Cette thèse propose une étude mathématique du comportement des solutions autour d'états stationnaires pour des systèmes cinétiques gravitationnels de type Vlasov. Les trois premières parties présentent des résultats théoriques. Tout d'abord, par une ap- proche variationnelle, on construit des états stationnaires pour le système de Vlasov-Manev et on montre leur stabilité orbitale. Ensuite, on prouve l'existence de solutions autosimi- laires explosant en temps fini autour d'un état stationnaire pour le système dit de "Vlasov- Manev pur". Enfin on démontre la stabilité orbitale d'une large classe d'états stationnaires pour le système de Vlasov-Poisson relativiste. Ces résultats s'appuient sur de nouvelles méthodes utilisant la rigidité du flot. Celles-ci permettent notamment d'obtenir la séparation d'états stationnaires en évitant l'étude d'équations d'Euler-Lagrange non locales, de résoudre un problème variationnel avec une infinité de contraintes et de prouver la stabilité orbitale de solutions stationnaires non nécessairement obtenues de manière variationnelle. Dans la quatrième et dernière partie, nous étudions numériquement l'équation de Vlasov-Poisson en coordonnées radiales. Après avoir choisi un système de variables adéquates, nous présentons des schémas numériques de différences finies conservant la masse et le Hamiltonien du système.

The challenge this thesis addresses is to speed up the development of concurrent programs by increasing the efficiency with which concurrent programs can be tested and consequently evolved. The goal of this thesis is to generate methods and tools that help software engineers increase confidence in the correct operation of their programs. To achieve this goal, this thesis advocates testing of concurrent software using a systematic approach capable of enumerating possible executions of a concurrent program. The practicality of the systematic testing approach is demonstrated by presenting a novel software infrastructure that repeatedly executes a program test, controlling the order in which concurrent events happen so that different behaviors can be explored across different test executions. By doing so, systematic testing circumvents the limitations of traditional ad-hoc testing, which relies on chance to discover concurrency errors. However, the idea of systematic testing alone does not quite solve the problem of concurrent software testing. The combinatorial nature of the number of ways in which concurrent events of a program can execute causes an explosion of the number of possible interleavings of these events, a problem referred to as state space explosion. To address the state space explosion problem, this thesis studies techniques for quantifying the extent of state space explosion and explores several directions for mitigating state space explosion: parallel state space exploration, restricted runtime scheduling, and abstraction reduction. In the course of its research exploration, this thesis pushes the practical limits of systematic testing by orders of magnitude, scaling systematic testing to real-world programs of unprecedented complexity.

Zugl.: Marburg, Univ., Diss., 2007

Thesis (D. Min.)--Trinity Evangelical Divinity School, Deerfield, Ill., 1998. / Abstract. Includes bibliographical references (leaves 125-130).

