Thèses : « Montée en charge »

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Cresson, Romain. « Etude du démarrage de procédés intensifs de méthanisation : impact des conditions hydrodynamiques et de la stratégie de montée en charge sur la formation et l’activité du biofilm ». Montpellier 2, 2006. http://www.theses.fr/2006MON20213.

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Moctar, m'baba Leyla. « Combining Blockchain and IoT for business processes deployment and mining ». Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAS010.

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Blockchain, initialement utilisé en 2009 pour les transactions de cryptomonnaie, a rapidement évolué au-delà des applications financières. La communauté BPM a reconnu son potentiel pour améliorer la gestion des processus métier (BPM) et favoriser les collaborations inter-organisationnelles. Malgré des recherches approfondies sur l'exécution des processus d'affaires basés sur la blockchain, l'exploration de données de la blockchain pour le process mining a récemment commencé à être explorée. Les études actuelles se concentrent principalement sur les processus centrés sur les activités, négligeant souvent les processus centrés sur les artefacts prévalents dans les applications blockchain. Les formats de journalisation traditionnels comme XES, bien que couramment utilisés, rencontrent des défis tels que la perte d'information et la dénormalisation lorsqu'ils sont appliqués à des données centrées sur les artefacts. L'introduction d'OCEL a partiellement abordé ces problèmes en permettant le stockage de données d'événements centrées sur les objets, mais il manque de prise en charge pour l'évolution et les relations des objets.Cette thèse relève ces défis en proposant ACEL, une extension d'OCEL qui prend en charge de manière complète le stockage des données d'événements centrées sur les artefacts. Nous présentons une méthode centrée sur les artefacts pour recueillir des données d'événements d'applications blockchain, les convertissant en logs ACEL. La viabilité de l'approche est évaluée en utilisant les applications Ethereum Cryptokitties et Augur. Nous comparons d'abord les capacités de process mining d'ACEL avec OCEL, puis introduisons une méthode de découverte utilisant le clustering hiérarchique et l'analyse du gain d'information pour dériver des modèles GSM, la norme pour les processus centrés sur les artefacts. Notre évaluation sur Cryptokitties confirme la faisabilité de cette approche et met en évidence les avantages d'ACEL dans le process mining centré sur les artefacts
Blockchain, first utilized in 2009 for cryptocurrency transactions, quickly evolved beyond financial applications. The BPM community recognized its potential for enhancing business process management (BPM) and fostering inter-organizational collaborations. Despite extensive research on blockchain-based business process execution, process mining from blockchain data has recently begun to be explored. Current studies mainly focus on activity-centric processes, often overlooking artifact-centric processes prevalent in blockchain applications. Traditional logging formats like XES, while commonly used, face challenges like information loss and denormalization when applied to artifact-centric data. The introduction of OCEL partially addressed these issues by enabling the storage of object-centric event data, but it lacks support for object evolution and relations.This thesis addresses these challenges by proposing ACEL, an extension of OCEL that comprehensively supports artifact-centric event data storage. We present an artifact-centric method to gather event data from blockchain applications, converting them into ACEL logs. The approach's viability is assessed using Cryptokitties and Augur Ethereum applications. We initially compare ACEL's process mining capabilities with OCEL, and then introduce a discovery method using hierarchical clustering and information gain analysis to derive GSM models, the standard for artifact-centric processes. Our evaluation on Cryptokitties confirms the feasibility of this approach and highlights the advantages of ACEL in artifact-centric process mining

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Aung, Pyie Phyo. « Monte Carlo Simulations of charge Transport in Organic Semiconductors ». University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1418272111.

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Jakobsson, Mattias. « Monte Carlo Studies of Charge Transport Below the Mobility Edge ». Doctoral thesis, Linköpings universitet, Beräkningsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-74322.

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Charge transport below the mobility edge, where the charge carriers are hopping between localized electronic states, is the dominant charge transport mechanism in a wide range of disordered materials. This type of incoherent charge transport is fundamentally different from the coherent charge transport in ordered crystalline materials. With the advent of organic electronics, where small organic molecules or polymers replace traditional inorganic semiconductors, the interest for this type of hopping charge transport has increased greatly. The work documented in this thesis has been dedicated to the understanding of this charge transport below the mobility edge. While analytical solutions exist for the transport coefficients in several simplified models of hopping charge transport, no analytical solutions yet exist that can describe these coefficients in most real systems. Due to this, Monte Carlo simulations, sometimes described as ideal experiments performed by computers, have been extensively used in this work. A particularly interesting organic system is deoxyribonucleic acid (DNA). Besides its overwhelming biological importance, DNA’s recognition and self-assembly properties have made it an interesting candidate as a molecular wire in the field of molecular electronics. In this work, it is shown that incoherent hopping and the Nobel prize-awarded Marcus theory can be used to describe the results of experimental studies on DNA. Furthermore, using this experimentally verified model, predictions of the bottlenecks in DNA conduction are made. The second part of this work concerns charge transport in conjugated polymers, the flagship of organic materials with respect to processability. It is shown that polaronic effects, accounted for by Marcus theory but not by the more commonly used Miller-Abrahams theory, can be very important for the charge transport process. A significant step is also taken in the modeling of the off-diagonal disorder in organic systems. By taking the geometry of the system from large-scale molecular dynamics simulations and calculating the electronic transfer integrals using Mulliken theory, the off-diagonal disorder is for the first time modeled directly from theory without the need for an assumed parametric random distribution.

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Krapohl, David. « Monte Carlo and Charge Transport Simulation of Pixel Detector Systems ». Doctoral thesis, Mittuniversitetet, Avdelningen för elektronikkonstruktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-24763.

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This thesis is about simulation of semiconductor X-ray and particledetectors. The simulation of a novel coating for solid state neutrondetectors is discussed as well as the implementation of a simulationframework for hybrid pixel detectors.Today’s most common thermal neutron detectors are proportionalcounters, that use 3He gas in large tubes or multi wire arrays. Globalnuclear disarmament and the increase in use for homeland securityapplications has created a shortage of the gas which poses a problemfor neutron spallation sources that require higher resolution and largersensors. In this thesis a novel material and clean room compatible pro-cess for neutron conversion are discussed. Simulations and fabricationhave been executed and analysed in measurements. It has been proventhat such a device can be fabricated and detect thermal neutrons.Spectral imaging hybrid pixel detectors like the Medipix chipare the most advanced imaging systems currently available. Thesechips are highly sophisticated with several hundreds of transistors perpixel to enable features like multiple thresholds for noise free photoncounting measurements, spectral imaging as well as time of arrivalmeasurements. To analyse and understand the behaviour of differentsensor materials bonded to the chip and to improve development offuture generations of the chip simulations are necessary. Generally, allparts of the detector system are simulated independently. However, itis favourable to have a simulation framework that is able to combineMonte Carlo particle transport, charge transport in the sensor as wellas analogue and digital response of the pixel read-out electronics. Thisthesis aims to develop such a system that has been developed withGeant4 and analytical semiconductor and electronics models. Further-more, it has been verified with data from measurements with severalMedipix and Timepix sensors as well as TCAD simulations.Results show that such a framework is feasible even for imagingsimulations. It shows great promise to be able to be extended withfuture pixel detector designs and semiconductor materials as well asneutron converters to aim for next generation imaging devices.

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Coco, Marco. « Monte Carlo study of charge and phonon transport in graphene ». Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3811.

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In this thesis, we investigate charge transport in graphene. Graphene is one of the most important new materials with a wide range of properties, rarely together in the same material, and it is the ideal candidate for future electronic devices. The dynamics of electrons in the conduction band is analyzed, by considering values of Fermi levels high enough to neglect the dynamics in the valence band. This is equivalent to a n-type doping for traditional semiconductors. Degeneracy effects are very important in graphene and then it becomes mandatory to consistently include the Pauli exclusion principle. We develop a new Direct Simulation Monte Carlo (DSMC) procedure to solve the Boltzmann transport equation, that properly takes into account the Pauli principle. For a cross-validation of the results, we also solve the Boltzmann equation in a deterministic way by using the Discontinuous Galerkin method. The agreement of the results is excellent. A comparison of the new DSMC results with those obtained by means of well established hydrodynamical models are presented as well, and again the agreement is very good. This new approach is applied to study the transport properties in suspended monolayer graphene and then in a layer of graphene on different substrates, obtaining the expected results as the degradation of mobilities. Regarding phonon transport, we investigate the thermal effects in a suspended monolayer graphene due to the charge flow under an applied electric field. A complete model is considered, with all the phonon branches, both in-plane and out of plane ones. Moreover, we describe the phonon populations without any approximation of the distribution with an equivalent Bose-Einstein one. The distribution is built by means of the intermediate results arising from the new DSMC, by counting the number of the emission and absorption processes due to the interaction between electrons and phonons. The phonon-phonon interaction is treated in a standard way with a BGK approximation. We are able to determine the increase of the temperature due to the charge flow and to predict its raise for any values of electric fields and Fermi energies. Moreover, it is shown that the inclusion of a complete phonon model leads to a lower heating effect with respect to other simplified models.

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Torfeh, Eva. « Monte Carlo microdosimetry of charged-particle microbeam irradiations ». Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0159/document.

