Yes / Purpose: We develop new quantitative methods to estimate the level of speculation and long-term sustainability of Bitcoin and Blockchain. Design/Methodology/Approach: We explore the practical application of speculative bubble models to cryptocurrencies. We then show how the approach can be extended to provide estimated brand values using data from Google Trends. Findings: We confirm previous findings of speculative bubbles in cryptocurrency markets. Relatedly, Google searches for cryptocurrencies seem to be primarily driven by recent price rises. Overall results are sufficient to question the long-term sustainability of Bitcoin with the suggestion that Ethereum, Bitcoin Cash and Ripple may all enjoy technical advantages relative to Bitcoin. Our results also demonstrate that Blockchain has a distinct value and identity beyond cryptocurrencies - providing foundational support for the second generation of academic work on Blockchain. However, a relatively low estimated long-term growth rate suggests that the benefi ts of Blockchain may take a long time to be fully realised. Originality/value: We contribute to an emerging academic literature on Blockchain and to a more established literature exploring the use of Google data within business analytics. Our original contribution is to quantify the business value of Blockchain and related technologies using Google Trends.

This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d\'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components Therefore, in accordance of the equipment\'s available in the two groups, the work will be conducted either at the Ecole des Mines d\'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUSR numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions. / Esta tese desenvolvida dentro do acordo de cooperação internacional celebrado entre a Escola Politécnica da Universidade de São Paulo (EPUSP) e a École des Mines d\'Albi-Carmaux tem como tema principal a análise da influência da evolução microestrutural sobre o comportamento mecânico de chapa de liga de titânio - Ti-6Al- 4V sob condições superplásticas e trabalho a quente. O objetivo desta pesquisa é contribuir para o desenvolvimento de processos de conformação não convencional de chapas de ligas a base de titânio utilizadas na manufatura de componentes metálicos. Como objetivo específico, estabelecer uma correlação entre comportamento mecânico e a mudança microestrutural a partir de três tipos de ligas com diferentes tamanhos de grão iniciais (0.5, 3.0 e 4.9 ?m). Os testes foram realizados na faixa de temperatura de 700 a 950 °C combinados às taxas de deformação na faixa de 10-1 s-1 - 10-4 s-1. Para a metodologia, estabeleceu-se uma estratégia de ensaios mecânicos capaz de testar as hipóteses sobre o comportamento do material formuladas no início desta pesquisa. Em seguida, os ensaios mecânicos foram divididos em três partes. Na primeira, utilizou-se um simulador termomecânico modelo Gleeble 3800 para os ensaios a quente variando-se a taxa de deformação (??) entre 10-1 s-1 a 10-3 s-1 e temperaturas da ordem de 700 °C a 850 °C. Na segunda parte dos testes, priorizouse taxas de deformação mais lentas (10-2 s-1 - 10-4 s-1) e temperaturas mais elevadas (800 °C - 950 °C) objetivando atingir as deformações superplásticas do material, nesta etapa utilizou-se como equipamento uma máquina de tração modelo MTS 50kN com câmara de aquecimento acoplada. A terceira parte dos ensaios experimentais envolveu a conformação na condição superplástica por pressão hidrostática (Bulge test) realizadas no LEL-IPT de São José dos Campos. A partir da análise dos dados experimentais levantou-se os parâmetros introduzidos no modelo numérico de comportamento mecânico baseado na evolução da microestrutura da chapa testada permitindo a calibração do modelo numérico a partir das equações constituintes e finalmente introduzido no software de elementos finitos (ABAQUS 6.12) e construído a simulação numérica da conformação superplástica por pressão hidrostática. Os principais resultados indicaram uma forte correlação entre microestrutura inicial da conformação superplástica e a quente de onde se pode observar que tanto menor a microestrutura inicial maior será a quantidade do crescimento de grão. Os resultados da conformação superplástica de expansão multiaxial do domo hemisférico foram, então, comparados à simulação numérica permitindo confrontar os dados do modelo numérico do comportamento mecânico com a lei de comportamento estudada, o que possibilitou um melhor entendimento dos mecanismos da conformação plástica em condições de superplasticidade e também de trabalho a aquente do material.

