Optimisation of postbuckling stiffened composite structures

The thesis starts off with an introductory chapter on composite materials. This includes a definition of composites, a brief history of composite materials, their use in aerostructures (primarily as stiffened structures), and also optimization of composite structures. A literature review is then presented on postbuckling stiffened structures. This includes both experimental investigations on stiffened composite panels and investigations into secondary instabilities and mode jumping as well as their numerical modelling. Next, the Finite Element (FE) modelling of posthuckling stiffened structures is discussed, relating how ABAQUS models are set up in order to trace stiffened composite panels' buckling and postbuckling responses. An experimental programme conducted on an I-stiffened panel is described, where the panel was tested in compression until collapse. The buckling and postbuckling characteristics of the panel are presented, and then an FE model is described together with its predicted numerical behaviour of the panel's buckling and postbuckling characteristics. Focus then shifts to the modelling of failure in composites, in particular delamination failure. A literature review is conducted, looking at the use of both the Virtual Crack Closure Technique (VCCT) and interface elements in delamination modelling. Two stiffener runout models, representing two specimens previously tested experimentally, are then developed to illustrate how interface elements may be used to model mixed mode delamination. The previously discussed panel is revisited, and a global-local modelling approach used to model the skin-stiffener interface. FE models of a stiffened cylindrical shell are also considered, and again the postbuckling characteristics of the shell are compared with experimental results. . The thesis then moves on to optimization of composite structures. This starts off with a literature review of existing optimization methodologies. A Genetic Algorithm (GA) is devised to increase the damage resistance of the I-stiffened panel. The global-local ABAQUS model discussed earlier is used in conjunction with the GA in order to find a revised stacking sequence of both the panel flanges and skin so as to minimize skin-stiffener debonding subject to a variety of design constraints. A second optimization is then presented, this time linked to the FE model of the stiffened cylindrical shell. The objective is to increase the collapse load of the shell, again subject to specific design constraints. The thesis concludes by summarising the importance of the work conducted. FE models were created and validated against experimental work in order to model a variety of composite stiffened structures in their buckling and postbuckling regimes. These models were able to capture the failure characteristics of these structures relating to delamination at the skin-stiffener interface, a phenomenon widely observed experimentally. Various optimizations, able to account for failure mechanisms which may occur prior to overall structural collapse, were then conducted on the analysed structures in order to obtain more damage resistant designs.Imperial Users onl

Investigation of novel thermal cyclisation reactions and studies on their application to the synthesis of selected natural products

The primary goal of this research project was to investigate the mechanism of a novel thermally activated cyclisation reaction discovered by Parsons et al. During these studies two novel reactions were discovered: For reaction see Abstract in pdf Reagents and Conditions: (i) Toluene 0.1M, reflux, 4h, 32%. For reaction see Abstract in pdf Reagents and Conditions: (i) Toluene, 0.01M, reflux, 4h, 53% Radical and ene pathways for the generation of these products were proposed. However, despite extensive empirical studies, no definitive proof for either mechanism was found. The breadth of the synthetic utility of the above reactions was also investigated by synthesizing various analogues. The general application of the Parsons’ cyclisation to the synthesis of steroid cored and the complex natural product Jiadifenin was also investigated. Advanced intermediates were synthesised and invaluable information on reactivity was gained, however these investigations could not be completed due to time constraint

Exploring the linkage between Euroscepticism and redistributive policies in the EU. Insights from the case of Italy.

openEuroscepticism has recently been manifested in areas that have been high recipients of EU funding manifested through Cohesion policy. As it is peculiar that instances of lack of support toward the Union be manifested in regions that receive significant support, it is worth looking into the connection that exists between Euroscepticism and Cohesion policy. In particular, the case of Italy is a valuable one, due to the recent surge in populist parties sharing a great deal of skepticism for the EU, and the traditional divide that has made many regions available for significant funding