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L’interaction des particules chargées avec la matière conduit à un dépôt d’énergie très localisé dans des traces de dimensions sub-micrométriques. Cette propriété unique rend ce type de rayonnement ionisant particulièrement intéressant pour disséquer les mécanismes moléculaires radio-induits suite à l’échelle de la cellule. L’utilisation de microfaisceaux de particules chargées offre en outre la capacité d’irradier sélectivement à l’échelle du micromètre avec une dose contrôlée jusqu’à la particule unique. Mon travail a porté sur des irradiations réalisées avec le microfaisceau de particules chargées de la plateforme AIFIRA (Applications Interdisciplinaires des Faisceaux d’Ions en Région Aquitaine) du CENBG. Ce microfaisceau délivre des protons et particules alpha et est dédié aux irradiations ciblées in vitro (cellules humains) et in vivo (C. elegans).En complément de l’intérêt qu’elles présentent pour des études expérimentales, les dépôts d’énergie et les interactions des particules chargées avec la matière peuvent être modélisés précisément tout au long de leur trajectoire en utilisant des codes de structures de traces basés sur des méthodes Monte Carlo. Ces outils de simulation permettent une caractérisation précise de la micro-dosimétrie des irradiations allant de la description détaillée des interactions physiques à l’échelle nanométrique jusqu’à la prédiction du nombre de dommages à l’ADN et leurs distributions dans l’espace.Au cours de ma thèse, j’ai développée des modèles micro-dosimétriques basés sur l’outil de modélisation Geant4-DNA dans deux cas. Le premier concerne la simulation de la distribution d’énergie déposée dans un noyau cellulaire et le calcul du nombre des différents types de dommages ADN (simple et double brin) aux échelles nanométrique et micrométrique, pour différents types et nombres de particules délivrées. Ces résultats sont confrontés à la mesure expérimentale de la cinétique de protéines de réparation de l’ADN marquées par GFP (Green Fluorescent Protein) dans des cellules humaines. Le second concerne la dosimétrie de l’irradiation d’un organisme multicellulaire dans le cadre d’études de l’instabilité génétique dans un organisme vivant au cours du développement (C. elegans). J’ai simulé la distribution de l’énergie déposée dans différents compartiments d’un modèle réaliste en 3D d’un embryon de C. elegans suite à des irradiations par protons. Enfin, et en parallèle de ces deux études, j’ai développé un protocole pour caractériser le microfaisceau d'AIFIRA à l’aide de détecteurs de traces fluorescent (FNTD) pour des irradiations par protons et par particules alpha. Ce type de détecteur permet en effet de visualiser les trajectoires des particules incidentes avec une résolution de l’ordre de 200 nm et d’examiner la qualité des irradiations cellulaires réalisées par le microfaisceau
The interaction of charged particles with matter leads to a very localized energy deposits in sub-micrometric tracks. This unique property makes this type of ionizing radiation particularly interesting for deciphering the radiation-induced molecular mechanisms at the cell scale. Charged particle microbeams (CPMs) provide the ability to target a given cell compartment at the micrometer scale with a controlled dose down to single particle. My work focused on irradiations carried out with the CPM at the AIFIRA facility in the CENBG (Applications Interdisciplinaires des Faisceaux d’Ions en Région Aquitaine). This microbeam delivers protons and alpha particles and is dedicated to targeted irradiation in vitro (human cells) and in vivo (C. elegans).In addition to their interest for experimental studies, the energy deposits and the interactions of charged particles with matter can be modeled precisely along their trajectory using track structure codes based on Monte Carlo methods. These simulation tools allow a precise characterization of the micro-dosimetry of the irradations from the detailed description of the physical interactions at the nanoscale to the prediction of the number of DNA damage, their complexity and their distribution in space.During my thesis, I developed micro-dosimetric models based on the Geant4-DNA modeling toolkit in two cases. The first concerns the simulation of the energy distribution deposited in a cell nucleus and the calculation of the number of different types of DNA damage (single and double strand breaks) at the nanometric and micrometric scales, for different types and numbers of delivered particles. These simulations are compared with experimental measurements of the kinetics of GFP-labeled (Green Fluorescent Protein) DNA repair proteins in human cells. The second is the dosimetry of irradiation of a multicellular organism to study the genetic instability in a living organism during development (C. elegans). I simulated the distribution of the energy deposited in different compartments of a realistic 3D model of a C. elegans embryo following proton irradiations. Finally, and in parallel with these two studies, I developed a protocol to characterize the AIFIRA microbeam using fluorescent nuclear track detector (FNTD) for proton and alpha particle irradiations. This type of detector makes it possible to visualize in 3D the incident particle tracks with a resolution of about 200 nm and to examine the quality of the cellular irradiations carried out by the CPM

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Volpi, Riccardo. « Charge Transport Simulations for Organic Electronics : A Kinetic Monte Carlo Approach ». Licentiate thesis, Linköpings universitet, Teoretisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122991.

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In this thesis we focus on the modelling and simulation of organic electronic devices, investigating their structural and electronic properties. Organic devices have attracted great interest for their innovative properties, but their functioning still represent a theoretical and technological challenge. They are composed by one or more organic materials depending on the particular application. The morphology of organic devices in the single phase or at the interface is known to strongly determine mobility and efficiency of the devices. The structural disorder is studied through molecular dynamics (MD) simulations. Marcus formula is used to calculate the hopping rate of the charge carriers and the model developed is tested by simulations in a Kinetic Monte Carlo scheme. The dependence of the transfer integrals on the relative molecular orientation is achieved through a weighted Mulliken formula or through a dimer projection approach using the semi-empirical Hartree Fock method ZINDO. Electrostatic effects, have been included through atomic charges and atomic polarizabilities, calculated at the B3LYP level of theory. The inclusion of electrostatic effects has been shown (through simulations in 4PV and C60) to be crucial to obtain a good qualitative agreement with experiments, for both mobility field and temperature dependence in the single phase. In particular the external reorganization energy, calculated through the polarization of the environment, has been shown to have a great impact on the conduction, shifting the inverse Marcus region and helping CT state separation at the interface (between C60 and anthracene).

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Gonçalves, Thomas. « Contributions à la parallélisation de méthodes de type transport Monte-Carlo ». Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAM047/document.

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Les applications de transport de particules Monte-Carlo consistent à étudier le comportement de particules se déplaçant dans un domaine de simulation. La répartition des particules sur le domaine de simulation n'est pas uniforme et évolue dynamiquement au cours de la simulation. La parallélisation de ce type d'applications sur des architectures massivement parallèles amène à résoudre une problématique complexe de répartition de charges de calculs et de données sur un grand nombre de cœurs de calcul.Nous avons d'abord identifié les difficultés de parallélisation des applications de transport de particules Monte-Carlo à l'aide d'analyses théoriques et expérimentales des méthodes de parallélisation de référence. Une approche semi-dynamique reposant sur des techniques de partitionnement a ensuite été proposée. Enfin, nous avons défini une approche dynamique capable de redistribuer les charges de calcul et les données tout en maintenant un faible volume de communication. L'approche dynamique a obtenu des accélérations en extensibilité forte et une forte réduction de la consommation mémoire par rapport à une méthode de réplication de domaine parfaitement équilibrée
Monte Carlo particle transport applications consist in studying the behaviour of particles moving about a simulation domain. Particles distribution among simulation domains is not uniform and change dynamically during simulation. The parallelization of this kind of applications on massively parallel architectures leads to solve a complex issue of workloads and data balancing among numerous compute cores.We started by identifying parallelization pitfalls of Monte Carlo particle transport applications using theoretical and experimental analysis of reference parallelization methods. A semi-dynamic based on partitioning techniques has been proposed then. Finally, we defined a dynamic approach able to redistribute workloads and data keeping a low communication volume. The dynamic approach obtains speedups using strong scaling and a memory footprint reduction compared to the perfectly balanced domain replication method

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Hjelm, Mats. « Monte Carlo Simulations of Homogeneous and Inhomogeneous Transport in Silicon Carbide ». Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3700.

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The importance of simulation is increasing in the researchon semiconductor devices and materials. Simulations are used toexplore the characteristics of novel devices as well asproperties of the semiconductor materials that are underinvestigation, i.e. generally materials where the knowledge isinsufficient. A wide range of simulation methods exists, andthe method used in each case is selected according to therequirements of the work performed. For simulations of newsemiconductor materials, extremely small devices, or deviceswhere non-equilibrium transport is important, the Monte Carlo(MC) method is advantageous, since it can directly exploit themodels of the important physical processes in the device.

One of the semiconductors that have attracted a lot ofattraction during the last decade is silicon carbide (SiC),which exists in a large number of polytypes, among which3C-SiC, 4H-SiC and 6H-SiC are most important. Although SiC hasbeen known for a very long time, it may be considered as a newmaterial due to the relatively small knowledge of the materialproperties. This dissertation is based on a number of MCstudies of both the intrinsic properties of different SiCpolytypes and the qualities of devices fabricated by thesepolytypes. In order to perform these studies a new full-bandensemble device MC simulator, the General Monte CarloSemiconductor (GEMS) simulator was developed. Algorithmsimplemented in the GEMS simulator, necessary when allmaterial-dependent data are numerical, and for the efficientsimulation of a large number of charge carriers in high-dopedareas, are also presented. In addition to the purely MC-relatedstudies, a comparison is made between the MC, drift-diffusion,and energy-balance methods for simulation of verticalMESFETs.

The bulk transport properties of electrons in 2H-, 3C-, 4H-and 6H-SiC are studied. For high electric fields the driftvelocity, and carrier mean energy are presented as functions ofthe field. For 4H-SiC impact-ionization coefficients,calculated with a detailed quantum-mechanical model ofband-to-band tunneling, are presented. Additionally, a study oflow-field mobility in 4H-SiC is presented, where the importanceof considering the neutral impurity scattering, also at roomtemperature, is pointed out.

The properties of 4H- and 6H-SiC when used in short-channelMOSFETs, assuming a high quality semiconductor-insulatorinterface, are investigated using a simple model for scatteringin the semiconductor-insulator interface. Furthermore, theeffect is studied on the low and high-field surface mobility,of the steps formed by the common off-axis-normal cutting ofthe 4H- and 6H-SiC crystals. In this study an extension of theprevious-mentioned simple model is used.

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Makris, Alexia Melissa. « A Monte Carlo Approach to Change Point Detection in a Liver Transplant ». Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4824.