This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d\'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components Therefore, in accordance of the equipment\'s available in the two groups, the work will be conducted either at the Ecole des Mines d\'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUSR numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions. / Esta tese desenvolvida dentro do acordo de cooperação internacional celebrado entre a Escola Politécnica da Universidade de São Paulo (EPUSP) e a École des Mines d\'Albi-Carmaux tem como tema principal a análise da influência da evolução microestrutural sobre o comportamento mecânico de chapa de liga de titânio - Ti-6Al- 4V sob condições superplásticas e trabalho a quente. O objetivo desta pesquisa é contribuir para o desenvolvimento de processos de conformação não convencional de chapas de ligas a base de titânio utilizadas na manufatura de componentes metálicos. Como objetivo específico, estabelecer uma correlação entre comportamento mecânico e a mudança microestrutural a partir de três tipos de ligas com diferentes tamanhos de grão iniciais (0.5, 3.0 e 4.9 ?m). Os testes foram realizados na faixa de temperatura de 700 a 950 °C combinados às taxas de deformação na faixa de 10-1 s-1 - 10-4 s-1. Para a metodologia, estabeleceu-se uma estratégia de ensaios mecânicos capaz de testar as hipóteses sobre o comportamento do material formuladas no início desta pesquisa. Em seguida, os ensaios mecânicos foram divididos em três partes. Na primeira, utilizou-se um simulador termomecânico modelo Gleeble 3800 para os ensaios a quente variando-se a taxa de deformação (??) entre 10-1 s-1 a 10-3 s-1 e temperaturas da ordem de 700 °C a 850 °C. Na segunda parte dos testes, priorizouse taxas de deformação mais lentas (10-2 s-1 - 10-4 s-1) e temperaturas mais elevadas (800 °C - 950 °C) objetivando atingir as deformações superplásticas do material, nesta etapa utilizou-se como equipamento uma máquina de tração modelo MTS 50kN com câmara de aquecimento acoplada. A terceira parte dos ensaios experimentais envolveu a conformação na condição superplástica por pressão hidrostática (Bulge test) realizadas no LEL-IPT de São José dos Campos. A partir da análise dos dados experimentais levantou-se os parâmetros introduzidos no modelo numérico de comportamento mecânico baseado na evolução da microestrutura da chapa testada permitindo a calibração do modelo numérico a partir das equações constituintes e finalmente introduzido no software de elementos finitos (ABAQUS 6.12) e construído a simulação numérica da conformação superplástica por pressão hidrostática. Os principais resultados indicaram uma forte correlação entre microestrutura inicial da conformação superplástica e a quente de onde se pode observar que tanto menor a microestrutura inicial maior será a quantidade do crescimento de grão. Os resultados da conformação superplástica de expansão multiaxial do domo hemisférico foram, então, comparados à simulação numérica permitindo confrontar os dados do modelo numérico do comportamento mecânico com a lei de comportamento estudada, o que possibilitou um melhor entendimento dos mecanismos da conformação plástica em condições de superplasticidade e também de trabalho a aquente do material.

This thesis proposes a hypothesis that a conventional, and essentially manual, HAZOP process can be improved with information obtained with model-based dynamic simulation, using a Monte Carlo approach, to update a Bayesian Belief model representing the expected relations between cause and effects - and thereby produce an enhanced HAZOP. The work considers how the expertise of a hazard and operability study team might be augmented with access to behavioural models, simulations and belief inference models. This incorporates models of dynamically complex system behaviour, considering where these might contribute to the expertise of a hazard and operability study team, and how these might bolster trust in the portrayal of system behaviour. With a questionnaire containing behavioural outputs from a representative systems model, responses were collected from a group with relevant domain expertise. From this it is argued that the quality of analysis is dependent upon the experience and expertise of the participants but this might be artificially augmented using probabilistic data derived from a system dynamics model. Consequently, Monte Carlo simulations of an improved exemplar system dynamics model are used to condition a behavioural inference model and also to generate measures of emergence associated with the deviation parameter used in the study. A Bayesian approach towards probability is adopted where particular events and combinations of circumstances are effectively unique or hypothetical, and perhaps irreproducible in practice. Therefore, it is shown that a Bayesian model, representing beliefs expressed in a hazard and operability study, conditioned by the likely occurrence of flaw events causing specific deviant behaviour from evidence observed in the system dynamical behaviour, may combine intuitive estimates based upon experience and expertise, with quantitative statistical information representing plausible evidence of safety constraint violation. A further behavioural measure identifies potential emergent behaviour by way of a Lyapunov Exponent. Together these improvements enhance the awareness of potential hazard cases.