Ce travail de thèse concerne la modélisation mathématique et l’étude du comportement d’une population de neurones. Dans tout ce travail on s’arrêtera principalement sur une population de neurones auto-excitateurs où chaque cellule du réseau est supposée suivre la loi de l’intègre et tire. Néanmoins nous aborderons au détour d’un chapitre la modélisation d’une population de neurones inhibiteurs, et dans une dernière partie, nous discuterons la modélisation d’une population de neurones obéissant au modèle Ermentrout-Kopell aussi appelé le théta-neurone. L’angle de vue adopté dans cette thèse est donné par l’approche densité de population. Cette approche, dont nous rappellerons en détail les hypothèses et la construction, a été introduite il ya maintenant plus d’une dizaine d’années afin de faciliter la simulation d’une grande population de neurones. Dit plus précisément, une telle approche donne une équation aux dérivées partielles sur la densité de population de neurones dans l’espace d’état formé des potentiels admissibles du neurone. Nous ferons de plus l’hypothèse que la réponse d’un neurone à l’arrivée d’une impulsion est une dépolarisation instantanée, autrement dit un saut de potentiel. Comme nous le verrons,cette équation aux dérivées partielles est non linéaire (à cause du couplage de la population) et non locale (à cause du saut de potentiel). Si cette idée est compliquée et abstraite, elle anéanmoins prouvé tout au long de ces dix dernières années son importance dans la simulation numérique des grands réseaux.Il s’agit avant tout dans ce travail de thèse de donner un cadre mathématique adéquat aux équations aux dérivées partielles qui surgissent d’une telle approche. Ainsi nous discuterons,selon les différents choix de modélisation, du caractère bien posé du modèle par densité de populationet de sa possible explosion en temps fini. Nous discuterons comment la prise en compte d’hypothèses réalistes supplémentaires dans la modélisation, comme le retard entre l’émission d’un potentiel d’action et sa réception ou encore la période réfractaire peut stopper l’explosionen temps fini et garantir l’existence d’une solution globale. Un autre aspect abordé dans ce travail concerne les explications et la prédiction de la synchronisation des neurones. Deux définitions de la synchronisation seront explicitées selon encoreune fois les choix de modélisation. Nous verrons qu’en interprétant l’explosion en temps fini dela solution comme l’arrivée d’une masse de Dirac dans le taux de décharge de la populationon peut relier l’explosion à la synchronisation. Toutefois, avec des hypothèses de modélisation plus réalistes, comme les retards et la période réfractaire, ce phénomène est exclu. Nous verrons néanmoins qu’avec ces paramètres physiques supplémentaires des solutions périodiques apparaissent offrant différents rythmes de décharge de la population. Encore une fois, l’apparition de ces oscillations sera perçue comme la synchronisation de la population. / This thesis concerns the mathematical modelling and the study of the behavior of a population of neurons. In this work we will mainly consider a population of excitatory neurons whe reall the cells of the network follow the integrate-and-fire model. Nonetheless, we will tackle in a chapter the modelling of an inhibitory population of neurons, and we will discuss in the lastchapter the modelling of a population of neurons that follows the Ermentrout-Koppell model.The point of view of this thesis is given by the population density approach that has beenintroduced more than a decade ago in order to facilitate the simulation of a large assembly ofneurons. More precisely, this approach gives a partial differential equation that describes thedensity of neurons in the state space that is the set of all admissible potential of a neuron. We will assume that when receiving an action potential, the potential of the neuron makes a small jump. As we will see this partial differential equation is non linear (due to the coupling betweenneurons) and non-local (due to the potential jump). If this idea is complicated and abstract, itallows to simulate easily a large neural network.First of all, the thesis gives a mathematical framework for the equations that arise from thisthe population density approach. Then we will discuss the existence and the possible blow upin finite time of the solution. We will discuss how the consideration of more realistic modellingassumptions, as the refractory period and the delay between the emission and the reception ofan action potential can stop the blow up of the solution and give a well posed model.We will also try to caracterise the occurence of synchronization of the neural network. Twodifferent ways of seeing the synchronization will be describe. One relates the blow up in finitetime of the solution to the occurence of a Dirac mass in the firing rate of the population.Nonetheless, taking into account the delays, this kind of blow up will not be observed anymore.Nonetheless, as we will see, with this additional features the model will generate some periodicalsolutions that can also be related to the synchronization of the population.

Much research has been undertaken to gain insight into business alignment of IT. This alignment basically aims to improve a firm’s performance by an improved harmonization of the business function and the IT function within a firm. The thesis discusses previous approaches and constructs an overall framework, which a potential approach needs to fit in. Being in a highly regulated industry, for airports there is little space left to increase revenues. However, the retailing business has proven to be an area that may contribute towards higher income for airport operators. Consequently, airport management should focus on supporting this business segment. Nevertheless, it needs to be taken into account that smooth airport operations are a precondition for successful retailing business at an airport. Applying the concept of information intensity, the processes of gate allocation and airport retailing have been determined to appraise the potential that may be realized upon (improved) synchronization of the two. It has been found that the lever is largest in the planning phase (i.e. prior to operations), and thus support by means of information technology (for information distribution and improved planning) may help to enable an improved overall retail performance. In order to determine potential variables, which might influence the output, a process decomposition has been conducted along with the development of an appropriate information model. The derived research model has been tested in different scenarios. For this purpose an adequate gate allocation algorithm has been developed and implemented in a purposewritten piece of software. To calibrate the model, actual data (several hundred thousand data items from Frankfurt Airport) from two flight plan seasons has been used. Key findings: The results show that under the conditions described it seems feasible to increase retail sales in the magnitude of 9% to 21%. The most influential factors (besides the constraining rule set and a retail area’s specific performance) proved to be a flight’s minimum and maximum time at a gate as well as its buffer time at gate. However, as some of the preconditions may not be accepted by airport management or national regulators, the results may be taken as an indication for cost incurred, in case the suggested approach is not considered. The transferability to other airport business models and limitations of the research approach are discussed at the end along with suggestions for future areas of research.