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Patient survival post liver transplant (LT) is important to both the patient and the center's accreditation, but over the years physicians have noticed that distant patients struggle with post LT care. I hypothesized that patient's distance from the transplant center had a detrimental effect on post LT survival. I suspected Hepatitis C (HCV) and Hepatocellular Carcinoma (HCC) patients would deteriorate due to their recurrent disease and there is a need for close monitoring post LT. From the current literature it was not clear if patients' distance from a transplant center affects outcomes post LT. Firozvi et al. (Firozvi AA, 2008) reported no difference in outcomes of LT recipients living 3 hours away or less. This study aimed to examine outcomes of LT recipients based on distance from a transplant center. I hypothesized that the effect of distance from a LT center was detrimental after adjusting for HCV and HCC status. Methods: This was a retrospective single center study of LT recipients transplanted between 1996 and 2012. 821 LT recipients were identified who qualified for inclusion in the study. Survival analysis was performed using standard methods as well as a newly developed Monte Carlo (MC) approach for change point detection. My new methodology, allowed for detection of both a change point in distance and a time by maximizing the two parameter score function (M2p) over a two dimensional grid of distance and time values. Extensive simulations using both standard distributions and data resembling the LT data structure were used to prove the functionality of the model. Results: Five year survival was 0.736 with a standard error of 0.018. Using Cox PH it was demonstrated that patients living beyond 180 miles had a hazard ratio (HR) of 2.68 (p-value<0.004) compared to those within 180 miles from the transplant center. I was able to confirm these results using KM and HCV/HCC adjusted AFT, while HCV and HCC adjusted LR confirmed the distance effect at 180 miles (p=0.0246), one year post LT. The new statistic that has been labeled M2p allows for simultaneous dichotomization of distance in conjunction with the identification of a change point in the hazard function. It performed much better than the previously available statistics in the standard simulations. The best model for the data was found to be extension 3 which dichotomizes the distance Z, replacing it by I(Z>c), and then estimates the change point c and tau. Conclusions: Distance had a detrimental effect and this effect was observed at 180 miles from the transplant center. Patients living beyond 180 miles from the transplant center had 2.68 times the death rate compared to those living within the 180 mile radius. Recipients with HCV fared the worst with the distance effect being more pronounced (HR of 3.72 vs. 2.68). Extensive simulations using different parameter values in both standard simulations and simulations resembling LT data, proved that these new approaches work for dichotomizing a continuous variable and finding a point beyond which there is an incremental effect from this variable. The recovered values were very close to the true values and p-values were small.

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Peucelle, Cécile. « Spatial fractionation of the dose in charged particle therapy ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS363/document.

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Malgré de récentes avancées, les traitements par radiothérapie (RT) demeurent insatisfaisants : la tolérance des tissus sains aux rayonnements limite la délivrance de fortes doses (potentiellement curatives) à la tumeur. Pour remédier à ce problème, de nouvelles approches basées sur des modes de dépôt de dose innovants sont aujourd’hui à l’étude. Parmi ces approches, la technique synchrotron “Minibeam Radiation Therapy” (MBRT) a démontré sa capacité à élever la résistance des tissus sains aux rayonnements, ainsi qu’à induire un important retard de croissance tumorale. La MBRT combine des faisceaux submillimétriques à un fractionnement spatial de la dose. Dans ce contexte, l’alliance de la balistique plus avantageuse des particules chargées (et leur sélectivité biologique) à la préservation des tissus sains observée en MBRT permettrait de préserver d’avantage les tissus sains. Cette stratégie innovante a été explorée durant ce travail de thèse. Deux voies ont notamment été étudiées: la MBRT par faisceaux de protons (pMBRT), et d’ions très lourds. Premièrement, la preuve de concept expérimentale de la pMBRT a été réalisée dans un centre clinique (Institut Curie, Centre de Protonthérapie d’Orsay). De plus, l'évaluation de potentielles optimisations de la pMBRT, à la fois en terme de configuration d’irradiation et de génération des minifaisceaux, a été menée dans une étude Monte Carlo (MC). Dans la seconde partie de ce travail, un nouvel usage potentiel des ions très lourds (néon et plus lourds) en radiothérapie a été évalué dans une étude MC. Les combiner à un fractionnement spatial permettrait de tirer profit de leur efficacité dans le traitement de tumeurs radiorésistantes (hypoxiques), un des principaux défis de la RT, tout en minimisant leurs effets secondaires. Les résultats obtenus au terme de ce travail sont favorables à une exploration approfondie de ces deux approches innovantes. Les données dosimétriques compilées dans ce manuscrit serviront à guider prochaines les expérimentations biologiques
Despite recent breakthroughs, radiotherapy (RT) treatments remain unsatisfactory : the tolerance of normal tissues to radiations still limits the possibility of delivering high (potentially curative) doses in the tumour. To overcome these difficulties, new RT approaches using distinct dose delivery methods are being explored. Among them, the synchrotron minibeam radiation therapy (MBRT) technique has been shown to lead to a remarkable normal tissue resistance to very high doses, and a significant tumour growth delay. MBRT allies sub-millimetric beams to a spatial fractionation of the dose. The combination of the more selective energy deposition of charged particles (and their biological selectivity) to the well-established normal tissue sparing of MBRT could lead to a further gain in normal tissue sparing. This innovative strategy was explored in this Ph.D. thesis. In particular, two new avenues were studied: proton MBRT (pMBRT) and very heavy ion MBRT. First, the experimental proof of concept of pMBRT was performed at a clinical facility (Institut Curie, Orsay, France). In addition, pMBRT setup and minibeam generation were optimised by means of Monte Carlo (MC) simulations. In the second part of this work, a potential renewed use of very heavy ions (neon and heavier) for therapy was evaluated in a MC study. Combining such ions to a spatial fractionation could allow profiting from their high efficiency in the treatment of hypoxic radioresistant tumours, one of the main challenges in RT, while reducing at maximum their side effects. The promising results obtained in this thesis support further explorations of these two novel avenues. The dosimetry knowledge acquired will serve to guide the biological experiments

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Islam, Sharnali. « ATOMISTIC MODELING OF UNINTENTIONAL SINGLE CHARGE EFFECTS IN NANOSCALE FETS ». OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/209.

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Numerical simulations have been performed to study the single-charge-induced ON current fluctuations (random telegraphic noise) in conventional (MOSFET) and non-conventional (silicon nanowire) nanoscale field-effect transistors. A semi-classical three-dimensional particle-based Monte Carlo device simulator (MCDS 3-D) has been integrated and used in this work. Quantum mechanical space-quantization effects have been accounted for via a parameter-free effective potential scheme that has been proved quite successful in describing charge set back from the interface and quantization of the energy (bandgap widening) within the channel region of the device. The effective potential is based on a perturbation theory around thermodynamic equilibrium and leads to a quantum field formalism in which the size of the electron depends upon its energy. To treat full Coulomb (electron-ion and electron-electron) interactions properly, the simulator implements two different real-space molecular dynamics (MD) schemes: the particle-particle-particle-mesh (P3M) method and the corrected Coulomb approach. For better accuracy, particularly in case of nanowire FETs, bandstructure parameters (bandgap, effective masses, and density of states) have been computed via a 20-band nearest-neighbor sp3d5s* tight-binding scheme. Also, since the presence of single impurities in the channel region represents a rare event in the carrier transport process, necessary event-biasing algorithms have been implemented in the simulator that, while enhancing the statistics, results in a faster convergence in the chan-nel current. The study confirms that, due to the presence of single channel charges, both the electrostatics (carrier density) and dynamics (mobility) are modified and, therefore, simultaneously play important roles in determining the magnitude of the current fluctuations. The relative impact (percentage change in the ON current) depends on an intricate interplay of device size, geometry, crystal direction, gate bias, temperature, and energetics and spatial location of the trap.

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Chesneau, Héléna. « Estimation personnalisée de la dose délivrée au patient par l’imagerie embarquée kV-CBCT et réflexions autour de la prise en charge clinique ». Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS059.

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Les protocoles de traitement du cancer par Radiothérapie Conformationnelle par Modulation d'Intensité (RCMI) ciblent avec une précision de plus en plus grande la tumeur. Pour cela, ils nécessitent des informations anatomiques précises du patient juste avant le traitement, qui peuvent d'être obtenues à l'aide de systèmes d'imagerie embarqués sur l'accélérateur linéaire médical délivrant le faisceau de traitement. Ces systèmes, composés d'un tube à rayons X et d'un détecteur 2D planaire, sont appelés kV-Cone Beam CT (kV-CBCT). Aujourd'hui, leur usage est très fortement répandu dans le cadre des traitements par RCMI. Cependant, ces examens kV-CBCT sont responsables d'une dose de rayonnements ionisants additionnelle qui est loin d'être négligeable et pouvant d'être à l'origine de l'apparition d'effets secondaires, tels que des cancers radio-induits chez les patients traités. Au cours de cette thèse, un simulateur basé sur la méthode de Monte-Carlo a été développé permettant ainsi d'estimer avec précision les doses délivrées aux organes lors des examens d'imagerie kV-CBCT. Cet outil a ensuite été utilisé afin d'étudier différentes stratégies de prise en compte clinique de ces doses additionnelles. L'étude présentée dans ce manuscrit propose notamment une méthode rapide d'estimation des niveaux de doses délivrés aux organes prenant en compte la morphologie de chaque patient. Cette stratégie a été développée à partir d'une cohorte de 50 patients incluant 40 enfants et 10 adultes. Ces travaux ont été réalisés en collaboration avec l'unité de physique médicale du Centre Eugène Marquis à Rennes qui a fourni les données cliniques nécessaires à l'étude
Protocols for cancer treatment using intensity-modulated radiation therapy (IMRT) allow to target the tumor with an increased precision. They require accurate anatomical information of the patient just before the treatment, which can be obtained using on-board imaging systems mounted on the medical linear accelerator delivering the treatment beam. These systems, composed of an X-ray tube and a 2D planar detector, are called kV-Cone Beam CT (kV-CBCT). Nowadays, they are widely used in the context of IMRT treatments. However, these kV-CBCT examinations are also responsible for an additional dose of ionizing radiations which is far to be negligible and could be the cause for secondary effects, such as radiation-induced second cancers for treated patients. During this PhD work, a simulator based on the Monte Carlo method was developed in order to calculate accurately the doses delivered to organs during kV-CBCT examinations. Then, this tool was used to study several strategies to take in account for the imaging additional doses in clinical environment. The study reported here includes, in particular, a fast and personalized method to estimate the doses delivered to organs. This strategy was developed using a cohort of 50 patients including 40 children and 10 adults. This work has been done in collaboration with the medical physics unit of the Eugène Marquis medical center in Rennes, which has collected the clinical data used for this study

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Zheng, Pingping. « Bayesian analysis of structural change in trend ». Thesis, Nottingham Trent University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391001.

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Camargo, Vinícius Valduga de Almeida. « Evaluating the impact of charge traps on MOSFETs and ciruits ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/150857.

