Tesi sul tema "Particles in cell (PIC)"
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1
Pierru, Julien. "Development of a Parallel Electrostatic PIC Code for Modeling Electric Propulsion". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/34597.
Abstract (sommario):
This thesis presents the parallel version of Coliseum, the Air Force Research Laboratory plasma simulation framework. The parallel code was designed to run large simulations on the world fastest supercomputers as well as home mode clusters. Plasma simulations are extremely computationally intensive as they require tracking millions of particles and solving field equations over large domains. This new parallel version will allow Coliseum to run simulations of spacecraft-plasma interactions in domain large enough to reproduce space conditions. The parallel code ran on two of the world fastest supercomputers, the NASA JPL Cosmos supercomputer ranked 37th on the TOP500 list and Virginia Tech's System X, ranked 7th. DRACO, the Virginia Tech PIC module to Coliseum, was modified with parallel algorithms to create a full parallel PIC code. A parallel solver was added to DRACO. It uses a Gauss-Seidel method with SOR acceleration on a Red-Black checkerboard scheme. Timing results were obtained on JPL Cosmos supercomputer to determine the efficiency of the parallel code. Although the communication overhead limits the code's parallel efficiency, the speed up obtained greatly decreases the time required to run the simulations. A speed up of 51 was reached on 128 processors. The parallel code was also used to simulate the plume expansion of an ion thruster array composed of three NSTAR thrusters. Results showed that the multiple beams merge to form a single plume similar to the plume created by a single ion thruster.Master of Science
2
Spicer, Randy Lee. "Validation of the DRACO Particle-in-Cell Code using Busek 200W Hall Thruster Experimental Data". Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/34460.
Abstract (sommario):
This thesis discusses the recent developments to the electric propulsion plume code DRACO as well as a validation and sensitivity analysis of the code using data from an AFRL experiment using a Busek 200 W Hall Thruster. DRACO is a PIC code that models particles kinematically while using finite differences schemes to solve the electric potential and field.
The DRACO code has been recently modified to improve simulation results, functionality and performance. A particle source has been added that uses the Hall Thruster device code HPHall as input for a source to model Hall Thrusters. The code is now also capable of using a non-uniform mesh that uses any combination of uniform, linear and exponential stretching schemes in any of the three directions. A stretched mesh can be used to refine simulation results in certain areas, such as the exit of a thruster, or improve performance by reducing the number of cells in a mesh. Finally, DRACO now has the capability of using a DSMC collision scheme as well as performing recombination collisions.
A sensitivity analysis of the newly upgraded DRACO code was performed to test the new functionalities of the code as well as validate the code using experimental data gathered at AFRL using a Busek 200 W Hall Thruster. A simulation was created that attempts to numerically recreate the AFRL experiment and the validation is performed by comparing the plasma potential, polytropic temperature, ion number density of the thruster plume as well as Faraday and ExB probe results. The study compares the newly developed HPHall source with older source models and also compares the variations of the HPHall source. The field solver and collision model used are also compared to determine how to achieve the best results using the DRACO code. Finally, both uniform and non-uniform meshes are tested to determine if a non-uniform mesh can be properly implemented to improve simulation results and performance.
The results from the validation and sensitivity study show that the DRACO code can be used to recreate a vacuum chamber simulation using a Hall Thruster. The best results occur when the newly developed HPHall source is used with a MCC collision scheme using a projected background neutral density and CEX collision tracking. A stretched mesh was tested and proved results that are as accurate as a uniform mesh, if not more accurate in locations of high mesh refinement.
Master of Science
3
Godar, Trenton J. "Testing of Two Novel Semi-Implicit Particle-In-Cell Techniques". Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1402492857.
4
Zahri, Abdellatif. "Développement du modèle PIC-MCC 2D : application aux décharges radiofréquence". Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1344/.
Abstract (sommario):
La méthode particle-In-Cell combinée avec la technique Monte-Carlo est une méthode bien établie pour la modélisation des plasmas, et elle est très utilisée pour simuler les réacteurs de faible pression pour les décharges radiofréquences (RF). Cette technique est une méthode simple et efficace permettant de résoudre une large variété de problèmes complexes impliquant un grand nombre de particules en mouvement sous l'action des forces engendrées par elles-mêmes ainsi que les forces externes appliquées. Le but de notre modèle est de comprendre et de caractériser le comportement du plasma à basse pression pour une géométrie à deux dimensions. Nous voulons comprendre ce qui se passe dans la gaine et en particulier le comportement des ions. Dans ce travail, nous décrivons les modèles PIC-MCC et leurs techniques indispensables à la construction de tels modèles. Nous avons choisi cette technique par sa qualité de description de la physique du plasma. En effet, cette technique fournit plus de précisions et sans aucune hypothèse sur la fonction de distribution des électrons ou des ions, ce qui est loin d'être le cas pour les autres modèles notamment les modèles fluides. Nous montrons certaines fonctions de distribution (densité et énergie des particules chargées, EEDF,. . . ), les caractéristiques électriques de la décharge seront étudiées. Ce travail s'inscrit dans le cadre du projet européen EMDPA: New Elemental and Molecular Depth Analysis of advanced materials by modulated radio frequency glow discharge time of flight mass spectrometry. Ce projet est financé par la commission européenne via le programme de recherche pour le développement technologiqueThe particle-in-cell method combined with the Monte Carlo techniques is a well established method for plasma modelling, and is widely used to simulate low pressure radiofrequency discharges. This technique is a simple and effective method for solving a wide variety of complex problems involving a large number of particles moving under the action of internal forces and external forces (electromagnetic fields. . . ) The purpose of our model is to understand and characterize the behaviour of low pressure plasmas in a two-dimensional geometry. We want to understand what is happening in the sheath and in particular the behaviour of the ions. In this work, we describe the PIC-MCC models and techniques needed to build such models. We chose this technique by its ability to describe correctly the plasma physics at low pressure. Indeed, this technique provides more details without any assumption on the distribution function of electrons or ions, which is far from being the case for other models including fluid models. We show some distribution functions (density and energy of charged particles, EEDF) ; the electrical characteristics of the discharge are presented. This work is part of the European project EMDPA : New Elemental and Molecular Depth Analysis of advanced materials by modulated radio frequency glow discharge time of flight mass spectrometry. This project is funded by the European Commission through the research program for technological development
5
Horken, Kempton M. "Isolation of photosynthetic membranes and submembranous particles from the cyanobacterium synechococcus PCC 7942". Virtual Press, 1996. http://liblink.bsu.edu/uhtbin/catkey/1036184.
Abstract (sommario):
Photosynthetic membranes were prepared from the cyanobacterium Synechococcus PCC 7942 with oxygen evolving specific activity of 250-300 µmoles 02/ mg chl/hr. The membranes retained activity with a half-life of 4-5 days when stored at 0°C, or when quickly frozen in liquid nitrogen, greater than 95% of the activity remained after 2 months. Attempts to purify homogeneous preparations of photosystem II complexes from these membranes by detergent extraction were unsuccessful as indicated by a lack of a significant increase in oxygen evolution specific activity of the detergent extracts. Photosynthetic membrane detergent extracts usually maintained the same oxygen evolution specific activity as the orginal membranes, and a considerable amount of Photosystem I activity (75 µmoles 02 consumed /mg chl/hr in the Mehler reaction) was still present. The donor side of the photosystem II particles in the detergent extract was intact since the artificial electron acceptor, 2,6-dichiorophenolindophenol (DCPIP), was reduced at a rate comparable to the oxygen evolving activity. All oxygen evolving activity of the detergent extracts was lost when ion-exchange chromatography was used to resolve the co-extracted photosystem II and photosystem I complexes.Department of Biology
6
Hammel, Jeffrey Robert. "Development of an unstructured 3-D direct simulation Monte Carlo/particle-in-cell code and the simulation of microthruster flows". Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0510102-153614.
7
Barsamian, Yann. "Pic-Vert : une implémentation de la méthode particulaire pour architectures multi-coeurs". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD039/document.
Abstract (sommario):
Cette thèse a pour contexte la résolution numérique du système de Vlasov–Poisson (modèle utilisé en physique des plasmas, par exemple dans le cadre du projet ITER) par les méthodes classiques particulaires (PIC pour "Particle-in-Cell") et semi-Lagrangiennes. La contribution principale de notre thèse est une implémentation efficace de la méthode PIC pour architectures multi-coeurs, écrite dans le langage C, dont le nom est Pic-Vert. Notre implémentation (a) atteint un nombre quasi-minimal de transferts mémoires avec la mémoire principale, (b) exploite les instructions vectorielles (SIMD) pour les calculs numériques, et (c) expose une quantité suffisante de parallélisme, en mémoire partagée. Pour mettre notre travail en perspective avec l'état de l'art, nous proposons une métrique permettant de comparer différentes implémentations sur différentes architectures. Notre implémentation est 3 fois plus rapide que d'autres implémentations récentes sur la même architecture (Intel Haswell)In this thesis, we are interested in solving the Vlasov–Poisson system of equations (useful in the domain of plasma physics, for example within the ITER project), thanks to classical Particle-in-Cell (PIC) and semi-Lagrangian methods. The main contribution of our thesis is an efficient implementation of the PIC method on multi-core architectures, written in C, called Pic-Vert. Our implementation (a) achieves close-to-minimal number of memory transfers with the main memory, (b) exploits SIMD instructions for numerical computations, and (c) exhibits a high degree of shared memory parallelism. To put our work in perspective with respect to the state-of-the-art, we propose a metric to compare the efficiency of different PIC implementations when using different multi-core architectures. Our implementation is 3 times faster than other recent implementations on the same architecture (Intel Haswell)
8
Doche, Antoine. "Particle acceleration with beam driven wakefield". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX023/document.
