniform meshes. Richardson extrapolation is applied on one of the tted mesh nite di erence method (those based on Shishkin mesh) as well as on the tted operator nite di erence method in order to improve the accuracy and/or the order of convergence. This is our main contribution to this eld and in fact we have achieved very good results after extrapolation on the tted operator finitete difference method. Extensive numerical computations are carried out on to confirm the theoretical results. / South Africa

For an ideal impact energy absorber, the initial peak force should be low and the average crushing force should be high. Also, a long stroke and a stable force history are expected. The thin-walled tube under axial loads is a kind of energy absorber that can produce controlled progressive collapse during a crash. It is a promising collapse mechanism for energy absorption with demonstrated success in industry. But the conventional thin-walled tubes still have high initial peak force and force fluctuations during a crushing process. To help to achieve a better energy absorbing structure, a research work has been carried out in this thesis. The aim of the present research is to achieve an improved understanding of the crushing behaviour of thin-walled tubes under axial loads. In the study, the entire crushing process, including the initial stage of collapse, its localization and the subsequent progressive folding has been carefully investigated by experiment. The relation between the localized plastic deformation and the corresponding crushing force is built by comparing the cross section of series of specimens and their load-displacement curves, which give a deep insight of the collapse mechanism of circular thin-walled tube under axial loads. Then some trigger systems are proposed, which is proved to be a good way to reduce the initial peak force and influence the collapse behaviour. To achieve higher energy absorbing efficiency, the multi-cell thin-walled tube has been investigated. Finally, based on the analysis in this study, a new multi-cell profile which is composed of coaxial tubes with different lengths and dented grooves is proposed. The new design is proved to be a good energy absorber with low initial peak force and very high energy absorption efficiency.

No description available.

The effect of initial out-of-straightness of steel beams with wide flange cross-sections on their elastic lateral torsional buckling strength is investigated analytically and numerically. A variational principle is first developed and then used to obtain the governing equilibrium conditions and associated boundary conditions for a beam with general patterns of initial out-of-straightness and initial angles of twist. The principle is then used to develop a finite element formulation to characterize the lateral torsional response of beams with initial out-of-straightness under general transverse loading. The validity of the finite element formulation is verified through comparison against results from models based thin-walled beam finite element and shell element models available in ABAQUS. Since the load lateral displacement responses do not exhibit a distinct point of loss of stability, two design criteria are proposed for the characterization of the failure. The first criterion is based on a threshold value for additional lateral displacement and the second criterial is based on a threshold value for the normal stresses. Both criteria are applied in conjunction with the analytical solution and finite element formulation in order to determine a moment resistance based on lateral torsional buckling that incorporates the effect of initial out-of-straightness. The moment capacity based on the displacement-based criterion is shown to solely depend on the ratio between the initial out-of-straightness component associated with the first buckling mode and the additional displacement threshold value specified. To the contrary, moment capacity based on the stress criterion, was found to depend upon the initial out-of-straightness magnitude, the normal stress threshold value and the geometry of the cross-section. The effects of the above parameters on the predicted moment capacity were investigated for beams with common sections in a systematic parametric study. Possible means of modifying the present provisions of CAN-CSA S16 relating to elastic lateral torsional buckling to incorporate the effect of initial out-of-straightness effects are discussed and illustrated through examples. The load-deformation plots for beams with initial out-of-straightens as predicted by the formulations developed in the present study are then used to extend the Southwell plot technique, originally developed for buckling of column with initial out-of-straightness, to the lateral torsional buckling of beams with initial out-of-straightness. The study shows that the plot, either experimentally or analytically obtained, of the applied load versus lateral displacement, at any point or angle of twist at any section, for a beam with initial out-of-straightness case can predict (a) the elastic critical moment of an analogous initially straight beam, and (b) the first buckling mode contribution to the initial out-of-straightness.