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Nesta tese são apresentados estudos do impacto de armadilhas no desempenho elétrico de MOSFETs em nível de circuito e um simulador Ensamble Monte Carlo (EMC) é apresentado visando a análise do impacto de armadilhas em nível de dispositivo. O impacto de eventos de captura e emissão de portadores por armadilhas na performance e confiabilidade de circuitos é estudada. Para tanto, um simulador baseado em SPICE que leva em consideração a atividade de armadilhas em simulações transientes foi desenvolvido e é apresentado seguido de estudos de caso em células SRAM, circuitos combinacionais, ferramentas de SSTA e em osciladores em anel. Foi também desenvolvida uma ferramenta de simulação de dispositivo (TCAD) atomística baseada no método EMC para MOSFETs do tipo p. Este simulador é apresentado em detalhes e seu funcionamento é testado conceitualmente e através de comparações com ferramentas comerciais similares.
This thesis presents studies on the impact of charge traps in MOSFETs at the circuit level, and a Ensemble Monte Carlo (EMC) simulation tool is developed to perform analysis on trap impact on PMOSFETs. The impact of charge trapping on the performance and reliability of circuits is studied. A SPICE based simulator, which takes into account the trap activity in transient simulations, was developed and used on case studies of SRAM, combinational circuits, SSTA tools and ring oscillators. An atomistic device simulator (TCAD) for modeling of p-type MOSFETs based on the EMC simulation method was also developed. The simulator is explained in details and its well function is tested.

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Hall, Jaclyn Marie. « Ecological change in Tanzanian montane rainforests from species to landscape / ». [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024372.

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Rhemtulla, Jeanine Marie. « Eighty years of change, the montane vegetation of Jasper National Park ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40099.pdf.

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Tejedor, Garavito Natalia. « Impact of climate change on extinction risk of montane tree species ». Thesis, Bournemouth University, 2014. http://eprints.bournemouth.ac.uk/21485/.

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The potential impacts of climate change on many species worldwide remains unknown, especially in those tropical regions that are centers of endemism and are highly biodiverse. This thesis provides an insight into the extinction risk of selected tree species using different species distribution modelling techniques and reviewing the current conservation status on montane forest in the Tropical Andes. Starting with a global analysis, the potential impacts of climate change on montane ecoregions is investigated, by identifying those that are more vulnerable to the expected changes in temperature and precipitation, from global predictions under different climate change scenarios. It then gives an insight on the current and potential threats to biodiversity in the Andean region, including the identification of those that are most likely to be responsible for increasing the extinction risk of the species. With the use of the IUCN Red List Categories and Criteria, selected tree species were assessed to identify their extinction risk. Information on the species’ current distribution was collated and used to estimate their potential distribution under climate change, by using different modelling techniques. These results were used to reassess the species using the IUCN Red List and establish the changes in Red List Category. Lastly, it provides a discussion that integrates all the results obtained throughout the thesis, to explore the implications for conservation, in order to highlight the overriding importance of including threatened tree species to target conservation efforts in the region, while considering the uncertainties that surround predictions under climate change scenarios, modelling techniques and the use of the IUCN Red List.

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Araujo, Jose Iranildo da Silva. « Performance of unit root tests with change in level cross-section dependence ». Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=9872.

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nÃo hÃ
Unit root tests have been widely used to validate or reject economic modelâs hypotheses. Because of this, many authors have created different versions of this kind of test in order to generate statistics which are more precise in identifying the presence of a unit root. Some authors have increased the power of these statistics using panel data. However, the use of panel data brings the possibility of dependence between cross-sections, this has been initially handled by the independence between cross-sections hypothesis. Only the second generation tests consider dependence between cross-sections. Nevertheless, in the literature there is no test which allows changes in the dependence between cross-sections over time. Thus, this paper uses Monte Carlo experiments to analyze the small sample properties of some statistics used to identify the presence of a unit root. It is noticed that the size of these statistics has a large distortion when the level of dependence between cross-sections changes.
Teste de raiz unitÃria tem sido muito importante no sentido de validar ou rejeitar as hipÃteses dos modelos econÃmicos. Devido essa importÃncia, diversos autores tÃm criado diferentes versÃes desse teste, a fim de gerar estatÃsticas que sejam mais precisas em identificar a presenÃa de raiz unitÃria. Usando dados em painel, alguns autores conseguiram aumentar o poder dessas estatÃsticas. No entanto, o uso de dados em painel trÃs a possibilidade de dependÃncia cross-section nos dados, fato esse inicialmente tratado pela hipÃtese de independÃncia cross-section. Somente nos testes chamados de segunda geraÃÃo Ã que se trata dependÃncia cross-section. Entretanto, nÃo hÃ na literatura nenhum teste que permita mudanÃas nesse nÃvel de dependÃncia ao longo do tempo. Com isso, esse trabalho pretende avaliar, por meio de um experimento de Monte Carlo, as propriedades de pequenas amostras de algumas estatÃsticas usadas para identificar a presenÃa de raiz unitÃria. Percebe-se que o tamanho dessas estatÃsticas sofre uma grande distorÃÃo para as situaÃÃes de mudanÃa no nÃvel de dependÃncia cross-section.

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Kundu, Ashoke. « Monte Carlo simulation of gas-filled radiation detectors ». Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/987/.

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Vazquez, Tyara Kiileialohalani. « Physiological Responses to Heat-stress in a Desert Montane Lizard ». University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544789284098965.

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Gali, Sai Manoj. « Modélisation des relations structure / propriétés de transport de charge dans les matériaux pour l'électronique organique ». Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0693/document.

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Les avancées technologiques et l'intégration massive de dispositifs électroniques nanométriques dans les objets de notre vie quotidienne ont généré une explosion des coûts de R&D, de conception et de production, ainsi que des inquiétudes sociétales quant à l'impact environnemental des déchets électroniques. En raison de procédés de production moins coûteux et à faible impact environnemental, de leur souplesse d’utilisation et de la possibilité de moduler leurs propriétés à l’infini, les molécules et polymères organiques constituent une classe de matériaux prometteuse pour la mise au point de nouveaux dispositifs électroniques. L’électronique organique couvre ainsi un vaste domaine d’applications, parmi lesquelles se trouvent les diodes électroluminescentes, les transistors à effet de champ ou les cellules photovoltaïques. Bien que la plupart de ces dispositifs soient déjà commercialisés, les processus gouvernant leur efficacité à l’échelle atomique sont loin d’être entièrement compris et maîtrisés. C’est en particulier le cas des processus de transport de charge, qui interviennent dans tous ces dispositifs.L'objectif de cette thèse est d’apporter une compréhension fondamentale des processus de transport de charge dans les semiconducteurs organiques, à partir d'approches théoriques combinant dynamique moléculaire, calculs quantiques et simulations Monte Carlo. Ce travail est développé suivant trois axes principaux:(I) Etude des relations liant l'organisation structurale et les propriétés de transport de cristaux moléculaires, et du rôle des fluctuations énergétiques dans des matériaux polymères amorphes. Des simulations Monte Carlo Cinétique (KMC) couplés au formalisme de Marcus-Levich-Jortner pour le calcul des taux de transfert ont été effectués afin de déterminer les mobilités des électrons et des trous au sein de dix structures cristallines de dérivés phtalocyanines. Dans une deuxième étude, une approche similaire a été employée afin de décrire les propriétés de transport de charge au sein d'un copolymère amorphe de fluorène-triphénylamine, ainsi que l'impact des fluctuations énergétiques sur ces dernières. La méthodologie développée permet d'obtenir, pour un faible coût calculatoire, une estimation semi-quantitative des mobilités des porteurs de charge dans ce type de système.(II) Etude de l'impact de contraintes mécaniques sur les propriétés de transport de matériaux organiques cristallins. La réponse électronique et les propriétés de transport de matériaux organiques soumis à une contrainte mécanique ont été étudiés à l'aide de simulations de dynamique moléculaire et de calculs DFT. Le rubrène cristallin et ses polymorphes, ainsi que les dérivés du BTBT, ont été considérés pour cette étude, qui révèle un couplage électromécanique inhabituel entre les différents axes cristallographiques. Les résultats démontrent en particulier que l'anisotropie structurale des monocristaux organiques conduit à une anisotropie du couplage électromécanique.(III) Etude du rôle du polyélectrolyte dans la conductivité des complexes conducteurs. Le polystyrène substitué par du bis(sulfonyl)imide est utilisé comme un contre-ion et un dopant dans les complexes conducteurs PEDOT-polyélectrolytes. En complément des analyses expérimentales, des simulations de dynamique moléculaire couplées à des calculs DFT ont été effectuées dans ces systèmes afin d'analyser l'impact de la conformation et de l'état de protonation du polyélectrolyte sur la conductivité du complexe formé avec le PEDOT.Les études décrites ci-dessus, réalisées sur différents types de matériaux en couplant différents types d'approches théoriques, ont permis d'apporter une compréhension fondamentale des propriétés de transport dans les semiconducteurs organiques. Elles mettent en particulier en évidence l'impact de l'organisation structurale, des interactions intermoléculaires et de l'application de contraintes mécaniques sur la mobilité des porteurs de charges dans ces matériaux
With the advancement of technology, miniaturized electronic devices are progressively integrated into our everyday lives, generating concerns about cost, efficiency and environmental impact of electronic waste. Organic electronics offers a tangible solution paving the way for low-cost, flexible, transparent and environment friendly devices. However, improving the functionalities of organic (opto) electronic devices such as light emitting diodes and photovoltaics still poses technological challenges due to factors like low efficiencies, performance stability, flexibility etc. Although more and more organic materials are being developed to meet these challenges, one of the fundamental concerns still arises from the lack of established protocols that correlate the inherent properties of organic materials like the chemical structure, molecular conformation, supra-molecular arrangement to their resulting charge-transport characteristics.In this context, this thesis addresses the prediction of charge transport properties of organic semiconductors through theoretical and computational studies at the atomistic scale, developed along three main axes :(I) Structure-charge transport relationships of crystalline organic materials and the role of energetic fluctuations in amorphous polymeric organic semiconductors. Kinetic Monte-Carlo (KMC) studies employing the Marcus-Levich-Jortner rate formalism are performed on ten crystalline Group IV phthalocyanine derivatives and trends linking the crystalline arrangement to the anisotropic mobility of electrons and holes are obtained. Subsequently, KMC simulations based on the simpler Marcus formalism are performed on an amorphous semiconducting fluorene-triphenylamine (TFB) copolymer, to highlight the impact of energetic fluctuations on charge transport characteristics. A methodology is proposed to include these fluctuations towards providing a semi-quantitative estimate of charge-carrier mobilities at reduced computational cost.(II) Impact of a mechanical strain on the electronic and charge transport properties of crystalline organic materials. Crystalline rubrene and its polymorphs, as well as BTBT derivatives (well studied high mobility organic materials) are subjected to mechanical strain and their electronic response is analyzed. Employing tools like Molecular Dynamic (MD) simulations and plane wave DFT (PW-DFT) calculations, unusual electro-mechanical coupling between different crystallographic axes is demonstrated, highlighting the role of inherent anisotropy that is present in the organic single crystals which translates in an anisotropy of their electro-mechanical coupling.(III) Protonation-dependent conformation of polyelectrolyte and its role in governing the conductivity of polymeric conducting complexes. Polymeric bis(sulfonyl)imide substituted polystyrenes are currently employed as counter-ions and dopants for conducting poly(3,4-ethylenedioxythiophene) (PEDOT), resulting in PEDOT-polyelectrolyte conducting complexes. Employing MD simulations and DFT calculations, inherent characteristics of the polyelectrolyte like its acid-base behavior, protonation state and conformation, are analyzed in conjunction with available experimental data and the role of these characteristics in modulating the conductivity of resulting PEDOT-polyelectrolyte conducting complexes is highlighted.The above studies, performed on different organic electronic systems, emphasize the importance of inherent characteristics of organic materials in governing the charge transport behavior in these materials. By considering the inherent characteristics of organic electronic materials and systematically incorporating them into simulation models, accuracy of simulation predictions can be greatly improved, thereby serving not only as a tool to design new, stable and high performance organic materials but also for optimizing device performances