Abstract (sommario):
Les accélérateurs par onde de sillage plasma produites par faisceaux de particules (PWFA) ou par faisceaux laser (LWFA) appartiennent à un nouveau type d’accélérateurs de particules particulièrement prometteur. Ils permettent d’exploiter des champs accélérateurs jusqu’à cent Gigaélectronvolt par mètre alors que les dispositifs conventionnels se limitent à cent Megaélectronvolt par mètre. Dans le schéma d’accélération par onde de sillage plasma, ou par onde de sillage laser, un faisceau de particules ou une impulsion laser se propage dans un plasma et créé une structure accélératrice dans son sillage : c’est une onde de densité électronique à laquelle sont associés des champs électromagnétiques dans le plasma. L’un des principaux résultats de cette thèse a été la démonstration de l’accélération par onde de sillage plasma d’un paquet distinct de positrons. Dans le schéma utilisé, un plasma de Lithium était créé dans un four, et une onde plasma était excitée par un premier paquet de positrons (le drive ou faisceau excitateur) et l’énergie était extraite par un second faisceau (le trailing ou faisceau témoin). Un champ accélérateur de 1,36 GeV/m a ainsi été obtenu durant l’expérience, pour une charge accélérée typique de 40 pC. Nous montrons également ici la possibilité d’utiliser différents régimes d’accélération qui semblent très prometteurs. Par ailleurs, l’accélération de particule par sillage laser permet quant à elle, en partant d’une impulsion laser femtoseconde de produire un faisceau d’électron quasi-monoénergétique d’énergie typique de l’ordre de 200 MeV. Nous présentons les résultats d’une campagne expérimentale d’association de ce schéma d’accélération par sillage laser avec un schéma d’accélération par sillage plasma. Au cours de cette expérience un faisceau d’électrons créé par laser est refocalisé lors d’une interaction dans un second plasma. Une étude des phénomènes associés à cette plateforme hybride LWFA-PWFA est également présentée. Enfin, le schéma hybride LWFA-PWFA est prometteur pour optimiser l’émission de rayonnement X par les électrons du faisceau de particule crée dans l’étage LWFA de la plateforme. Nous présentons dans un dernier temps la première réalisation expérimentale d’un tel schéma et ses résultats prometteursPlasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed
9
Drouin, Mathieu. "Vers la simulation particulaire réaliste de l'interaction laser-plasma surcritique : conception d'un schéma implicite avec amortissement ajustable et fonctions de forme d'ordre élevé". Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2009. http://tel.archives-ouvertes.fr/tel-00442715.
Abstract (sommario):
Le caractère éminemment cinétique et hors équilibre de l'interaction laser-plasma et du transport électronique nécessite de résoudre le système complet des équations de Vlasov-Maxwell. Cette thèse se concentre sur les méthodes PIC (‘‘Particle-In-Cell''), et vise à en accroître le régime de fonctionnement. Tout d'abord, nous présentons l'analyse de stabilité linéaire d'un algorithme PIC explicite incluant l'effet de la discrétisation spatio-temporelle. Cette analyse met en exergue l'instabilité d'aliasing, que nous relions au problème, plus général, du chauffage numérique dans les codes PIC en régime surcritique. Nous montrons l'influence bénéfique de la montée en ordre du facteur de forme pour réduire ce chauffage, permettant ainsi d'atteindre des régimes de densité jusque là inaccessibles. Les codes PIC implicites ne sont pas soumis aux mêmes contraintes de stabilité que leurs équivalents explicites. En particulier nous ne sommes plus tenus de résoudre les modes haute fréquence électroniques. Une telle propriété est particulièrement précieuse lorsqu'on modélise l'interaction entre un laser à ultra-haute intensité et un plasma fortement sur-critique. Nous présentons ici l'extension relativiste de la méthode implicite dite directe, en y incluant un paramètre d'amortissement ajustable et des facteurs de forme d'ordre élevé. Ce formalisme a été implémenté dans le code ELIXIRS, 2D en espace et 3D en vitesse. Ce code est validé sur de nombreux problèmes de physique des plasmas, allant de l'expansion d'un plasma à une ou deux températures électroniques, à l'interaction laser-plasma à haut-flux, en passant par les instabilités ‘‘deux faisceaux'' et de filamentation en régime relativiste. Nous montrons notamment la capacité du code à capturer les principales caractéristiques de l'interaction laser-plasma, malgré une discrétisation spatio-temporelle dégradée, autorisant ainsi des gains substantiels en temps de calcul.
10
YADAV, MONIKA. "SOME ASPECTS OF LASER-PLASMA INTERACTION FOR ELECTRON ACCELERATION". Thesis, DELHI TECHNOLOGICAL UNIVERSITY, 2021. http://dspace.dtu.ac.in:8080/jspui/handle/repository/18736.
Abstract (sommario):
This thesis focuses on investigation of laser-plasma interaction relevant to
electron acceleration to high energies. This work explores various ideas for
producing an energetic and good quality electron beam from laser wakefield
acceleration (LWFA) in plasmas. In LWFA, a high-intensity laser pulse excites a
plasma wave, which propagates behind the laser pulse with the equal speed of the
laser group velocity. For efficient accelerations, electrons should be injected into
the wakefield. Thus, the wakefield evolution and electron injection both are quite
important aspects in LWFA. In order to draw the maximum output from the
wakefield structure, which is called wakefield bubble in case of high-intensity
laser, the basic understanding behind the factors controlling electron injection into
wake structure must be very clear. This thesis work focus toward controlling the
electron beam quality by understanding the factors affecting bubble wake
evolution. The dependence of beam energy and the beam quality on the shape of
the bubble is the main motivation behind this investigation. Particle-in-cell (PIC)
simulations are conducted to study the bubble dynamics for optimum electron
accelerations. A good quality electron bunch with pC to nC charge are obtained
with current laser-plasma parameters. During LWFA, generation of wakefield
results in variation of refractive index that may distort the laser pulse shape. Thus,
the laser pulse shape may be a significant factor to control the electron beam
parameters in LWFA. Various shapes such as q-Gaussian laser pulse and
flattened-Gaussian laser pulse have been taken into account to observe the laser
pulse effect on electron beam parameters in LWFA. The implications of laser
pulse shape was shown to control and optimize the bunch charge as well as the
bunch energy. Our insights into the acceleration process might be quite
supportive in the future optimization of electron beam stability and quality. The
electron bunch generated by LWFA could be used to obtain femtosecond x-rays
and subsequent applications in medical sciences.
11
Drouin, Mathieu. "Vers la simulation particulaire réaliste de l'interaction laser-plasma surcritique : conception d'un schéma implicite avec amortissement ajustable et fonctions de forme d'ordre élevé". Phd thesis, Cachan, Ecole normale supérieure, 2009. https://theses.hal.science/tel-00442715/fr/.
Abstract (sommario):
Le caractère éminemment cinétique et hors équilibre de l'interaction laser-plasma et du transport électronique nécessite de résoudre le système complet des équations de Vlasov-Maxwell. Cette thèse se concentre sur les méthodes PIC (‘‘Particle-In-Cell''), et vise à en accroître le régime de fonctionnement. Tout d'abord, nous présentons l'analyse de stabilité linéaire d'un algorithme PIC explicite incluant l'effet de la discrétisation spatio-temporelle. Cette analyse met en exergue l'instabilité d'aliasing, que nous relions au problème, plus général, du chauffage numérique dans les codes PIC en régime surcritique. Nous montrons l'influence bénéfique de la montée en ordre du facteur de forme pour réduire ce chauffage, permettant ainsi d'atteindre des régimes de densité jusque là inaccessibles. Les codes PIC implicites ne sont pas soumis aux mêmes contraintes de stabilité que leurs équivalents explicites. En particulier nous ne sommes plus tenus de résoudre les modes haute fréquence électroniques. Une telle propriété est particulièrement précieuse lorsqu'on modélise l'interaction entre un laser à ultra-haute intensité et un plasma fortement sur-critique. Nous présentons ici l'extension relativiste de la méthode implicite dite directe, en y incluant un paramètre d'amortissement ajustable et des facteurs de forme d'ordre élevé. Ce formalisme a été implémenté dans le code ELIXIRS, 2D en espace et 3D en vitesse. Ce code est validé sur de nombreux problèmes de physique des plasmas, allant de l'expansion d'un plasma à une ou deux températures électroniques, à l'interaction laser-plasma à haut-flux, en passant par les instabilités ‘‘deux faisceaux'' et de filamentation en régime relativiste. Nous montrons notamment la capacité du code à capturer les principales caractéristiques de l'interaction laser-plasma, malgré une discrétisation spatio-temporelle dégradée, autorisant ainsi des gains substantiels en temps de calculLaser-plasma interaction and electronic transport are pure kinetic processes thus requiring to solve the complete Vlasov-Maxwell system of equations. This thesis focuses on PIC (‘‘Particle-In-Cell'') methods, and is intended to widen the operating regime of such methods. First, we present the linear stability analysis of an explicit PIC algorithm including spatial and temporal step size effects. This study highlights the aliasing instability, which we link to the more intricate issue of numerical heating in PIC codes in the overcritical regime. We show the beneficial influence of using an increasingly high order weight function to drop this heating, thereby allowing to reach overcritical regimes relevant for comparison with experiments. Implicit PIC codes are not submitted to the constraints affecting their explicit counterparts. Particularly we can relax the need to solve high frequency electronic modes. Such a property is extremely valuable when we model the interaction between a high intensity laser and a highly overcritical plasma. Here, we give the relativistic extension of the direct implicit method, provided with an adjustable damping parameter and high order weight functions. This formalism was implemented in the code ELIXIRS, 2D in space and 3D in velocity. This code was validated for various plasma physics configurations, among them one or two electronic temperatures plasma expansions, high intensity laser-plasma interaction, and also beam-plasma instabilities in the relativistic regime. Especially, we prove the capability of the code to catch the main characteristics of the aforementioned phenomena, despite a crude spatio-temporal discretisation, thus providing significant gains of computation time
12
Nakata, Michael Takeshi. "Simulating the FTICR-MS Signal of a Decaying Beryllium-7 Ion Plasma in a 2D Electrostatic PIC Code". Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3370.pdf.