L'adaptation en-ligne du logiciel de tolérance aux fautes permet de renforce la sûreté de fonctionnement du système et prenant en compte son environnement. L’adaptation nécessite de nouvelles techniques de conception. Ces travaux visent à comprendre et maîtriser l'impact des modifications du logiciel de tolérance aux fautes en opération sur les fonctionnalités du système, pour en maîtriser les effets de bords. L’approche proposée introduit une architecture réflexive à composants et une modélisation du logiciel. Un modèle structurel du logiciel permet de calculer et appliquer les modifications du contenu du logiciel. Un modèle comportemental décrit les observations attendues en fonctionnement. Il permet de déterminer les états permettant d’appliquer les modifications, d’amener et de maintenir le système dans ces états. Ces travaux montrent que, grâce aux capacités de manipulation et de contrôle en ligne du logiciel, la modification des mécanismes de tolérance aux fautes peut être réalisée en ligne de manière maîtrisée. / On-line fault tolerance adaptation aims at enforcing system dependability by taking into account operational conditions and environment. Adapting the system requires new design techniques. This work aims at understanding and mastering the impact of such software modification in operation, especially regarding side effects on functionalities and dependability properties. Our approach relies on a reflective architecture based on components and models of the software that reflects on the one hand the content of the software in terms of state and algorithms (architectural model) and on the other hand the expected correct behaviour (behavioural model). The first one is used to determine the modifications and apply them at runtime, and the second one is used to drive the system in a state in which modifications can be done consistently, and maintain the system in such a state. We show that; thanks to manipulation capabilities and execution control, we can master the modification of fault tolerance software and ensure correctness properties.

In this study, a method is developed for modelling and classifying behaviour of maritime vessels in a piracy situation. Prior knowledge is used to construct a probabilistic graphical model of maritime vessel behaviour. This model is a novel variant of a dynamic Bayesian network (DBN), that extends the switching linear dynamic system (SLDS) to accommodate contextual information. A generative model and a classifier model are developed. The purpose of the generative model is to generate simulated data by modelling the behaviour of fishing vessels, transport vessels and pirate vessels in a maritime piracy situation. The vessels move, interact and perform various activities on a predefined map. A novel methodology for evaluating and optimising the generative model is proposed. This methodology can easily be adapted to other applications. The model is evaluated by comparing simulation results with 2011 pirate attack reports. The classifier model classifies maritime vessels into predefined categories according to their behaviour. The classification is performed by inferring the class of a vessel as a fishing, transport or pirate vessel class. The classification method is evaluated by classifying the data generated by the generative model and comparing it to the true classes of the simulated vessels. / Thesis (PhD)--University of Pretoria, 2014. / tm2015 / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

Cette thèse s’est déroulée dans le cadre d’une cotutelle internationale entre l’IMT - École des Mines d’Albi-Carmaux et l’Ecole Polytechnique de l’Université de Sao Paulo (EPUSP). Elle a pour but de contribuer à l’étude du comportement mécanique des alliages de titane Ti6Al4V, et plus spécialement dans le domaine du formage superplastique et du formage à chaud. L’objectif général de ce doctorat est de contribuer au développement de procédés de formages non conventionnels des alliages de titane pour applications aéronautiques. C’est pourquoi, en fonction des équipements disponibles sur les deux sites, les travaux de recherche se sont déroulés soit à l’Ecole des Mines soit à l’EPUSP. Cette thèse adresse la problématique scientifique des interactions entre le comportement mécanique dans le domaine du formage superplastique et de formage à chaud d’une part et la microstructure initiale et son évolution dans le domaine de sollicitation d’autre part. Pour cela une stratégie d’essais et de caractérisation a été développée et suivie. Les essais incluent des essais mécaniques uniaxiaux à haute température sur différents alliages Ti6Al4V présentant des microstructures initiales différentes (taille de grain 0,5; 3,0 et 4,9 μm). Une attention particulière a été portée à l’évolution microstructurale avant essai - c’est- à-dire durant sa montée en température et la stabilisation thermique de l’échantillon – et durant l’essai. Les conditions d’essai ont été choisies de façon à couvrir le domaine du formage à chaud et du formage superplastique, température de 700°C à 950°C et vitesse de déformation entre 10-1 s-1 et 10-4 s-1. La croissance de grain dépend de la microstructure initiale mais aussi de la durée de l’essai en température (croissance statique) et de la vitesse de déformation (croissance dynamique). Afin d’améliorer la validité du modèle des observations microstructurales de taille de grain sont effectués après les essais mécaniques par micrographie optique et Microscope Electronique à Balayage. Un modèle de comportement unifié a été introduit de façon à être capable de couvrir toute la plage de température et de vitesse de déformation : écrouissage cinématique non linéaire, sensibilité à la vitesse de déformation et loi de croissance de la taille des grains sont inclus dans le modèle. Afin de pouvoir valider le modèle, il a été introduit dans le code de simulation ABAQUS®. Les résultats des simulations (en particulier déformation macroscopique et taille de grain locale) ont été comparés, pour l’un des matériaux de l’étude, aux résultats d’un essai de gonflage axisymétrique de tôle. Pour obtenir un cycle de contrôle simple, les essais effectués au laboratoire de l’IPT/LEL à Sao José dos Campos au Brésil ont été opérés à vitesse de déformation constante. Les résultats montrent une très bonne corrélation avec les prédictions et permettent de conclure à une validation du modèle de comportement développé dans la thèse dans des conditions industrielles de formage de l’alliage de titane. / This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components. Therefore, in accordance of the equipment’s available in the two groups, the work will be conducted either at the Ecole des Mines d'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUS numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions.