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Bokun, G. S., Ya G. Groda, R. N. Lasovsky et V. S. Vikhrenko. « Charge Distribution Around Nanoscale Nonhomogeneities in Solid State Ionics ». Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42717.

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The system of Nernst-Planck-Poisson equations is modified by including the gradient terms in the chemical potential expression. The gradient terms are important in the regions of significant inhomogeneities, e. g. near the interface boundaries. These modified equations are used for investigating the particle density distribution in the vicinity of interphase boundary of a solid electrolyte. The differential equation of the fourth order for the problem of contact between two solid phases is formulated. Its analytic solution which describes non monotonic distribution of charge in both phases is obtained. It is shown that the gradient component added in the transport equations makes a decisive contribution in the double layer region. The approach is further expanded to the system composed of bulk phases and the intergrain layer between them. The particle density distributions at different conditions are investigated. The quasy-one dimensional lattice model of the fuel cell is considered in the frame of kinetic Monte Carlo simulation. It is shown that the electrostatic interaction between ions makes a significant contribution to the activation energy of migration of the particles. On the other hand, the fluctuations of the energy barriers slightly increase the particle migration activation energy. It is found that at blocked electrodes in the near electrode regions electrical double layers are formed. The thickness of the electrical double layer is around few lattice constants.

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Renoud, Raphaël. « Simulation par la méthode de Monte-Carlo de la charge d'un isolant soumis au bombardement d'un faisceau électronique focalisé ». Lyon 1, 1995. http://www.theses.fr/1995LYO10029.

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La caracterisation des materiaux isolants (par exemple par la methode du miroir) passe par une connaissance approfondie de la physique de la charge d'espace. La distribution des charges, la forme du potentiel et du champ electrostatique, ainsi que les rendements de l'emission secondaire, sont autant d'indicateurs essentiels pour apprecier la tenue dielectrique d'un materiau soumis a une contrainte (electrique, mecanique, thermique,). Dans ce cadre, nous simulons le bombardement d'un echantillon isolant par un faisceau electronique tel qu'on le realise dans un microscope electronique a balayage. En utilisant la methode de monte-carlo, il est alors possible de suivre les trajectoires electroniques dans l'echantillon. Dans la premiere partie de ce memoire, nous exposons les fondements theoriques necessaires a notre etude. Nous insistons notamment sur les proprietes des isolants (polarisation, champ electrique, piegeage) et sur la propagation des electrons a l'interieur de ces milieux (modele d'interaction electron-isolant). Nous abordons aussi l'etude du phenomene de l'emission electronique secondaire, dont le role est important pour confronter notre modele a l'experience. L'expose de la technique de simulation de monte-carlo fait l'objet de la seconde partie. Nous y indiquons notamment comment convertir les lois physiques en informations et modeles exploitables par un ordinateur. Nous detaillons en particulier le traitement du champ electrique. Dans la troisieme partie sont exposes les resultats obtenus. Nous calculons alors les taux d'emission secondaire, ce qui nous permet de valider notre modele. Nous pouvons ainsi calculer, a divers instants de la charge, la distribution des charges piegees, en fonction des caracteristiques du materiau, et nous en deduisons le champ et le potentiel en tout point de l'espace. Une etude du taux d'emission secondaire permet de deduire les caracteristiques de piegeage du materiau

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Couderc, Elsa. « Transport de charges dans des couches minces hybrides à base de polymère conjugué et de nanocristaux de semi-conducteurs ». Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENY068/document.

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Cette thèse a pour but d'étudier le transport de charges pho- togénérées dans des matériaux hybrides composés de polymères π-conjugués et de nanocristaux de semi- conducteurs, conçus pour des applications en opto-électronique. La synthèse chimique permet d'obtenir des nanocristaux de CdSe à l'échelle du gramme ayant une faible polydispersité et des formes contrôlées (sphériques, branchées). Les ligands de surface des nanocristaux de CdSe sont échangés par de petites molécules (pyridine, éthanedithiol, phénylènediamine, butylamine, benzènedithiol) afin d'augmenter leur conductivité. L'échange de ligands modifie les niveaux énergétiques des nanocristaux, comme le montrent des études optiques et électrochimiques. Le poly(3-hexylthiophène) déposé sous forme de couches minces présente différents degrés de couplage intermoléculaire et de désordre énergétique selon la méthode de dépôt et le solvant utilisé. Dans les films hybrides, des mesures de diffraction de rayons X en incidence rasante montrent que la structuration cristalline de la matrice organique est modifiée par la présence des nanocristaux. Les mesures de Temps-de-Vol dans les couches hybrides montrent que les mobilités des trous et des électrons varient avec le contenu en nanocristaux, ainsi qu'avec leur forme et leurs ligands. De faibles fractions de nanocristaux provoquent une amélioration de la mobilité des trous, tandis que de plus grandes fractions la détériorent. Les mobilités électroniques sont soumises à une fraction-seuil, as- similable à un seuil de percolation. La fraction optimale de nanocristaux, du point de vue des mobilités des trous et des électrons, est de 36% en volume pour les nanocristaux sphériques avec les ligands de synthèse. Enfin, les simulations Monte-Carlo des courants transitoires photo-générés, dans un échantillon de poly(3-hexylthiophène) et dans un hybride, montrent d'une part que la distribution énergétique du poly(3-hexylthiophène) domine l'allure des courants simulés et d'autre part que les nanocristaux peuvent être assimilés à des sites difficilement accessibles du réseau cubique
The aim of this work is the study of photogenerated charge transport in hybrid films composed of π-conjugated polymers and of semiconductor nanocrystals, designed for applications in optoelectronics. Chemical synthesis provides gram-scale samples of CdSe nanocrystals, of low polydispersity and con- trolled shapes (spherical, branched). In order to enhance their conductivity, the surface ligands of CdSe nanocrystals (stearic acid, oleylamine) are exchanged by smaller molecules, namely pyridine, ethanedithiol, phenylenediamine, butylamine and benzenedithiol. Optical and electrochemical studies show that the lig- and exchange modifies the nanocrystals' energy levels. Poly(3-hexylthiophene) thin films exhibit varying degrees of energetical disorder and of intermolecular coupling, depending on the processing method and on the solvent used. In hybrid films, the crystallinity of P3HT, probed by grazing incidence X-ray diffraction, is modified by the presence of nanocrystals. Time-of-Flight measurements of hybrid films show that elec- tron and hole mobilities vary with the content of nanocrystals, with their shape, and with their ligands. Small volume fractions of nanocrystals enhance the hole mobility, and large fractions degrade it. Electron mobilities are percolation-limited: they reach a stable value for a threshold fraction of nanocrystals. The optimal fraction of nanocrystals for electron and hole mobilities is 36 vol% in hybrids made of spherical nanocrystals with their synthesis synthesis ligands. Finally, Monte Carlo simulations of photogenerated current transients in pristine poly(3-hexylthiophene) and in a hybrid sample show on one hand that the energy distribution of poly(3-hexylthiophene) rules the shape of the simulated transients, and on the other hand that nanocrystals can be described as little accessible sites of the hopping lattice

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Kühl, Jesper J. « Microeconomic studies on risk, poverty and climate change / ». Copenhagen, 2005. http://www.gbv.de/dms/zbw/489052436.pdf.

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Sridharan, Sriraaman. « Design and theoretical study of Wurtzite GaN HEMTs and APDs via electrothermal Monte Carlo simulation ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47526.

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A self-consistent, full-band, electrothermal ensemble Monte Carlo device simulation tool has been developed. It is used to study charge transport in bulk GaN, and to design, analyze, and improve the performance of AlGaN/GaN high electron mobility transistors (HEMTs) and avalanche photodiodes (APDs). Studies of electron transport in bulk GaN show that both peak electron velocity and saturated electron velocity are higher for transport in the basal plane than along the c-axis. Study of the transient electron velocity also shows a clear transit-time advantage for electron devices exploiting charge transport perpendicular to the c-axis. The Monte Carlo simulator also enables unique studies of transport under the influence of high free carrier densities but with low doping density, which is the mode of transport in AlGaN/GaN HEMTs. Studies of isothermal charge transport in AlGaN/GaN HEMTs operating at high gate bias show a drain current droop with increasing drain-source bias. The cause of the droop is investigated and a design utilizing source- or gate-connected field plate is demonstrated to eliminate the drain current droop. Electrothermal aspects of charge transport in AlGaN/GaN HEMTs are also investigated, and the influence of non-equilibrium acoustic and optical phonons is quantified. The calculated spatial distribution of non-equilibrium phonon population reveals a hot spot in the channel that is localized at low drain-source bias, but expands towards the drain at higher bias, significantly degrading channel mobility. Next, Geiger mode operation of wurtzite GaN-based homojunction APDs is investigated. The influences of dopant profile, active region thickness, and optical absorption profile on single photon detection efficiency (SPDE) are quantified. Simulations of linear mode gain as a function of multiplication region thickness and doping profile reveal that weakly n-type active regions may be exploited to achieve higher avalanche gain, without penalty to either applied bias or active region thickness. A separate absorption and multiplication APD (SAM-APD) utilizing a AlGaN/GaN heterojunction is also investigated. The presence of strong piezo-electric and spontaneous polarization charges at the heterojunction enables favorable electric field profile in the device to reduce dark current, improve excess noise factor, improve quantum efficiency, and improve breakdown probability. To maximize SPDE, a new device structure with a buried absorber is proposed and improved SPDE is demonstrated. Lastly, a new approach for the direct generation of self-sustaining millimeter-wave oscillations is proposed. In contrast to Gunn diodes, which exploit a bulk-like active region, periodic oscillation is achieved in the proposed structures through the creation, propagation and collection of traveling dipole domains supported by fixed polarization charge and the associated two-dimensional electron gas along the plane of a polar heterojunction. Numerical simulation of induced oscillations in a simple triode structure commonly used for AlGaN/GaN HEMTs reveals two distinct modes of self-sustaining millimeter-wave oscillation.