13
Ferri, Julien. "Étude des rayonnements Bétatron et Compton dans l'accélération d'électrons par sillage laser". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX094/document.
Abstract (sommario):
Une impulsion laser ultra-courte et ultra-intense se propageant dans un gaz de faible densité est capable d'accélérer une partie des électrons de ce gaz à des énergies relativistes, de l'ordre de quelques centaines de MeV, sur des distances de seulement quelques millimètres. Pendant leur accélération et dû à leur mouvement transverse, ces électrons émettent de plus un rayonnement X fortement collimaté et dirigé vers l'avant appelé rayonnement bétatron. Les caractéristiques de cette source la rendent intéressante pour son utilisation en imagerie à ultra-haute résolution.Dans ce manuscrit, nous explorons trois axes de travail autour de cette source à l'aide de simulations réalisées avec les codes Particle-In-Cell CALDER et CALDER-Circ. Nous commençons ainsi par étudier la création d'une source bétatron avec des impulsions laser de durée picoseconde et d'énergie kilojoule, donc plus longues et plus puissantes que celles habituellement utilisées par la communauté. Nous montrons que malgré les paramètres inhabituels de ces impulsions lasers il est toujours possibles de générer des sources X, et ce dans deux régimes différents.Ensuite, afin de comprendre une partie des différences généralement observées entre expériences et simulations, nous montrons dans une autre étude que l'utilisation dans les simulations de profils lasers réalistes au lieu de profils parfaitement Gaussiens dégrade fortement les performances de l'accélérateur laser-plasma et de la source bétatron. De plus, ceci conduit à un meilleur accord qualitatif et quantitatif avec l'expérience.Enfin nous explorons plusieurs techniques pour augmenter l'émission X basées sur une manipulation des profils de plasmas utilisés pour l'accélération. Nous trouvons que l'utilisation d'un gradient transverse ou d'une marche de densité conduisent tous deux à une augmentation de l'amplitude du mouvement transverse des électrons, et donc de l'énergie émise par la source bétatron. Alternativement, nous montrons que cet objectif peut-être atteint par la transition d'un régime de sillage laser vers un régime d'accélération par sillage plasma induit par une augmentation de la densité. L'accélération des électrons est optimisée dans le premier régime, tandis que l'émission X est fortement favorisée dans le secondAn ultra-short and ultra-intense laser pulse propagating in a low-density gas can accelerate in its wake a part of the electrons ionized from the gas to relativistic energies of a few hundreds of MeV over distances of a few millimeters only. During their acceleration, as a consequence of their transverse motion, these electrons emit strongly collimated X-rays in the forward direction, which are called betatron radiations. The characteristics of this source turn it into an interesting tool for high-resolution imagery.In this thesis, we explore three different axis to work on this source using simulations on the Particles-In-Cells codes CALDER and CALDER-Circ. We first study the creation of a betatron X-ray source with kilojoule and picosecond laser pulses, for which duration and energy are then much higher than usual in this domain. In spite of the unusual laser parameters, we show that X-ray sources can still be generated, furthermore in two different regimes.In a second study, the generally observed discrepancies between experiments and simulations are investigated. We show that the use of realistic laser profiles instead of Gaussian ones in the simulations strongly degrades the performances of the laser-plasma accelerator and of the betatron source. Additionally, this leads to a better qualitative and quantitative agreement with the experiment.Finally, with the aim of improving the X-ray emission, we explore several techniques based on the manipulation of the plasma density profile used for acceleration. We find that both the use of a transverse gradient and of a density step increases the amplitude of the electrons transverse motions, and then increases the radiated energy. Alternatively, we show that this goal can also be achieved through the transition from a laser wakefield regime to a plasma wakefield regime induced by an increase of the density. The laser wakefield optimizes the electron acceleration whereas the plasma wakefield favours the X-ray emission
14
Donderici, Burkay. "Time-Domain Solvers for Complex-Media Electrodynamics and Plasma Physics". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1216744283.
15
Penkal, Bryan James. "Steps in the Development of a Full Particle-in-Cell, Monte Carlo Simulation of the Plasma in the Discharge Chamber of an Ion Engine". Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1367586856.
16
Revel, Adrien. "Modélisation des plasmas magnétisés. Application à l'injection de neutres pour ITER et au magnétron en régime impulsionnel haute puissance". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112083/document.
Abstract (sommario):
Un plasma est défini comme un gaz partiellement ou totalement ionisé. Bien que très présent dans l'univers visible, les plasmas naturels sont rares sur Terre. Cependant, ils représentent un intérêt majeur pour les industries et les instituts de recherche (traitement de surface, propulsion spatiale). Toutefois, la compréhension du comportement d'un plasma est complexe et fait appel à de nombreux domaines de la physique. De plus, ces plasmas peuvent être magnétisé i.e. lorsqu'un champ magnétique extérieur ou induit influence significativement la trajectoire des particules : r/L<1 où r est le rayon de Larmor et L la longueur caractéristique du système. Ce travail de thèse s'intéresse à la modélisation du comportement du plasma présent dans deux dispositifs : l'accélérateur de l'Injecteur de Neutres (IdN) rapides d'ITER et le magnétron en régime DC ou HiPIMS. La réalisation de la fusion nucléaire sur Terre fait actuellement l'objet de nombreuses recherche dans le monde. Du fait de l'énergie nécessaire au franchissement de la barrière de répulsion coulombienne, le plasma doit être confiné. Dans le cas d'ITER, le confinement est réalisé par de puissant champ magnétique. Cependant, pour atteindre les conditions nécessaires aux réactions de fusion, notamment en température, un injecteur de particules neutres à haute énergie (1MeV) est nécessaire. L'accélération de ces particules est une phase critique dans la création du faisceau de neutres et elle représente un défi technologique qui fait l'objet d'une étude dans ce travail de thèse. Le magnétron est un procédé industriel permettant la réalisation de couches minces par pulvérisation cathodique. Les ions créés par un plasma de décharge arrachent les atomes de la cathode qui se déposent sur l'anode. Le champ magnétique créé par des aimants permanents piège les électrons à proximité de la cathode augmentant l'efficacité du dispositif. Le comportement du plasma magnétron est ainsi étudié en régime continu ou pulsé ainsi que l'apparition de structures auto-organisées en rotation autour de l'axe du magnétron dans certaines conditions. Afin d'étudier ces dispositifs, plusieurs programmes de simulation numérique ont été développés. La méthode Paticle-In-Cell a été choisie car elle permet de prendre en compte la charge d'espace des particules de manière auto-cohérente. Diverses techniques (technique de collision nulle, Monte Carlo Collision, a posteriori Monte Carlo) et améliorations (maillage non uniforme, projections de charges au troisième ordre) ont été développées et implémentées. De plus, une méthode originale, Pseudo 3D, permettant un traitement à trois dimension du magnétron a été utilisées avec succès. Enfin, ces programmes ont été parallélisés afin de réduire le temps de calculA plasma is defined as a partially or completely ionized gas. Even though, they are very present in the visible universe, natural plasmas are rare on Earth. However, they are a major interest for industries and research institutes (surface treatment, spatial propulsion). Nevertheless, the understanding of plasma behavior is complicated because of the numerous physical fields involved. Moreover, theses plasmas can be magnetized, i.e., a magnetic field, external or induced, affects significantly the particle trajectories: r/L<1 where r is the Larmor radius and L the typical length of the system. This thesis is focused on the plasma modeling in two device: the accelerator of the ITER's neutral beam injector (NBI) and the magnetron in DC or HiPIMS regime. The feasibility of nuclear fusion on Earth is subject of numerous research around the world. Because of the energy necessary to get over the Coulomb barrier, the plasma must be confined. For ITER, the confinement is achieved by intense magnetic fields. However, to reach the required conditions of nuclear fusion reactions, especially in temperature, a high energy (1MeV) neutral beam injector is needed. The particle acceleration is a critical part in the creation of the neutral beam and it represents a technical challenge which is studied in this thesis work. The magnetron is an industrial process for creating thin film by physical sputtering. The ions created by a plasma discharge tear the atoms out of the cathode which are then deposited on the anode. The magnetic field created by permanent magnets trap the electrons near the cathode improving the process efficiency. The plasma behavior inside the magnetron is studied in direct and pulsed current as well as the appearance of self-organized structures in rotation around the magnetron axis. To study these devices, several program of numerical simulation have been developed. The Particle-In-Cell methode has been chosen because it takes into account, self-consistently, the space charge of the particules. Several techniques (null collision technique, Monte Carlo Collision, a posteriori Monte Carlo) and improvement (Non uniform mesh, third order charge projection) have been developed and implemented. Moreover, an original method, Pseudo 3D, allowing a three dimensional study of the magnetron, has been used with success. Finally, these programs have been parallelized to reduce the computation time
17
Spirkin, Anton M. "A three-dimensional particle-in-cell methodology on unstructured Voronoi grids with applications to plasma microdevices". Link to electronic dissertation, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050506-145257/.
18
Faure, Nicolas. "Modélisation électromagnétique en présence de charges d’espace : application à l’étude de tubes électroniques de type magnétron". Limoges, 2006. http://aurore.unilim.fr/theses/nxfile/default/c0847439-d574-4838-b1c8-f9b3ab431dbb/blobholder:0/2006LIMO0022.pdf.
Abstract (sommario):
Ce travail est basé sur la modélisation électromagnétique en présence de charges d’espace. Nous avons d’une part développé un code Particle-In-Cell cartésien avec un algorithme de type Finite Difference Time Domain. Après réalisation et validation d’un code PIC 2D sur une structure de type rising sun, nous avons étendu puis validé le code en 3D. D’autre part, nous avons étudié les aspects statique et électromagnétique inhérents au fonctionnement de tubes électroniques de type magnétron. Cette approche nous a permis de mieux cerner l’influence de divers éléments comme les straps et d’émettre in fine certaines règles pour facilité la synthèse de nouvelles sources. Cette étude permet de disposer de codes pour optimiser ou développer de nouvelles sourcesThis work deals with electromagnetic modelisation in the presence of space charges. On the one hand, we developed a Particle-In-Cell code with an algorithm of the Finite Difference Time Domain type. After realisation and validation of a 2D PIC code on a rising sun structure, we extended then validated the code in 3D. In addition, we studied the inherent static and electromagnetic aspects in the electronics tubes of magnetron type operation. This approach allowed us best encircled influence of various elements like the straps and to emit at last certain rules to optimise the synthesis of new sources. This study makes it possible to have codes to optimise or develop new sources
19
Sprenkle, Robert Tucker. "Ion Friction at Small Values of the Coulomb Logarithm". BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6979.