Empirical approaches for near-term climate predictions

Climate variations on seasonal to decadal time scales can have enormous social, economical and environmental impacts. As such, the ability to make skilful and reliable climate predictions at these time scales offers many benefits for climate preparedness, adaptation and resilience. In the recent years, major progress has been made in the development of such predictions with the advent of simulations with global climate models that are initialized from the current climate state. However, many challenges remain including an understanding of the underlying physical mechanisms for skilful predictions and whether such predictions could be improved. The purpose of this thesis is to establish new benchmarks for seasonal to decadal predictions in diverse components of the climate system and to provide some pieces of evidence that help to understand what are the drivers for these predictable patterns. Specifically, we use a suite of empirical models to perform predictions of oceanic and atmospheric variables together with initialized climate predictions to: 1. Understand the contribution of remote and local factors to the predictability of North and Tropical Pacific Oceans Sea Surface Temperature and Land Surface Temperature over Western North America; 2. Provide a higher baseline level skill for the state-of-art global prediction systems, from seasonal to decadal time scales; 3. Explore possible sources of errors in the global climate model simulations using statistical predictive models.First, we isolate contributions to the forecast skill from different spatial and time scales in the Pacific Ocean using a Liner Inverse Modelling (LIM) approach, showing the importance of temporal scale interactions in improving the predictions on decadal time scales. Specifically, we show that the Extratropical North Pacific is a source of predictability for the tropics on seasonal to interannual time scales, while the tropics enhance the forecast skill for the decadal component. We then show that the skill for an empirically-built LIM is comparable to and sometimes better than that from two state-of-art global prediction systems, from seasonal to decadal timescales and for several regions around the globe. These results indicate that the evolution of the system in those areas may not be not fully driven by unpredictable dynamics and that there may be some room for improvement in the dynamical models predictions, given that a low-dimensional linear model is able to generate better skill than the fully-coupled nonlinear model. Bearing that in mind, we use the LIM linear feedback matrix to explore possible sources of errors in the dynamical model simulations and we find that some of the simulated atmospheric and oceanic local and remote feedbacks differ in several key regions from that obtained with observations. These results may indicate sources of error in the dynamical models and therefore in its prediction skill that merit focused attention.We then investigate the role of remote and local predictors in seasonal predictors of minimum and maximum air temperatures over the Western North America, using a Canonical Correlation Analysis approach. We show that remote predictors, in the form of Pacific climate modes, provide the best predictive skill for temperature over land, particularly during wintertime. Lastly, considering that persistence is the widely-used measure when evaluating the predictive skill for dynamical models, we suggest the use of CCA as a much higher benchmark for seasonal predictions of land surface air temperatures

El derecho a un proceso con todas las garantías ante los cambios de paradigma de la inteligencia artificial

El presente trabajo analiza cómo la tutela judicial efectiva, que constituye el centro del sistema de justicia en el Estado de Derecho, se está adaptando a la irrupción de las tecnologías de inteligencia artificial. A tal fin, tras analizar los roles y las funciones que los algoritmos pueden asumir en las distintas fases de la justicia penal, en virtud de su carácter poliédrico y polifacético, se reflexionará sobre la necesidad de un estatuto procesal europeo de la IA. Para ello, se centrará en las razones por las que es necesario regular el «due process of law algorítmico», lo cual exige repensar las categorías básicas del Derecho, a través del juicio de compatibilidad, y en el estado de la cuestión, haciendo referencia a cómo se está progresivamente regulando y especialmente a la Propuesta de Reglamento de la UE sobre la IA, adoptada en abril de 2021, cuyo objetivo es construir un «ecosistema de garantías»

A CONFIGURAÇÃO DE UM PRIMEIRO LIMITE À DISCRICIONARIEDADE NACIONAL SOBRE O USO DO VÉU: CASO LACHIRI V. BÉLGICA

Este trabalho tem como objetivo analisar alguns aspectos do caso Lachiri v. Bélgica, famoso postulado jurídico oriundo da jurisprudência do Tribunal Europeu dos Direitos do Homem (TEDH). Tendo em vista o progressivo aumento de fluxo migratório e o crescente sentimento anti-islâmico que assolam a Europa, torna-se um risco que os princípios fundamentais de uma sociedade democrática, como os de pluralidade e tolerância, venham a se chocar. O caso Lachiri v. Bélgica ilustra como a discricionariedade permitida aos decisores pode ser uma aliada a posicionamentos restritivos direcionados a grupos minoritários. Este trabalho se propôs a elucidar o contexto sócio-jurídico em que se situam essas discussões e sinalizar para uma abertura jurisprudencial para o fomento ao respeito à crença e diversidade em uma sociedade multicultural

Les systèmes monoaminergiques : implication dans la physiopathologie et la thérapie de la maladie de Parkinson