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Mathieson, Keith. « Modelling semiconductor pixel detectors ». Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368733.

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Waidacher, Christoph. « Charge properties of cuprates : ground state and excitations ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2000. http://nbn-resolving.de/urn:nbn:de:swb:14-998985918593-73513.

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This thesis analyzes charge properties of (undoped) cuprate compounds from a theoretical point of view. The central question considered here is: How does the dimensionality of the CU-O sub-structure influence its charge degrees of freedom? The model used to describe the Cu-O sub-structure is the three- (or multi-) band Hubbard model. Analytical approaches are employed (ground-state formalism for strongly correlated systems, Mori-Zwanzig projection technique) as well as numerical simulations (Projector Quantum Monte Carlo, exact diagonalization). Several results are compared to experimental data. The following materials have been chosen as candidates to represent different Cu-O sub-structures: Bi2CuO4 (isolated CuO4 plaquettes), Li2CuO2 (chains of edge-sharing plaquettes), Sr2CuO3 (chains of corner-sharing plaquettes), and Sr2CuO2Cl2 (planes of plaquettes). Several results presented in this thesis are valid for other cuprates as well. Two different aspects of charge properties are analyzed: 1) Charge properties of the ground state 2) Charge excitations. (gekürzte Fassung)

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Waidacher, Christoph. « Charge properties of cuprates : ground state and excitations ». Doctoral thesis, Technische Universität Dresden, 1999. https://tud.qucosa.de/id/qucosa%3A24786.

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This thesis analyzes charge properties of (undoped) cuprate compounds from a theoretical point of view. The central question considered here is: How does the dimensionality of the CU-O sub-structure influence its charge degrees of freedom? The model used to describe the Cu-O sub-structure is the three- (or multi-) band Hubbard model. Analytical approaches are employed (ground-state formalism for strongly correlated systems, Mori-Zwanzig projection technique) as well as numerical simulations (Projector Quantum Monte Carlo, exact diagonalization). Several results are compared to experimental data. The following materials have been chosen as candidates to represent different Cu-O sub-structures: Bi2CuO4 (isolated CuO4 plaquettes), Li2CuO2 (chains of edge-sharing plaquettes), Sr2CuO3 (chains of corner-sharing plaquettes), and Sr2CuO2Cl2 (planes of plaquettes). Several results presented in this thesis are valid for other cuprates as well. Two different aspects of charge properties are analyzed: 1) Charge properties of the ground state 2) Charge excitations. (gekürzte Fassung)

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DALL'Ò, ELISABETTA. « Il cambiamento in-visibile : l’area del Monte Bianco tra antropocene, cambiamenti climatici e diniego ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/198928.

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Il caso del Monte Bianco, prima ancora che questioni sullo scioglimento dei ghiacciai, sulla sicurezza, sulla prevenzione e sulla gestione del rischio, ci pone delle domande epocali sull’Antropocene, sul nostro modello economico, sul nostro rapporto col territorio, l’ambiente e l’ecosistema, sul modo di concepire il turismo, lo sport, sul nostro modo di costruire e vivere il territorio, sulle nostre istituzioni, sulla rappresentanza e la partecipazione di chi agisce sul territorio. Come scrive l’antropologa Elena Bougleux, il cambiamento climatico è una questione che riguarda al tempo stesso aspetti “estremamente scientifici” e aspetti “completamente sociali”: « non esiste evidenza significativa, aspetto problematico né discorso sul clima senza una società che lo vive, lo commenta, lo misura, lo confronta con il proprio passato, tanto recente quanto lontano ». Il discorso che ruota attorno ai cambiamenti climatici, proprio in quanto descrive dei “cambiamenti”, implica uno stato precedente di normalità, un “prima”, rispetto al “poi” del loro verificarsi. Anzi, si potrebbe dire, ha senso proprio in funzione di un preesistente stato di “normalità”. Come nozione, quella di “cambiamento climatico” si può dire che « esiste in quanto esito complesso di un processo di costruzione sociale della nozione di clima “normale” ». Ma che cosa intendiamo per “normale”, quando ci riferiamo alla nozione di clima? Conosciamo lo stato preesistente? E quali sono i riferimenti a cui ci rifacciamo per decretarne un avvenuto mutamento? In base a cosa lo possiamo stabilire? Un ruolo essenziale, come è logico, lo gioca la Storia, o meglio, le tante storie che su questa nozione vengono a convergere: la storia climatica, fatta di scale di misurazione, dati quantitativi, ma anche qualitativi — basti pensare ai lavori di Le Roy Ladurie che qui avremo modo di discutere ampiamente —, e la storia di quelle società che nel tempo ne hanno osservato e interpretato gli effetti, adattandosi costantemente. Il clima è dunque l’effetto di una evoluzione e di una negoziazione reciproche nel corso del tempo, tra “dato climatico misurato” e “significato sociale attribuito”. Queste due dimensioni vanno intese nel loro “senso evolutivo”, “legate alla storia”, “mutevoli nel tempo”. Il concetto stesso di clima richiede allora una continua negoziazione di significati, mai dati una volta per tutte, e un « compromesso continuo e instabile tra il quadro quantitativo registrato e lo scenario soggettivo percepito ». Parlare di clima, e farlo “sulle Alpi dell’Antropocene” significa includere nel discorso tutta una serie di nozioni, che vanno dalle serie storiche ai modelli matematici, dai dati di memoria alle “memorie di futuro” fino agli scenari calcolati o attesi, e ai rischi e ai disastri. Parlare di clima significa trattare elementi « così epistemologicamente diversi da non avere neanche termini descrittivi comuni che li racchiudano tutti ». Inoltre, ricorda ancora Bougleux, queste nozioni “vivono vite diverse”, con “cronologie distinte”, che possono essere valide, o coerenti, oppure utili su diverse scale, in epoche diverse, e in diversi spazi, ma che non possono esser prese e accostate senza un’operazione critica o analitica. « Forse è possibile per alcune classi di scienziati arrivare ad una definizione localmente coerente di clima, ma di certo non si arriva a disegnare una nozione accettabile e coerente di cambiamento del clima per gruppi estesi di persone, per esperti di diverse discipline, attraverso lunghi periodi di tempo ».
the case of Mont Blanc sets us questions about anthropocene, our relation with land.

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Beck, William A. « Semiclassical, Monte Carlo model of atomic collisions : stopping and capture of heavy charged particles and exotic atom formation / ». Thesis, Connect to this title online ; UW restricted, 1997. http://hdl.handle.net/1773/9796.

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Montén, Anna [Verfasser], Marcel [Akademischer Betreuer] Thum et Alexander [Akademischer Betreuer] Kemnitz. « The provision of local public goods and demographic change / Anna Montén. Gutachter : Marcel Thum ; Alexander Kemnitz. Betreuer : Marcel Thum ». Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://d-nb.info/1068443324/34.

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Yahya, Bokhari. « Discovering driver somatic mutations, copy number alterations and methylation changes using Markov Chain Monte Carlo ». VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3266.

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Nowadays we have tremendous amount of genetic data needing to be interpreted. Somatic mutations, copy number variations and methylation are example of the genetics data we are dealing with. Discovering driver mutations from these combined data types is challenging. Mutations are unpredictable and have broad heterogeneity, which makes our goal hard to accomplish. Many methods have been proposed to solve the mystery of genetics of cancer. In this project we manipulate those above mentioned genetics data types and choose to use and modified an existing method utilizing Markov Chain Monte Carlo (MCMC). The method introduced two properties, coverage and exclusivity. We obtained the data from The Cancer Genome Atlas (TCGA). We used MCMC method with three cancer types: Glioblastoma Multiform (GBM) with 214 patients, Breast Invasive Carcinoma (BRCA) with 474 patients and Colon Adenocarcinoma (COAD) with 233 patients.

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Chenevix-Trench, Philida Clare. « People and cattle : agents of ecological change in a dry montane forest, Samburu District, Kenya ». Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264894.

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Shoo, Luke Paul. « Predicting and Detecting the Impacts of Climate Change on Montane Fauna in Australian Tropical Rainforests ». Thesis, Griffith University, 2005. http://hdl.handle.net/10072/365299.