Abstract (sommario):
We create a dual-species ultracold neutral plasma (UNP) by photo-ionizing Yb and Ca atoms in a dual-species magneto-optical trap. Unlike single-species UNP expansion, these plasmas are well outside of the collisionless (Vlasov) approximation. We observe the mutual interaction of the Yb and Ca ions by measuring the velocity distribution for each ion species separately. We model the expansion using a fluid code including ion-ion friction and compare with experimental results to obtain a value of the Coulomb logarithm of Λ= 0.04.
20
Pebernet, Laura. "Etude d'un modèle Particle-In-Cell dans une approximation Galerkin discontinue pour les équations de Maxwell-Vlasov : recherche d'une solution hybride non conforme efficace". Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1080/.
Abstract (sommario):
Cette thèse présente l'étude et le développement d'un outil de simulation numérique efficace pour la modélisation de l'interaction plasma/micro-ondes, à partir d'un solveur électromagnétique basé sur une approximation Galerkin Discontinue (GD). Le travail est organisé en deux parties principales. Tout d'abord, nous développons un modèle Particle-In-Cell (PIC) approprié au schéma GD. Pour cela, d'une part, nous proposons un modèle de correction hyperbolique pour la prise en compte de la loi de conservation de la charge et, d'autre part, nous intégrons des modèles physiques propres au plasma tels que les sources micro-ondes de forte puissance, les surfaces d'émission de particules et les faisceaux d'électrons. Ensuite, nous nous orientons vers la recherche de performances optimales pour le couplage Maxwell-Vlasov afin d'augmenter l'efficacité et la taille des applications à traiter. Cette recherche conduit à l'étude d'une hybridation non conforme de méthodes pour résoudre le problème Maxwell-Vlasov. Dans un premier temps, nous travaillons sur une méthode hybride entre différents schémas numériques pour la résolution d'un problème Maxwell 1D sur des maillages non conformes. Dans un second temps, nous nous intéressons au cas d'un problème 2D en mode TE, dans l'optique d'introduire un modèle PIC. Finalement, nous réalisons une hybridation FDTD/FDTD sur deux maillages non coïncidents pour les équations Maxwell-Vlasov 2DThis thesis presents the study and the development of an efficient numerical simulation's tool for the modeling of plasma/microwave interaction in an electromagnetic software based upon a Discontinuous Galerkin (DG) scheme. This work is organized following two main steps. First, we develop a Particle-In-Cell (PIC) model appropriate for DG scheme. For this, on the one hand, we propose a hyperbolic corrector method to take into account the charge conservation law and, on the other hand, we integrate physical plasma models such as high power microwave sources, emission particles surfaces and electrons beams. Then, we propose also optimal performances for the coupling of Maxwell-Vlasov equations in order to increase the efficiency and the size of the applications to treat. This leads to study a non conformal hybridization of methods to solve the Maxwell-Vlasov problem. In the first time, we work on a hybrid method between different numerical schemes to solve a 1D Maxwell problem on non conformal meshes. In the second time, we interest in a 2D TE Maxwell problem, in order to introduce a PIC model. Finally, we realise a FDTD/FDTD hybridization on two non coincident meshes for the 2D Maxwell-Vlasov system
21
Bourgeois, Pierre-Louis. "Modélisation de sources X générées par interaction laser-plasma en régime relativiste". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX073.
Abstract (sommario):
Lors de la propagation d'une impulsion laser ultra courte, ultra intense dans un gaz de faible densité, un plasma est créé et une partie des électrons vont pouvoir être accélérés grâce à la technique de sillage laser à des énergies de plusieurs GeV en quelques centimètres.Ces électrons, lors de leur accélération, émettent un rayonnement X appelé bêtatron, qui est fortement collimaté et possède de très bonnes propriétés spatiales et temporelles, lui donnant de nombreuses applications dont l'imagerie ultra-haute résolution.Dans cette thèse, on étudie comment améliorer les outils numériques utilisés pour simuler ces phénomènes physiques : les codes Particle-In-Cell (CALDER). On s'intéresse notamment à un artefact numérique appelé rayonnement Cherenkov numérique, qui survient lorsque les particules accélérés se déplacent à des vitesses proches de la vitesse de la lumière dans le vide.On démontre que cet artefact a un effet néfaste sur le comportement du faisceau d'électrons accélérés, en particulier sur son mouvement transverse, ce qui conduit à des erreurs importantes sur le calcul du rayonnement bêtatron à partir des simulations PIC. On propose alors une nouvelle approche pour limiter l'impact de ce rayonnement Cherenkov numérique sur les simulations d'accélération par sillage laser en modifiant la méthode d'interpolation des champs habituellement utilisée dans un code PIC. Les résultats obtenus avec cette nouvelle technique mettent en évidence une nette amélioration de la modélisation du mouvement des électrons, qui se rapproche du comportement attendu théoriquement. Fort de ces premiers résultats, d'autres applications de cette technique sont ensuite explorées, pour améliorer la modélisation des sources bêtatron, de l'accélération par laser dans le vide ou de l'accélération directe par laser.La plus grande précision sur le calcul du mouvement transverse des particules qu'apporte cette nouvelle méthode permet d'améliorer les résultats mais aussi d'étudier des phénomènes physiques aux effets subtils qui sont autrement cachés par le bruit numérique des simulationsWhen an ultra-short ultra-intense laser impulsion propagates through a low density gas jet, a plasma is created and a bunch of electrons can be accelerated through laser wakefield acceleration to Gev energies in only a few centimetres. Those accelerated electrons then emit what is called Betatron radiation: a highly focused X-ray source with extremely good spatial and temporal properties, which has a lot of possible applications including ultra-high resolution imaging.In this thesis, we investigate possible improvements to one of the main numerical tools used to simulate those phenomenons: the Particle-In-Cell codes (CALDER). We have especially studied a numerical artefact called the numerical Cherenkov radiation, that occurs when relativistic particles move at speeds aproaching the speed of light in a vaccuum.We show that this artefact has a negative impact on the behaviour of the accelerated electron beam, especially on its transverse motion, which leads to important errors on the betatron radiation calculated using PIC simulations.We then introduce a new approach to mitigate the impact of this numerical Cherenkov radiation on laser wakefield acceleration simulation with a simple modification of the electromagnetic field interpolation method used in PIC codes. The results obtained with this new technique show a meaningful improvement on the electron motion wich becomes close to the theoretically expected behaviour.We then explore other possible applications for this new technique, notably improving the modelization of betatron sources, vacuum laser acceleration or direct laser acceleration.The improvement of the computation of the particles transverse motion thanks to this new method leads to more accurate results but also enables us to study physical phenomenon with subtle effects that would otherwise be hidden among the numerical noise of the simulation
22
Hägg, Martin. "Theoretical analysis and simulation of microwave-generation from a coaxial vircator". Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316595.
Abstract (sommario):
High-power microwave, HPM, systems can be used as non-lethal weapons with the ability to destroy or disturb electronics, by damaging internal circuits and inducing high currents. Today microwave sources are being developed with peak powers exceeding 1 GW, one of these devices is the vircator, a narrowband source which is unique to the HPM community. In order to understand and develop microwave sources like the vircator it is necessary to have computer models, as simulations gives an invaluable understanding of the mechanisms involved during operation, saving time and development costs. This thesis presents the results from a theoretical analysis and a simulation study using a well known electromagnetic particle-in-cell code, Computer Simulation Technology Particle Studio. The results are then compared to measured data from a HPM system, the Bofors HPM Blackout. The results show that CST PS can be used to design and study the coaxial vircator with good results.
23
Blaclard, Guillaume. "Ultra-High Intense Laser on Dense Plasmas : from Periodic to Chaotic Dynamics". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS133.