Ce travail doctoral vise à étudier le rôle de la confiance initiale dans la phase d'établissement de la relation entre le consommateur et une marque. Pour ce faire, nous avons tout d'abord effectué une étude qualitative exploratoire auprès d'un échantillon de 24 personnes. Dans le cadre de cette étude, nous avons opté pour le cas d'une marque nouvelle pour les interviewés car c'est précisément dans ce cas de figure que la confiance initiale devrait être le plus difficile à établir pour la marque. Les résultats de cette étude exploratoire révèlent l'existence d'une confiance initiale du consommateur envers une nouvelle marque. Celle-ci fait référence à une présomption par le consommateur que la nouvelle marque puisse être fiable et intègre. Elle se forme à partir de quatre types de facteurs : les facteurs liés à la marque, les facteurs liés aux tiers, les facteurs liés au consommateur et le facteur situationnel. Enfin, elle engendre deux conséquences : l'intention d'achat de la nouvelle marque et l'intention de recommander la nouvelle marque à l'entourage. Nous avons ensuite réalisé une enquête en ligne auprès d'un échantillon de 421 femmes afin de vérifier nos hypothèses de recherche. Elle s'est effectuée par le biais d'un questionnaire précédé d'un scénario et portait sur une nouvelle marque de crème anti-rides qui a été conçue pour les besoins de la recherche. Les résultats de cette étude montrent que : (1) la confiance initiale envers une nouvelle marque est un concept unidimensionnel et non bidimensionnel ; (2) certains facteurs influencent positivement la confiance initiale envers une nouvelle marque : la perception positive du bouche à oreille, du point de vente, du pays d'origine et du packaging de cette marque ; (3) d'autres facteurs influencent négativement la confiance initiale envers une nouvelle marque (la perception du prix élevé de cette marque) ou n'ont pas d'influence sur cette dernière (la perception positive de la publicité de cette marque, la propension à faire confiance et l'ouverture d'esprit du consommateur) ; (4) le risque perçu lié à la catégorie de produits a un effet modérateur sur les relations entre la perception positive des signaux émis par les entreprises (le prix, le pays d'origine, le point de vente, le packaging et la publicité) et les tiers (le bouche à oreille) d'une part, et la confiance initiale envers une nouvelle marque d'autre part ; (5) la confiance initiale envers une nouvelle marque est un déterminant de l'intention d'achat et l'intention de recommander cette marque.Mots clés : confiance, confiance initiale, marque. / This doctoral research aims to investigate the role of initial trust in the establishment phase of the relationship between consumer and brand. We first conducted an exploratory qualitative study with a sample of 24 subjects. In this study, we opted for a new brand for the interviewees, since it is precisely in this case that the initial trust should be more difficult to establish for the brand. The results of this exploratory study reveal an initial consumer trust towards a new brand which refers to a presumption by the consumer that the new brand is reliable and honest. It is formed from four types of factors: factors related to the brand, to third parties, to individual consumer and to risk perception. In addition, it generates two outcomes that are intention to buy and intention to recommend the brand. We then conducted an online survey among a sample of 421 women to test our research hypotheses. This is done through a questionnaire preceded by a scenario focused on a new brand of anti-wrinkle cream which is designed for research purposes. The results of this study show that: (1) the initial trust towards a new brand is one-dimensional and not two-dimensional concept; (2) some factors positively influence initial trust towards a new brand: the positive perception of word of mouth, point of sale, country of origin and packaging of this brand; (3) other factors negatively influence the initial trust towards a new brand (the perceived high price of this brand) or have no effect on the latter (positive perception of the brand advertising, the propensity to trust, and openness of the consumer); (4) the perceived risk associated with the product category has a moderating effect on the relationship between positive perception of signals emit by companies (the price, country of origin, point of sale, packaging and advertising) and third (word of mouth) on the one hand, and initial trust towards a new brand on the other hand; (5) the initial trust towards a new brand is a determinant of intention to buy and intention to recommend this brand.Keywords: trust, initial trust, brand

This diploma thesis deals with Business Intelligence. First, it describes the architecture and various components of BI solutions. The basic concepts related to this issue are explained. Mentioned are also possible fields of application and end-users. The next section compares the advantages and disadvantages of three possible options for BI solutions (OSS BI, ERP + BI applications, commercial BI). From a practical standpoint, it is focused on the implementation process and its various stages that are described in more detail. In the last part is introduced a real company and is prepared initial study, the first stage in the whole process of implementing Business Intelligence.

Numerical relativity is concerned with the generation of solutions to Einstein's equations by numerical means. In general, the construction of such a spacetime is accomplished in two stages: 1) the determination of initial data which is specified on a single spacelike hypersurface and satisfies four initial value equations, and 2) the evolution of the initial data to generate the spacetime or some portion of it. One of the key problems is the development of efficient algorithms for the solutions of these equations, as they are sufficiently complex to tax the fastest present computers. This thesis presents a comparison of various algorithms for the solution of the initial value equations, concentrating on the recently developed multi-grid method. The specific problem examined has been previously studied by Bowen, Piran and York. Their initial data has been interpreted as representing "snapshots" of three new families of black holes. Three of the four initial value equations possess analytic solutions. The remaining 2-dimensional nonlinear partial differential equation is solved numerically in this thesis using finite difference techniques. The performance of the multi-grid method, with respect to three more well-known methods, is evaluated through numerical experiments. The speed and reliability of the multi-grid algorithm are found to be very good. In addition, the results which had been previously calculated numerically by Piran are essentially reproduced, with the correction of some errors in that work. Possible extensions of the work to more complex initial value problems are also discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This paper is predicated on determining the effectiveness of angles-only initial orbit determination (IOD) methods when limited observational data is available for low-Earth orbit (LEO) rocket body debris. The analysis will be conducted with data obtained from Lockheed Martin Space’s Space Object Tracking (SpOT) facility, focusing on their observational data from 2018 that contains tracking of rocket body debris for less than one minute per overhead pass. After the IOD accuracies are better understood, a feasibility study will follow that investigates the possibility of cataloguing LEO orbital debris from a single optical observation facility with similar observational capabilities as that of the SpOT facility. The IOD accuracy analysis will investigate nine different rocket bodies, with a total of 50 orbital passes of data included in the research. Three main IOD approaches will be tested for each data set to determine the best method in achieving high levels of IOD accuracy: a traditional three-point method, an iterative method, and an assumed-circular orbit method. Application of the iterative approach results in increased accuracy for the resultant initial orbit determination as compared to the three-point IOD method, and an assumed-circular orbit assumption allows for a further increase in accuracy, especially for observed objects in near-circular orbits. The feasibility of cataloguing debris from a singular optical facility shows promise, as subsequent target acquisition after an object’s initial observation is determined to be achievable under the correct circumstances. By choosing a correct telescope pointing angle based on the IOD results from one pass of data, an observed rocket body debris object would pass through the field of view of SpOT’s spotter scope (0.7-degrees) during its next overhead pass for two different test cases. An increase field of view would increase both the likelihood of acquiring the target object and the amount of time the object is visible by the telescope.