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Global climates are changing rapidly and biological responses are becoming increasingly apparent. Some models indicate that climate warming impacts will largely consist of latitudinal and altitudinal shifts in potential species' distributions while others suggest that the complete disappearance of critical climate types and dependent species are possible. While early investigations have focused on high latitudes where warming has been most pronounced, there is an increasing recognition of the need to understand impacts in biodiverse tropical regions that support many spatially and climatically restricted species. The vertebrate fauna of the Wet Tropics biogeographic region of north-eastern Australia provides a unique opportunity to address this deficiency. First, endemic species are typically associated with cool, wet and relatively aseasonal upland environments; characteristics considered to have predisposed the fauna to being particularly vulnerable to future global climate change. Second, recent projections of species responses to future climate scenarios suggest strong systematic change in the extent and location of species' distributions with even small amounts of warming. Altitude is effectively a surrogate for turnover in temperature in the region and impacts of increasing temperature are expected to be most noticeable along this gradient. Focusing on two ecologically disparate taxa (ie. rainforest birds and microhylid frogs) empirical abundance patterns across altitudinal gradients and predicted altitudinal range shifts are used to: (1) predict changes in total population size; (2) estimate change in total population size relative to distribution area; and (3) quantify the sensitivity and bias of widely used measures for assessing contemporary range shifts along altitudinal gradients. According to the most conservative model scenario, 41 of 55 (74 %) rainforest birds and 6 of 6 (100%) microhylid frogs examined are predicted to become threatened as a result of projected mid-range warming expected within the next 100 years. Extinction risk varied according to where along the altitudinal gradient a species was most abundant. Upland species were most affected and are likely to be immediately threatened by even small increases in temperature. In contrast, there is a capacity for the population size of lowland species to increase, at least in the short term. In the context of climate warming impacts, a documented decline in distribution area will not necessarily reflect the extent of change in total population size. For 9 out of 12 species of regionally-endemic birds and 5 out of 6 species of microhylid frogs, total population size is expected to decline more rapidly than distribution area with increasing temperature. For both groups combined, only 4 species (22%) showed either a comparable or slower decline in population size with change in distribution area. The disproportional loss in population size suggests that extinction risk associated with climate change can be more severe than that expected from decline in distribution area alone. Detection and measurement of climate induced change is crucial if we are to improve predictions of future change and attempt to mitigate impacts to biodiversity. Randomisations of available data suggest that the mean position of presence records allows for a smaller minimum detectable range shift than change measured at upper or lower range boundaries. For a moderate survey effort of 96 surveys, measurements of change in the mean altitude of 34 rainforest birds has the capacity to provide strong inference for mean altitudinal range shifts as small as 40 m across the species assemblage. Randomizations also demonstrate that range shifts measured at range boundaries can be potentially misleading when differences in sampling effort between contemporary and historical data sets are not taken into account. In conclusion, abundance data collected across climatic gradients will be fundamental to gaining an understanding of population size change associated with climate warming. Complex spatial variability in species' abundance along with area constraints of mountain systems undermine the ability of documented change in distribution area to predict important change in population size. There is therefore an urgent need to not only track changes in location and extent of distribution area but also spatial patterns in the relative abundance of species within current and future distributions. Randomisations suggest that change in the mean altitude of species will allow for the detection of smaller range shifts than change measured at range boundaries. As detection limit is dependent on sampling effort, analyses of statistical power should be considered an integral first step in designing future monitoring programs
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental and Applied Science
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Samaniego-Eguiguren, Luis Eduardo. « Hydrological consequences of land use - land cover and climatic changes in mesoscale catchments ». [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10720630.

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Henderson, Amanda, et Amanda Henderson. « Productivity of Montane Meadows in a Warming World : Evidence from an Elevation Gradient and a Warming Experiment ». Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/622892.

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Climate change is expected to disproportionately impact high elevation ecosystems by disrupting current temperature and precipitation regimes. The future carbon balance of these systems is uncertain, given the interplay between longer growing season length and the potential for increased drought. Currently, the most robust inferences about ecosystem responses to changing climate come from the integration of experimental and observational methods. In this thesis, I utilize evidence from a warming experiment and an elevational gradient to gain insights into how aspects of ecosystem productivity and community functional composition change in response to the abiotic environment. First, I show that ecosystem productivity was similar in the heated and ambient treatment groups of the warming experiment. Net ecosystem productivity (NEP) was similar between treatments with only slightly increased NEP in the early season in the heated treatment. Important leaf functional traits (leaf mass per area, LMA; leaf dry matter content, LDMC) shifted with heating in directions associated with higher productivity, both at the community level and within species. While these results are counterintuitive, potential insight was provided by a soil cooling effect found in the heated plots in the early season. Second, I investigate ecosystem productivity across spatial and temporal gradients using phenology cameras. I show strong relationships between greenness indices generated from camera images and on-the-ground measurements of gross primary productivity (GPP). I also used changes in greenness indices early season to infer green-up rates, and found a strong pattern of increasing green-up rate with increasing elevation. Together, these studies highlight the importance of comparing experimental and gradient methods to assess how different spatial and temporal scales influence our conclusions about the effect of climate change on ecosystems.

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Nathan, Roger P. « Numerical modelling of environmental dose rate and its application to trapped-charge dating ». Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:3da656e8-5514-4fed-85d1-8664e5dc1932.

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Accurate estimation of environmental dose rate is essential for high-resolution trapped-charge dating. Beta and gamma emissions from simulated sediments containing radioactive uranium, thorium and potassium are modelled in contexts that are spatially heterogeneous. Dose rate was modelled using Monte Carlo radiation transport codes MCNP and PENELOPE. A number of key issues that affect dose rate evaluation are examined and updated corrections are calculated. Granular structures used for geometrical input into the models were simulated using randomly packed ellipsoids. The pair correlation function and chord length distributions were derived. The effects of water content on dose rate were modelled and compared with cavity theory. Apart from activity dilution, the variation of grain size or water content was shown to be significant for gamma radiations due to the transition from charged particle equilibrium. The standard correction for beta dose rate due to grain size was found to be satisfactory although sensitivity to grain shape and material should be taken into account. Dose rate modeling was applied to three dating studies of early human fossils: Skhul V, Israel skull; Hofmeyr, South Africa skull and the Forbes’ Quarry, Gibraltar skull. The spatial modelling was implemented using computerised tomographic (CT) images and dose rate found to be modified significantly by the presence of the skull in the sediment. Time evolution of the dose rate was examined for the latter two skulls and dates of 36±3ka (Hofmeyr) and 55-95ka (Forbes’ Quarry) were calculated.

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Pereira, De Oliveira Luís Carlos. « Développement d'une méthodologie de modélisation cinétique de procédés de raffinage traitant des charges lourdes ». Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00839871.

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Une nouvelle méthodologie de modélisation cinétique des procédés de raffinage traitant les charges lourdes a été développée. Elle modélise, au niveau moléculaire, la composition de la charge et les réactions mises en œuvre dans le procédé.La composition de la charge est modélisée à travers un mélange de molécules dont les propriétés sont proches de celles de la charge. Le mélange de molécules est généré par une méthode de reconstruction moléculaire en deux étapes. Dans la première étape, les molécules sont créées par assemblage de blocs structuraux de manière stochastique. Dans la deuxième étape, les fractions molaires sont ajustées en maximisant un critère d'entropie d'information.Le procédé de raffinage est ensuite simulé en appliquant, réaction par réaction, ses principales transformations sur le mélange de molécules, à l'aide d'un algorithme de Monte Carlo.Cette méthodologie est appliquée à deux cas particuliers : l'hydrotraitement de gazoles et l'hydroconversion de résidus sous vide (RSV). Pour le premier cas, les propriétés globales de l'effluent sont bien prédites, ainsi que certaines propriétés moléculaires qui ne sont pas accessibles dans les modèles traditionnels. Pour l'hydroconversion de RSV, dont la structure moléculaire est nettement plus complexe, la conversion des coupes lourdes est correctement reproduite. Par contre, la prédiction des rendements en coupes légères et de la performance en désulfuration est moins précise. Pour les améliorer, il faut d'une part inclure de nouvelles réactions d'ouverture de cycle et d'autre part mieux représenter la charge en tenant compte des informations moléculaires issues des analyses des coupes de l'effluent.

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Kaiser, Waldemar [Verfasser], Alessio [Akademischer Betreuer] Gagliardi, Alessio [Gutachter] Gagliardi et David [Gutachter] Egger. « Kinetic Monte Carlo Study of Charge and Exciton Transport in Organic Solar Cells / Waldemar Kaiser ; Gutachter : Alessio Gagliardi, David Egger ; Betreuer : Alessio Gagliardi ». München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1237413273/34.

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Srinivasan, Madhusudan P. « THE ECOLOGY OF DISTURBANCES AND GLOBAL CHANGE IN THE MONTANE GRASSLANDS OF THE NILGIRIS, SOUTH INDIA ». UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/213.

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Biodiversity rich regions worldwide face threats from various global change agents. This research quantifies environmental influences on vegetation, and the impacts of exotic woody plant invasion and anthropogenic nitrogen (N) deposition in a global biodiversity hotspot. The study was conducted in the montane grasslands of the Nilgiris, Western Ghats, and outlines potential management options for this region. Specifically, I examined (1) the role of environmental factors in influencing native plant distribution and ecosystem properties, (2) the status and impact of exotic shrub (Scotch broom, henceforth broom) invasion, (3) the role of disturbances in the success of broom, (4) the role of fire in restoring invaded grasslands, and (5) the impacts of terrestrial N loading on the grassland ecosystem. I used experiments and surveys to assess these. Distributions of several key species were explained by a few complex environmental gradients. In invaded-grasslands, broom populations consisted mainly of intermediate size and age classes, with no clear indication of population decline. Invasion negatively impacted plant community structure and drastically changed composition, favoring shade-tolerant and weedy species. However, invasion did not greatly alter ecosystem function. Fire successfully eliminated mature broom stands, but resulted in a short-term increase in broom seedling recruitment. At the end of 18 months, the fire effects on uninvaded-grasslands were not apparent, but there was no conclusive evidence of the formerly invaded patches attaining the composition of uninvaded-grasslands following burning. N fertilization strongly influenced soil N dynamics, and shoot N concentrations, but effects on aboveground production were weak. Surprisingly, N enrichment had positive effects on diversity in the short-term. It is clear that these grasslands need immediate management intervention to forestall degradation from invasion. Fire could be used to eliminate mature broom stands and deplete persistent seedbanks, which will facilitate colonization by shade-intolerant grassland plants. Active restoration should be mindful of environmental preferences of framework species. Long-term studies of the impacts of N deposition in the context of disturbances will help determine realistic critical thresholds and utilize disturbances to buffer the potential adverse effects of increasing N loading.

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Rocheman, Simon. « Validation expérimentale des outils de simulation des réactions nucléaires induites par les neutrons et les protons dans le silicium : irradiation d'une diode silicium et d'une caméra CCD ». Montpellier 2, 2008. http://www.theses.fr/2008MON20241.