Abstract (sommario):
L'émergence des lasers ultra-brefs et ultra-intenses a permis le développement d'une nouvelle branche de la physique encore largement inexplorée : la physique UHI (pour Ultra-High Intensity). Lors de la réflexion d'un tel laser sur une cible solide, l'intensité au foyer I₀ peut atteindre des valeurs aussi importantes que 10¹⁸⁻²⁰ W.cm⁻², suffisamment pour ioniser complétement la matière. Le plasma ainsi formé se détend sur une longueur caractéristique Lg, nommée longueur de gradient. Quand Lg <<λ₀ (longueur d'onde du laser), le plasma dense se comporte comme un miroir de qualité optique capable de réfléchir spéculairement la lumière incidente : c'est un miroir plasma. Ce système physique remarquable peut être utilisé dans de multiples applications principalement comme source compacte de faisceaux de particules à hautes charges et hautes énergies ou de lumière intense, principalement ultraviolet ou X, grâce à un phénomène de génération d'harmoniques d'ordres élevés. Le bon contrôle de ces sources nécessite de clairement identifier les différents mécanismes de couplage entre lumière et matière en jeu lors de l'interaction. Dans ce manuscrit, cela est rendu possible grâce à de précises simulations de type Particle-In-Cell (PIC) réalisées avec le code WARP+PXR. Ce nouveau code emploie un solveur pseudo-spectral pour résoudre les équations de Maxwell. Celui-ci améliore grandement la précision des simulations et notamment des émissions harmoniques et électroniques, que les solveurs plus standards ne parviennent à décrire, même à hautes résolutions. Grâce à des simulations WARP+PXR, nous avons étudié l'influence de Lg sur les observables expérimentales que sont les émissions de lumière et de particules, quand un laser de puissance (I₀ = 10¹⁹ W.cm⁻²) se réfléchit sur un plasma dense. Notre étude révèle une claire transition entre un mécanisme périodique en temps et un processus chaotique quand l'interface devient plus lisse. Nous nous sommes principalement concentrés sur le deuxième mécanisme, appelé chauffage stochastique pour lequel des études en profondeur vont être menées en fonction de différents paramètres d'interaction. Dans ce régime, les électrons de la partie sous-dense du plasma subissent une dynamique chaotique dans l'onde stationnaire formée par la superposition des ondes incidente et réfléchie, ce qui leur permet d'absorber une importante part de l'énergie laser. La nature fondamentale de la dynamique en jeu est révélée grâce aux équations du mouvement au sein des deux ondes que l'on peut réduire en équations de pendules forcés (comme celui de Kapitza), systèmes bien connus comme chaotiques. Cette correspondance apporte une intuition physique profonde sur le comportement des électrons pour différentes configurations laser. Ceci nous permet in fine de prédire les principaux aspects du chauffage stochastiqueThe advent of high power femtosecond lasers has paved the way to a promising and still largely unexplored branch of physics called Ultra-High Intensity physics (UHI). Once such a laser is focused on a solid target, the laser intensity I₀ can reach values as large as 10¹⁸⁻²⁰ W.cm⁻², for which matter is fully ionized. The plasma thus formed expands towards vacuum on a spatial scale characterized by a quantity Lg called the density gradient scale length. When Lg << λ₀ (laser wavelength), the dense plasma therefore acts as an optical mirror that specularly reflects the incident light: it is a plasma mirror. This remarkable physical system can be used in many scientific applications as compact source of high-energy and high-charge particle beams (electrons, ions) or bright source of radiations ranging from extreme ultraviolet-rays to X-rays through high harmonic generation processes. In order to finely control these sources, it is required to properly identify the different coupling mechanisms between light and matter at play during the interaction. In this manuscript, this has been made possible by performing accurate Particle-In-Cell (PIC) simulations with the WARP+PXR code. This recently developed code advances Maxwell’s equations in Fourier space, which proves to correctly model harmonic/electron emissions that standard codes fail to accurate describe even at high resolution. Based on WARP+PXR PIC simulations, we investigate the influence of Lg on the experimentally observed emission of light and particles, when a high-power laser pulse (I₀ = 10¹⁹ W.cm⁻²) reflects off a dense plasma. Our study reveals an unambiguous transition from a temporally periodic mechanism to a chaotic process as the interface becomes smoother. In particular, the latter mechanism, named stochastic heating, is fully characterized as well as its domain of validity in terms of laser-plasma parameters. In this regime, electrons in the underdense part of the gradient are exposed to the standing wave formed in front of the overcritical part of the plasma by superposition of incidence and reflected beams. While evolving in the two waves, electrons behave chaotically and absorb an important fraction of the laser energy. The nature of the interaction is revealed by reducing the equations of motion of particles in two waves to physical systems, such Kapitza’s pendulum, well-known to exhibit chaos. That correspondence gives deep physical intuitions on how electrons behave in different laser configurations, which allows us to predict major features of stochastic heating
24
Betar, Homam. "Kinetic Effects in Magnetic Reconnection". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0043.
Abstract (sommario):
Les plasmas sont des systèmes gazeux d'ions et d'électrons qui interagissent avec les champs électromagnétiques et affichent des propriétés collectives. Parmi ceux-ci, il y a la notion de "connexion" de lignes magnétiques. Ceci exprime le fait que, dans des régimes dans lesquels les particules chargées s'enroulent suffisamment vite le long des lignes d'induction magnétique, ces dernières sont liées au mouvement du plasma massif et acquièrent une identité topologique qui leur interdit de se rompre, se croiser et se reconnecter. Cette identité topologique peut cependant être localement violée grâce à un certain nombre d'effets cinétiques, comme les collisions entre les particules, lorsque les courants dans le plasma sont suffisamment intenses : on parle de “reconnexion magnétique”. La reconnexion magnétique est un ingrédient important de l'auto-organisation du plasma et a une importance pour les plasmas spatiaux et de laboratoire, car elle est à la base de phénomènes naturels comme les éruptions solaires et les aurores polaires, ou de processus disruptifs dans les expériences de fusion thermonucléaire. Un problème de longue date dans l'étude des plasmas de laboratoire et astrophysiques est de comprendre les mécanismes d'accélération des électrons et des ions, lorsqu’un champ magnétique se reconnecte et libère de l'énergie. Dans ce travail, nous avons étudié les effets cinétiques sur les instabilités de reconnexion se développant spontanément dans les nappes de courant statique (modes de déchirement) et en combinaison avec une classe d'instabilités cinétiques (instabilités de Weibel) qui sont pertinentes à la fois pour les jets de plasma astrophysiques et pour les expériences d'interaction laser-plasma. Nous avons effectué cette étude en utilisant des modèles fluides réduits et cinétiques, et nous avons étudié la concurrence entre les modes de type déchirement et les instabilités de type Weibel au moyen de simulations cinétiques complètes avec codes semi-lagrangiennes Vlasov-Maxwell et de type “Particle-In-Cell“Plasmas are gaseous systems of ions and electrons which interact via electromagnetic fields and display collective properties. Among these, is the notion of the magnetic line "connection". This expresses the fact that, in regimes in which charged particles spiral sufficiently fast along lines of magnetic induction, the latter is linked to the bulk plasma motion and acquire a topological identity which forbids them to break, intersect and reconnect. This topological identity, however, can be locally violated thanks to a number of kinetic effects, such as particle collisions, when the currents in the plasma are sufficiently intense: one speaks of "magnetic reconnection". Magnetic reconnection is an important ingredient of the plasma self-organization and has significance for both space and laboratory plasmas since it is at the basis of natural phenomena like solar flares and polar lights, or of disruptive processes in thermonuclear fusion experiments. A long-standing problem in the study of laboratory and astrophysical plasmas is to understand the mechanisms of acceleration of electrons and ions, as a magnetic field reconnect and release energy. In this work, we studied kinetic effects on reconnection instabilities developing spontaneously in static current sheets (tearing modes) and in combination with a class of kinetic instabilities (Weibel instabilities) that are relevant both to astrophysical plasma jets and to laser-plasma interaction experiments. We performed this study using reduced-fluid and kinetic models and we investigated the competition between tearing-type modes and Weibel-type instabilities by means of both semi-lagrangian full kinetic Vlasov-Maxwell simulations and particles in cell simulations
25
Jolivet, Laurent. "Étude de l'influence de l'émission électronique secondaire sur le phénomène de gaine et application aux propulseurs de satellite à effet Hall". Toulouse, ENSAE, 2000. http://www.theses.fr/2000ESAE0020.
Abstract (sommario):
"Lorsqu'un matériau est exposé à un plasma, une région interface nommée gaine se développe et régule les interactions plasma-matériau. Cette thèse est consacrée à l'étude du phénomène de gaine en présence d'émission électronique secondaire qui est l'émission d'électrons par le matériau consécutive à l'impact des électrons provenant du plasma. Afin de s'affranchir des contraintes fortes des modèles analytiques de ce phénomène, telles que la condition de plasma Maxwellien, un modèle numérique (PIXIE) de type Particle-In-Cell a été développé. Une méthode, dite de "temps numériques", est proposée et permet de simuler des plasmas complexes d'ions lourds avec des temps de calcul relativement faibles. Après validation, PIXIE a été appliqué à l'étude des interactions entre le plasma et le matériau de la chambre de décharge des propulseurs à effet Hall pour satellites. Nous avons ainsi pu mettre en évidence la capacité de l'émission secondaire à jouer un rôle prépondérant dans la conductivité électronique de ce type de propulseur. Une conséquence de l'emission secondaire étant une modification du potentiel de la surface du matériau, nous avons conçu et mis en œuvre une méthode expérimentale permettant de mesurer ce potentiel pour un diélectrique exposé à un plasma. "
26
Baraka, Suleiman. "Etude de l'interactionentre le vent solaire et la magnetosphere de la Terre: Modele theorique et Application sur l'analyse de donnees de l'evenement du Halloween d'octobre 2003". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00138416.
Abstract (sommario):
Une nouvelle approche, en utilisant un 3D code électromagnétique (PIC), est présentée pour étudier la sensibilité de la magnétosphère de la terre à la variabilité du vent solaire. Commençant par un vent solaire empiétant sur une terre magnétisée, le temps a été laissé au système ainsi une structure d'état d'équilibre de la magnétosphère a été atteinte. Une perturbation impulsive a été appliquée au système par changeant la vitesse du vent solaire pour simuler une dépression en sa pression dynamique, pour zéro, au sud et du nord du champ magnétique interplanétaire(IMF). La perturbation appliquée, un effet de trou d'air qui pourrait être décrit comme espace ~15Re est formé pour tous les cas d'état de IMF. Dès que le trou d'air a frappé le choc d'arc initial de la magnétosphère régulière, une reconnexion entre le champ magnétique de la terre et le IMF sud a été notée à la coté jour magnétopause(MP). Pendant la phase d'expansion du système, la frontière externe de la coté jour du MP a enfoncé quand IMF=0, et pourtant elle sa forme de balle quand un IMF au sud et nordique étaient inclus. La relaxation de temps du MP pour les trois cas de IMF a été étudiée. Le code est alors appliqué pour étudier l'événement d'Halloween de l'octobre 2003. Notre simulation a produit un nouveau genre de trou d'air, un espace raréfié qui a été produit après un gradient fort en IMF d'empiétement. Un tel dispositif est tout à fait semblable aux anomalies chaudes observées d'écoulement et peut avoir la même origine
27
Feister, Scott. "Efficient Acceleration of Electrons by an Intense Laser and its Reflection". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461225902.
28
Coche, Philippe. "Modélisation cinétique d’un propulseur à effet Hall". Toulouse 3, 2013. http://thesesups.ups-tlse.fr/1995/.