La conception en vue de la fiabilité (DFR, Design for Reliability) consiste à simuler le vieillissement électrique des composants élémentaires pour évaluer la dégradation d'un circuit complet. C'est dans ce contexte de fiabilité et de simulation de cette dernière, qu'une stratégie de conception en vue de la fiabilité a été développée au cours de ses travaux. Cette stratégie, intégrant une approche « système » de la simulation, s'appuie sur l'ajout de deux étapes intermédiaires dans la phase de conception. La première étape est une étape de construction de modèles comportementaux compacts à l'aide d'une méthodologie basée sur une approche de modélisation multi niveaux (du niveau transistor au niveau circuit) des dégradations d'un circuit. La seconde étape consiste alors l'analyse descendante de la fiabilité de ce circuit, à l'aide de simulations électriques utilisant ses modèles comportementaux dits « dégradables », afin de déterminer les blocs fonctionnels et/ou les composants élémentaires critiques de l'architecture de ce dernier, vis-à-vis d'un mécanisme de défaillance et un profil de mission donnés. Cette analyse descendante permet aussi d'évaluer l'instant de défaillance de ce circuit. Les dispersions statiques, lies au procédé de fabrication utilisé, sur les performances d'un lot de CIs ont aussi été prises en compte afin d'évaluer leur impact sur la dispersion des instants de défaillance des circuits intégrés. Ces méthodes ont été appliquées à deux mécanismes de dégradation : les porteurs chauds et les radiations. / Design for reliability (DFR) consists in assessing the impact of electrical ageing of each elementary component, using electrical simulations, on performance degradations of a full device. According to DFR concept and reliability simulation, theses works present a new DFR strategy. This strategy based on the integration of two intermediate phases in the ICs and SoC design flow. The first phase is a bottom-up ageing behavioural modelling phase of a circuit (from transistor level to circuit level). The second phase is a « top-down reliability analyses » phase of this circuit, performing electrical simulations using its ageing behavioural models, in order to determine critical functional blocks and / or elementary components of its architecture according to a failure mechanism and a given mission profile. Theses analyses also allow determining the failure time of this circuit. Statistical dispersions on ICs performances, due to the used manufacturing process, have been taking into account in order to assess their impact on failure time dispersions of a ICs lot. The method has been applied on two degradation mechanisms: hot carriers and radiations.

Tato práce pojednává o technikách behaviorálního modelování pro speciální úlohy v elektromagnetismu, které je možno formulovat jako problém aproximace, klasifikace, odhadu hustoty pravděpodobnosti nebo kombinatorické optimalizace. Zkoumané methody se dotýkají dvou základních problémů ze strojového učení a combinatorické optimalizace: ”bias vs. variance dilema” a NP výpočetní komplexity. Boltzmanův stroj je v práci navržen ke zjednodušování komplexních impedančních sítí. Bayesovský přístup ke strojovému učení je upraven pro regularizaci Parzenova okna se snahou o vytvoření obecného kritéria pro regularizaci pravděpodobnostní a regresní neuronové sítě.