Devido às crises ocorridas no setor petroleiro, além do interesse em reduzir a emissão de gás carbônico (CO2), vários países buscam o desenvolvimento de novos combustíveis. Atualmente, mais de 80% da frota de veículos no Brasil rodam ou somente com etanol ou com uma mistura de etanol e gasolina. Desta forma, o bioetanol é considerado um combustível renovável alternativo com grande potencial para substituir os combustíveis oriundos do petróleo. Para atender a crescente demanda de etanol, sem competir com áreas cultiváveis voltadas para produção de alimentos, fontes de materiais lignocelulósicos podem ser utilizadas com o intuito de se aproveitar a fração celulósica para obtenção de açúcar fermentável para produção de bioetanol. Neste trabalho, o objetivo foi avaliar o efeito de tecnologias de pré-tratamento (convencionais e não convencionais) dos subprodutos sucroalcooleiros (bagaço e palha de cana), seguida ou não de uma etapa de deslignificação, sobre a conversão enzimática da celulose de cada biomassa vegetal, além de testar e avaliar o efeito que a mistura das duas biomassas (antes do pré-tratamento), em diferentes proporções, pode causar na produção de etanol 2G. Em uma primeira parte do trabalho, a palha de cana foi submetida ao pré-tratamento hidrotérmico e ao pré-tratamento por ultrassom, seguido de uma etapa de deslignificação alcalina. Para o pré-tratamento hidrotérmico, foram testadas três temperaturas (160, 170 e 180°C) nos tempos de 10, 20, 30, 40 e 50 min para cada temperatura. Para o teste com ultrassom, os experimentos foram conduzidos em três meios diferentes (ácido, alcalino e meio aquoso - controle) nos tempos de 1 a 30 minutos para cada condição. As amostras pré-tratadas por ultrassom e pelo método hidrotérmico foram deslignificadas com solução de NaOH 1%(m/v) por 1 hora. Após pré-tratamento e deslignificação, os ensaios de hidrólise enzimática foram realizados empregando Celluclast 1.5L (15 FPU/g de amostra) e ?-Glucosidase (12,5 UI/g de amostra). A condição de pré-tratamento hidrotérmico mais promissora para a palha foram a 170°C por 10 min, mostrando que a palha não necessita de tratamentos mais severos para obter uma maior digestibilidade no processo de hidrolise enzimática. Já o método por ultrassom provocou o aumento da recalcitrância do material lignocelulósico tanto para o agente deslignificante como para as celulases. Em uma segunda parte do trabalho, palha e bagaço de cana foram pré-tratados por explosão a vapor catalisado por SO2 nas seguintes condições para cada biomassa: 190, 195 e 200°C, por 5 min e 3% de SO2 (m/m). Após encontrar a condição ideal para ambas biomassas (190°C, 5 min, 3% SO2), três proporções diferentes de misturas de palha e bagaço foram testadas: 90% de palha / 10% de bagaço, 90% bagaço / 10% de palha e 50% de palha / 50% de bagaço e estas misturas foram prétratadas na condição otimizada. Em todas as etapas, a hidrólise enzimática foi realizada. Observou-se que a recuperação mais elevada de açúcar foi encontrada na amostra 50% bagaço/50% palha. Curiosamente, quando comparado com uma biomassa tratada isoladamente, todas as três misturas apresentam uma maior recuperação de açúcar. / Due to the crises in the oil sector, in addition to interest in reducing the emission of carbon dioxide (CO2), many countries seek to develop new fuels. Currently, over 80% of the vehicle fleet in Brazil only run on ethanol or a mixture of ethanol and gasoline. Thus, bioethanol is considered an alternative renewable fuel with great potential to replace petroleum derived fuels. To meet the growing ethanol demand, without competing with cultivable areas focused on food production, lignocellulosic materials sources can be used in order to take advantage of the cellulosic fraction to obtain fermentable sugar for bioethanol production. In this study, the objective was to evaluate the effect of pretreatment technologies (conventional and unconventional) of sugar and alcohol byproducts (bagasse and straw) followed or not by a delignification step on the enzymatic conversion of each biomass, besides test and evaluate the effect that mixing of the two biomasses (before pretreatment), in different proportions, can cause in the production of 2G ethanol. In the first part of the study, sugarcane straw was submitted to the hydrothermal pre-treatment and pre-treatment by ultrasound, followed by an alkaline delignification step. For the hydrothermal pretreatment, three temperatures were tested (160, 170 and 180°C) in the times of 10, 20, 30, 40 and 50 min for each temperature. For the test with ultrasound, the experiments were conducted in three different enviroments (acid, alkaline and aqueous medium - control) in the times of 1-30 minutes for each condition. The pretreated by ultrasound and by hydrothermal method samples were delignified with NaOH solution 1% (w/v) for 1 hour. After pre-treatment and delignification, the enzymatic hydrolysis assays were performed using Celluclast 1.5L (15 FPU/g of substrate) and ?-glucosidase (12.5 IU/g of substrate). The hydrothermal pretreatment condition most promising for the straw was at 170°C for 10 min, showing that the straw doesn\'t require more severe treatments to obtain a higher digestibility of the enzymatic hydrolysis process. Yet the ultrasound method led to increased recalcitrance of lignocellulosic material for both the delignificant agent as for cellulases. In a second part of the study, straw, and bagasse were pre-treated by steam explosion catalyzed by SO2 under the following conditions for each biomass: 190, 195 and 200°C for 5 min and 3% of SO2 (m/m). After finding the optimal condition for both biomasses (190°C, 5 min, 3% SO2), three different ratios of mixtures of straw and bagasse were tested: 90% straw / 10% bagasse, 90% bagasse / 10% straw and straw 50% / 50% bagasse and these mixtures were pretreated in the optimized condition. At all stages, the enzymatic hydrolysis was carried out. It was observed that the higher sugar recovery was found in the sample 50% bagasse / 50% straw. Interestingly, when compared with a treated biomass separately, all three blends exhibit a greater sugar recovery.