Abstract (sommario):
Les propulseurs à effet Hall sont utilisés pour le maintien en poste des satellites géostationnaires. La singularité de ce type de moteur est l'utilisation d'un champ magnétique dont le rôle est de piéger des électrons et de permettre la formation d'une région à fort champ électrique. Les ions formés sont accélérés dans ce champ électrique puis extraits du plasma pour fournir la poussée. La compréhension du transport des électrons à travers les lignes de champ magnétique reste un enjeu crucial pour prédire le fonctionnement du moteur. Plusieurs mécanismes de transport comme les phénomènes collisionnels et la turbulence ont été identifiés mais leur contribution exacte n'a pas encore été élucidée. Sur la base de deux modèles numériques particulaires ("Particle-In-Cell"), composés de schémas de discrétisation des trajectoires explicite et implicite, ce travail de thèse se propose d'analyser le déroulement d'une décharge type afin d'isoler les mécanismes de transport électronique mais aussi, de mieux cerner l'influence de la turbulence plasma sur la nature de la décharge. L'accent est mis sur le caractère fortement instationnaire de celle-ci. Nous étudions aussi un mécanisme de transport particulier, gouverné par la turbulence et les collisions volumiques, à l'aide d'un modèle numérique particule-testHall effect thrusters are used for station-keeping of satellites in geostationary orbit. The originality of this kind of thruster is the use of a magnetic field which traps the electrons and creates a high electric field region. In this region, the ions are accelerated and extracted from the plasma to provide a thrust. Electron transport across the magnetic field lines is a major issue in predicting the thruster performance. Several transport mechanisms as collision phenomena and plasma turbulence have been identified to play a role but their exact contribution is still not clear. Based on two numerical particle models ("Particle-In-Cell"), composed of an explicit and implicit trajectory-tracking schemes, this work thesis aims at analyzing the proceeding of a discharge in order to isolate the transport mechanisms of electrons. It also aims at providing a better understanding of the plasma turbulence on the discharge behavior. We emphasize the strong unstationnary character of the discharge. We also study a particular transport mechanism, governed by turbulence and volumic collisions, using a particle-test numerical model
29
Kučera, Pavel. "USB host s mikrokontroléry PIC". Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2010. http://www.nusl.cz/ntk/nusl-235542.
Abstract (sommario):
The aim of master thesis is implementation of USB host in a microcontroller PIC. The thesis contains description of ways of peripherals to computer connections with detailed description of USB bus. There are also discussed several approaches in implementations USB host for embedded systems. A concept of layered USB host system is designed on the basis of analysis of the state of the art. Finally, the designed system is implemented in microcontroller. Resulting firmware of development kit is tested on real USB device.
30
Forestier-Colleoni, Pierre. "Etude expérimentale des champs magnétiques en surface d'une cible irradiée par laser et leurs implications sur le faisceau d'électrons". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0036/document.
Abstract (sommario):
Cette thèse porte sur la caractérisation des champs magnétiques générés par l'interaction entre un laser d'intensité de 1017 W/cm2 à 1018 W/cm2 et de cibles solides, et leurs effets sur le faisceau d'électrons chauds. En effet, les différents champs magnétiques créés lors de cette interaction ont un rôle fondamental sur les caractéristiques du faisceau d'électrons chauds : sa source et son transport dans la matière. Des diagnostics de polarimétrie et d'interférométrie croisée ont été développés lors de cette thèse pour observer le champ magnétique en surface de la cible irradiée par laser et en particulier leurs évolutions spatiale et temporelle. Deux différents régimes ont été observés selon le contraste en intensité de l'impulsion laser : un possédant une montée rapide de champ magnétique suivie d'une décroissance plus lente créées par le déplacement des électrons chauds dans la matière, et un possédant une croissance plus lente de forme logarithmique créée par la pré-impulsion du laser par effet thermoélectrique. L'interprétation de nos résultats obtenues par ces diagnostics ont permis d'évaluer la résistivité du plasma. Cette résistivité nommée anormale dans la littérature se comprend en estimant l'influence du champ magnétique sur l'anisotropie du transport des électrons et donc sur la résistivité. Le dernier diagnostic permettant l'estimation du champ magnétique détaillé dans cette thèse est la déflectométrie protonique. Elle permet d'observer la déviation d'un faisceau de protons lors de sa propagation sous l'effet de champs électrique et magnétique. D'autres expériences se sont focalisées sur la divergence de ce faisceau d'électrons. Deux diagnostics principaux ont été utilisés : l'imagerie K α et l'imagerie du rayonnement de transition cohérente (C.T.R.) en face arrière de ciblesThis thesis concerns magnetic fields, generated by the interaction between strong laser pulse (intensity up to1018 W/cm2) and solid target, and their effects on the fast electron beam. Indeed, the various magnetic fields created during this interaction can inuence the divergence of the fast electron beam. The magnetic field createdduring this interaction have a fundamental role on the fast electron beam characteristics : its source and its transportin the material. Diagnotics of polarimetry and crossed interferometry were developed during this thesis to observethe on-surface magnetic field of the target, and in particular, their spatial and temporal evolutions. Two types oftemporal evolution of the magnetic field were observed according to the contrast in intensity of the laser pulse : afast rise of magnetic field followed by a slower decrease created by the travel of the fast electrons in the material,and a slower growth of logarithmic form created by the pre-pulse of the laser by thermoelectric effect. The interpretation of our results obtained by these diagnotics allowed us to estimate the resistivity of the plasma.This resistivity named "anomalously high resistivity" in the literature can be explained by taking into account theinuence of the magnetic field on the electrons transport (creation of an anisotropy) and thus on the resitivity.The last diagnotic allowing the estimation of the magnetic field detailed in this thesis is the proton deectometry. itallows to observe the deviation of a proton beam during its propagation under the inuence of electric and magneticfields. Other experiments were focused on the fast electron beam divergence. Two main diagnotics were used : the K α imaging and the coherent transition radiation (C.T.R) imaging at the rear side of solid targets. These diagnoticsallowed to estimate the fast electron beam divergence for two distinct energetic electron populations. The differenceof divergence coming from characteristics of both diagnotics (electrons in charge of the emissions in different energies). The diagnotics of on-surface magnetic fields of target irradiated by intense laser, such as the technics of polarimetry and crossed interferometry developed in this thesis, are dedicated to be combined with diagnotics determining the evolution of the radial size of the fast electron beam generated by the laser-matter interaction. Their simultaneous use, and the correlation between their respective data, should allow to establish experimentally, in the short term, the inuence of the on-surface magnetic fields on the fast electron beam initial characteristics, in particular the angular and energy distributions. Our results of polarimetry on the spatio-temporal evolution of the magnetic fields of surface establish the state of the art for this type of measures. There are possible improvements, in particular as regards their use in conditions of irradiation by lasers of intensities > 1018 W/cm2. These perspectives are also the object of discussions in this manuscript
31
Pitsillides, Costas M. 1973. "Selective cell targeting with light-absorbing particles". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89257.
32
Druma, Calin. "A particle in cell formulation for extrusion of fluoropolymers". Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1178048890.
33
Adams, Christopher Francis. "Assessment of magnetic particles for neural stem cell-based therapies". Thesis, Keele University, 2015. http://eprints.keele.ac.uk/2494/.
Abstract (sommario):
Transplantation of genetically engineered neural stem cells (NSCs) into sites of central nervous system (CNS) disease/injury is a promising strategy to promote repair of damaged tissue. However, translating this strategy into the clinic requires several challenges to be overcome including facilitating ‘combinatorial therapy’ (achieving multiple therapeutic goals – essential in CNS injury/disease). Nanotechnologies are emerging as multifunctional platforms capable of meeting this requirement. For example, magnetic particles (MPs) and implantable hydrogels offer several biomedical advantages for transplant populations, including: safe genetic manipulation; non-invasive cell tracking, via MRI; and safe and efficient accumulation of cells at sites of injury. However, the use of these nanotechnologies remains to be explored in detail for NSC transplantation therapies. In this thesis, it is shown that MPs can mediate gene delivery to NSCs grown as neurospheres and monolayers with the most efficient transfection efficiencies achieved using oscillating magnetofection protocols (9.4% and 32.2% respectively). In both culture systems, developed protocols had no effect on key regenerative properties of NSCs such as cell viability, proliferation, stemness and differentiation. Further, ‘magnetofected’ monolayer NSCs were shown to have survived and differentiated in a cerebellum slice model acting as host tissue, indicating safety of the procedures. It was also shown that assessing procedural safety and extent of transfection of magnetofection protocols may be feasible by employing mass spectrometry and proteomics analysis. It was also found that tailored enhancement of particle magnetite content offers a means to efficiently label NSCs, up to a maximum of 95.8%. Labelling procedures had no effect on cell viability, proliferation, stemness or differentiation. In addition, labelled cells could survive and differentiate in a slice model of spinal cord injury indicating safety of the labelling procedures. Functional labelling was also demonstrated by magnetic capture of labelled cells in an in vitro flow system. Hydrogels offer major advantages for delivery of transplant populations into injury sites. Here it was shown that an intraconstruct genetic engineering approach was feasible for NSCs cultured with a clinically translatable, collagen hydrogel system. Magnetofection protocols safely increased MP mediated transfection of NSCs grown in ‘2-D’ and ‘3-D’ hydrogel cultures.
34
Almaghrabi, Mohammednoor Naher. "Flotation of coarse particles in a modified flotation column cell". Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240560.
35
Jenkins, Stuart Iain. "Applications of magnetic particles for oligodendrocyte precursor cell transplantation strategies". Thesis, Keele University, 2013. http://eprints.keele.ac.uk/3821/.