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L'environnement spatial est un environnement radiatif principalement composé de protons. En plus de représenter un danger pour l'électronique, ces particules sont à l'origine de neutrons secondaires dans l'atmosphère. Lorsqu'elles traversent la matière, ces protons et ces neutrons peuvent provoquer des réactions nucléaires et ainsi créer des particules ionisantes. Par ce biais, les réactions nucléaires induites avec le silicium des composants électroniques peuvent provoquer des dysfonctionnements. Ces erreurs posent de réels problèmes dans les applications avioniques et spatiales. Des outils de simulation de réactions nucléaires ont été développés pour prévoir l'occurrence de ces erreurs. Des bases de données décrivant les réactions nucléaires neutron – silicium et proton – silicium entre 1 MeV et 200 MeV ont été générées à partir d'un code de calcul. L'objectif de ce travail de thèse est de valider ces bases de données. Dans un premier temps, des données expérimentales publiques de physique nucléaire nous ont permis de vérifier certains aspects des bases de données. Dans un second temps, nous avons irradié deux détecteurs à base de silicium (une diode et un capteur de caméra CCD) et confronté les simulations de ces expériences à l'aide des bases de données aux résultats expérimentaux
The spatial environment is a radiative environment mostly composed of protons. These particles are not only a danger for electronic component but they also leads to secondary neutrons in the atmosphere. When these protons and neutrons go through matter, they can induce nuclear reaction and then create ionizing particles. By this mean, nuclear reactions induced with silicon in electronic component can cause malfunctions. These mistakes are a real issue for applications in planes or space. Some nuclear reaction simulation tools have been developed to predict the error rate. For neutron - silicon and proton - silicon reactions between 1 and 200 MeV, databases have been generated by a nuclear physic code. The aim of this work of thesis is to validate the databases. In a first step, nuclear physic public experimental data have been used to verify some aspects of the databases. In addition, we irradiated two silicon based sensors (a diode and a CCD camera) and we confronted the simulation of these experiment using databases to experimental results

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Rossetto, Alan Carlos Junior. « Modeling and simulation of self-heating effects in p-type MOS transistors ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/186033.

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The complementary metal-oxide-semiconductor (CMOS) scaling process of the recent decades, coupled with new device structures and materials, has aggravated thermal problems and turned them into major reliability issues for deeply-scaled devices. As a consequence, the thermal transport dynamic and its impact on the device performance at submicron dimensions is established as a contemporary theme. In this context, a new selfconsistent electro-thermal particle-based device simulator for the study of self-heating effects in p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) based in silicon is developed and presented. The electrical module of the tool utilizes the Ensemble Monte Carlo method to perform the charge transport, whereas the thermal module evaluates the non-isothermal temperature profiles by solving the phonon energy balance equations for both acoustic and optical phonon baths. These temperature profiles are fed back into the electrical module, which adjusts the carriers’ scattering rate accordingly, thus, properly accounting for the device current capability degradation. The developed tool proved to be suitable for sub-100 nm device simulations, and it was used to perform relevant case study simulations of 24-nm channel length bulk and fully-depleted siliconon- insulator (FD-SOI) MOSFETs. General device parameters extracted from the simulations are qualitatively in agreement with the expected behavior, as well as data from the literature, ensuring the proper operation of the tool. Electro-thermal simulations of bulk and FD-SOI devices provided both acoustic and optical phonon temperature profiles across the transistor structure, as well as the heat generation map and the device power dissipation. Some results were also extracted via Joule heating thermal model, and they are presented for comparison. The current degradation due to self-heating was found to be significant for FD-SOI devices, but very modest for bulk ones. At a fixed bias point of VD =VG = 1:5 V, for instance, bulk devices presented a current variation of as much as 0:75%, whereas for FD-SOI devices it reached up to 8:82% for Tgate = 400 K. Hot spot acoustic (lattice) and optical phonon temperatures were extracted as a function of the applied bias for both topologies. The lattice temperature rise, for instance, exceeded 10 K and 150 K over the heat sink temperature for bulk and FD-SOI transistors, respectively, observing the same bias point and gate temperature presented earlier. The particle-based nature of the tool is also suitable for the study of the impact of trap activity in MOSFETs and its interplay with self-heating effects. Simulations of charge traps were used to analyze the statistical distribution of the current deviations in 25-nm bulk MOSFETs due to traps. The simulations showed that these deviations are exponentially-distributed, as experimentally observed and reported in the literature. Electro-thermal simulations of charge traps in bulk and FD-SOI transistors revealed that the largest degradation on the device current occurs when the effects of self-heating and trap activity take place simultaneously. At lower biases, the impact of charge traps dominates the current degradation, whereas the self-heating component prevails for larger biases.

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Kirkpatrick, Trevor Joe. « Impact of Specification Changes on Chloride Induced Corrosion Service Life of Virginia Bridge Decks ». Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34056.

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A model to determine the time to first repair and subsequent rehabilitation of concrete bridge decks exposed to chloride deicer salts that recognizes and incorporates the statistical nature of factors affecting the corrosion process is developed. The model expands on an existing deterministic model using statistical computing techniques, including resampling techniques such as the parametric and simple bootstrap. Emphasis was placed on the diffusion portion of the diffusion-cracking model, but advances can be readily included for the time for corrosion deterioration after corrosion initiation. Data collected from ten bridge decks built in Virginia between 1981 and 1994 was used to model the surface chloride concentration, apparent diffusion coefficient, and clear cover depth. Several ranges of the chloride corrosion initiation concentration, as determined from the available literature, were investigated. The time to first repair and subsequent rehabilitation predicted by the stochastic model is shorter than the time to first repair and subsequent rehabilitation predicted by the deterministic model, but is believed to more accurately reflect the true nature of bridge deck deterioration. The model was validated using historical service life data for 129 bridge decks built in Virginia between 1968 and 1972. The time to rehabilitation predicted for the set of bridge decks built between 1981 and 1994 by the stochastic model was approximately 13 years longer than the normalized time to rehabilitation projected for the bridge decks built between 1968 and 1972 using historical data. The increase in time to rehabilitation for the newer set of bridge decks was attributed to a reduction in the specified maximum water/cement ratio and increase in clear cover depth.
Master of Science

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Harrower, William Laughton. « Changes in trophic structure along a gradient of water availability in temperate montane grasslands ». Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/60600.

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Predators and plants are inextricably linked by the flow of energy in ecosystems. However, we still lack good descriptions of how predators affect the diversity, function, and stability of ecosystems under different environmental conditions. If water availability to plants modifies the interactions between predators and plants, and changes in these species interactions lead to a modification of trophic structure, then the direction and strength of trophic cascades must depend on the availability of water to plants. I use the unifying concept of the trophic cascade and an underlying gradient of water availability to investigate how species interactions in a montane grassland influence the diversity and function of these ecosystems. Firstly, I examine the distribution, abundance, and community composition of grassland songbirds. I show that as water becomes more abundant, the number of species increases more slowly than the number of songbird individuals. Second, I manipulate the presence of vertebrate predators along the gradient. I found that changes in the abundance of both songbirds, small mammals and their prey alters feeding behavior and restructures communities. These changes in intraguild predation work in conjunction with the metabolic demands of consumers to determine trophic structure and alter the strength of the trophic cascade in response to water availability. Finally, I show that predators mediate apparent competition between herbivore and detritivore food chains. In the montane grassland I studied, an apparent trophic cascade becomes established as detritus food chains emerge with increasing water availability. I show that the reversal of trophic control typical of ecosystems with allochthonous external subsidies does not occur with autochthonous detritus subsidies in my system. The direction of trophic control in the grazing food chain remains bottom-up, but the detritus food chain is instead controlled by generalist predators. These interactions between predators and plants regulate the diversity of plants and arthropod functional groups, and affect ecosystem functions such as plant biomass production and decomposition. My results show that as water availability to plants increases in semi-arid and temperate grasslands, food webs become shorter, broader, more reticulate, and are more resistant to the effect of species losses and drought.
Science, Faculty of
Botany, Department of
Graduate

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Hudebine, Damien. « Reconstruction moléculaire de coupes pétrolières ». Lyon, École normale supérieure (sciences), 2003. http://www.theses.fr/2003ENSL0250.

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La reconstruction des coupes pétrolières comprend l'ensemble des méthodes permettant de créer des mélanges de molécules à partir de données analytiques partielles. Dans le cadre de cette thèse, deux approches différentes ont été mises en place. La méthode de reconstruction stochastique suppose que les mélanges pétroliers peuvent être décrits par des distributions de blocs structuraux. Le choix des blocs et des distributions se fait en intégrant des expertises, le passage d'un jeu distributions à un mélange de molécules s'obtient par une méthode déchantillonnage Monte Carlo et l'optimisation des distributions est effectuée par un recuit simulé. Cette approche est adaptée aux coupes pétrolières les plus lourdes. La méthode de reconstruction par maximisation d'entropie est basée sur une bibliothèque prédéfinie de molécules dont les fractions molaires sont ajustées de manière à obtenir un mélange pétrolier cohérent avec les analyses. L'optimisation des fractions se fait en maximisant un critère entropique en présence de contraintes linéaires. Cette méthode est adaptée aux coupes pétrolières légères et moyennes. En dehors du développement et de l'amélioration de ces deux méthodes, plusieurs cas d'application ont été fournis. Pour les essences de FCC, l'utilisation de la reconstruction par maximisation d'entropie permet de retrouver la composition moléculaire d'une essence à partir de son analyse PIONA et de sa distillation simulée. Pour les gazoles LCO, le couplage reconstruction stochastique / maximisation d'entropie permet d'estimer des analyses manquantes à partir de la spéctrométrie de masse et de la distillation. Pour les résidus sous vide, la reconstruction stochastique est comparée aux travaux de Trauth. Dans tous ces cas, les applications valident les mélanges pétroliers en terme de propriétés physico-chimiques. L'étape suivante pourrait consister à tutiliser des études cinétiques moléculaires afin d'effectuer une validation en terme de propriétés réactives.

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Cauchemez, Simon. « Estimation des paramètres de transmission dans les modèles épidémiques par échantillonnage de Monte Carlo par chaine de Markov ». Paris 6, 2005. http://www.theses.fr/2005PA066572.

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Lu, Haiyan [Verfasser], Klaus [Forscher] Butterbach-Bahl et Ralf [Akademischer Betreuer] Kiese. « The influence of land management and simulated climate change on N2O and CH4 exchange of montane grassland soils ». Freiburg : Universität, 2016. http://d-nb.info/1124005196/34.

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