Doctor of Philosophy / Department of Physics / Daniel Rolles / Imaging the structures of molecules, understanding the molecular dynamics in onization and dissociation processes and, most importantly, observing chemical reactions, i.e. the making and breaking of chemical bonds in real time, have become some of the most exciting topics in the atomic and molecular physics. The rapid advances of experimental tools such as synchrotron radiation light sources, free-electron lasers and continuing advances of tabletop femtosecond ultrashort lasers that provide laser pulses at a variety of wavelengths have opened new avenues for understanding the structure of matter and the dynamics of the chemical interactions. In addition, significant improvements in computational techniques and molecular dynamic simulations have provided complementary theoretical predictions on structures and chemical dynamics. The Coulomb explosion imaging method, which has been developed and applied in many studies in the last three decades, is a powerful way to study molecular structures. The method has mostly been applied to small diatomic molecules and to simple polyatomic molecules. In this thesis, Coulomb explosion imaging is applied to study the structure of isomers, molecules that have the same chemical formula but different chemical structures. Specifically, by taking inner-shell photoionization as well as strong-field ionization approaches to ionize and fragment the molecules and by using coincidence electron-ion-ion momentum imaging techniques to obtain the three-dimensional momentum of fragment ions, structures of isomers are distinguished by using the correlations among product ion momentum vectors. At first, the study aims to understand if the Coulomb explosion imaging of geometrical isomers can identify and separate cis and trans structures. Secondly, in order to extend the application of the Coulomb explosion imaging method to larger organic molecules to test the feasibility of the method for identifying structural isomers, photoionization studiesof 2,6- and 3,5-difluoroiodobenzene have been conducted. In addition, using the full three-dimensional kinematic information of multi-fold coincidence channels, breakup dynamics of both cis/trans geometric isomers and structural isomers, and in particular, sequential fragmentation dynamics of the difluoroiodobenzene isomers are studied. Furthermore, for each study, Coulomb explosion model simulations are conducted to complement the experimental results. The results of the Coulomb explosion imaging reseach in this thesis paves the way for future time-resolved Coulomb explosion imaging experiments aiming to understand the transient molecular dynamics such as photoinduced ring opening reactions and cis/trans isomerization processes in gas-phase molecules.