Abstract (sommario):
Oligodendrocyte precursor cells (OPCs) are a major transplant population to promote myelin repair and central nervous system (CNS) regeneration in conditions such as Multiple Sclerosis and spinal cord injury. Magnetic particles (MPs) can offer a multifunctional platform for cell therapies, facilitating labelling for cell tracking (e.g. by MRI and histopathology); biomolecule delivery (including nonviral gene delivery, enhanceable by novel ‘magnetofection’ strategies); and magnetic cell targeting of transplant populations. However, MP-based applications for neural tissue engineering have received limited attention to date. This thesis demonstrates that ~60% of OPCs (derived from a primary source) can be safely labelled using two well-characterised MP formulations, including a novel multimodal MP with transfection plus cell labelling capabilities. A rapid, technically simple, high-throughput ultrastructural imaging technique, OTOTO SEM, has been developed to study the surface interactions of MPs with precursor cells. Safe MP-mediated transfection of OPCs was demonstrated, including with multiple and therapeutic genes. Transfection efficiency was enhanced by static/oscillating ‘magnetofection’ techniques (~21%; competitive with nonviral alternatives). Organotypic cerebellar slice cultures were developed as a model of ‘host’ neural tissue, and ‘magnetofected’ OPCs exhibited normal migration, proliferation and differentiation profiles following transplantation onto such slices. Safe labelling (~45%) and transfection (enhanced by static/oscillating magnetofection strategies: ~6%) of oligodendrocytes was achieved utilising identical protocols to those developed for OPCs. A comparative intralineage analysis demonstrated that MP-uptake and amenability to transfection were significantly lower in oligodendrocytes compared to OPCs. Inter-cellular comparisons of MP-handling by the four major CNS glial subtypes (viz. OPCs, oligodendrocytes, astrocytes, microglia; derived from the same primary source) revealed major differences in the rate/extent of MP uptake, amenability to transfection, optimal magnetofection frequency, and MP-associated toxicity. Finally, a stoichiometrically-defined glial co-culture model was developed and utilised to test the hypothesis that microglia represent an ‘extracellular barrier’ to MP uptake by other glia.
36
Valley-Omar, Ziyaad. "RNA transmission and expression from inert HIV candidate vaccine virus-like-particles". Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4345.
Abstract (sommario):
Includes abstract.Includes bibliographical references (leaves 136-158).
HIV-1 Gag virus-like-particles (VLPs) produced in various expression systems are potent stimulators of both cellular and humoral immune responses in animal models. The encapsidation of large concentrations of random cellular RNA species is known to accompany the assembly of HIV virus particles. This RNA plays a crucial role by serving as a molecular scaffold for the assembly of Gag structural proteins into particles. Non-pseudotyped VLPs that do not present any HIV envelope glycoproteins are regarded as inert particles as they contain no replicative nucleic acid and are presumed to be unable to deliver encapsidated RNA for expression in inoculated individuals. Live virus cellular entry studies have shown that non-pseudotyped Gag particles are destined for degradation in acidified vesicles subsequent to receptor independent cellular entry. In addition to host cell RNA incorporation, Gag VLPs produced in insect cell-based, baculovirus expression systems have been observed to incorporate the baculovirus-derived Gp64 envelope glycoprotein. Gp64 has been shown to be efficient at enabling the delivery and expression of genes from recombinant baculoviruses and other Gp64 pseudotyped live viruses in mammalian cell lines both in vivo and in vitro. This study, therefore, set out to establish for the first time whether inert, baculovirus-derived (Gp64 pseudotyped) Gag VLPs could mediate delivery and expression of randomly encapsidated RNAs in mammalian cell lines.
37
Chaudhuri, Nazia. "The role of cell networks in response to diesel exhaust particles". Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521907.
38
Hopkins, Sally. "Applications of Sub-Micron Poly ( N-isopropyl acrylamide) Particles in Cell Culture". Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522411.
39
Hu, Bin. "Tissue engineering applications of selective activation of cell mechanosensitive receptors using magnetic particles". Thesis, Keele University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602978.
Abstract (sommario):
Mechanical cues play important roles in controlling cell function and have implications fo1' generating functional tissues for clinical use. This thesis investigates the potential of using magnetic particle (MNP) mediated mechanical stimulation techniques through Magnetic Force Bioreactor (MFB) to alternatively activate mechanical sensitive cell membrane receptors for the tissue engineering applications and the study of mechanotransduction. In this study, broad cell types including primary human mesenchymal stem cells (hMSCs), transformed mouse embryonic stem cells (mESCs) and HEK293 cells have been used and two different strategies for improving selective targeting cell membrane receptors, in that antibodies or peptides are employed as functionalizing biomolecules to facilitate various cell membrane receptors targeting, have been utilized. The long term application of mechanical stimulation in the osteogenic induction of hMSCs and mESCs mediated by MNPs has been undertaken. The cellular response to MNP mediated stimulation has becn examined by immunofluorescence, ELISA, qRT-PCR, histology, FTIR and uCT.
40
Marnett, Laura Ann. "The preparation of composite particles and their use in removal flow cell studies". Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393944.
41
Chen, Mu. "A study of polystyrene microgel particles with conjugated polymers and perovskite solar cell". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/a-study-of-polystyrene-microgel-particles-with-conjugated-polymers-and-perovskite-solar-cell(dc219cad-afc1-4a57-a8f8-87d22f9e97be).html.
Abstract (sommario):
This thesis presents a study of polystyrene (PS) microgel (MG), hole transfer materials (HTMs) and perovskite solar cells (PSCs) and associated effects to combine them together to increase the stabilities of PSCs. PSCs are a disruptive technology which attract a lot of attention because of their remarkable power conversion efficiency (PCE). However, PSCs are very fragile and easy to be damaged by moisture and oxygen. The PS MGs are solvent-swellable, inherently colloidally stable, hydrophobic, and have good film-forming properties. In the study, we mixed PS MG with three different HTMs, poly(3-hexylthiophene) (P3HT), Poly[bis(4-phenyl)(2,5,6-trimethylphenyl)amine (PTAA) and 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) to establish a diagram of concentrations of each component to form films. We investigated the morphology and light absorption and photoluminescence (PL) of HTM-MG films spin-coated from HTM-MG dispersions. The films containing flattened MG with an aspect ratio of around 10. MG islands containing packed particles were evident for both pure MG and P3HT-MG.
42
Lindemann, Dirk, Kristin Stirnnagel, Daniel Lüftenegger, Annett Stange, Anka Swiersy, Erik Müllers, Juliane Reh et al. "Analysis of Prototype Foamy Virus particle-host cell interaction with autofluorescent retroviral particles". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-176566.
Abstract (sommario):
Background
The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive.
Results
In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction.
Conclusions
We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.
43
Lindemann, Dirk, Kristin Stirnnagel, Daniel Lüftenegger, Annett Stange, Anka Swiersy, Erik Müllers, Juliane Reh et al. "Analysis of Prototype Foamy Virus particle-host cell interaction with autofluorescent retroviral particles". BMC, 2010. https://tud.qucosa.de/id/qucosa%3A28868.
Abstract (sommario):
Background
The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive.
Results
In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction.
Conclusions
We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.
44
Dao, Thi Phuong Tuyen. "Hybrid polymer/liquid vesicles as new particles for drug delivery and cell mimics". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0190/document.
Abstract (sommario):
Les vésicules hybrides polymère/lipides sont des structures récemment développées dans la littérature. Idéalement, celles-ci peuvent présenter la biocompatibilité et la biofonctionnalité des liposomes, ainsi que la robustesse, la faible perméabilité et la versatilité de fonctionnalisation chimique conférées par les chaînes de copolymères. Cependant, à ce jour, les facteurs régissant la séparation des phases dans ces membranes hybrides ne sont pas bien compris. Dans ce travail, nous avons étudié en détail la formation et la séparation de phases dans les membranes de vésicules géantes (GHUVs) et de taille nanométriques(100nm) (LHUVs) constituées de phospholipides en phase fluide ou gel et de copolymères à base de poly (diméthylsiloxane) et de poly (éthylène glycol). Différentes architectures(greffée, tribloc) et masses molaires ont été utilisées. La séparation de phase a été étudiée sur les vésicules géantes à l’échelle micrométrique et nanométrique respectivement par microscopie confocale et imagerie de fluorescence résolue en temps (FLIM), tandis que pour les LHUVs, différentes techniques comme la diffusion de neutrons, la Cryo-microscopie et la spectroscopie de fluorescence résolue dans le temps ont été combinées. Nous avons pu montrer que la fraction lipide/polymère, l'état physique du lipide et la tension de la ligne aux interfaces lipide/polymère modulable par la masse molaire et l'architecture du copolymère sont les facteurs importants régissant la formation et la structuration des vésicules hybrides. Enfin, nous avons montré que les propriétés élastiques de la membrane peuvent être modulées via la composition polymère lipideHybrid copolymer/lipid vesicle are recently developed self-assembled structures that could present biocompatibility and biofunctionality of liposomes, as well as robustness, low permeability and functionality variability conferred by the copolymer chains. However, to date, physical and molecular parameters governing copolymer/lipid phase separation in these hybrid membranes are not well understood. In this work, we studied in detail the formation and phase separation in the membranes of both Giant Unilamellar Hybrid Vesicles(GHUVs) and Large Unilamellar Hybrid Vesicles (LHUVs) obtained from the mixture of phospholipids in the fluid (liquid disordered) or gel state (solid ordered) with various copolymers based on poly(dimethylsiloxane) (PDMS) and poly(ethylene glycol) (PEO) with different architectures (grafted, triblock) and molar masses. For GHUVs, phase separation at the micron scale and nanoscale was evaluated through confocal microscopy, and Fluorescence lifetime imaging microscopy technique (FLIM) respectively, where as acombination of Small angle neutron scattering (SANS), Cryo-transmission electron microscopy (Cryo-TEM) and Time-resolved Förster resonance energy transfer (TR-FRET) techniques was used for LHUVs. We demonstrate that the lipid/polymer fraction, lipid physical state, and the line tension at lipid polymer/lipid boundaries which can be finely modulated by the molar mass and architecture of the copolymer are important factors that govern the formation and structuration of hybrid vesicles. We also evidence that elasticity ofthe hybrid membrane can be modulated via the lipid polymer composition, through the use of micropipettes techniques
45
QUATTROCCHI, NICOLETTA. "Biological camouflage imparts cell-like activity to injectable particles: the leukolike delivery system". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/20195.