Parkinson’s disease is characterized by the manifestation of motor symptoms mostlyassociated with the degeneration of dopaminergic neurons. While Parkinson’s disease is oftenfocused on motor deficits, the disease is also characterized by non-motor deficits, includinganxiety and depression, which are under studied and consequently are not well treated.Whereas some clinical studies suggested that anxiety and depression could be linked to thedegeneration of dopaminergic neurons, others suggested the involvement of norepinephrineand serotonin in the observed symptoms and also in the efficacy of Levodopa and deep brainstimulation of the subthalamic nucleus.In a first time, we investigated the respective role of the neuronal degeneration of dopamine,noradrenaline and serotonin in the manifestation of motor and non-motor parkinsonian-likedisorders in the rat. Our results demonstrate that despite the importance of the dopaminergicsystem, the disturbances in the three-monoaminergic systems play a key role in themanifestation of motor and non-motor deficits.In a second time, we studied the impact of monoamine depletions on the efficacy ofantiparkinsonian treatments, the Levodopa and deep brain stimulation of the subthalamicnucleus. Our results showed that the combined depletions could deteriorate the efficacy of theLevodopa and of the deep brain stimulation on some deficits. Together, these results canexplain the lack of efficacy of the antiparkinsonian treatments in some patients and thedifficulty to treat all the symptoms.Finally, we investigated the link between the subthalamic nucleus, which is an excitatorystructure of the basal ganglia, and the motor deficits, as well as the involvement of thebasolateral amygdala and the lateral habenula in emotional control of the behavior, and nonmotordeficits. We showed the parallel between changes in the neuronal activity of thesubthalamic nucleus and the motor deficits, of the basolateral amygdala and anxiety and ofthe lateral habenula and depression.Results from this thesis provide new evidences on the involvement of the threemonoaminergicsystems in the pathophysiology and the therapy of Parkinson’s disease.La maladie de Parkinson est caractérisée par la manifestation de symptômes moteursprincipalement dus à la dégénérescence du système dopaminergique. Malgré l'accent mis surles déficits moteurs, la maladie de Parkinson est également caractérisée par des symptômesnon moteurs, incluant l'anxiété et la dépression, qui sont sous-étudiés et de ce fait pas bientraités. Alors que certaines études cliniques ont suggéré que l'anxiété et la dépressionpourraient être associées à la dégénérescence des neurones dopaminergiques, d'autres ontsuggéré l'implication de la dégénérescence des neurones noradrénergiques etsérotoninergiques dans les troubles observés mais également dans les effets induits par laLévodopa et la stimulation cérébrale profonde du noyau sous-thalamique.Dans un premier temps, nous avons étudié le rôle respectif de la dopamine, de lanoradrénaline et de la sérotonine dans la manifestation des déficits parkinsoniens moteurs etnon moteurs chez le rat. L’ensemble de nos résultats démontre que malgré l’importance dusystème dopaminergique, la perturbation des trois systèmes monoaminergiques joue un rôleimportant à la fois dans la manifestation des troubles moteurs et non moteurs.Nous avons également étudier l’impact des monoamines sur l’efficacité des traitementsantiparkinsoniens, à savoir, la Lévodopa et la stimulation cérébrale profonde du noyau sousthalamique,sur les troubles observés. Nos résultats montrent que la déplétion combinée dessystèmes monoaminergiques peut altérer l’efficacité de la Lévodopa ainsi que de lastimulation cérébrale profonde sur certains troubles. Ces résultats peuvent expliquer lemanque d’efficacité des traitements antiparkinsoniens chez certains patients et la difficulté àtraiter tous les symptômes.Pour finir, nous avons voulu mettre en évidence le lien entre le noyau sous-thalamique,structure excitatrice des ganglions de la base et les troubles moteurs, ainsi que l’amygdalebasolatérale et l’habénula latérale, structures impliquées dans les comportements émotionnels,et les troubles non moteurs. Nous avons mis en évidence le parallèle existant entre lesmodifications du mode de décharge des neurones du NST et les troubles moteurs, leschangements de l’amygdale basolatérale et les troubles anxieux ainsi que ceux de l’habénulalatérale et les troubles dépressifs.Les résultats de ces travaux de thèse ont donc permis d’apporter de nouvelles évidences surl’implication des trois systèmes monoaminergiques dans la physiopathologie et la thérapie dela maladie de Parkinson