Nous nous intéressons dans cette thèse aux équations de Navier-Stokes pour un fluide visqueux incompressible. Dans la première partie, nous étudions le cas d’un fluide homogène. Rappelons que la grande question de la régularité globale en dimension 3 est plus ouverte que jamais : on ne sait pas si la solution de l’équation correspondant à un état initial suffisamment régulier mais arbitrairement loin du repos, va perdurer indéfiniment dans cet état (régularité globale) ou exploser en temps fini(singularité). Une façon d’aborder le problème est de supposer cette éventuelle rupture de régularité et d’envisager les différents scenarii possibles. Après un rapide survol de la structure propre aux équations de Navier-Stokes et des résultats connus à ce jour (chapitre 1), nous nous intéressons(chapitre 2) à l’existence locale (en temps) de solutions dans des espaces de Sobolev qui ne sont pas invariants d’échelle. Partant d’une donnée initiale qui produit une singularité, on prouve l’existence d’une constante optimale qui minore le temps de vie de la solution. Cette constante, donnée parla méthode rudimentaire du point fixe, fournit ainsi un bon ordre de grandeur sur le temps de vie maximal de la solution. Au chapitre 3, nous poursuivons les investigations sur le comportement de telles solutions explosives à la lumière de la méthode des éléments critiques.Dans le seconde partie de la thèse, nous sommes intéressés à un modèle plus réaliste du point de vue de la physique, celui d’un fluide incompressible à densité variable. Ceci est modélisé par les équations de Navier-Stokes incompressible et inhomogènes. Nous avons étudié le caractère globalement bien posé de ces équations dans la situation d’un fluide évoluant dans un tore de dimension 3, avec des données initiales appartenant à des espaces critiques et sans hypothèse de petitesse sur la densité. / This thesis is concerned with incompressible Navier-Stokes equations for a viscous fluid. In the first part, we study the case of an homogeneous fluid. Let us recall that the big question of the global regularity in dimension 3 is still open : we do not know if the solution associated with a data smooth enough and far from the immobile stage will last over time (global regularity) or on the contrary will stop living in finite time and blow up (singularity). The goal of this thesis is to study this regularity break. One way to deal witht his question is to assume that such a phenomen on occurs and to study differents scenarii. The chapter 1 is devoted to a recollection of well-known results. In chapter 2, we are interesting in the local (in time) existence of a solution in some Sobolev spaces which are not invariant under the natural sclaing of Navier-Stokes. Starting with a data generating a singularity, we can prove there exists an optimal lower boundary of the lifes pan of such a solution. In this way, the lower boundary provided by the elementary procedure of fixed-point, gives the correctorder of magnitude. Then, we keep on investigations about the behaviour of regular solution near the blow up, thanks to the method of critical elements (chapter 3).In the second part, we are concerned with a more relevant model, from a physics point of view : the inhomogeneous Navier-Stokes system. We deal with the global well poseness of such a model for a inhomogeneous fluid, evolving on a tor us in dimension 3, with critical data and without smallnes sassumption on the density.

This thesis explores the relationship between state and civil-society in Lebanon. Earlier research show that there has been a presence of capable local NGOs in Lebanon for many years and that this has shaped the society. There is a gap in the research on the role of local NGOs after the Beirut harbour explosion on the 4th of August 2020. The aim of this research is to shed light on the contribution of local NGOs in Lebanon by exploring the contribution of local NGO Offre Joie and what difficulties they found when taking on some of the emergency response and rebuilding work after the explosion at Beirut Harbour. My theoretical approach states that a state owes a duty to care and protect its citizen and that in this case some of this responsibility was absent and instead taken on by the civil society and NGOs. Qualitative case study on Offre Joie, methods for collecting data include a semi-structured, in-depth interview with one Offre Joie board member, content analysis on a panel discussion that Offre Joies president was a part of and an impact report realised by Offre Joie. I found that they did encounter challenges but that these were not major enough to stop them in their efforts to rebuild and assist the community. They contributed by rebuilding the most affected areas and by utilising volunteers they brought a human side to the crisis. This human relationship and the solidarity between the people affected and the volunteers has been one of the biggest contributions. The role that Offre Joie took on after the explosion points to the reality of mismanaged governmental institutions, and that the role of local NGOs is extremely important at this current time to protect and safeguard the people within Lebanon’s civil society.