Abstract (sommario):
The objective of this thesis is to demonstrate that increased localization of theranostic particles at the tumor site can be achieved by developing a novel biomimetic hybrid DDS capable of simultaneously escaping biobarriers, while targeting the cancerous lesion. In order to improve the stealth properties of the drug delivery system (DDS) an innovative liposome formulation composed of natural phospholipids obtained through the extraction of the cellular membranes of leukocytes isolated from the peripheral blood has been proposed. This new generation of liposomes composed of the same lipids and proteins of the blood circulating leukocytes are biologically inert and weakly immunogenic. Moreover the presence of some membrane proteins can transfer to the liposomes their biological functions thus improving the liposome targeting ability without requiring following surface functionalization. The leukocyte-derived liposomes can be used as coating material for the realization of biomimetic DDS called “leukolike” system (LS), since it combine the natural properties of leukocyte cells (free circulation in the blood stream, transendothelial migration and tropism towards the inflammatory site) with the characteristics of an artificial delivery system (biodegradability, biocompatibility, agents loading and release).
The LS thus demonstrates the advantages of a novel delivery strategy able to bestow a DDS with prolonged circulation, selective tumor targeting and enhanced tumor accumulation and retention.
46
Halsey, Richard James. "Construction and characterization of chimaeric human immunodefiency virus type 1 subtype C Gag virus-like particles". Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4269.
Abstract (sommario):
Includes bibliographical references (leaves 114-128).In this study I explored the possibility of making HIV-1 subtype C Pr55gag-based chimaeric virus-like particles (VLPs) as a boost to the HIV-IC multigene DNA vaccine pTHr.grttnC, which encodes a modified Gag-RT-Tat-Nef fusion protein (GRTTN). Furthermore, an attempt was made to produce VLP analogues to the HIV-IA polyepitope DNA vaccine pTHr.HIVA. A range of in-frame fusions with the C-termini of myristylation-competent p6-truncated Gag and native Pr55gag were made to test how the length of polypeptide and its sequence might affect VLP formation and structure.
47
Wang, Desheng. "CDSE Quantum Dots and Luminescent/Magnetic Particles for Biological Applications". ScholarWorks@UNO, 2005. http://scholarworks.uno.edu/td/142.
Abstract (sommario):
CdSe semiconductor nanocrystals (quantum dots--QDs) with diameters ranging between 1.5 and 8 nm exhibit strong, tunable luminescence [1-5]. They have been widely investigated for their size-dependent optoelectronic properties [6], and for their potential use in optical devices [7], biological labels [8] and sensors [9]. Luminescent quantum dots (QDs) show higher photostability and narrower emission peaks compared to organic fluorophores [8]. The objective of my project was to apply QDs magnetic/luminescent nanoparticle as biological labels in cells. Luminescent CdSe QDs emit bright visible light with high quantum yield and sharp emission peak. The CdSe QDs were capped with a ZnS layer. This increased their emission efficiency and photostability due to the larger band gap of ZnS. The QDs were transferred from organic solvent (e.g. chloroform, hexane) to water by exchanging the capping group (Trioctylphosphine Oxide—TOPO) with mercaptoacetic acid. To develop a separation and detection tool for cells, we combined γ-Fe2O3 magnetic particles with CdSe/ZnS QDs in core-shell composite. The composite nanoparticles showed strong fluorescence emission and high water solubility. Different antibodies were attached to the particles through EDAC coupling. The antibody-coated particles were used to successfully separate and detect breast cancer cells in blood cells.
48
Mustafa, Kamal. "Cellular responses to titanium surfaces blasted with TiO₂ particles /". Stockholm, 2001. http://diss.kib.ki.se/2001/91-628-4951-4/.
49
Ahmed, Kawther Khalid. "Tumor cells surface-engineered with polymeric particles for use as cancer vaccines". Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/6026.
Abstract (sommario):
Cancer is a group of diseases caused by aberrant continuously proliferating cells capable of metastasis. Despite significant advances in preventive, diagnostic and treatment measures, cancer is one of the major causes of death in the United States, second only to heart diseases. Main treatment approaches are surgery, radiotherapy, chemotherapy, and the recently expanding immunotherapeutic approaches. The main challenge in treating cancer is the ability of cancer cells to mutate and develop resistance to drug treatments therefore lowering the efficacy of chemotherapy in preventing metastatic tumors. Cancer vaccines are a treatment modality that employs the potential of the immune system to recognize and eliminate tumor cells by unmasking tumor cell antigens and generating an effective anti-tumor immune response with an immune memory capable of preventing metastases formation. This dissertation describes and evaluates an innovative cell-particle hybrid cancer vaccine construct involving irradiated tumor cell surface-engineered with polymeric particles using streptavidin-biotin cross-linking. The tumor cells were biotinylated indirectly using biotin-linked antibodies targeting a surface integrin and the particles were loaded with an immune adjuvant and coated with streptavidin. The tumor cells served as the source of tumor antigens and the anchored particles served to confine loaded immune adjuvant to the tumor cells. The vaccine construct was designed to co-deliver tumor antigens and the immune adjuvant to the same antigen presenting cell, a criteria that has been suggested recently to be important for optimal cancer vaccine potency.
The first report on this cell-particle construct was published in my master’s thesis defended in May 2013. In that report, the feasibility of assembling the cell-particle hybrid was demonstrated. However, loading of the immune adjuvant, CpG ODN (cytosine phosphate guanine oligonucleotide), into streptavidin-coated particles was not optimal. In the current studies, this problem was addressed and the cancer vaccine potential of the cell-particle construct was assessed.
We first evaluated a new TLR4 (toll like receptor 4) agonist, PET lipid A (pentaeryhtritol lipid A), for its potential use in cancer vaccines with the intention to incorporate it in the cell-particle hybrid. PET lipid A is a fully synthetic lipid A analog that has been demonstrated to have immunostimulatory properties. We evaluated the potential use of PET lipid A in cancer vaccine applications and the effect of particulate formulations on its adjuvant properties. Results showed improved in vitro immunostimulatory properties for particle based formulations. Upon testing the immunostimulatory properties of PET lipid A in vivo, moderate enhancement in antigen specific cytotoxic T cells stimulation was observed when PET lipid A was delivered in particles, which then translated into a corresponding trend toward increased survival in a prophylactic tumor study. PET lipid A was concluded to be a weak potential cancer vaccine adjuvant and was not chosen as the immune adjuvant to use in the cell-particle hybrid assembly. Instead, CpG ODN (TLR9 agonist) was chosen due to its strong record of efficacy as a cancer vaccine adjuvant.
The second part of this research project aimed at addressing the challenges we encountered previously in achieving acceptable CpG ODN loading of the final streptavidin-coated PLGA (Polylactic-co-glycolic acid) particles. The approach taken was to modify the method used earlier to make the particles in order to circumvent CpG ODN loss. In the modified method the number of steps required to make streptavidin-coated CpG ODN-loaded PLGA particles was reduced and the fabrication media was altered to allow simultaneous particle fabrication and activation of surface carboxyl groups. The modified method resulted in 5-fold higher loading in the final streptavidin-coated particles compared to the original method.
Subsequent to establishing the feasibility of constructing the cell-particle hybrid and characterizing the assembled hybrid in vitro, the in vivo cancer vaccine potential of the designed construct was examined. Two independent murine tumor models were chosen for this purpose, namely prostate cancer and melanoma. The proposed cell-particle hybrid vaccine construct had significant therapeutic outcomes in the prostate cancer tumor model where mice vaccinated with cell-particle hybrids were the only group to show significant improvement in survival compared to untreated controls whereas no other vaccine formulation had such an effect. Unfortunately, no prophylactic benefit was observed from any of the vaccine formulations used in the melanoma tumor model involving irradiated GM-CSF (granulocyte macrophage colony stimulating factor)-secreting B16.F10 cells. In vitro examination of the immunostimulatory properties of all cell lines used in these studies revealed that transfected and parent B16.F10 cells (representing murine melanoma) were possibly immunoinhibitory whereas RM11 (representing murine prostate cancer) cells lacked such immunosuppressive effect in vitro.
Our objective was to design and evaluate a new cancer vaccine construct that improved the immunostimulatory properties of irradiated tumor cell based vaccines. The approach taken was to surface engineer tumor cells with immune adjuvant loaded polymeric particles. We reported a simple method for fabricating streptavidin-coated PLGA particles and a versatile method of tumor cell surface engineering. We found that the efficacy of tumor cell-based vaccines can be inconsistent across tumor models and the in vitro immunosuppressive effect of tumor cells might be a contributing factor.
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Beck, Alexander J. "Determining Bed Failure Depth in Unconsolidated Submarine Sediments Using Particles in Cell Numerical Modeling". Thesis, University of Louisiana at Lafayette, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10685053.
Abstract (sommario):
The cause for low angle submarine landslide (SML) failures, at slope angles less than 4°, currently cannot be readily predicted using conventional terrestrial sources (i.e. excess pore pressure, weak horizons). Numerous models that have been developed pertaining to mass wasting on continental margins generally fall into two categories: post landslide occurrence (Tsunami wave run-up modeling) on coast lines and core sample description on costal margins. To date, there has been limited research on determining bed failure depth of submarine landslides through modeling. We propose a new method of 2D numerical modeling of rupture surface within unconsolidated sediments using the “Particle in Cell” method in combination with a conservative finite volume scheme. The software is written in Python, using the Numerical Python (NumPy) library to reach compiled-code-like performance. The Particle in Cell method was tested for accuracy, advection, and numerical diffusion. A set of six numerical model simulations are presented in which we investigate the role of material and external properties (i.e. hydraulic diffusivity and sedimentation rate), and geometry in the quest to determine bed failure depth. Through initial modeling simulations, it is confirmed that yield strength, diffusivity and sediment loading all play a role in predicting failure.